title: Vitamin D receptor deletion leads to reduced level of IkappaBalpha protein through protein translation, protein-protein interaction, and post-translational modification.
abstract: Vitamin D receptor plays an essential role in the regulation of inflammation. Previous studies demonstrate that vitamin D receptor negatively modulates the proinflammatory NF-kappaB pathway. However, it is unknown how vitamin D receptor regulates IkappaBalpha, the endogenous inhibitor of NF-kappaB. Here we investigated the molecular mechanism of vitamin D receptor deletion and IkappaBalpha expression. We found that cells lacking vitamin D receptor had significantly increased levels of IkappaBalpha mRNA and simultaneously decreased levels of IkappaBalpha protein. Lacking vitamin D receptor abolished its binding to the IkappaBalpha promoter. Moreover, the levels of protein translation regulators and the rate of protein synthesis were both decreased in cells lacking vitamin D receptor. At the post-translational level, IkappaBalpha ubiquitination was enhanced, indicating increased degradation of IkappaBalpha in the absence of vitamin D receptor. We further transfected cells with a plasmid carrying either wild-type or mutant IkappaBalpha. The expression of wild-type IkappaBalpha was much higher in the cells with vitamin D receptor than in the cells without vitamin D receptor, whereas the expression of exogenous IkappaBalpha was equally high in both cell lines. In summary, vitamin D receptor deletion affects IkappaBalpha through mRNA transcription, protein translation, protein-protein interaction, post-translational modification, and protein degradation, thus reducing the level of IkappaBalpha protein. Cells lacking vitamin D receptor are known in a proinflammatory state with activation of NF-kappaB. Our study provides new insight into vitamin D receptor regulation of an inhibitor of NF-kappaB in inflammation. Deletion of vitamin D receptor contributes to the activation of NF-kappaB on multiple levels.
authors.affiliation: Department of Medicine, Gastroenterology & Hepatology Division, University of Rochester, 601 Elmwood Ave., Rochester, NY 14642, USA.
authors.forename: Shaoping
authors.initials: S
authors.lastname: Wu
authors.forename: Yinglin
authors.initials: Y
authors.lastname: Xia
authors.forename: Xingyin
authors.initials: X
authors.lastname: Liu
authors.forename: Jun
authors.initials: J
authors.lastname: Sun
mesh_terms: D000107:Acetylation; D000483:Alleles; D000818:Animals; D002460:Cell Line; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D017353:Gene Deletion; D005786:Gene Expression Regulation; D020672:I-kappa B Proteins / Q000096:biosynthesis* / Q000378:metabolism*; D007249:Inflammation / Q000378:metabolism; D051379:Mice; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D054875:Ubiquitination; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D015852:Eukaryotic Initiation Factor-2; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606205:Nfkbia protein, mouse; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D000072000:NF-KappaB Inhibitor alpha; D019892:eIF-2 Kinase; D046988:Proteasome Endopeptidase Complex