The organic anion transporter SLCO2A1 constitutes the core component of the Maxi‐Cl channel

• Published in: The EMBO journal Vol. 36; no. 22; pp. 3309 - 3324
• Main Authors: Sabirov, Ravshan Z, Merzlyak, Petr G, Okada, Toshiaki, Islam, Md Rafiqul, Uramoto, Hiromi, Mori, Tomoko, Makino, Yumiko, Matsuura, Hiroshi, Xie, Yu, Okada, Yasunobu
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 15.11.2017; John Wiley and Sons Inc
• Subjects: Adenosine Triphosphate - metabolism; Amphibians; Animals; anion channel; Anion channels; Anions; ATP; Cell Fractionation; Cell lines; Cell Membrane - drug effects; Cell Membrane - metabolism; Conductance; CRISPR; CRISPR-Cas Systems - genetics; Dinoprostone - pharmacology; Female; Fluxes; Gene Deletion; Gene Silencing - drug effects; Genetic screening; Green Fluorescent Proteins - metabolism; HEK293 Cells; Humans; Ion Channel Gating - drug effects; Ion channels; Ion Channels - metabolism; Ischemia; Maxi‐Cl; Membrane Proteins - metabolism; Mice, Inbred C57BL; molecular entity; Mutation - genetics; organic anion transporter; Organic Anion Transporters - metabolism; Protein transport; Proteins; Proteolipids - drug effects; Proteolipids - metabolism; Proteomics; Recombinant Proteins - metabolism; Reperfusion; Reperfusion Injury - pathology; Resistance; RNA-mediated interference; Rodents; Screening; siRNA; SLCO2A1; organic anion transporter; Maxi‐Cl; molecular entity; anion channel; SLCO2A1
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.201796685

The maxi‐anion channels (MACs) are expressed in cells from mammals to amphibians with ~60% exhibiting a phenotype called Maxi‐Cl. Maxi‐Cl serves as the most efficient pathway for regulated fluxes of inorganic and organic anions including ATP. However, its molecular entity has long been elusive. By subjecting proteins isolated from bleb membranes rich in Maxi‐Cl activity to LC‐MS/MS combined with targeted siRNA screening, CRISPR/Cas9‐mediated knockout, and heterologous overexpression, we identified the organic anion transporter SLCO2A1, known as a prostaglandin transporter (PGT), as a key component of Maxi‐Cl. Recombinant SLCO2A1 exhibited Maxi‐Cl activity in reconstituted proteoliposomes. When SLCO2A1, but not its two disease‐causing mutants, was heterologously expressed in cells which lack endogenous SLCO2A1 expression and Maxi‐Cl activity, Maxi‐Cl currents became activated. The charge‐neutralized mutant became weakly cation‐selective with exhibiting a smaller single‐channel conductance. Slco2a1 silencing in vitro and in vivo, respectively, suppressed the release of ATP from swollen C127 cells and from Langendorff‐perfused mouse hearts subjected to ischemia–reperfusion. These findings indicate that SLCO2A1 is an essential core component of the ATP‐conductive Maxi‐Cl channel. Synopsis A combination of proteomics, RNAi screening, and reconstitution approaches identifies prostaglandin transporter SLC02A1 as a core component of the maxi‐anion channel, thus illustrating the ability of a transporter protein to moonlight as an ion channel. Bleb membrane proteomics and CRISPR/Cas9‐mediated knockout reveal SLCO2A1 as a component of the Maxi‐Cl channel. Heterologous expression of wildtype SLCO2A1, but not disease‐causing mutants, elicits Maxi‐Cl activity. Recombinant SLCO2A1 exhibits Maxi‐Cl activity in reconstituted proteoliposomes. SLCO2A1 is involved in ATP release from cultured cell lines and perfused hearts, an activity linked to the Maxi‐Cl channel. A combination of proteomics, RNAi screening, and reconstitution approaches reveals the molecular identity of the long‐sought maxi‐anion channel activity in cells.