Cigarette smoke condensate-induced level of adenomatous polyposis coli blocks long-patch base excision repair in breast epithelial cells

Abstract

Our previous studies have shown that treatment with cigarette smoke condensate (CSC) transforms normal breast epithelial cell line, MCF-10A. In the present study, the mechanism of CSC-induced transformation of breast epithelial cells was examined. We first determined whether benzo[a]pyrene (B[a]P)-and CSC-induced levels of APC are capable of inhibiting long-patch base excision repair (LP-BER) since our earlier studies had shown that an interaction of APC with DNA polymerase b (pol-b) blocks strand-displacement synthesis. With the use of a novel in vivo LP-BER assay, it was demonstrated that increased and decreased APC levels in different breast cancer cell lines were associated with a decrease or increase in LP-BER activity, respectively. The effect of APC on LP-BER in malignant and pre-malignant breast epithelial cell lines was produced by either overexpression or knockdown of APC. Furthermore, it was shown that the decreased LP-BER in B[a]P-or CSC-treated premalignant breast epithelial cells is associated with an increased level of APC and decreased cell growth. Our results suggest that the decreased growth allows cells to repair the damaged DNA before mitosis, and failure to repair damaged DNA has the potential to transform premalignant breast epithelial cells.

Mechanism of Adenomatous Polyposis Coli (APC)-Mediated Blockage of Long-Patch Base Excision Repair

“…If the DNA damage of a cell is not efficiently repaired, then cells can adapt either programmed cell death or proceed through the cell cycle with damaged DNA and cause carcinogenesis (62), which suggests a paradoxical role for APC. In fact, recently, we have shown a link of APC with carcinogenesis in which cigarette smoke condensate-induced levels of APC was associated with the blockage of LP-BER and transformation of normal breast epithelial cells (33). Thus, depending upon the environment of the cell, APC may act as a tumor suppressor by inducing cell death or causing carcinogenesis by helping to accumulate mutations.…”

“…In our future studies, we will use purified APC protein to address this concern more precisely. Nonetheless, we have backed up our findings by using in vivo gene-reporter and comet assays to describe the involvement of APC in LP-BER (32,33).…”

“…Best to our knowledge, there is no suitable in vivo BER assay system available. Thus, we developed a reporter plasmid-based in vivo BER assay system (33). We randomly modified multiple cytosine (C) residues of the p21(Waf1/Cip1)-luciferase promoter DNA into uracil (U) residues (U-p21P; a substrate for SP-BER).…”

“…One of the roles of APC in the nucleus is to regulate β-catenin levels, which bind to Tcf/Lef transcription factors and regulate transcriptional activity of number of target genes (30,31). Our recent findings implicate another role of nuclear APC in the regulation of DNA repair (32,33). We have previously shown that APC gene expression is induced upon exposure to DNA-damaging agents in colon cancer cells (34,35), suggesting a possibility of the interaction of APC with DNA repair machinery.…”

Base Excision Repair Manipulation in Breast Carcinoma: A Prospective Avenue to Potentiate Genome Insulting Approach

“…Inhibition of AP-endonuclease (APE) lead to increased sensitivity of cancer cells to alkylating chemotherapeutics [84]. When AP-sites are oxidized or reduced, they become resistant to elimination and cannot be excised by the dRP lyase activity of pol [85]. Many genes play a key role in BER like X-ray repair cross-complementing group 1 (XRCC1), OGG1 gene, PARP-1 and APE1 genes [55].…”