title: Mutant K-ras promotes carcinogen-induced murine colorectal tumourigenesis, but does not alter tumour chromosome stability.
abstract: K-ras (KRAS) mutations are observed in around 40% of human colorectal adenomas and carcinomas. Previously, we developed and characterized a strain of transgenic mice with inducible intestinal epithelial expression of K-ras{Val12} via a Cre/LoxP system. To evaluate the influence of mutant K-ras on carcinogen-induced colorectal tumourigenesis, we induced neoplastic alterations in the large intestines of wild-type and K-ras{Val12} mice using the colon-selective carcinogen 1,2-dimethylhydrazine (DMH), which has been widely used to induce colorectal tumours that are histopathologically similar to those observed in humans. K-ras{Val12} expression significantly promoted DMH-induced colorectal tumourigenesis: the average lifespan of the mice decreased from 38.52 ± 1.97 weeks for 40 control mice to 32.42 ± 2.17 weeks for 26 K-ras{Val12} mice (mean ± SEM, p < 0.05) and the abundance of large intestinal tumours increased from 2.27 ± 0.15 per control mouse to 3.85 ± 0.20 in K-ras{Val12} mice (mean ± SEM, p < 0.01). Adenomas from DMH-treated K-ras{Val12} mice showed significantly higher proportions of Ki-67-positive proliferating cells (10.9 ± 0.69%) compared with those from DMH-treated wild-type mice (7.77 ± 0.47%) (mean ± SEM, p < 0.01) and a mild increase in apoptotic nuclei staining for cleaved caspase-3 (1.94 ± 0.21% compared with 1.15 ± 0.14%, mean ± SEM, p < 0.01). In the adenomas from DMH-treated K-ras{Val12} mice, K-ras{Val12} transgene recombination and expression were confirmed, with immunohistochemical evidence of strong Erk/MapK and mild PI3K/Akt pathway activation compared with adenomas from DMH-treated wild-type mice. Microarray hybridization and clustering analysis demonstrated different expression profiles in adenomas from DMH-treated wild-type and DMH-treated K-ras{Val12} mice, indicating involvement of different molecular mechanisms including Erk/MapK and PI3K/Akt signalling in K-ras{Val12}-expressing adenomas. Array-comparative genomic hybridization analysis showed chromosome stability in both cohorts, with only a very few tiny alterations observed in one adenoma from a DMH-treated K-ras{Val12} mouse. Taken together, these data show that mutant K-ras significantly promotes DMH-induced colorectal tumourigenesis, resulting in distinct changes in cell signalling and proliferation, but does not alter chromosome stability in the tumours.
authors.affiliation: Department of Pathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK.
authors.forename: Feijun
authors.initials: F
authors.lastname: Luo
authors.forename: George
authors.initials: G
authors.lastname: Poulogiannis
authors.forename: Hongtao
authors.initials: H
authors.lastname: Ye
authors.forename: Rifat
authors.initials: R
authors.lastname: Hamoudi
authors.forename: Wenyan
authors.initials: W
authors.lastname: Zhang
authors.forename: Gehong
authors.initials: G
authors.lastname: Dong
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Arends
mesh_terms: D019813:1,2-Dimethylhydrazine; D000236:Adenoma / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002273:Carcinogens; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism; D043171:Chromosomal Instability / Q000235:genetics*; D016000:Cluster Analysis; D015179:Colorectal Neoplasms / Q000139:chemically induced / Q000235:genetics* / Q000378:metabolism; D004195:Disease Models, Animal; D020869:Gene Expression Profiling / Q000379:methods; D011905:Genes, ras / Q000235:genetics*; D020935:MAP Kinase Signaling System / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009363:Neoplasm Proteins / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods; D051176:beta Catenin / Q000378:metabolism
chemical_list: D002273:Carcinogens; D009363:Neoplasm Proteins; D051176:beta Catenin; D019813:1,2-Dimethylhydrazine