Kishor K. Bhakat, Ph.D.Dr. Bhakat

Assistant Professor, Biochemistry & Molecular Biology, Scientist, Sealy Center for Molecular Medicine

kkbhakat@utmb.edu

Research Interests

Hypertension is a silent but very common cardiovascular disorder that affects more than 65 million people in the US, and 75% of the population older than 65. The paracrine and endocrine mechanisms that regulate blood pressure are now generally understood, and provide the pharmacological basis for most antihypertensive therapies. In contrast, the intracellular molecular events that control blood pressure are still only poorly understood. The renin angiotensin system (RAS) plays a major role in regulating the blood pressure and fluid/electrolyte homeostasis. Calcium has always been considered as a critical intracellular second messenger for controlling renin synthesis and its secretion from the kidneys. Renin expression is downregulated at the level of transcription, as increased [Ca2+]i leads to decreased renin mRNA levels. This is mediated by the binding of cognate trans-acting factors to negative calcium response elements (nCaRE) -B in the renin promoter. Human AP-endonuclease (APE1/Ref-1) is a component of the complex that binds to nCaRE-B. A recent study showing that APE1 heterozygous (APE1+/-) mice have elevated blood pressure is consistent with its negative regulatory role for renin expression. While APE1 plays a very important role in [Ca2+]i-mediated downregulation of renin, and so in maintaining blood pressure, the molecular mechanisms by which APE1 regulates renin expression as a function of [Ca2+]i is unclear. We have shown that acetylation of APE1 at Lys6 and Lys7 by the histone acetyltransferase p300 enhances binding of APE1 to nCaRE-B in the human renin promoter and overexpression of APE1, but not of its nonacetylable K6R/K7R mutant, decreased renin mRNA levels. Our research objective is to elucidate how APE1 and its acetylation are involved in Ca2+-mediated downregulation of the renin gene. Our long-term goal is to understand how the transcriptional regulatory function of APE1 helps control blood pressure, by modulating renin gene expression, and use this information to develop new therapeutic approaches to blood pressure control.

Selected Publications

  1. 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. 2006; 26:1654-1665.
  2. Das, A., Hazra, T. K., Boldogh, I., Mitra, S., and Bhakat, K. K. Induction of the human oxidized base-specific DNA glycosylase NEIL1 by reactive oxygen species. J. Biol. Chem. 2005; 280:35272-35280.
  3. 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. 2005; 102:5739-5743.
  4. Bhakat, K. K., Hazra, T. K. and Mitra, S. Acetylation of the human DNA glycosylase NEIL2 and inhibition of its activity. Nucleic Acids Research 2004; 32:3033-3039.
  5. Szczesny, B., Bhakat, K. K., Mitra, S., and Boldogh, I. Age-dependent modulation of DNA repair enzymes by covalent modification and subcellular distribution. Mech. Ageing Dev. 2004; 125: 755-765.
  6. Boldogh, I., Bhakat, K. K., Bocangel, D., Gokul C. Das, CG. and Mitra S. “Regulation of DNA Repair and Apoptosis by p53 and its impact on alkylating drug resistance of tumor cells.” In: DNA Repair in Cancer Therapy. Humana Press, 2004; 73-108.
  7. 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. 2003; 22: 6299-6309.
  8. Bhakat, K. K., Yang S.H. and Mitra S. Acetylation of human AP-endonuclease 1, a critical enzyme in DNA repair and transcription regulation. Methods in Enzymology 2003; 371: part D, 292-300.
  9. Bhakat, K. K. and Mitra, S. CpG methylation-dependent repression of the human 06-methylguanine-DNA methyltransferase gene linked to chromatin structure alteration. Carcinogenesis, 2003; 24, 1337-1345.
  10. Bhakat, K. K., and Mitra, S. Regulation of the human o6-methylguanine-DNA methyltransferase gene by transcriptional coactivators cAMP response element-binding protein-binding protein and p300. J. Biol. Chem. 2000; 275:34197-34204.