[CANCER RESEARCH 47, 1302-1307, March 1, 1987]
Differential Effects of Various Protein Kinase C Activators on Protein
Phosphorylation in Human Acute Myeloblastic Leukemia Cell Line
KG-1 and Its Phorbol Ester-resistant Subline KG-la1
/olÃ-anKiss, Eva Deli, Mamoru Shoji, H. Phillip Koeffler,2 George R. Pettit, William R. Vogler, and J. F. Kuo
Departments of Pharmacology [Z. K., E. £>.,J. F. K.¡and Medicine (Hematology and Oncology) [M. S., W. R. V.], Emory University School of Medicine,
Atlanta, Georgia 30322; Department of Medicine (Hematology/Oncology) [H. P. K.J, University of California at Los Angeles, Los Angeles, California 90024; and Cancer
Research Institute and Department of Chemistry ¡C.R. P.], Arizona State University. Tempe. Arizona 85287
ABSTRACT
Human myeloid leukemia KG-1 cells are induced to differentiate to
macrophage-like cells by tumor-promoting phorbol esters, such as 12-0tetradecanoylphorbol-13-acetate (TPA). Cells from the cloned subline,
KG-la, unlike the parental line, are resistant to the differentiating effect
of TPA. In the present studies, we investigated in these cells protein
phosphorylation stimulated by various protein kinase C activators, in
cluding l-oleoyl-2-acetylglycerol in the presence of the diacylglycerol
kinase inhibitor RS9022, TPA, mezerein, and bryostatin. All the agents
stimulated, to a greater extent and with a higher potency, phosphorylation
of several proteins in KG-1 cells than in KG-la cells. On the other hand,
these agents markedly stimulated phosphorylation of other proteins in
KG-la cells compared to that in KG-1 cells. The findings indicated that
the actions of the diacylglycerol, l-oleoyl-2-acetylglycerol, and the nonmetabolizable activators (TPA, mezerein, and bryostatin) were very
similar but not fully equivalent; and that KG-la cells exhibited altered
(increased or decreased) phosphorylation patterns, perhaps related to the
TPA resistance characteristic of this subline of cells.
INTRODUCTION
The only currently recognized mediator of the actions of
tumor-promoting phorbol esters is phospholipid/Ca2+-dependent protein kinase or PKC3 (1,2). The enzyme, shown to occur
widely in animal tissues and cells (3) and found also in certain
plants (4, 5), is indistinguishable from the phorbol ester recep
tors (6-9). A physiological activator of PKC is 1,2-diacylglycerol, which accumulates transiently as a consequence of the
receptor-mediated inositol lipid breakdown (10-12). Having
the same cellular target, phorbol esters and diacylglycerol are
likely to act similarly; indeed, they regulate many cellular events
in a similar manner (13-19). Recent evidence, however, indi
cates that synthetic permeable diglycerides, such as OAG, failed
to mimic TPA effects on differentiation of HL60 cells (20, 21),
platelet activation (22), maturation of granulosa cells (23), and
synthesis of phosphatidylcholine (24). One likely explanation
for the apparent inability of OAG to completely substitute for
TPA is that diacylglycerol can be metabolized and inactivated
rapidly. Consistent with this contention are the findings that
PKC phosphorylated several membrane proteins more effec
tively when the enzyme was activated by TPA instead of diolein
(25). Separation of proteins by high-resolution two-dimensional
gel electrophoresis has demonstrated recently that, in certain
cell types, TPA stimulated phosphorylation of more proteins
than did diacylglycerol (20, 26). This, nonetheless, raises the
possibility that some of the protein phosphorylations and phys
iological responses induced by TPA might be unrelated to PKC
activation.
TPA has been shown to induce the myeloid leukemia cells
blocked at the myeloblast-promyelocyte stage of maturation,
such as KG-1 (27) and HL60 (28), to differentiate to macro
phage-like cells. On the other hand, TPA has no effect on
differentiation of the cells blocked at the earlier, less-differen
tiated myeloblast stage of maturation, such as K562 (27) and
KG-la (27). The molecular basis for the TPA resistance is still
unclear. The resistant cells may be modified at the TPA binding
sites; however, this is not the case for KG-la cells, because the
cells have similar density of the high affinity [3H]phorboI 12,13dibutyrate binding sites as the responsive parent line KG-1 cells
(29). The cells of HL60 and the TPA-resistant subline (R-35)
of HL60 also have a similar number of binding sites (30).
Because PKC is the only known receptor protein for phorbol
esters, it is plausible that a modification characteristic of resist
ance to TPA might reside on the steps beyond receptor binding.
In fact, Anderson et ai. (31 ) reported a decreased phosphoryl
ation of several proteins stimulated by TPA in resistant subline
R-94 cells compared to the responsive parental HL60 cells,
suggesting a block in signal transduction via protein phospho
rylation by PKC in resistant cells. In the present studies, we
investigated protein phosphorylation stimulated by mezerein, a
non-phorbol ester tumor promoter (32), bryostatin, a macrocyclic lactone mitogen shown to mimic TPA (33, 34), and
compared that with the effects of TPA or OAG plus R59022,
an inhibitor of diacylglycerol kinase, in KG-1 and KG-la cells
(35). We found that phosphorylation of many proteins was
decreased, but paradoxically phosphorylation of a set of pro
teins was increased in the TPA-resistant KG-la cells.
MATERIALS
AND METHODS
Materials. TPA, mezerein, IBMX, and prostaglandin E2 were pur
chased from Sigma Chemical Co. (St. Louis, MO); OAG was from
Avanti Polar Lipids, Inc. (Birmingham, AL); Compound RS9022 was
from Janssen Life Sciences Products (Beerse, Belgium); ampholites
(pH range, 3.5 to 10 and 5 to 7) were from LKB (Gaithersburg, MD);
and [32P]orthophosphate (carrier free, in water) was from ICN Kadi
oc IK-micaIs (Irvine, CA). Bryostatin I was purified from marine animal
Bugula neritina (36).
Cell Culture. The KG-1 human acute myeloblastic leukemia cloned
cell line was established from a patient with human acute myeloid
Received 7/30/86; revised 11/13/86; accepted 12/1/86.
leukemia (37). A cloned subline of KG-1, known as KG-la, is morpho
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
logically, histochemically, and functionally arrested at an undifferenaccordance with 18 U.S.C. Section 1734 solely to indicate this fact.
tiated blast stage (38). Unlike KG-1 cells, KG-la cells are resistant to
'Supported by USPHS Research Grants CA-36777, HL-15696, and NSTPA-induced
differentiation (27). The cells from both lines were con
17608 (J. F. K.). CA-26038 and CA-32737 (H. P. K.), CA-29850 (W. R. V.), and
CA-16094 and N01-CM-97262 (G. R. P.).
tinuously cultured as nonadherent single-cell suspensions in RPMI
2 Recipient of USPHS Research Career Development Award and a member of
1640 (GIBCO) supplemented with either 20% (KG-1 cells) or 10%
Johnson Cancer Center.
heat-inactivated fetal calf serum (KG-la cells) as well as L-glutamine
'The abbreviations used are: PKC, protein kinase C; OAG, l-oleoyl-2-acetyl(2 DIM) and penicillin-streptomycin (100 units/ml and 100 ¿ig/ml,
glycerol; TPA, 12-O-tetradecanoylphorbol-13-acetate;
IBMX, isobutyryl methylxanthine; die ».
dioctanoylglycerol; cAMP, cyclic AMP.
respectively).
1302
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PROTEIN
PHOSPHORYLATION
Radiolabeling and Preparation of Cell Extracts. Cells were incubated
in the same medium in which they were grown with 32P¡
(0.5 mCi/ml)
at a density of 106/ml for 7 h. Aliquots (1 ml) of cells were transferred
to small Eppendorf tubes containing 10 M' of various PKC activators,
and incubations were continued for another 45 min. Compound R59022
(25 MMfinal concentration) was added 15 min before OAG. 32P-labeling
of proteins was terminated by centrifuging the samples for 5 s at 20,000
x K. aspirating the supernatants, and lysing the cells with 50 n\ of gel
sample buffer (39). Stock solutions (10 mM) of TPA, mezerein, and
bryostatin were made in dimethyl sulfoxide; final concentration of this
solvent never exceeded 0.1% which had no detectable effect on cellular
protein phosphorylation.
Determination of Cell Differentiation and Viability. KG-1 and KG-la
cells (0.2 x 106/ml) were treated with various PKC activators for 48 h
as indicated in Table 1. The number of cells adherent to the plastic
culture dishes, a characteristic of differentiating cells, was estimated
microscopically after gently shaking the dishes to remove suspended
(undifferentiating) cells. The cell viability was determined by trypan
blue dye exclusion.
Two-Dimensional Polyacrylamide Gel Electrophoresis. The 2-dimensional gel electrophoresis procedure described by O'Farrell (40) was
used with modifications described by Steinberg and Coffino (39). The
first-dimension isoelectric focusing gels contained 9.2 M urea and 6%
ampholite (1.5% of ampholite, pH 3.5 to 10; and 4.5% of ampholite,
pH 5 to 7). Aliquots, corresponding to about 35 Mg of protein and
containing 2.1 x 10s cpm of acid-precipitable radioactivity, were loaded
onto the first-dimension gels. Radioactivities in any of the samples
differed from each other by less than 10%. The first-dimension gels
were run for 7000 V •
h. The second-dimension sodium dodecyl sulfate
gels contained 10% (w/v) polyacrylamide. Proteins were stained with
Coomassie blue. The 32P-labeled proteins were detected by autoradiography of dried gels for 4 days at -20*C using Kodak XAR-5 film
between Kodak Omatic intensifying screens. The acidic proteins of the
gel are to the right. Each experiment was performed in duplicates which
yielded very similar gel patterns. The experiments with 2 and 500 n\i
TPA, 20 Mg/rol of OAG, as well as 20 nM mezerein or bryostatin were
repeated twice; the results of both experiments were similar to those
that are shown in Figs. 1 to 4.
Measurement of Radioactivity in Specific Proteins. In order to quantitate the changes in the 32Pcontent, the respective proteins were excised
and counted for 32P in a liquid scintillation spectrometer after autoradiography of gels for 4 days. A piece of gel of identical size, correspond
ing to the appropriate proteins, was excised from radioactivity-free
areas in the gel and served as a blank.
RESULTS
Effects of Various PKC Activators on Differentiation. Adher
ence to substratum is characteristic of differentiating leukemic
cells. We observed that 20 nmol of various PKC activators
(TPA, mezerein, or bryostatin) induced adherence in 54 to 72%
of KG-1 cells, compared to only 5% in the nontreated (control)
cells (Table 1). These agents, however, were without effect on
differentiation of the KG-la subline at 20 nmol (Table 1) or
200 nmol (data not shown). The findings were consistent with
Table 1 Comparative effects of various PKC activators on differentiation
(adherence) of KG-1 and KG-la cells
The cells were treated for 48 h with various PKC activators, as indicated.
Adherent cells
(% of total)
activatorNone
PKC
±2"
(control)
<I
72 ±5
TPA (20 nm)
<I
Mezerein (20 nM)
66 ±3
54 ±7
<1
Bryostatin (20 nM)
OAG (20 Mg/ml) + R59022 (25 MM)KG-15 ND*KG-la<1 ND°
" Mean ±SE of the percentage of cells which became adherent in 3 to 5 dishes
for each treatment.
b NO, not determined due to 60 to 70% cell death in 48 h.
IN KG-1 AND KG-la CELLS
the report of Koeffler et al. (27) that TPA induced differentia
tion in KG-1 but not in KG-la cells, and the hypothesis that
other PKC activators can mimic certain actions of TPA. OAG
(20 Mg/ml) in the presence of R59022 (25 MM) was highly
cytotoxic, causing a viability loss in 60 to 70% of KG-1 and
KG-la cells. The effect of OAG plus R59022 on the differen
tiation of the two cell lines, therefore, could not be determined.
Merrill et al. (41 ) reported recently that HL60 cells are induced
to differentiation only by a repeated addition of diC8, and this
effect is quite variable, probably because of a cytotoxicity and
rapid metabolism of the diacylglycerol. It should be noted here
that TPA, mezerein, or bryostatin was without significant effect
on the cell viability under the same experimental conditions.
Effects of TPA and OAG plus R59022 on Protein Phospho
rylation in KG-1 and KG-la Cells. The tumor promoter TPA is
metabolized only very slowly in cells, and its effects are hence
considered long lasting (20-24). In contrast, the second mes
senger diacylglycerol is rapidly metabolized by diacylglycerol
kinase, yielding only transient effects. An inhibitor of diacyl
glycerol kinase, R59022, has been developed recently and
shown to potentiate the effect of OAG on platelets (35). In
order to maximize the action of OAG and to better compare it
with that of TPA, R59022 (25 MM)was used in combination
with OAG in the present studies; R59022, by itself, was without
effect on protein phosphorylation (data not shown). Because
there is no information available, we assumed here that TPA is
not readily metabolized in KG-1 and KG-la cells, as commonly
considered in other cell types (20-24).
The patterns of protein phosphorylation in the TPA-responsive KG-1 cells and the TPA-resistant KG-la cells under the
basal conditions (i.e., in the absence of added PKC activators)
were remarkably similar (Fig. 1, comparing a and d). In KG-1
cells, 100 HM TPA (Fig. Ib) or 20 Mg/ml of OAG (Fig. le)
stimulated phosphorylation of a similar but nonidentical set of
proteins. Phosphorylation of Protein A (pi = 5.1; A/r 76,000)
and proteins in Blocks / (pi = 5.45 to 5.65; Mr 60,000 to
64,000), /// (pi = 5.6; M, 80,000), and IV(pl = 5.2; M, 84,000)
were similarly stimulated by these two agents. In KG-la cells,
both TPA (Fig. le) and OAG (Fig. I/) stimulated phosphoryl
ation of proteins in Blocks /, ///, and II'. although the extent
of their stimulation was lower compared to that seen for KG-1
cells shown above (Fig. 1, b and c). Of interest, phosphorylation
of Protein A (and probably Proteins B and C), either basal or
stimulated by PKC activators, was much higher in KG-la cells
than in KG-1 cells. Phosphorylation of several other minor
proteins (Proteins 1, 2, 3, B, C, T,, T2, O,, O2) in KG-1 and
KG-la cells was stimulated to variable extents by TPA or OAG
plus R59022 (Fig. 1). For the reason of simplicity, these phosphoproteins were not further considered in subsequent studies.
8-Bromo cAMP (1 mM), dibutyryl cAMP (1 HIM), or prostaglandin E2 (0.1 MM)plus IBMX (50 MM),agents that directly or
indirectly activate cAMP-dependent protein kinase and do not
induce differentiation, on the other hand, practically had no
effect on the phosphorylation in KG-1 cells (data not shown).
Comparative Effects of TPA, Mezerein, and Bryostatin on
Protein Phosphorylation in KG-1 and KG-la Cells. The dosedependent effects of various nonmetabolizable PKC activators
on the two cell lines were examined to reveal possible differ
ences in protein phosphorylation patterns, which may consti
tute a basis for their selective sensitivity to the differentiating
effect of TPA. The 32P activity of representative phosphopro-
teins in the dry gels (from which autoradiograms, such as shown
in Figs. 1 to 4, were obtained) was measured directly; the data
for Protein A and proteins (combined) in Block I are summa1303
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PROTEIN
PHOSPHORYLATION
IN KG-1 AND KG-la CELLS
f
Fig. 1. Comparison of the effects of TPA
and OAG on protein phosphorylation in KG1 and KG-1 a cells. KG-1 (a to c) and KG-la
cells (d to/) were labeled with '•']',
for a total
period of 7 h and 45 min without (a, d) or with
100 nw TPA (*, e) or OAG, 20 Mg/ml, plus 25
/»M
R59022 (c,f) present during the final 45
min of the labeling period. Equal amounts of
proteins (35 jig)<containing 2.1 x IO5cpm of
acid-precipitable radioactivity from the two
cell lines, were loaded onto gels. Auloradiographs were exposed for 4 days. Other exper
imental details were as described in "Materials
and Methods."
H
W
(O
Table 2 Comparative effects of various PKC activators on the phosphorylation of
representative proteins in KG-1 and KG-la cells
Data presented are the mean of two determinations of '•'!'
activity in excised
2 nM TPA did not increase phosphorylation of proteins in
Blocks I, III, and IV, but it was slightly increased by 20 nM or
500 HMTPA (Fig. 2, e to A;Table 2). In KG-la cells 2 HMTPA
spots from the gels, shown in Figs. 1 to 4, or from similar experiments. Proteins
I and 2 as well as proteins in Block I were combined for the measurement. All
did not stimulate phosphorylation of most proteins, but in
experiments were performed at the same time, and thus the values are directly
creased phosphorylation of Protein A about 2.9-fold (Fig. 2/;
comparable.
Table 2), compared to a 1.9-fold increase seen in KG-1 cells
increase)AAdditionNone
32P-labeling of proteins (-fold
(Fig. 2b\ Table 2). As mentioned in Fig. 1, the extent of
IKG-1
phosphorylation of Protein A, either in the absence or presence
KG-la1.0(172)
of TPA (2, 20, or 500 nM), was much higher in KG-la cells
(control)TPA
1.0(136)1.92.82.93.1 than in KG-1 cells.
The effect of mezerein, a non-phorbol ester tumor promoter
niu)TPA
(2
shown to activate PKC (38), was found to be similar to that of
nM)TPA(lOOnM)TPA
(20
TPA; mezerein stimulated phosphorylation of proteins in
nM)Mezerein
(500
;2.03.42.12.33.5.0.4.9!.0.1.7.0.2.4
Blocks I, III, and IV in KG-1 cells and that of Protein A in
nM)Mezerein
(20
KG-la cells (Fig. 3). Mezerein was as potent as TPA in stimu
nM)Bryostatin
(500
nM)Bryostatin
(20
lating phosphorylation of these proteins in both cell lines (Table
nM)OAG (500
2).
(20 /ig/ml) + R59022 (25 »IM)KG-11.0(23)°1.93.13.23.43.44.12.63.11.9KG-la1.0(66)2.94.44.24.24.45.03.64.82.4Block
" Numbers in parentheses, actual radioactivity (cpm) measured.
Bryostatin, a macroiactone that activates PKC in a manner
similar to TPA (39, 40), at 20 HMcaused a near-maximal or
maximal phosphorylation of many proteins in KG-1 cells (Fig.
rized (Table 2). The data from OAG experiments (Fig. 1) are 4, comparing a to c), indicating that its potency was comparable
also included in Table 2 for comparison. In KG-1 cells, 2 nM to that of TPA (Fig. 2) or mezerein (Fig. 3). Bryostatin was less
TPA (Fig. 2b\ Table 2) caused about half-maximal whereas 20 effective than other PKC activators in stimulating phosphoryl
nM TPA (Fig. 2c; Table 2) caused a near-maximal phosphoryl
ation of many proteins in KG-la cells compared to KG-1 cells.
ation of proteins in Blocks I, III, and IV. No further increase For example, in KG-la cells, 20 nM bryostatin failed to stimu
in phosphorylation of these proteins occurred at 100 and 500 late phosphorylation of proteins in Block I, whereas 20 HM
nMTPA (Fig. 2d\ Table 2). A different phosphorylation pattern TPA (Fig. 2) or 20 nM mezerein (Fig. 3) both markedly stimu
was observed for the TPA-resistant KG-la cells. In these cells, lated phosphorylation of these proteins. Bryostatin, however,
1304
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PROTEIN
PHOSPHORYLATION
IN KG-1 AND KG-la CELLS
* l
^
¿
-67
t
-43
(a)
9
««T-t
~
t
Ä
. -
_
Fig. 2. Concentration-dependent effect of TP A on protein phosphorylation in KG-1 and KG-la cells. KG-1 (a to rf) and KG-la (e to A)cells were labeled with 32Pi
for a total period of 7 h and 45 min without (a, e) or with 2 nM (¿>,/),20 nM (c, g), or 500 nM TPA (a1,A) present during the final 45 min of the labeling period.
Other aspects of the experiment were as described in Fig. 1.
-67
f
Fig. 3. Concentration-dependent
effect of
mezerein on protein phosphorylation in KG-1
and KG-la cells. KG-1 (a to c) and KG-la (il
to /) cells were labeled with 32P for a total
period of 7 h and 45 min without (a, d) or with
20 nM (A,e) or 500 nM mezerein (c,/) present
during the final 45 min of the labeling period.
Other aspects of the experiment were as de
scribed in Fig. 1.
-43
*
(O
1305
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PROTEIN PHOSPHORYLATION
IN KG-1 AND KG-la CELLS
6.0 <—PH—>
5.0
Fig. 4. Concentration-dependent
effect of
Bryostatin I on protein phosphorylation in
KG-1 and KG-la cells. KG-1 (a to c) and KGla cells (d to/) were labeled with 32P for a
total period of 7 h and 45 min without (a, d)
or with 20 nM (6, e) or 500 nM bryostatin (c,
f) present during the final 45 min of the la
beling period. Other aspects of the experiment
were as described in Fig. 1.
„-3
-43
i
•-„ fr)
like the other activators, invariably stimulated phosphorylation
of Protein A to a greater extent in KG-la cells compared to
KG-1 cells.
DISCUSSION
There were three major observations from the present studies
which seemed worth noting, (a) The patterns of the basal
phosphorylation in KG-1 and KG-la cells were very similar;
(b) either one of the PKC activators (TPA, OAG plus R59022,
mezerein and bryostatin) tested invariably stimulated phospho
rylation of proteins in Blocks I, III, and IV to a greater extent
in KG-1 than in KG-la cells; and (c) the basal phosphorylation
of Protein A as well as its phosphorylation stimulated by the
PKC activators was conversely much lower in KG-1 than in
KG-la cells. The data, reflecting the characteristics of the two
cell lines, were consistent with the contention that an increased
phosphorylation of these proteins was catalyzed by PKC. This
was further supported by the findings that the increased phos
phorylation was decreased by H-7, an inhibitor of protein kinase
C (42), and that 8-bromo cAMP, dibutyryl cAMP, or prostaglandin E2 plus IBMX (both increase cellular cAMP), all of
which would lead to activation of cAMP-dependent protein
kinase, were unable to mimic the actions of the PKC activators
(data not shown). The precise role of protein phosphorylation
in cell differentiation is unclear. However, a high sensitivity of
phosphorylation of proteins in Blocks I, III, and IV in KG-1
cells and that of Protein A in KG-la cells seemed to be related
to the selective responsiveness of two cell lines to the differen
tiating effect of TPA, mezerein, and bryostatin. Anderson et al.
(31) observed that phosphorylation of at least 10 proteins in
HL60 cells, including those having Mr of 56,000 to 60,000, was
stimulated by TPA and that their phosphorylation was lower
in the TPA-resistant variant R-94 cells. Proteins showing a
higher phosphorylation stimulated by TPA were not identified
in R-94 cells. In this respect, Protein A in KG-la cells is of
interest and might be specifically related to resistance to the
differentiating effect of TPA.
Kreutter et al. (20) reported that, in HL60 cells, TPA induced
phosphorylation of 14 proteins, 9 of which were also induced
by OAG. They also observed that TPA and OAG both stimu
lated choline lipid metabolism. In spite of the similar biochem
ical effects of TPA and OAG, repeated additions of OAG to
the culture (attempting to maintain OAG level in cells) failed
to mimic TPA in inducing maturation of HL60 cells. In the
present studies, we used OAG in combination with R59022 in
the hope of maintaining an effective concentration of the diacylglycerol in KG-1 cells. Although acutely stimulating phos
phorylation of a number of proteins as other PKC activators,
we were unable to accurately assess the differentiation of KG-1
cells in response to OAG plus R59022 because of an excessive
cytotoxicity (loss of cell viability) of the two agents under the
experimental conditions. It is of interest that Merrill et al. (41)
reported recently that repeated additions of diCg, another syn
thetic permeable diacylglycerol, could induce HL60 cell differ
entiation, although it was less effective than TPA, and the
results are variable. It appeared that PKC activation can be
dissociated from the TPA-induced differentiation of HL60
cells. This contention is largely based upon the findings that
diacylglycerols failed to completely mimic the effect of TPA,
probably reflecting the unique pleiotropic nature of the actions
of the phorbol ester. Despite the involvement of PKC in differ
entiation of HL60 and KG-1 cells, PKC activation alone prob
ably is not sufficient to trigger and maintain the maturation
process. A definite answer to the problem is unlikely unless the
following parameters are also considered, including possible
differential and localized distribution of TPA and OAG (or
diCg), and subsequent preferential activation of PKC and phos
phorylation of specific and crucial proteins at certain cellular
organelles. The observations that TPA has profound and sus-
1306
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PROTEIN
PHOSPHORYLATION
tained effects on PKC translocation in HL60 cells (43) and KG1 cells4 and on the down-regulation of PKC in HL60 cells (44)
can further complicate the interpretations of the experimental
results.
IN KG-1 AND KG-1 a CELLS
22.
23.
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Downloaded from cancerres.aacrjournals.org on July 31, 2017. © 1987 American Association for Cancer Research.
Differential Effects of Various Protein Kinase C Activators on
Protein Phosphorylation in Human Acute Myeloblastic
Leukemia Cell Line KG-1 and Its Phorbol Ester-resistant Subline
KG-1a
Zoltan Kiss, Eva Deli, Mamoru Shoji, et al.
Cancer Res 1987;47:1302-1307.
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