Ergocalciferol and cycloheximide in vivo stimulate protein kinase C of intestinal crypt cells

Previous reports have suggested that 1,25-dihydroxychole-calciferol regulated cellular differentiation via its effects on protein kinase C activity. This study examined the in vivo effects of ergocalciferol on the activity of protein kinase C, and whether the differentiation of crypt intestinal cells is dependent on the activation of this enzyme. Ergocalciferol in saline was injected intramuscularly into rats and the animals sacrificed 24 hr after fasting. Protein kinase C specific activity was determined from the rate of incorporation of (32)p-ATP into protamine. Injections of 60 mu g ergocalcifero1/200 g of body wt raised protein kinase C specific activity to 59818 +/- 4010 (SEM, n = 5) cpm (32)p-protamine/min/mg cell protein, compared with a control of 46173 +/- 4612 (P < 0.0005). Optimal specific activities were seen within 72 hr of injection. Administration of 120 mu g ergocalcifero1/200 g of body wt, raised the concentrations of serum calcium to 9.8 and 10.4 mg/dl following the intramuscular injection by 24 and 72 hr, respectively, compared with a control of 7.7 mg/dl. Actinomycin D (intramuscular, 100 mu g/200 g of body wt) together with ergocalciferol (120 mu g/200 g of body wt) reduced protein kinase C specific activity by 51% 24 hr after injection. Cycloheximide blocked the activation, but when injected alone stimulated endogenous protein kinase C activity by 34% 24 hr after injection. The study shows activation of crypt protein kinase C by ergocalciferol. The inhibition of activation by actinomycin D and cycloheximide suggests the involvement of both transcriptional and translational processes in this activation.