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Advances in Brief |
Division of Oncology Research, Mayo Clinic, Rochester, Minnesota 55905 [E. C. B., D. F. L., L. M. K., J. N. S.], and Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina 27710 [R. T. A.]
| ABSTRACT |
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-radiation-induced G2 checkpoint. In contrast to
hChk1, the hChk2 kinase was 100-fold more resistant to inhibition by
UCN-01 (IC50, 1040 nM). These results suggest
that disruption of the DNA damage-induced G2 checkpoint by
UCN-01 is mediated through the inhibition of the Cdc25C kinases, hChk1
and cTAK1, and that hChk2 activity is not sufficient to enforce the
G2 checkpoint in cells treated with a pharmacological
inhibitor of hChk1. | Introduction |
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The induction of a G2 arrest after DNA damage depends, in part, on inhibition of cyclin B1/Cdk1 activity through phosphorylation of the Cdk1 subunit at Thr14 and Tyr15 (5) . The dynamic changes in the phosphorylation of Cdk1 during both the normal cell cycle and in response to DNA damage are controlled by an interplay between the enzymatic activities of the Wee1-like kinases and the Cdc25C phosphatase. In recent years, the signaling pathways controlling Cdc25C activation and subcellular localization have been partially elucidated. Current models suggest that the serine-threonine kinases hChk1 and hChk2 are activated by DNA damage signaling pathway(s) dependent on the ATM family of protein kinases (6, 7, 8) . Activated hChk1 and/or hChk2 then phosphorylate Cdc25C on Ser216, which creates a consensus binding site for 14-3-3 proteins. In undamaged interphase cells, Ser216 also is phosphorylated by a third, constitutively active kinase, the Cdc25C-associated protein kinase (cTAK1). Association with 14-3-3 proteins leads to sequestration of phosphorylated Cdc25C in the cytoplasm and prevents premature dephosphorylation of Cdk1 and activation of the cyclin B1/Cdk1 complex.
Staurosporine and UCN-01 are capable of inhibiting the phosphotransferase activities of several serine-threonine protein kinases (4) . Because the kinase activity of Wee1 is resistant to UCN-01 (9) , we hypothesized that the mechanism of UCN-01-mediated checkpoint abrogation might involve inhibition of one or more of the kinases that regulate Cdc25C. In this study, we show that UCN-01 inhibits hChk1 and cTAK1 at drug concentrations associated with abrogation of the G2 checkpoint. In contrast, hChk2 was relatively resistant to checkpoint inhibitory concentrations of UCN-01. These data identify hChk1 as a relevant molecular target for UCN-01 and suggest that specific hChk1 inhibitors will efficiently disrupt the G2 checkpoint.
| Materials and Methods |
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Immune Complex Kinase Assays.
The hChk1 and hChk2 kinase assays were performed as described
previously for hChk1 (11)
. Kinase assays for cTAK were
performed essentially as described for hChk1 except for minor changes
in the immunoprecipitation conditions. K562 cells transiently
expressing epitope-tagged cTAK1 were lysed in buffer (20 mM
HEPES, 0.15 M NaCl, 1.5 mM
MgCl2, and 1 mM EGTA, pH 7.4)
containing 1 mM DTT, 10 µg/ml aprotinin, 5 µg/ml
pepstatin, 5 µg/ml leupeptin, 20 nM microcystin, 10
mM ß-glycerophosphate, and 0.5% Triton X-100. After
immunoprecipitation with HA.11 and protein A-Sepharose beads,
immunoprecipitates were washed twice in lysis buffer, twice in
high-salt buffer [0.1 M Tris-HCl (pH 7.4), 0.6
M NaCl], and twice in kinase buffer [50 mM
Tris (pH 7.4), 10 mM MgCl2]. Kinase
assays were then performed as outlined previously for hChk1
(11)
. All kinase reactions were performed under linear
reaction conditions.
Flow Cytometry.
Ethanol-fixed cells were stained with propidium iodide and analyzed by
flow cytometry as described previously (12)
.
Cdc25C Mobility.
K562 cells were treated with graded concentrations of UCN-01 and then
lysed in TNE buffer [50 mM Tris (pH 8.0), 150
mM sodium chloride, 5 mM EDTA, 1% NP40, and
0.1% SDS] containing 0.1 mM sodium orthovanadate, 10
µg/ml aprotinin, 5 µg/ml pepstatin, 5 µg/ml leupeptin, 20
nM microcystin, 200 µM dephostatin, 10
µM cypermethrin, 200 nM okadaic acid, and 25
nM tautomycin. The detergent-soluble proteins were then
processed for immunoblotting with Cdc25C-specific antisera.
hChk1/hChk2 Mobility Shift.
K562 cells were lysed in TNE buffer containing 1 mM DTT, 10
µg/ml aprotinin, 5 µg/ml pepstatin, 5 µg/ml leupeptin, 20
nM microcystin, and 10 mM ß-glycerophosphate.
The detergent-soluble proteins were then processed for immunoblotting
with the HA.11 monoclonal antibody.
Statistics.
All statistical analyses were performed with the Sigma Plot 5.0 (SPSS)
software package. The kinase inhibition data were fit with the Hill
four-parameter model by the least-squares method. The concentrations of
UCN-01 resulting in half-maximal inhibition
(IC50) for the respective kinases were calculated
by solving the model for a relative activity of 0.5.
| Results and Discussion |
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-radiation and graded concentrations of UCN-01. After 21 h,
80% of cells were arrested in G2 after
irradiation alone, which is consistent with the lack of a DNA
damage-inducible G1 checkpoint in this p53-null
cell line. In contrast, treatment of cells with 100 nM
UCN-01 completely abrogated the radiation-induced
G2 arrest (Fig. 1)
100 nM.
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-radiation-induced hChk2 activation requires ATM kinase activity and
raise the possibility that hChk2 may be involved in regulation of the
G2 checkpoint (6
, 14
, 15)
. Because
recombinant hChk2 can phosphorylate Cdc25C on
Ser216 in vitro, we predicted that
inhibition of hChk2 by UCN-01 would be required for abrogation of the
G2 checkpoint. Contrary to this hypothesis, the
kinase activity of hChk2 was 100-fold more resistant to the inhibitory
effects of UCN-01 (Fig. 2B
The phosphorylation of Cdc25C on Ser216 and the
exclusion of Cdc25C from the nucleus are maintained throughout
interphase. In unstressed cells, this phosphorylation is presumably
maintained by the cTAK1 kinase (10)
. We evaluated the
sensitivity of cTAK1 to UCN-01 to complete our survey of known protein
kinases that can phosphorylate Cdc25C on Ser216.
Interestingly, cTAK1 was nearly as sensitive as hChk1 to the inhibitory
effects of UCN-01 in immune-complex kinase assays with an
IC50 of 27 nM (Fig. 2C)
.
Although cTAK1 has no known function in the DNA damage checkpoint
responses, we cannot exclude the possibility that inhibition of cTAK1
kinase activity by UCN-01 could contribute to the checkpoint inhibitory
effects of this drug.
The results presented, to this point, support the hypothesis that the
checkpoint inhibitory effects of UCN-01 are related to the inhibition
of hChk1 but not hChk2 kinase activities. Both hChk1 and hChk2 are
inducibly phosphorylated in response to genotoxic agents, and these
modifications are presumed to be important in checkpoint activation
(6
, 16)
. Therefore, a UCN-01-induced block in an upstream
event modulating hChk1 or hChk2 activation also might lead to
abrogation of the G2 checkpoint. To evaluate the
effects of UCN-01 on the integrity of these upstream signaling
pathways, we assessed whether UCN-01 affected the DNA damage-induced
phosphorylation of transiently expressed hChk1 and hChk2 in K562 cells
treated with 10 mM HU or 20 Gy
-radiation. The mobility
of hChk1 on SDS-PAGE was appreciably retarded 1 h after
irradiation or continuous exposure to HU (data not shown), and
pretreatment with 1 µM UCN-01 had no effect on this hChk1
mobility shift (Fig. 3A)
. Likewise, the radiation-induced mobility shift of hChk2
also was unchanged by UCN-01 pretreatment (Fig. 3B)
.
Consistent with this observation, we have shown previously that the ATM
kinase, which functions directly upstream of hChk2, also is resistant
to inhibition by UCN-01 (11)
. Thus, in contrast to the
protein kinase activity of hChk1 itself, the pathways leading to hChk1
and hChk2 activation in damaged cells are not sensitive to UCN-01.
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-radiation. After 16 h, 95% of cells were arrested in
G2. Treatment of this
G2-arrested cell population with 100
nM UCN-01 resulted in a significant increase in the
nonphosphorylated, relative to the phosphorylated, form of Cdc25C
within 15 min of drug
addition.4
Moreover, graded concentrations of UCN-01 resulted in considerable
accumulation of the nonphosphorylated Cdc25C species (Fig. 3C)
The ATM and ATR proteins appear to control downstream signaling events
in the G2 checkpoint pathway
(19, 20, 21)
. We have shown previously that the checkpoint
inhibitory effects of the radiosensitizing agent caffeine were related
to the inhibition of ATM and ATR kinase activities (11)
.
Both epistasis experiments in yeast and genetic studies in mammalian
cells suggest that these protein kinases participate in the activation
of hChk1 and hChk2, which can then phosphorylate downstream targets
such as Cdc25C. The present findings suggest that inhibition of hChk1
and cTAK1 kinase activities is sufficient to abrogate the
G2 checkpoint. Strikingly, the relative
resistance of the hChk2 kinase to inhibition by UCN-01 suggests that
activation of the hChk2 kinase, in the absence of hChk1 and cTAK1
kinase activities, is insufficient to maintain the
-radiation-induced G2 arrest. This implies
either that phosphorylation of Cdc25C by hChk2 alone is insufficient to
arrest cell cycle progression or that hChk2 is not a physiologically
relevant protein kinase for Cdc25C in DNA-damaged cells. Although we
cannot exclude the potential role for cTAK1 in the induction and/or
maintenance of the checkpoint, our results reinforce the notion that a
specific inhibitor of hChk1 would be an effective inhibitor of the
G2 checkpoint.
Recent evidence suggests that the therapeutic efficacies of certain
DNA-damaging anticancer drugs are causally related to the loss of
normal DNA damage checkpoint controls during the process of
carcinogenesis (22
, 23)
. These studies suggest that agents
that interfere with checkpoint-related proteins may show selectivity
for tumor cells bearing intrinsic defects in specific checkpoint
pathways. One of the most common mutations that affects checkpoint
integrity is inactivation of the p53 tumor suppressor protein. Because
p53 functions in several checkpoint pathways (19)
, the
loss of p53 might leave tumor cells more vulnerable to pharmacological
inhibition of components of the remaining checkpoints in these cells.
The expected outcome of checkpoint inhibitor treatment in this setting
would be a selective increase in the sensitivities of cancer cells to
conventional genotoxic cancer therapies. In fact, both caffeine and
UCN-01 selectively abrogate the G2 checkpoint in
tumor cells that have lost p53-dependent checkpoint controls (2
, 24, 25, 26)
. The recent demonstration that homozygous deletion of
14-3-3
in HCT116 colon cancer cells compromises the
G2 checkpoint provides novel insight into a
potential mechanism for the selective pharmacological inhibition of the
G2 checkpoint (Fig. 4)
. In normal cells, DNA damage leads to a p53-dependent accumulation of
14-3-3
, which binds to and sequesters cyclin B1/Cdk1 complexes in
the cytoplasm (27)
. With cyclin B1/Cdk1 excluded from the
nucleus, pharmacological disruption of the hChk1-dependent checkpoint
pathway controlling Cdc25C localization will not lead to premature
entry into mitosis. However, in tumor cells deficient in p53 function,
the integrity of the G2 arrest is solely
dependent on the hChk1-dependent pathway, and disruption of this
pathway could then lead to checkpoint abrogation.
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| Note Added in Proof |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 This work was supported by the Mayo Foundation,
Mayo Cancer Center, and by grants from the Fraternal Order of Eagles
and the NIH CA52995 (to R. T. A.), CA69709 (to J. N. S.), and
CA80829 (to J. N. S.). ![]()
2 To whom requests for reprints should be
addressed, at Mayo Foundation, Guggenheim Building, Room 1301, 200
First Street S.W., Rochester, MN 55905. Phone: (507) 266-5232; Fax:
(507) 284-3906; E-mail: sarkaria.jann{at}mayo.edu ![]()
3 The abbreviations used are: UCN-01,
7-hydroxystaurosporine; Cdk, cyclin-dependent kinase; ATM, ataxia
telangiectasia mutated; HA, hemagglutinin; PKC, protein
kinase C; HU, hydroxyurea; hChk, checkpoint kinase; cTAK1,
Cdc25C-associated protein kinase 1; ATR, AT and Rad3-related. ![]()
4 J. N. Sarkaria and D. F. Leistritz,
unpublished data. ![]()
Received 12/ 9/99. Accepted 3/ 2/00.
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S. J. H. Arlander, A. K. Eapen, B. T. Vroman, R. J. McDonald, D. O. Toft, and L. M. Karnitz Hsp90 Inhibition Depletes Chk1 and Sensitizes Tumor Cells to Replication Stress J. Biol. Chem., December 26, 2003; 278(52): 52572 - 52577. [Abstract] [Full Text] [PDF] |
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J. R. A. Hutchins, D. Dikovskaya, and P. R. Clarke Regulation of Cdc2/Cyclin B Activation in Xenopus Egg Extracts via Inhibitory Phosphorylation of Cdc25C Phosphatase by Ca2+/Calmodium-dependent Kinase II Mol. Biol. Cell, October 1, 2003; 14(10): 4003 - 4014. [Abstract] [Full Text] [PDF] |
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C. C. S. Chini and J. Chen Human Claspin Is Required for Replication Checkpoint Control J. Biol. Chem., August 8, 2003; 278(32): 30057 - 30062. [Abstract] [Full Text] [PDF] |
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M. Roshal, B. Kim, Y. Zhu, P. Nghiem, and V. Planelles Activation of the ATR-mediated DNA Damage Response by the HIV-1 Viral Protein R J. Biol. Chem., July 3, 2003; 278(28): 25879 - 25886. [Abstract] [Full Text] [PDF] |
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D. Amico, A. M. Barbui, E. Erba, A. Rambaldi, M. Introna, and J. Golay Differential response of human acute myeloid leukemia cells to gemtuzumab ozogamicin in vitro: role of Chk1 and Chk2 phosphorylation and caspase 3 Blood, June 1, 2003; 101(11): 4589 - 4597. [Abstract] [Full Text] [PDF] |
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T. Furuta, H. Takemura, Z.-Y. Liao, G. J. Aune, C. Redon, O. A. Sedelnikova, D. R. Pilch, E. P. Rogakou, A. Celeste, H. T. Chen, et al. Phosphorylation of Histone H2AX and Activation of Mre11, Rad50, and Nbs1 in Response to Replication-dependent DNA Double-strand Breaks Induced by Mammalian DNA Topoisomerase I Cleavage Complexes J. Biol. Chem., May 23, 2003; 278(22): 20303 - 20312. [Abstract] [Full Text] [PDF] |
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R. S. Weiss, P. Leder, and C. Vaziri Critical Role for Mouse Hus1 in an S-Phase DNA Damage Cell Cycle Checkpoint Mol. Cell. Biol., February 1, 2003; 23(3): 791 - 803. [Abstract] [Full Text] |
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H. Miao, J. A. Seiler, and W. C. Burhans Regulation of Cellular and SV40 Virus Origins of Replication by Chk1-dependent Intrinsic and UVC Radiation-induced Checkpoints J. Biol. Chem., January 31, 2003; 278(6): 4295 - 4304. [Abstract] [Full Text] [PDF] |
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E. A. Kohn, C. J. Yoo, and A. Eastman The Protein Kinase C Inhibitor Go6976 Is a Potent Inhibitor of DNA Damage-induced S and G2 Cell Cycle Checkpoints Cancer Res., January 1, 2003; 63(1): 31 - 35. [Abstract] [Full Text] [PDF] |
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E. Okubo, J. M. Lehman, and T. D. Friedrich Negative Regulation of Mitotic Promoting Factor by the Checkpoint Kinase Chk1 in Simian Virus 40 Lytic Infection J. Virol., December 20, 2002; 77(2): 1257 - 1267. [Abstract] [Full Text] [PDF] |
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T. P. Heffernan, D. A. Simpson, A. R. Frank, A. N. Heinloth, R. S. Paules, M. Cordeiro-Stone, and W. K. Kaufmann An ATR- and Chk1-Dependent S Checkpoint Inhibits Replicon Initiation following UVC-Induced DNA Damage Mol. Cell. Biol., December 15, 2002; 22(24): 8552 - 8561. [Abstract] [Full Text] [PDF] |
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B. Zhao, M. J. Bower, P. J. McDevitt, H. Zhao, S. T. Davis, K. O. Johanson, S. M. Green, N. O. Concha, and B.-B. S. Zhou Structural Basis for Chk1 Inhibition by UCN-01 J. Biol. Chem., November 22, 2002; 277(48): 46609 - 46615. [Abstract] [Full Text] [PDF] |
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H. Zhao, J. L. Watkins, and H. Piwnica-Worms Disruption of the checkpoint kinase 1/cell division cycle 25A pathway abrogates ionizing radiation-induced S and G2 checkpoints PNAS, November 12, 2002; 99(23): 14795 - 14800. [Abstract] [Full Text] [PDF] |
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X. Wang, G. C. Li, G. Iliakis, and Y. Wang Ku Affects the CHK1-dependent G2 Checkpoint after Ionizing Radiation Cancer Res., November 1, 2002; 62(21): 6031 - 6034. [Abstract] [Full Text] [PDF] |
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V. Patel, T. Lahusen, C. Leethanakul, T. Igishi, M. Kremer, L. Quintanilla-Martinez, J. F. Ensley, E. A. Sausville, J. S. Gutkind, and A. M. Senderowicz Antitumor Activity of UCN-01 in Carcinomas of the Head and Neck Is Associated with Altered Expression of Cyclin D3 and p27KIP1 Clin. Cancer Res., November 1, 2002; 8(11): 3549 - 3560. [Abstract] [Full Text] [PDF] |
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Q. Yu, J. La Rose, H. Zhang, H. Takemura, K. W. Kohn, and Y. Pommier UCN-01 Inhibits p53 Up-Regulation and Abrogates {gamma}-Radiation-induced G2-M Checkpoint Independently of p53 by Targeting Both of the Checkpoint Kinases, Chk2 and Chk1 Cancer Res., October 15, 2002; 62(20): 5743 - 5748. [Abstract] [Full Text] [PDF] |
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A. Eastman, E. A. Kohn, M. K. Brown, J. Rathman, M. Livingstone, D. H. Blank, and G. W. Gribble A Novel Indolocarbazole, ICP-1, Abrogates DNA Damage-induced Cell Cycle Arrest and Enhances Cytotoxicity: Similarities and Differences to the Cell Cycle Checkpoint Abrogator UCN-01 Mol. Cancer Ther., October 1, 2002; 1(12): 1067 - 1078. [Abstract] [Full Text] [PDF] |
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D. Sampath, Z. Shi, and W. Plunkett Inhibition of Cyclin-Dependent Kinase 2 by the Chk1-Cdc25A Pathway during the S-Phase Checkpoint Activated by Fludarabine: Dysregulation by 7-Hydroxystaurosporine Mol. Pharmacol., September 1, 2002; 62(3): 680 - 688. [Abstract] [Full Text] [PDF] |
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A. F.W. Frijhoff, C. J. Conti, and A. M. Senderowicz Second Symposium of Novel Molecular Targets for Cancer Therapy Oncologist, August 1, 2002; 7(90003): 1 - 3. [Full Text] [PDF] |
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A. M. Senderowicz The Cell Cycle as a Target for Cancer Therapy: Basic and Clinical Findings with the Small Molecule Inhibitors Flavopiridol and UCN-01 Oncologist, August 1, 2002; 7(90003): 12 - 19. [Abstract] [Full Text] [PDF] |
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E. A. Kohn, N. D. Ruth, M. K. Brown, M. Livingstone, and A. Eastman Abrogation of the S Phase DNA Damage Checkpoint Results in S Phase Progression or Premature Mitosis Depending on the Concentration of 7-Hydroxystaurosporine and the Kinetics of Cdc25C Activation J. Biol. Chem., July 12, 2002; 277(29): 26553 - 26564. [Abstract] [Full Text] [PDF] |
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H. Wang, X. Wang, X.-Y. Zhou, D. J. Chen, G. C. Li, G. Iliakis, and Y. Wang Ku Affects the Ataxia and Rad 3-related/CHK1-dependent S Phase Checkpoint Response after Camptothecin Treatment Cancer Res., May 1, 2002; 62(9): 2483 - 2487. [Abstract] [Full Text] [PDF] |
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X.-Y. Zhou, X. Wang, B. Hu, J. Guan, G. Iliakis, and Y. Wang An ATM-independent S-Phase Checkpoint Response Involves CHK1 Pathway Cancer Res., March 1, 2002; 62(6): 1598 - 1603. [Abstract] [Full Text] [PDF] |
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N. Guo, D. V. Faller, and C. Vaziri Carcinogen-induced S-Phase Arrest Is Chk1 Mediated and Caffeine Sensitive Cell Growth Differ., February 1, 2002; 13(2): 77 - 86. [Abstract] [Full Text] [PDF] |
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T. Yamauchi, M. J. Keating, and W. Plunkett UCN-01 (7-Hydroxystaurosporine) Inhibits DNA Repair and Increases Cytotoxicity in Normal Lymphocytes and Chronic Lymphocytic Leukemia Lymphocytes Mol. Cancer Ther., February 1, 2002; 1(4): 287 - 294. [Abstract] [Full Text] [PDF] |
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K. Yamane, X. Wu, and J. Chen A DNA Damage-Regulated BRCT-Containing Protein, TopBP1, Is Required for Cell Survival Mol. Cell. Biol., January 15, 2002; 22(2): 555 - 566. [Abstract] [Full Text] [PDF] |
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N. T. Rundle, L. Xu, R. J. Andersen, and M. Roberge G2 DNA Damage Checkpoint Inhibition and Antimitotic Activity of 13-Hydroxy-15-oxozoapatlin J. Biol. Chem., December 14, 2001; 276(51): 48231 - 48236. [Abstract] [Full Text] [PDF] |
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C. J. Rothblum-Oviatt, C. E. Ryan, and H. Piwnica-Worms 14-3-3 Binding Regulates Catalytic Activity of Human Wee1 Kinase Cell Growth Differ., December 1, 2001; 12(12): 581 - 589. [Abstract] [Full Text] [PDF] |
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H. Wang, J. Guan, H. Wang, A. R. Perrault, Y. Wang, and G. Iliakis Replication Protein A2 Phosphorylation after DNA Damage by the Coordinated Action of Ataxia Telangiectasia-Mutated and DNA-dependent Protein Kinase Cancer Res., December 1, 2001; 61(23): 8554 - 8563. [Abstract] [Full Text] [PDF] |
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Y. A. Elsayed and E. A. Sausville Selected Novel Anticancer Treatments Targeting Cell Signaling Proteins Oncologist, December 1, 2001; 6(6): 517 - 537. [Abstract] [Full Text] [PDF] |
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C. Feijoo, C. Hall-Jackson, R. Wu, D. Jenkins, J. Leitch, D. M. Gilbert, and C. Smythe Activation of mammalian Chk1 during DNA replication arrest: a role for Chk1 in the intra-S phase checkpoint monitoring replication origin firing J. Cell Biol., September 3, 2001; 154(5): 913 - 924. [Abstract] [Full Text] [PDF] |
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Y. Hirose, M. S. Berger, and R. O. Pieper Abrogation of the Chk1-mediated G2 Checkpoint Pathway Potentiates Temozolomide-induced Toxicity in a p53-independent Manner in Human Glioblastoma Cells Cancer Res., August 1, 2001; 61(15): 5843 - 5849. [Abstract] [Full Text] [PDF] |
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E. A. Sausville Combining Cytotoxics and 17-Allylamino, 17-Demethoxygeldanamycin: Sequence and Tumor Biology Matters : Commentary re: P. Munster et al., Modulation of Hsp90 Function by Ansamycins Sensitizes Breast Cancer Cells to Chemotherapy-induced Apoptosis in an RB- and Schedule-dependent Manner. Clin. Cancer Res., 7: 2228-2236, 2001. Clin. Cancer Res., August 1, 2001; 7(8): 2155 - 2158. [Full Text] [PDF] |
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M. A. Shah and G. K. Schwartz Cell Cycle-mediated Drug Resistance: An Emerging Concept in Cancer Therapy Clin. Cancer Res., August 1, 2001; 7(8): 2168 - 2181. [Abstract] [Full Text] [PDF] |
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H. Zhao and H. Piwnica-Worms ATR-Mediated Checkpoint Pathways Regulate Phosphorylation and Activation of Human Chk1 Mol. Cell. Biol., July 1, 2001; 21(13): 4129 - 4139. [Abstract] [Full Text] [PDF] |
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E. A. Sausville, S. G. Arbuck, R. Messmann, D. Headlee, K. S. Bauer, R. M. Lush, A. Murgo, W. D. Figg, T. Lahusen, S. Jaken, et al. Phase I Trial of 72-Hour Continuous Infusion UCN-01 in Patients With Refractory Neoplasms J. Clin. Oncol., April 15, 2001; 19(8): 2319 - 2333. [Abstract] [Full Text] [PDF] |
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H. Miyata, Y. Doki, H. Yamamoto, K. Kishi, H. Takemoto, Y. Fujiwara, T. Yasuda, M. Yano, M. Inoue, H. Shiozaki, et al. Overexpression of CDC25B Overrides Radiation-induced G2-M Arrest and Results in Increased Apoptosis in Esophageal Cancer Cells Cancer Res., April 1, 2001; 61(7): 3188 - 3193. [Abstract] [Full Text] |
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Y. Hirose, M. S. Berger, and R. O. Pieper p53 Effects Both the Duration of G2/M Arrest and the Fate of Temozolomide-treated Human Glioblastoma Cells Cancer Res., March 1, 2001; 61(5): 1957 - 1963. [Abstract] [Full Text] |
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V. Gottifredi, O. Karni-Schmidt, S.-Y. Shieh, and C. Prives p53 Down-Regulates CHK1 through p21 and the Retinoblastoma Protein Mol. Cell. Biol., February 15, 2001; 21(4): 1066 - 1076. [Abstract] [Full Text] |
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Z. Shi, A. Azuma, D. Sampath, Y.-X. Li, P. Huang, and W. Plunkett S-Phase Arrest by Nucleoside Analogues and Abrogation of Survival without Cell Cycle Progression by 7-Hydroxystaurosporine Cancer Res., February 1, 2001; 61(3): 1065 - 1072. [Abstract] [Full Text] |
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N Rhind and P Russell Chk1 and Cds1: linchpins of the DNA damage and replication checkpoint pathways J. Cell Sci., January 11, 2000; 113(22): 3889 - 3896. [Abstract] [PDF] |
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B. Hu, X.-Y. Zhou, X. Wang, Z.-C. Zeng, G. Iliakis, and Y. Wang The Radioresistance to Killing of A1-5 Cells Derives from Activation of the Chk1 Pathway J. Biol. Chem., May 18, 2001; 276(21): 17693 - 17698. [Abstract] [Full Text] [PDF] |
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X. Wu, S. R. Webster, and J. Chen Characterization of Tumor-associated Chk2 Mutations J. Biol. Chem., January 19, 2001; 276(4): 2971 - 2974. [Abstract] [Full Text] [PDF] |
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D. Curman, B. Cinel, D. E. Williams, N. Rundle, W. D. Block, A. A. Goodarzi, J. R. Hutchins, P. R. Clarke, B.-B. Zhou, S. P. Lees-Miller, et al. Inhibition of the G2 DNA Damage Checkpoint and of Protein Kinases Chk1 and Chk2 by the Marine Sponge Alkaloid Debromohymenialdisine J. Biol. Chem., May 18, 2001; 276(21): 17914 - 17919. [Abstract] [Full Text] [PDF] |
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W. A. Cliby, K. A. Lewis, K. K. Lilly, and S. H. Kaufmann S Phase and G2 Arrests Induced by Topoisomerase I Poisons Are Dependent on ATR Kinase Function J. Biol. Chem., January 4, 2002; 277(2): 1599 - 1606. [Abstract] [Full Text] [PDF] |
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P. B. Deming, C. A. Cistulli, H. Zhao, P. R. Graves, H. Piwnica-Worms, R. S. Paules, C. S. Downes, and W. K. Kaufmann The human decatenation checkpoint PNAS, October 9, 2001; 98(21): 12044 - 12049. [Abstract] [Full Text] [PDF] |
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