Branched-chain Aminotransferase Research Articles

BCAT1 redox function maintains mitotic fidelity.

The metabolic enzyme branched-chain amino acid transaminase 1 (BCAT1) drives cell proliferation in aggressive cancers such as glioblastoma. Here, we show that BCAT1 localizes to mitotic structures and has a non-metabolic function as a mitotic regulator. Furthermore, BCAT1 is required for chromosome segregation in cancer and induced pluripotent stem cells and tumor growth in human cerebral organoid and mouse syngraft models. Applying gene knockout and rescue strategies, we show that the BCAT1 CXXC redox motif is crucial for controlling cysteine sulfenylation specifically in mitotic cells, promoting Aurora kinase B localization to centromeres, and securing accurate chromosome segregation. These findings offer an explanation for the well-established role of BCAT1 in promoting cancer cell proliferation. In summary, our data establish BCAT1 as a component of the mitotic apparatus that safeguards mitotic fidelity through a moonlighting redox functionality.

Reprograming of proteasomal degradation by branched chain amino acid metabolism.

Branched-chain amino acid (BCAA) metabolism is a central hub for energy production and regulation of numerous physiological processes. Controversially, both increased and decreased levels of BCAAs are associated with longevity. Using genetics and multi-omics analyses in Caenorhabditis elegans, we identified adaptive regulation of the ubiquitin-proteasome system (UPS) in response to defective BCAA catabolic reactions after the initial transamination step. Worms with impaired BCAA metabolism show a slower turnover of a GFP-based proteasome substrate, which is suppressed by loss-of-function of the first BCAA catabolic enzyme, the branched-chain aminotransferase BCAT-1. The exogenous supply of BCAA-derived carboxylic acids, which are known to accumulate in the body fluid of patients with BCAA metabolic disorders, is sufficient to regulate the UPS. The link between BCAA intermediates and UPS function presented here sheds light on the unexplained role of BCAAs in the aging process and opens future possibilities for therapeutic interventions.

Inhibitory Effects of Gabapentin on the Proliferation and Cell Motility of Hepatocellular Carcinoma Cells

Background: Gabapentin, originally an antiepileptic agent, was found to have anti-cancer activity on multiple cancer cells. However, its effects on hepatocellular carcinoma (HCC) and associated molecular mechanisms are unclear. Objectives: In this study, we investigated the anti-cancer effects of gabapentin against HCC cells in vitro and in vivo. Methods: Human HCC cells were inoculated with various levels of gabapentin for 24 and 48 h. We utilized the MTT assay to detect the proliferation of HCC cells after gabapentin treatment. The effect of gabapentin on the migration of HCC cells was detected by transwell migration assay. We established a model of subcutaneously transplanted HCC in nude mice and observed the impact of gabapentin on HCC cell tumorigenicity in vivo. The changes in RNA expression in gabapentin-treated HCC cells were evaluated by RNA sequencing analysis, and the results were analyzed and further validated by qRT-PCR. Results: Gabapentin significantly inhibited the proliferation of a variety of human HCC cells in a time- and dose-dependent approach. After treatment with 10 mM gabapentin for 12 h, the transendothelial migration of HCC cells via membrane remarkably reduced. Three weeks after the hypodermic transplanting of HCC in nude mice with Huh7 cell line, the gabapentin-treated group had a dramatic decrease in mean tumor volume and weight relative to the controls. Relative to the normal Huh7 cell line, the results of RNA sequencing of Huh7 cells treated with gabapentin for 24 h showed the differential enrichment of genes involved in "energy metabolism", "cancers", "signal transduction", and "folding, sorting, and degradation". The genes CDH11 and ARHGAP15 related to cell migration were further verified by qRT-PCR. Conclusions: Our results suggested that gabapentin has an inhibitory effect on the growth, migration, and tumor formation of hepatoma cells, and the mechanism of gabapentin’s inhibition on HCC cells may be related to some signaling pathways, which will lay a foundation for the future studies on branched-chain aminotransferase 1 (BCAT1) as a target for HCC treatment.

Substrate specificity of branched chain amino acid aminotransferases: The substitution of glycine to serine in the active site determines the substrate specificity for α-ketoglutarate

A branched chain aminotransferase from Thermoproteus tenax has been identified, cloned, over-expressed and biochemically characterised. A molecular modelling approach has been used to predict the 3D structure allowing its comparison with other related enzymes. This enzyme has high similarity to a previously characterised aminotransferase from Thermoproteus uzoniensis however its substrate specificity shows key differences towards the substrate α-ketoglutarate. Examination of the active sites of the two related enzymes reveals a single amino acid substitution of a glycine residue to a serine residue which could be responsible for this difference. When Gly104 in T. tenax was mutated to a serine residue and the resultant enzyme characterised, this single amino acid change resulted in a dramatic reduction in activity towards α-ketoglutarate with an 18-fold reduction in Vmax and a 20-fold Km increase, resulting in a 370-fold lower catalytic efficiency. Structural comparisons between the two related Thermoproteus enzymes and another branched chain aminotransferase from Geoglobus acetivorans has revealed that the serine residue affects the flexibility of a key loop involved in catalysis. This subtle difference has provided further insight into our understanding of the substrate specificity of these industrially important enzymes.

The proatherosclerotic function of BCAT1 in atherosclerosis development of aged-apolipoprotein E-deficient mice

Atherosclerosis (AS) is an inflammatory vascular disease. Branched-chain amino acid transaminase 1 (BCAT1) has been implicated in inflammatory diseases, while its role in AS is unclear yet. In ApoE−/− mice with a high fat diet (HDF), BCAT1 was highly up-regulated and more pronounced in aged than in young ApoE−/− mice, which was abundantly expressed in macrophages located in AS lesions. The function of BCAT1 in AS was explored using lentivirus-mediated BCAT1 overexpression. ApoE−/− mice fed a HFD with BCAT1 overexpression exhibited the worsening lipid deposition and pathological injury of aortic tissues, accompanied by aggravated hyperlipidemia as proved by increased serum triglyceride, total cholesterol, and low-density lipoprotein-cholesterol levels. Immunohistochemical staining of vascular cell adhesion molecule-1 (VCAM-1), monocyte chemoattractant protein-1 (MCP-1), and CD68 in the aortic root plaque suggested that BCAT1 overexpression could induce monocyte-endothelial cell adhesion and macrophages infiltration, thereby contributing inflammatory response by promoting TNF-α, IL-6, and IL-1β expression. Further, in vivo experiments, lipid accumulation, and inflammatory response induced by oxidized-LDL in RAW267.4 cells were also intensified or alleviated by BCAT1 overexpression or knockdown. Finally, BCAT1 overexpression aggravated AS development. These adverse effects of BCAT1 on hyperlipidemia, lipid accumulation, foaming cell formation, and inflammation suggested that the modulation of BCAT1 might be a potential approach to prevent AS disease.

Magnetic Nanoparticle-Based Electrochemical Sensing Platform Using Ferrocene-Labelled Peptide Nucleic Acid for the Early Diagnosis of Colorectal Cancer.

Diagnostic biomarkers based on epigenetic changes such as DNA methylation are promising tools for early cancer diagnosis. However, there are significant difficulties in directly and specifically detecting methylated DNA regions. Here, we report an electrochemical sensing system based on magnetic nanoparticles that enable a quantitative and selective analysis of the methylated septin9 (mSEPT9) gene, which is considered a diagnostic marker in early stage colorectal cancer (CRC). Methylation levels of SEPT9 in CRC samples were successfully followed by the selective recognition ability of a related peptide nucleic acid (PNA) after hybridization with DNA fragments in human patients’ serums and plasma (n = 10). Moreover, this system was also adapted into a point-of-care (POC) device for a one-step detection platform. The detection of mSEPT9 demonstrated a limit of detection (LOD) value of 0.37% and interference-free measurement in the presence of branched-chain amino acid transaminase 1 (BCAT1) and SRY box transcription factor 21 antisense divergent transcript 1 (SOX21-AS1). The currently proposed functional platform has substantial prospects in translational applications of early CRC detection.

The mechanism of branched-chain amino acid transferases in different diseases: Research progress and future prospects.

It is well known that the enzyme catalyzes the first step of branched-chain amino acid (BCAA) catabolism is branched-chain amino transferase (BCAT), which is involved in the synthesis and degradation of leucine, isoleucine and valine. There are two main subtypes of human branched chain amino transferase (hBCAT), including cytoplasmic BCAT (BCAT1) and mitochondrial BCAT (BCAT2). In recent years, the role of BCAT in tumors has attracted the attention of scientists, and there have been continuous research reports that BCAT plays a role in the tumor, Alzheimer’s disease, myeloid leukaemia and other diseases. It plays a significant role in the growth and development of diseases, and new discoveries about this gene in some diseases are made every year. BCAT usually promotes cancer proliferation and invasion by activating the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin pathway and activating Wnt/β-catenin signal transduction. This article reviews the role and mechanism of BCAT in different diseases, as well as the recent biomedical research progress. This review aims to make a comprehensive summary of the role and mechanism of BCAT in different diseases and to provide new research ideas for the treatment, prognosis and prevention of certain diseases.

Branched-chain amino acid transaminase 1 inhibition attenuates childhood asthma in mice by effecting airway remodeling and autophagy

Childhood asthma is a common chronic childhood disease. Branched-chain amino acid transaminase 1 (BCAT1) was reported to be upregulated in chronic airway diseases, while its role in childhood asthma is unclear. Asthma mouse models were established in neonatal mice by 10 µg ovalbumin (OVA) intraperitoneal injection and 3% OVA inhalational challenge. In OVA-challenged mice, BCAT1 levels were upregulated. BCAT1 inhibitor alleviated airway structure and inflammation by suppressing IgE, OVA-specific IgE and inflammatory cytokine release and inflammatory cell infiltration. BCAT1 inhibitor alleviated airway remodeling by inhibiting goblet cell hyperplasia, mucus secretion and the expression of α-SMA and collagen I/III. The BCAT1 inhibitor prevented OVA-enhanced autophagy by decreasing Beclin-1, Atg5 and LC3I/II and increasing p65 levels. In IL-13-stimulated BEAS-2B cells, rapamycin promoted inflammatory cytokine release and autophagy after BCAT1 inhibitor administration. Our research revealed that BCAT1 was upregulated in neonatal asthmatic mice and that a BCAT1 inhibitor might restrain airway inflammation and remodeling by decreasing autophagy, which offered a novel mechanistic understanding of childhood asthma.

Enhancement of BCAT2-Mediated Valine Catabolism Stimulates β-Casein Synthesis via the AMPK-mTOR Signaling Axis in Bovine Mammary Epithelial Cells.

Valine, a kind of branched-chain amino acid, plays a regulatory role beyond that of a building block in milk protein synthesis. However, the underlying molecular mechanism through which valine stimulates β-casein synthesis has not been clarified. Therefore, our study aimed to evaluate the effect of valine on β-casein synthesis and shed light into the molecular mechanism using an in vitro model. Results showed that valine supplementation significantly increased β-casein synthesis in bovine mammary epithelial cells (BMECs). Meanwhile, the supplementation of valine resulted in high levels of branched-chain aminotransferase transaminase 2 (BCAT2), TCA-cycle intermediate metabolites, and ATP, AMP-activated protein kinase (AMPK) inhibition, and mammalian target of rapamycin (mTOR) activation. Furthermore, the inhibition of BCAT2 decreased the β-casein synthesis and downregulated the AMPK-mTOR pathway, with similar results observed for AMPK activation. Together, the present data indicate that valine promotes the synthesis of β-casein by affecting the AMPK-mTOR signaling axis and that BCAT2-mediated valine catabolism is the key target.

Circular RNA VPS18 Promotes Glioblastoma Progression by Regulating miR-1229-3p/BCAT1 Axis.

Circular RNAs (circRNAs) have been verified to play important roles in malignant tumors, including glioblastoma. The aim of this study is to explore the biological roles and underlying mechanisms of circRNA vacuolar protein sorting 18 homolog (circVPS18) in glioblastoma. A quantitative real-time polymerase chain reaction (qRT-PCR) was performed to measure the expression of circVPS18, microRNA (miR)-1299-3p, and branched-chain amino acid transaminase 1 (BCAT1). In vitro experiments were conducted using 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, transwell, and tube formation assays, respectively. Western blot was conducted to examine all protein levels. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were employed to confirm the interaction between miR-1229-3p and circVPS18 or BCAT1. The murine xenograft model was established to conduct in vivo assay. CircVPS18 and BCAT1 were highly expressed while miR-1229-3p was lowly expressed in glioblastoma tissues and cells. CircVPS18 knockdown inhibited glioblastoma progression by inhibiting cell proliferation, migration, invasion, and angiogenesis, and promoting cell apoptosis. Moreover, miR-1229-3p could be targeted by circVPS18; inhibition of miR-1229-3p could invert the suppressive effect of circVPS18 knockdown on glioblastoma tumorigenesis. Furthermore, BCAT1 was a target of miR-1229-3p; functionally, BCAT1 overexpression could reverse the inhibitory effects of miR-1229-3p upregulation on glioblastoma cell malignant phenotypes. Moreover, we also verified that circVPS18A could regulate BCAT1 expression by sponging miR-1229-3p. Additionally, circVPS18 silencing also restrained tumor growth and metastasis in vivo. CircVPS18 accelerated glioblastoma progression by miR-1229-3p/BCAT1 axis, providing a potential therapeutic target for glioblastoma.

Small Molecule Inhibitors in Adult High-Grade Glioma: From the Past to the Future.

Glioblastoma is the most common primary malignant tumor in the brain and has a dismal prognosis despite patients accepting standard therapies. Alternation of genes and deregulation of proteins, such as receptor tyrosine kinase, PI3K/Akt, PKC, Ras/Raf/MEK, histone deacetylases, poly (ADP-ribose) polymerase (PARP), CDK4/6, branched-chain amino acid transaminase 1 (BCAT1), and Isocitrate dehydrogenase (IDH), play pivotal roles in the pathogenesis and progression of glioma. Simultaneously, the abnormalities change the cellular biological behavior and microenvironment of tumor cells. The differences between tumor cells and normal tissue become the vulnerability of tumor, which can be taken advantage of using targeted therapies. Small molecule inhibitors, as an important part of modern treatment for cancers, have shown significant efficacy in hematologic cancers and some solid tumors. To date, in glioblastoma, there have been more than 200 clinical trials completed or ongoing in which trial designers used small molecules as monotherapy or combination regimens to correct the abnormalities. In this review, we summarize the dysfunctional molecular mechanisms and highlight the outcomes of relevant clinical trials associated with small-molecule targeted therapies. Based on the outcomes, the main findings were that small-molecule inhibitors did not bring more benefit to newly diagnosed glioblastoma, but the clinical studies involving progressive glioblastoma usually claimed “noninferiority” compared with historical results. However, as to the clinical inferiority trial, similar dosing regimens should be avoided in future clinical trials.

Obese Skeletal Muscle-Expressed Interferon Regulatory Factor 4 Transcriptionally Regulates Mitochondrial Branched-Chain Aminotransferase Reprogramming Metabolome.

In addition to the significant role in physical activity, skeletal muscle also contributes to health through the storage and use of macronutrients associated with energy homeostasis. However, the mechanisms of regulating integrated metabolism in skeletal muscle are not well-defined. Here, we compared the skeletal muscle transcriptome from obese and lean control subjects in different species (human and mouse) and found that interferon regulatory factor 4 (IRF4), an inflammation-immune transcription factor, conservatively increased in obese subjects. Thus, we investigated whether IRF4 gain of function in the skeletal muscle predisposed to obesity and insulin resistance. Conversely, mice with specific IRF4 loss in skeletal muscle showed protection against the metabolic effects of high-fat diet, increased branched-chain amino acids (BCAA) level of serum and muscle, and reprogrammed metabolome in serum. Mechanistically, IRF4 could transcriptionally upregulate mitochondrial branched-chain aminotransferase (BCATm) expression; subsequently, the enhanced BCATm could counteract the effects caused by IRF4 deletion. Furthermore, we demonstrated that IRF4 ablation in skeletal muscle enhanced mitochondrial activity, BCAA, and fatty acid oxidation in a BCATm-dependent manner. Taken together, these studies, for the first time, established IRF4 as a novel metabolic driver of macronutrients via BCATm in skeletal muscle in terms of diet-induced obesity.

Abstract 2179: Increased BCAT1 expression creates a pseudo-hypoxic environment that promotes cell proliferation in a subtype of glioblastoma

Abstract Background: BCAT1 (Branched Chain Amino Transferase 1) has been shown to be upregulated in human IDH (isocitrate dehydrogenase) wild-type glioblastoma (GBM) and BCAT1 knockdown leads to reduced cell proliferation in vitro and in vivo1. Here we investigated the role of BCAT1 in human patient-derived glioblastoma cells and the corresponding orthotopically implanted xenografts to understand how upregulation of the enzyme leads to a more aggressive phenotype. Methods: The expression of BCAT1 was investigated in a panel of patient derived IDH wild-type glioblastoma cells and BCAT1 expression modulation was achieved using lentiviral expression of a doxycycline-inducible shRNA, to knockdown BCAT1 and expression of a BCAT1 cDNA to overexpress BCAT1. Effects of BCAT1 knockdown and overexpression were investigated in vitro in cell culture and in vivo, following intracranial implantation of mice with the relevant cells. Results: Variable levels of BCAT1 expression were identified in different patient-derived cell lines. RNA sequencing analysis of BCAT1 knockdown in BCAT1 expressing glioblastoma cells revealed that knockdown led to significant downregulation of HIF 1α (Hypoxia Inducible Factor 1α) and its targets, which was confirmed by Western Blot analysis of Carbonic Anhydrase IX (CAIX) and Hexokinase II (HKII) in cell and tumor lysates. The opposite was observed following BCAT1 overexpression. BCAT1 knockdown also led to higher DNA demethylation levels. Treatment with membrane permeant dimethyl-alpha ketoglutarate mimicked the effect of BCAT1 knockdown. These data suggest that decreased cell proliferation following BCAT1 knockdown in BCAT1 expressing cells is mediated by accumulation of alpha-ketoglutarate, a substrate of BCAT1. Cells that had no BCAT1 expression showed a similar growth profile and overexpression had no effect on proliferation, suggesting that these cells are not dependent on BCAT1 expression. Conclusion: We conclude that in a subtype of GBM characterized by upregulated BCAT1, BCAT1 expression results in lowered levels of alpha-ketoglutarate, leading to reduced prolyl hydroxylase activity and stabilization of HIF 1α and therefore a pseudo-hypoxic state, resulting in a transcriptome that favors a high proliferation rate. This makes BCAT1 a potential therapeutic target, for tumors that show BCAT1 upregulation.1. Tönjes M, Barbus S, Park YJ, et al. BCAT1 promotes cell proliferation through amino acid catabolism in gliomas carrying wild-type IDH1. Nat Med. 2013;19(7):901-908. doi:10.1038/nm.3217 Citation Format: Maria Fala, Susana Ros, Ashley Sawle, Kevin M. Brindle. Increased BCAT1 expression creates a pseudo-hypoxic environment that promotes cell proliferation in a subtype of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2179.

Abstract 3617: METTL16 drives leukemogenesis and maintains leukemia stem cell self-renewal via reprogramming BCAA metabolism

Abstract Background: As the most prevalent internal decorations in mammalian mRNA, N6-methyladenosine (m6A) has been reported to be involved in many physiological and pathological processes, including acute myeloid leukemia (AML). METTL3 and METTL14, the well-recognized m6A methyltransferase complex, contribute to AML. METTL16 is a recently identified m6A methyltransferase that has been reported to deposit m6A in a few targets. While, unlike METTL3/14, the biological functions of METTL16 are largely unknown. Here, we explored the function and mechanism of METTL16 in AML pathogenesis and evaluated its therapeutic potential for AML treatment. Methods: We performed CRISPR-Cas9 screen to evaluate the dependency of METTL16 in AML cells. We created METTL16 knockout (KO) cells and conditional KO mice to evaluate its role in leukemogenesis and normal hematopoiesis. We employed bone marrow transplantation (BMT), xenograft, and AML patient-derived xenograft (PDX) models to determine its role in AML development and progression. To identify the targets of METTL16, we performed m6A-seq and RNA-seq, followed m6A-qPCR, CLIP-qPCR, in vitro methyltransferase assays and RNA stability assays. To examine the effect of METTL16 on branched chain amino acid (BCAA) metabolism, we performed metabolic profiling with 13C, 15N-leucine. Results: CRISPR-Cas9 screen showed METTL16 is one of the most essential genes for the survival of AMLs. The AML cells display more robust dependency on METTL16 than METTL3/14. We found METTL16 is highly expressed in AML patients compared to healthy controls. METTL16 KO significantly inhibited AML cell proliferation, promoted cell apoptosis and myeloid differentiation in vitro, which could be totally reversed by forced expression of wild-type METTL16, but not catalytic-dead mutant. METTL16 depletion dramatically inhibited AML progression and prolonged survival of recipient mice in the BMT, xenograft and PDX models. In addition, METTL16 is highly expressed in LSCs contrast to leukemic bulk cells and METTL16 KO significantly attenuates LSC self-renewal in vitro and in vivo. By contrast, the role of METLL16 is largely spared in normal hematopoietic cells. Via integrated analysis of m6A-seq data and RNA-seq data, we identified two bona fide targets of METTL16, BCAT1 and BCAT2, which encode two critical BCAA transaminases in BCAA biosynthesis pathway. METTL16 promotes the expression of BCAT1 and BCAT2 via an m6A dependent manner. Metabolomics with 13C, 15N-leucine tracing showed that METTL16 KO results in suppressed pools of TCA cycle intermediates, some non-essential amino acids and nucleotides. Conclusion: We uncover a tumor-promoting role of METTL16 in AML and LSC self-renewal via reprogramming BCAA metabolism, in which METTL16 functions as an m6A methyltransferase to regulate expression of BCAT1 and BCAT2. Our data suggest that METTL16 is an attractive target for AML therapy. Citation Format: Li Han, Lei Dong, Keith Leung, Zhicong Zhao, Yangchan Li, Ying Qing, Jianhuang Xue, Chao Shen, Zhenhua Chen, Lei Gao, Kitty Wang, Keren Zhou, Wei Li, Brandon Tan, Zheng Zhang, Xi Qin, Rui Su, Xiaolan Deng, Jianjun Chen. METTL16 drives leukemogenesis and maintains leukemia stem cell self-renewal via reprogramming BCAA metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3617.

BCAT1 promotes osteoclast maturation by regulating branched-chain amino acid metabolism

Branched-chain aminotransferase 1 (BCAT1) transfers the amine group on branched-chain amino acids (BCAAs) to alpha-ketoglutarate. This generates glutamate along with alpha-keto acids that are eventually oxidized to provide the cell with energy. BCAT1 thus plays a critical role in sustaining BCAA concentrations and availability as an energy source. Osteoclasts have high metabolic needs during differentiation. When we assessed the levels of amino acids in bone marrow macrophages (BMMs) that were undergoing receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation, we found that the BCAA levels steadily increase during this process. In vitro analyses then showed that all three BCAAs but especially valine were needed for osteoclast maturation. Moreover, selective inhibition of BCAT1 with gabapentin significantly reduced osteoclast maturation. Expression of enzymatically dead BCAT1 also abrogated osteoclast maturation. Importantly, gabapentin inhibited lipopolysaccharide (LPS)-induced bone loss of calvaria in mice. These findings suggest that BCAT1 could serve as a therapeutic target that dampens osteoclast formation.

Characterization of a lactic acid bacteria using branched-chain amino acid transaminase and protease from Jinhua Ham and application in myofibrillar protein model

This study was to screen a strain with both branched-chain amino acid transaminase (BCAT) and protease activities for producing methyl-branched flavor compounds in a myofibrillar protein extract model. Lactic acid bacteria (LAB) was isolated from Jinhua ham and screened with BCAT activity by an electrochemical sensor and protease activity by the agar plate method. In the culture medium, strain L6 was selected with high utilization rate and characteristic metabolites content of branched-chain amino acids (BCAAs), and identified as Lactobacillus fermentum YZU-06 (L. fermentum). Compared with the previously reported L. plantarum, L. fermentum exhibited an excellent capacity of hydrolyzing myofibrillar protein with the higher contents of free amino acids, peptides and small molecular weight proteins. Moreover, L. fermentum group presented more BCAAs metabolites of 2-methylbutanal and 3-methylbutanal than that of L. plantarum group. In conclusion, L. fermentum YZU-06 is a promising starter culture to improve the flavor of fermented meat products.

Impaired expression of BCAT1 relates to muscle atrophy of mouse model of sarcopenia

BackgroundThe underlying mechanism of muscle atrophy in sarcopenia is still not fully understood; branched chain aminotransferase 1(BCAT1) isocitrate dehydrogenase-1 encodes an evolutionarily conserved cytoplasmic aminotransferase for glutamate and branched-chain amino acids (BCAAs), thus constituting a regulatory component of cytoplasmic amino and keto acid metabolism. In human gliomas carrying wild-type isocitrate dehydrogenase-1, BCAT1 promotes cell proliferation through amino acid catabolism. Hence, the goals of this study were to unravel the potential role of BCAT1 expression in muscle atrophy and to explore the mechanisms underlying this process.MethodsWe first measured Bcat1 expression by RT-qPCR and western blotting in murine and cellular models of muscle atrophy. To understand how the Bcat1-driven changes sustained muscle cell growth, we analyzed reactive oxygen species (ROS) levels and activation of the mTORC1/S6K1 pathway in muscle cells. Furthermore, we performed Cell Counting Kit-8(CCK8) assays and fluorescence staining to evaluate growth rate of cells and ROS levels. Finally, we verified that depletion of Bcat1 impairs the growth rate of muscle cells and increases ROS levels, indicating that muscle atrophy resulted from the downregulation of the mTORC1/S6K1 pathway. Data were analyzed by two-tailed unpaired Student’s t-test or Mann-Whitney U test for two groups to determine statistical significance. Statistical analyses were performed using GraphPad Prism version 6.0 and SPSS 16.0 software.ResultsBcat1 expression level in skeletal muscles was lower in murine and cellular models of sarcopenia than in the control groups. Bcat1 knockdown not only suppressed the growth of muscle cells but also increased the production of ROS. Impaired cell growth and increased ROS production was rescued by co-introduction of an shRNA-resistant Bcat1 cDNA or addition of the mTORC1 stimulator MYH1485. Muscle cells with Bcat1 knockdown featured lower mTORC1 and S6K1 phosphorylation (pS6K1) than NT muscle cells. Addition of either shRNA-resistant Bcat1 cDNA or MYH1485 rescued the suppression of cell growth, increase in ROS production, and decrease in pS6K1.ConclusionsThe branched chain amino acids catabolic enzyme BCAT1 is essential for the growth of muscle cells. BCAT1 expression contributes to sustained growth of muscle cells by activating mTOR signaling and reducing ROS production.

A comparative transcriptomics and eQTL approach identifies SlWD40 as a tomato fruit ripening regulator.

Although multiple vital genes with strong effects on the tomato (Solanum lycopersicum) ripening process have been identified via the positional cloning of ripening mutants and cloning of ripening-related transcription factors (TFs), recent studies suggest that it is unlikely that we have fully characterized the gene regulatory networks underpinning this process. Here, combining comparative transcriptomics and expression QTLs, we identified 16 candidate genes involved in tomato fruit ripening and validated them through virus-induced gene silencing analysis. To further confirm the accuracy of the approach, one potential ripening regulator, SlWD40 (WD-40 repeats), was chosen for in-depth analysis. Co-expression network analysis indicated that master regulators such as RIN (ripening inhibitor) and NOR (nonripening) as well as vital TFs including FUL1 (FRUITFUL1), SlNAC4 (NAM, ATAF1,2, and CUC2 4), and AP2a (Activating enhancer binding Protein 2 alpha) strongly co-expressed with SlWD40. Furthermore, SlWD40 overexpression and RNAi lines exhibited substantially accelerated and delayed ripening phenotypes compared with the wild type, respectively. Moreover, transcriptome analysis of these transgenics revealed that expression patterns of ethylene biosynthesis genes, phytoene synthase, pectate lyase, and branched chain amino transferase 2, in SlWD40-RNAi lines were similar to those of rin and nor fruits, which further demonstrated that SlWD40 may act as an important ripening regulator in conjunction with RIN and NOR. These results are discussed in the context of current models of ripening and in terms of the use of comparative genomics and transcriptomics as an effective route for isolating causal genes underlying differences in genotypes.

The Oncogene MYC Regulates the Branched Chain Amino Acid Metabolism and mTOR Signaling in Diffuse Large B Cell Lymphoma

Diffuse large B‐cell Lymphoma (DLBCL) is the most common type of aggressive non‐Hodgkin lymphoma (NHL) worldwide. While therapeutic strategies to combat DLBCL have advanced, these malignancies continue to be challenging to treat due to their heterogeneity and frequently recurring mutations. Aberrations in the oncogene MYC are commonly found in high grade DLBCL and are associated with poor responses to standard therapy.In search of downstream targets of MYC in DLBCL, we found MYC‐binding sites in the promoter regions of BCAT1, BCAT2, and BCKDHA. These genes encode enzymes in the metabolism of the branched chain amino acids (BCAAs), and they have been previously linked to cancer progression. BCAT1 and 2 encode the cytosolic (BCATc) and mitochondrial (BCATm) branched‐chain aminotransferases, while BCKDHA encodes the E1α subunit of the branched‐chain ketoacid dehydrogenase complex. We hypothesized that MYC activates these genes in DLBCL tissues leading to upregulation of BCAA metabolism and lymphoma growth.Human tissues collected from DLBCL patients (n=89) or controls (n=33) were used to analyze the gene expression of MYC, BCAT1, BCAT2 and BCKDHA followed by correlative analysis of the expression of these genes and the survival of DLBCL patients. Next, human DLBCL and B‐lymphoblast (control) cells were treated with the MYC inhibitor 10058‐F4 (0, 25, 50, 100 µM), the BCAA antagonist N‐acetyl leucine amide (NALA, 0, 10, 20, 40 mM) and the BCATc inhibitor gabapentin (0, 5, 10, 20 mM). 24 hours post treatment, the cell viability and cell proliferation, as well as the protein expression of BCATc, BCATm, and E1α, and the total and phosphorylation states of the ribosomal protein S6 (a downstream target of the mammalian target of rapamycin, mTOR) were determined.Results showed that the gene expression of BCAT1, BCAT2and BCKDHA were significantly elevated in tumor tissues from DLBCL patients compared to controls, and there was a positive correlation between their expression and the upregulation of MYC in DLBCL tissues. The high expression of MYC and BCAT2, but not that of BCAT1 and BCKDHA, correlated with poor overall cancer survival. Inhibiting the MYC function by 10058‐F4, the BCAA uptake by NALA, and the BCATc activity by gabapentin led to concentration dependent reductions in the cell viability and proliferation of the DLBCL cells. The protein expression of BCATm and E1α were reduced in the presence of 10058‐F4, which correlated with downregulation of mTOR signaling as measured by the deceased phosphorylation state of S6 in treated DLBCL cells. These results support the hypothesis that MYC is an upstream regulator of genes associated with BCAA metabolism. The results also demonstrate that DLBCL cells need MYC and BCAAs to upregulate mTOR signaling and to survive and may represent a new molecular mechanism via which MYC exerts its effects in DLBCL lymphoma.

Targeting the Cytosolic Branched Chain Aminotransferase (BCATc) for T Cell Driven Anti‐Lymphoma Immunotherapy

The lymphoma microenvironment is a dynamic network between lymphoma cells and non‐malignant components that may promote tumor growth and consequently drug resistance. Progress in T cell metabolism has demonstrated that T cells experience metabolic disadvantage in the tumor microenvironment, which commonly manifests in T cell exhaustion and jeopardizes their potential to destroy cancer cells. We identified the cytosolic branched chain aminotransferase (BCATc) as a novel metabolic checkpoint of T cell activation. BCATc catalyzes the first step in the degradation of the essential amino acid leucine, which is a well‐known activator of complex 1 of the mammalian target of rapamycin (mTORC1). In T cells, BCATc is induced upon T cell activation and is a part of a negative feedback loop regulation of mTORC1. Based on extensive earlier research, we proposed that BCATc exerts immunosuppressive properties in the tumor microenvironment and we hypothesized that deleting BCATc from T cells renders them effective in eradicating lymphoma tumors.By using our newly designed mouse model with BCATc deleted from CD4+ and CD8+ T cells (T‐BCATcKO mice), we performed tumor studies where male and female mice were subcutaneously injected with 2.5x105 murine EL‐4 lymphoma cells [n=8] or phosphate‐buffered saline [n=4‐6]. As controls, mice expressing the floxed BCATc gene (T‐BCATcfl/flmice, n=9) were used. Tumor growth, body weight, and food intake were monitored for up to 15 days followed by collection of tumor tissues and organs. In addition, CD4+ T cells were isolated from spleens of T‐BCATcfl/fl and T‐BCATcKO mice, activated with a plate‐bound anti‐CD3 and soluble anti‐CD28 and left untreated or treated with 5 mM gabapentin (a competitive inhibitor of BCATc) or 10 mM N‐acetyl‐leucine amide (NALA, a structural analog of leucine) for 24‐72 hours to measure changes in the secretion of interferon gamma (IFNγ) from T helper 1 (Th1) cells or the expression of Foxp3, a master activator of regulatory T cells (CD4+CD25+ T reg cells).Deletion of BCATc from T cells or inhibition of the BCATc activity by gabapentin caused a significant increase in the secretion of IFNγ from Th1 cells after 24‐72 hours of activation, while CD4+CD25+ T reg cells expressed reduced levels of Foxp3 in response to gabapentin. In contrast, NALA blocked the IFNγ secretion and caused an increase in the expression of Foxp3. Following tumor inoculation, the T‐BCATcKO mice demonstrated a significant delay in tumor appearance and growth (~50 % reduction in tumor volumes) and the final tumor masses were reduced by 25% compared to control mice. None of the animals differed in body, organ weights or food intake and deletion of BCATc from T cells did not lead to systemic overactivation of the immune system. This study revealed that deleting BCATc from T cells may offer an advantage to better fight lymphoma and identified BCATc as a new therapeutic target to improve the efficiency of checkpoint inhibitors and help increase the low rates of remission seen in lymphoma patients.