A role for the phosphatidylinositol 3-kinase - protein kinase C zeta-Sp1 pathway in the 1,25-dihydroxyvitamin D3 induction of the 25-hydroxyvitamin D3 24-hydroxylase gene in human kidney cells

The molecular mechanisms that underlie non-genomic induction of the 25-hydroxyvitamin D3 24-hydroxylase (CYP24) gene promoter by the steroid hormone, 1,25-Dihydroxyvitamin D3 (1,25D). are poorly understood. Although we have previously identified a functional inverted GC-box in the early promoter at - 113/-105 bp, it is not known whether this site is important for 1,25D induction of the promoter. Using transfected human embryonic kidney (HEK) 293 T cells, we now report the functional characterisation of the GC-boxand that 1,25D induction of the promoter requires PI3-kinase, PKC xi and Sp1 but not Sp3. The data show that 1,25D rapidly stimulates P13-kinase activity which is required for the activation of PKC xi and the phosphorylation of Sp1. The effects of the PI3-kinase inhibitor, LY294002, and a dominant negative PKC xi mutant on 1,25D induction of wild-type and a GC-box mutated CYP24 promoter constructs are consistent with the Sp1 site being the target of both kinases. However, these kinases are not required for basal expression of the CYP24 promoter. The data establish a novel non-genomic mechanism which couples 125D to the induction of CYP24 gene transcription via the PI3-kinase - PKC xi - Sp1 pathway acting through the GC-box. (C) 2009 Elsevier Inc. All rights reserved.