RAS signaling in colorectal carcinomas through alterations of RAS, RAF, NF1 and/or RASSF1A

• Published in: Neoplasia (New York, N.Y.) Vol. 10; no. 7
• Main Authors: Ahlquist, T, Bottillo, I, Danielsen, SA, Meling, GI, Rognum, TO, Lind, GE, Dallapiccola, B, Lothe, R A
• Format: Journal Article
• Language: English
• Published: 01-07-2008
• ISSN: 1522-8002
• DOI: 10.1593/neo.08312

More than half of all colorectal carcinomas are known to exhibit an activated MAPK (mitogen-activated protein kinase) pathway. The NF1 gene, a negative regulator of KRAS has not previously been examined in a series of colorectal cancer. In the present study, primary colorectal carcinomas stratified according to microsatellite instability status were analyzed. The whole coding region of NF1 was analyzed for mutations using dHPLC and sequencing, and the copy number alterations of NF1 were examined using MLPA and RealTime PCR. The mutation hotspots in KRAS and BRAF were sequenced and promoter hypermethylation status of RASSF1A was assessed with methylation-specific PCR. One sample had two missense mutations in NF1, while nine additional tumors had intronic mutations likely to affect exon splicing. Interestingly, 8 of these 10 tumors were microsatellite unstable. Four other tumors showed a duplication of NFL Mutations in KRAS and BRAF were mutually exclusive, and present at 40% and 22%, respectively. RASSF1A was hypermethylated in 31% of the samples. We show that the RAS signaling network is extensively dysregulated in colorectal carcinomas, as more than 70% of the tumors had an alteration in one or more of the four examined components.