title: Differential regulation of vitamin D responsive elements in normal and transformed keratinocytes.
abstract: Squamous cell carcinomas (SCC) derived from human epidermis fail to differentiate normally under the influence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] despite the presence of the vitamin D receptor. Previous studies from our laboratory showed that phospholipase C-gamma1 (PLC-gamma1) was upregulated transcriptionally by 1,25(OH)2D3 in normal human keratinocytes, and a vitamin D responsive element (VDRE) in its promoter region has been identified. To examine the inducibility of human PLC-gamma1 transcription by 1,25(OH)2D3 and/or retinoic acid in SCC cell lines, we transiently transfected SCC4 and SCC12B2 cells with human PLC-gamma1 promoter-luciferase constructs containing the VDRE and tested the response of these constructs to 1,25(OH)2D3 and/or all-trans retinoic acid. The induction of the human PLC-gamma1 VDRE by 1,25(OH)2D3 was synergistic with all-trans retinoic acid in normal human keratinocytes, but none of the constructs was induced by 1,25(OH)2D3 and/or all-trans retinoic acid in SCC4 and SCC12B2 cells. In contrast, the construct containing the VDRE of the human 24-hydroxylase gene was induced several fold by 1,25(OH)2D3 in normal human keratinocytes and by both 1,25(OH)2D3 and all-trans retinoic acid in SCC4 and SCC12B2 cells. DNA mobility shift assays showed that both the vitamin D receptor and the retinoic acid receptor in SCC4 and SCC12B2 cells bound the human PLC-gamma1 VDRE similarly to that seen in normal keratinocytes. The data indicate that the VDRE in the human PLC-gamma1 gene is not functional in SCC4 and SCC12B2 cells, unlike normal human keratinocytes, even though vitamin D receptors bind normally to it. Failure of transcriptional control of the PLC-gamma1 gene by 1,25(OH)2D3 suggests the lack of a cofactor(s) linking the VDRE to the transcriptional machinery.
authors.affiliation: Endocrine Unit, VA Medical Center, University of California, San Francisco 94121, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Xie
authors.forename: D D
authors.initials: DD
authors.lastname: Bikle
mesh_terms: D002117:Calcitriol / Q000494:pharmacology*; D002461:Cell Line, Transformed; D004357:Drug Synergism; D004790:Enzyme Induction / Q000502:physiology; D006801:Humans; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D015603:Keratinocytes / Q000187:drug effects* / Q000502:physiology*; D051966:Phospholipase C gamma; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D012016:Reference Values; D013237:Stereoisomerism; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000235:genetics* / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid; D014212:Tretinoin; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002117:Calcitriol