TGF-BETA AND CALCITRIOL

Vitamin D-3 and transforming growth factor-beta (TGF-beta) are molecul es from unrelated families that share identical actions on cell growth and differentiation. The active metabolite of vitamin D-3, calcitriol (1 alpha,25 dihydroxyvitamin D-3), induces an inhibitory effect on th e growth of various cell types, and the expression of different marker s of cell differentiation. As the receptor of vitamin D-3 is ubiquitou s, these effects are widespread in the organism. TGF-beta is a growth factor produced by many cell types, and is a known inhibitor of the pr oliferation of epithelial cells. Because of the similarity in their ac tions, many studies have been aimed at defining some interactions betw een the two substances. The purpose of this article is to illustrate t he nature of the interactions, and two examples are developed. In norm al or transformed epithelial cells, it has been demonstrated that the inhibitory effect of calcitriol on cell growth could be related to an induction of TGF-beta synthesis, and of a paracrine/autocrine loop. In bone, where both compounds play a very important role on the mechanis ms controlling bone formation and remodeling, the interplay is more co mplex, and even includes the receptors of the two substances. Interest in this topic is growing and will surely lead to the establishment of new links between those two compounds. (C) 1998 Elsevier Science Inc.