Submitted on June 9, 2008
Revised on September 23, 2008
Accepted on October 9, 2008
Retinoic acid-dependent activation of the polycystic kidney disease-1 (PKD1) promoter
M. Rafiq Islam, Sanjeev Puri, Marianna Rodova, Brenda S. Magenheimer, Robin L. Maser1, and James P. Calvet2*
1 Biology
2 University of Kansas Medical Center
* To whom correspondence should be addressed. E-mail: jcalvet{at}kumc.edu.
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 RXR
or RAR. 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. siRNA knockdown of Sp1 in mammalian cells completely blocked RXR 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.
