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Regulation of Rat Cytochrome P450C24 (CYP24) Gene Expression

2000; Elsevier BV; Volume: 275; Issue: 1 Linguagem: Inglês

10.1074/jbc.275.1.47

1083-351X

Prem P. Dwivedi, John L. Omdahl, Ismail Kola, David Hume, Brian K. May,

Retinoids in leukemia and cellular processes

Transcription of the rat CYP24 gene is induced by 1,25-dihydroxyvitamin D 3 (1,25-(OH) 2 D 3 ) through two vitamin D response elements (VDREs). A functional Ras-dependent Ets-binding site (EBS) was located downstream from the proximal VDRE and was critical to 1,25(OH) 2 D 3 -mediated induction. Cotransfection of Ets-1 and Ets-2 stimulated induction, which was lost when the EBS was mutated. Multiple nuclear-protein complexes from COS-1 cells bound to the EBS in which three complexes were immunologically related to Ets-1. Transcriptional synergy was observed between the proximal VDRE and adjacent EBS as was the attendant formation of a ternary complex between vitamin D receptor- retinoid X receptor (VDR·RXR) and Ets-1. In the absence of 1,25-(OH) 2 D 3 or in the presence of an inactive proximal VDRE, the EBS failed to respond to exogenous Ets-1. However, Ets-1 increased basal expression when cotransfected with a mutant VDR. The inductive action of 1,25-(OH) 2 D 3 was substantially increased by Ras, which was ablated by mutagenesis of the EBS or by expression of a mutated Ets-1 protein (T38A). EBS contribution to hormone induction was prevented by manumycin A, an inhibitor of Ras farnesylation. A fundamental role was established for transcriptional cooperation between Ras-activated Ets proteins and the VDR·RXR complex in mediating 1,25-(OH) 2 D 3 action on the CYP24 promoter.