The SLC22 drug transporter family

The SLC22 family comprises organic cation transporters (OCTs), zwitterion/cation transporters (OCTNs), and organic anion transporters (OATs). These transporters contain 12 predicted -helical transmembrane domains (TMDs) and one large extracellular loop between TMDs 1 and 2. Transporters of the SLC22 family function in different ways: (1) as uniporters that mediate facilitated diffusion in either direction (OCTs), (2) as anion exchangers (OAT1, OAT3 and URAT1), and (3) as Na⁺/l-carnitine cotransporter (OCTN2). They participate in the absorption and/or excretion of drugs, xenobiotics, and endogenous compounds in intestine, liver and/or kidney, and perform homeostatic functions in brain and heart. The endogenous substrates include monoamine neurotransmitters, choline, l-carnitine, -ketoglutarate, cAMP, cGMP, prostaglandins, and urate. Defect mutations of transporters of the SLC22 family may cause specific diseases such as "primary systemic carnitine deficiency" or "idiopathic renal hypouricemia" or change drug absorption or excretion.     

The sodium-dependent glucose cotransporter SLC5A11 as an autoimmune modifier gene in SLE

Genetic studies in several human autoimmune diseases suggest that the pericentromeric region of chromosome 16 might harbor an autoimmune modifier gene. We hypothesized that the sodium-dependent glucose cotransporter gene SLC5A11 is such a gene, and so might interact with immune-related genes. Herein, this hypothesis was tested in a genetic evaluation of the multiple gene effect in systemic lupus erythematosus (SLE). We used the case-control candidate gene association approach. Eight immune-related genes involved in inflammation and autoantibody generation and clear-up [interleukin 1 receptor antagonist (IL1RN), interleukin 1-beta (IL1-beta), tumor necrosis factor-alpha (TNF-alpha), lymphotoxin-alpha (LTA), tumor necrosis factor ligand superfamily, member 6 (TNFSF6), programmed cell death 1 (PDCD1), C2, and complement component 4 (C4)] were selected for study. Frequency of each candidate's genotype and allele between case and control were compared. Results were stratified by reanalyzing genotype data with relevant symptoms. Finally, improved computational data mining was used to analyze the phenotypes in a large data set. In the frequency analysis, only IL1-beta was significantly associated with SLE. Stratification analysis showed a significant association with SLE symptoms between SLC5A11 and the other immune-related genes, with the exceptions of TNFSF6 and C4. SLC5A11 was significantly associated with low C4 (as was TNF-alpha), anti-Smith antibody (anti-Sm) (as was C2), serositis, and alopecia. Finally, SLC5A11 interacted with PDCD1, TNF-alpha, LTA, and C4. After our study, we concluded that SLC5A11 is involved with some immune effects and interacts with immune-related gene(s), consistent with its function as an autoimmune modifier gene. Furthermore, SLC5A11 might induce apoptosis through the TNF-alpha, PDCD1 pathway. The present genotype-phenotype mapping approach should be applicable to genetic study of other complex diseases.     

The human sugar-phosphate/phosphate exchanger family SLC37

The SLC37 family of four predicted proteins is an almost unexplored group of transmembrane sugar transporters. Of the four proteins/genes assigned to date to this family, only one is well known, the SLC37A4 gene (also known as the glucose-6-phosphate transporter 1, G6PT1) mutated in the glycogen storage disease non-1A type. Data on SLC3A1 gene expression are available for humans, while data on SLC37A2 are available for mice. The last SLC37 family member, SLC37A3, is only a putative gene/protein identified by in silico analyses. The four genes are not clustered in a single chromosome as regions and the identity of their predicted polypeptides is between 60 and 20%. Here we propose a new nomenclature for the SLC37 proteins (SPX: sugar-phosphate exchangers) numbered according to the gene numbering.     

一个中国耳聋家系的SLC26A4基因分析

目的 确定一个非综合征型耳聋家系的致病基因。方法 应用聚合酶链反应-直接测序方法，对溶质转运蛋白家族26，成员4（solute carrier family 26，member 4；SLC26A4）基因的所有外显子及其与内含子交界处进行测序寻找突变。结果 在该家系先证者发现SLC26A4基因的N392Y、S448X复合杂合突变，其父亲为S448X的杂合突变，其母亲为N392Y的杂合突变。结论 SLC26A4基因的N392Y、S448X复合杂合突变是导致该先证者耳聋发生的原因。     

Missense mutations in the sodium borate cotransporter SLC4A11 cause late‐onset Fuchs corneal dystrophya

Homozygous mutations in the Borate Cotransporter SLC4A11 cause two early‐onset corneal dystrophies: congenital hereditary endothelial dystrophy (CHED) and Harboyan syndrome. More recently, four sporadic patients with late‐onset Fuchs corneal dystrophy (FCD), a common age‐related disorder, were also reported to harbor heterozygous mutations at this locus. We therefore tested the hypothesis that SLC4A11 contributes to FCD and asked whether mutations in SLC4A11 are responsible for familial cases of late‐onset FCD. We sequenced SLC4A11 in 192 sporadic and small nuclear late‐onset FCD families and found seven heterozygous missense novel variations that were absent from ethnically matched controls. Familial data available for one of these mutations showed segregation under a dominant model in a three‐generational family. In silico analyses suggested that most of these substitutions are intolerant, whereas biochemical studies of the mutant protein indicated that these alleles impact the localization and/or posttranslational modification of the protein. These results suggest that heterozygous mutations in SLC4A11 are modest contributors to the pathogenesis of adult FCD, suggesting a causality continuum between FCD and CHED. Taken together with a recent model between FCD and yet another early onset corneal dystrophy, PPCD, our data suggest a shared pathomechanism and genetic overlap across several corneal dystrophies. Hum Mutat 31:1–8, 2010. © 2010 Wiley‐Liss, Inc.     

Identification of novel mutations in the SLC25A15 gene in hyperornithinemia‐hyperammonemia‐homocitrullinuria (HHH) syndrome: A clinical,molecular, and functional study

Hyperornithinemia‐hyperammonemia‐homocitrullinuria (HHH) syndrome is an autosomal recessive disorder of the urea cycle. With the exception of the French‐Canadian founder effect, no common mutation has been detected in other populations. In this study, we collected 16 additional HHH cases and expanded the spectrum of SLC25A15/ORC1 mutations. Eleven novel mutations were identified including six new missense and one microrearrangement. We also measured the transport properties of the recombinant purified proteins in reconstituted liposomes for four new and two previously reported missense mutations and proved that the transport activities of these mutant forms of ORC1 were reduced as compared with the wild‐type protein; residual activity ranged between 4% and 19%. Furthermore, we designed three‐dimensional (3D)‐modeling of mutant ORC1 proteins. While modeling the changes in silico allowed us to obtain new information on the pathomechanisms underlying HHH syndrome, we found no clear‐cut genotype–phenotype correlations. Although patient metabolic alterations responded well to low‐protein therapy, predictions concerning the long‐term evolution of HHH syndrome remain uncertain. The preference for a hepatic rather than a neurological presentation at onset also continues, largely, to elude us. Neither modifications in oxidative metabolism‐related energy, such as those expected in different mtDNA haplogroups, nor sequence variants in SLC25A2/ORC2 seem to be crucial. Other factors, including protein stability and function, and ORC1‐ORC2 structural interactions should be further investigated. Hum Mutat 0, 1–8, 2009. © 2009 Wiley‐Liss, Inc.     

Seven novel mutations in the ORNT1 gene (SLC25A15) in patients with hyperornithinemia,hyperammonemia, and homocitrullinuria syndrome

Eight unrelated Italian patients with the hyperornithinemia, hyperammonemia, and homocitrullinuria (HHH) syndrome were analyzed for mutations in the ORNT1 gene. Seven novel mutations were identified (Q89X, G27R, G190D, R275Q, c.861insG, c.164insA, and IVS5+1G→A). Other previously described variants were a heterozygous deletion of a phenylalanine residue (F188del) in one allele and the R179X in two. The G27R mutation was carried by two patients. Analyses of ORNT1 mRNA in four patients showed that mutant alleles were stable and of the predicted size. The current study expands the spectrum of mutations in ORNT1 gene. © Wiley‐Liss, Inc.     

PNPT1, MYO15A,PTPRQ, and SLC12A2-associated genetic and phenotypic heterogeneity among hearing impaired assortative mating families in Southern India

The study was conducted between 2018 and 2020. From a cohort of 113 hearing impaired (HI), five non-DFNB12 probands identified with heterozygous CDH23 variants were subjected to exome analysis. This resolved the etiology of hearing loss (HL) in four South Indian assortative mating families. Six variants, including three novel ones, were identified in four genes: PNPT1 p.(Ala46Gly) and p.(Asn540Ser), MYO15A p.(Leu1485Pro) and p.(Tyr1891Ter), PTPRQ p.(Gln1336Ter), and SLC12A2 p.(Pro988Ser). Compound heterozygous PNPT1 variants were associated with DFNB70 causing prelingual profound sensorineural hearing loss (SNHL), vestibular dysfunction, and unilateral progressive vision loss in one family. In the second family, MYO15A variants in the myosin motor domain, including a novel variant, causing DFNB3, were found to be associated with prelingual profound SNHL. A novel PTPRQ variant was associated with postlingual progressive sensorineural/mixed HL and vestibular dysfunction in the third family with DFNB84A. In the fourth family, the SLC12A2 novel variant was found to segregate with severe-to-profound HL causing DFNA78, across three generations. Our results suggest a high level of allelic, genotypic, and phenotypic heterogeneity of HL in these families. This study is the first to report the association of PNPT1, PTPRQ, and SLC12A2 variants with HL in the Indian population.     

Molecular Genetic Analysis of SLC3A1 and SLC7A9 Genes in Czech and Slovak Cystinuric Patients

Cystinuria is a frequently inherited metabolic disorder in the Czech population (frequency 1/5,600) caused by a defect in the renal transport of cystine and dibasic amino acids (arginine, lysine and ornithine). The disease is characterized by increased urinary excretion of the amino acids and often leads to recurrent nephrolithiasis. Cystinuria is classified into two subtypes (type I and type non‐I). Type I is caused predominantly by mutations in the SLC3A1 gene (2p16.3), encoding heavy subunit (rBAT) of the heterodimeric transporter. Cystinuria non‐I type is caused by mutations in the SLC7A9 gene (19q13.1). In this study, we present results of molecular genetic analysis of the SLC3A1 and the SLC7A9 genes in 24 unrelated cystinuria families. Individual exons of the SLC3A1 and SLC7A9 genes were analyzed by direct sequencing. We found ten different mutations in the SLC3A1 gene including six novel ones: three missense mutations (G140R), D179Y and R365P), one splice site mutation (1137‐2A>G), one deletion (1515_1516delAA), and one nonsense mutation (Q119X). The most frequent mutation, M467T; was detected in 36% of all type I classified alleles. In the SLC7A9 gene we found six mutations including three new ones: one missense mutation (G319R), one insertion (611_612insA) and one deletion (205_206delTG). One patient was compound heterozygote for one SLC3A1 and one SLC7A9 mutation. Our results confirm that cystinuria is a heterogeneous disorder at the molecular level, and contribute to the understanding of the distribution and frequency of mutations causing cystinuria in the Caucasian population.     

The mitochondrial transporter family (SLC25): physiological and pathological implications

The mitochondrial carriers (MCs) shuttle a variety of metabolites across the inner mitochondrial membrane (i.m.m.). In man they are encoded by the SLC25 genes. Some MCs have isoforms encoded by different SLC25 genes, whereas the phosphate carrier has two variants arising from an alternative splicing of SLC25A3. Six MCs have been sequenced after purification, and many more have been identified from their transport and kinetic properties following heterologous over-expression and reconstitution into liposomes. All MCs of known function belong to the same protein family, since their polypeptide chains consist of three tandemly related sequences of about 100 amino acids, and the repeats of the different carriers are homologous. They probably function as homodimers, each monomer being folded in the membrane into six transmembrane segments. The functional information obtained in studies with mitochondria and/or the reconstituted system has helped to gain an insight into the physiological role of the MCs in cell metabolism, as have tissue distribution, the use of knock-out mice (and/or yeast) and over-expression in human cell lines (or yeast) of individual carriers and isoforms. At the same time, the cloning and functional identification of many SLC25 genes has made it possible (i) to identify the genes (and their defects) responsible for some diseases, e.g. Stanley syndrome and Amish microcephaly, and (ii) where the genes were already known, to characterize the function of the gene products and hence understand the molecular basis and the symptoms of the diseases, e.g. hyperornithinaemia, hyperammonaemia and homocitrullinuria (HHH) syndrome and type II citrullinemia. It is likely that further extension and functional characterization of the SLC25 gene family will elucidate other diseases caused by MC deficiency.Abbreviations AAC ADP/ATP carrier - AGC aspartate/glutamate carrier - ANC peroxisomal adenine nucleotide carrier - BKA bongkrekic acid - CAC carnitine/acylcarnitine carrier - CATR carboxyatractyloside - CoA coenzyme A - CIC citrate carrier - DIC dicarboxylate carrier - DNC deoxynucleotide carrier - GC glutamate carrier - GDC Graves disease carrier - i.m.m. inner mitochondrial membrane - MC mitochondrial carrier - MCF mitochondrial carrier family - MTSEA (2-aminoethyl)-methanethiosulphonate hydrobromide - OAA oxaloacetate - ODC oxodicarboxylate carrier - OGC oxoglutarate carrier - OMIM Online Mendelian Inheritance in Man (database) - ORC ornithine carrier - PEP phosphoenolpyruvate - PiC phosphate carrier - SLC25 name of the human mitochondrial solute carrier gene family, assigned by the Human Genome Organisation (HUGO) nomenclature committee - TMS transmembrane segment - UCP uncoupling protein This revised version was published in December 2003 because additional corrections were requested by the guest editor.     

Direct or indirect association in a complex disease: the role of SLC22A4 and SLC22A5 functional variants in Crohn disease

A common haplotype spanning 250 kb on chromosome 5q31 is strongly associated with Crohn disease (CD). Recently, two functional variants within the SLC22A4 and SLC22A5 genes at this locus (IBD5), L503F (c.1507C > T) and G-207C (c.-207G > C), have been proposed to contribute directly to susceptibility to CD. However, extensive linkage disequilibrium at the IBD5 locus has complicated efforts to distinguish causal variants from association of the general risk haplotype. We genotyped the SLC22A4 and SLC22A5 variants and other polymorphisms across the risk haplotype in four populations of European origin, and applied regression-based haplotype analysis to over 1,200 fully genotyped case-control pairs, modeling case/control status on the presence of one or more SNPs to test for conditional association and to identify risk haplotypes. We found highly significant association of SNPs at the IBD5 locus with Crohn disease in all populations tested. However, the frequencies of L503F and G-207C in individuals who did not carry the general IBD5 risk haplotype were not significantly different in cases and controls, with associated disease odds ratios (ORs) of 0.90 (95% CI, 0.57-1.40) and 0.90 (95% CI, 0.65-1.23), respectively. Haplotype analysis showed that addition of the SLC22A4 and SLC22A5 variants to a null model that included the background risk haplotype did not significantly improve the model fit. In addition to the common risk haplotype, several rare haplotypes had an increased frequency in cases compared to controls. This study suggests that the molecular basis for Crohn disease susceptibility at the IBD5 locus remains to be defined, and highlights the challenge of the identification of causal variants in a complex disease in regions of extensive linkage disequilibrium.     

Identification and characterization of the human and mouse SLC19A3 gene: a novel member of the reduced folate family of micronutrient transporter genes

We report here the isolation, characterization, and chromosomal localization of the genes encoding the human and corresponding murine orthologue of solute carrier family 19A member 3 (SLC19A3). Human SLC19A3 encodes a 496-amino-acid residue protein with a predicted molecular weight of 56 kDa that shares sequence similarity to both SLC19A1 (reduced folate transporter (RFC-1)) and SLC19A2 (high affinity thiamine transporter (THTR-1)). Like the SLC19A1 and SLC19A2 proteins, SLC19A3 contains 12 putative transmembrane domains. The human SLC19A3 gene is widely expressed, with the most abundant expression observed in placenta, kidney, and liver, and has been mapped to chromosome 2q37. The murine SLC19A3 gene maps to central chromosome 1 in the region defined as a seizure susceptibility locus in the DBA/2J mouse strain. This article describes the identification of SLC19A3, a gene encoding a novel solute transporter, and establishes murine SLC19A3 as a candidate gene for seizures in the DBA/2J mouse.     

钾依赖钠钙交换蛋白－6（SLC24A6）的基因克隆与蛋白表达

目的：克隆和表达钾依赖钠钙交换蛋白-6（ SLC24A6） 基因，为进一步阐明其与胰岛素分泌的关系奠定基础。方法：利用RT-PCR观察SLC24A6基因在胰岛素瘤和正常胰腺组织中的表达，并克隆SLC24A6基因全 长，将SLC24A6基因构建到原核表达载体pET32a，在大肠杆菌ROSSET菌（DE3）中诱导表达纯 化；将SLC24A6基因构建到绿色荧光真核表达载体pEGFP-C3，利用共聚焦显微镜观察SLC24A6 在小鼠胰岛素瘤β-TC3细胞中的定位。结果：SLC24A6基因在胰岛素瘤组 织表达明显高于正常胰腺；成功获得原核表达纯化蛋白，大小约80 kD；重组载体 pEGFP-C3 -SLC24A6转染后，定位于小鼠胰岛素瘤β-TC3细胞膜上。结论：SLC24A6 可能与胰岛素分泌有关，SLC24A6全长原核表达为进一步研究SLC24A6的生物学功能和蛋白质 晶体结构奠定了基础，SLC24A6在胰岛素瘤细胞的定位为进一步阐明其与胰岛素分泌的关系 提供了理论依据。     

Monosomy and trisomy of 15q24→qter in a family with a translocation t(6;15)(P25;q24)

A child with multiple anomalies, including growth retardation, a left-sided diaphragmatic hernia with lung hypoplasia, and cerebral malformations is described. Cytogenetic investigation demonstrated a deletion of the distal part of one chromosome 15, del(15)(q24qter), an aberration not previously described. Family studies revealed that the mother had a balanced translocation, t(6;15)(p25;q24). Two of her subsequent pregnancies resulted in abortions after prenatal diagnosis: one fetus was trisomic for 15q24→qter, while the other had monosomy 15q24→qter and a left-sided diaphragmatic hernia similar to the first child.     

Novel SLC5A2 Variants Contribute to Renal Glucosuria in Chinese Families: Abnormal Expression and Dysfunction of Variant SLC5A2

Familial renal glucosuria (FRG) is characterized by persistent glucosuria despite normal serum glucose and the absence of overt tubular dysfunction. Variants in solute carrier family 5 (sodium–glucose cotransporter), member 2 (SLC5A2) have been reported in FRG patients. However, the functional and expression‐related consequences of such variants have been scarcely investigated. In the current study, we studied five FRG families and identified six missense mutations, including four novel variants (c.1051T>C/.(C351R), c.1400T>C/p.(V467A), c.1420G>C/p.(A474P), c.1691G>A/p.(R564Q); RNA not analyzed) and two variants that had been previously reported (c.294C>A/p.(F98L), c.736C>T/p.(P246S); RNA not analyzed). The probands were either heterozygous or compound heterozygous for SLC5A2 variants and had glucosuria of 5.9%–19.6 g/day. Human 293 cells were transfected with plasmid constructs to study the expression and function of SLC5A2 variants in vitro. Western blotting revealed that the expression levels of SLC5A2–351R‐GFP, SLC5A2–467A‐GFP, SLC5A2–474P‐GFP, and SLC5A2–564Q‐GFP were significantly decreased compared with wild‐type SLC5A2‐GFP (37%–55%). Confocal microscopy revealed that three variants (c.1400T>C, c.1420G>C, c.1691G>A) resulted in a loss of the punctate membrane pattern typical of wild‐type SLC5A2. All variants had a significantly lower transport capacity in than the wild‐type control. The current study provides a starting point to further investigate the molecular mechanism of SLC5A2 in FRG families and provides functional clues for antidiabetes drugs.     

Upregulated SLC1A5 promotes cell growth and survival in colorectal cancer

Glutamine metabolism is essential for tumorigenesis of colorectal cancer, cancer cells remodel their glutamine metabolic pathways to fuel rapid proliferation. SLC1A5 is an important transporter of glutamine various cancer cells. In this study, we investigated SLC1A5 protein expression in colorectal cancer and evaluated its clinical significance and functional importance. Immunohistochemical analysis was performed on tissue microarrays containing 90 pairs of cancer and adjacent normal tissues from colorectal cancer patients, we found that SLC1A5 expression increased significantly in colorectal cancer compared with normal mucosa tissues (P < 0.001). We further validated SLC1A5 overexpression in 12 pairs of fresh cancer and adjacent normal mucosa tissues from colorectal cancer patients by Western blot (P < 0.05). SLC1A5 expression levels were strongly associated with T stage of tumor (P < 0.05), and the tubular adenocarcinoma subtype (P < 0.001). Moreover, downregulation of SLC1A5 by synthetic siRNA could suppress proliferation and induce apoptosis in colorectal cancer cell lines HT29 and HCT116. In conclusion, our results provide for the first time the differential expression in human colorectal cancer and normal tissues, and a functional link between SLC1A5 expression and growth and survival of colorectal cancer, making it an attractive target in colorectal cancer treatment.     

The SLC2 family of facilitated hexose and polyol transporters

The SLC2 family of glucose and polyol transporters comprises 13 members, the glucose transporters (GLUT) 1–12 and the H⁺-myo-inositol cotransporter (HMIT). These proteins all contain 12 transmembrane domains with both the amino and carboxy-terminal ends located on the cytoplasmic side of the plasma membrane and a N-linked oligosaccharide side-chain located either on the first or fifth extracellular loop. Based on sequence comparison, the GLUT isoforms can be grouped into three classes: class I comprises GLUT1–4; class II, GLUT6, 8, 10, and 12 and class III, GLUT5, 7, 9, 11 and HMIT. Despite their sequence similarity and the presence of class-specific signature sequences, these transporters carry various hexoses and HMIT is a H⁺/myo-inositol co-transporter. Furthermore, the substrate transported by some isoforms has not yet been identified. Tissue- and cell-specific expression of the well-characterized GLUT isoforms underlies their specific role in the control of whole-body glucose homeostasis. Numerous studies with transgenic or knockout mice indeed support an important role for these transporters in the control of glucose utilization, glucose storage and glucose sensing. Much remains to be learned about the transport functions of the recently discovered isoforms (GLUT6–13 and HMIT) and their physiological role in the metabolism of glucose, myo-inositol and perhaps other substrates.An erratum to this article can be found at     

Immunohistochemical detection of a specific receptor for lipocalin2 (solute carrier family 22 member 17, SLC22A17) and its prognostic significance in endometrial carcinoma

Background

We previously reported the overexpression of lipocalin2 (LCN2), a 25 kDa secretory protein involved in iron-transportation, in endometrial carcinoma and its possible contribution to endometrial carcinogenesis. Recently, a specific receptor for LCN2, solute carrier family 22 member 17 (SLC22A17), was identified. The present study was undertaken to investigate the expression of SLC22A17 in endometrial carcinoma.

Methods

The expression of the SLC22A17 and LCN2 proteins was examined immunohistochemically using 69 cases of endometrial carcinoma and adjacent normal endometrial tissues. Immunoreactivity was evaluated according to the percentage of positive cells and described as a positivity index (PI, full score 100).

Results

The expression of SLC22A17 was negligible in normal endometria, but positive staining for SLC22A17 (PI ≧ 1) was observed in 35 cases of endometrial carcinoma. The PI for SLC22A17 was significantly higher in cases with histological grade 3 (P < 0.0005), advanced FIGO stage (P = 0.002), deep myometrial invasion (P = 0.029), positive lymph-vascular space invasion (P = 0.029), positive intraperitoneal cytology (P = 0.020) and adnexal metastasis (P = 0.029). The expression of SLC22A17 and LCN2 was positively correlated with a significant difference (P = 0.002), and the patients who overexpressed both SLC22A17 and LCN2 showed poorer survival than those without the expression of SLC22A17 or LCN2 (P = 0.002). Moreover, the overexpression of both SLC22A17 and LCN2 was indicated to be an independent prognostic factor by multivariable analysis.

Conclusions

These results suggested that SLC22A17, in cooperation with LCN2, to be involved in the acquisition of aggressive behavior among endometrial carcinoma cells.