KRAS, BRAF oncogene mutations and tissue specific promoter hypermethylation of tumor suppressor SFRP2, DAPK1, MGMT, HIC1 and p16 genes in colorectal cancer patients

BACKGROUND: Colorectal cancer is a serious disease that causes significant morbidity and mortality in developed countries. Genetic changes, such as mutations in proto-oncogenes and DNA repair genes, and loss of function in the tumor suppressor genes cause colorectal cancer development. Abnormal DNA methylation is also known to play a crucial role in colorectal carcinogenesis. OBJECTIVE: In this study, frequencies of KRAS and BRAF mutations, promoter hypermethylation profiles of SFRP2, DAPKI, MGMT, HIC1 and p16 genes, and possible associations between hypermethylation of these genes and KRAS and BRAF mutations were aimed to find out. METHODS: Ninety three colorectal cancer tissues and 14 normal colon mucosas were included in the study. Common twelve KRAS gene mutation were investigated with using reverse-hybridization strip assay method. BRAF V600E mutations were investigated with RFLP method. Hypermethylation status of five tumor suppressor genes were detected by using reverse-hybridization strip assay method after bisulfite modification of DNA. RESULTS: KRAS and BRAF mutation frequencies were determined as 54.84% and 12.9%, respectively. Promoter hypermethylation frequencies of tumor suppressor genes SFRP2, DAPK1, MGMT, HIC1 and p16 were determined as 66.7%, 45.2%, 40.9%, 40.9% and 15.1%, respectively. Statistically significant associations were found between BRAF mutation and SFRP2 and p16 tumor suppressor genes hypermethylation (SFRP2; p = 0.005, p16; p = 0.016). Compared to rectum, SFRP2 (p = 0.017) and MGMT (p = 0.013) genes have statistically significantly higher promoter hypermethylation in colon. CONCLUSIONS: Results of the current study have confirmed that KRAS mutations and SFRP2 hypermethylation can be used as genetic markers in colorectal cancer.