SLC7A6

SLC7A6 (y+LAT-2/LAT-2) is a light-chain subunit of a heteromeric amino acid transporter that obligatorily associates with the heavy chain 4F2hc (CD98) to traffic to the plasma membrane, where it mediates sodium-independent, trans-stimulated exchange of zwitterionic and dibasic amino acids (PMID:10391915). In polarized epithelia, SLC7A6 localizes to the basolateral membrane and participates in transepithelial cystine/cysteine reabsorption and betaine uptake; its transport kinetics are modulated through formation of a supramolecular complex with CD98 and ICAM-1, whose ligation triggers threonine phosphorylation that reciprocally adjusts Km and Vmax (PMID:12660317, PMID:12716892, PMID:24599290). SLC7A6 transcription is epigenetically regulated by a STAT5A–CDYL2 axis that controls H3K4me3 at the SLC7A6 promoter, and reduced SLC7A6 expression suppresses amino acid import and downstream mTORC1/S6K signaling in hepatocellular carcinoma (PMID:35314791).

1. 1999 High

   Establishing the fundamental identity and mechanism of SLC7A6: the gene encodes a light-chain amino acid transporter subunit that is retained intracellularly unless heterodimerized with 4F2hc, and functions as a sodium-independent, broad-specificity exchanger.

   Evidence Reconstituted transport in Xenopus oocytes with co-immunoprecipitation, tagged-protein localization, and trans-stimulation assays

   PMID:10391915

   Open questions at the time

   • Physiological tissue-specific roles not established
   • Mechanism of 4F2hc-dependent trafficking not resolved
   • Structural basis of substrate selectivity unknown
2. 2003 High

   Determining SLC7A6's physiological role in epithelia: it mediates basolateral cystine/cysteine efflux in proximal tubule cells and forms a regulatable ternary complex with CD98 and ICAM-1 in intestinal epithelium, revealing that transport kinetics are tuned by extracellular signals through threonine phosphorylation of the complex.

   Evidence Antisense knockdown with transepithelial flux measurements in OK cells; reciprocal co-IP, antibody cross-linking, and kinetic transport analysis in Caco2-BBE monolayers

   PMID:12660317 PMID:12716892

   Open questions at the time

   • Identity of kinase(s) mediating threonine phosphorylation unknown
   • Stoichiometry of the CD98/LAT-2/ICAM-1 complex not determined
   • Whether ICAM-1 regulation operates in non-intestinal tissues not tested
3. 2005 Medium

   Revealing that the two y+L system light chains (y+LAT-1 and y+LAT-2) can functionally interfere with each other: an LPI-associated SLC7A7 mutant dominantly inhibits SLC7A6-mediated transport, implying possible multiheteromeric complex formation.

   Evidence Co-expression of SLC7A7 mutants with SLC7A6 in oocytes and mammalian cells with transport assays

   PMID:15756301

   Open questions at the time

   • Direct physical interaction between y+LAT-1 and y+LAT-2 not demonstrated by reciprocal biochemistry
   • In vivo relevance to LPI pathogenesis unclear
   • Stoichiometry of any putative multiheteromeric complex undefined
4. 2014 Medium

   Extending substrate scope beyond canonical amino acids: SLC7A6 in cumulus cells mediates betaine uptake that is subsequently relayed to the oocyte through gap junctions, linking the transporter to osmolyte delivery during oocyte maturation.

   Evidence Radiolabeled betaine transport, inhibitor profiling, and gap junction blockade in mouse cumulus-oocyte complexes

   PMID:24599290

   Open questions at the time

   • Whether betaine is a direct SLC7A6 substrate or enters via an associated carrier not reconstituted in purified system
   • Na+-dependent component differs from canonical SLC7A6 mode—molecular explanation unclear
   • Role in fertility phenotypes not tested genetically
5. 2022 Medium

   Placing SLC7A6 within an epigenetic–signaling axis: CDYL2 represses SLC7A6 transcription by reducing H3K4me3 at its promoter, and SLC7A6 loss suppresses mTORC1/S6K signaling, establishing a STAT5A→CDYL2→SLC7A6→mTORC1 pathway in hepatocellular carcinoma.

   Evidence ChIP-seq for H3K4me3, gain/loss-of-function, western blot for mTORC1/S6K phosphorylation, and in vivo xenograft in HCC models

   PMID:35314791

   Open questions at the time

   • Which amino acid substrates of SLC7A6 are rate-limiting for mTORC1 activation not identified
   • Pathway generalizability beyond HCC not demonstrated
   • Direct link between SLC7A6-transported amino acids and mTORC1 sensors (e.g., Sestrin2, CASTOR1) not tested
6. 2024 Medium

   Identifying a retained-intron isoform (SLC7A6-RI) as a functional noncoding RNA that suppresses tumor growth and negatively regulates PI3K–Akt–mTOR signaling in colon cancer, distinct from the canonical transporter function.

   Evidence siRNA knockdown of SLC7A6-RI intronic region, xenograft tumor assays, western blotting for p-mTOR and PCNA

   PMID:39403788

   Open questions at the time

   • Mechanism by which the retained-intron transcript inhibits PI3K–Akt–mTOR not determined
   • Whether SLC7A6-RI is translated or functions as a noncoding RNA not resolved
   • Relationship between SLC7A6-RI and canonical SLC7A6 transporter expression not clarified

• Whether SLC7A6 directly transports GSSG and regulates ferroptosis through redox homeostasis, as computationally predicted, remains unresolved; no direct transport reconstitution with GSSG has been performed.
• GSSG transport by SLC7A6 supported only by AlphaFold3 prediction and indirect metabolite measurements—awaits reconstitution
• No high-resolution experimental structure of SLC7A6 or the 4F2hc–SLC7A6 heterodimer
• In vivo genetic models (knockout mice) for SLC7A6 have not been reported