Krüppel-like factor 5 is a crucial mediator of intestinal tumorigenesis in mice harboring combined Apc(Min )and KRAS(V12 )mutations

BACKGROUND: Both mutational inactivation of the adenomatous polyposis coli (APC) tumor suppressor gene and activation of the KRAS oncogene are implicated in the pathogenesis of colorectal cancer. Mice harboring a germline Apc(Min )mutation or intestine-specific expression of the KRAS(V12 )gene have been developed. Both mouse strains develop spontaneous intestinal tumors, including adenoma and carcinoma, though at a different age. The zinc finger transcription factor Krüppel-like factor 5 (KLF5) has previously been shown to promote proliferation of intestinal epithelial cells and modulate intestinal tumorigenesis. Here we investigated the in vivo effect of Klf5 heterozygosity on the propensity of Apc(Min)/KRAS(V12 )double transgenic mice to develop intestinal tumors. RESULTS: At 12 weeks of age, Apc(Min)/KRAS(V12 )mice had three times as many intestinal tumors as Apc(Min )mice. This increase in tumor number was reduced by 92% in triple transgenic Apc(Min)/KRAS(V12)/Klf5(+/- )mice. The reduction in tumor number in Apc(Min)/KRAS(V12)/Klf5(+/- )mice was also statistically significant compared to Apc(Min )mice alone, with a 75% decrease. Compared with Apc(Min)/KRAS(V12), tumors from both Apc(Min)/KRAS(V12)/Klf5(+/- )and Apc(Min )mice were smaller. In addition, tumors from Apc(Min )mice were more distally distributed in the intestine as contrasted by the more proximal distribution in Apc(Min)/KRAS(V12 )and Apc(Min)/KRAS(V12)/Klf5(+/- )mice. Klf5 levels in the normal-appearing intestinal mucosa were higher in both Apc(Min )and Apc(Min)/KRAS(V12 )mice but were attenuated in Apc(Min)/KRAS(V12)/Klf5(+/- )mice. The levels of β-catenin, cyclin D1 and Ki-67 were also reduced in the normal-appearing intestinal mucosa of Apc(Min)/KRAS(V12)/Klf5(+/- )mice when compared to Apc(Min)/KRAS(V12 )mice. Levels of pMek and pErk1/2 were elevated in the normal-appearing mucosa of Apc(Min)/KRAS(V12 )mice and modestly reduced in Apc(Min)/KRAS(V12)/Klf5(+/- )mice. Tumor tissues displayed higher levels of both Klf5 and β-catenin, irrespective of the mouse genotype from which tumors were derived. CONCLUSIONS: Results of the current study confirm the cumulative effect of Apc loss and oncogenic KRAS activation on intestinal tumorigenesis. The drastic reduction in tumor number and size due to Klf5 heterozygosity in Apc(Min)/KRAS(V12 )mice indicate a critical function of KLF5 in modulating intestinal tumor initiation and progression.