Physiological function of the novel Vitamin D receptor isoform

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Vitamin D regulates a wide range of physiological systems including those involved in control of calcium blood level and bone health as well as regulation of the immune system and of cell growth. Vitamin D action is mediated through the vitamin D receptor (VDR), a member of a large family of proteins that regulate the activity of specific target genes that control numerous biological functions. A novel, larger form of the human VDR has recently been described in our laboratory. This novel form shows differences in activity from the shorter VDR form (VDRA) and also has an unusual distribution within the nucleus of the cell that may relate to its function. The present project focuses on further analysis of the relevance of this novel VDR isoform to normal physiology. We hypothesise that the larger VDR isoform has unique characteristics that may modify how vitamin D works in different cells and tissues, on specific target genes and in response to different active forms of vitamin D. These differences depend on this novel isoform s interaction with specific nuclear proteins that regulate the actions of other hormone receptors. The specific aims of this project are to study the functions of the novel VDR isoform in comparison to VDRA: * On different target genes that are either activated or inhibited in response to vitamin D, and on different cell lines from tissues where vitamin D has important roles, like intestine, kidney and bone * In their response to natural and synthetic vitamin D compounds, because of their possible therapeutic applications * In their interactions with intranuclear regulatory proteins, to understand the underlying mechanisms The study of these two forms of the VDR will help to clarify their potentially different cellular roles and their contribution to the wide range of physiological processes regulated by the vitamin D endocrine system. This understanding may open new paths for treatments of human bone and calcium-related diseases.