The DNA mismatch repair (MMR) system is essential for correcting mispaired nucleotides in double-stranded DNA. Defects in the MMR pathway are evidenced by microsatellite instability, elevated mutation rates, enhanced recombination events, and tolerance to cytotoxic effects of alkylating agents. Loss of DNA MMR in humans is correlated with hereditary nonpolyposis colorectal cancer (HNPCC) and a subset of sporadic tumors. Our overall research program focuses on elucidating the full extent of MMR activity within human cells that contributes towards maintenance of genomic integrity. We have previously determined that fidelity of MMR can be substantially altered at an oncogenic hot spot of mutation, and that this is partially dependent on whether the mismatch-containing plasmid is introduced during cellular quiescence or proliferation. It is not yet known if MMR proficient mammalian cells have decreased MMR activity at phases of the cell cycle other than G2. Most investigations of MMR protein expression within mammalian cells, including ours, have demonstrated constitutive expression of the four key MMR mRNAs and proteins throughout the cell cycle; hMSH2 + hMSH6 (hMutS-alpha) and hMLH1 + hPMS2 (hMutL-alpha). Therefore, if MMR activity in human cells correlates with the E. coil post-replication model of MMR, then post-translational modification of these key MMR proteins may play an important role in the modulation of cellular MMR activities. We hypothesize that alterations in efficiency or fidelity of MMR in the human cell are dependent on phase of the cell cycle and require post-translational MMR protein modification. Our first specific aim is to investigate if the process of DNA replication is required for high efficiency and fidelity of MMR. Specifically, does the frequency of correct MMR differ during G1 (quiescent) versus S (DNA synthesis) or G2 (post synthetic) phase of the human cell cycle? Our second specific aim is to analyze phosphorylation/dephosphorylation events of the key MMR proteins at each different phase of the cell cycle and to determine if this post-translational modification plays a significant role in regulation of specific MMR activities.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Special Emphasis Panel (ZRG1-TPM (03))
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Okano, Paul
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University of Toledo
Schools of Medicine
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Gupte, Maithili; Tuck, Andrew N; Sharma, Vishal P et al. (2013) Major differences between tumor and normal human cell fates after exposure to chemotherapeutic monofunctional alkylator. PLoS One 8:e74071
Edelbrock, Michael A; Kaliyaperumal, Saravanan; Williams, Kandace J (2013) Structural, molecular and cellular functions of MSH2 and MSH6 during DNA mismatch repair, damage signaling and other noncanonical activities. Mutat Res 743-744:53-66
Kaliyaperumal, Saravanan; Patrick, Steve M; Williams, Kandace J (2011) Phosphorylated hMSH6: DNA mismatch versus DNA damage recognition. Mutat Res 706:36-45
Schroering, Allen G; Kothandapani, Anbarasi; Patrick, Steve M et al. (2009) Prolonged cell cycle response of HeLa cells to low-level alkylation exposure. Cancer Res 69:6307-14
Edelbrock, Michael A; Kaliyaperumal, Saravanan; Williams, Kandace J (2009) DNA mismatch repair efficiency and fidelity are elevated during DNA synthesis in human cells. Mutat Res 662:59-66
Schroering, Allen G; Williams, Kandace J (2008) Rapid induction of chromatin-associated DNA mismatch repair proteins after MNNG treatment. DNA Repair (Amst) 7:951-69