DNA polymerase beta expression differences in selected human tumors and cell lines

A long-standing question in cancer biology has been the extent to which DNA repair may be altered during the process of carcinogenesis. We have shown recently that DNA polymerase beta (P-pol) provides a rate-determining funct ion during in vitro repair of abasic sites by one of the mammalian DNA base excision repair pathways. Therefore, altered expression of beta-pol during carcinogenesis could alter base excision repair and, consequently, be crit ical to the integrity of the mammalian genome. We examined the expression o f beta-pol in several cell lines and human adenocarcinomas using a quantita tive immunoblotting method. In cell lines from normal breast or colon, the level of beta-pol was similar to 1 ng/mg cell extract, whereas in all of th e breast and colon adenocarcinoma cell lines tested, a higher level of beta -pol was observed, In tissue samples, colon adenocarcinomas had a higher le vel of beta-pol than adjacent normal mucosa. Breast adenocarcinomas exhibit ed a wide range of beta-pol expression: one tumor had a much higher level o f beta-pol (286 ng/mg cell extract) than adjacent normal breast tissue, whe reas another tumor had the same level of beta-pol as adjacent normal tissue . Differences in beta-pol expression level, from normal to elevated, were a lso observed with prostate adenocarcinomas. All kidney adenocarcinomas test ed had a slightly lower beta-pol level than adjacent normal tissue. This st udy reveals that the base excision repair enzyme DNA polymerase beta is upr egulated in some types of adenocarcinomas and cell lines, but not in others .