Kishor Bhakat, PhD

Associate Professor


Department of Genetics, Cell Biology and Anatomy
985805 Nebraska Medical Center
Omaha, NE 68198-5805


PhD, Indian Institute of Chemical Biology, India, 1999
Post-doc, University of Texas Medical Branch, Galveston, TX

Academic Appointments:
Co-Course Director, IPBS 802 Molecular Cell Biology
Co-Course Director, MGCB 903 Journal Club

Mitotic gene bookmarking: A novel dimension of epigenetic memory in post-mitotic transcriptional reactivation
Cells must remember which genes were active before mitosis entry and transmit this information to their daughter cells so expression patterns can be faithfully re-established in progeny cells.  The major focus of my laboratory is to understand how cancer cells remember and transmit the transcriptional memory to daughter cells for maintaining their sustained proliferation and survival. Our research is aimed at a better understanding of transcriptional regulation and epigenetic memory in cancer with the goal of identifying novel epigenetic marks as an early diagnostic and prognostic biomarker for cancer. Furthermore, we are also involved in elucidating the molecular mechanisms of drug resistance of tumor cells.

APE1 and its Acetylation: A potential prognostic and predictive biomarker in cancer
We have been working on a ubiquitous and multifunctional protein, mammalian AP endonuclease 1 (APE1). APE1 plays a central role in the repair of both endogenous and environmentally induced oxidative and drug-induced alkylation damage in the genome via the base excision repair (BER) pathway. APE1 also has a second function as a transcriptional coregulator to control multiple cellular pathways. APE1 was shown to activate DNA-binding of many stress-inducible transcription factors (TF) (including c-Jun, p53 and NF-kB) by reducing specific Cys residues in the TF through its redox activator (Ref-1) function. Thus APE1 has a critical role in linking DNA repair to regulation of signaling pathways. Invariable overexpression of APE1 in tumor cell lines and various cancer tissues including glioma, head and neck, breast, and NSCLC, and its association with resistance to various anticancer drugs strongly implicates APE1 as a target for cancer therapy.

We discovered earlier that human APE1 is acetylated primarily at Lys6 and Lys7 by the histone acetyltransferase p300 both invitro and in cells, and that acetylation modulates its transcriptional regulatory function. Subsequently, we and others have established APE1’s acetylation-dependent (redox-independent) transcriptional regulatory function in activation of the multidrug resistance gene MDR1, cell-cycle control gene PTEN, and in calcium-dependent downregulation of PTH and Bax genes. The importance of APE1 acetylation became more evident with our findings that oxidative stress or treatment with clinically relevant drug cisplatin increased APE1 acetylation and that APE1 acetylation modulates its interaction with partner proteins. We showed that APE1 inactivation induces apoptosis in conditionally APE1-nullizygous mouse embryo fibroblasts (MEFs), which can be prevented by ectopic APE1 expression. Importantly, APE1 mutants lacking either repair activity or Lys6/7 acetylation sites could not prevent apoptosis of MEFAPE1null cells alone, indicating that both APE1’s repair function and acetyl-acceptor sites are essential for cell survival. Because our published studies and preliminary results show that cancer tissues have elevated levels of APE1 and its acetylation plays a key role in DNA damage repair in replicating genome and that APE1 regulates the expression of the key drug efflux protein MDR1, DNA damage-responsive cell cycle arrest protein p21 or checkpoint protein Nek11 and many other genes, the beneficial effects of chemotherapies might depend on the APE1 levels or expression of some its target genes. Our goals are to examine what signal triggers APE1 levels in tumor cells, to investigate how dysregulated APE1 in cancer cells is linked with their sustained proliferation and chemo-drug resistance, and to identify novel factor as an early diagnostic or prognostic biomarker.

Publications listed in PubMed

  1. Bhakat, K. K., Izumi, T., Yang, S. H., Hazra, T. K. and Mitra, S. Role of acetylated human AP-endonuclease (APE1/Ref-1) in regulation of the parathyroid hormone gene. EMBO J. 22, 6299-6309 (2003).
  2. Izumi, T., Brown, D. B., Naidu, C. V., Bhakat, K. K., MacInnes, M. A., Saito, H., Chen, D. J. and Mitra, S. Two Essential but Distinct Functions of the Mammalian AP-Endonuclease. Proc. Natl. Acad. Sci. 102:5739-5743 (2005).
  3. Bhakat, K. K., Mokkapati, S. K., Boldogh, I., Hazra, T. K., and Mitra, S. Acetylation of human 8-oxoguanine-DNA glycosylase by p300 and its role in 8-oxoguanine repair in vivo. Mol. Cell. Biol. 26:1654-1665 ( 2006).
  4. Zaky, A., Busso, C., Izumi,T., Chattopadhyay, R., Bassiouny, A., Mitra,S.,and Bhakat K. K. Regulation of the human AP-endonuclease (APE1/Ref-1) expression by the tumor suppressor p53 in response to DNA damage. Nucleic Acids Res. 36: 1555-1566 (2008).
  5. Chattopadhyay, R., Das, S., Maiti, AK., Boldogh, I., Xie, J., Hazra, TK., Kohno, K., Mitra, S., and Bhakat, K. K. Regulatory role of human AP-endonuclease (APE1) in YB-1-mediated activation of the multidrug resistance Gene MDR1.Mol. Cell. Biol. 23: 7066-7088 (2008).
  6. Bhattaracharyya, A., Chattopadhyay, R., Burnette, R., Cross, J., Mitra, S., Ernst, P.,. Bhakat, K. K., and Crowe, S. Acetylation of Apurinic/Apyrimidinic Endonuclease-1 Regulates Helicobacter pylori-Mediated Gastric Epithelial Cell Apoptosis. Gastroenterology, 136: 2258-2269 (2009).
  7. Bhakat, K. K., Mantha, AK., Mitra, S. Transcriptional regulatory functions of mammalian AP-endonuclease (APE1/Ref-1), an essential multifunctional protein. Antioxid Redox Signal. 11: 621-637 (2009).
  8. Bocangel, D., Mitra, S. and Bhakat, K. K., p53-meidated downregulation of the human DNA repair gene O6-methylguanine-DNA-methyltransferase(MGMT) via. interaction with Sp1 transcription factor. Anticancer Res. 29: 3741-3750 (2009).
  9. Sengupta, S., Mantha, A.K. Mitra, S., and Bhakat K. K.. Human AP-endonuclease (APE1/Ref1) and its acetylation regulate YB-1/p300 recruitment and RNA polymerase II loading in the drug induced activation of multidrug resistance gene MDR1. Oncogene, 30: 482-493 (2011).
  10. Sengupta, S, Mitra, S. and Bhakat K. K. Dual Regulatory Roles of Human AP-Endonuclease (APE1/Ref-1) in CDKN1A/p21 Expression. PloS One Jul 1610.1371/journal.pone.0068467 (2013).