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Dr. Sujatha (Venkataraman)
Kumar
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Research Scientist
Inotek Pharmaceuticals
Beverly, MA
Graduate Education
Dr. Randal Tibbets,
Advisor at U.W. Madison 2001-2006
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Research Interest:
Student Seminar Abstract:
The DNA synthesis inhibitor hydroxyurea (HU) is an antineoplastic agent
most commonly used in the treatment of chronic myelogenous leukemia. HU
induces apoptosis in a cell-type dependent manner; with the cells of hematopoietic
origin typically demonstrating heightened sensitivity. The mechanisms
through which HU elicits cytotoxicity in leukemia cells are not well characterized.
We have employed a human myeloid leukemia cell line (ML-1) as a model
system to investigate the mechanisms of HU-induced apoptosis. We demonstrated
that ML-1 cells are remarkably sensitive to HU relative to other leukemic
cell lines. Features of apoptosis, including membrane blebbing, phopshatidylserine
translocation, PARP cleavage, and nuclear condensation appeared approximately
4 h after HU treatment. We found that HU induced p53 in ML-1 cells but
not HU-resistant Molt-3 cells, and that p53 accumulation required the
ATR protein kinase. Interestingly, HU-induced apoptosis was delayed by
the microtubule inhibitor Nocodazole, suggesting that premature mitosis,
or another microtubule-dependent event might underlie HU hypersensitivity.
Consistent with this notion, ML-1 cells showed apparent defect in the
expression of Checkpoint kinase 1(CHK1) protein kinase, which is required
for the suppression of mitosis and for replication fork stabilization
in response to replication stress. CHK-1-depedent degradation of Cdc25A
phosphatase in response to HU was also defective in ML-1 cells indicating
that Chk1 function is, in fact, compromised. Although we did not detect
obvious signs of premature mitosis in HU-treated ML-1 cells, the results
are consistent with a model whereby CHK1 insufficiency contributes to
apoptosis through a microtubule-dependent event. ML-1 cells may be a useful
model system for delineating the steps of HU-induced apoptosis, and for
studying the impact of checkpoint inhibitors on cellular sensitivity to
this drug.
Recent Publications: Articles on PubMed
- Kumar S, Dodson GE, Trinh A, Puchalski JR, and Tibbetts RS. (2005). ATR activation necessary but not sufficient for p53 induction and apoptosis in hydroxyurea-hypersensitive myeloid leukemia cells. Cell Cycle. 4:1667-1674. PMID 16258278
- Shi Y, Venkataraman S, Dodson
GE, Mabb AM, LeBlanc S, and Tibbetts, RS. (2004). Direct regulation of
CREB transcriptional activity by ATM in response to genotoxic stress. PNAS. 101:5898-5903. PDF PMID 15073328
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