Posttranscriptional regulation of thiamin transporter-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). PACs obtain thiamin from their surrounding circulation via transport across the plasma membrane, a process that is mediated by thiamin transporter (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 posttranscriptional regulation of the uptake event. We addressed this by focusing on the predominant thiamin transporter THTR-1 (encoded by gene) in PACs. Transfecting pmirGLO- 3'-untranslated region (UTR) into mouse-derived PAC 266-6 cells leads to a significant reduction in luciferase activity compared with cells transfected with empty vector. Subjecting the 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 that transfecting PAC 266-6 and human primary PACs (hPACs) with mimic miR-200a-3p leads 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 leads to an increase in THTR-1 expression and thiamin uptake. Additionally, truncating the region carrying miR-200a-3p binding site in 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 posttranscriptional regulation by microRNAs. The findings of this study show, for the first time, that the membrane transporter of vitamin B1, i.e., thiamin transporter-1 (THTR-1), is subject to regulation by microRNAs (specifically miR-200a-3p) in mouse and human primary pancreatic acinar cells (PACs). The results also show that this posttranscriptional regulation has functional consequences on the ability of PACs to take in the essential micronutrient thiamin.