Define role of Vitamin D in controlling gene expression?
Vitamin D is a secosteroid that is metabolically activated and degraded through the actions of three cytochrome P450 hydroxylase enzymes. Bio activation occurs through the sequential actions of cytochromes (P450C25 and P450Cl) resulting in synthesis of the pleiotropic hormone 1,25-dihydroxyvitamin D (1,25VD), which regulates over 60 genes whose actions include those associated with calcium homeostasis and immune responses, as well as, cellular growth, differentiation and apoptosis, as you may recall studying earlier in Unit 7. Inactivation of 1,25VD occurs by C23/C24 oxidation pathways that are catalyzed by the multifunctional cytochrome P450C24 enzyme. Both P450C1 and P450C24 are highly regulated enzymes whose differential expression is controlled in response to numerous cellular modulatory agents such as parathyroid hormone (PTH), calcitonin, interferon gamma, calcium, phosphorus and pituitary hormones, as well as, the secosteroid hormone 1,25VD.