Novel genetic and epigenetic alterations in ... - Ous-research.no

Neoplasia Vol. 10, No. 7, 2008 RAS Signaling in Colorectal Carcinomas Ahlquist et al. 683Figure 1. Site distribution of mutations within each gene. The mutations for the respective gene are placed according to their sequenceposition. In (a) and (b), only the exons in blue have been analyzed. In (c), all exons are analyzed, and the exons in orange indicate thosethat are only expressed in isoforms. To the right, representative sequencing results of mutant samples are presented.RASSF1ABy MSP analysis, we found that 18 (31%) of 59 samples were hypermethylatedin the promoter of RASSF1A. Methylation of the genewas more frequent in the distally located tumors (P = .041), but wasnot overlapping with the MSS phenotype. In eight tumors, hypermethylationof RASSF1A was the only observed alteration among thefour genes analyzed here. We found no covariance between RASSF1Amethylation and mutation status of either of the analyzed genes.Dysregulation of RAS SignalingWhen looking at concurrent mutations in individual tumors, wefound that KRAS and BRAF were mutually exclusive because allBRAF mutations occurred in wild type KRAS tumors and vice versa(P < .0001). The sample with NF1 missense mutations was MSIpositive,proximally located, and harbored a BRAF mutation. Whenincluding the intronic mutations in the number of NF1 mutations,six of eight BRAF mutations occurred in NF1-mutated samples