Retinoic acid-dependent activation of the polycystic kidney disease-1 (PKD1) promoter

1 Department of Biochemistry and Molecular Biology, and the Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas; 2 Department of Chemistry/Physics, Northwest Missouri State University, Maryville, Missouri; and 3 Department of Biochemistry, Panjab University, Chandigarh, India Submitted 9 June 2008 ; accepted in final form 9 October 2008 The retinoic acids all- trans retinoic acid (AT-RA) and 9- cis retinoic acid (9C-RA) and the retinoic acid receptors RAR and RXR significantly induce transcriptional activity from a 200-bp PKD1 proximal promoter in transfected mammalian cells. This PKD1 promoter region contains Ets, p53, and GC box motifs, but lacks a canonical RAR/RXR motif. Mutagenesis of the Ets sites did not affect RA induction. In contrast, GC box mutations completely blocked stimulation by AT-RA and by RXRβ or RARβ. Mithramycin A, which prevents Sp1 binding, significantly reduced basal promoter activity and suppressed upregulation by AT-RA and RXR. The 200-bp proximal promoter could not be induced by AT-RA in Drosophila SL2 cells, which lack Sp1, but could be activated in these cells transfected with exogenous Sp1. Small interfering RNA knockdown of Sp1 in mammalian cells completely blocked RXRβ upregulation of the promoter. These data indicate that induction of the PKD1 promoter by retinoic acid is mediated through Sp1 elements. RT-PCR showed that AT-RA treatment of HEK293T cells increased the levels of endogenous PKD1 RNA, and chromatin immunoprecipitation showed the presence of both RXR and Sp1 at the PKD1 proximal promoter. These results suggest that retinoids and their receptors may play a role in PKD1 gene regulation. all- trans retinoic acid; 9- cis retinoic acid; RAR; RXR Address for reprint requests and other correspondence: J. P. Calvet, Dept. of Biochemistry and Molecular Biology, Univ. of Kansas Medical Center, MS3030, Kansas City, KS 66160 (e-mail: jcalvet{at}kumc.edu )