The long-term goal of this project is to understand the molecular mechanism by which DNA mismatch repair (MMR) maintains to genomic stability. MMR plays an important role in replication fidelity by correcting mispairs generated during DNA replication. Mismatch recognition protein hMutS?, a heterodimer consisting of hMSH2 and hMSH6 subunits, is arguably the most important component in MMR. The hMSH6 subunit contains a PCNA interaction protein motif (called PIP box) and a PWWP domain at its N-terminus. While no clear function has been assigned to the PWWP domain, the PIP box was previously thought to be involved in recruiting hMutS? to mismatched DNA. Interestingly, recent studies have shown that depletion of the PIP box only moderately increases mutation frequencies, and does not affect hMutS? chromatin localization. Surprisingly, we show recently that the MSH6 PWWP domain physically interacts with histone mark H3K36me3 and is responsible for localizing hMutS? to replicating chromatin. These observations suggest that the PCNA-hMSH6 interaction is not for hMutS? recruitment and that the epigenetic H3K36me3 histone mark plays a critical role in MMR and genomic stability. Given the abundance of H3K36me3 in S phase and that PCNA interacts with both hMutS? and replicative DNA polymerases ? and ?, we hypothesize that the H3K36me3-hMutS? interaction in individual nucleosomes determines mutation rates in the corresponding DNA sequences, and that the PCNA-hMutS? interaction coordinates the DNA replication and MMR reactions at the replication fork. To test these hypotheses, three specific aims are proposed.
Specific aim 1 is to determine genome-wide distributions of and interactions between H3K36me3 and hMutS? by ChIP- Seq analysis.
Specific aim 2 is to study molecular details as to how the PCNA-hMutS? interaction regulates DNA synthesis and MMR.
Specific aim 3 is to determine the impact of hMutS? interactions with H3K36me3 and PCNA on gene mutations using Exome-Sequencing analysis and a mutagenesis assay, respectively. A successful completion of the proposed study will not only elucidate novel mechanisms by which MMR maintains genome stability, but also provide potentially new biomarkers for cancer detection and therapy.

Public Health Relevance

Despite that great progress has been made in colorectal cancer detection and therapy, the disease is still the second leading cause of cancer deaths among adults in the United States. A major reason is that the cause for 15-20% of colorectal cancer is still unknown. This application aims to identify the factor(s) responsible for the 15-20 of colorectal cancer, which will improve both colorectal cancer detection and treatment.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Genetics B Study Section (MGB)
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Reddy, Michael K
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University of Southern California
Schools of Medicine
Los Angeles
United States
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Huang, Yaping; Li, Guo-Min (2018) DNA mismatch repair preferentially safeguards actively transcribed genes. DNA Repair (Amst) :
Fang, Jun; Huang, Yaping; Mao, Guogen et al. (2018) Cancer-driving H3G34V/R/D mutations block H3K36 methylation and H3K36me3-MutS? interaction. Proc Natl Acad Sci U S A 115:9598-9603
Huang, Yaping; Gu, Liya; Li, Guo-Min (2018) H3K36me3-mediated mismatch repair preferentially protects actively transcribed genes from mutation. J Biol Chem 293:7811-7823