| MRP1, also termed ABCC1, is a full transporter of the ATP‑binding cassette C subfamily that resides predominantly in the plasma membrane and functions as a multispecific organic anion efflux pump for endogenous metabolites, conjugated lipids, and a wide range of xenobiotics, including many anticancer drugs. The protein comprises three membrane‑spanning domains with 17 transmembrane helices and two cytosolic nucleotide‑binding domains; the extra N‑terminal transmembrane bundle contributes to correct targeting and surface stability, while the canonical core transmembrane domains form a bipartite substrate‑binding cavity that couples ATP binding and hydrolysis to large conformational changes that alternate substrate access between the cytoplasmic and extracellular sides. MRP1 recognizes and transports lipophilic anionic substrates with particular preference for glutathione (GSH) conjugates and GSH‑dependent complexes, including leukotriene C4, oxidized glutathione, estradiol‑17β‑glucuronide, bilirubin, sulfated bile acids, and many drug–GSH pairs, and it also transports GSH‑independent substrates such as methotrexate and selected cyclic dinucleotides. Cryo‑EM analyses show that ABCC1 uses a plastic binding pocket that accommodates GSH conjugates, bimolecular GSH–substrate pairs, and non‑GSH ligands, and that ATP binding and hydrolysis drive transitions through substrate‑loaded, pre‑release, and post‑release states with sequential nucleotide release from the two nucleotide‑binding sites, which resets the transporter for further cycles. MRP1 is widely expressed in barrier and detoxification tissues, including lung, intestine, liver, testis, placenta, blood–brain barrier, and hematopoietic cells, where basolateral localization in polarized epithelia and high expression at the blood–brain and blood–placenta interfaces support export of organic anions and xenobiotics toward blood or maternal circulation and contribute to tissue protection from toxic compounds and lipid peroxidation products. The transporter participates in glutathione and eicosanoid pathways by exporting GSH conjugates and cysteinyl leukotrienes, influences cellular redox homeostasis by controlling levels of oxidized glutathione and 4‑hydroxynonenal adducts, and exports immunostimulatory cyclic GMP–AMP to propagate cGAS–STING–dependent innate immune signaling between cells. In oncology, MRP1 confers multidrug resistance by reducing intracellular accumulation of anthracyclines, vinca alkaloids, epipodophyllotoxins, camptothecin derivatives, and several targeted agents, and high ABCC1 expression associates with poor response and adverse prognosis in cancers such as lung, breast, prostate tumors, and neuroblastoma, where it often coincides with other transporters including P‑gp. |
