Specific modulation of intestinal epithelial brush border enzyme expression by a phorbol ester

Much is known about intestinal epithelial regulation by growth factors and nutrients but the intracellular signals governing cell phenotype are less well understood. In an initial attempt to evaluate the role of protein kinase C in these events, we studied the effects of protein kinase C modulation by the phorbol ester TPA upon the differentiation, motility, and doubling time of the human intestinal epithelial Caco-2 cell line, a common model for enterocytic brush border enzyme expression. We also compared the effects of TPA to those of 4 alpha-phorbol 12,13-didecanoate, which does not modulate protein kinase C activity. Differentiation was studied by quantitating brush order dipeptidyl peptidase (DPDD)-specific activity in protein-matched Caco-2 lysates via synthetic substrate digestion. Alkaline phosphatase (AP) was studied for comparison. Doubling time was assessed by log transformation of serial cell counts and motility by monolayer expansion across type I collagen. TPA (0.03-0.7 micrograms/ml) dose-dependently stimulated DPDD, with a maximal 455 +/- 26% increase at 0.7 micrograms/ml (P < 0.01, n = 5). However, TPA dose-dependently inhibited AP to a maximal 91.6 +/- 0.3% decrease (P < 0.01, n = 5). TPA also dose-dependently prolonged the cell doubling time from 26.5 +/- 0.4 to 64.5 +/- 8.8 hr (n = 20, P < 0.01) with a maximal effect at 1.0 micrograms/ml and inhibited migration with essentially complete ablation of cell motility at 0.1 micrograms/ml (n = 10, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)