The primary aim of our proposed studies is to examine the mechanisms which control the normal growth and migration of colonic epithelial cells and which lead to proliferative abnormalities in populations at a high risk for colon cancer. Our studies will focus on the role of several putative signals to cell growth which are derived from enhanced membrane phospholipid turnover, specifically activation of protein kinase C and the generation of prostanoids, lipoxygenase products and reactive oxygen. Activation of the inositol phospholipid/protein kinase C signalling pathway, as assessed by translocation of enzyme activity from the soluble to the particulate fraction is associated with rapid cell growth in several cell systems including colonic epithelium. In the proposed studies we plan to further examine the functional and physiologic significance of the increase in particulate protein kinase C activity by producing polyclonal antibodies to protein kinase C and determining the subcellular localization of the enzyme by immunohistochemical techniques in colonic epithelium as a function of altered proliferative activity. Previous studies have supported a reciprocal relationship between cAMP and protein kinase C as a function of altered growth. Protein kinase C is activated and cAMP is reduced in association with enhanced proliferative activity in isolated proliferative versus surface colonocytes and in aspirin treated rats. Moreover, cAMP and cAMP agonists such as PGE2 suppress colonic epithelial proliferative activity in clonic explants in vitro. In the proposed studies we will further assess the relationship between cAMP and protein kinase C and examine the hypothesis that the suppressive effects of cAMP on colonic epithelial proliferation are due to suppression of the inositol phospholipid/protein kinase C signalling pathway. Chronic treatment of rats with aspirin results in suppression of colonic prostaglandin and cAMP production and a sustained increase in proliferative activity. By contrast, indomethacin treatment has been reported to suppress tumorigenesis in response to colon carcinogens. It is doubtful that prostaglandin synthesis and cAMP were suppressed by the dose of indomethacin employed in the studies of indomethacin effects on colon tumorigenesis. Accordingly, in the proposed studies we will examine the impact of a sustained increase in proliferative activity of colon mucosa on dysplasia and colon tumorigenesis in response to 1,2 dimethylhydrazine in rats treated with aspirin at a dose which results in suppression of PGE2 and cAMP production.
