{'fraction_non_alphanumeric': 0.02806824435883324, 'fraction_numerical': 0.014859658778205834, 'mean_word_length': 5.401408450704225, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Regulation of the Brain Organic Cation Transporter Plasma Membrane Monoamine Transporter (PMAT) by Alternative Splicing

PMAT is a polyspecific organic cation transporter highly expressed at the blood‐cerebrospinal fluid (CSF) barrier and facilitates the removal of monoamine neurotransmitters, organic cation drugs and toxicants from the CSF. We found that human SHSY5Y neuronal cells co‐express the full‐length wild type (wt) PMAT mRNA with two alternatively spliced mRNA species. One spliced variant (PMAT_v1) introduced a premature stop codon before transmembrane domain (TMD) 3 and the other (PMAT_v2) had a frame shift resulting in the deletion of TMD 3‐4. The goal of this study was to determine 1) the function and expression of the spliced variants in normal human tissues; 2) if the spliced variants exhibit a regulatory role on wt PMAT. Variant‐specific PCR indicated the spliced variants were co‐expressed with wt PMAT in all tested human tissues (whole brain, choroid plexus, small intestine and colon) at levels 37‐84% of the wt PMAT. When expressed in HEK293 cells, wt PMAT‐expressing cells showed up to 20‐fold increase in [3H]MPP+ uptake as compared to vector‐transfected cells. In contrast, there was no significant increase in uptake in cells‐expressing PMAT_v1 or PMAT_v2. PMAT_v1 protein was not detected by immunocytochemistry in HEK cells while PMAT_v2 was exclusively expressed in intracellular organelles. Co‐expression of PMAT_v1 or PMAT_v2 with wt PMAT in HEK293 cells did not significantly interfere with the normal activity of wt PMAT. Together our data showed PMAT pre‐mRNA is alternatively spliced in normal human tissues; and the overall PMAT activity in certain human tissues and cells may be regulated by altering the ratio between the functional and the non‐functional mRNA species.