Abstract A48: The K-ras let-7 miRNA binding site variant and K-ras mutations in colon cancer

Abstract

Abstract The K-ras gene is one of the most commonly mutated genes in cancer. The ras proteins act as functional switches in the activation of the MAPK pathway in a complex signaling network coupling growth factor receptors to the intracellular kinases. Mutations in the K-ras gene lead to the constitutive activation of the protein and consequently of the MAPK pathway. K-ras mutations are early events in colorectal carcinogenesis and are observed in 30-40 % of the colorectal cancers. Mutations mostly occur at codons 12, 13 and 61 of the gene and result in the deregulation of the protein activity. Several studies have shown that patients with K-ras mutations do not benefit from therapies with anti-EGFR monoclonal antibodies. miRNAs are global regulators of gene expression by binding to the 3'-untranslated region of the target mRNA. Recently, it has been shown that the K-ras gene is regulated at the translational level by binding of the let-7 miRNA. The let-7 family of miRNAs is known to play an important role in several cancer types. A germline SNP at the 3'-UTR of the K-ras gene (rs: 61764370 T-G) has been shown to disrupt binding of the let-7 molecule to K-ras resulting in overexpression of the gene and was found to confer increased susceptibility for distinct cancer types. The let-7 miRNA variant was found to be associated with poor outcome in lunh and head and neck cancers. However, the frequency and association of this variant with other cancer types has not been investigated widely. In this study we evaluated the frequency of the K-ras gene variant in 145 patients with colon cancer and 85 healthy individuals and its possible association with the K-ras gene mutations. The K-Ras gene variant was analyzed by polymerase chan reaction-restriction fragment length polymorphism (PCR-RFLP) analysis, K-ras gene mutations were investigated by real time-PCR. The results were evaluated using the Chi-square test. The variant allele of the K-ras gene was observed in 23 patients (15.9%) in the heterozygote form. A single patient was homozygous for the variant allele. The variant allele was detected in 12 % of the control group. K-ras gene mutations were present in 46 (32 %) of the patients. The frequency of the variant allele was 13 % among the patients harboring a K-ras gene mutation. The distribution of the variant allele is in accordance with a report on the US control population and no significant difference was observed between the patients and the controls. Citation Format: Nejat Dalay, Zubeyde Yalniz, Orkun Gurbuz. The K-ras let-7 miRNA binding site variant and K-ras mutations in colon cancer. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A48. doi: 10.1158/1557-3125.RASONC14-A48