Identification of overexpression of orphan G protein-coupled receptor GPR49 in human colon and ovarian primary tumors

We used gene expression profiling to probe differences in transcriptional output between 15 panels of colon tumor and matched normal colon tissues. This analysis revealed that GPRA9, an orphan G Protein-Coupled Receptor (GPCR) is overexpressed in 66% (10115) colon tumors compared with normal colon tissues. Subsequent analysis of an additional 39 sets of matched normal and tumor colon tissues by real-time quantitative reverse transcriptase confirmed the upregulation of this receptor. The differential expression of GPR49 between normal and tumor tissue was significant (p > 0.001). GPR49 was upregulated in 25 of 39 (64%) colon primary tumor tissues. In addition to colon tumors, GPRA9 was also found to be upregulated in 18 of 33 (53%) ovarian primary tumor tissues analyzed by RT-PCR. Moreover, the expression level of GPRA9 in colon and ovarian tumors increased in more advanced tumors suggesting a role for the receptor in tumor progression. The selective overexpression of GPR49 in tumor tissues was further illustrated by specific immunohistochemical staining of colon and ovarian tumor tissues, a finding that correlates with the mRNA expression of the receptor. In addition, expression of GPRA9 induced transformation in a ligand-dependent manner and Knockdown of GPR49 mRNA level induced apoptosis in colon tumor cells. These novel findings provide a foundation for further studies and suggest a potential role for GPR49 in tumorigenesis.