Nuclear Vitamin D (VDR) and Estrogen (ER) Receptors in the Membrane of Muscle and Breast Cancer Cells
1α,25-dihydroxy-vitamin D3 (lα,25(OH)2D3; calcitriol) and estrogen (17β-estradiol) act, as other steroid hormones, through two different mechanisms. In addition to regulating expression of target genes via their specific nuclear receptors (VDR and ER, respectively), both hormones induce fast, non transcriptional responses involving stimulation of transmembrane signal transduction pathways. The rapid nature and specificity by which 1α,25(OH)2D3 and 17β-estradiol trigger the activation of second messengers has led to the concept that interaction with a plasma membrane receptor is responsible for the initiation of their effects. However, there is controversy over its molecular characteristics. Among several models for non-genomic steroid receptor identity, has been proposed the existence of membrane-associated forms of either the classical receptors or alternatively of novel 1α,25(OH)2D3 and 17β- estradiol binding proteins. In this chapter we report the presence of the nuclear VDR and ER in the plasma membrane of avian muscle and mammalian breast cells and furnish data suggesting that they may be involved in non-genomic signalling by their cognate ligands.
KeywordsEstrogen Tyrosine Iodide Baran Estradiol
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