miR-122-5p is involved in post-transcriptional regulation of the mitochondrial thiamin pyrophosphate transporter ( SLC25A19 ) in pancreatic acinar cells.

Thiamin (vitamin B1) plays a vital role in cellular energy metabolism/ATP production. Pancreatic acinar cells (PACs) obtain thiamin from circulation and convert it to thiamin pyrophosphate (TPP) in the cytoplasm. TPP is then taken up by the mitochondria via a carrier-mediated process that involves the mitochondrial TPP transporter (MTPPT; encoded by the gene SLC25A19 ). We have previously characterized different aspects of the mitochondrial carrier-mediated TPP uptake process, but nothing is known about its possible regulation at the post-transcriptional level. We address this issue in the current investigations focusing on the role of miRNAs in this regulation. First, we subjected the human (and rat) 3'-untranslated region (3'-UTR) of the SLC25A19 to three in-silico programs, and all have identified putative binding sites for miR-122-5p. Transfecting pmirGLO-h SLC25A19 3'-UTR into rat PAC AR42J resulted in a significant reduction in luciferase activity compared to cells transfected with pmirGLO-empty vector. Mutating as well as truncating the putative miR-122-5p binding sites in the h SLC25A19 3'-UTR led to abrogation of inhibition in luciferase activity in PAC AR42J. Further experiments with PAC AR42J and human primary PACs showed that transfecting/transducing these cells with mimic of miR-122-5p to lead to a significant inhibition in the level of expression of the MTPPT mRNA and protein as well as in mitochondrial carrier-mediated TPP uptake. Conversely, transfecting PAC AR42J with an inhibitor of miR-122-5p increased MTPPT expression and function. These findings show, for the first time, that expression and function of the MTPPT in PACs are subject to post-transcriptional regulation by miR-122-5p.