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East China University of Science and Technology
Thesis Advisor: Zhiyuan Shen, MD, PhD
Graduate Program of Cellular and Molecular Pharmacology
Cancer Institute of New Jersey
Monday, October 26, 2009
BCCIP is a BRCA2- and p21-interacting protein, which regulates BRCA2 and RAD51 nuclear focus formation, DSB-induced HR and cell cycle progression. However, it has not been clear whether BCCIP has other function in regulating cellular activity. We identified a new BCCIP interacting protein – SETD4, which is a potential protein lysine methyltransferase. SETD4 involves in the regulation of DNA double strand break repair. Knockdown of SETD4 in HT1080 cells and HEK293 cells induces the cellular sensitivity to ionizing radiation , as well as the inhibition of both homologous recombination and none homologous end joining repair pathway, although the level of BCCIP is not affected by SETD4 knockdown. In HT1080 cells, SETD4 recruits to the DNA damage sites after the treatment of UV laser scissor, and stays at the damage site for two hours after the DNA damage. SETD4 mutants,which contain mutations that may disrupt the methyltransferase activity of SETD4, do not recruit to the DNA damage sites after the treatment. We also investigate the regulation of p21 cellular distribution by BCCIP. p21 (CDKN1A, Waf1, or Cip1) protein plays a critical role in regulation of G1-S transition during the cell cycle progression. The inhibition of G1-S transition by p21 is mainly mediated in the nucleus. However, the cytoplasmic p21 has been shown to play a pro-proliferation and anti-apoptosis role. Thus, the regulation of p21 intracellular distribution has significant implication for cell fate determination. We show that the BCCIP-p21 interaction can be enhanced in response to DNA damage using Fluorescent Resonance Energy Transfer (FRET) technique. We find that that down-regulation of BCCIP reduces nuclear p21 and increase cytoplasm p21. This p21 redistribution effect is not caused by the reduced expression of endogenous p21 resulting from BCCIP down-regulation. The BCCIP regulation of p21 distribution is not related to the status of Thr-145 phosphorylation that is known to cause cytoplasmic distribution. These data suggest a new mechanism by which BCCIP regulates p21 function through controlling its intracellular distribution.