1,25-Dihydroxyvitamin D₃ targets PKC-βII but not PKC-α to the basolateral plasma membranes of rat colonocytes

Prior studies by our laboratory have shown that 1,25-dihydroxyvitamin D₃ activated PKC-α, but not PKC-δ, -ε, or -ζ, in normal rat colonocytes. In the present studies we demonstrate for the first time that this secosteroid also activated PKC-βII, another DAG- and Ca²⁺-dependent PKC isoform recently shown to be present in these cells. Moreover, this activation of PKC-βII by 1,25-dihydroxyvitamin D₃ treatment of isolated colonocytes was shown to be lost in cells from vitamin D-deficient rats and, at least partially, restored by repleting these animals with this secosteroid for 7 days. Under basal conditions, the expression of PKC-α and -βII in brush-border membranes was comparable to their respective expression in basolateral plasma membranes of rat colonocytes. In contrast, the expression of PKC-δ was significantly greater in brush-border membranes, whereas PKC-ε and -ζ were enriched in the basolateral plasma membranes. Furthermore, 1,25-dihydroxyvitamin D₃ specifically induced the translocation of PKC-βII, but not PKC-α, to the basolateral, but not brush-border plasma membranes of rat colonocytes, via a pp60(c-src)-dependent mechanism.