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Dietary Fibers and Fats Alter Rat Colon Protein Kinase C Activity: Correlation to Cell Proliferation^{1, 2,}

Department of Animal Science and the Graduate Faculty of Nutrition, Texas A&M University, College Station, TX 77843-2471

Protein kinase C activity and cell proliferation in rat proximal colonic mucosa were determined following diet modification with select fibers and fats for 3 wk. Rats were assigned to one of nine dietary groups: three fibers (cellulose or pectin at 6 g/100 g diet or fiber free) x three fats (beef tallow, corn oil, fish oil at 15 g/100 g diet). Protein kinase C activity was determined by measuring the phosphorylation of a highly selective synthetic peptide derived from myelin basic protein. In vivo cell proliferation was measured by bromodeoxyuridine incorporation into DNA. There was a significant main effect of fat (P = 0.0008) but not fiber (P = 0.375) on the ratio of membrane to cytosolic protein kinase C with diets containing fish oils resulting in the highest ratios, corn oils in the lowest ratios and beef tallow producing an intermediate ratio. There was an interactive effect of fat and fiber on the proliferative zone (P = 0.04). Pectin resulted in a significantly greater proliferative zone than did cellulose and the fiber-free diet but only when the fat source was corn oil. There was a positive correlation between proliferative zone and both membrane protein kinase C activity (r = 0.76, P = 0.02) and protein kinase C membrane:cytosol ratio (r = 0.64, P = 0.06). Although the positive relationship between proliferative zone and protein kinase C activity has been reported previously, the high membrane protein kinase C activity found with fish oil supplementation compared to the low activity found with corn oil supplementation was unexpected. These data suggest that other factors (e.g., different protein kinase C isoforms, non-protein kinase C dependent signal transduction pathways) may be important intracellular signaling factors regulating colonic cell proliferation.

KEY WORDS: • protein kinase C • cell proliferation • dietary fiber • dietary fat • rats

¹ Portions of this study were presented at the Annual Meeting of the Federation of American Societies for Experimental Biology, April 1992, Anaheim, CA [Gao, J., Lee, D. Y., Lupton, J. R. & Chapkin, R. S. (1992) Effect of dietary fibers and fats on rat colon protein kinase C activity: correlation to cell proliferation. FASEB J. 6: A1494 (abs.)].

² Supported by a grant from American Institute for Cancer Research.

³ To whom correspondence should be addressed: Molecular and Cell Biology Group, Department of Animal Science, Texas A&M University, College Station, TX 77843-2471.

Manuscript received 18 August 1992. Revision accepted 3 December 1992.