Alternative titles; symbols
HGNC Approved Gene Symbol: SLC16A1
SNOMEDCT: 715830008, 766715000;
Cytogenetic location: 1p13.2 Genomic coordinates (GRCh38): 1:112,911,847-112,956,196 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 1p13.2 | Erythrocyte lactate transporter defect | 245340 | Autosomal dominant | 3 |
| Hyperinsulinemic hypoglycemia, familial, 7 | 610021 | Autosomal dominant | 3 | |
| Monocarboxylate transporter 1 deficiency | 616095 | Autosomal dominant; Autosomal recessive | 3 |
The SLC16A1 gene encodes a monocarboxylate transporter (MCT1) that mediates the movement of lactate and pyruvate across cell membranes. Import and export of these substrates by tissues such as erythrocytes, muscle, intestine, and kidney are ascribed largely to the action of a proton-coupled MCT (Garcia et al., 1994).
In a Chinese hamster ovary (CHO) cell line, Kim et al. (1992) identified a mutant protein, designated Mev, that acted as a mevalonate transporter. The corresponding cDNA was isolated by an expression cloning strategy and found to encode a protein with 12 putative membrane-spanning regions. The cloned mutant 'mevalonate transporter' differed from its wildtype progenitor by 1 amino acid in the tenth membrane-spanning region, which changed a phenylalanine (wildtype) to a cysteine (mutant). The mutant cells were heterozygous for this dominant gain-of-function mutation. The finding that the wildtype cDNA did not elicit increased mevalonate transport in transfected cells suggested that the wildtype protein is a transporter for a molecule other than mevalonate (i.e., lactate). The mRNA transcribed from the wildtype gene was expressed in highest levels in heart. Subsequent studies by Garcia et al. (1994) showed that the wildtype protein, which they designated MCT1, could transport lactate, pyruvate, and related monocarboxylates. MCT1 exhibited properties resembling those of the erythrocyte MCT, including proton symport, transacceleration, and sensitivity to alpha-cyanocinnamates. The amino acid sequence of MCT1 did not resemble that of any known protein, suggesting that MCT1 may represent a new class of solute carriers (solute carrier family 16).
Garcia et al. (1994) isolated cDNA clones corresponding to human MCT1 from a heart cDNA library. The deduced 500-residue protein showed 86% identity to the hamster protein.
Using primers derived from the human heart MCT1 cDNA isolated by Garcia et al. (1994), Ritzhaupt et al. (1998) cloned MCT1 from human colon mRNA. The heart and colon MCT1 cDNAs are identical. Northern blot analysis detected a 3.3-kb transcript in ileal and colonic RNA. Western blot analysis detected MCT1 at an apparent molecular mass of 40 kD in colonic luminal membrane vesicles.
Cuff and Shirazi-Beechey (2002) determined that the SLC16A1 gene contains 5 exons and spans about 44 kb. The first exon is noncoding, and the first intron is more than 26 kb long. The promoter region lacks a TATA box, but it contains potential binding sites for several transcription factors.
Garcia et al. (1994) mapped the SLC16A1 gene to chromosome 1p13.2-p12 by PCR analysis of panels of human/rodent cell hybrid lines and by fluorescence in situ hybridization.
Using radiolabeled lactate, Ritzhaupt et al. (1998) examined the properties of the L-lactate transporter in human and pig colonic luminal membrane vesicles. L-lactate uptake was stimulated in the presence of an outward-directed anion gradient at an extravesicular pH of 5.5. Transport of L-lactate into anion-loaded colonic membrane vesicles appeared to be via a proton-activated, anion exchange mechanism. L-lactate uptake was competitively inhibited by pyruvate, butyrate, propionate, and acetate, but not by Cl- or SO4(2-), and it was pharmacologically inhibited by several mercurial compounds. Based on these findings, Ritzhaupt et al. (1998) concluded that MCT1 is the protein responsible for L-lactate transport into colonic luminal membrane vesicles.
Lee et al. (2012) showed that the most abundant lactate transporter in the central nervous system, MCT1 (also known as SLC16A1), is highly enriched within oligodendroglia and that disruption of this transporter produces axon damage and neuron loss in animal and cell culture models. In addition, this same transporter is reduced in patients with, and in mouse models of, amyotrophic lateral sclerosis (ALS; see 105400), suggesting a role for oligodendroglial MCT1 in pathogenesis. Lee et al. (2012) concluded that the role of oligodendroglia in axon function and neuron survival has been elusive; this study defines a new fundamental mechanism by which oligodendroglia support neurons and axons.
In a genomewide haploid genetics screen to identify resistance mechanisms to 3-bromopyruvate (3-BrPA), a cancer drug candidate that inhibits glycolysis, Birsoy et al. (2013) identified the SLC16A1 gene product, MCT1, as the main determinant of 3-BrPA sensitivity. MCT1 is necessary and sufficient for 3-BrPA uptake by cancer cells. Breast cancer cell lines with high amounts of MCT1 protein were sensitive to 3-BrPA, whereas those with low or no MCT1 concentration were resistant to even high concentrations of 3-BrPA. SLC16A1 mRNA levels were most elevated in glycolytic cancer cells. Forced MCT1 expression in 3-BrPA-resistant cancer cells sensitized tumor xenografts to 3-BrPA treatment in vivo.
Using RNA sequencing to characterize the transcriptional program of phagocytes actively engulfing apoptotic cells, Morioka et al. (2018) identified a genetic signature involving 33 members of the solute carrier family of membrane transport proteins, in which expression is specifically modulated during efferocytosis, but not during antibody-mediated phagocytosis. Morioka et al. (2018) assessed the functional relevance of these solute carriers in efferocytic phagocytes and observed a robust induction of an aerobic glycolysis program, initiated by SLC2A1 (138140)-mediated glucose uptake, with concurrent suppression of the oxidative phosphorylation program. The different steps of phagocytosis, 'smell' (find-me signals or sensing factors released by apoptotic cells), 'taste' (phagocyte-apoptotic cell contact), and 'ingestion' (corpse internalization), activated distinct and overlapping sets of genes, including several SLC genes, to promote glycolysis. SLC16A1 was upregulated after corpse uptake, increasing the release of lactate, a natural by-product of aerobic glycolysis. Whereas glycolysis within phagocytes contributed to actin polymerization and the continued uptake of corpses, lactate released via SLC16A1 promoted the establishment of an antiinflammatory tissue environment. Morioka et al. (2018) concluded that their data revealed an SLC program that is activated during efferocytosis, identified a reliance on aerobic glycolysis during apoptotic cell uptake, and showed that glycolytic by-products of efferocytosis can influence surrounding cells.
Tasdogan et al. (2020) demonstrated that metabolic differences among melanoma cells confer differences in metastatic potential as a result of differences in the function of the MCT1 transporter. In vivo isotope tracing analysis in patient-derived xenografts revealed differences in nutrient handling between efficiently and inefficiently metastasizing melanomas, with circulating lactate being a more prominent source of tumor lactate in efficient metastasizers. Efficient metastasizers had higher levels of MCT1, and inhibition of MCT1 reduced lactate uptake. MCT1 inhibition had little effect on the growth of primary subcutaneous tumors, but resulted in depletion of circulating melanoma cells and reduced the metastatic disease burden in patient-derived xenografts and in mouse melanomas. In addition, inhibition of MCT1 suppressed the oxidative pentose phosphate pathway and increased levels of reactive oxygen species. Antioxidants blocked the effects of MCT1 inhibition on metastasis. MCT1-high and MCT1-null/low cells from the same melanomas had similar capacities to form subcutaneous tumors, but MCT1-high cells formed more metastases after intravenous injection. Tasdogan et al. (2020) concluded that metabolic differences among cancer cells thus confer differences in metastatic potential as metastasizing cells depend on MCT1 to manage oxidative stress.
Erythrocyte Lactate Transporter Defect
In a patient with erythrocyte lactate transporter defect (245340) originally reported by Fishbein (1986), Merezhinskaya et al. (2000) identified a heterozygous mutation in the SLC16A1 gene (600682.0001). Two additional patients were found to be heterozygous for another SLC16A1 mutation (600682.0002). All 3 patients had erythrocyte lactate clearance rates that were 40 to 50% of normal control values. The authors suggested that homozygous individuals would be more severely compromised.
Hyperinsulinemic Hypoglycemia 7
In affected members of 2 Finnish families, previously examined by Otonkoski et al. (2003) and segregating autosomal dominant exercise-induced hyperinsulinemic hypoglycemia (610021) mapping to chromosome 1p, Otonkoski et al. (2007) identified a 163G-A transition (600682.0003) in the noncoding exon 1 and a 25-bp duplication (600682.0004), in the promoter region of the SLC16A1 gene, respectively. In a German proband previously reported by Meissner et al. (2001), they identified several sequence variants, including a 2-bp insertion. All 3 mutations were located within the binding sites of several transcription factors; patient fibroblasts displayed abnormally high SLC16A1 transcript levels, although monocarboxylate transport activities were not changed in those cells, reflecting additional posttranscriptional control of MCT1 levels in extrapancreatic tissues. In contrast, functional studies in beta cells demonstrated that these mutations resulted in increased protein binding to the corresponding promoter elements and a marked (3- to 10-fold) increase in transcription. Thus, promoter-activating mutations in patients with hyperinsulinemic hypoglycemia induce SLC16A1 expression in beta cells, where this gene is not usually transcribed, permitting pyruvate uptake and pyruvate-stimulated insulin release despite ensuing hypoglycemia. Otonkoski et al. (2007) stated that this represented a novel disease mechanism based on the failure of cell-specific transcriptional silencing of a gene that is highly expressed in other tissues.
Quintens et al. (2008) noted that repression of certain ubiquitously expressed housekeeping genes is necessary in pancreatic beta cells, in order to prevent the insulin toxicity that might result from exocytosis under conditions when circulating insulin is unwanted, citing low-K(m) hexokinases (see HK1, 142600) and monocarboxylic acid transporters (MCTs) as examples. The absence of MCTs in beta cells explains the so-called 'pyruvate paradox' whereby pyruvate, despite being an excellent substrate for mitochondrial ATP production, does not stimulate insulin release when added to beta cells. The importance of this disallowance is exemplified by patients who have gain-of-function MCT1 promoter mutations and loss of the pyruvate paradox, with resultant exercise-induced inappropriate insulin release.
Using immunohistochemistry in mouse testis, Mannowetz et al. (2012) showed that Bsg (109480) was expressed in elongating spermatid cytoplasm and sperm tails, whereas Emb (615669) localized in sperm tails only. Mct1 was detectable in spermatozoa tails and plasma membranes of both spermatocytes and spermatids, whereas Mct2 (603654) was present in sperm tails and cytoplasm of Sertoli cells. The distribution of Bsg, Emb, Mct1, and Mct2 differed in epididymis and epididymal sperm. Bsg colocalized with Mct1 and Mct2 in spermatozoa, but Emb did not colocalize and was detected in the principal piece and the acrosome. Immunoblot analysis showed that in epididymal sperm, Bsg was expressed as a 51-kD protein, Emb as a 40-kD protein, Mct1 as a 40- to 48-kD protein, and Mct2 as a 40-kD protein. Mct1 and Mct2 coimmunoprecipitated with Bsg, but not Emb, in cauda sperm preparations. Functional analysis showed that Mct1 and Mct2 were active and provided the cells with L-lactate. Mannowetz et al. (2012) proposed that BSG interacts with MCT1 and MCT2 to locate them properly in the membrane of spermatogenic cells and that this may enable sperm to use lactate as an energy substrate.
Monocarboxylate Transporter 1 Deficiency
In 9 patients with monocarboxylate transporter-1 deficiency (MCT1D; 616095) manifest as severe ketoacidosis, Van Hasselt et al. (2014) identified 8 mutations (7 frameshift or termination mutations and 1 missense mutation affecting the catalytic site) in the MCT1 gene. Three patients had homozygous mutations, and 6 had heterozygous mutations. Eight patients with MCT1 mutations were identified from a cohort of 96 patients with recurrent ketoacidosis in whom known ketolytic defects had been ruled out enzymatically. The initial patient underwent whole-exome sequencing, which identified the homozygous MCT1 mutation; the patients in the cohort were screened by Sanger sequencing of MCT1, MCT2 (SLC16A7; 603654), MCT3 (SLC16A8; 610409), and MCT4 (SLC16A3; 603877), as well as BSG (109480), which interacts with MCT1.
In a patient with erythrocyte lactate transporter defect (245340) originally reported by Fishbein (1986), Merezhinskaya et al. (2000) identified a heterozygous 610A-G transition in the SLC16A1 gene, resulting in a lys204-to-glu (K204E) substitution in a highly conserved residue. The substitution occurs in the early part of the large central cytoplasmic loop between transmembrane segments 6 and 7. The substitution was not identified in 90 healthy control individuals. Erythrocyte lactate clearance was 40 to 50% that of normal control values.
In 2 unrelated male patients with erythrocyte lactate transporter defect (245340), Merezhinskaya et al. (2000) identified a heterozygous 1414G-A transition in the SLC16A1 gene, resulting in a gly472-to-arg (G472R) substitution halfway along the cytoplasmic C-terminal chain. The substitution is not conserved, but was not identified in 90 healthy control individuals. Erythrocyte lactate clearance was 40 to 50% that of normal control values.
In affected members of a Finnish family segregating autosomal dominant exercise-induced hyperinsulinemic hypoglycemia (610021), including the female patient originally reported by Meissner et al. (2001), Otonkoski et al. (2007) identified heterozygosity for a 163G-A transition in exon 1 of the SLC16A1 gene, located within a binding site for nuclear matrix protein-1 (RAD21; 606462) and predicted to disrupt the binding sites of 2 potential transcriptional repressors. The mutation was not found in 92 Finnish and German controls. Functional studies in beta cells demonstrated increased protein binding to the corresponding promoter elements, resulting in a 3-fold increase in transcription.
In affected members of a Finnish family segregating autosomal dominant exercise-induced hyperinsulinemic hypoglycemia (610021), Otonkoski et al. (2007) identified heterozygosity for a 25-bp insertion at nucleotide -24 of the SLC16A1 gene, introducing additional binding sites for the ubiquitous transcription factors SP1 (189906), USF (see 191523), and MXF1 (194550). The mutation was not found in 92 Finnish and German controls. Functional studies in beta cells demonstrated increased protein binding to the corresponding promoter elements, resulting in a 10-fold increase in transcription.
In an 8-year-old girl, born to consanguineous Syrian parents, who presented at 3.5 months of age with severe ketoacidosis indicative of monocarboxylate transporter-1 deficiency (MCT1D; 616095), van Hasselt et al. (2014) identified a homozygous single-nucleotide insertion in the MCT1 gene (c.41dupC) that resulted in a frameshift at asp15 (Asp15fs). Both healthy parents were heterozygous for the mutation. The child had 5 episodes of profound ketosis. She had microcephaly and developed moderate intellectual disability. Cardiac ultrasound revealed atrial septal defect as well as hypoplastic left pulmonary artery. The mutation was not identified in the 1000 Genomes Project or Exome Variant Server databases.
In a 21-year-old female, born to unrelated Irish parents, who presented at 1 year of age with profound ketoacidosis (MCT1D; 616095), van Hasselt et al. (2014) identified a homozygous c.937C-T transition in the MCT1 gene, resulting in an arg313-to-ter (R313X) substitution. Both healthy parents were heterozygous for the mutation. The patient had had 4 ketotic events. She had moderate intellectual disability and developed epilepsy.
In a 9-year-old male, born to third-degree Turkish cousins, who presented at 23 months of age with profound ketoacidosis (MCT1D; 616095), van Hasselt et al. (2014) identified a homozygous c.982C-T transition in the MCT1 gene, resulting in an arg328-to-ter (R328X) substitution. Both healthy parents were heterozygous for the mutation. In addition to the single episode of profound ketoacidosis, the patient had mild intellectual disability. He was born with a cleft palate and had coughing attacks during exercise.
In a 10-year-old boy with ketoacidosis with massive ketonuria and a history of cyclic vomiting (MCT1D; 616095), van Hasselt et al. (2014) identified a heterozygous c.586C-T transition in the MCT1 gene, resulting in an arg196-to-ter (R196X) substitution. The patient, who was born to unrelated British parents, had normal development but developed migraines.
In 2 sibs of British origin, born to nonconsanguineous parents, with monocarboxylate transporter-1 deficiency (MCT1D; 616095), van Hasselt et al. (2014) identified a heterozygous 4-bp deletion in the MCT1 gene (747_750del) leading to a frameshift mutation at asn250 (N250). The 20-year-old brother had had 10 ketotic events associated with massive ketonuria; his initial presentation was at 3 years 8 months of age, and his last was at 14 years. He also had migraines. Development was normal. His 22-year-old sister had her first of 5 ketotic episodes at 6 years 3 months of age and experienced ketoacidosis with massive ketonuria. She had also experienced pregnancy-related vomiting. Development was normal, and she had no other clinical features.
In an 11-year-old female, born to unrelated British parents, who experienced 5 ketotic events associated with exaggerated ketotic hypoglycemia and ketoacidosis with massive ketonuria (MCT1D; 616095), van Hasselt et al. (2014) identified a heterozygous single-basepair deletion at nucleotide 499 (c.499del) resulting in frameshift at val167 (Val167fs). The patient presented at 1.5 years of age. Development was normal, and she had no other clinical features.
In a 10-year-old boy, born to unrelated Dutch parents, who had experienced 4 episodes of ketoacidosis with massive ketonuria (MCT1D; 616095), van Hasselt et al. (2014) identified a heterozygous single-basepair insertion (c.490dupC) in the MCT1 gene, resulting in a frameshift at leu164 (Leu164fs). The patient's first ketotic episode occurred at 3 years 2 months of age. Development was intact, and he had short stature.
In a 22-year-old male of Dutch ancestry who had had 5 episodes of ketoacidosis with massive ketonuria (MCT1D; 616095), a history of cyclic vomiting, and exercise intolerance, van Hasselt et al. (2014) identified heterozygosity for a c.938G-A transition in the MCT1 gene, resulting in an arg313-to-gln (R313Q) substitution. The mutation was located at the catalytic site of the enzyme. The patient presented with his first ketotic episode at 2 years 6 months of age, and his last episode occurred at 6 years 5 months of age.
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