APC tumor suppressor gene in sporadic colon cancer

Abstract

Goal of study: Colorectal carcinomas are characterized by multiple genetic aberrations that occur during tumorigenesis. Several tumor suppressor genes associated with colorectal carcinoma have been identified: MCC and APC on chromosome 5q, p53 on chromosome 17p, nm23-H1 on chromosome 17q, and DCC and DPC4 on chromosome 18q. We examined 46 cases of human sporadic colon cancer and corresponding normal tissue samples to evaluate the loss of heterozygosity (LOH) at the APC gene loci. The purpose of this study was also to evaluate whether the LOH at the APC gene is associated with clinicopathological characteristics in sporadic colon cancer. In addition, we also investigated the presence and the frequency of three most common APC gene mutations (codon 1309, 1061 and 1465) and APC E1317Q variant in Croatian colorectal cancer patients. Methods: DNAs were used for PCR, RFLP, VNTR, LOH and heteroduplex analysis. PCR was performed using specific pairs of primers. PCR products were analyzed by RFLP analysis, VNTR or heteroduplex analysis. To analyze LOH at the APC gene loci we used five polymorphic markers: three RFLP markers (exon 11 RsaI, exon 15 MspI and exon 15 AspHI) and two VNTR markers (D5S409 and D5S433). Conclusions: Using these five markers all patients were found heterozygous and informative for LOH analysis. DNA from 14 ( 30.4%) tumors exhibited LOH at the APC locus. The majority APC gene LOH was observed in Dukes' B (54.5%) and in the moderately differentiated tumors (42.1%). Analysis of the APC gene mutations showed that only 1309 mutation was present in our samples with the frequency of 2.2% ( 1/46). APC E1317Q germ-line variant was also present with the frequency of 2.2% (1/46).