Krüppel-like Factors in Lymphocyte Biology
Geoffrey T. Hart, Kristin A. Hogquist and Stephen C.
Jameson
This information is current as
of June 15, 2017.
Subscription
Permissions
Email Alerts
This article cites 72 articles, 34 of which you can access for free at:
http://www.jimmunol.org/content/188/2/521.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 © 2012 by The American Association of
Immunologists, Inc. All rights reserved.
Print ISSN: 0022-1767 Online ISSN: 1550-6606.
Downloaded from http://www.jimmunol.org/ by guest on June 15, 2017
References
J Immunol 2012; 188:521-526; ;
doi: 10.4049/jimmunol.1101530
http://www.jimmunol.org/content/188/2/521
Krüppel-like Factors in Lymphocyte Biology
Geoffrey T. Hart, Kristin A. Hogquist, and Stephen C. Jameson
T
he founding member of the Krüppel-like factor (KLF)
family was found to regulate development in Drosophila melanogaster, mutants in this gene leading to
embryonic deformity (1, 2), hence the name Krüppel (which
means cripple in German). All KLFs, which are related to the
sp1 family of transcription factors, share a highly homologous
set of three DNA-binding zinc fingers at the C terminus that
imparts specificity for CACCC boxes and related GC-rich
DNA regions (3, 4). Individual factors are distinguished by
regions that dictate regulation and binding partner specificity.
There are at least 17 KLFs in mammals, and they have been
implicated in numerous biological processes, especially in the
context of cell differentiation and quiescence. For example,
KLF1 (also called EKLF) is critical for the switch to adult
hemoglobin expression in developing erythrocytes, whereas
KLF4 (GKLF) is well studied as a factor involved in reprogramming mature cells to become induced pluripotent stem
cells (3, 4).
Interest in the KLF family among immunologists was
sparked by a report from Leiden’s group (5), which showed that
deficiency for KLF2 (LKLF) caused upregulation of T cell activation markers and a dramatic loss of peripheral T cells.
This led to the hypothesis that KLF2 enforced naive T cell
quiescence (5–7). However, as we discuss next, further study on
the function of KLF2 have lead to reinterpretation of its
function. This serves as a good example of how the varied activities of KLFs in lymphocyte biology can confound simple
characterization of their role.
While the function of individual KLFs is still being deciphered, some general principles are emerging. One principle
Department of Laboratory Medicine and Pathology, Center for Immunology, University
of Minnesota, Minneapolis, MN 55414
Received for publication September 19, 2011. Accepted for publication November 3,
2011.
This work was supported by National Institutes of Health Grant AI R3738903 (to
S.C.J.) and Predoctoral Training Grant T32 AI07313 (to G.T.H.).
Address correspondence and reprint requests to Stephen C. Jameson, University of Minnesota Medical Center, 2101 6th Street SE, Minneapolis, MN 55414. E-mail address:
[email protected]
www.jimmunol.org/cgi/doi/10.4049/jimmunol.1101530
is that KLFs participate in multiple aspects of lymphocyte
differentiation, trafficking, and function, especially in the context of regulating late stages of maturation. Another principle is
the appreciation that distinct KLFs may balance each other in
control of certain differentiation steps; this is illustrated by the
reciprocal effects of KLF2 and KLF13 deficiency in NKT cell
differentiation, and by examples of both cooperation and antagonism in the control of B cell subset differentiation by KLF2
and KLF3. The well-characterized functions of KLFs are illustrated in Fig. 1, but it is likely that we have only scratched
the surface of regulation by this versatile family of transcription
factors.
Lymphocyte quiescence
T cells. KLF2 is induced late during maturation of thymocytes
and is maintained in peripheral naive T cells (5, 8–11). Upon
T cell activation, KLF2 expression is lost, a process that is
thought to initiate with KLF2 protein degradation (probably
involving ubiquitination) and subsequent loss of KLF2 mRNA
(5, 7, 12–15). Re-expression of KLF2 occurs late in the effector phase of the CD8 T cell response, as memory cells
begin to differentiate (a process that can be directed by appropriate cytokines) (5, 7, 12–15). These expression patterns,
together with data showing that KLF2-deficient thymocytes
display activation markers suggested that KLF2 was important
for maintaining naive T cell quiescence. In this model, the
loss of KLF2 induced inappropriate activation of mature
thymocytes and their subsequent cell death (5, 6). This idea
was reinforced by studies indicating that KLF2 inhibits cell
cycle progression, as dramatically shown by the capacity of
KLF2 overexpression to halt tumor cell line proliferation and
by evidence that KLF2 inhibits expression of c-myc while
promoting transcription of p21WAF1/CIP1 (7, 16–19). KLF4,
a close relative of KLF2, is also downregulated upon T cell
activation (20), and it is interesting to note that KLF4deficient memory CD8+ T cells show a gradual increase in
representation over time, in keeping with a role for KLF4 in
restraining cell cycle progression (20).
Subsequent data have led to the re-evaluation of the role of
KLFs in quiescence. For example, the deficit of naive KLF22/2
T cells in peripheral lymphoid sites is explained by the role of
KLF2 in lymphocyte trafficking rather than spontaneous cell
Abbreviations used in this article: FO, follicular; iNKT, invariant NKT; KLF, Krüppellike factor; MZ, marginal zone; S1PR1, sphingosine 1-phosphate receptor 1; Treg,
regulatory T cell.
Copyright Ó 2012 by The American Association of Immunologists, Inc. 0022-1767/12/$16.00
Downloaded from http://www.jimmunol.org/ by guest on June 15, 2017
The Krüppel-like factor family of transcription factors
plays an important role in differentiation, function,
and homeostasis of many cell types. While their role
in lymphocytes is still being determined, it is clear that
these factors influence processes as varied as lymphocyte
quiescence, trafficking, differentiation, and function.
This review will present an overview of how these factors
operate and coordinate with each other in lymphocyte
regulation. The Journal of Immunology, 2012, 188:
521–526.
522
BRIEF REVIEWS: THE ROLE OF KRÜPPEL-LIKE FACTORS IN LYMPHOCYTES
death (8, 15), and the immune response of KLF22/2 CD8+
T cells shows normal magnitude and kinetic characteristics (13).
But what of the spontaneous activated phenotype of KLF2deficient T cells? This is especially marked on KLF22/2 CD81
thymocytes, which show upregulation of markers such as
CXCR3, CD44, and CD122 typically observed on memory
cells and CD69 expression, which is normally induced upon
activation (5, 8, 21–23). It has become clear that the acquisition of memory markers on CD8+ T cells is actually due to
production of IL-4 from an expanded population of KLF22/2
NKT cells (22, 23), and that this activated phenotype is not
autonomous to KLF2 deficiency. Indeed, KLF2-deficient thymocytes maturing in the absence of the aberrant NKT cell
population did not upregulate memory markers (22, 23),
showing that the KFL2 does not itself cause a loss of the naive,
quiescent T cell phenotype.
We will return to the specific roles of KLF2 in T cell trafficking and differentiation later, but highlighting these points
is important to illustrate that what appeared to be a clear-cut
role of KLF2 in quiescence regulation could be explained
by a composite of different functions.
At the same time, overexpression studies clearly show that
KLF2 can inhibit cell cycle progression; therefore, we should
not completely exclude its potential for control of quiescence. At
issue is the function of KLF2 expressed at physiologic levels.
Studies on activated CD8+ T cells provides a useful opportunity to test how normal KLF2 reinduction influences expression of cell cycle regulatory factors. Interestingly, expression of
c-myc and p21CIP1 mRNA were found to be independent of
KLF2 expression in postactivated CD8+ T cells, and KLF2
deficiency did not lead to dysregulated T cell expansion in vivo
(13). Such findings do not rule out redundancy between distinct KLFs for control of cell cycle progression in T cells, or
that KLF2 (and/or related KLFs) enforce T cell quiescence
Lymphocyte trafficking
T cells. To exit the thymus and peripheral lymphoid tissues,
mature CD4+ and CD8+ T cells need to express sphingosine
1-phosphate receptor 1 (S1PR1), which detects the high levels
of S1P maintained in blood and lymph (31, 32). We and
others found that KLF2 is required for thymocyte expression
of S1PR1 (8, 15), suggesting that the lack of peripheral T cells
in KLF2-deficient mice can arise as a consequence of thymic
retention (8). Indeed, the accumulation of mature KLF2deficient T cells in the thymus is prevented by overexpression of S1PR1 (33), suggesting that this factor is the
key target of KLF2 for thymic emigration. Incidentally, the
upregulation of CD69 on KLF22/2 thymocytes can also be
attributed to impaired S1PR1 expression, because basal cell
surface expression of CD69 is restrained by a protein–protein
interaction with S1PR1 (34, 35). In addition, KLF2 directly
promotes expression of L-selectin (CD62L), which is relevant
for access of naive T cells to lymph nodes (8, 15), indicating
that this KLF coordinates distinct aspects of lymphocyte
trafficking. Whereas those studies focused on TCRab T cells,
similar changes in trafficking molecule expression were observed
for TCRgd T cells (36).
KLF2-deficient thymocytes also show depressed levels of b7
integrin and elevated expression of the CXCR3 chemokine
receptor (8, 21); however, subsequent studies suggest that these
changes are induced by IL-4 (produced by KLF2-deficient
NKT cells), rather than a consequence of direct gene control
by KLF2 (22, 23).
KLF2 is constitutively expressed in naive T cells, but is rapidly extinguished after T cell stimulation, a situation that
may help to retain activated T cells in lymphoid sites through
Downloaded from http://www.jimmunol.org/ by guest on June 15, 2017
FIGURE 1. KLFs regulate numerous processes in lymphocytes. The figure
illustrates known roles of KLFs in various aspects of lymphocyte differentiation and function. The KLFs written in green promote the indicated activity,
while KLFs indicted by red text inhibit the response. Note that KLFs expressed in the same cell may cooperate or antagonize with each other. The
role of KLF2 and KLF4 in control of T cell quiescence is shown with a dotted
line, since the physiologic significance of this pathway is unclear. The capacity
of KLF3 to oppose KLF2 in the control of some lymphocyte trafficking
molecules has been shown in B cells, but not yet addressed in T cells;
therefore, KLF3 is written in parenthesis. Details of individual functions are
provided in the text.
under certain circumstances. However, in contrast with more
clear-cut examples of factors regulating naive T cell quiescence,
such as recent studies on Foxp1 (24, 25), the role of KLFs is
currently unclear.
B cells. KLFs have also been proposed to control B cell quiescence. As for T cells, KLF2 and KLF4 are expressed in naive
B cells and are downregulated with B cell activation (26–28).
KLF4 overexpression was shown to induce cell cycle arrest of
transformed mouse pro/pre-B cell lines (29), whereas forced
expression of KLF4 or KLF9 caused reduced proliferation of
naive and memory human B cells after stimulation through
the BCR or CD40 (28). Because expression of KLF4 and
KLF9 were found to be lower in memory versus naive B cells,
these data offer a potential explanation for the superior proliferation of memory B cells (28). In contrast, Klaewsongkram
et al. (26) reported that KLF4 deficiency also causes a block
in B cell proliferation. KLF42/2 B cells (activated by BCR/
CD40) exhibited decreased progression through the cell cycle;
this correlated with reduced expression of cyclin D2 and the
finding that KLF4 directly binds the cyclin D2 promoter
(26). The apparent contradictions between these reports
reinforces the emerging concept that the function of KLF4
(and perhaps other KLFs) depends on the context of other
cell-cycle-regulatory factors (30). This concept adds to the difficulty in determining the significance of KLFs for enforcing
lymphocyte quiescence. Although several KLFs have been
shown to have the potential to strongly limit lymphocyte
cycle entry, their physiologic role in controlling quiescence
is not well defined.
The Journal of Immunology
Interestingly, manipulation of another KLF family member,
KLF3, mirrors some phenotypic changes observed in KLF2
deficient B cells. For example, a subset of KLF3 transgenic
follicular B cells expressed reduced CD62L levels, whereas
expression and function of CXCR5 and S1PR1 was not affected (49). Likewise, KLF3-deficient MZ B cells demonstrate
elevated expression of CD62L and b7-integrin (50). These
data suggest that KLF3 and KLF2 exert opposing functions
on these aspects of B cell trafficking (Fig. 1).
Lymphocyte development
Studies on KLF factors have suggested a minimal role in
early lymphocyte development—exceptions being a proposed
role for KLF5 in germline transcription from the Db1 promoter in thymocytes (51) and data showing that KLF4 deficiency leads to slightly decreased pre-B cell numbers (26).
However, recent work has revealed significant roles for KLFs
in differentiation of mature T and B cell subsets.
NKT and TCRgd T cells. It has become clear that distinct KLFs
promote and oppose differentiation of NKT cells during thymic
differentiation. Loss of KLF2 leads to an increase in thymic
CD1d-restricted invariant NKT (iNKT) cells (23). In addition,
KLF2-deficient mice have an exaggerated representation of an
unusual subset of TCRgd T cells that use Vd6.3/2 and bear the
CD4 coreceptor (36). Like iNKT cells, these nonconventional
TCRgd T cells express the transcription factor PLZF and have
been termed gd-NKT. The altered representation of these
populations is not simply a consequence of impaired S1PR1
expression by KLF22/2 T cells, because the frequency of these
subsets is not enhanced in S1PR12/2 animals (23, 36).
However, other genetic defects (including loss of Itk and CBP
and forced expression of class II MHC molecules on mouse
thymocytes) lead to a similar enhancement of PLZF+ iNKT
and/or gd-NKT cells (23, 52).
A surprising consequence of the enhanced production of
thymic iNKT cells is the appearance of memory-phenotype
T cells (especially CD8+ T cells) in the KLF2-deficient thymus (22, 23). Through a series of studies, this effect was
found to result from PLZF+ NKT cell production of IL-4,
which acted directly on mature thymocytes, leading to upregulation of the transcription factor Eomes and acquisition
of memory markers (22, 23, 52). As a result, this striking
change in thymocyte differentiation is not a direct effect of
KLF2 deficiency, but reflects a nonautonomous effect. Such
findings are useful to underscore the difficulty in dissecting
direct and indirect effects of KLF manipulation.
Interestingly, the expansion of PLZF+ NKT cells (and attendant IL-4–mediated bystander effect) is evident in some
normal mouse strains (e.g., BALB/c) but not others (e.g.,
C57BL/6) (23). Recent studies show that a different KLF,
KLF13, is also involved in this phenomena (53). KLF13 first
came to prominence as a transcription factor induced late in
T cell activation, which was found to be critical for induction
of the chemokine RANTES (CCL5) and regulation of T cell
apoptosis (54, 55). Newer studies show that KLF13 also
mediates control of PLZF+ NKT thymocyte development, as
revealed by the reduced numbers of such cells (and the absence of bystander memory-phenotype CD8+ thymocytes) in
KLF13-deficient BALB/c mice (53). Although KLF2 and
KLF13 deficiency have reciprocal effects on PLZF+ thymocyte differentiation, it is not clear whether and how these
Downloaded from http://www.jimmunol.org/ by guest on June 15, 2017
transcriptional downregulation of S1PR1 (12–15). Likewise,
KLF2 re-expression in postactivated CD8+ T cells is necessary for
S1PR1 and CD62L re-expression (13, 15), and this may be key
to allow late effector CD8+ T cells to begin recirculation again.
Such studies on the trafficking role of KLF2 have helped
define signaling pathways that control its expression. A key
mechanism in regulation of KLF2 expression involves PI3K
signaling. Strong induction of this pathway leads to activation
of AKT, which in turn induces sequestration of the transcription factor Foxo1 outside the nucleus (37). Foxo1 promotes expression of KLF2 in mature T cells (38–40), and
additional Foxo factors may also contribute to this regulation
(37). As has been discussed in a recent review, this pathway
provides a mechanism by which the strength of PI3K signaling can directly regulate T cell trafficking mediated, at least
in part, by control of KLF2 (41). Cytokines have a central role
in dictating KLF2 regulation. For activated mouse CD8+
T cells, high-dose IL-2 promotes efficient PI3K activation,
leading to low KLF2 expression, whereas exposure to IL-7, IL15, or weaker IL-2R signals permits KLF2 re-expression (13–
15, 42). In addition, cytokines involved in active effector
differentiation, such as IL-12 and IL-4, act to acutely repress
KLF2 re-expression (14, 15, 43, 44). The signaling pathways
involved in these processes are not well defined, although
JAK/STAT signaling appears to be critical (15, 43, 44). An
emerging picture is that changes in the cytokine milieu that an
activated T cell encounters has a dramatic effect on whether
the T cell is equipped to traffic (via KLF2 re-expression and
subsequent induction of S1PR1) or whether the cell is
retained in its local tissue. Indeed, recent studies have indicated that Th2 cells use a specialized mechanism to initiate
trafficking from lymph nodes. Th2 cells produce the protein
ECM1, which attenuates IL-2 signaling allowing for expression of KLF2 and S1PR1 and subsequent egress of Th2 cells
from peripheral lymphoid tissues (45).
B cells. Because S1PR1 is also required for recirculation of B cells
and, like T cells, B cells downregulate KLF2 after activation,
it would be reasonable to predict that KLF2 induces S1PR1
expression in the B cell pool. However, three recent studies
describing B cell-specific KLF2-deficient mice reached the
surprising conclusion that S1PR1 expression and function on
follicular B cells was minimally altered (46, 47) or actually
enhanced (48) by KLF2 loss. Whether distinct KLFs regulate
S1PR1 in B cells is unclear, but the role of KLF2 is clearly
different in T and follicular B cells. At the same time, the
representation of KLF2-deficient B cells in the blood was
significantly reduced, arguing for a partial effect on follicular
B cell recirculation. KLF2-deficient follicular B cells also
exhibited reduced CD62L and a4b7 integrin expression (46,
47), mirroring the phenotypic changes observed in KFL22/2
mature thymocytes (8). In one study, it was proposed that
KLF2 loss also leads to reciprocal patterns of dysregulated
CXCR5 expression by follicular and marginal zone B cells
(leading to mislocalization of follicular [FO] cells in the
marginal zone), and that KLF2 is required for S1PR1
expression by marginal zone (MZ) but not FO B cells (48).
These findings were not confirmed in other reports (46, 47),
and additional studies will be needed to test the idea that KLF2
exerts distinct effects on trafficking molecule expression in
different B cell subsets.
523
524
BRIEF REVIEWS: THE ROLE OF KRÜPPEL-LIKE FACTORS IN LYMPHOCYTES
been proposed to operate in complex networks (4, 50, 60),
and the activity of KLF2 and KLF3 in control of B cell subset
differentiation appears a good example of how factor may
have cooperative or opposite roles even within the same
lymphocyte lineage (Fig. 1).
Activated lymphocyte differentiation
In addition to alterations in lymphocyte development, it has
become clear that KLFs may also influence expansion and
differentiation of activated T and B cells.
Regulatory T cells. Foxp3-expressing regulatory CD4+ T cells
(Tregs) are vital for protecting against autoagressive responses,
and TGF-b is crucial for differentiation of a least some Treg
populations (61). KLF10 is rapidly induced by TGF-b (hence
the alternative name of KLF10 as TIEG1) and is important for
maturation and function of Tregs. KLF10 deficiency lead to
reduced differentiation of Foxp3+ CD4+ T cells and impaired
capacity of these cells to suppress airway inflammation in vivo
(62). Complementary studies showed that KLF10 overexpression
induces CD4+, CD252 cells to express TGF-b1 and FOXP3
(63). KLF10 activity hinges on differential ubiquitination,
with monoubiquination (involving the E3 ligase Itch) being
necessary for KLF10 to induce Foxp3 transcription, whereas
polyubiquitination of KLF10 (as occurs downstream of IL-6
signals) leads to KLF10 exclusion from the nucleus (62, 64).
Th17. Another family member, KLF4, has recently been implicated in differentiation of Th17 CD4+ T cells, which are
significant for their role in control of certain extracellular
bacteria as well as autoimmune diseases (65, 66). KLF4 was
found to be necessary for Th17 cell differentiation in vitro,
and in an adoptive transfer EAE model, and chromatin immunoprecipitation assays revealed that KLF4 occupies the
promoter of the IL-17 gene (67, 68). It is not clear how KLF4
integrates with other transcription factors that dictate Th17
differentiation, including RORgt, RORa, and STAT3 (65,
66); nor is it known whether KLF4 plays a similar role in
control of CD8+ Tc17 cells.
Recent studies have reported that HIF-1a is important for
the differentiation of Th17 and Treg cells (69). Interestingly,
studies in myeloid cells indicate that KLF2 can act as a negative regulator for HIF-1a expression (70), and it will be important to determine whether KLF2 has any similar activity
in lymphocytes.
B cell activation. Studies of KLF2 deficient B cells indicated
that they were compromised in the proliferation, survival, and
maintenance of responding follicular B cells (46–48). After in
vitro anti-BCR stimulation, KLF2-deficient follicular B cells
exhibited impaired proliferation and a substantial survival
defect, a situation that could be corrected by simultaneous
stimulation of BCR and CD40 (46). Because CD40 engagement is potent at activation of NF-kB signals (71), this
pathway may be promising for additional investigations into
the role of KLF2 in B cell priming. Following in vivo priming
for T dependent responses, Wilkelmann et al. (47) reported
a reduction in Ag specific Ig, a result that may be partially
explained by fewer KLF22/2 plasma cells/Ab secreting cells
in the bone marrow. It is unclear whether this relates to
compromised survival of activated B cells, or relates to the
proposed relevance of KLF2 in migration of plasma cells to
the bone marrow (72).
Downloaded from http://www.jimmunol.org/ by guest on June 15, 2017
factors intersect. Loss of KLF13 leads to reduced PLZF expression levels in thymic iNKT cells, and this could influence
the efficiency of their development (53). However, loss of
KLF2 does not appear to change PLZF expression levels (23),
and it is possible that the capacity of KLF2 to restrain proliferation acts to contain the size of the PLZF+ thymocyte
pool. Regardless, these findings serve as another example of
how different KLF family members intervene in lymphocyte
differentiation programs.
B cells subsets. Recent studies suggest that KLF2 and KLF3 have
opposing roles in the development of mature B cell subsets.
The three major mature B cell subsets—FO, MZ, and B1
B cells—show distinct phenotypic, functional, and tissue localization characteristics. Whereas the signals that determine
B cell subset differentiation are incompletely defined, some
transcription factors have been implicated in dictating FO,
MZ, or B1 generation. For example, Notch2 and Aiolos are
required for differentiation of MZ B cells (56). KLF2 shows
an intriguing pattern of gene expression in B cell lineage cells,
being uniformly expressed at the large pre-B cell stage (46,
57), but then showing differential expression in mature
B cells, following the order MZ , FO , B1 (46, 47). This
heterogeneity in expression correlates with a profound impact
on B cell subset generation in KLF2-deficient animals (46–
48). Using B cell specific conditional knockout approaches,
loss of KLF2 was shown to have a relatively modest effect on
the FO pool, but it lead to an increase in the size of the MZ
subset while the peritoneal B1 population was severely
depleted (46–48). Changes in the splenic transitional and
marginal zone precursor populations of B cells suggest these
effects reflect a role of KLF2 in B cell subset differentiation,
although an impact on homeostasis has not been ruled out.
Furthermore, it is currently unclear whether KLF2 deficiency
causes a loss of B1 cells or alterations in their trafficking (46–
48).
KLF3 may play a reciprocal role to KLF2 in controlling
the differentiation and homeostasis of certain B cell subsets.
KLF3 overexpression leads to substantial enhancement of
MZ B cell numbers (49), whereas the opposite phenotype has
been observed in KLF3 knockout mice (50). The capacity of
KLF3 overexpression to promote MZ B cell generation was
sufficiently strong to overcome CD19 deficiency and
blockade of the BAFF-family factor TACI (both of which are
important for MZ cell development/survival) but could not
substitute for the loss of Notch2, suggesting KLF3 is not
downstream of Notch2 (49). The finding that the loss of
KLF2 leads to increased KLF3 expression is consistent with
the idea that the two factors have antagonistic roles in B cell
subset differentiation. Interestingly, gene expression studies
indicate that KLF2-deficient (and also KLF3 transgenic) FO
B cells bear some transcriptional characteristics of MZ
B cells, suggesting that the regulation of KLF2 and KLF3 is
important for dictating FO B cell identity (46, 47, 49). It
remains to be seen whether these differentiation effects relate
to alterations in BCR signaling (as has been proposed previously) (58, 59) or altered trafficking. Alternatively, development or maintenance of B1 B cells evidently involves
distinct regulation, because deficiency for either KLF2 or
KLF3 caused a reduction in the size of the peritoneal B1
pool, whereas KLF3 overexpression leads to enhanced B1
B cell frequencies (46–50). Regulation between KLFs has
The Journal of Immunology
Conclusions
Acknowledgments
We thank Jamequist laboratory members, past and present, for discussions
and Merlin Crossley and Richard Pearson for communicating data ahead of
publication.
Disclosures
The authors have no financial conflicts of interest.
References
1. Wieschaus, E., C. Nusslein-Volhard, and H. Kluding. 1984. Krüppel, a gene whose
activity is required early in the zygotic genome for normal embryonic segmentation.
Dev. Biol. 104: 172–186.
2. Nüsslein-Volhard, C., and E. Wieschaus. 1980. Mutations affecting segment
number and polarity in Drosophila. Nature 287: 795–801.
3. McConnell, B. B., and V. W. Yang. 2010. Mammalian Krüppel-like factors in
health and diseases. Physiol. Rev. 90: 1337–1381.
4. Pearson, R., J. Fleetwood, S. Eaton, M. Crossley, and S. Bao. 2008. Krüppel-like
transcription factors: a functional family. Int. J. Biochem. Cell Biol. 40: 1996–2001.
5. Kuo, C. T., M. L. Veselits, and J. M. Leiden. 1997. LKLF: A transcriptional regulator of single-positive T cell quiescence and survival. Science 277: 1986–1990.
6. Di Santo, J. P. 2001. Lung Krüpple-like factor: a quintessential player in T cell
quiescence. Nat. Immunol. 2: 667–668.
7. Buckley, A. F., C. T. Kuo, and J. M. Leiden. 2001. Transcription factor LKLF is
sufficient to program T cell quiescence via a c-Myc—dependent pathway. Nat.
Immunol. 2: 698–704.
8. Carlson, C. M., B. T. Endrizzi, J. Wu, X. Ding, M. A. Weinreich, E. R. Walsh,
M. A. Wani, J. B. Lingrel, K. A. Hogquist, and S. C. Jameson. 2006. Kruppel-like
factor 2 regulates thymocyte and T-cell migration. Nature 442: 299–302.
9. Endrizzi, B. T., and S. C. Jameson. 2003. Differential role for IL-7 in inducing lung
Kruppel-like factor (Kruppel-like factor 2) expression by naive versus activated
T cells. Int. Immunol. 15: 1341–1348.
10. McCaughtry, T. M., M. S. Wilken, and K. A. Hogquist. 2007. Thymic emigration
revisited. J. Exp. Med. 204: 2513–2520.
11. Weinreich, M. A., S. C. Jameson, and K. A. Hogquist. 2011. Postselection thymocyte maturation and emigration are independent of IL-7 and ERK5. J. Immunol.
186: 1343–1347.
12. Grayson, J. M., K. Murali-Krishna, J. D. Altman, and R. Ahmed. 2001. Gene
expression in antigen-specific CD8+ T cells during viral infection. J. Immunol. 166:
795–799.
13. Takada, K., X. Wang, G. T. Hart, O. A. Odumade, M. A. Weinreich,
K. A. Hogquist, and S. C. Jameson. 2011. Kruppel-like factor 2 is required for
trafficking but not quiescence in postactivated T cells. J. Immunol. 186: 775–783.
14. Schober, S. L., C. T. Kuo, K. S. Schluns, L. Lefrancois, J. M. Leiden, and
S. C. Jameson. 1999. Expression of the transcription factor lung Krüppel-like factor
is regulated by cytokines and correlates with survival of memory T cells in vitro and
in vivo. J. Immunol. 163: 3662–3667.
15. Bai, A., H. Hu, M. Yeung, and J. Chen. 2007. Kruppel-like factor 2 controls T cell
trafficking by activating L-selectin (CD62L) and sphingosine-1-phosphate receptor
1 transcription. J. Immunol. 178: 7632–7639.
16. Zhang, X., S. V. Srinivasan, and J. B. Lingrel. 2004. WWP1-dependent ubiquitination and degradation of the lung Krüppel-like factor, KLF2. Biochem. Biophys.
Res. Commun. 316: 139–148.
17. Wu, J., and J. B. Lingrel. 2004. KLF2 inhibits Jurkat T leukemia cell growth via
upregulation of cyclin-dependent kinase inhibitor p21WAF1/CIP1. Oncogene 23:
8088–8096.
18. Conkright, M. D., M. A. Wani, and J. B. Lingrel. 2001. Lung Krüppel-like factor
contains an autoinhibitory domain that regulates its transcriptional activation by
binding WWP1, an E3 ubiquitin ligase. J. Biol. Chem. 276: 29299–29306.
19. Haaland, R. E., W. Yu, and A. P. Rice. 2005. Identification of LKLF-regulated
genes in quiescent CD4+ T lymphocytes. Mol. Immunol. 42: 627–641.
20. Yamada, T., C. S. Park, M. Mamonkin, and H. D. Lacorazza. 2009. Transcription
factor ELF4 controls the proliferation and homing of CD8+ T cells via the Krüppellike factors KLF4 and KLF2. Nat. Immunol. 10: 618–626.
21. Sebzda, E., Z. Zou, J. S. Lee, T. Wang, and M. L. Kahn. 2008. Transcription factor
KLF2 regulates the migration of naive T cells by restricting chemokine receptor
expression patterns. Nat. Immunol. 9: 292–300.
22. Weinreich, M. A., K. Takada, C. Skon, S. L. Reiner, S. C. Jameson, and
K. A. Hogquist. 2009. KLF2 transcription-factor deficiency in T cells results in
unrestrained cytokine production and upregulation of bystander chemokine
receptors. Immunity 31: 122–130.
23. Weinreich, M. A., O. A. Odumade, S. C. Jameson, and K. A. Hogquist. 2010.
T cells expressing the transcription factor PLZF regulate the development of
memory-like CD8+ T cells. Nat. Immunol. 11: 709–716.
24. Feng, X., H. Wang, H. Takata, T. J. Day, J. Willen, and H. Hu. 2011. Transcription factor Foxp1 exerts essential cell-intrinsic regulation of the quiescence of
naive T cells. Nat. Immunol. 12: 544–550.
25. Feng, X., G. C. Ippolito, L. Tian, K. Wiehagen, S. Oh, A. Sambandam, J. Willen,
R. M. Bunte, S. D. Maika, J. V. Harriss, et al. 2010. Foxp1 is an essential transcriptional regulator for the generation of quiescent naive T cells during thymocyte
development. Blood 115: 510–518.
26. Klaewsongkram, J., Y. Yang, S. Golech, J. Katz, K. H. Kaestner, and N. P. Weng.
2007. Krüppel-like factor 4 regulates B cell number and activation-induced B cell
proliferation. J. Immunol. 179: 4679–4684.
27. Yusuf, I., M. G. Kharas, J. Chen, R. Q. Peralta, A. Maruniak, P. Sareen,
V. W. Yang, K. H. Kaestner, and D. A. Fruman. 2008. KLF4 is a FOXO target
gene that suppresses B cell proliferation. Int. Immunol. 20: 671–681.
28. Good, K. L., and S. G. Tangye. 2007. Decreased expression of Kruppel-like factors
in memory B cells induces the rapid response typical of secondary antibody
responses. Proc. Natl. Acad. Sci. USA 104: 13420–13425.
29. Kharas, M. G., I. Yusuf, V. M. Scarfone, V. W. Yang, J. A. Segre, C. S. Huettner,
and D. A. Fruman. 2007. KLF4 suppresses transformation of pre-B cells by ABL
oncogenes. Blood 109: 747–755.
30. Rowland, B. D., and D. S. Peeper. 2006. KLF4, p21 and context-dependent opposing forces in cancer. Nat. Rev. Cancer 6: 11–23.
31. Cyster, J. G. 2005. Chemokines, sphingosine-1-phosphate, and cell migration in
secondary lymphoid organs. Annu. Rev. Immunol. 23: 127–159.
32. Spiegel, S., and S. Milstien. 2011. The outs and the ins of sphingosine-1-phosphate
in immunity. Nat. Rev. Immunol. 11: 403–415.
33. Zachariah, M. A., and J. G. Cyster. 2010. Neural crest-derived pericytes promote
egress of mature thymocytes at the corticomedullary junction. Science 328: 1129–1135.
34. Shiow, L. R., D. B. Rosen, N. Brdicková, Y. Xu, J. An, L. L. Lanier, J. G. Cyster,
and M. Matloubian. 2006. CD69 acts downstream of interferon-alpha/beta to inhibit S1P1 and lymphocyte egress from lymphoid organs. Nature 440: 540–544.
35. Bankovich, A. J., L. R. Shiow, and J. G. Cyster. 2010. CD69 suppresses sphingosine
1-phosophate receptor-1 (S1P1) function through interaction with membrane helix
4. J. Biol. Chem. 285: 22328–22337.
36. Odumade, O. A., M. A. Weinreich, S. C. Jameson, and K. A. Hogquist. 2010.
Krüppel-like factor 2 regulates trafficking and homeostasis of gammadelta T cells. J.
Immunol. 184: 6060–6066.
37. Hedrick, S. M. 2009. The cunning little vixen: Foxo and the cycle of life and death.
Nat. Immunol. 10: 1057–1063.
38. Kerdiles, Y. M., D. R. Beisner, R. Tinoco, A. S. Dejean, D. H. Castrillon,
R. A. DePinho, and S. M. Hedrick. 2009. Foxo1 links homing and survival of naive
T cells by regulating L-selectin, CCR7 and interleukin 7 receptor. Nat. Immunol.
10: 176–184.
39. Fabre, S., F. Carrette, J. Chen, V. Lang, M. Semichon, C. Denoyelle, V. Lazar,
N. Cagnard, A. Dubart-Kupperschmitt, M. Mangeney, et al. 2008. FOXO1 regulates L-Selectin and a network of human T cell homing molecules downstream of
phosphatidylinositol 3-kinase. J. Immunol. 181: 2980–2989.
40. Gubbels Bupp, M. R., B. Edwards, C. Guo, D. Wei, G. Chen, B. Wong,
E. Masteller, and S. L. Peng. 2009. T cells require Foxo1 to populate the peripheral
lymphoid organs. Eur. J. Immunol. 39: 2991–2999.
41. Finlay, D., and D. A. Cantrell. 2011. Metabolism, migration and memory in cytotoxic T cells. Nat. Rev. Immunol. 11: 109–117.
42. Sinclair, L. V., D. Finlay, C. Feijoo, G. H. Cornish, A. Gray, A. Ager,
K. Okkenhaug, T. J. Hagenbeek, H. Spits, and D. A. Cantrell. 2008.
Phosphatidylinositol-3-OH kinase and nutrient-sensing mTOR pathways control
T lymphocyte trafficking. Nat. Immunol. 9: 513–521.
43. Rao, R. R., Q. Li, K. Odunsi, and P. A. Shrikant. 2010. The mTOR kinase
determines effector versus memory CD8+ T cell fate by regulating the expression of
transcription factors T-bet and Eomesodermin. Immunity 32: 67–78.
44. Li, Q., C. Eppolito, K. Odunsi, and P. A. Shrikant. 2006. IL-12-programmed longterm CD8+ T cell responses require STAT4. J. Immunol. 177: 7618–7625.
45. Li, Z., Y. Zhang, Z. Liu, X. Wu, Y. Zheng, Z. Tao, K. Mao, J. Wang, G. Lin,
L. Tian, et al. 2011. ECM1 controls T(H)2 cell egress from lymph nodes through
re-expression of S1P(1). Nat. Immunol. 12: 178–185.
46. Hart, G. T., X. Wang, K. A. Hogquist, and S. C. Jameson. 2011. Krüppel-like
factor 2 (KLF2) regulates B-cell reactivity, subset differentiation, and trafficking
molecule expression. Proc. Natl. Acad. Sci. USA 108: 716–721.
Downloaded from http://www.jimmunol.org/ by guest on June 15, 2017
It is becoming clear that KLFs play multiple and varied roles
in lymphocyte development and function, and that individual
KLF family members can reinforce or antagonize each others’
functions. However, substantial questions remain, based partly
on the complexity of this family. Whereas mRNA expression
of individual KLFs within lymphocyte subsets can be readily
determined, posttranscriptional regulation of KLFs has been
observed in several systems, making it harder to predict functional KLF protein expression. The fact that many KLFs share
a similar DNA binding site motif, together with the shortage
of studies (such as chromatin immunoprecipitation) to define
which genes are actually occupied by a given factor, means that
there is a dearth of information on identification and characterization of key transcriptional targets. Redundancy and
competition between KLFs for gene regulation adds yet another layer of complexity to understanding their roles. Still, as
exemplified by the burst of information over the last few years,
we are approaching a renaissance in understanding the functions and significance of KLFs in lymphocyte biology.
525
526
BRIEF REVIEWS: THE ROLE OF KRÜPPEL-LIKE FACTORS IN LYMPHOCYTES
61. Josefowicz, S. Z., and A. Rudensky. 2009. Control of regulatory T cell lineage
commitment and maintenance. Immunity 30: 616–625.
62. Venuprasad, K., H. Huang, Y. Harada, C. Elly, M. Subramaniam, T. Spelsberg,
J. Su, and Y. C. Liu. 2008. The E3 ubiquitin ligase Itch regulates expression of
transcription factor Foxp3 and airway inflammation by enhancing the function of
transcription factor TIEG1. Nat. Immunol. 9: 245–253.
63. Cao, Z., A. K. Wara, B. Icli, X. Sun, R. R. Packard, F. Esen, C. J. Stapleton,
M. Subramaniam, K. Kretschmer, I. Apostolou, et al. 2009. Kruppel-like factor
KLF10 targets transforming growth factor-beta1 to regulate CD4(+)CD25(-) T cells
and T regulatory cells. J. Biol. Chem. 284: 24914–24924.
64. Peng, D. J., M. Zeng, R. Muromoto, T. Matsuda, K. Shimoda, M. Subramaniam,
T. C. Spelsberg, W. Z. Wei, and K. Venuprasad. 2011. Noncanonical K27-linked
polyubiquitination of TIEG1 regulates Foxp3 expression and tumor growth. J.
Immunol. 186: 5638–5647.
65. Pepper, M., and M. K. Jenkins. 2011. Origins of CD4(+) effector and central
memory T cells. Nat. Immunol. 12: 467–471.
66. Yang, X. O., B. P. Pappu, R. Nurieva, A. Akimzhanov, H. S. Kang, Y. Chung,
L. Ma, B. Shah, A. D. Panopoulos, K. S. Schluns, et al. 2008. T helper 17 lineage
differentiation is programmed by orphan nuclear receptors ROR alpha and ROR
gamma. Immunity 28: 29–39.
67. Lebson, L., A. Gocke, J. Rosenzweig, J. Alder, C. Civin, P. A. Calabresi, and
K. A. Whartenby. 2010. Cutting edge: The transcription factor Kruppel-like factor
4 regulates the differentiation of Th17 cells independently of RORgt. J. Immunol.
185: 7161–7164.
68. An, J., S. Golech, J. Klaewsongkram, Y. Zhang, K. Subedi, G. E. Huston,
W. H. Wood, 3rd, R. P. Wersto, K. G. Becker, S. L. Swain, and N. Weng. 2011.
Kruppel-like factor 4 (KLF4) directly regulates proliferation in thymocyte development and IL-17 expression during Th17 differentiation. FASEB J. 25: 3634–3645.
69. Shi, L. Z., R. Wang, G. Huang, P. Vogel, G. Neale, D. R. Green, and H. Chi.
2011. HIF1alpha-dependent glycolytic pathway orchestrates a metabolic checkpoint
for the differentiation of TH17 and Treg cells. J. Exp. Med. 208: 1367–1376.
70. Mahabeleshwar, G. H., D. Kawanami, N. Sharma, Y. Takami, G. Zhou, H. Shi,
L. Nayak, D. Jeyaraj, R. Grealy, M. White, et al. 2011. The myeloid transcription
factor KLF2 regulates the host response to polymicrobial infection and endotoxic
shock. Immunity 34: 715–728.
71. Stadanlick, J. E., M. Kaileh, F. G. Karnell, J. L. Scholz, J. P. Miller, W. J. Quinn,
III, R. J. Brezski, L. S. Treml, K. A. Jordan, J. G. Monroe, et al. 2008. Tonic B cell
antigen receptor signals supply an NF-kappaB substrate for prosurvival BLyS signaling. Nat. Immunol. 9: 1379–1387.
72. Kabashima, K., N. M. Haynes, Y. Xu, S. L. Nutt, M. L. Allende, R. L. Proia, and
J. G. Cyster. 2006. Plasma cell S1P1 expression determines secondary lymphoid
organ retention versus bone marrow tropism. J. Exp. Med. 203: 2683–2690.
Downloaded from http://www.jimmunol.org/ by guest on June 15, 2017
47. Winkelmann, R., L. Sandrock, M. Porstner, E. Roth, M. Mathews, E. Hobeika,
M. Reth, M. L. Kahn, W. Schuh, and H. M. Jäck. 2011. B cell homeostasis and
plasma cell homing controlled by Krüppel-like factor 2. Proc. Natl. Acad. Sci. USA
108: 710–715.
48. Hoek, K. L., L. E. Gordy, P. L. Collins, V. V. Parekh, T. M. Aune, S. Joyce,
J. W. Thomas, L. Van Kaer, and E. Sebzda. 2010. Follicular B cell trafficking within
the spleen actively restricts humoral immune responses. Immunity 33: 254–265.
49. Turchinovich, G., T. T. Vu, F. Frommer, J. Kranich, S. Schmid, M. Alles,
J. B. Loubert, J. P. Goulet, U. Zimber-Strobl, P. Schneider, et al. 2011. Programming of marginal zone B-cell fate by basic Kruppel-like factor (BKLF/KLF3).
Blood 117: 3780–3792.
50. Vu, T. T., D. Gatto, V. Turner, A. P. Funnell, K. S. Mak, L. J. Norton, W. Kaplan,
M. J. Cowley, F. Agenes, J. Kirberg, R. Brink, R. C. Pearson, and M. Crossley.
2011. Impaired B Cell Development in the Absence of Kruppel-like Factor 3.
J Immunol. 187: 5032–5042.
51. Yang, X. O., R. T. Doty, J. S. Hicks, and D. M. Willerford. 2003. Regulation of Tcell receptor D beta 1 promoter by KLF5 through reiterated GC-rich motifs. Blood
101: 4492–4499.
52. Lee, Y. J., S. C. Jameson, and K. A. Hogquist. 2011. Alternative memory in the
CD8 T cell lineage. Trends Immunol. 32: 50–56.
53. Lai, D., J. Zhu, T. Wang, J. Hu-Li, M. Terabe, J. A. Berzofsky, C. Clayberger, and
A. M. Krensky. 2011. KLF13 sustains thymic memory-like CD8(+) T cells in
BALB/c mice by regulating IL-4-generating invariant natural killer T cells. J. Exp.
Med. 208: 1093–1103.
54. Zhou, M., L. McPherson, D. Feng, A. Song, C. Dong, S. C. Lyu, L. Zhou, X. Shi,
Y. T. Ahn, D. Wang, et al. 2007. Kruppel-like transcription factor 13 regulates
T lymphocyte survival in vivo. J. Immunol. 178: 5496–5504.
55. Krensky, A. M., and Y. T. Ahn. 2007. Mechanisms of disease: regulation of
RANTES (CCL5) in renal disease. Nat. Clin. Pract. Nephrol. 3: 164–170.
56. Cariappa, A., M. Tang, C. Parng, E. Nebelitskiy, M. Carroll, K. Georgopoulos, and
S. Pillai. 2001. The follicular versus marginal zone B lymphocyte cell fate decision is
regulated by Aiolos, Btk, and CD21. Immunity 14: 603–615.
57. Schuh, W., S. Meister, K. Herrmann, H. Bradl, and H. M. Jäck. 2008. Transcriptome analysis in primary B lymphoid precursors following induction of the preB cell receptor. Mol. Immunol. 45: 362–375.
58. Pillai, S., A. Cariappa, and S. T. Moran. 2004. Positive selection and lineage commitment during peripheral B-lymphocyte development. Immunol. Rev. 197: 206–218.
59. Niiro, H., and E. A. Clark. 2002. Regulation of B-cell fate by antigen-receptor
signals. Nat. Rev. Immunol. 2: 945–956.
60. Eaton, S. A., A. P. Funnell, N. Sue, H. Nicholas, R. C. Pearson, and M. Crossley.
2008. A network of Krüppel-like Factors (Klfs). Klf8 is repressed by Klf3 and activated by Klf1 in vivo. J. Biol. Chem. 283: 26937–26947.