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Dietary Fat and Fiber Alter Rat Colonic Protein Kinase C Isozyme Expression^1,2,

Faculty of Nutrition and Molecular and Cell Biology Group, Texas A&M University, College Station, TX 77843-2471

To better understand the biochemical mechanisms by which select fats and fibers modulate colonic cell proliferation, we determined the profile of protein kinase C (PKC) isozymes and cell proliferation in rat proximal and distal colonic mucosa following diet manipulation, because enhanced cell proliferation has been correlated with colon cancer incidence. Rats were assigned to one of four diets (each with 15 g fat + 6 g fiber/100 g diet) for 3 wk: fiber-free fish oil (FF), fiber-free corn oil (FC), cellulose + corn oil (CC), or pectin + corn oil (PC). Steady-state levels of colonic mucosal cytosolic and membrane PKC isozymes were determined. In vivo cell proliferation was determined by bromodeoxyuridine incorporation into DNA. In addition, viable exfoliated colonic epithelial cells were isolated from feces using Percoll-bovine serum albumin gradients. We found that 1) proximal and distal colonic mucosa possessed different steady-state levels and relative proportions of PKC isozymes; 2) PKC and expression were significantly greater in distal membrane of the PC-fed group compared with the other dietary groups; 3) the number of exfoliated cells per 4-h fecal collection generally was proportional to the diet-induced changes in cell proliferation (PC>FC>CC>FF). These data demonstrate that dietary treatment altered colonic PKC isozyme expression, with animals fed the fiber-containing diets generally expressing higher steady-state levels of PKC and .

KEY WORDS: • rats • colonic mucosa • fiber • protein kinase C isozymes • fat

¹ Supported in part by a grant from the American Institute for Cancer Research and the Texas A&M Interdisciplinary Research Initiatives Enhancement Program. H.M.A. is supported in part by a fellowship from the Natural Sciences and Engineering Research Council of Canada.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 7 March 1994. Revision accepted 22 July 1994.

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