Molecular Cloning and Expression of Human xCT, the Light Chain of Amino Acid Transport System x_c¯

Abstract

Transport of system xc- is an exchange agency with high specificity for anionic form of cystine and glutamate. The protein mediating this transport is a disulfide-linked heterodimer of a light chain named xCT and a heavy chain previously known as 4F2hc. We have isolated two cDNAs encoding xCT from the human cDNA library. One clone coded for a protein of 501 amino acids with 12 putative transmembrane domains. When functionally expressed in Xenopus oocytes together with the human 4F2hc, human xCT induced the transport activity whose characteristics are similar to those of system xc-. Another clone seemed to contain a partial human xCT and a long 3' untranslated region. The human xCT gene was localized at chromosome 4q28-31. Analysis of the 5'-flanking region of the human xCT gene revealed several sites for potentially binding of transcriptional factors, including NF-E2 and AP-1. Transport of cystine via system xc- has been known as a regulatory factor for the intracellular glutathione level, and its transport activity is induced in response to the oxygen tension in culture. Northern blot analysis demonstrated that the expression of both xCT and 4F2hc was significantly enhanced by oxygen. The results suggest that oxygen regulates the activity of system xc- by modulating the expression of both xCT and 4F2hc mRNAs.

Electrophile Response Element-mediated Induction of the Cystine/Glutamate Exchange Transporter Gene Expression

“…7). EpRE-1 is completely conserved in the 5Ј-flanking region of the human xCT gene (26). Judging from these, the main region responsible for the DEM-inducible tran- scription is probably EpRE-1.…”

Interleukin 1β Regulation of the System xc− Substrate-specific Subunit, xCT, in Primary Mouse Astrocytes Involves the RNA-binding Protein HuR

“…xCT is encoded by the Slc7a11 gene and confers substrate specificity, whereas 4F2hc is common to several amino acid transporters and allows plasma membrane expression of the functional Sx c Ϫ (3)(4)(5)(6). Sx c Ϫ exports glutamate to the extracellular space and concomitantly imports cystine into the cytosol of cells, where it is rapidly reduced to cysteine to be incorporated into various catabolic processes, including protein synthesis and synthesis of the antioxidant GSH (7,8).…”

“…In this regard, the 5Ј-flanking region of the murine xCT gene contains multiple putative transcription factor binding sites that contribute to the stimulus and/or cell type-dependent regulation of xCT gene transcription (3,7,13,(33)(34)(35)(36). In addition to transcriptional regulation, the mRNA of xCT contains a long 3Ј-UTR, ϳ7366 nucleotides, raising the possibility for post-transcriptional regulation as well.…”

Disruption of xCT inhibits cancer cell metastasis via the caveolin-1/β-catenin pathway

“…Once inside the cells, cystine is rapidly reduced to cysteine, the rate-limiting substrate for glutathione (GSH) synthesis. Therefore, system xc-plays an important role in maintaining the cellular redox balance by regulating the intracellular GSH level (Sato et al, 1999(Sato et al, , 2000Kim et al, 2001).…”