Synergism between K-rasVal12 and mutant Apc accelerates murine large intestinal tumourigenesis

Abstract

Abstract. K-ras (KRAS) is mutated in 40-50% of human colorectal adenomas and carcinomas and plays key roles in cell proliferation, apoptosis, motility and differentiation, but its functional contribution to intestinal tumourigenesis in vivo remains incompletely understood. We have previously crossed K-rasVal12 transgenic mice with Ah-Cre mice to produce K-ras Val12 /Cre offspring that inducibly express K-ras Val12 4A and 4B in the intestines, but this alone showed no significant effect on intestinal adenoma formation. Here, we crossed these mice with Min mice to evaluate the effect of K-ras Val12and Apc mutation on intestinal tumourigenesis in vivo. the double mutant K-ras Val12 /Cre/Apc Min/+ mice showed a moderate (1.86-fold) increase in adenomas in the small intestines, but a striking acceleration (6-fold increase) of large intestinal adenoma formation (P<0.01) and significantly reduced survival (by ~5 weeks) compared with control Apc Min/+ mice (p<0.01). there was recombination of the mutant K-rasVal12 transgene in 80% of large intestinal adenomas with expression of both K-ras Val12 4A and 4B isoform transcripts and expression of K-ras Val12 protein. the large intestinal adenomas showed immunohistochemical evidence of activation of MapK, Akt and Wnt signaling pathways and this was confirmed by quantitative rt-pcr analysis of relative transcript expression levels of target genes using a panel of 23 selected genes evaluated in both adenomas and non-tumour-bearing intestines. several genes including Tiam1, Gastrin, CD44, uPA, Igfbp4, VEGF and Cox-2 that are known to be transcriptionally regulated by activation of the Wnt signaling pathway were found to be expressed at higher levels in the large intestinal adenomas from K-ras Val12 /Cre/Apc Min/+ mice compared with those from controls, although other Wnt signaling pathway target genes remained unchanged. these data show that intestinal expression of K-rasVal12 accelerates Apc-initiated intestinal adenomagenesis in vivo with particularly striking tumour promotion in the large intestines and indicate synergistic effects between mutant K-ras and mutant Apc in this process. IntroductionHuman colorectal carcinomas accumulate multiple mutations in cancer-related genes, including oncogenes such as KRAS and tumour suppressor genes, such as APC (adenomatous polyposis coli), SMAD 2/4, p53 and others (1,2). KRAS mutations can be detected at all stages of colorectal cancer development, from dysplastic aberrant crypt foci (AcF) and hyperplasic polyps to late adenomas and carcinomas (3,4). Mutational activation of the KRAS gene reduces or abolishes the protein's intrinsic gtpase activity, locking it in its gtp-bound conformation that results in constitutive activation of MApK and pI3K/AKt signal transduction pathways (5), modulating cell proliferation, apoptosis, senescence, motility and differentiation (6-10), but its roles in colorectal tumour initiation and progression are still incompletely understood.the APC gene, is known as the 'gatekeeper' of colorectal cancer, and...

Genomic profiling of stage II and III colon cancers reveals APC mutations to be associated with survival in stage III colon cancer patients

“…Furthermore, enhanced WNT activity was reported in cells with a KRAS mutation in addition to APC loss [26]. In mice, presence of a KRAS mutation in an APC mutant background was also associated with reduced survival due to accelerated growth of intestinal tumors [26, 27]. Interestingly, data from the Genomics of Drug Sensitivity in Cancer (GDSC) initiative [28] indicate that APC mutations confer increased sensitivity to the MAPK pathway MEK1/2 inhibitor PD-0325901 (www.cancerRxgene.org, release version 5.0).…”