Post-transcriptional regulation of thiamin transporter-1 (THTR-1) expression by microRNA-200a-3p in pancreatic acinar cells.

The water-soluble vitamin B1 (thiamin) plays essential roles in normal metabolism and function of all human/mammalian cells, including the pancreatic acinar cells (PACs). Pancreatic acinar cells (PACs) obtain thiamin from their surrounding (circulation) via transport across the plasma membrane, a process that is mediated by THTR-1 and THTR-2. We have previously characterized different aspects of thiamin uptake by mouse and human primary PACs, but little is known about post-transcriptional regulation of the uptake event. We addressed this by focusing on the predominant thiamin transporter THTR-1 (encoded by SLC19A2 gene) in PACs. Transfecting pmirGLO-SLC19A2 3'-UTR into mouse-derived PAC 266-6 cells lead to a significant reduction in luciferase activity compared to cells transfected with empty vector. Subjecting the SLC19A2 3'-UTR to different in-silico algorithms identified multiple putative microRNA binding sites in this region. Focusing on miR-200a-3p (since it is highly expressed in mouse and human pancreas) we found transfecting PAC 266-6 and human primary PACs (hPACs) with mimic miR-200a-3p lead to a significant inhibition of THTR-1 expression (both protein and mRNA levels) and in thiamin uptake. In contrast, transfection by miR-200a-3p inhibitor lead to an increase in THTR-1 expression and thiamin uptake. Additionally, truncating the region carrying miR-200a-3p binding site in SLC19A2 3'-UTR and mutating the binding site lead to abrogation in the inhibitory effect of this microRNA on luciferase activity in PAC 266-6. These results demonstrate that expression of THTR-1 and thiamin uptake in PACs is subject to post-transcriptional regulation by microRNAs.