Dietary fat and fiber modulate the effect of carcinogen on colonic protein kinase C lambda expression in rats

To elucidate the mechanisms by which dietary factors influence the risk of colon cancer, we investigated the effect of select dietary fats and fibers on atypical protein kinase C (PKC) lambda expression. Azoxymethane- and saline (control)-injected rats were fed diets containing either corn oil or fish oil (15 g/100 g) and either cellulose or pectin (6 g/100 g) and killed at two time points (15 and 37 wk) in a 2 x 2 x 2 x 2 factorial design. Colonic PKC lambda protein and mRNA levels were determined using immunoblotting and relative competitive polymerase chain reaction, respectively. Azoxymethane suppressed cytosolic PKC lambda protein levels compared with the saline controls at both time points, and this suppression was partially blocked by fish oil feeding at 15 wk and pectin at 37 wk. Also, at 15 wk, azoxymethane-injected rats fed corn oil had higher levels of membrane PKC lambda relative to the other treatment groups. Overall, expression of PKC lambda mRNA was not correlated with differences in the respective isozyme protein levels. Therefore, the chemopreventive effects of dietary fish oil and pectin are associated with the blockage of azoxymethane-induced alterations in colonic PKC lambda protein expression.