Abstract
In the present investigation, we report a previously unsuspected function of the tumor suppressor protein, APC (adenomatous polyposis coli), in the regulation of base excision repair (BER). We identified a proliferating cell nuclear antigen-interacting protein-like box sequence in APC that binds DNA polymerase beta and blocks DNA polymerase beta-mediated strand-displacement synthesis in long patch BER without affecting short patch BER. We further showed that the colon cancer cell line expressing the wild-type APC gene was more sensitive to a DNA-methylating agent due to decreased DNA repair by long patch BER than the cell line expressing the mutant APC gene lacking the proliferating cell nuclear antigen-interacting protein-like box. Experiments based on RNA interference showed that the wild-type APC gene expression is required for DNA methylation-induced sensitivity of colon cancer cells. Thus, APC may play a critical role in determining utilization of long versus short patch BER pathways and affect the susceptibility of colon cancer cells to carcinogenic and chemotherapeutic agents.
Highlights
We further showed that the colon cancer cell line expressing the wild-type APC gene was more sensitive to a DNA-methylating agent due to decreased DNA repair by long patch base excision repair (BER) than the cell line expressing the mutant APC gene lacking the proliferating cell nuclear antigen-interacting protein-like box
We find that the APC peptide that contains a PIP-like box blocks pol--mediated strand displacement synthesis of long patch (LP)-BER without affecting short patch (SP)-BER
PCNA, flap endonuclease 1 (Fen-1), and DNA ligase were unable to relieve the block. These results provide evidence that APC distinguishes between the LP-BER and SP-BER pathways and suggest a mechanism by which the LP-BER and SP-BER pathways may be regulated differentially within the cells
Summary
It is mediated through two pathways that are differentiated by the size of the repair gap and the enzymes involved (2, 3) These pathways are designated “single nucleotide BER,” referred to as “short patch (SP) BER,” and “multinucleotide (2–13-nucleotide repair patch) BER,” referred to as “long patch (LP) BER.”. Several enzymes, acting in an orderly fashion, participate in DNA synthesis and the filling of the gaps, including N-glycosylase, AP endonuclease (APE), pol- ( has deoxyribose phosphatase activity), or polymerase ␦/⑀, flap endonuclease 1 (Fen-1), and DNA ligase I (reviewed in Ref. 4). It has been suggested that the utilization of the SP- and LP-BER pathways is determined by the type of damage encountered on DNA (reviewed in Ref. 7). We provide evidence that APC plays a role in regulating DNA repair by interacting directly with pol- and blocking its ability to mediate LP-BER strand displacement synthesis. The blocked LP-BER increases sensitivity of colon cancer cells to DNA-methylating agent, which in turn causes DNA damage that is repaired by LP-BER
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