Abstract
A novel protein RGPR‐p117 was discovered as regucalcin gene promoter region‐related protein that binds to the TTGGC motif using a yeast one‐hybrid system. RGPR‐p117 is localized in the nucleus of kidney cells, and overexpression of RGPR‐p117 can modulate regucalcin protein and its mRNA expression in the cloned normal rat kidney proximal tubular epithelial NRK52E cells. This study was undertaken to determine whether overexpression of RGPR‐p117 enhances the regucalcin promoter activity using the −710/+18 LUC construct (wild‐type) or −710/+18 LUC construct (mutant) with deletion of −523/−435 including TTGGC motif. NRK52E cells (wild‐type) or stable HA‐RGPR‐p117/phCMV2‐transfected cells (transfectant) were cultured in Dulbecco's minimum essential medium (DMEM) containing 5% bovine serum (BS). Wild‐type cells or transfectants were transfected with the −710/+18 LUC construct vector or the −710/+18 LUC construct with deletion of −523/−435. Wild‐type cells or transfectants with subconfluency were cultured for 48 h in a DMEM medium containing either vehicle, BS (5%), or parathyroid hormone (1–34) (PTH; 10^−7^ M). Luciferase activity in wild‐type cells was significantly increased with culture of BS or PTH. This increase was significantly blocked in the presence of various protein kinase inhibitors (staurosporine and PD 98059). Luciferase activity in transfectants was significantly increased as compared with that of wild‐type cells in the absence of BS or PTH. The increase in luciferase activity in transfectants was completely decreased in mutant with deletion of −523/−435 sequence of regucalcin promoter. This was also seen using the −710/+18 LUC construct with deletion of −523/−503 sequence containing TTGGC motif. The increase in luciferase activity in transfectants was not significantly enhanced with culture of BS (5%), PTH (10^−7^ M), Bay K 8644 (10^−6^ M), phorbol 12‐myristate 13‐acetate (PMA; 10^−6^ M), or N^6^, 2′‐dibutyryl cyclic adenosine 3′, 5′‐monophosphate (DcAMP; 10^−4^ M). The increase in luciferase activity in transfectants was completely inhibited with culture of dibucaine (10^−6^ M), staurosporine (10^−9^ M), PD 98059 (10^−8^ M), wortmannin (10^−8^ M), genistein (10^−6^ M), vanadate (10^−6^ M), or okadaic acid (10^−6^ M) which are inhibitors of various kinases and protein phosphatases. This study demonstrates that RGPR‐p117 can enhance the regucalcin promoter activity which is related to the NF‐1 consensus sequences including TTGGC motif, and that its enhancing effect is partly mediated through phosphorylation and dephosphorylation in NRK52E cells. J. Cell. Biochem. 99: 589–597, 2006. © 2006 Wiley‐Liss, Inc.