VITAMIN-D(3) AND CALCIPOTRIOL ENHANCE THE SECRETION OF TRANSFORMING GROWTH FACTOR-BETA(1) AND FACTOR-BETA(2) IN CULTURED MURINE KERATINOCYTES

Vitamin D3 and its analogue calcipotriol (MC 903) inhibit the proliferation of cultured keratinocytes and induce their differentiation. Since TGFbetas are very potent inhibitors of keratinocyte growth we studied the effects of vitamin D3 and calcipotriol on the secretion of TGFbeta in cultured murine keratinocytes. Vitamin D3 and calcipotriol (10(-6)-10(-9) M) inhibited the DNA-synthesis of mouse keratinocytes by 50-80% in a time and dose-dependent manner as measured by [H-3]-thymidine incorporation. Analysis of the conditioned medium of the keratinocytes indicated that the cells secreted into their medium activity that inhibited the growth of indicator Mv1Lu mink lung epithelial cells. Neutralizing antibodies against TGFbeta1 and TGFbeta2 decreased, and when used together, prevented the observed growth inhibition of the indicator cells. Heat treatment of the conditioned medium, which activates latent forms of TGFbeta, revealed higher levels of growth inhibitory activity in the medium from vitamin D3 and calcipotriol treated than from control cultures indicating that a fraction of TGFbeta was in a latent form. Active TGFbeta was, however, detected considerably more in vitamin D3 and calcipotriol treated cultures than in control cultures. Immunoblotting analysis of the medium revealed enhanced secretion of TGFbeta protein. These results indicate that enhanced TGFbeta1 and TGFbeta2 secretion and activity is associated with vitamin D3-mediated growth inhibition of cultured keratinocytes.