Regulation and Function of Cyclin D2 in B
Lymphocyte Subsets
Thomas C. Chiles
This information is current as
of June 16, 2017.
Subscription
Permissions
Email Alerts
This article cites 91 articles, 60 of which you can access for free at:
http://www.jimmunol.org/content/173/5/2901.full#ref-list-1
Information about subscribing to The Journal of Immunology is online at:
http://jimmunol.org/subscription
Submit copyright permission requests at:
http://www.aai.org/About/Publications/JI/copyright.html
Receive free email-alerts when new articles cite this article. Sign up at:
http://jimmunol.org/alerts
The Journal of Immunology is published twice each month by
The American Association of Immunologists, Inc.,
1451 Rockville Pike, Suite 650, Rockville, MD 20852
Copyright © 2004 by The American Association of
Immunologists All rights reserved.
Print ISSN: 0022-1767 Online ISSN: 1550-6606.
Downloaded from http://www.jimmunol.org/ by guest on June 16, 2017
References
J Immunol 2004; 173:2901-2907; ;
doi: 10.4049/jimmunol.173.5.2901
http://www.jimmunol.org/content/173/5/2901
OF
THE
JOURNAL IMMUNOLOGY
BRIEF REVIEWS
Regulation and Function of Cyclin D2 in B Lymphocyte
Subsets1
Thomas C. Chiles2
he cell cycle is divided into an interphase, in which cell
growth and DNA replication occurs, and a mitotic
phase, in which cell division occurs. The point in the
G1 phase that represents an irreversible commitment to replicate the genome and undergo cell division has been termed the
“restriction point” (1). Growth factors function by signaling
passage through the restriction point, at which time continued
cell cycle progression proceeds independent of extracellular cues
(Fig. 1). Proper control of restriction point progression is essential for maintaining normal levels of cell growth and proliferation (2). Accumulating evidence indicates that passage through
the restriction point is regulated by the retinoblastoma tumor
suppressor gene product pRb and by the related proteins p107
and p130 (3). pRb functions to repress transcription of genes
whose products are required for transition through the restriction point and S-phase progression (3). This repression is
achieved through the binding of numerous proteins, notably
members of the E2F/DP-1 family of transcription factors, and
by recruiting histone deacetylases and chromatin remodeling
SWI/SNF complexes to E2F-responsive gene promoters (reviewed in Ref. 4). pRb is inactivated by sequential phosphorylation initiated early in the G1 phase by a subset of cyclin-dependent kinases (cdk4 and cdk6),3 followed by cdk2 in the late
T
Department of Biology, Boston College, Chestnut Hill, MA 02467
Received for publication April 5, 2004. Accepted for publication May 27, 2004.
The costs of publication of this article were defrayed in part by the payment of page charges.
This article must therefore be hereby marked advertisement in accordance with 18 U.S.C.
Section 1734 solely to indicate this fact.
1
Research in this review was supported by grants from the National Institutes of Allergy
and Infectious Diseases.
Copyright © 2004 by The American Association of Immunologists, Inc.
G1 phase (Fig. 1; Refs. 4 and 5). The proper timing and duration of cdk4/6 activation are controlled by: 1) the binding of
regulatory proteins, including activators (i.e., D-type cyclins,
composed of D1, D2, and D3) and inhibitors (composed of the
INK4 and Cip/Kip families); and 2) phosphorylation of the cyclin and cdk4/6 subunits (6 –14).
Much functional data support the view that D-type cyclins
play a role in G1-S progression. Notably, forced expression of
cyclin D1 can shorten the G1 phase period, and the overexpression of cyclin D1-cdk4 can suppress a pRb-induced G1 block
(15, 16). Even more compelling are experiments demonstrating
that cyclin D1 is dispensable in vertebrate cells lacking pRb
(17). However, this view of the function of cyclin D-cdk4 has
been challenged by reports that cyclin D1, cyclin D2, and cdk4
knockout mice are viable (18 –21). Notably, cdk4-deficient
mice are smaller and have smaller cells where examined, indicating a role for cdk4 in cellular growth (18). An important and
unresolved question concerns whether D-type cyclins possess
distinct biological functions. The high degree of amino acid
homology (50 – 60% identity throughout the coding region)
between the mammalian D-type cyclins suggests functional redundancy. Indeed, gene targeting of individual D-type cyclins
in mice reveals only limited tissue-specific abnormalities, particularly in the retina and breast for cyclin D1-deficient mice
and in the testes and ovaries for cyclin D2-deficient mice (19 –
21). Like cdk4-null mice, cyclin D1-deficient mice exhibit
dwarfism-like phenotype, further implicating cyclin D-cdk4 in
the regulation of animal growth. Mice expressing a single Dtype cyclin manifest narrowly restricted abnormalities, suggesting that the functions of the three D-type cyclins during development, proliferation, and differentiation of the majority of
tissues are interchangeable (22).
Cyclin D2: an essential mediator of BCR-induced proliferation of
mature B lymphocytes
Early investigations of mouse splenic B cells implicated cyclins
D2- and D3-, but not cyclin D1-containing cdk4 complexes as
crucial links between mitogenic stimuli (e.g., anti-Ig, LPS, or
CD40 agonists) and pRb phosphorylation (23–27). In general,
2
Address correspondence and reprint requests to Dr. Thomas C. Chiles, Department of Biology,
Boston College, 414 Higgins Hall, Chestnut Hill, MA 02467. E-mail address: [email protected]
3
Abbreviations used in this paper: cdk, cyclin-dependent kinase; DLBCL, diffuse
large B cell lymphoma; GC, germinal center; Btk, Bruton’s tyrosine kinase; BLNK, B
cell linker protein; PLC, phospholipase C; PKC, protein kinase C; HPK, hemopoietic
progenitor kinase; MEKK, MEK kinase; IKK, I␬B kinase; GCB, GC B-like; ABC,
activated B cell-like.
0022-1767/04/$02.00
Downloaded from http://www.jimmunol.org/ by guest on June 16, 2017
Abs produced by B lymphocytes play an essential role in
humoral immunity against pathogens. This response is dependent upon the extent of genome replication, which in
turn allows clonal expansion of Ag-specific B cell precursors. Thus, there is considerable interest in understanding
how naive B cells commit to genome replication following
Ag challenge. The BCR is a key regulator of B cell growth
responses in the bone marrow and the periphery. The importance of identifying BCR-coupled signaling networks
and their cell cycle targets is underscored by the recognition that aberrant cell cycle control can lead to lymphoproliferative disorders or lymphoid malignancies. This review focuses on recent progress toward understanding the
function of cyclin D2 in cell cycle control, and in the development of murine B lymphocytes. The Journal of Immunology, 2004, 173: 2901–2907.
BRIEF REVIEWS: Cyclin D2 IN B LYMPHOCYTE SUBSETS
FIGURE 1. The mammalian cell cycle. The panel depicts the assembly of
D-type cyclins with cdk4/6 and cyclin E-cdk2 during G1 phase and at the G1/S
transition, respectively, in response to mitogenic signals. More than 10 different
cyclins and cdks have been identified in animal cells and are expressed in distinct combinations during specific phase of the cell cycle. Not shown is cdc2/
cyclin A and B complexes that control the G2/M transition. The inhibitory
proteins Cip/Kip and Ink4 attenuate cell cycle progression by targeting cyclin
E-cdk2, cyclin A-cdk2, and D-type cyclin-cdk4/6 complexes, respectively.
induction has been recently observed in transitional-2 B cells
(IgMhighIgDhighCD21highCD24highCD23high) stimulated to
proliferate in response to BCR cross-linking, but not induced in
transitional-1 B cells (IgMhighIgDlowCD21lowCD24highC
D23low), which fail to proliferate following anti-Ig stimulation
(29, 30). An important caveat to these studies concerns the
proliferative response of transitional B cells. Although there is
good agreement that T1 cells do not proliferate following BCR
ligation, disagreement exists over whether T2 cells actually
proliferate (31–33). That said, a cautionary note is warranted
insofar as these results collectively might be interpreted to mean
that cyclin D2 induction alone is sufficient to promote S-phase
entry in B cells. Important in this regard is the observation that
BCR cross-linking of primary immature B lymphocytes leads to
G1-phase entry, but not proliferation, despite induction of
cyclin D2 that is comparable to that of anti-Ig-stimulated
mature B cells (34); significantly, cyclin E is not induced by
anti-Ig. It is probable that, in immature B cells, cyclin D2-cdk4
initiates pRb phosphorylation, yet in the absence of cyclin E,
subsequent phosphorylation and inactivation of pRb by cdk2
are not achieved, thereby accounting for impaired S-phase
entry.
The first definitive evidence that induction of cyclin D2 is
necessary for BCR-mediated B cell clonal expansion was
gleaned from mice homologous for a genetic ablation of cyclin
D2 (35). Notably, cyclin D2-deficient splenic B cells exhibit
defective proliferation in response to anti-Ig, but not to CD40or LPS-induced proliferation (35). Along these lines, gene expression profiling of BCR/ABL-transformed BaF3 cells has revealed dysregulated cyclin D2 expression, occurring throughout
the cell cycle (36). BCR/ABL is a constitutively active protein
tyrosine kinase responsible for chronic myelogenous leukemia
(36). Retroviral transduction of the BCR/ABL gene is sufficient
to induce proliferation of infected bone marrow cells from wildtype, but not cyclin D2-deficient mice.
both cyclins D2 and D3 are capable of forming active pRb kinase complexes comprised of cdk4 and, to a lesser extent, cdk6
(23). Many of these studies also document for the first time
changes in Ink4 and Cip/Kip protein levels following Ag receptor cross-linking; however, the biological significance of these
observations to the humoral immune response remains to be
investigated. The notable exception is p18INK4c, which has
been shown to be essential for cell cycle arrest and differentiation of nonsecreting plasmacytoid cells to Ab-secreting plasma
cells (reviewed in Ref. 28).
The idea that cyclin D2 is necessary for BCR-induced G1to-S phase progression was initially formulated on the basis of
correlative data gathered from studies comparing the induction
of cyclin D2 following the stimulation of B cells with partial vs
complete mitogens. These studies demonstrated an absence of
cyclin D2 induction in B cells stimulated with partial mitogens
that act to promote G1-phase, but not S-phase entry, whereas
CD40 or BCR agonists induced sustained expression of cyclin
D2 (23–25). In keeping with these earlier studies, cyclin D2
FIGURE 2. Cyclin D2 in B cell development. The
processes in B lymphopoiesis that require cyclin D2.
HSC, Hemopoietic stem cell; ProB, Sca-1⫹B220⫹ progenitor B cell; preB, pre-B cell; ImmB, immature B cell;
T1, transitional-1 B cell; T2, transitional-2 B cell;
Mat-B, mature B cell; Act-B, activated B cell; B-1a,
peritoneal CD5⫹ B cell; BCR, denotes signaling
through the BCR; LPS, denotes stimulation by LPS;
CD40, denotes stimulation by CD40 agonists. Cyclin
D2-deficient mice exhibit decreased serum IgG3 and IgA.
Cyclin D2 function in B cell development
Mice with cyclin D2 deficiency do not appear to exhibit hemopoietic abnormalities (20). Initial evaluation of the lymphoid,
myeloid, and erythroid progenitor lineages in the bone marrow
do not reveal significant differences in the numbers of
Downloaded from http://www.jimmunol.org/ by guest on June 16, 2017
2902
The Journal of Immunology
Cyclin D2 function in B cell development: insights from global gene
expression profiling of B cell subsets
Gene expression profiling of distinct stages of human and
mouse B cell development has confirmed earlier studies of Dtype cyclin expression in mature B cell populations, while at the
same time arousing speculation that cyclin D2 exhibits new activities unrelated to its function as a cdk4/6 activator and probably independent of its function as a regulator of pRb. Using
microarrays to characterize gene expression patterns, Alizadeh
et al. (41) analyzed a variety of adult lymphoid malignancies
together with normal human lymphocyte subpopulations under a range of activation conditions. This study reveals that
cyclin D2 is expressed at a constitutively high level in diffuse
large B cell lymphomas (DLBCLs) (see below). Cyclin D2 is induced in activated human peripheral blood B cells and is not
detectable in human blood naive CD27⫺ or memory CD27⫹
human peripheral blood B cells (42). Yet a subsequent report by
Klein et al. (43) shows that cyclin D2 is expressed in both human
tonsillar naive and memory B cells. At present, it is unknown
whether the differences observed in these studies are due to potential artifacts introduced during the B cell isolation or, alter-
natively, reflect subtle differences in the activation status of the
B cell subsets.
One of the most striking observations uncovered by these
studies is the apparent absence of cyclin D2 gene expression in
germinal center (GC) centroblasts and centrocytes, despite the
highly proliferative nature of the former B cell subset (42, 43).
How these cells proliferate in the absence of cyclin D2 is not
known. One possibility is that cyclin D3 may compensate for
the loss of cyclin D2 expression and restore proliferation. In
support of this, cyclin D3 gene expression and not cyclin D1, has
been identified by expression profiling in human GC B cells
(41, 43). Another possibility relates to the finding that several
genes known to participate in the G1/S and G2/M phases of the
cell cycle (e.g., cyclins E1/E2, GADD45, DP-1, cyclin B1-cdc2,
pLK, CENP-E/F, Mad2, and survivin) are highly expressed in
GC B cells in comparison with other human B cell populations
(41– 43). In mouse GC B cells, the c-myc gene, which encodes
a transcription factor that regulates G1-to-S phase progression,
is expressed at a high level (44). Thus, the expression of these
genes may account for the highly proliferative nature of GC B
cells in the absence of cyclin D2. Of note, in many instances it
has not been established whether the protein levels of individual
D-type cyclins correlate with mRNA levels measured by gene
expression profiling. This is an important consideration given
an earlier study of discordant protein and mRNA levels for
Bcl-2 in GC and mantle zone B cells (45).
Perhaps more intriguing is the matter of why cyclin D2 is repressed in such a highly proliferative cellular compartment.
One possibility is that cyclin D2 may have additional functions,
independent of its role in G1-to-S progression. Recent studies
have established cyclin D as an important regulator of cell
growth. For example, homozygous inactivation of the cyclin D1
gene produces a small mouse phenotype and manipulating the
cyclin D pathway in Drosophila results in altered organism
growth (19, 21, 46, 47). Important in this regard, Shaffer et al.
(42) have noted that the gene expression signature of GC B cells
favors cell proliferation at the expense of cellular growth. This
observation raises the possibility that cyclin D2 might be important in the intracellular pathway leading to B cell growth. If
so, GC cells may opt to repress cyclin D2 expression and, thus,
to forego cellular growth in favor of cell proliferation.
Several studies have implicated D-type cyclins in modulating
differentiation programs (47). Cyclins D1 and D2 were shown
to inhibit myogenic differentiation through inactivation of the
muscle transcription factor MyoD (47– 49). In addition, cyclins D2 and D3, but not D1 inhibit the ability of 32D myeloid
cells to undergo neutrophil differentiation in response to
G-CSF (50). By extension, a role for cyclin D2 may be envisaged in modulating B cell fate within the GC. Naive splenic B
cells in the GC environment respond to Ag either by becoming
activated and differentiating into plasmacytic cells in the periarteriolar lymphoid sheath or, alternatively, by differentiating
into GC B cells in the follicular region. BCL-6, a transcriptional
repressor expressed in GC B cells, appears to function by skewing B cells away from plasmacytic differentiation and toward
GC differentiation (42, 44). Microarray analysis of B cell lines
engineered to express BCL-6 reveals a subset of genes that are
specifically repressed by BCL-6, including cyclin D2 (42, 44).
Should cyclin D2 function to inhibit GC B cell differentiation
program, its repression by BCL-6 might then be a requisite step
in GC B cell differentiation.
Downloaded from http://www.jimmunol.org/ by guest on June 16, 2017
B220⫹IgM⫺ pre-B cells between cyclin D2-deficient and wildtype mice (35). However, a recent study suggests that cyclin
D2-deficient mice exhibit half the number of Sca-1⫹B220⫹ B
cell progenitors in comparison to wild-type mice (37). In vitro
clonal analysis of bone marrow reveals a preponderance of
B220⫹CD19low pre-B cell colonies derived from cyclin D2-deficient mice, whereas wild-type bone marrow yields a higher
proportion of B220⫹, CD19high pre-B cell colonies. Whether
these data point to impaired proliferation or perhaps decreased
survival of an early pro-B220⫹CD19⫺ B cell population in cyclin D2-deficient mice remains to be established (Fig. 2). In
contrast, analysis of bone marrow and splenic B220⫹IgM⫹ B
cell populations reveals near-normal levels in cyclin D2-deficient mice compared with wild type (35). The apparent normal
development of IgM⫹ B cells in the absence of cyclin D2 may
be an indication of an alternate pathway for the development of
IgM⫹ B cells that is dependent upon cyclin D3. The likelihood
of this scenario is supported by gene expression profiling of
mouse bone marrow B cell subsets, which reveals cyclin D3 expression during early B cell development (38).
In an earlier study, Tanguay et al. (39) demonstrated that
peritoneal CD5⫹B-1a cells express a low level of cyclin D2,
which is up-regulated in a rapid and transient manner in response to mitogenic stimulation. In contrast, cyclin D3 is expressed near the G1/S transition, and its expression occurs in the
absence of detectable cyclin D2 (40). The nonoverlapping expression of cyclins D2 and D3 suggests that these D-type cyclins may provide distinct functions in B-1a cells, with the latter
contributing to restriction point control. Interestingly, assessment of B-lymphoid populations in the peritoneal cavity from
cyclin D2⫺/⫺ mice reveals diminished numbers of peritoneal
CD5⫹B-1a cells, than in wild-type mice, whereas the numbers
of conventional IgMlowIgDhigh B cells in the peritoneal compartment are not significantly altered (Fig. 2) (35). The loss of
peritoneal CD5⫹B-1a cells in cyclin D2-deficient mice points
to an essential nonredundant function of cyclin D2 in this B cell
subset.
2903
BRIEF REVIEWS: Cyclin D2 IN B LYMPHOCYTE SUBSETS
Defects in signalosome components reveal insights into the signal
transduction pathways that regulate cyclin D2 induction
WEHI-231 cells. Lee and Koretzky (56) reported that overexpression of MAPK phosphatase-1, a phosphatase that can
dephosphorylate and inactivate ERK, blocked apoptosis of
WEHI-231 cells. However, it is possible that MAPK phosphatase-1, in addition to inhibiting ERK, may inactivate JNK
and/or p38MAPK in WEHI-231 cells; both JNK and p38MAPK
have been shown to play a role in BCR-induced apoptosis in
human B cell lines (57, 58).
Insights into the mechanism by which MEK1/2-ERK promotes BCR-mediated proliferation in mature B cells has been
provided recently by Piatelli et al. (59) with the observation that
inhibition of MEK1/2-ERK blocks de novo cyclin D2 gene
expression and phosphorylation of endogenous pRb. The upstream signals that regulate ERK activation include a contribution from both phospholipase C (PLC)␥2 and protein kinase C
(PKC), with the latter activating Raf-1 (60, 61). Recent studies
in splenic B cells and DT40 B cells point to a role for the B
lymphocyte adaptor molecule of 32 kDa (Bam32) in regulating
ERK activation in response to BCR cross-linking (62, 63).
Presumably Bam32, Sos-Ras, and PLC␥2-PKC function as
upstream regulators of ERK activity, however, the degree of
cross-talk between these pathways has not been established.
Bam32-deficient B cells are characterized by signaling defects in the ERK upstream regulators, hemopoietic progenitor
kinase (HPK1) and MEK kinase 1 (MEKK1) (62– 64). Bam32deficient B cells also exhibit defective BCR-induced proliferation
(62, 65); however, it has not been reported whether induction
of cyclin D2 is impaired in these B cells. These findings suggest
a model wherein the BCR signals cyclin D2 induction via a
Bam32-HPK1-MEKK1-MEK1/2-ERK signaling conduit (Fig. 3).
The observation that BLNK-deficient and xid B cells exhibit
defective NF-␬B signaling in addition to defective expression of
cyclin D2 suggests that NF-␬B activity may be required for cyclin D2 induction following BCR ligation (53, 66, 67). Definitive support for the regulation of cyclin D2 by NF-␬B was obtained from studies probing the molecular mechanisms
underlying the dependency of BCR-mediated proliferation on
PI3K activity (68, 69). The PI3Ks are divided into four classes
(IA, IB, II, and III) (70). The class IA enzymes are heterodimers
composed of a regulatory subunit (comprised of five different
subunits: p85␣, p55␣, p50␣, p85␤, and p55␥) and a catalytic
subunit (comprised of three different subunits: p110␣, -␤, and
-␦). The p85␣, p55␣, and p50␣ subunits are expressed by alternative splicing of the same gene; deletion of the first exon
results in a loss of p85␣ expression, but not of p55␣ and p50␣
(71). These mice exhibit a partial block in B cell development at
the pro- to pre-B cell transition, reduced numbers of mature
splenic B cells, and impaired T cell-independent Ab production. Reconstitution of Rag2⫺/⫺ embryos with p85␣⫺/⫺
p55␣⫺/⫺p50␣⫺/⫺ embryonic stem cells results in mice that
share many of the phenotypes found in p85␣⫺/⫺ mice (72).
Our laboratory and other investigators have recently demonstrated that p85␣-deficient splenic B cells do not proliferate in
response to BCR ligation due to a failure to phosphorylate pRb
(73, 74). A key determinant contributing to defective pRb phosphorylation is the complete absence of cyclin D2 induction (73,
74). Anti-Ig-stimulated p85␣-deficient splenic B cells display
normal ERK, yet exhibit impaired activation of the I␬B kinase
(IKK)␣,␤,␥-I␬B␣-NF-␬B pathway (73). Inhibition of PI3K
by wortmannin or LY294002 in normal splenic B cells recapitulates the NF-␬B and cyclin D2-cdk4/pRb signaling defects
The first evidence supporting the concept that the signalosome
is involved in regulating cyclin D2 expression was gleaned from
the analysis of splenic B cells from Bruton’s tyrosine kinase
(Btk)-deficient and xid mice (26, 51, 52). The latter immunodeficiency results from a naturally occurring point mutation in
the pleckstrin homology domain of Btk (reviewed in Ref. 52).
In particular, xid splenic B cells fail to proliferate in response to
thymus-independent type-II Ags due to impaired de novo cyclin D2 mRNA induction. Subsequently, it was shown that
adaptor protein B cell linker (BLNK)- and Vav-deficient
splenic B cells do not proliferate in response to BCR cross-linking due to defective cyclin D2 induction (53, 54). The reported
loss of cyclin D2 induction in Vav-deficient B cells results, at
least in part, from a failure of these cells to sustain normal calcium flux following BCR ligation (Fig. 3).
More recently, DeFranco and coworkers (55) demonstrated
that BCR-dependent proliferation of mature B cells requires
MEK1/2-ERK activation. These studies also ruled out a requirement for MEK1/2-ERK signaling in BCR-induced apoptosis of WEHI-231 cells and immature splenic B cells derived
from autoreconstituted mice. However, there does exist disparity regarding the role of ERK in BCR-induced apoptosis of
FIGURE 3. BCR-induced signal transduction pathways that positively regulate cyclin D2 expression. In response to BCR cross-linking, the signalosome
components, Btk, BLNK, and Vav, contribute to PLC␥2 activation, which in
turn leads to the generation of diacylgycerol (DAG) and inositol 1,4,5-trisphosphate (InsP3) and subsequent increase in intracellular Ca2⫹ and activation of
PKC, both of which are necessary for cyclin D2 induction. PKC and Sos-Grb2Ras activate the Raf1-MEK1/2-ERK signaling module; MEK1/2 is also activated by the Bam32-HPK1-MEKK1 signaling module. The p85␣ subunit of
PI3K acts to link the BCR to cyclin D2 induction by way of a PKC-Carma1IKK-I␬B␣-NF-␬B signaling module. In addition, the production of phosphatidylinositol 3,4,5-trisphosphates by PI3K represents an important target of
pleckstrin homology (PH) domain-containing proteins, including Btk, Vav,
and PLC␥2. CD19 is one of the main regulators of PI3K activity in B cells. The
cytosolic tail of CD19 contains tandem YXXM motifs that are phosphorylated
following BCR ligation and associate with the Src homology 2 domains of class
I PI3K regulatory subunits. The individual signal transduction molecules,
which have not yet been definitively linked to cyclin D2 induction in B cells, are
highlighted in red.
Downloaded from http://www.jimmunol.org/ by guest on June 16, 2017
2904
The Journal of Immunology
Is cyclin D2 a direct target of Myc in B cells?
Left unanswered by these studies is the identity of the transacting factors that couple NF-␬B or MEK1/2-ERK activities to
cyclin D2 gene promoter activation in B cells. In regard to the
former, previous studies have indicated that Rel is necessary for
c-myc transcription in response to BCR cross-linking (82). The
mouse c-myc gene promoter is a direct target of Rel/NF-␬B proteins and these trans-acting factors bind two sequence elements
(URE and IRE) positioned upstream of the P1 promoter and in
exon 1, respectively (82). In keeping with our studies in p85␣deficient B cells, Grumont et al. (83) have shown that PI3K
inhibition blocks I␬B␣ phosphorylation and degradation, nuclear translocation of NF-␬B1/c-Rel, and c-myc expression.
Several lines of evidence now support the notion that cyclin
D2 is a direct target gene of Myc (84, 85). For example, in primary human fibroblasts, conditional Myc expression results in
induction of cyclin D2 transcription (84). The cyclin D2 promoter contains two canonical E-boxes, of which only the distal
E-box appears to be a target of Myc (86). Bouchard et al. (86)
have shown that the cyclin D2 gene promoter is positively regulated by the recruitment of Myc/Max heterodimers to the distal E-box. In contrast, repression of cyclin D2 gene transcription
is mediated by Mad/Max complexes binding to the distal Ebox. An analogous role for Myc in cyclin D2 transcriptional regulation via the BCR has not been established; however, a recent
study in T cells suggests that Myc is not involved in IL-2R-mediated cyclin D2 induction, in part, because the E-boxes appear
to preferentially bind upstream stimulatory factor-1 and upstream stimulatory factor-2 (87). Moreover, both E-boxes are
dispensable for cyclin D2 gene promoter activation (87). Cyclin
D2 transcription appears to be mediated by Stat5, which binds
to an enhancer element located at ⫺1204 in the cyclin D2 gene
promoter (87, 88). Interestingly, IL-2R-induced cyclin D2 transcription is dependent on PI3K activity in T cells, similar to the
situation in B cells stimulated through the BCR.
The NF-␬B-cyclin D2 pathway and B cell lymphomas
Understanding the signal transduction pathways leading to B
cell proliferation has important implications for designing molecularly targeted therapies for the treatment of B cell diseases.
DLBCL represents the most common type of non-Hodgkins
lymphoma, comprising 30 – 40% of adult non-Hodgkin lymphomas (89). From a clinical perspective, only 40% of these
patients are cured by chemotherapeutic regimens. Gene expression profiling of DLBCL tumors has made clear the existence of
two DLBCL subgroups that are characterized by distinct gene
expression signatures (41). Notably, GC B-like (GCB) DLBCLs are characterized by a gene expression signature that resembles normal tonsillar GC B cells, whereas activated B cell-like
(ABC) DLBCLs express a gene signature mirroring that of human peripheral blood B cells following BCR cross-linking (41).
GCB DLBCLs correlate with a more favorable prognosis compared with ABC DLBCLs (41). DNA microarrays reveal that
ABC DLBCLs express genes known to be NF-␬B targets,
whereas GCB DLBCLs generally have low expression of these
genes (41, 42). The NF-␬B target genes include among others,
I␬B␣ and cyclin D2. ABC DLBCL cell lines exhibit constitutive
IKK, I␬B␣ degradation, and nuclear NF-␬B activity, whereas
GCB DLBCL cell lines are devoid of constitutive NF-␬B activity (90). Ectopic expression of a superrepressor form of I␬B␣ or
a dominant-interfering IKK␤ results in cell death to ABC DLBCL cell lines. The activity of NF-␬B is also required for cell
cycle progression insofar as inhibition of NF-␬B signaling results in G1-phase arrest in ABC DLBCLs. Interestingly, the human cyclin D2 gene promoter contains two NF-␬B binding sites
(91), suggesting that G1-phase arrest in response to inhibition
of NF-␬B in ABC DLBCLs is due to a loss of sustained cyclin
D2 gene expression. Because cell cycle arrest causes apoptosis in
many tumor cell types, the loss of NF-␬B-targeted cyclin D2
Downloaded from http://www.jimmunol.org/ by guest on June 16, 2017
observed in p85␣-deficient B cells. Moreover, selective inhibition of individual components of the NF-␬B pathway in normal B cells abolishes anti-Ig-stimulated cyclin D2-cdk4/pRb
pathway activation. These data together define a PI3K/NF-␬Bdependent pathway that is essential for BCR-mediated cyclin
D2 induction (Fig. 3).
Although it is well established that PI3K regulates NF-␬B activation, the nature of the proximal signals that link PI3K to
NF-␬B activity is not fully understood. An important consideration is the downstream effector of PI3K, Akt, which has been
reported to interact directly with and phosphorylate IKK␣
(75). However, the PKC inhibitor Gö6983 blocks BCR-induced I␬B␣ degradation without affecting Akt phosphorylation, suggesting that PKC may represent a key upstream regulator of IKK␣,␤,␥ in splenic B cells (69). PI3K might then
initiate NF-␬B activation via the downstream effector serine/
threonine kinase, 3⬘-phosphoinositide-dependent kinase 1,
which has been shown to phosphorylate and activate conventional PKCs and PKC-␨ and -␦ (76, 77). The idea that a conventional or novel PKC may be involved is supported by the
finding that Gö6850, an inhibitor of conventional/novel
PKCs, blocks cyclin D2 induction following BCR ligation (74).
Whether the Gö6850-sensitive PKC functions in the pathway
leading to Raf-1/MEK1/2-ERK activation, IKK␣,␤,␥-I␬B␣NF-␬B activation, or both has not been established (Fig. 3).
PKC␦ is probably not involved given recent reports that 1)
BCR-induced NF-␬B activation is normal in PKC␦-deficient
splenic B cells; and 2) treatment of normal B cells with the
PKC␦ inhibitor, rottlerin, does not inhibit BCR-induced
NF-␬B activation (78, 79). An attractive candidate is PKC␤
based on the finding that PKC␤-deficient mice do not activate
NF-␬B in response to BCR cross-linking (80). Recent studies
indicate that the caspase recruitment domain protein Bcl10
may function to couple PKC␤ to NF-␬B activation, apparently
via a mechanism that involves phosphorylation of Bcl10 by the
adaptor protein caspase recruitment domain-MAGUK1
(Carma-1) (reviewed in Ref. 64). However, BCR-mediated cyclin D2 induction is normal in PKC␤-deficient splenic B cells
despite loss of NF-␬B activity (81). These findings suggest a
requirement for an NF-␬B-independent pathway in cyclin D2
induction. It would seem likely that components of the ERK
pathway may be sufficient to signal cyclin D2 induction in the
absence of NF-␬B activation and do so via activity of a PKC(s)
other than PKC␤. Yet, signaling through MEK1/2-ERK is intact in BLNK- and p85␣-deficient splenic B cells, which exhibit
neither NF-␬B activation nor cyclin D2 induction (54, 73).
These results raise the possibility that a compensatory MEK1/
2-ERK- and NF-␬B-independent pathway may be up-regulated in PKC␤-deficient B cells to facilitate cyclin D2 induction.
2905
2906
induction may contribute to the cytotoxic effects in ABC DLBCLs. These findings suggest that molecularly targeted therapies that inhibit components of the NF-␬B/cyclin D2 pathway
may prove useful in treating clinically intractable DLBCLs.
Concluding remarks
Recent work has suggested some new ways to think about the
function of cyclin D2 in B cells. That cyclin D2 may have additional roles in B cells, beyond regulating cdk4/6 and pRb,
represents an exciting area of investigation that may provide
novel insights into the regulation of B lymphocyte growth and
differentiation. We are also beginning to define the signal transduction networks that serve to link the BCR to cyclin D2 induction in mature B cells. On this point, MEK1/2-ERK and
NF-␬B pathways have emerged as major signaling conduits. Finally, understanding the regulation of cyclin D2 has important
implications for the treatment of lymphoid malignancies, such
as DLBCL.
I apologize to those investigators whose work was not cited due to space limitations. I thank Dr. Jennifer Mataraza (Department of Biology, Boston College,
Chestnut Hill, MA) and Craig Kasprzak (Boston College) for a critical reading
of the manuscript. I also thank Dr. Edward A. Clark (Departments of Microbiology and Immunology, University of Washington, Seattle, WA) for providing helpful comments.
References
1. Pardee, A. B. 1989. G1 events and regulation of cell proliferation. Science 246:603.
2. Craxton, A., K. L. Otipoby, A. Jiang, and E. A. Clark. 1999. Signal transduction pathways that regulate the fate of B lymphocytes. Adv. Immunol. 73:79.
3. Nevins, J. R. 1998. Toward an understanding of the functional complexity of the E2F
and retinoblastoma families. Cell Growth Differ. 9:585.
4. Sherr, C. J. 2000. The Pezcoller lecture: cancer cell cycles revisited. Cancer Res.
60:3689.
5. Ekholm, S. V., and S. I. Reed. 2000. Regulation of G1 cyclin-dependent kinases in the
mammalian cell cycle. Curr. Opin. Cell Biol. 12:676.
6. Meyerson, M., and E. Harlow. 1994. Identification of G1 kinase activity for cdk6, a
novel cyclin D partner. Mol. Cell. Biol. 14:2077.
7. Matsushime, H., M. E. Ewen, D. K. Strom, J.-Y. Kato, S. K. Hanks, M. F. Roussel,
and C. J. Sherr. 1992. Identification and properties of an atypical catalytic subunit
(p34PSK-J3/Cdk4) for mammalian D-type G1 cyclins. Cell 71:323.
8. Xiong, Y., T. Connolly, B. Futcher, and D. Beach. 1991. Human D-type cyclin. Cell
65:691.
9. Matsushime, H., M. F. Roussel, R. A. Ashmun, and C. J. Sherr. 1991. Colony-stimulating factor 1 regulates novel cyclins during the G1 phase of the cell cycle. Cell
65:701.
10. Motokura, T., T. Bloom, H. G. Kim, H. Juppner, J. V. Ruderman,
H. M. Kronenberg, and A. Arnold. 1991. A novel cyclin encoded by the bcl1-linked
candidate oncogene. Nature 350:512.
11. Sherr, C. J., and J. M. Roberts. 1999. CDK inhibitors: positive and negative regulators
of G1-phase progression. Genes Dev. 13:1501.
12. Morgan, D. O. 1995. Principles of CDK regulation. Nature 374:131.
13. Kato, J.-Y., M. Matsuoka, D. K. Strom, and C. J. Sherr. 1994. Regulation of cyclin
D-dependent kinase 4 (cdk4) by cdk4-activating kinase. Mol. Cell. Biol. 14:2713.
14. Cheng, M., V. Sexl, C. J. Sherr, and M. F. Roussel. 1998. Assembly of cyclin Ddependent kinase and titration of p27Kip1 regulated by mitogen-activated protein kinase kinase (MEK1). Proc. Natl. Acad. Sci. USA 95:1091.
15. Resnitzky, D., M. Gossen, H. Bujard, and S. I. Reed. 1994. Acceleration of the G1/S
phase transition by expression of cyclins D1 and E with an inducible system. Mol. Cell.
Biol. 14:1669.
16. Herrera, R. E., V. P. Sah, B. O. Williams, T. P. Makela, R. A. Weinberg, and T. Jacks.
1996. Altered cell cycle kinetics, gene expression, and G1 restriction point regulation
in Rb-deficient fibroblasts. Mol. Cell. Biol. 16:2402.
17. Lukas, J., H. Muller, J. Bartkova, D. Spitkovsky, A. A. Kjerulff, P. Jansen-Durr,
M. Strauss, and J. Bartek. 1994. DNA tumor virus oncoproteins and retinoblastoma
gene mutations share the ability to relieve the cell’s requirement for cyclin D1 function
in G1. J. Cell Biol. 125:625.
18. Tsutsui, T., B. Hesabi, D. S. Moons, P. P. Pandolfi, K. S. Hansel, A. Koff, and H.
Kiyokawa. 1999. Targeted disruption of CDK4 delays cell cycle entry with enhanced
p27(Kip1) activity. Mol. Cell. Biol. 19:7011.
19. Sicinski, P., J. L. Donaher, S. B. Parker, T. Li, A. Fazeli, H. Gardner, S. Z. Haslam,
R. T. Bronson, S. J. Elledge, and R. A. Weinberg. 1995. Cyclin D1 provides a link
between development and oncogenesis in the retina and breast. Cell 82:621.
20. Sicinski, P., J. L. Donaher, Y. Geng, S. B. Parker, H. Gardner, M. Y. Park,
R. L. Robker, J. S. Richards, L. K. McGinnis, J. D. Biggers, et al. 1996. Cyclin D2 is
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
an FSH-responsive gene involved in gonadal cell proliferation and oncogenesis. Nature 384:470.
Fantl, V., G. Stamp, A. Andrews, I. Rosewell, and C. Dickson. 1995. Mice lacking
cyclin D1 are small and show defects in eye and mammary gland development. Genes
Dev. 9:2364.
Ciemerych, M. A., A. M. Kenney, E. Sicinska, I. Kalaszczynska, R. T. Bronson,
D. H. Rowitch, H. Gardner, and P. Sicinski. 2002. Development of mice expressing
a single D-type cyclin. Genes Dev. 16:3277.
Tanguay, D. A., and T. C. Chiles. 1996. Regulation of the catalytic subunit (p34PSKJ3/cdk4) for the major D- type cyclin in mature B lymphocytes. J. Immunol. 156:539.
Solvason, N., W. W. Wu, N. Kabra, X. Wu, E. Lees, and M. C. Howard. 1996. Induction of cell cycle regulatory proteins in anti-immunoglobulin- stimulated mature B
lymphocytes. J. Exp. Med. 184:407.
Reid, S., and E. C. Snow. 1996. The regulated expression of cell cycle-related proteins
as B-lymphocytes enter and progress through the G1 cell cycle stage following delivery
of complete versus partial activation stimuli. Mol. Immunol. 33:1139.
Brorson, K., M. Brunswick, S. Ezhevsky, D. G. Wei, R. Berg, D. Scott, and
K. E. Stein. 1997. xid affects events leading to B cell cycle entry. J. Immunol. 159:135.
Lam, E. W., J. Glassford, L. Banerji, N. S. Thomas, P. Sicinski, and G. G. Klaus.
2000. Cyclin D3 compensates for loss of cyclin D2 in mouse B-lymphocytes activated
via the antigen receptor and CD40. J. Biol. Chem. 275:3479.
Chen-Kiang, S. 2003. Cell cycle control of plasma cell differentiation and tumorigenesis. Immunol. Rev. 194:39.
Su, T. T., and D. J. Rawlings. 2002. Transitional B lymphocyte subsets operate as
distinct checkpoints in murine splenic B cell development. J. Immunol. 168:2101.
Su, T. T., B. Guo, B. Wei, J. Braun, and D. J. Rawlings. 2004. Signaling in transitional type 2 B cells is critical for peripheral B-cell development. Immunol. Rev. 197:
161.
Loder, F., B. Mutschler, R. J. Ray, C. J. Paige, P. Sideras, R. Torres, M. C. Lamers, and
R. Carsetti. 1999. B cell development in the spleen takes place in discrete steps and is
determined by the quality of B cell receptor-derived signals. J. Exp. Med. 190:75.
Allman, D., R. C. Lindsley, W. DeMuth, K. Rudd, S. A. Shinton, and R. R. Hardy.
2001. Resolution of three nonproliferative immature splenic B cell subsets reveals
multiple selection points during peripheral B cell maturation. J. Immunol. 167:6834.
Chung, J. B., R. A. Sater, M. L. Fields, J. Erikson, and J. G. Monroe. 2002. CD23
defines two distinct subsets of immature B cells which differ in their responses to T cell
help signals. Int. Immunol. 14:157.
Carman, J. A., R. J. Wechsler-Reya, and J. G. Monroe. 1996. Immature stage B cells
enter but do not progress beyond the early G1 phase of the cell cycle in response to
antigen receptor signaling. J. Immunol. 156:4562.
Solvason, N., W. W. Wu, D. Parry, D. Mahony, E. W. Lam, J. Glassford,
G. G. Klaus, P. Sicinski, R. Weinberg, Y. J. Liu, et al. 2000. Cyclin D2 is essential for
BCR-mediated proliferation and CD5 B cell development. Int. Immunol. 12:631.
Jena, N., M. Deng, E. Sicinska, P. Sicinski, and G. Q. Daley. 2002. Critical role for
cyclin D2 in BCR/ABL-induced proliferation of hematopoietic cells. Cancer Res.
62:535.
Mohamedali, A., I. Soeiro, N. C. Lea, J. Glassford, L. Banerji, G. J. Mufti, E. W.-F.
Lam, and S. B. Thomas. 2003. Cyclin D2 controls B cell progenitor numbers. J. Leukocyte Biol. 74:1139.
Hoffmann, R., T. Seidl, M. Neeb, A. Rolink, and F. Melchers. 2002. Changes in gene
expression profiles in developing B cells of murine bone marrow. Genome Res. 12:98.
Tanguay, D. A., T. P. Colarusso, S. Pavlovic, M. Irigoyen, R. G. Howard, J. Bartek,
T. C. Chiles, and T. L. Rothstein. 1999. Early induction of cyclin D2 expression in
phorbol ester-responsive B-1 lymphocytes. J. Exp. Med. 189:1685.
Tanguay, D. A., T. P. Colarusso, C. Doughty, S. Pavlovic, T. L. Rothstein, and
T. C. Chiles. 2001. Differences in the signaling requirements for activation of assembled cyclin D3-cdk4 complexes in B-1 and B-2 lymphocytes. J. Immunol. 166:4273.
Alizadeh, A. A., M. B. Eisen, R. E. Davis, C. Ma, I. S. Lossos, A. Rosenwald,
J. C. Boldrick, H. Sabet, T. Tran, X. Yu, et al. 2000. Identification of molecularly and
clinically distinct types of diffuse large B-cell lymphoma by gene expression profiling.
Nature 403:503.
Shaffer, A. L., A. Rosenwald, E. M. Hurt, J. M. Giltnane, L. T. Lam, O. K. Pickeral,
and L. M. Staudt. 2001. Signatures of the immune response. Immunity 15:375.
Klein, U., Y. Tu, G. A. Stolovitzky, J. L. Keller, J. Haddad, Jr., V. Miljkovic,
G. Cattoretti, A. Califano, and R. Dalla-Favera. 2003. Transcriptional analysis of the
B cell germinal center reaction. Proc. Natl. Acad. Sci. USA 100:2639.
Shaffer, A. L., X. Yu, Y. He, J. Boldrick, E. P. Chan, and L. M. Staudt. 2000. BCL-6
represses genes that function in lymphocyte differentiation, inflammation, and cell
cycle control. Immunity 13:199.
Chleq-Deschamps, C. M., D. P. LeBrun, P. Huie, D. P. Besnier, R. A. Warnke, R. K.
Sibley, and M. L. Cleary. 1993. Topographical dissociation of BCL-2 messenger RNA
and protein expression in human lymphoid tissues. Blood 81:293.
Datar, S. A., H. W. Jacobs, A. F. de la Cruz, C. F. Lehner, and B. A. Edgar. 2000. The
Drosophila cyclin D-Cdk4 complex promotes cellular growth. EMBO J. 19:4543.
Coqueret, O. 2002. Linking cyclins to transcriptional control. Gene 299:35.
Skapek, S. X., J. Rhee, D. B. Spicer, and A. B. Lassar. 1995. Inhibition of myogenic
differentiation in proliferating myoblasts by cyclin D1-dependent kinase. Science
267:1022.
Rao, S. S., C. Chu, and D. S. Kohtz. 1994. Ectopic expression of cyclin D1 prevents
activation of gene transcription by myogenic helix-loop-helix regulators. Mol. Cell.
Biol. 14:5259.
Kato, J.-Y., and C. J. Sherr. 1993. Inhibition of granulocyte differentiation by G1
cyclins, D2 and D3, but not D1. Proc. Natl. Acad. Sci. USA 90:11513.
Forssell, J., A. Nilsson, and P. Sideras. 1999. Bruton’s tyrosine-kinases-deficient murine B lymphocytes fail to enter S phase when stimulated with anti-immunoglobulin
plus interleukin-4. Scand. J. Immunol. 49:155.
Downloaded from http://www.jimmunol.org/ by guest on June 16, 2017
Acknowledgments
BRIEF REVIEWS: Cyclin D2 IN B LYMPHOCYTE SUBSETS
The Journal of Immunology
73. Piatelli, M. J., C. Wardle, J. Blois, C. Doughty, B. R. Schram, T. L. Rothstein, and
T. C. Chiles. 2004. Phosphatidylinositol 3-kinase-dependent mitogen-activated protein/extracellular signal-regulated kinase kinase 1/2 and NF-␬B signaling pathways are
required for B cell antigen receptor-mediated cyclin D2 induction in mature B cells.
J. Immunol. 172:2753.
74. Glassford, J., I. Soeiro, S. M. Skarell, L. Banerji, M. Holman, G. G. B. Klaus,
T. Kadowaki, S. Koyasu, and E. W.-F. Lam. 2003. BCR targets cyclin D2 via Btk and
the p85␣ subunit of PI3-K to induce cell cycle progression in primary mouse B cells.
Oncogene 22:2248.
75. Ozes, O. N., L. D. Mayo, J. A. Gustin, S. R. Pfeffer, L. M. Pfeffer, and D. B. Donner.
1999. NF-␬B activation by tumor necrosis factor requires the Akt serine-threonine
kinase. Nature 401:82.
76. Le Good, J. A., W. H. Ziegler, D. B. Parekh, D. R. Alessi, P. Cohen, and P. J. Parker.
1998. Protein kinase C isotypes controlled by phosphoinositide 3-kinase through the
protein kinase PDK1. Science 281:2042.
77. Dutil, E. M., A. Toker, and A. C. Newton. 1998. Regulation of conventional protein
kinase C isozymes by phosphoinositide-dependent kinase 1 (PDK-1). Curr. Biol.
8:1366.
78. Antony, P., J. B. Petro, G. Carlesso, N. P. Shinners, J. Lowe, and W. N. Khan. 2003.
B cell receptor directs the activation of NFAT and NF-␬B via distinct molecular mechanisms. Exp. Cell Res. 291:11.
79. Mecklenbräuker, I., K. Saijo, N.-Y. Zheng, M. Leitges, and A. Tarakhovsky. 2002.
Protein kinase C␦ controls self-antigen-induced B-cell tolerance. Nature 416:860.
80. Saijo, K., I. Mecklenbrauker, A. Santan, M. Leitger, C. Schmedt, and A. Tarakhovsky.
2002. Protein kinase C␤ controls nuclear factor ␬B activation in B cells through selective regulation of the I␬B kinase ␣. J. Exp. Med. 195:1647.
81. Su, T. T., B. Guo, Y. Kawakami, K. Sommer, K. Chae, L. A. Humphries, R. M. Kato,
S. Kang, L. Patrone, R. Wall, et al. 2002. PKC-␤ controls I␬B kinase lipid raft recruitment and activation in response to BCR signaling. Nat. Immunol. 3:780.
82. Lee, H., M. Arsura, M. Wu, M. P. Duyao, A. J. Buckler, and G. E. Sonenshein. 1995.
Role of the Rel-related factors in control of c-myc gene transcription in receptor-mediated apoptosis of the murine B cell WEHI 231 line. J. Exp. Med. 181:1169.
83. Grumont, R. J., A. Strasser, and S. Gerondakis. 2002. B cell growth is controlled by
phosphatidylinositol 3-kinase-dependent induction of Rel/NF-␬B regulated c-myc
transcription. Mol. Cell 10:1283.
84. Coller, H. A., C. Grandori, P. Tamayo, T. Colbert, E. S. Lander, R. N. Eisenman, and
T. R. Golub. 2000. Expression analysis with oligonucleotide microarrays reveals that
MYC regulates genes involved in growth, cell cycle, signaling, and adhesion. Proc.
Natl. Acad. Sci. USA 97:3260.
85. Bouchard, C., K. Thieke, A. Mairer, R. Saffrich, J. Hanley-Hyde, W. Ansorge,
S. Reed, P. Sicinski, J. Bartek, and M. Eilers. 1999. Direct induction of cyclin D2 by
Myc contributes to cell cycle progression and sequestration of p27. EMBO J. 18:5321.
86. Bouchard, C., O. Dittrich, A. Kiermaier, K. Dohmann, A. Menkel, M. Eilers, and
B. Luscher. 2001. Regulation of cyclin D2 gene expression by the Myc/Max/Mad network: Myc-dependent TRRAP recruitment and histone acetylation at the cyclin D2
promoter. Genes Dev. 15:2042.
87. Moon, J. J., E. D. Rubio, A. Martino, A. Krumm, and B. H. Nelson. 2004. A permissive role for phosphatidylinositol 3-kinase in the Stat5-mediated expression of cyclin D2 by the interleukin-2 receptor. J. Biol. Chem. 279:5520.
88. Martino, A., J. H. Holmes IV, J. D. Lord, J. J. Moon, and B. H. Nelson. 2001. Stat5
and Sp1 regulate transcription of the cyclin D2 gene in response to IL-2. J. Immunol.
166:1723.
89. 1997. A clinical evaluation of the International Lymphoma Study Group classification
of non-Hodgkin’s lymphoma: the Non-Hodgkin’s Lymphoma Classification Project.
Blood 89:3909.
90. Davis, R. E., K. D. Brown, U. Siebenlist, and L. M. Staudt. 2001. Constitutive nuclear
factor ␬B activity is required for survival of activated B cell-like diffuse large B cell
lymphoma cells. J. Exp. Med. 194:1861.
91. Brooks, A. R., D. Shiffman, C. S. Chan, E. E. Brooks, and P. G. Milner. 1996. Functional analysis of the human cyclin D2 and cyclin D3 promoters. J. Biol. Chem.
271:9090.
Downloaded from http://www.jimmunol.org/ by guest on June 16, 2017
52. Satterthwaite, A. B., and O. N. Witte. 2000. The role of Bruton’s tyrosine kinase in
B-cell development and function: a genetic perspective. Immunol. Rev. 175:120.
53. Tan, J. E -L., S.-W. Wong, S. K.-E. Gan, S. Xu, and K.-P. Lam. 2001. The adaptor
protein BLNK is required for B cell antigen receptor-induced activation of nuclear
factor-␬B and cell cycle entry and survival of B lymphocytes. J. Biol. Chem.
276:20055.
54. Glassford, J., M. Holman, L. Banerji, E. Clayton, G. G. B. Klaus, M. Turner, and
E. W.-F. Lam. 2001. Vav is required for cyclin D2 induction and proliferation of
mouse B lymphocytes activated via the antigen receptor. J. Biol. Chem. 276:41040.
55. Richards, J. D., S. H. Dave, C.-H. G. Chou, A. A. Mamchak, and A. L. DeFranco.
2001. Inhibition of the MEK/ERK signaling pathway blocks a subset of B cell responses to antigen. J. Immunol. 166:3855.
56. Lee, J. R., and G. A. Koretzky. 1998. Extracellular signal-regulated kinase-2, but not
c-Jun NH2-terminal kinase, activation correlates with surface IgM-mediated apoptosis in the WEHI 231 B cell line. J. Immunol. 161:1637.
57. Graves, J. D., K. E. Draves, A. Craxton, J. Saklatvala, E. G. Krebs, and E. A. Clark.
1996. Involvement of stress-activated protein kinase and p38 mitogen-activated protein kinase in mIgM-induced apoptosis of human B lymphocytes. Proc. Natl. Acad.
Sci. USA 93:13814.
58. Sutherland, C. L., A. W. Heath, S. L. Pelech, P. R. Young, and M. R. Gold. 1996.
Differential activation of the ERK, JNK, and p38 mitogen-activated protein kinases
by CD40 and the B cell antigen receptor. J. Immunol. 157:3381.
59. Piatelli, M. J., C. Doughty, and T. C. Chiles. 2002. Requirement for a hsp90 chaperone-dependent MEK1/2-ERK pathway for B cell antigen receptor-induced cyclin
D2 expression in mature B lymphocytes. J. Biol. Chem. 277:12144.
60. Jacob, A., D. Cooney, M. Pradhan, and K. M. Coggeshall. 2002. Convergence of
signaling pathways on the activation of ERK in B cells. J. Biol. Chem. 277:23420.
61. Gold, M. R., J. S. Stewart, and S. L. Pelech. 1992. Selective activation of p42 mitogenactivated protein (MAP) kinase in murine B lymphoma cell lines by membrane immunoglobulin cross-linking: evidence for protein kinase C-independent and -dependent mechanisms of activation. Biochem. J. 287:269.
62. Han, A., K. Saijo, I. Mecklenbrauker, A. Tarakhovsky, and M. C. Nussenzweig. 2003.
Bam32 links the B cell receptor to ERK and JNK and mediates B cell proliferation but
not survival. Immunity 19:621.
63. Niiro, H., A. Maeda, T. Kurosaki, and E. A. Clark. 2002. The B lymphocyte adaptor
molecule of 32 kD (Bam32) regulates B cell antigen receptor signaling and cell survival. J. Exp. Med. 195:143.
64. Niiro, H., and E. A. Clark. 2003. Branches of the B cell antigen receptor pathway are
directed by protein conduits Bam32 and Carma1. Immunity 19:637.
65. Fournier, E., S. J. Isakoff, K. Ko, C. J. Cardinale, G. G. Inghirami, Z. Li,
M. A. Curotto de Lafaille, and E. Y. Skolnik. 2003. The B cell SH2/PH domaincontaining adaptor Bam32/DAPP1 is required for T cell-independent II antigen responses. Curr. Biol. 13:1858.
66. Petro, J. B., S. M. Rahman, D. W. Ballard, and W. N. Khan. 2000. Bruton’s tyrosine
kinase is required for activation of I␬B kinase and nuclear factor ␬B in response to B
cell receptor engagement. J. Exp. Med. 191:1745.
67. Bajpai, U. D., K. Zhang, M. Teutsch, R. Sen, and H. H. Wortis. 2000. Bruton’s
tyrosine kinase links the B cell receptor to nuclear factor ␬B activation. J. Exp. Med.
191:1735.
68. Brennan, P., A. M. Mehl, M. Jones, and M. Rowe. 2002. Phosphatidylinositol 3-kinase is essential for the proliferation of lymphoblastoid cells. Oncogene 21:1263.
69. Bone, H., and N. A. Williams. 2001. Antigen-receptor cross-linking and lipopolysaccharide trigger distinct phosphoinositide 3-kinase-dependent pathways to NF-␬B activation in primary B cells. Int. Immunol. 13:807.
70. Fruman, D. A., and L. C. Cantley. 2002. Phosphoinositide 3-kinase in immunological
systems. Semin. Immunol. 14:7.
71. Suzuki, H., Y. Terauchi, M. Fujiwara, S. Aizawa, Y. Yazaki, T. Kadowaki, and
S. Koyasu. 1999. Xid-like immunodeficiency in mice with disruption of the p85␣
subunit of phosphoinositide 3-kinase. Science 283:390.
72. Fruman, D. A., S. B. Snapper, C. M. Yballe, L. Davidson, J. Y. Yu, F. W. Alt, and
L. C. Cantley. 1999. Impaired B cell development and proliferation in absence of
phosphoinositide 3-kinase p85␣. Science 283:393.
2907