1,25-DIHYDROXYVITAMIN D-3 TARGETS PKC-BETA-II BUT NOT PKC-ALPHA TO THE BASOLATERAL PLASMA-MEMBRANES OF RAT COLONOCYTES

Prior studies by our laboratory have shown that 1,25-dihydroxyvitamin D-3 activated PRC-alpha, but not PKC-delta, -epsilon, or -zeta, in nor mal rat colonocytes. In the present studies we demonstrate for the fir st time that this secosteroid also activated PKC-beta II, another DAG- and Ca2+-dependent PKC isoform recently shown to be present in these cells. Moreover, this activation of PKC-beta II by 1,25-dihydroxyvitam in Da treatment of isolated colonocytes was shown to be lost in cells from vitamin D-deficient rats and, at least partially, restored by rep leting these animals with this secosteroid for 7 days. Under basal con ditions, the expression of PKC-alpha and -beta II in brush-border memb ranes was comparable to their respective expression in basolateral pla sma membranes of rat colonocytes. In contrast, the expression of PKC-d elta was significantly greater in brush-border membranes, whereas PKC- epsilon and -zeta were enriched in the basolateral plasma membranes. F urthermore, 1,25-dihydroxyvitamin D-3 specifically induced the translo cation of PKC-beta II, but not PKC-alpha, to the basolateral, but not brush-border plasma membranes of rat colonocytes, via a pp60(c-src)-de pendent mechanism. (C) 1998 Academic Press.