Alterations in protein kinase C system of colonic epithelium during fasting-refeeding. Evidence for protein kinase C independent pathway of enhanced proliferative activity.

In the present study, we compared (1) incorporation of [3H]dThd into DNA, (2) total protein kinase C (PKC) activity, (3) the subcellular distribution of PKC, and (4) PKC isozyme (alpha, beta and gamma) mass in colonic mucosal scrapings and isolated superficial and proliferative colonic epithelial cells from 48-hr fasted, 48-hr fasted-refed, and ad libitum-fed rats. Total colonic mucosal PKC activity and PKC alpha mass were higher and the in vivo rate of [3H]dThd incorporation into mucosal DNA was markedly depressed in 48-hr fasted rats compared to ad libitum-fed or fasted-refed rats. These alterations were localized predominantly to the proliferative pool of colonic epithelial cells. Despite an 11-fold increase in mucosal DNA synthesis, no alterations in total mucosal PKC activity were detected in fasted-refed rats compared to rats fed ad libitum. Moreover, no differences in the subcellular distribution of PKC were noted among any of the dietary groups. Intrarectal instillation of deoxycholate activated PKC and increased DNA synthesis 1.5- to 2-fold. Deoxycholate-induced increases in DNA synthesis, but not those induced by refeeding, were inhibited by treatment of rats with the PKC inhibitors H-7, sphingosine, or staurospaurine. The results do not support a role for PKC in the mediation of increased proliferative activity of colonic mucosa induced by refeeding.