Previous investigations have demonstrated that besides the intestine at least 20 tissues including kidney, pancreas, skin and brain all have receptors for 1,25-dihydroxy-vitamin D3 (1,25(OH)2D3) and/or a vitamin D induced calcium binding protein (CaBP); thus suggesting a wider role for the vitamin D endocrine system in calcium metabolism than mere intestinal calcium absorption. The object of this proposal is to obtain a better understanding of the multiple actions of the vitamin D endocrine system by studying the biochemistry, function and regulation of the mammalian vitamin D-dependent calcium binding proteins and by testing the hypothesis that proteins other than CaBP are induced by 1,25(OH)2D3. The mammalian vitamin D-dependent calcium binding proteins will be biochemically characterized and compared to other calcium binding proteins. Also, in order to determine whether the mammalian vitamin D-dependent CaBPs have enzyme modulating abilities, similar to calmodulin, we will test the ability of these proteins to activate Ca/Mg ATPase, alkaline phosphatase and phosphodiesterase. Binding to phenothiazine and cross-reactivity in the calmodulin redioimmunoassay will also be investigated. We will test how dietary alterations affect renal CaBP as well as how vitamin D deficiency and vitamin D administration affect both renal CaBP as well as how vitamin D deficiency and vitamin D administration affect both renal and brain CaBP. We also propose to study, using a reticulocyte lysate cell free system, the molecular mechanisms involved in the induction of CaBP in mammalian kidney and brain. 2-D gel electrophoretic patterns of mRNA translation products will be used to examine the specificity of the response at the mRNA level in the kidney and brain. Studies to determine whether proteins other than calcium binding protein are induced in rat kidney are also proposed. This study, by extending provocative preliminary findings, will increase our understanding of the vitamin D endocrine system and therefore of the many disease processes associated with abnormalities in the calcium homeostatic process such as osteomalacia, osteoporosis, and pertubations of parathyroid function. Additionally, this study may lead to an increased understanding of the role of the vitamin D endocrine system in normal brain function as well as in brain disorders involving calcium dependent functions.
