ACTIVATION OF ADENOMATOUS POLYPOSIS-COLI (APC) GENE-EXPRESSION BY THEDNA-ALKYLATING AGENT N-METHYL-N'-NITRO-N-NITROSOGUANIDINE REQUIRES P53

Development of colon cancer is a multistep process frequently involvin g mutations in both the APC and p53 tumor suppressor genes. In this st udy we treated the HCT-116 colon cancer cell line with alkylating agen ts including N-methyl-N'-nitro-N-nitrosoguanidine (MNNG),which is know n to cause colon cancer in animals, and examined the expression of bot h APC and p53 genes. Exposure of cells with MNNG caused an 8-12-fold i ncrease in the level of APC mRNA and protein. APC induction was shown to result from increased nuclear transcription of the APC gene and cor related with a concomitant increase in the p53 protein level after MNN G treatment. A necessary role for p53 in APC gene regulation is suppor ted by the failure of MNNG to induce APC expression in cell lines eith er expressing very low levels of p53 (HeLa cells) or no p53 (K562 eryt hroleukemia cells). The overexpression of wild-type p53 gene into HCT- 116 cells mimicked the effect of MNNG-induced expression of APC mRNA. A direct causal role for p53 in APC gene regulation was further evalua ted by transfecting the wild-type p53 gene into K562 cells and observi ng a B-fold increase in the APC gene expression. These results support a model featuring a direct link between p53 and APC in response to al kylation-induced DNA damage and suggest a novel role for p53 in a stre ss-response pathway involving APC.