Vitamin D metabolism and associated diseases
Abstract
High vitamin D status has been shown to potentially be beneficial against obesity and cancer. The active form of vitamin D, 1α,25-dihydroxyvitamin D (1,25(OH)2D) is generated from its precursor, 25-hydroxyvitamin D, by the enzyme 25-hydroxyvitamin D-1α-hydroxylase (1α-hydroxylase). The 1α-hydroxylase is primarily expressed in the kidney, but is also expressed at lower levels in extra-renal tissues. In our first study we detected the expression of the 1α-hydroxylase in tissues that are active in energy metabolism from male Wistar rats, including liver, skeletal muscle, and adipose tissue and the expression was not regulated by dietary calcium and vitamin D in Wistar rats. In addition, the 1α-hydroxylase enzyme was active in cultured 3T3-L1 preadipocytes. Thus, locally produced 1,25(OH)2D by 1α-hydroxylase might have a physiological role through paracrine effects in adipocytes. The active form of vitamin D, 1,25(OH)2D, regulates the transcription of specific genes through its vitamin D receptor (VDR) to, as well as rapidly activating signaling pathways, and it is not clear how rapid signaling of 1,25(OH)2D exerts its proposed anti-neoplastic effect against cancers, such as prostate cancers. Our results demonstrate that, although 1,25(OH) 2D suppresses the growth of mouse prostate epithelial cells (MPECs), it does not rapidly activate protein kinase C α or extracellular regulated kinase 1/2 as it does in other cell types studied. Therefore, the activation of these rapid signals are not required for the 1,25(OH)2D-mediated growth suppression. In addition, the results of our studies demonstrated that the amino acid Y147 is critical for maximal VDR transcriptional activity. In these studies the wildtype or mutated VDR was transfected into the VDR knock out mouse prostate epithelial cells (MPEC VDR KO) and VDR transactivity tested by its ability to induce CYP24 luciferase reporter gene. The VDR containing Y147F did not show differential VDR expression, heterodimerization with RXRα, or coactivator recruitment with SRC-1 compared to wildtype VDR. However, the mutants, Y147F VDR, impaired ligand-induced association of VDR with chromatin. Therefore Y147 is important for chromatin association of the liganded VDR and thus VDR transcriptional activity.
Degree
Ph.D.
Advisors
Teegarden, Purdue University.
Subject Area
Molecular biology|Nutrition
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.