MiR-103a-3p targets the 5′ UTR of GPRC5A in pancreatic cells

MicroRNAs (miRNAs) are short noncoding RNAs that regulate the expression of their targets in a sequence-dependent manner. For protein-coding transcripts, miRNAs regulate expression levels through binding sites in either the 3' untranslated region (3' UTR) or the amino acid coding sequence (CDS) of the targeted messenger RNA (mRNA). Currently, for the 5' untranslated region (5' UTR) of mRNAs, very few naturally occurring examples exist whereby the targeting miRNA down-regulates the expression of the corresponding mRNA in a seed-dependent manner. Here we describe and characterize two miR-103a-3p target sites in the 5' UTR of GPRC5A, a gene that acts as a tumor suppressor in some cancer contexts and as an ongocene in other cancer contexts. In particular, we show that the interaction of miR-103a-3p with each of these two 5' UTR targets reduces the expression levels of both GPRC5A mRNA and GPRC5A protein in one normal epithelial and two pancreatic cancer cell lines. By ectopically expressing "sponges" that contain instances of the wild-type 5' UTR targets we also show that we can reduce miR-103a-3p levels and increase GPRC5A mRNA and protein levels. These findings provide some first knowledge on the post-transcriptional regulation of this tumor suppressor/oncogene and present additional evidence for the participation of 5' UTRs in miRNA driven post-transcriptional regulatory control.