PCNA tyrosine phosphorylation by EGFR promotes genome instability

Abstract

The proliferating cell nuclear antigen (PCNA) is an essential component for DNA replication and repair, including DNA mismatch repair (MMR), an essential mechanism that ensures replication fidelity. PCNA is required for MMR at both the initiation and re‐synthesis steps. Recent studies have shown that PCNA is phosphorylated at tyrosine 211 (Y211) by epidermal growth factor receptor (EGFR), whose overexpression is associated with during tumor progression. We therefore hypothesize that the EGFR tumor‐promotion function is through PCNA Y211 phosphorylation by altering the MMR function. To test this hypothesis, we directly examined the influence of PCNA Y211 phosphorylation on MMR activity using a functional in vitro repair assay. We demonstrate here that nuclear extracts derived from tumor cells with high levels of phosphorylated PCNA are defective in MMR, and that the deficiency can be restored by purified non‐phosphorylated PCNA, suggesting that PCNA Y211 phosphorylation inhibits MMR. The inhibition was due to the inability of the phosphorylated PCNA to interact with mismatch recognition proteins MutSα and MutSβ. We also show that the PCNA‐phosphorylated nuclear extracts have a delayed DNA resynthesis during MMR, which is coupled with nucleotide misincorporations, leading to an elevated mutation frequency. Our study therefore demonstrates that a posttranslational modification promotes genome instability and tumor progression by negatively regulating the MMR function and DNA synthesis. Thus, the work provides a potential new biomarker for cancer progression.