Role of Protein Kinase C Iota in Colon Carcinogenesis
Colon cancer results from progressive disregulation of the normal growth inhibitory, differentiation and apoptotic signals in colonic epithelial cells. Our long-term goal is to understand the role of protein kinase C (PKC) isozymes in colonic epithelial cell biology and colon carcinogenesis. Several lines of evidence suggest that the atypical PKC iota isoform (PKCi) plays an important promotive role in colon carcinogenesis. First, PKC expression is elevated in colon tumors relative to uninvolved colonic epithelium. Second, expression of PKCi protects cancer cells from apoptosis by activating NF-kB. Third, PKCi plays a requisite role in the transformation of intestinal epithelial cells by activated Ras, an oncogene commonly mutated in colon cancer. Fourth, inhibition of PKCi activity by dietary omega-3 fatty acids correlates with the cancer-preventive effects of omega-3 fatty acids. Taken together these data indicate that PKCi plays a key role in colon carcinogenesis by enhancing cell survival. We hypothesize that PKCi protects colonic epithelial cells against apoptosis and that elevated PKCi in the colonic epithelium will result in an increased susceptibility to colon carcinogenesis. We have generated transgenic mice that express constitutively active (ca) or dominant-negative (dn) mutant forms of PKCi in the colonic epithelium and have detected a decrease in basal apoptosis in the colonic epithelium of mice expressing caPKCi. In Specific Aim 1, we will determine the role of PKCi in colonic epithelial cell homeostasis by further characterizing our caPKCi and dnPKCi transgenic mice. Specific Aim 2 will assess the role of PKCi in mediating the effects of K-ras on colonic epithelial cell homeostasis and colon carcinogenesis in-vivo. Specific Aim 3 will determine the role of PKCi in Ras transformation and NF-kB signaling in intestinal epithelial cells in-vitro and in the colonic epithelium in-vivo. Specific Aim 4 will assess the role of PKCi in dietary fat-mediated changes in colonic epithelial cell homeostasis and colon carcinogenesis. These aims will be accomplished through the use of complementary transgenic mouse and rat intestinal epithelial cell models to assess the function of PKCi in the colonic epithelium.
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