Increased PKC activity in cultured human keratinocytes and fibroblasts after treatment with 1α,25‐dihydroxyvitamin D 3

1α,25‐Dihydroxyvitamin D 3 (10 −12 M to 10 −8 M) caused a dose dependent increase in PKC activity in the solubilized membrane fractions of cultured human keratinocytes and in the cytosolic fractions of cultured human fibroblasts. Maximum activity was induced by 1α,25‐dihydroxyvitamin D 3 at 24 h. Sphingosine, which is believed to inhibit PKC mediated biological responses, blunted 1α,25(OH) 2 D 3 ′s inducement of PKC activity in both keratinocytes and fibroblasts. Identical hormone treatment of vitamin D receptor deficient fibroblasts did not increase PKC activity. Treatment of keratinocytes and fibroblasts with 1β,25‐dihydroxyvitamin D 3 , which is believed to be ineffective in inducing genomic responses, did not induce PKC activity.