Vitamin D3and Calcipotriol Enhance the Secretion of Transforming Growth Factor-β1 and -β2 in Cultured Murine Keratinocytes

Abstract

Vitamin D3 and its analogue calcipotriol (MC 903) inhibit the proliferation of cultured keratinocytes and induce their differentiation. Since TGF beta s are very potent inhibitors of keratinocyte growth we studied the effects of vitamin D3 and calcipotriol on the secretion of TGF beta 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 [3H]-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 TGF beta 1 and TGF beta 2 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 TGF beta, 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 TGF beta was in a latent form. Active TGF beta 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 TGF beta protein. These results indicate that enhanced TGF beta 1 and TGF beta 2 secretion and activity is associated with vitamin D3-mediated growth inhibition of cultured keratinocytes.