EFFECTS OF VITAMIN-D METABOLITES ON PROLIFERATION AND DIFFERENTIATION OF CULTURED HUMAN EPIDERMAL-KERATINOCYTES GROWN IN SERUM-FREE OR DEFINED CULTURE-MEDIUM

We examined the effects of 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3], 25-hydroxyvitamin D-3 (25OHD(3)), and vitamin D-3 On human keratinocyte proliferation and differentiation in a serum-free or defined culture system. Concentrations greater than 10(-8) M 1,25-(OH)(2)D-3 Or 10(-7) M 25(OH)(2)D-3 caused marked inhibition of cell growth. Growth inhibition with high doses of 1,25-(OH)(2)D-3 was not stringent, but was mainly exerted in the G(1) phase of the cell cycle. Early release from the cell cycle block restored the proliferation of human keratinocytes. The calcium concentration in the medium had no significant effect on the antiproliferative action of 1,25-(OH)(2)D-3, 25OHD(3), and vitamin D-3 We also show that human keratinocyte proliferation is enhanced at doses of 1,25-(OH)(2)D-3 and 25OH(2)D(3) of 10(-9) M or less. Enhanced proliferation of human keratinocytes with physiological concentrations of 1,25-(OH)(2)D-3 could only be shown in fully defined medium that contained no vitamin D-3, related sterols, or bovine pituitary extract. Human keratinocyte differentiation was enhanced with higher doses of 1,25-(OH)(2)D-3 when cells were grown in the presence of high calcium concentrations. These studies demonstrate that the lower, physiological concentrations of vitamin D-3 metabolites are capable of stimulating the proliferation of epidermal keratinocytes grown under selected conditions that eliminate confounding or unidentified medium culture factors. Vitamin Dg metabolites are shown to exert mitogenic trophic effects in cultured human epithelial cells similar to their established activities in vivo.