Systematic study of GPRC5A in the context of pancreatic ductal adenocarcinoma

Honglei Zhou, Thomas Jefferson University

Abstract

The G protein-coupled receptor, class C, group 5, member A (GPRC5A), also known as Retinoic acid-induced gene 3 (RAI3) or Retinoic acid-induced gene 1 (RAIG1) was first cloned in 1998. It is an orphan G-protein coupled receptor with an intriguing dual behavior, acting as an oncogene in some cancers and as a tumor suppressor in other cancers. In the pancreatic cancer context, very little is known about GPRC5A. Through analyzing messenger RNA (mRNA) expression data in public database we found that GPRC5A’s abundance in pancreatic cancer is highest (cell lines) or second highest (TCGA) among all tissues and cancer types in the database. Further analyses of an independent set of 252 pancreatic normal and cancer samples showed GPRC5A mRNA to be more than two-fold up-regulated in primary tumor samples compared to normal pancreas (P-val<10-5), and even further up-regulated in pancreatic cancer metastases to various organs (P-val=0.0021). Immunostaining of a pancreatic tissue microarray showed generally low expression of GPRC5A protein in normal pancreatic ductal cells, while in primary ductal cancer samples, GPRC5A protein levels were dramatically increased in pancreatic ductal cells. In vitro studies of multiple pancreatic ductal cell lines showed that inhibition of GPRC5A expression impaired pancreatic cancer cell growth and migration, while an increase in GPRC5A protein levels in normal pancreatic epithelial cell promoted cell growth and migration. In addition, we found that gemcitabine (2´,2´-difluorodeoxycytidine) treatment in pancreatic cancer cells could induce GPRC5A expression. On the other hand, when we knocked down GPRC5A we sensitized pancreatic cancer cells to gemcitabine. Additionally, we showed two regulators involved in post-transcriptional regulation of GPRC5A. One is microRNA (miRNA) —miR-103a-3p. Specially, we described and characterized two miR-103a-3p target sites in the 5´UTR of GPRC5A mRNA. The interaction of miR-103a-3p with each of these two 5´UTR targets reduced the expression levels of both GPRC5A mRNA and GPRC5A protein in one normal epithelial and two pancreatic cancer cell lines. The second is the RNA-binding protein HuR, which is an established key mediator of gemcitabine’s efficacy in cancer cells that play key roles on the up-regulation of GPRC5A by gemcitabine. As we discovered, the interaction between GPRC5A and HuR is mediated by at least one HuR binding site in GPRC5A’s mRNA. Our findings confirm that GPRC5A is up-regulated in pancreatic ductal cancer, and show that GPRC5A is part of a molecular axis that involves miR-103a-3p, gemcitabine and HuR, and, possibly, other protein-coding and non-coding transcripts and RNA binding proteins. In addition, our results reveal that both RNA binding proteins and miRNAs could be involved in the post-transcriptional regulation of GPRC5A, expanding the understanding of regulatory networks on GPRC5A’s expression.

Subject Area

Molecular biology|Cellular biology|Bioinformatics

Recommended Citation

Zhou, Honglei, "Systematic study of GPRC5A in the context of pancreatic ductal adenocarcinoma" (2016). ETD Collection for Thomas Jefferson University. AAI10164829.
https://jdc.jefferson.edu/dissertations/AAI10164829

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