Vitamin D₃ and 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 TGFβs are very potent inhibitors of keratinocyte growth we studied the effects of vitamin D₃ and calcipotriol on the secretion of TGFβ in cultured murine keratinocytes. Vitamin D, 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 TGFβ1 and TGFβ2 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 TGFβ, 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 TGFβ was in a latent form. Active TGFβ 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 TGFβ protein. These results indicate that enhanced TGFβ1 and TGFβ2 secretion and activity is associated with vitamin D₃-mediated growth inhibition of cultured keratinocytes.

This work was presented in part at the Keystone Symposium “Negative Growth Control”, Keystone, CO, Jan. 26-Feb. 2, 1992 (Koli and Keski-Oja 1992).

Key Words:

• vitamin D₃
• calcipotriol
• keratinocyte
• transforming growth factor-β
• growth inhibition
• keratinocyte differentiation