GPR41 Gene Expression Is Mediated by Internal Ribosome Entry Site (IRES)-dependent Translation of Bicistronic mRNA Encoding GPR40 and GPR41 Proteins

GPR41 is a G protein-coupled receptor activated by short chain fatty acids. The gene encoding GPR41 is located immediately downstream of a related gene encoding GPR40, a receptor for long chain fatty acids. Expression of GPR41 has been reported in a small number of cell types, including gut enteroendocrine cells and sympathetic ganglia, where it may play a role in the maintenance of metabolic homeostasis. We now demonstrate that GPR41, like GPR40, is expressed in pancreatic beta cells. Surprisingly, we found no evidence for transcriptional control elements or transcriptional initiation in the intergenic GPR40-GPR41 region. Rather, using 5'-rapid amplification of cDNA ends analysis, we demonstrated that GPR41 is transcribed from the promoter of the GPR40 gene. We confirmed this finding by generating bicistronic luciferase reporter plasmids, and we were able to map a potential internal ribosome entry site-containing region to a 2474-nucleotide region of the intergenic sequence. Consistent with this, we observed m(7)G cap-independent reporter gene expression upon transfection of RNA containing this region. Thus, GPR41 expression is mediated via an internal ribosome entry site located in the intergenic region of a bicistronic mRNA. This novel sequence organization may be utilized to permit coordinated regulation of the fatty acid receptors GPR40 and GPR41.