Mechanisms underlying the induction of the putative human tumor suppressor GPRC5A by Retinoic acid

Abstract

Retinoic acid regulates the expression of genes involved in cell proliferation, differentiation and survival by direct control of gene transcription via activation of nuclear retinoid receptors bound to response elements in the promoters of target genes or by indirect mechanisms. Herein, we investigated the mechanism by which retinoic acid induces the expression of the human tumor suppressor GPRC5A. The proximal 5' upstream region of the GPRC5A gene was found to contain two potential RAR/RXR binding sites (RAREs) and one VDR/RXR binding site with direct repeat 5 (DR5) motifs designated DR5I (-489 to -473), DR5II (-136 to -120) and DR5III (-81 to -65). DR5II and DR5III but not DR5I were conserved among vertebrates. However, only DR5III (5'-TGT CCC TCT GCT CAC CC-3') was found to be the functional RARE for mediating induction of GPRC5A as indicated by electrophoretic mobility shift assay using wild type and mutated synthetic oligonucleotides representing different fragments of the promoter for competition with retinoic acid receptor beta RARE. Chromatin immunoprecipitation assay confirmed the binding of retinoic acid receptors alpha and gamma and retinoid X receptors alpha and beta to DR5III in intact cells. These results demonstrate the importance of functional analysis for validating the activity of predicted response elements.

GPRC5A: A potential tumor suppressor and oncogene

“…Four putative p53 binding sites were identified in the GPRC5A promoter. Two of these were also identified in the smaller promoter region studied by Ye et al 5 Chromatin immunoprecipitation analysis was conducted and showed that p53 binds to at least one of the four putative p53 binding sites in the promoter region. To test the role of GPRC5A during tumorigenesis, HEK-293 cells were stably transfected with GPRC5A and an increase in colony formation was observed.…”

“…Likewise, there have been no studies examining gene amplification or other regulatory mechanisms to explain the increased expression of GRPC5A in breast tumors. The detailed analysis of the proximal promoter of the human GPRC5A gene presented in the paper by Ye et al 5 will make these studies more feasible.…”

Molecular evolution of a chordate specific family of G protein-coupled receptors

“…Expression of RARα was found to be synchronized with that of GPRC5B, indicating the involvement of GPRC5B in RA-dependent morphogenesis/angiogenesis [13]. Induction of receptor expression was found to be mediated by a functional RAR/RXR binding site identified in the proximal 5' upstream region of the GPRC5A gene [14]. Since RA plays crucial roles in many physiological events, such as embryonic development, reproduction, metabolism and homeostasis [15], RAIGs are considered essential to RA-dependent physiological events.…”

“…The role of these receptors in the tissues they are expressed in is so far unknown. In vitro studies showed that expression of GPRC5 receptors can be upregulated by retinoic acid (RA), a metabolite of vitamin A, which lead to their classification as retinoic acid inducible genes (RAIG) [10,13,14]. The finding of transcriptional regulation of GPRC5 receptors by RA is remarkable, because RA is known to play crucial roles in cell differentiation and neurogenesis [15].…”

Vertebrate patatin-like phospholipase domain-containing protein 4 (PNPLA4) genes and proteins: a gene with a role in retinol metabolism

“…Retinol and related retinoid compounds play key roles in the body including supporting vision (Palczewski 2011), regulating epithelial cell growth and differentiation (Long et al 2010), contributing to the growth of bone tissue (Oki et al 2008), immune function (Pino-Lagos et al 2010) and the activation of tumor suppressor genes (Ye et al 2009). This retinol-ester metabolic role is in contrast to functions reported for other PNPLA-like enzymes including ATGL (or adipose triglyceride lipase) in triglyceride hydrolysis in adipocyte and non-adipocyte lipid droplets (Zimmermann et al 2004; Haemmerle et al 2011); PNPLA3 in contributing to hepatic fat metabolism and non-alcoholic fatty liver disease (Romeo et al 2008); PNPLA6 (or neuropathy target esterase) which contributes to membrane lipid homeostasis and assists in maintaining axonal integrity (Zaccheo et al 2004; Rainier et al 2008); and PNPLA8 which serves as a calcium-independent phospholipase A2 and catalyzes the hydrolysis of membrane phospholipids (Tanaka et al 2000; Mancuso et al 2000).…”