3qC. View the map and BAC clones (data from UCSC genome browser).
Note: BAC RP23-22O3 restored the normal pigmentation to sut mutants(Chintala, et al ).
Slc7a11/NM_011990: 12 exons, 72,621bp, chr3:49,959,006-50,031,626.
The figure below shows the structure of the Slc7a11 gene (data from UCSC genome browser).
Search the 5'UTR and 1kb upstream regions (seq1=human SLC7A11, seq2=mouse Slc7a11) by CONREAL with 80% Position Weight Matrices (PWMs) threshold (view results here). Two amino acid response elements (AAREs), each located in the opposite direction with an intervening sequence, were found in the 5'-flanking region of the mouse xCT gene (Sato, et al (2004)). The 5'-deletion analysis revealed that the sequence between -116 and -82 is essential for the basal expression and the sequence between -226 and -116 containing EpRE-1 is essential in response to diethyl maleate(Sasaki, et al).
Slc7a11 (NM_011990), 2,216bp, view ORF and the alignment to genomic.
Using 3'RACE of brain mRNA, two alternative transcripts with different polyA signals (AY766236) were identified, while in sut brain mRNA, an alternative exon 12' was identified (AY766237) (Chintala, et al ).
Tissue specificity: Widely expressed, highly expressed in brain and melanocytes. By in situ hybridization, the xCT mRNA was expressed in the area postrema, subfornical organ, habenular nucleus, hypothalamic area, and ependymal cells of the lateral wall of the third ventricle in the adult mouse brain. A strong signal was also detected in the meninges in both adult and fetal mouse brains (Sato, et al (2002)). Both xCT and 4F2hc were found to localize predominantly to neurons in the mouse and human brain, but some glial cells were labeled as well. Border areas between the brain proper and periphery including the vascular endothelial cells, ependymal cells, choroid plexus and leptomeninges were also highly positive for the system x(-)c components. xCT and 4F2hc are also present at the brush border membranes in the kidney and duodenum (Burdo, et al). In embryonic and adult rat brain, xCT protein was enriched at the CSF-brain barrier (i.e., meninges) and also expressed in the cortex, hippocampus, striatum, and cerebellum (Shih, et al).
Affymetrix microarray expression pattern in SymAtlas from GNF is shown below.
xCT (NP_036120): 502aa, UniProtKB/Swiss-Prot entry Q9WTR6.
Synonym: Amino acid transport system xc-, Cystine/glutamate transporter, solute carrier family 7 (cationic amino acid transporter, y+ system) member 11
|Protein||NP_055146 (501aa)||XP_227120 (502aa)||XP_540941 (551aa)||XP_426289 (580aa)|
|Identities||89% /500aa||99% /502aa||91% /482aa||71% /581aa|
View multiple sequence alignment (PDF file) by ClustalW and GeneDoc.
(1) Domains predicted by SMART:
AA_permease: 48- 482
(2) Transmembrane domains predicted by SOSUI:
This amino acid sequence is of a MEMBRANE PROTEIN which have 11 transmembrane helices.
|No.||N terminal||transmembrane region||C terminal||type||length|
(3) Graphic view of InterPro domain structure.
(1) Predicted results by ScanProsite:
a) N-glycosylation site: 19 to 22 NMSG; 180 to 183 NSTS.
b) cAMP- and cGMP-dependent protein kinase phosphorylation site: 42 to 45 KKIT; 478 to 481 RRLS.
c) Protein kinase C phosphorylation site: 7 sites.
d) Casein kinase II phosphorylation site: 5 sites.
e) N-myristoylation site: 8 sites.
(2) Predicted results of subprograms by PSORT II:
a) N-terminal signal peptide: none
b) 11 tentative TMs, membrane topology: type 3a
c) KDEL ER retention motif in C-terminus: none
d) ER membrane retention signals:
XXRR-like motif in the N-terminus: VRKP; KKXX-like motif in the C-terminus: DSKE
e) VAC possible vacuolar targeting motif: none
f) Actinin-type actin-binding motif: type 1: none; type 2: none
g) Prenylation motif: none
h) memYQRL transport motif from cell surface to Golgi: none
i) Tyrosines in the tail: none
j) Dileucine motif in the tail: none
(1)ModBase predicted comparative 3D structure of Q9WTR6 from UCSC Genome Sorter.
From left to right: Front, Top, and Side views of predicted protein.
This protein does not exist in the current release of SWISS-2DPAGE.
Computed theoretical MW=55,456Da, pI=9.31 (NP_036120).
(1) Biological process: amino acid transport.
(2) Pheomelanin production.
(3) Oxidative stress.
(4) Belongs to the amino acid-polyamine-organocation (APC) superfamily. L-type amino acid transporter (LAT) (TC 2.A.3.8) family.
Integral membrane protein. Transport system xc- was found in plasma membrane of cultured mammalian cells (Sato, et al (1999)).
SLC7A11 (xCT), together with SLC3A2 (4F2hc) linked by a disulfide bond at residue C158, encodes the heterodimeric amino acid transport system x(c)(-), which mediates cystine-glutamate exchange and thereby regulates intracellular glutathione levels. System x(c)- activity is important to maintain both intracellular glutathione levels and the redox balance between cystine and cysteine in the extracellular milieu. rBAT can replace 4F2hc in the expression of the activity of system x(c)(-) (Wang, et al).
In mouse NIH3T3 cells, the activity of system x(c)(-) and xCT mRNA is induced not only by deprivation of cystine but also by deprivation of other amino acids via a genomic cis-element termed amino acid response element (AARE) (Sato, et al (2004)). Overexpression of Nrf-2 in astrocytes specifically increases expression of the xCT cystine/glutamate antiporter and other thiol synthesis-related proteins, to promote cell survival (Qiang, et al). Cys(327) is a functionally important residue accessible to the aqueous extracellular environment and is structurally linked to the permeation pathway and/or the substrate binding site (Jimenez-Vidal, et al).
A CD44 variant (CD44v) interacts with xCT and controls the intracellular level of reduced glutathione (GSH). Ablation of CD44 induced loss of xCT from the cell surface and suppressed tumor growth in a transgenic mouse model of gastric cancer. It also induced activation of p38(MAPK), a downstream target of ROS, and expression of the gene for the cell cycle inhibitor p21(CIP1/WAF1)(Ishimoto, et al).
Kaposi's sarcoma-associated herpesvirus (KSHV, human herpesvirus 8) is the causative agent of Kaposi's sarcoma and other lymphoproliferative syndromes often associated with HIV/AIDS. xCT has been identified as a receptor mediating KSHV cell fusion (Kaleeba, et al).
miR-26b, which is down-regulated in human breast cancer specimens and cell lines, impairs viability and triggers apoptosis of human breast cancer MCF7 cells. SLC7A11 is identified as a direct target of miR-26b and its expression is remarkably increased in both breast cancer cell lines and clinical samples (Liu, et al (2011)).
System x(c)(-) is a sodium-independent, high-affinity transporter of anionic amino acids with high specificity for anionic form of cystine and glutamate. Chintala, et al have reported that Slc7a11 regulates the pheomelanin production and cell proliferation. In melanosomes, dopaquinone reacts with cysteine to yield cysteinldopa, which is a precursor of pheomelanin. Cysteine is a component of the tripeptide glutathione. Glutathione metabolism pathway is described in KEGG Pathways.
SNPs deposited in dbSNP.
|Intron 11||del 481,280 bp||del exon 12||D482-L502 del||gross deletion||sut (C3H/HeSnJ)||Chintala, et al|
The deletion creates a new splice site and replacement of exon 12 with exon 12'(sequence is shown in AY766237 ). A new stop codon in exon 12' is predicted to produce a modified and trancated carboxyl terminus (482AYYPPEKEG490). In Northern blots, the normal 9kb (brain) or 9.5kb (melanocytes) transcripts are markedly deficient, which reveals a possible null mutation in sut mice.(Chintala, et al).
Mutation in the Slc7a11 gene is the cause of recessive subtle gray (sut) mutant (Chintala, et al). The sut allele arose spontaneously in the C3H/HeSnJ strain. The strain is described in more detail in JAX Mice database
Homozygotes have diluted coat color, with which yellow hair pigment is reduced, but black pigment is unaffected (Lane, et al). The sut mouse is also a model for a mild form of Hermansky-Pudlak syndrome, in which bleeding times of mutant mice were significantly prolonged (3.4-fold) in comparison with those in normal sut/+ controls (Swank, et al).
Chintala, et al reported that transport of cystine by xCT is critical for normal cultured cell growth, glutathione production, and protection from oxidative stress in cultured cells. Similarly, in the xCT-knock out (KO) mice, the embryonic fibroblasts failed to survive in routine culture medium (Sato, et al (2005)). Qiao, et al has demonstrated that the death of cultured sut cells is caused by apoptosis mediated by JNK activation with the involvement of both oxidative stress and ER stress.
The sut mice developed brain atrophy by early adulthood, exhibiting ventricular enlargement, thinning of the cortex, and shrinkage of the striatum. Astrocytes and meningeal cells derived from sut/sut mice showed greatly reduced proliferation in culture attributable to increased oxidative stress and thiol deficiency (Shih, et al). Deletion of xCT did not result in decreased glutathione levels in striatum. Accordingly, no signs of increased oxidative stress could be observed in striatum or substantia nigra of xCT(-/-) mice. However, xCT(-/-) mice were less susceptible to 6-hydroxydopamine (6-OHDA)-induced neurodegeneration in the substantia nigra pars compacta compared to their age-matched wild-type littermates. This reduced sensitivity to a PD-inducing toxin might be related to the decrease of 70% in striatal extracellular glutamate levels that was observed in mice lacking xCT (Massie, et al). xCT(-/-) mice do not have a lower hippocampal glutathione content, increased oxidative stress or brain atrophy, nor exacerbated spatial reference memory deficits with aging. Together, loss of system x(c)(-) does not induce oxidative stress in vivo. Young xCT(-/-) mice did however display a spatial working memory deficit. In contrast, significantly lower extracellular hippocampal glutamate concentrations in xCT(-/-) mice were measures compared to wild-type littermates. Correspondingly, xCT deletion in mice elevated the threshold for limbic seizures and abolished the proconvulsive effects of N-acetylcysteine (De Bundel, et al). Interestingly, rates of cell proliferation in the denate gyrus (DG) but not in the subventricular zone (SVZ) were elevated in both 3- and 11-month-old sut mice compared to the controls (Liu, et al (2007)).