Regulation of smooth muscle cell differentiation and proliferation by sex steroids

Steroids effects are mediated by their receptors. These proteins define the large family of steroid hormone receptors, characterized by the presence of 3 functional domains: a transactivation domain, a DNA-binding domain and a ligand-binding domain. Receptor activation induces the modulation of transcription of specific genes, and as a consequence, the modulation of production of specific proteins. Sex steroid receptors are located in the nucleus. This nuclear localization is in fact a dynamic situation resulting from a continuous shuttling of the receptor between the cytoplasm and the nucleus. The recent discovery that an additional estrogen receptor is present in various tissues has advanced our understanding of the mechanism underlying estrogen signalling. Non genomic effects of steroids have also been described Sex steroids inhibit proliferation of smooth muscle cells. On the contrary they stimulate proliferation of tumoral muscle cells. The mechanisms of sex steroid effects on cellular proliferation are complex, and may involve transcriptional or non transcriptional phenomenons.