Cloning and expression of a plasma membrane cystine/glutamate exchange transporter composed of two distinct proteins

Transport system x(c)(-) found in plasma membrane of cultured mammalian cel ls is an exchange agency for anionic amino acids with high specificity for anionic form of cystine and glutamate, We have isolated cDNA encoding the t ransporter for system x(c)(-) from mouse activated macrophages by expressio n in Xenopus oocytes. The expression of system x(c)(-) activity in oocytes required two cDNA transcripts, and the sequence analysis revealed that one is identical with the heavy chain of 4F2 cell surface antigen (4F2hc) and t he other is a novel protein of 502 amino acids with 12 putative transmembra ne domains. The latter protein, named xCT, showed a significant homology wi th those recently reported to mediate cationic or zwitterionic amino acid t ransport when co-expressed with 4F2hc, Thus xCT is a new member of a family of amino acid transporters that form heteromultimeric complex with 4F2hc, with a striking difference in substrate specificity. The expression of syst em x(c)(-) was highly regulated, and Northern blot analysis demonstrated th at the expression of both 4F2hc and xCT was enhanced in macrophages stimula ted by lipopolysaccharide or an electrophilic agent. However, the expressio n of xCT was more directly correlated with the system x(c)(-), activity.