Monocarboxylate Transporter Genes Research Articles

MCT1 plays crucial roles in conidiation, lactate metabolism and pathogenicity in Colletotrichum gloeosporioides

Monocarboxylate transporters (MCTs) play vital roles in carbon source assimilation, drug resistance, and virulence. However, the underlying function of MCTs in fungal pathogenesis and development has not been investigated in detail. In this study, we identified and characterized the monocarboxylate transporter gene MCT1 of Colletotrichum gloeosporioides, which is the causal agent of Glomerella leaf spot of apple. Mct1 is localized to the mitochondria and may mediate the uptake of lactate to the cell. However, MCT1 was constitutively expressed but showed an enhanced expression level in response to the presence of the extracellular lactate. Our results indicate that Mct1 plays a role in the metabolism of lactate. More importantly, the Δmct1 mutant showed significantly poor conidiation and a defect in host infection. Taken together, our studies provide evidence for Mct1 as a mitochondrial transmembrane protein mediating conidiation, the metabolism of lactate, and the pathogenicity of C. gloeosporioides.

Mycoparasitism illuminated by genome and transcriptome sequencing of Coniothyrium minitans, an important biocontrol fungus of the plant pathogen Sclerotinia sclerotiorum.

Coniothyrium minitans is a mycoparasite of the notorious plant pathogen Sclerotinia sclerotiorum. To further understand the parasitism of C. minitans, we assembled and analysed its genome and performed transcriptome analyses. The genome of C. minitans strain ZS-1 was assembled into 350 scaffolds and had a size of 39.8 Mb. A total of 11 437 predicted genes and proteins were annotated, and 30.8 % of the blast hits matched proteins encoded by another member of the Pleosporales, Paraphaeosphaeria sporulosa, a worldwide soilborne fungus with biocontrol ability. The transcriptome of strain ZS-1 during the early interaction with S. sclerotiorum at 0, 4 and 12 h was analysed. The detected expressed genes were involved in responses to host defenses, including cell-wall-degrading enzymes, transporters, secretory proteins and secondary metabolite productions. Seventeen differentially expressed genes (DEGs) of fungal cell-wall-degrading enzymes (FCWDs) were up-regulated during parasitism, with only one down-regulated. Most of the monocarboxylate transporter genes of the major facilitator superfamily and all the detected ABC transporters, especially the heavy metal transporters, were significantly up-regulated. Approximately 8 % of the 11 437 proteins in C. minitans were predicted to be secretory proteins with catalytic activity. In the molecular function category, hydrolase activity, peptidase activity and serine hydrolase activity were enriched. Most genes involved in serine hydrolase activity were significantly up-regulated. This genomic analysis and genome-wide expression study demonstrates that the mycoparasitism process of C. minitans is complex and a broad range of proteins are deployed by C. minitans to successfully invade its host. Our study provides insights into the mechanisms of the mycoparasitism between C. minitans and S. sclerotiorum and identifies potential secondary metabolites from C. minitans for application as a biocontrol agent.

Genetic variations in the monocarboxylate transporter genes (SLC16A1, SLC16A3, and SLC16A11) in the Japanese population

MCT1 (SLC16A1), MCT4 (SLC16A3), and MCT11 (SLC16A11) are members of the monocarboxylate transporter (MCT) family. MCT1 and MCT4 transport pH-related monocarboxylates, such as lactate and pyruvate. MCT11 may also be a proton-coupled monocarboxylate transporter. Although alterations of these substrates are involved in the pathology of cancer and diabetes, little is known about MCT polymorphisms. In this study, genetic variation was evaluated in SLC16A1, SLC16A3, and SLC16A11 in the Japanese population (healthy volunteers, n = 92). Polymorphisms in the coding regions of the SLC16A1, SLC16A3, and SLC16A11 genes were screened by DNA sequencing. A single polymorphism that caused a change in the amino acid sequence was found in SLC16A1 (rs1049434 (T1470A, D490E)) and in SLC16A3 (rs368788465 (C641T, S214F)). Five polymorphisms were detected in the SLC16A11 gene (rs117767867 (G337A, V113I), rs13342692 (A380G, D127G), rs13342232 (T561C, silent), rs75418188 (G1018A, G340S), and rs75493593 (C1327A, P443T)). This information for a healthy population provides a comparison for further studies of patients with various diseases such as cancer and diabetes.

BcMctA, a putative monocarboxylate transporter, is required for pathogenicity in Botrytis cinerea.

Monocarboxylate transporters have a central role in mammalian metabolism, but rarely reported in phytopathogenic fungi. In this study, a putative monocarboxylate transporter gene in Botrytis cinerea [B. cinerea MctA (BcMctA)] was identified in the research of a B. cinerea transfer DNA (T-DNA) insertional mutant (74). Disruption of the gene decreased the growth rate on the medium with monocarboxylate (acetate or pyruvate) as the sole carbon sources, but not affected on lactate. The pyruvate contents in BcmctA deletion mutants decreased about 35% compared with the wild strain. Besides, the conidial yield was increased about two times in BcmctA disruption mutant. The pathogenicity assay indicated that disruption of BcmctA significantly reduced the virulence of B. cinerea on cucumber and tomato leaves. Our results demonstrated that BcMctA is related to pyruvate uptake and pathogenicity of B. cinerea on cucumber and tomato leaves.

Genetic variations in monocarboxylate transporter genes as predictors of clinical outcomes in non-small cell lung cancer.

Non-small cell lung cancer (NSCLC) is characterized by poor prognosis and only a few molecular markers may be potentially used to predict clinical outcomes. Previous studies have demonstrated that monocarboxylate transporters (MCTs) play important roles in the development and progression of many cancers. The purpose of this study was to assess the effects of single nucleotide polymorphisms (SNPs) of MCT genes on prognosis of NSCLC patients in Chinese Han population. Nine functional SNPs in MCT1, MCT2, and MCT4 genes were selected and genotyped using Sequenom iPLEX genotyping system in 500 Chinese NSCLC patients receiving surgery. Multivariate Cox proportional hazards model and Kaplan-Meier curve were used for the prognostic analysis. TT genotype of SNP rs1049434 (MCT1) was significantly associated with better overall survival (OS) (HR = 0.56, P = 0.026) and recurrence-free survival (RFS) (HR = 0.57, P = 0.016) of NSCLC patients. TT genotype of another SNP rs995343 (MCT2) exhibited an association with worse RFS of NSCLC patients (HR = 1.46, P = .039). Unfavorable genotypes of SNP rs1049434 and rs995343 showed a significant cumulative effect on OS and RFS of NSCLC patients. Moreover, we found that patients carrying AA+AT genotypes of rs1049434 showed significant OS and RFS benefits from adjuvant chemotherapy, but those with TT genotype did not. Our findings suggest that SNPs in MCT1 and MCT2 genes may affect clinical outcomes and can be used to predict the response to adjuvant chemotherapy in NSCLC patients who received surgical treatment once validated in future study.

Polymorphisms of monocarboxylate transporter genes are associated with clinical outcomes in patients with colorectal cancer.

Previous studies have demonstrated that monocarboxylate transporters (MCTs) play important roles in the development and progression of many cancers. The purpose of this study was to assess the effects of single-nucleotide polymorphisms (SNPs) of MCT genes on prognosis of colorectal cancer (CRC) patients. Nine functional SNPs in three MCT genes (MCT1, MCT2 and MCT4) were selected and genotyped using Sequenom iPLEX genotyping system in 697 Chinese CRC patients receiving surgery. Multivariate Cox proportional hazards model and Kaplan-Meier curve were used for the prognostic analysis. One SNP (MCT1: rs1049434/exon) was significantly associated with overall survival of CRC patients (HR 0.74; P = 0.046). Two other SNPs (MCT1: rs60844753/5' near gene and MCT2: rs995343/intron) exhibited associations with recurrence-free survival of CRC patients (HR 0.67; P = 0.078 and HR 0.74; P = 0.036, respectively). Our study also showed that MCT1 rs1049434, rs60844753 and MCT2 rs995343 SNPs had a cumulative effect on CRC recurrence-free survival (P for trend 0.011). Those who carrying three unfavorable genotypes (WW for all SNPs) had a 2.06-fold increased risk of recurrence compared with patients carrying no unfavorable genotypes (P = 0.016). Moreover, we found that patients carrying no <2 risk genotypes showed significant OS and RFS benefits from adjuvant chemotherapy. Our findings suggest that SNPs in MCT1 and MCT2 genes may affect clinical outcomes and can be used to predict the response to adjuvant chemotherapy in CRC patients who received surgical treatment once validated in future study.

Monocarboxylate transporter genes in the mammary gland of lactating cows

This study is the first to examine the expression of the 14 monocarboxylate transporter genes (MCT1-MCT14) in the mammary gland of mammals. RT-PCR, Western blot, immunohistochemistry, and immunofluorescence confocal laser microscopy were applied in a comprehensive approach to assess the expression and cellular localization of MCTs in the mammary gland of lactating cattle. RT-PCR revealed the existence of nine MCT isoforms, namely MCT1, MCT2, MCT3, MCT4, MCT5, MCT8, MCT10, MCT13, and MCT14 in cow mammary gland. The amplified cDNA segments were confirmed by sequence analysis and deposited in the GenBank. Using the commercially available antibodies against MCT1-MCT8, Western blotting verified the protein expression of MCT1, MCT2, MCT3, MCT4, MCT5, and MCT8 in the cow mammary gland. The precise cellular localization of the identified MCT proteins showed that both MCT1 and MCT2 were basolaterally localized on the cow mammary alveolar epithelial cells. In contrast, MCT4 protein signal was expressed on the apical membrane of these alveolar epithelia. MCT8, however, was predominantly localized on the basolateral membranes of the lactocytes, along with its weak labeling on the apical membrane of the same cells. No immunoreactive staining for MCT3 and MCT5 proteins could be detected histochemically in lactating bovine mammary tissue. Additionally, we proved the colocalization of CD147 with both MCT1 and MCT4 on the boundaries of the cow mammary alveolar epithelia. The existence and localization pattern of MCT genes in the mammary gland of lactating cows suggest their possible involvement in the transport of essential elements required for milk synthesis and secretion.

Evolution and functional divergence of monocarboxylate transporter genes in vertebrates

Monocarboxylate transporters (MCTs) form a gene family with an ancient past. The identification of MCTs (MCHs) from bacteria, protozoa, fungi, invertebrates, as well as vertebrates, but not from plants and virus, allowed illuminating the phylogenetic and evolutionary history of this gene family. The significant expansion of vertebrate MCT genes should have primarily occurred after the divergence of vertebrates and invertebrates, but before the divergence time between ray-finned fish and mammals. The divergence of insect MCTs should have at least occurred in the common ancestor of fruit fly, beetle, and honeybee. Fungi monocarboxylate transporter homologues (MCHs) might evolve independently from an ancient ancestor. The results of functional divergence analysis provided statistical evidences for shifted evolutionary rate and/or changes of amino acid property after gene duplication. The sliding window analysis of the d N/ d S ratio values showed that strong functional constraints must impose on the N- and C-terminal domains of vertebrate MCTs. These corresponding regions may play crucial roles for functionality of MCT proteins.

Testicular regulation of neuronal glucose and monocarboxylate transporter gene expression profiles in CNS metabolic sensing sites during acute and recurrent insulin-induced hypoglycemia

Recurrent insulin-induced hypoglycemia (RIIH) impairs glucose counter-regulatory function in male humans and rodents and, in the latter, diminishes neuronal activation in CNS structures that monitor metabolic homeostasis, including the lateral hypothalamic area (LHA) and dorsal vagal complex (DVC). We investigated whether habituated neuronal reactivity in CNS sensing sites to hypoglycemia is correlated with modified monocarboxylate and/or glucose uptake by using quantitative real-time RT-PCR to analyze neuronal monocarboxylate transporter (MCT2) and glucose transporter variant (GLUT and GLUT4) gene expression profiles in the microdissected LHA, ventromedial nucleus hypothalamus (VMH), and DVC after one or multiple insulin injections. Because orchidectomy (ORDX) maintains uniform glycemic responses to RIIH in male rats, we also examined whether regional gene response patterns are testes dependent. In the intact male rat DVC, MCT2, GLUT3, and GLUT4 gene expression was not altered by acute hypoglycemia but was enhanced by RIIH. MCT2 and GLUT3 mRNA levels in the ORDX rat DVC did not differ among groups, but GLUT4 transcripts were progressively increased by acute and recurrent hypoglycemia. Precedent hypoglycemia decreased or increased basal MCT2 and GLUT4 gene expression, respectively, in the intact rat LHA; LHA GLUT3 transcription was augmented by RIIH in intact rats only. Acute hypoglycemia suppressed MCT2, GLUT3, and GLUT4 gene expression in the intact rat VMH, a response that was abolished by RIIH. In ORDX rats, VMH gene transcript levels were unchanged in response to one dose of insulin but were selectively diminished during RIIH. These data demonstrate site-specific, testes-dependent effects of acute and recurrent hypoglycemia on neuronal metabolic substrate transporter gene expression in characterized rat brain metabolic sensing loci and emphasize the need to assess the impact of potential alterations in glucose and lactate uptake during RIIH on general and specialized, e.g., metabolic monitoring, functions of neurons in those sites.

A Novel Syndrome Combining Thyroid and Neurological Abnormalities Is Associated with Mutations in a Monocarboxylate Transporter Gene

Thyroid hormones are iodothyronines that control growth and development, as well as brain function and metabolism. Although thyroid hormone deficiency can be caused by defects of hormone synthesis and action, it has not been linked to a defect in cellular hormone transport. In fact, the physiological role of the several classes of membrane transporters remains unknown. We now report, for the first time, mutations in the monocarboxylate transporter 8 (MCT8) gene, located on the X chromosome, that encodes a 613-amino acid protein with 12 predicted transmembrane domains. The propositi of two unrelated families are males with abnormal relative concentrations of three circulating iodothyronines, as well as neurological abnormalities, including global developmental delay, central hypotonia, spastic quadriplegia, dystonic movements, rotary nystagmus, and impaired gaze and hearing. Heterozygous females had a milder thyroid phenotype and no neurological defects. These findings establish the physiological importance of MCT8 as a thyroid hormone transporter.

Lactate Transport and Lactate Transporters in Skeletal Muscle

The study of lactate transport in skeletal muscle had until recently been hampered by the lack of suitable sarcolemmal vesicle preparations. Researchers are now at the threshold of developing some very new understandings about the movement of lactate into and out of skeletal muscle with (a) evidence for a lactate transport system in skeletal muscle, (b) the very recent cloning of several monocarboxylate transporter genes, (c) the expression of at least one monocarboxylate transporter protein that facilitates the transport of lactate in heart and skeletal muscle, and (d) the realization that lactate transport can be altered with changes in chronic muscle activity. The MCT1 expression patterns in metabolically heterogeneous skeletal suggests that a primary role of this lactate transporter is to take up lactate into the oxidative muscle fibers where it may be used as a fuel in mitochondrial oxidation. Increments in both MCT1 and lactate transport with training support this role.