Effect of 1,25-dihydroxyvitamin D3 on human keratinocytes grown under different culture conditions.

1,25-Dihydroxyvitamin D3 (1,25-(OH)2-D3) is known to decrease the proliferation and increase the differentiation of different cell types including human keratinocytes. The growth and differentiation of keratinocytes in the presence of 1,25-(OH)2-D3 using serum-free media formulations has been described previously. This investigation extends these studies to describe various culture conditions with human foreskin keratinocytes to determine the optimal antiproliferative activity of 1,25-(OH)2-D3. Keratinocytes were plated onto tissue culture dishes using one of three basic serum-free media protocols; a) with no feeder layer in keratinocyte growth medium (KGM); b) onto mitomycin C-treated 3T3 mouse embryo fibroblasts; or c) onto mitomycin C-treated dermal human fibroblasts. The last two protocols utilized Dulbecco's modified Eagle's Medium (DMEM) supplemented with growth factors. Keratinocyte cell growth was greatest in the KGM medium. Although the growth of keratinocytes on either feeder layer was similar, there were differences in the ability of the cells to form envelopes in the presence of 1,25-(OH)2-D3. The addition of hydrocortisone and cholera toxin to the medium also affected the response of the keratinocytes to 1,25-(OH)2-D3. The antiproliferative effect of 1,25-(OH)2-D3 was not altered by varying the extracellular calcium levels from 0.25 to 3 mM. The antiproliferative activity of 1,25-(OH)2-D3 is attenuated in cells at low density. Our results suggest that an optimal condition to investigate the ability of 1,25-(OH)2-D3 to inhibit keratinocyte proliferation is at preconfluent cell density in the presence of KGM supplemented with 1.5 mM calcium without a feeder layer. These conditions are not appropriate for investigating the enhancement of differentiation by 1,25-(OH)2-D3, but can be used to assay other agents that modulate keratinocyte proliferation.