S-adenosylmethionine and proliferation: new pathways, new targets

Comparative effects of dietary methionine and cysteine supplementation on redox status and intestinal integrity in immunologically challenged-weaned pigs

Sulfur-containing amino acids such as methionine and cysteine play critical roles in immune system and redox status. A body of evidence shows that metabolic aspects of supplemented Met and Cys may differ in the body. Therefore, the study aimed to investigate the effects of dietary Met and Cys supplementation in immunologically challenged weaned pigs. Forty weaned piglets (6.5 ± 0.3 kg) were randomly allocated to five treatment groups. The treatment included: (1) sham-challenged control (SCC), (2) challenged control (CC), (3) MET (CC + 0.1% _DL-Met), (4) CYS (CC + 0.1% _L-Cys), and (5) MET + CYS (CC + 0.1% _DL-Met + 0.1% _L-Cys). On day 7, all pigs were intramuscularly injected with either Escherichia coli O55:B5 lipopolysaccharides (LPS) or phosphate-buffered saline. Blood, liver, and jejunum samples were analyzed for immune response and redox status. The CC group had lower (P < 0.05) villus surface area and higher (P < 0.05) flux of 4-kDa fluorescein isothiocyanate dextran (FD4) than the SCC group. A lower (P < 0.05) glutathione (GSH) concentration was observed in the jejunum of pigs in the CC group than those in the SCC group. Dietary Cys supplementation increased (P < 0.05) villus surface area, GSH levels, and reduced (P < 0.05) the flux of FD4 in the jejunum of LPS-challenged pigs. Dietary Met supplementation enhanced (P < 0.05) hepatic GSH content. Pigs challenged with LPS in the MET group had lower serum IL-8 concentration than those in the CC group. There was a Met × Cys interaction (P < 0.05) in serum IL-4 and IL-8 concentrations, and Trolox equivalent antioxidant capacity. Dietary _L-Cys supplementation restored intestinal integrity and GSH levels that were damaged by lipopolysaccharides administration. Dietary _DL-Met supplementation improved hepatic GSH and reduced systemic inflammatory response, but antagonistic interaction with dietary _L-Cys supplementation was observed in the inflammatory response and redox status.

Poor prognosis, hypomethylation, and immune infiltrates are associated with downregulation of INMT in head and neck squamous cell carcinoma

Background: Indiolethylamine-N-methyltransferase (INMT) is a methyltransferase responsible for transferring methyl groups from methyl donor SAM to its substrate. S-adenosyl-l-methionine (SAM), obtained from the methionine cycle, is a naturally occurring sulfonium compound that is vital to cellular metabolism. The expression of INMT is down-regulated in many tumorous tissues, and it may contribute to tumor invasion and metastasis. Nevertheless, the expression of INMT and its relationship to methylation and immune infiltrates in head and neck squamous cell carcinoma (HNSC) remains a mystery. Thus, we evaluated expression, clinicopathological features, prognosis, several critical pathways, DNA methylation, and immune cell infiltration for the first time.

Methods: Analysis of the clinicopathological characteristics of INMT expression, several tumor-related bioinformatics databases were utilized. In addition, the role of INMT expression was analyzed for prognosis. Several INMT-related pathways were enriched on the LinkedOmics website. In addition, we have analyzed the methylation of INMT in HNSC in detail by using several methylation databases. Lastly, the relationship between INMT gene expression and immune infiltration was analyzed with ssGSEA, Timer, and TISIDB.

Results: In HNSC, mRNA and protein levels were significantly lower than in normal tissues. The low expression of INMT was statistically associated with T stage, histological grade, gender, smoking history, and alcohol consumption. HNSC patients with low INMT expression have a poorer OS (overall survival) compared to those with high levels of expression. In addition, the multivariate analysis revealed INMT expression to be a remarkable independent predictor of prognosis in HNSC patients. An analysis of gene enrichment showed that several pathways were enriched in INMT, including the Ras signaling pathway, the cGMP-PKG signaling pathway, and others. Moreover, methylation patterns of INMT detected in a variety of methylation databases are closely associated with mRNA expression and prognosis. Finally, INMT was significantly correlated with immune infiltration levels.

Conclusion: HNSC with low levels of INMT exhibits poor survival, hypomethylation, and immune infiltration. For HNSC, this study presented evidence that INMT is both a biomarker of poor prognosis and a target of immunotherapy.

Effects of Polygonatum sibiricum saponin on hyperglycemia, gut microbiota composition and metabolic profiles in type 2 diabetes mice

Diabetes is a global disease that endangers human health. As reported, saponins are effective bioactive compounds for treating type 2 diabetes mellitus (T2DM) and have nontoxic side effects. This study aimed to examine the hypoglycemic effects of Polygonatum sibiricum saponin (PSS) on T2DM mice. We found that PSS could significantly decrease the levels of insulin secretion and fasting blood glucose (FBG) in T2DM mice. And the level of triacylglycerol (TG), total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) in the blood was decreased. In contrast, the content of high-density lipoprotein cholesterol (HDL-C) was increased. 16S rDNA sequencing was used to evaluate the changes in the gut microbiota of T2DM mice, and metabolites were analyzed by metabolomic profiling. The results showed that PSS could decrease the abundance of Firmicutes in T2DM mice, increase the abundance of Bacteroidetes. It also increased the abundance of some bacterial genera (Lactobacillus, Lachnospiraceae_NK4A136_group and Intestinimonas). The phenotypes of the gut microbiome also changed accordingly. Metabolomics analysis showed that carbohydrate metabolism and amino acid metabolisms, such as L-alanine and L-glutamic acid, were greatly affected by PSS. In addition, the levels of inositol and chlorogenic acid in metabolites also increased significantly under PSS intervention. In general, PSS could exert its hypoglycemic effect, regulate the gut microbiota and affect the metabolism of T2DM mice.

S-Adenosyl-l-Methionine Overcomes uL3-Mediated Drug Resistance in p53 Deleted Colon Cancer Cells

Purpose: In order to study novel therapeutic approaches taking advantage of natural compounds showing anticancer and anti-proliferative effects, we focused our interest on S-adenosyl-l-methionine, a naturally occurring sulfur-containing nucleoside synthesized from adenosine triphosphate and methionine by methionine adenosyltransferase, and its potential in overcoming drug resistance in colon cancer cells devoid of p53. Results: In the present study, we demonstrated that S-adenosyl-l-methionine overcomes uL3-mediated drug resistance in p53 deleted colon cancer cells. In particular, we demonstrated that S-adenosyl-l-methionine causes cell cycle arrest at the S phase; inhibits autophagy; augments reactive oxygen species; and induces apoptosis in these cancer cells. Conclusions: Results reported in this paper led us to propose S-adenosyl-l-methionine as a potential promising agent for cancer therapy by examining p53 and uL3 profiles in tumors to yield a better clinical outcomes.

Methionine Supplementation Affects Metabolism and Reduces Tumor Aggressiveness in Liver Cancer Cells

Liver cancer is one of the most common cancer worldwide with a high mortality. Methionine is an essential amino acid required for normal development and cell growth, is mainly metabolized in the liver, and its role as an anti-cancer supplement is still controversial. Here, we evaluate the effects of methionine supplementation in liver cancer cells. An integrative proteomic and metabolomic analysis indicates a rewiring of the central carbon metabolism, with an upregulation of the tricarboxylic acid (TCA) cycle and mitochondrial adenosine triphosphate (ATP) production in the presence of high methionine and AMP-activated protein kinase (AMPK) inhibition. Methionine supplementation also reduces growth rate in liver cancer cells and induces the activation of both the AMPK and mTOR pathways. Interestingly, in high methionine concentration, inhibition of AMPK strongly impairs cell growth, cell migration, and colony formation, indicating the main role of AMPK in the control of liver cancer phenotypes. Therefore, regulation of methionine in the diet combined with AMPK inhibition could reduce liver cancer progression.

Insights into the SAM Synthetase Gene Family and Its Roles in Tomato Seedlings under Abiotic Stresses and Hormone Treatments

S-Adenosyl-L-methionine (SAM) is a key enzyme involved in many important biological processes, such as ethylene and polyamine biosynthesis, transmethylation, and transsulfuration. Here, the SAM synthetase (SAMS) gene family was studied in ten different plants (Arabidopsis, tomato, eggplant, sunflower, Medicago truncatula, soybean, rice, barley, Triticum urartu and sorghum) with respect to its physical structure, physicochemical characteristics, and post-transcriptional and post-translational modifications. Additionally, the expression patterns of SAMS genes in tomato were analyzed based on a real-time quantitative PCR assay and an analysis of a public expression dataset. SAMS genes of monocots were more conserved according to the results of a phylogenetic analysis and the prediction of phosphorylation and glycosylation patterns. SAMS genes showed differential expression in response to abiotic stresses and exogenous hormone treatments. Solyc01g101060 was especially expressed in fruit and root tissues, while Solyc09g008280 was expressed in leaves. Additionally, our results revealed that exogenous BR and ABA treatments strongly reduced the expression of tomato SAMS genes. Our research provides new insights and clues about the role of SAMS genes. In particular, these results can inform future functional analyses aimed at revealing the molecular mechanisms underlying the functions of SAMS genes in plants.

Effects of S‑adenosyl‑L‑methionine on the invasion and migration of head and neck squamous cancer cells and analysis of the underlying mechanisms

S-Adenosyl-L-methionine (AdoMet) is the principal methyl donor in transmethylation reactions fundamental to sustaining epigenetic modifications. Over the past decade, AdoMet has been extensively investigated for its anti- proliferative, pro-apoptotic and anti-metastatic roles in several types of human cancer. Head and neck squamous cell carcinoma (HNSCC) is the sixth most common type of cancer worldwide, and is an aggressive type of cancer that is associated with a high recurrence rate, metastasis and poor treatment outcomes. The present study demonstrates, for the first time, to the best of our knowledge, that AdoMet induces cell cycle arrest and inhibits the migratory and invasive ability of two different HNSCC cell lines, oral Cal-33 and laryngeal JHU-SCC-011 cells. In both cell lines, AdoMet attenuated cell cycle progression, decreased the protein level of several cyclins and downregulated the expression of p21 cell cycle inhibitor. Moreover, AdoMet was able to inhibit Cal-33 and JHU-SCC-011 cell migration in a dose-dependent manner after 24 and 48 h, respectively, and also induced a significant reduction in the cell invasive ability, as demonstrated by Matrigel invasion assay monitored by the xCELLigence RTCA system. Western blot analysis of several migration and invasion markers confirmed the inhibitory effects exerted by AdoMet on these processes and highlighted AKT, β-catenin and small mothers against decapentaplegic (SMAD) as the main signaling pathways modulated by AdoMet. The present study also demonstrated that the combination of AdoMet and cisplatin synergistically inhibited HNSCC cell migration. Taken together, these findings demonstrate that the physiological compound, AdoMet, affects the motility and extracellular matrix invasive capability in HNSCC. Thus, AdoMet may prove to be a good candidate for future drug development against metastatic cancer.

Structures of catalytic cycle intermediates of the Pyrococcus furiosus methionine adenosyltransferase demonstrate negative cooperativity in the archaeal orthologues

Methionine adenosyltransferases catalyse the biosynthesis of S-adenosylmethionine, the primary methyl group donor in biochemical reactions, through the condensation of methionine and ATP. Here, we report the structural analysis of the Pyrococcus furiosus methionine adenosyltransferase (PfMAT) captured in the unliganded, substrate- and product-bound states. The conformational changes taking place during the enzymatic catalytic cycle are allosterically propagated by amino acid residues conserved in the archaeal orthologues to induce an asymmetric dimer structure. The distinct occupancy of the active sites within a PfMAT dimer is consistent with a half-site reactivity that is mediated by a product-induced negative cooperativity. The structures of intermediate states of PfMAT reported here suggest a distinct molecular mechanism for S-adenosylmethionine synthesis in Archaea, likely consequence of the evolutionary pressure to achieve protein stability under extreme conditions.

Transcriptomic and proteomic analysis reveals mechanisms of low pollen-pistil compatibility during water lily cross breeding

BACKGROUND

In water lily (Nymphaea) hybrid breeding, breeders often encounter non-viable seeds, which make it difficult to transfer desired or targeted genes of different Nymphaea germplasm. We found that pre-fertilization barriers were the main factor in the failure of the hybridization of Nymphaea. The mechanism of low compatibility between the pollen and stigma remains unclear; therefore, we studied the differences of stigma transcripts and proteomes at 0, 2, and 6 h after pollination (HAP). Moreover, some regulatory genes and functional proteins that may cause low pollen-pistil compatibility in Nymphaea were identified.

RESULTS

RNA-seq was performed for three comparisons (2 vs 0 HAP, 6 vs 2 HAP, 6 vs 0 HAP), and the number of differentially expressed genes (DEGs) was 8789 (4680 were up-regulated), 6401 (3020 were up-regulated), and 11,284 (6148 were up-regulated), respectively. Using label-free analysis, 75 (2 vs 0 HAP) proteins (43 increased and 32 decreased), nine (6 vs 2 HAP) proteins (three increased and six decreased), and 90 (6 vs 0 HAP) proteins (52 increased and 38 decreased) were defined as differentially expressed proteins (DEPs). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that the DEGs and DEPs were mainly involved in cell wall organization or biogenesis, S-adenosylmethionine (SAM) metabolism, hydrogen peroxide decomposition and metabolism, reactive oxygen species (ROS) metabolism, secondary metabolism, secondary metabolite biosynthesis, and phenylpropanoid biosynthesis.

CONCLUSIONS

Our transcriptomic and proteomic analysis highlighted specific genes, incuding those in ROS metabolism, biosynthesis of flavonoids, SAM metabolism, cell wall organization or biogenesis and phenylpropanoid biosynthesis that warrant further study in investigations of the pollen-stigma interaction of water lily. This study strengthens our understanding of the mechanism of low pollen-pistil compatibility in Nymphaea at the molecular level, and provides a theoretical basis for overcoming the pre-fertilization barriers in Nymphaea in the future.

S-Adenosyl Methionine and Transmethylation Pathways in Neuropsychiatric Diseases Throughout Life

S-Adenosyl methionine (SAMe), as a major methyl donor, exerts its influence on central nervous system function through cellular transmethylation pathways, including the methylation of DNA, histones, protein phosphatase 2A, and several catecholamine moieties. Based on available evidence, this review focuses on the lifelong range of severe neuropsychiatric and neurodegenerative diseases and their associated neuropathologies, which have been linked to the deficiency/load of SAMe production or/and the disturbance in transmethylation pathways. Also included in this review are the present-day applications of SAMe in the treatment in these diseases in each age group.

S-Adenosylmethionine-mediated apoptosis is potentiated by autophagy inhibition induced by chloroquine in human breast cancer cells

The naturally occurring sulfonium compound S-adenosyl-L-methionine (AdoMet) is an ubiquitous sulfur-nucleoside that represents the main methyl donor in numerous methylation reactions. In recent years, it has been shown that AdoMet possesses antiproliferative properties in various cancer cells, but the molecular mechanisms at the basis of the effect induced by AdoMet have been only in part investigated. In the present study, we found that AdoMet strongly inhibited the proliferation of breast cancer cells MCF-7 by inducing both autophagy and apoptosis. AdoMet consistently enhanced the levels of the autophagy markers beclin-1 and LC3B-II, and caused a significant increase of pro-apoptotic Bax/Bcl-2 ratio paralleled by poly (ADP ribose) polymerase (PARP) and caspase 9, and 6 cleavage. Notably, AdoMet, already at low doses, raised the percentage of cells in G₂ /M phase of cell cycle by down-regulating the expression of cell cycle-regulatory proteins cyclin B and cyclin E with a remarkable increase of p53, p27, and p21. We also evaluated the combination of AdoMet and the autophagy inhibitor chloroquine (CLC) showing that autophagy block is synergistic in inducing both growth inhibition and apoptosis. These effects were paralleled by a strong inhibition of the activity of AKT and of the downstream effector mTOR and by an increased cleavage of caspase-6 and PARP. These data suggest, for the first time, that autophagy can act as an escape mechanism from the apoptotic activity of AdoMet, and that AdoMet could be used in combination with CLC or its analogs in the treatment of breast cancer.

S-adenosylmethionine reduces airway inflammation and fibrosis in a murine model of chronic severe asthma via suppression of oxidative stress

Increased oxidative stress has an important role in asthmatic airway inflammation and remodeling. A potent methyl donor, S-adenosylmethionine (SAMe), is known to protect against tissue injury and fibrosis through modulation of oxidative stress. The aim of this study was to evaluate the effect of SAMe on airway inflammation and remodeling in a murine model of chronic asthma. A mouse model was generated by repeated intranasal challenge with ovalbumin and Aspergillus fungal protease twice a week for 8 weeks. SAMe was orally administered every 24 h for 8 weeks. We performed bronchoalveolar lavage (BAL) fluid analysis and histopathological examination. The levels of various cytokines and 4-hydroxy-2-nonenal (HNE) were measured in the lung tissue. Cultured macrophages and fibroblasts were employed to evaluate the underlying anti-inflammatory and antifibrotic mechanisms of SAMe. The magnitude of airway inflammation and fibrosis, as well as the total BAL cell counts, were significantly suppressed in the SAMe-treated groups. A reduction in T helper type 2 pro-inflammatory cytokines and HNE levels was observed in mouse lung tissue after SAMe administration. Macrophages cultured with SAMe also showed reduced cellular oxidative stress and pro-inflammatory cytokine production. Moreover, SAMe treatment attenuated transforming growth factor-β (TGF-β)-induced fibronectin expression in cultured fibroblasts. SAMe had a suppressive effect on airway inflammation and fibrosis in a mouse model of chronic asthma, at least partially through the attenuation of oxidative stress and TGF-β-induced fibronectin expression. The results of this study suggest a potential role for SAMe as a novel therapeutic agent in chronic asthma.

S-Adenosylmethionine Affects ERK1/2 and Stat3 Pathways and Induces Apotosis in Osteosarcoma Cells

Osteosarcoma is a very aggressive bone tumor. Its clinical outcome remains discouraging despite intensive surgery, radiotherapy, and chemotherapy. Thus, novel therapeutic approaches are demanded. S-Adenosylmethionine (AdoMet) is a naturally occurring molecule that is synthesized in our body by methionine adenosyltransferase isoenzymes and is also available as a nutritional supplement. AdoMet is the principal methyl donor in numerous methylation reactions and is involved in many biological functions. Interestingly, AdoMet has been shown to exert antiproliferative action in various cancer cells. However, the underlying molecular mechanisms are just starting to be studied. Here, we investigated the effects of AdoMet on the proliferation of osteosarcoma U2OS cells and the underlying mechanisms. We carried out direct cell number counting, MTT and flow cytometry-based assays, and immunoblotting experiments in response to AdoMet treatment. We found that AdoMet strongly inhibits proliferation of U2OS cells by slowing-down cell cycle progression and by inducing apoptosis. We also report that AdoMet consistently causes an increase of p53 and p21 cell-cycle inhibitor, a decrease of cyclin A and cyclin E protein levels, and a marked increase of pro-apoptotic Bax/Bcl-2 ratio, with caspase-3 activation and PARP cleavage. Moreover, the AdoMet-induced antiproliferative effects were dynamically accompanied by profound changes in ERK1/2 and STAT3 protein and phosphorylation levels. Altogether, our data enforce the evidence of AdoMet acting as a biomolecule with antiproliferative action in osteosarcoma cells, capable of down-regulating ERK1/2 and STAT3 pathways leading to cell cycle inhibition and apoptosis, and provide a rationale for the possible use of AdoMet in osteosarcoma therapy.

The methyl donor S-adenosylmethionine potentiates doxorubicin effects on apoptosis of hormone-dependent breast cancer cell lines

In this work, we have investigated the antiproliferative effect of AdoMet and Doxorubicin (Doxo), alone or in combination, on different breast cancer cell lines. For the evaluation of synergism, we have calculated the combination index (CI) by the Calcusyn software and we have evaluated the effects of the combination on apoptosis occurrence at FACS analysis in hormone-dependent CG5 cell line. We have found that AdoMet and Doxo given in combination were strongly synergistic in the hormone-dependent CG5 and MCF-7 human breast cancer cell line, as a CI50 < 0.5 was found after 72 h of treatment while the effect was only additive in hormone-independent MDA-MB 231 cells. On the basis of our results, we have selected a combination of AdoMet and Doxo, that was highly synergistic and we have found that the AdoMet in combination with Doxo increased apoptosis induced by Doxo alone, suggesting that the synergism on growth inhibition was largely due to apoptosis. Notably, the AdoMet/Doxo combination induced a significant activation of caspases 3, and 8, while no effect was found on caspase 9 cleavage. In contrast, no significant changes of the expression of cleaved caspase 8 and 9 were found in cells treated with AdoMet and Doxo alone. Moreover, the combination induced a significant increase of Fas and FasL expression. These results highlight the importance of the synergistic effect of AdoMet with Doxo in the regulation of hormone-dependent breast cancer cell proliferation and emphasize the anti-tumor activity of these molecules.

TRAIL-producing NK cells contribute to liver injury and related fibrogenesis in the context of GNMT deficiency

Glycine-N-methyltransferase (GNMT) is essential to preserve liver homeostasis. Cirrhotic patients show low expression of GNMT that is absent in hepatocellular carcinoma (HCC) samples. Accordingly, GNMT deficiency in mice leads to steatohepatitis, fibrosis, cirrhosis, and HCC. Lack of GNMT triggers NK cell activation in GNMT(-/-) mice and depletion of TRAIL significantly attenuates acute liver injury and inflammation in these animals. Chronic inflammation leads to fibrogenesis, further contributing to the progression of chronic liver injury regardless of the etiology. The aim of our study is to elucidate the implication of TRAIL-producing NK cells in the progression of chronic liver injury and fibrogenesis. For this we generated double TRAIL(-/-)/GNMT(-/-) mice in which we found that TRAIL deficiency efficiently protected the liver against chronic liver injury and fibrogenesis in the context of GNMT deficiency. Next, to better delineate the implication of TRAIL-producing NK cells during fibrogenesis we performed bile duct ligation (BDL) to GNMT(-/-) and TRAIL(-/-)/GNMT(-/-) mice. In GNMT(-/-) mice, exacerbated fibrogenic response after BDL concurred with NK1.1(+) cell activation. Importantly, specific inhibition of TRAIL-producing NK cells efficiently protected GNMT(-/-) mice from BDL-induced liver injury and fibrogenesis. Finally, TRAIL(-/-)/GNMT(-/-) mice showed significantly less fibrosis after BDL than GNMT(-/-) mice further underlining the relevance of the TRAIL/DR5 axis in mediating liver injury and fibrogenesis in GNMT(-/-) mice. Finally, in vivo silencing of DR5 efficiently protected GNMT(-/-) mice from BDL-liver injury and fibrogenesis, overall underscoring the key role of the TRAIL/DR5 axis in promoting fibrogenesis in the context of absence of GNMT. Overall, our work demonstrates that TRAIL-producing NK cells actively contribute to liver injury and further fibrogenesis in the pathological context of GNMT deficiency, a molecular scenario characteristic of chronic human liver disease.

Biochemical characterization of a thermostable adenosylmethionine synthetase from the archaeon Pyrococcus furiosus with high catalytic power

Adenosylmethionine synthetase plays a key role in the biogenesis of the sulfonium compound S-adenosylmethionine, the principal widely used methyl donor in the biological methylations. We report here, for the first time, the characterization of adenosylmethionine synthetase from the hyperthermophilic archaeon Pyrococcus furiosus (PfMAT). The gene PF1866 encoding PfMAT was cloned and expressed, and the recombinant protein was purified to homogeneity. PfMAT shares 51, 63, and 82% sequence identity with the homologous enzymes from Sulfolobus solfataricus, Methanococcus jannaschii, and Thermococcus kodakarensis, respectively. PfMAT is a homodimer of 90 kDa highly thermophilic with an optimum temperature of 90 °C and is characterized by remarkable thermodynamic stability (Tm, 99 °C), kinetic stability, and resistance to guanidine hydrochloride-induced unfolding. The latter process is reversible as demonstrated by the analysis of the refolding process by activity assays and fluorescence measurements. Limited proteolysis experiments indicated that the proteolytic cleavage site is localized at Lys148 and that the C-terminal peptide is necessary for the integrity of the active site. PfMAT shows kinetic features that make it the most efficient catalyst for S-adenosylmethionine synthesis among the characterized MAT from Bacteria and Archaea. Molecular and structural characterization of PfMAT could be useful to improve MAT enzyme engineering for biotechnological applications.

Manipulating multi-system of NADPH regulation in Escherichia coli for enhanced S-adenosylmethionine production

NADPH regulation strategies were applied to increase the availability of NADPH in theS-adenosylmethionine biosynthesis, and they are also potentially applicable to various processes for enhancing the NADPH-dependent chemicals production.

Steatosis in the liver

Accumulation of triacylglycerols within the cytoplasm of hepatocytes to the degree that lipid droplets are visible microscopically is called liver steatosis. Most commonly, it occurs when there is an imbalance between the delivery or synthesis of fatty acids in the liver and their disposal through oxidative pathways or secretion into the blood as a component of triacylglycerols in very low density lipoprotein. This disorder is called nonalcoholic fatty liver disease (NAFLD) in the absence of alcoholic abuse and viral hepatitis, and it is often associated with insulin resistance, obesity and type 2 diabetes. Also, liver steatosis can be induced by many other causes including excessive alcohol consumption, infection with genotype 3 hepatitis C virus and certain medications. Whereas hepatic triacylglycerol accumulation was once considered the ultimate effector of hepatic lipotoxicity, triacylglycerols per se are quite inert and do not induce insulin resistance or cellular injury. Rather, lipotoxic injury in the liver appears to be mediated by the global ongoing fatty acid enrichment in the liver, paralleling the development of insulin resistance. A considerable number of fatty acid metabolites may be responsible for hepatic lipotoxicity and liver injury. Additional key contributors include hepatic cytosolic lipases and the "lipophagy" of lipid droplets, as sources of hepatic fatty acids. The specific origin of the lipids, mainly triacylglycerols, accumulating in liver has been unraveled by recent kinetic studies, and identifying the origin of the accumulated triacylglycerols in the liver of patients with NAFLD may direct the prevention and treatment of this condition.

Role of HGF in obesity-associated tumorigenesis: C3(1)-TAg mice as a model for human basal-like breast cancer

Obesity is associated with basal-like breast cancer (BBC), an aggressive breast cancer subtype. The objective of this study was to determine whether obesity promotes BBC onset in adulthood and to evaluate the role of stromal-epithelial interactions in obesity-associated tumorigenesis. We hypothesized that hepatocyte growth factor (HGF) plays a promoting role in BBC, which express the HGF receptor, c-Met. In C3(1)-T(Ag) mice, a murine model of BBC, we demonstrated that obesity leads to a significant increase in HGF secretion and an associated decrease in tumor latency. By immunohistochemical analysis, normal mammary gland exhibited obesity-induced HGF, c-Met and phospho-c-Met, indicating that the activation of the cascade was obesity-driven. HGF secretion was also increased from primary mammary fibroblasts isolated from normal mammary glands and tumors of obese mice compared to lean. These results demonstrate that obesity-induced elevation of HGF expression is a stable phenotype, maintained after several passages, and after removal of dietary stimulation. Conditioned media from primary tumor fibroblasts from obese mice drove tumor cell proliferation. In co-culture, neutralization of secreted HGF blunted tumor cell migration, further linking obesity-mediated HGF-dependent effects to in vitro measures of tumor aggressiveness. In sum, these results demonstrate that HGF/c-Met plays an important role in obesity-associated carcinogenesis. Understanding the effects of obesity on risk and progression is important given that epidemiologic studies imply a portion of BBC could be eliminated by reducing obesity.

Linking metabolism and epigenetic regulation in development of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common form of cancer globally and is rarely curable once detected. The 5-year survival rate of patients diagnosed with late-stage HCC may be as low as 27%. HCC is a cancer largely driven by epigenetic changes that arise from exposure to exogenous environmental factors rather than coding sequence mutations. The liver is susceptible to effects from Hepatitis C and Hepatitis B viruses, exposure to aflatoxin and continuous excessive consumption of alcohol. The liver is a highly metabolic organ balancing many vital biochemical processes; exposure to any of the above environmental factors is associated with loss of liver function and is a major risk factor for the development of HCC. Emerging studies aim to examine the underlying metabolic processes that are abrogated in cancer and lead to the altered flux and availability of key metabolites important for epigenetic processes. Metabolites have been shown to act as substrates for many canonical epigenetic regulators. These enzymes are responsible for regulating histone modification, DNA methylation and micro RNA expression. By studying the impact of altered liver metabolism, we may better understand the long-term epigenetic processes, which lead to the development and progression of HCC.

Conserved SAMS function in regulating egg-laying in C. elegans

S-adenosyl-L-methionine (SAM) is an intermediate metabolite of methionine and serves as the methyl donor for many biological methylation reactions. The synthesis of SAM is catalyzed by SAM synthetase (SAMS), which transfers the adenosyl moiety of adenosine-5'-triphosphate to methionine. In the nematode Caenorhabditis elegans, four sams family genes, sams-1, -3, -4 and -5, are predicted to encode SAMS proteins. However, their physiological roles remain unclear. Here we show that the four predicted SAMS proteins in fact have the ability to catalyze the formation of SAM in vitro, and revealed that only sams-1 mutant animals among the family genes exhibited a significant reduction in egg-laying. Using transgenic animals carrying a transcriptional reporter for each sams gene promoter, we observed that each sams promoter confers a distinct expression pattern with respect to tissue, time of expression and expression level (i.e. promoter specificity). Promoter-swap experiments revealed that the ectopic expression of SAMS-3, -4 or -5 driven by the sams-1 promoter completely rescued egg-laying in sams-1 mutants. These data indicate that SAMS protein function is conserved throughout the entire family.

Methionine metabolic pathway in alcoholic liver injury

PURPOSE OF REVIEW

To outline recent advances in the understanding of the consequences of the alterations in the methionine metabolic pathway and to present new treatment options for alcoholic liver disease (ALD).

RECENT FINDINGS

ALD is a major healthcare problem worldwide. Findings in many laboratories, including ours, have demonstrated that ethanol consumption impairs several of the multiple steps in methionine metabolism that ultimately impairs the activity of many methyltransferases critical for normal functioning of the liver. Recent studies buttress the important role genetics may play in the development and progression of alcoholic liver injury. Treatment modalities using two important metabolites of the pathway, S-adenosylmethionine and betaine, have been shown to attenuate ethanol-induced liver injury in a variety of experimental models of liver disease. S-adenosylmethionine has been used in several clinical studies; however, the outcomes have been unclear and its efficacy in liver diseases continues to be debated. To date, no clinical trials have been conducted for treatment of ALD with betaine.

SUMMARY

Future treatment modalities for ALD should consider loss-of-function polymorphisms in the enzymes of the methionine metabolic and related pathways. Further new treatment modalities for ALD should consider supplementation with betaine that may prove to be a promising therapeutic agent.

High-frequency ultrasound imaging for longitudinal evaluation of non-alcoholic fatty liver disease progression in mice

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of hepatic damage in developed countries. For this reason, mouse models of NAFLD have been developed to show progression of the disease because it perfectly resembles the human pathology. Here we show that diagnostic high-frequency ultrasound imaging (US) may be used as an effective method for monitoring the progression of liver disease, from steatosis to hepatocellular carcinoma in the methionine adenosyl transferase and glycine N-methyltransferase-deficient mice models. US reliably detected murine liver lesions associated with NAFLD in the two mice strains tested, with excellent agreement among US images, gross pathology and histological sections. Our results suggest US as a relevant approach for the study of NAFLD in mice, with interesting technical and therapeutic implications.

Metabolomic analysis of sulfur-containing substances and polyamines in regenerating rat liver

We studied the significance of alterations in the metabolomics of sulfur-containing substances in rapidly regenerating rat livers. Male rats were subjected to two-thirds partial hepatectomy (PHx), and the changes in hepatic levels of major sulfur-containing amino acids and related substances were monitored for 2 weeks. Liver weight began to increase from 24 h after the surgery, and appeared to recover fully in 2 weeks. Serum alanine aminotransferase and aspartate aminotransferase activities were elevated immediately after the surgery and returned slowly to normal levels in 2 weeks. Methionine, S-adenosylmethionine (SAM), cystathionine and cysteine were increased rapidly and remained elevated for longer than 1 week. Hepatic glutathione concentration was increased gradually for 24 h, and then decreased thereafter, whereas hypotaurine was elevated drastically right after the surgery. Hepatic concentrations of polyamines were altered significantly by PHx. In the hepatectomized livers putrescine concentration was elevated rapidly, reaching a level 40- to 50-fold greater than normal in 6-12 h. Ornithine, the metabolic substrate for putrescine synthesis, was also elevated markedly. Spermidine was increased significantly, whereas spermine was depressed below normal, which appeared to be due to the increased consumption of decarboxylated SAM for spermidine biosynthesis. The results show that the metabolomics of sulfur-containing amino acids and related substances is altered profoundly in regenerating rat livers until the original weight is recovered. Hepatic concentrations of polyamines after PHx are closely associated with the alteration in the metabolomics of sulfur-containing substances. The implication of these changes in the progression of liver regeneration is discussed.

What choline metabolism can tell us about the underlying mechanisms of fetal alcohol spectrum disorders

The consequences of fetal exposure to alcohol are very diverse and the likely molecular mechanisms involved must be able to explain how so many developmental processes could go awry. If pregnant rat dams are fed alcohol, their pups develop abnormalities characteristic of fetal alcohol spectrum disorders (FASD), but if these rat dams were also treated with choline, the effects from ethanol were attenuated in their pups. Choline is an essential nutrient in humans, and is an important methyl group donor. Alcohol exposure disturbs the metabolism of choline and other methyl donors. Availability of choline during gestation directly influences epigenetic marks on DNA and histones, and alters gene expression needed for normal neural and endothelial progenitor cell proliferation. Maternal diets low in choline alter development of the mouse hippocampus, and decrement memory for life. Women eating low-choline diets have an increased risk of having an infant with a neural tube or orofacial cleft birth defect. Thus, the varied effects of choline could affect the expression of FASD, and studies on choline might shed some light on the underlying molecular mechanisms responsible for FASD.

S-Adenosylmethionine regulates connexins sub-types expressed by hepatocytes

Intercellular communication via GAP Junctions plays an important role in tissue homeostasis, apoptosis, carcinogenesis, cell proliferation and differentiation. Hepatocyte connexins (Cx) 26 and 32 levels are decreased during the de-differentiation process of primary hepatocytes in culture, a situation that is also characterized by a decrease in S-Adenosylmethionine (SAMe) levels. In this current study, we show that SAMe supplementation in cultured hepatocytes every 12h, leads to an up-regulation of Cx26 and 32 mRNA and protein levels and blocks culture-induced Cx43 expression, although it failed to increase Cx26 and 32 membrane localization and GAP junction intracellular communication. SAMe reduced nuclear β-catenin accumulation, which is known to stimulate the TCF/LEF-dependent gene transcription of Cx43. Moreover SAMe-induced reduction in Cx43 and β-catenin was prevented by the proteasome inhibitor MG132, and was not mediated by GSK3 activity. SAMe, and its metabolite 5'-methylthioadenosine (MTA) increased Cx26 mRNA in a process partially mediated by Adenosine A(2A) receptors but independent of PKA. Finally livers from MAT1A knockout mice, characterized by low hepatic SAMe levels, express higher Cx43 and lower Cx26 and 32 protein levels than control mice. These results suggest that SAMe maintains a characteristic expression pattern of the different Cxs in hepatocytes by differentially regulating their levels.

HuR/methyl-HuR and AUF1 regulate the MAT expressed during liver proliferation, differentiation, and carcinogenesis

BACKGROUND & AIMS

Hepatic de-differentiation, liver development, and malignant transformation are processes in which the levels of hepatic S-adenosylmethionine are tightly regulated by 2 genes: methionine adenosyltransferase 1A (MAT1A) and methionine adenosyltransferase 2A (MAT2A). MAT1A is expressed in the adult liver, whereas MAT2A expression primarily is extrahepatic and is associated strongly with liver proliferation. The mechanisms that regulate these expression patterns are not completely understood.

METHODS

In silico analysis of the 3' untranslated region of MAT1A and MAT2A revealed putative binding sites for the RNA-binding proteins AU-rich RNA binding factor 1 (AUF1) and HuR, respectively. We investigated the posttranscriptional regulation of MAT1A and MAT2A by AUF1, HuR, and methyl-HuR in the aforementioned biological processes.

RESULTS

During hepatic de-differentiation, the switch between MAT1A and MAT2A coincided with an increase in HuR and AUF1 expression. S-adenosylmethionine treatment altered this homeostasis by shifting the balance of AUF1 and methyl-HuR/HuR, which was identified as an inhibitor of MAT2A messenger RNA (mRNA) stability. We also observed a similar temporal distribution and a functional link between HuR, methyl-HuR, AUF1, and MAT1A and MAT2A during fetal liver development. Immunofluorescent analysis revealed increased levels of HuR and AUF1, and a decrease in methyl-HuR levels in human livers with hepatocellular carcinoma (HCC).

CONCLUSIONS

Our data strongly support a role for AUF1 and HuR/methyl-HuR in liver de-differentiation, development, and human HCC progression through the posttranslational regulation of MAT1A and MAT2A mRNAs.

Analysis of the liver mitochondrial proteome in response to ethanol and S-adenosylmethionine treatments: novel molecular targets of disease and hepatoprotection

S-adenosylmethionine (SAM) minimizes alcohol hepatotoxicity; however, the molecular mechanisms responsible for SAM hepatoprotection remain unknown. Herein, we use proteomics to determine whether the hepatoprotective action of SAM against early-stage alcoholic liver disease is linked to alterations in the mitochondrial proteome. For this, male rats were fed control or ethanol-containing liquid diets +/- SAM and liver mitochondria were prepared for proteomic analysis. Two-dimensional isoelectric focusing (2D IEF/SDS-PAGE) and blue native gel electrophoresis (BN-PAGE) were used to determine changes in matrix and oxidative phosphorylation (OxPhos) proteins, respectively. SAM coadministration minimized alcohol-dependent inflammation and preserved mitochondrial respiration. SAM supplementation preserved liver SAM levels in ethanol-fed rats; however, mitochondrial SAM levels were increased by ethanol and SAM treatments. With use of 2D IEF/SDS-PAGE, 30 proteins showed significant changes in abundance in response to ethanol, SAM, or both. Classes of proteins affected by ethanol and SAM treatments were chaperones, beta oxidation proteins, sulfur metabolism proteins, and dehydrogenase enzymes involved in methionine, glycine, and choline metabolism. BN-PAGE revealed novel changes in the levels of 19 OxPhos proteins in response to ethanol, SAM, or both. Ethanol- and SAM-dependent alterations in the proteome were not linked to corresponding changes in gene expression. In conclusion, ethanol and SAM treatment led to multiple changes in the liver mitochondrial proteome. The protective effects of SAM against alcohol toxicity are mediated, in part, through maintenance of proteins involved in key mitochondrial energy conserving and biosynthetic pathways. This study demonstrates that SAM may be a promising candidate for treatment of alcoholic liver disease.

Intestinal metabolism of sulfur amino acids

The gastrointestinal tract (GIT) is a metabolically significant site of sulfur amino acid (SAA) metabolism in the body and metabolises about 20 % of the dietary methionine intake which is mainly transmethylated to homocysteine and trans-sulfurated to cysteine. The GIT accounts for about 25 % of the whole-body transmethylation and trans-sulfuration. In addition, in vivo studies in young pigs indicate that the GIT is a site of net homocysteine release and thus may contribute to the homocysteinaemia. The gut also utilises 25 % of the dietary cysteine intake and the cysteine uptake by the gut represents about 65 % of the splanchnic first-pass uptake. Moreover, we recently showed that SAA deficiency significantly suppresses intestinal mucosal growth and reduces intestinal epithelial cell proliferation, and increases intestinal oxidant stress in piglets. These recent findings indicate that intestinal metabolism of dietary methionine and cysteine is nutritionally important for intestinal mucosal growth. Besides their role in protein synthesis, methionine and cysteine are precursors of important molecules. S-adenosylmethionine, a metabolite of methionine, is the principal biological methyl donor in mammalian cells and a precursor for polyamine synthesis. Cysteine is the rate-limiting amino acid for glutathione synthesis, the major cellular antioxidant in mammals. Further studies are warranted to establish how SAA metabolism regulates gut growth and intestinal function, and contributes to the development of gastrointestinal diseases. The present review discusses the evidence of SAA metabolism in the GIT and its functional and nutritional importance in gut function and diseases.

Sulfur amino acid deficiency upregulates intestinal methionine cycle activity and suppresses epithelial growth in neonatal pigs

We recently showed that the developing gut is a significant site of methionine transmethylation to homocysteine and transsulfuration to cysteine. We hypothesized that sulfur amino acid (SAA) deficiency would preferentially reduce mucosal growth and antioxidant function in neonatal pigs. Neonatal pigs were enterally fed a control or an SAA-free diet for 7 days, and then whole body methionine and cysteine kinetics were measured using an intravenous infusion of [1-(13)C;methyl-(2)H(3)]methionine and [(15)N]cysteine. Body weight gain and plasma methionine, cysteine, homocysteine, and taurine and total erythrocyte glutathione concentrations were markedly decreased (-46% to -85%) in SAA-free compared with control pigs. Whole body methionine and cysteine fluxes were reduced, yet methionine utilization for protein synthesis and methionine remethylation were relatively preserved at the expense of methionine transsulfuration, in response to SAA deficiency. Intestinal tissue concentrations of methionine and cysteine were markedly reduced and hepatic levels were maintained in SAA-free compared with control pigs. SAA deficiency increased the activity of methionine metabolic enzymes, i.e., methionine adenosyltransferase, methionine synthase, and cystathionine beta-synthase, and S-adenosylmethionine concentration in the jejunum, whereas methionine synthase activity increased and S-adenosylmethionine level decreased in the liver. Small intestine weight and protein and DNA mass were lower, whereas liver weight and DNA mass were unchanged, in SAA-free compared with control pigs. Dietary SAA deficiency induced small intestinal villus atrophy, lower goblet cell numbers, and Ki-67-positive proliferative crypt cells in association with lower tissue glutathione, especially in the jejunum. We conclude that SAA deficiency upregulates intestinal methionine cycle activity and suppresses epithelial growth in neonatal pigs.

Much to know about proteolysis: intricate proteolytic machineries compromise essential cellular functions

Proteolysis has traditionally been considered as a radical way to terminate the function of a protein. However, protein destruction also is the starting point for many processes as they can only occur when the way has been cleared for the action of other proteins. Protein destruction can occur virtually in all compartments and organelles of the cell, associated with cell membranes or large protein complexes, it determines subcellular partitioning, association with positive or negative regulators which conditions the action of many critical cellular factors. The third intracellular proteolysis meeting held by the University La Laguna, Canary Islands, Spain, included speakers working with some of the most important proteolytic systems present in higher eukaryotes, such as the UPS (ubiquitin–proteasome system) and autophagy. Owing to the fact that these pathways directly or indirectly regulate many cell functions, this meeting brought together an audience with a wide range of research interests, including genetic, cell biological, biochemical and structural aspects of protein degradation. Some of these topics inspired interesting discussions and a significant number of these are developed in the issues reviewed herein.