DIETARY MODULATION OF RAT COLONIC CAMP-DEPENDENT PROTEIN-KINASE ACTIVITY

Malignant transformation of cells is associated with enhanced prolifer ation and alterations in cAMP-dependent protein kinase (PKA) activity. To investigate the role of PKA in normal colonic cell proliferation, PKA was characterized in rat colonic mucosa. In addition, rats were fe d diets containing different fats (corn oil, fish oil) and fibers (pec tin, cellulose, fiber free) to elicit varying levels of colonic cell p roliferation in order to study this signaling system under normal phys iologic conditions. Overall, PKA activities were higher in cytosolic c ompared to membrane fractions. PKA type II (PKA II) isozyme contribute d 89 +/- 1% and 96 +/- 1% of total PKA activity in cytosolic and membr ane fractions, respectively. Reverse transcriptase-polymerase chain re action (RT-PCR) analysis revealed the presence of mRNA for both the al pha and beta isoforms of the regulatory subunits of PKA II. PKA activi ties were 21-33% higher in distal membrane and total distal fractions in rats fed a cellulose/corn oil diet compared to animals consuming th e other fiber/fat diets. These effects were seen only in the distal co lon, where the number of cells per crypt column was elevated only in a nimals fed the cellulose/corn oil diet relative to other diets. Diet-i nduced mitogenic responses did not involve significant changes in the relative activity of PKA I and II isozymes. These data demonstrate tha t dietary effects on PKA activity in the distal colon may be related t o changes in cell differentiation as indicated by the number of cells per crypt column.