Intracellular S-adenosylmethionine Levels Research Articles

S-adenosylmethionine biosynthesis is a targetable metabolic vulnerability in multiple myeloma.

Multiple myeloma (MM) is the second most prevalent hematologic malignancy and is incurable because of the inevitable development of drug resistance. Methionine adenosyltransferase 2α (MAT2A) is the primary producer of the methyl donor S-adenosylmethionine (SAM) and several studies have documented MAT2A deregulation in different solid cancers. As the role of MAT2A in MM has not been investigated yet, the aim of this study was to clarify the potential role and underlying molecular mechanisms of MAT2A in MM, exploring new therapeutic options to overcome drug resistance. By analyzing publicly available gene expression profiling data, MAT2A was found to be more highly expressed in patient-derived myeloma cells than in normal bone marrow plasma cells. The expression of MAT2A correlated with an unfavorable prognosis in relapsed patients. MAT2A inhibition in MM cells led to a reduction in intracellular SAM levels, which resulted in impaired cell viability and proliferation, and induction of apoptosis. Further mechanistic investigation demonstrated that MAT2A inhibition inactivated the mTOR-4EBP1 pathway, accompanied by a decrease in protein synthesis. MAT2A targeting in vivo with the small molecule compound FIDAS-5 was able to significantly reduce tumor burden in the 5TGM1 model. Finally, we found that MAT2A inhibition can synergistically enhance the anti-MM effect of the standard-of-care agent bortezomib on both MM cell lines and primary human CD138+ MM cells. In summary, we demonstrate that MAT2A inhibition reduces MM cell proliferation and survival by inhibiting mTOR-mediated protein synthesis. Moreover, our findings suggest that the MAT2A inhibitor FIDAS-5 could be a novel compound to improve bortezomib-based treatment of MM.

Functional analysis of 3'-UTR hairpins supports a two-tiered model for posttranscriptional regulation of MAT2A by METTL16.

S-adenosylmethionine (SAM) is the methyl donor for nearly all cellular methylation events, so cells need to carefully control SAM levels. MAT2A encodes the only SAM synthetase expressed in the majority of human cells, and its 3'-UTR has six conserved regulatory hairpins (hp1-6) that can be methylated by the N6-methyladenosine methyltransferase METTL16. Hp1 begins 8 nt from the stop codon, whereas hp2-6 are clustered further downstream (∼800 nt). These hairpins have been proposed to regulate MAT2A mRNA levels in response to intracellular SAM levels by regulating intron detention of the last intron of MAT2A and by modulating the stability of the fully spliced mRNA. However, a dissection of these two posttranscriptional mechanisms has not been previously reported. Using a modular reporter system, we show that hp1 functions primarily when the detained intron is included in the reporter and when that intron has a suboptimal polypyrimidine tract. In contrast, the hp2-6 cluster modulates mRNA stability independent of the detained intron, although hp1 may make a minor contribution to the regulation of decay as well. Taken with previously published reports, these data support a two-tiered model for MAT2A posttranscriptional regulation by METTL16 through its interactions with hp1 and hp2-6. In the upstream tier, hp1 and METTL16 control MAT2A intron detention, whereas the second tier involves METTL16-dependent methylation of hp2-6 to control MAT2A mRNA stability. Thus, cells use a similar set of molecular factors to achieve considerable complexity in the posttranscriptional regulation of SAM homeostasis.

Imaging intracellular metabolite and protein changes in live mammalian cells with bright fluorescent RNA-based genetically encoded sensors

Fluorescent RNA (FR)-based genetically encoded sensors have been engineered to detect various essential metabolites in living systems. However, the unfavorable characteristics of FR impede sensor applications. Here, we describe a strategy for converting Pepper fluorescent RNA into a series of fluorescent sensors to detect their cognate targets both in vitro and in live cells. Compared to previously developed FR-based sensors, Pepper-based sensors exhibited expanded emission of up to 620 nm and markedly improved cellular brightness, allowing robust and real-time monitoring of the pharmacologic-triggered dynamics changes in the intracellular level of S-adenosylmethionine (SAM) and the optogenetic manipulated protein translocation in live mammalian cells. Furthermore, signal amplification in fluorescence imaging of the target was achieved using the CRISPR-display strategy by incorporating a Pepper-based sensor into the sgRNA scaffold. Together, these results demonstrate that Pepper can be readily developed into high-performance FR-based sensors to detect various cellular targets.

NNMT-DNMT1 Axis is Essential for Maintaining Cancer Cell Sensitivity to Oxidative Phosphorylation Inhibition.

Lacking a clear understanding of the molecular mechanism determining cancer cell sensitivity to oxidative phosphorylation (OXPHOS) inhibition limits the development of OXPHOS-targeting cancer treatment. Here, cancer cell lines sensitive or resistant to OXPHOS inhibition are identified by screening. OXPHOS inhibition-sensitive cancer cells possess increased OXPHOS activity and silenced nicotinamide N-methyltransferase (NNMT) expression. NNMT expression negatively correlates with OXPHOS inhibition sensitivity and functionally downregulates the intracellular levels of S-adenosyl methionine (SAM). Expression of DNA methyltransferase 1 (DNMT1), a SAM consumer, positively correlates with OXPHOS inhibition sensitivity. NNMT overexpression and DNMT1 inhibition render OXPHOS inhibition-sensitive cancer cells resistant. Importantly, treatments of OXPHOS inhibitors (Gboxin and Berberine) hamper the growth of mouse tumor xenografts by OXPHOS inhibition sensitive but not resistant cancer cells. What's more, the retrospective study of 62 tumor samples from a clinical trial demonstrates that administration of Berberine reduces the tumor recurrence rate of NNMTlow /DNMT1high but not NNMThigh /DNMT1low colorectal adenomas (CRAs). These results thus reveal a critical role of the NNMT-DNMT1 axis in determining cancer cell reliance on mitochondrial OXPHOS and suggest that NNMT and DNMT1 are faithful biomarkers for OXPHOS-targeting cancer therapies.

SAM homeostasis is regulated by CFIm-mediated splicing of MAT2A.

S-adenosylmethionine (SAM) is the methyl donor for nearly all cellular methylation events. Cells regulate intracellular SAM levels through intron detention of MAT2A, the only SAM synthetase expressed in most cells. The N6-adenosine methyltransferase METTL16 promotes splicing of the MAT2A detained intron by an unknown mechanism. Using an unbiased CRISPR knock-out screen, we identified CFIm25 (NUDT21) as a regulator of MAT2A intron detention and intracellular SAM levels. CFIm25 is a component of the cleavage factor Im (CFIm) complex that regulates poly(A) site selection, but we show it promotes MAT2A splicing independent of poly(A) site selection. CFIm25-mediated MAT2A splicing induction requires the RS domains of its binding partners, CFIm68 and CFIm59 as well as binding sites in the detained intron and 3´ UTR. These studies uncover mechanisms that regulate MAT2A intron detention and reveal a previously undescribed role for CFIm in splicing and SAM metabolism.

MTORC1 stimulates cell growth through SAM synthesis and m6A mRNA-dependent control of protein synthesis

The mechanistic target of rapamycin complex 1 (mTORC1) regulates metabolism and cell growth in response to nutrient, growth, and oncogenic signals. We found that mTORC1 stimulates the synthesis of the major methyl donor, S-adenosylmethionine (SAM), through the control of methionine adenosyltransferase 2 alpha (MAT2A) expression. The transcription factor c-MYC, downstream of mTORC1, directly binds to intron 1 of MAT2A and promotes its expression. Furthermore, mTORC1 increases the protein abundance of Wilms' tumor 1-associating protein (WTAP), the positive regulatory subunit of the human N6-methyladenosine (m6A) RNA methyltransferase complex. Through the control of MAT2A and WTAP levels, mTORC1 signaling stimulates m6A RNA modification to promote protein synthesis and cell growth. A decline in intracellular SAM levels upon MAT2A inhibition decreases m6A RNA modification, protein synthesis rate, and tumor growth. Thus, mTORC1 adjusts m6A RNA modification through the control of SAM and WTAP levels to prime the translation machinery for anabolic cell growth.

Mechanism of Activation of Mechanistic Target of Rapamycin Complex 1 by Methionine.

Nutrients are closely involved in the regulation of lifespan and metabolic health. Cellular activities, such as the regulation of metabolism, growth, and aging, are mediated by a network of nutrients and nutrient-sensing pathways. Among the nutrient-sensing pathways, the mechanistic target of rapamycin complex 1 (mTORC1) acts as the central regulator of cellular functions, which include autophagy. Autophagy plays a significant role in the removal of protein aggregates and damaged or excess organelles, including mitochondria, to maintain intracellular homeostasis, which is involved in lifespan extension and cardiometabolic health. Moreover, dietary methionine restriction may have a beneficial effect on lifespan extension and metabolic health. In contrast, methionine may activate mTORC1 and suppress autophagy. As the mechanism of methionine sensing on mTORC1, SAMTOR was identified as a sensor of S-adenosyl methionine (SAM), a metabolite of methionine, in the cytoplasm. Conversely, methionine may activate the mTORC1 signaling pathway through the activation of phosphatase 2A (PP2A) because of increased methylation in response to intracellular SAM levels. In this review, we summarized the recent findings regarding the mechanism via which methionine activates mTORC1.

A Benchtop Approach To Measuring S-AdenosylMethionine Metabolite Levels Using HILIC UPLC-MS

S-adenosylmethionine (SAMe) is the most common methyl donor found in living organisms. It is the second most common cellular enzyme substrate and is an essential molecule in the carbon metabolic cycle. SAMe is widely used in both a clinical setting and as a nutritional supplement to treat a variety of disorders ranging from liver disease to osteoarthritis in both humans and animals. Demand for SAMe is rapidly expanding and the yeast Saccharomyces cerevisiae is often used as an industrial production host. Increasing clinical research into SAMe, as well as increasing commercial demand, has led to the need for rapid, accurate measurement of SAMe levels from a variety of sources. We report here a novel hydrophilic interaction liquid chromatography (HILIC) UltraPerformance liquid chromatography – mass spectrometry (UPLC-MS) benchtop method to measure intracellular levels of SAMe from S. cerevisiae. Research is ongoing to understand the cellular impact of variations in SAMe levels as well as mutation screens to identify yeast strains with increased SAMe production. This UPLC method allows researchers to measure SAMe with increased resolution, speed, and sensitivity while decreasing both cost and environmental impact, and has the potential to be adapted for the measure of many other metabolites.

Structural Basis for Regulation of METTL16, an S-Adenosylmethionine Homeostasis Factor

S-adenosylmethionine (SAM) is an essential metabolite that acts as a cofactor for most methylation events in the cell. The N6-methyladenosine (m6A) methyltransferase METTL16 controls SAM homeostasis by regulating the abundance of SAM synthetase MAT2A mRNA in response to changing intracellular SAM levels. Here we present crystal structures of METTL16 in complex with MAT2A RNA hairpins to uncover critical molecular mechanisms underlying the regulated activity of METTL16. The METTL16-RNA complex structures reveal atomic details of RNA substrates that drive productive methylation by METTL16. In addition, we identify a polypeptide loop in METTL16 near the SAM binding site with an autoregulatory role. We show that mutations that enhance or repress METTL16 activity invitro correlate with changes in MAT2A mRNA levels in cells. Thus, we demonstrate the structural basis for the specific activity of METTL16 and further suggest the molecular mechanisms by which METTL16 efficiency is tuned to regulate SAM homeostasis.

Balance between MAT2A intron detention and splicing is determined cotranscriptionally.

Transcriptome analysis of human cells has revealed that intron retention controls the expression of a large number of genes with diverse cellular functions. Detained introns (DI) constitute a subgroup of transcripts with retained introns that are not exported to the cytoplasm but instead remain in the nucleus. Previous studies reported that the splicing of DIs in the CLK1 transcript is post-transcriptionally induced to produce mature mRNA in the absence of new transcription. Thus, CLK1-DI serves as a precursor or “reservoir” for the CLK1 mRNA. However, whether this is a universal mechanism for gene regulation by intron detention remains unknown. The MAT2A gene encodes S-adenosylmethionine (SAM) synthetase and it contains a DI that is regulated in response to intracellular SAM levels. We used three independent assays to assess the precursor–product relationship between MAT2A-DI and MAT2A mRNA. In contrast to CLK1-DI, these data support a model in which the MAT2A-DI transcript is not a precursor to mRNA but is instead a “dead-end” RNA fated for nuclear decay. Additionally, we show that in SAM-deprived conditions the cotranscriptional splicing of MAT2A detained introns increases. We conclude that polyadenylated RNAs with DIs can have at least two distinct fates. They can serve as nuclear reservoirs of pre-mRNAs available for rapid induction by the cell, or they constitute dead-end RNAs that are degraded in the nucleus.

S-Adenosylmethionine Synthesis Is Regulated by Selective N6-Adenosine Methylation and mRNA Degradation Involving METTL16 and YTHDC1

S-adenosylmethionine (SAM) is an important metabolite as a methyl-group donor in DNA and histone methylation, tuning regulation of gene expression. Appropriate intracellular SAM levels must be maintained, because methyltransferase reaction rates can be limited by SAM availability. In response to SAMdepletion, MAT2A, which encodes a ubiquitous mammalian methionine adenosyltransferase isozyme, was upregulated through mRNA stabilization. SAM-depletion reduced N6-methyladenosine (m6A) in the 3' UTR of MAT2A. Invitro reactions using recombinant METTL16 revealed multiple, conserved methylation targets in the 3' UTR. Knockdown of METTL16 and the m6A reader YTHDC1 abolished SAM-responsive regulation of MAT2A. Mutations of the target adenine sites of METTL16 within the 3'UTR revealed that these m6As were redundantly required for regulation. MAT2A mRNA methylation by METTL16 is read by YTHDC1, and we suggest that this allows cells to monitor and maintain intracellular SAM levels.

MAT2B promotes adipogenesis by modulating SAMe levels and activating AKT/ERK pathway during porcine intramuscular preadipocyte differentiation

Intramuscular fat (IMF) has been demonstrated as one of the crucial factors of livestock meat quality. The MAT2B protein with MAT2α catalyzes the formation of methyl donor S- adenosylmethionine (SAMe) to mediate cell metabolism including proliferation and apoptosis. However, the regulatory effect of MAT2B on IMF deposition is still unclear. In this study, the effect of MAT2B on adipogenesis and its potential mechanism during porcine intramuscular preadipocyte differentiation was studied. The results showed that overexpression of MAT2B promoted adipogenesis and significantly up-regulated the mRNA and protein levels of adipogenic marker genes including FASN, PPARγ and aP2, consistently, knockdown of MAT2B inhibited lipid accumulation and down-regulated the mRNA and protein levels of the above genes. Furthermore, flow cytometry and EdU-labeling assay indicated that MAT2B regulate adipogenesis was partly due to influence intracellular SAMe levels and further affect cell clonal expansion. Also, increased expression of MAT2B activated the phosphorylations of AKT and ERK1/2, whereas knockdown of MAT2B blocked AKT signaling and repressed the phosphorylation of ERK1/2. Moreover, the inhibitory effect of LY294002 (a specific PI3K inhibitor) on the activities of AKT and ERK1/2 was partially recovered by overexpression of MAT2B in porcine intramuscular adipocytes. Finally, Co-IP experiments showed that MAT2B can directly interact with AKT. Taken together, our findings suggested that MAT2B acted as a positive regulator through modifying SAMe levels as well as activating AKT/ERK signaling pathway to promote porcine intramuscular adipocyte differentiation.

One-carbon metabolism and epigenetics: understanding the specificity.

One-carbon metabolism is a metabolic network that integrates nutrient status from the environment to yield multiple biological functions. The folate and methionine cycles generate S-adenosylmethionine (SAM), which is the universal methyl donor for methylation reactions, including histone and DNA methylation. Histone methylation is a crucial part of the epigenetic code and plays diverse roles in the establishment of chromatin states that mediate the regulation of gene expression. The activities of histone methyltransferases (HMTs) are dependent on intracellular levels of SAM, which fluctuate based on cellular nutrient availability, providing a link between cell metabolism and histone methylation. Here we discuss the biochemical properties of HMTs, their role in gene regulation, and the connection to cellular metabolism. Our emphasis is on understanding the specificity of this intriguing link.

Characterization of methionine adenosyltransferase 2β gene expression in skeletal muscle and subcutaneous adipose tissue from obese and lean pigs

Methionine adenosyltransferase (MAT) catalyzes the biosynthesis of S-adenosylmethionine. Two genes (MAT1A and MAT2A) encode for the catalytic subunit of MAT, while a third gene (MAT2beta) encodes for a regulatory subunit (MAT II beta) that regulates the activity of the MAT2A-encoded isoenzyme and intracellular S-adenosylmethionine levels. Our previous work identified MAT2beta as a candidate gene for intramuscular fat (IMF) deposition in porcine skeletal muscle by microarray technology. Here, we cloned porcine MAT2beta cDNA and compared its expression pattern in subcutaneous adipose tissue and skeletal muscle from obese (Rongchang Breed) and lean (Pig Improvement Company, PIC) pigs (n = 6). The porcine MAT2beta cDNA was 1,800 bp long and encodes for 334 amino acids sharing high similarity with other species. MAT2beta is expressed at a higher level in liver and duodenum, followed by the stomach, fat and longissinus dorsi muscle. As expected, both subcutaneous fat content and IMF content were higher in obese than in lean pigs (both P < 0.01). MAT2beta mRNA abundance was lower in both subcutaneous adipose tissue and skeletal muscle in obese pigs compared with lean pigs (both P < 0.01). MAT II beta protein content was lower in skeletal muscle in obese than in lean pigs (P < 0.05), whereas the opposite was observed in subcutaneous adipose tissue (P < 0.01). These data demonstrated an obesity-related expression variation of the MAT II beta subunit in skeletal muscle and adipose tissue in pigs, and suggest a novel role for the MAT2beta gene in regulation of IMF deposition in skeletal muscle.

S-adenosylmethionine regulates thiopurine methyltransferase activity and decreases 6-mercaptopurine cytotoxicity in MOLT lymphoblasts

Six-mercaptopurine (6-MP) is a pro-drug widely used in treatment of various diseases, including acute lymphoblastic leukaemia (ALL). Side-effects of thiopurine therapy have been correlated with thiopurine methyltransferase (TPMT) activity.We propose a novel TPMT-mediated mechanism of S-adenosylmethionine (SAM)-specific effects on 6-mercaptopurine (6-MP) induced cytotoxicity in a model cell line for acute lymphoblastic leukemia (MOLT). Our results show that exogenous SAM (10–50μM) rescues cells from the toxic effects of 6-MP (5μM) by delaying the onset of apoptosis. We prove that the extent of methylthioinosine monophosphate (MeTIMP) induced inhibition of de novo purine synthesis (DNPS) determines the concentrations of intracellular ATP, and consequently SAM, which acts as a positive modulator of TPMT activity. This leads to a greater conversion of 6-MP to inactive 6-methylmercaptopurine, and thus lower availability of thioinosine monophosphate for the biotransformation to cytotoxic thioguanine nucleotides (TGNs) and MeTIMP. We further show that the addition of exogenous SAM to 6-MP treated cells maintains intracellular SAM levels, TPMT activity and protein levels, all of which are diminished in cells incubated with 6-MP. Since TPMT mRNA levels remained unaltered, the effect of SAM appears to be restricted to protein stabilisation rather than an increase of TPMT expression. We thus propose that SAM reverses the extent of 6-MP cytotoxicity, by acting as a TPMT-stabilizing factor.This study provides new insights into the pharmacogenetics of thiopurine drugs. Identification of SAM as critical modulator of TPMT activity and consequently thiopurine toxicity may set novel grounds for the rationalization of thiopurine therapy.

Changes in the expression of methionine adenosyltransferase genes and S-adenosylmethionine homeostasis during hepatic stellate cell activation

Hepatic stellate cell (HSC) activation is an essential event during liver fibrogenesis. Methionine adenosyltransferase (MAT) catalyzes biosynthesis of S-adenosylmethionine (SAMe), the principle methyl donor. SAMe metabolism generates two methylation inhibitors, methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH). Liver cell proliferation is associated with induction of two nonliver-specific MATs: MAT2A, which encodes the catalytic subunit alpha2, and MAT2beta, which encodes a regulatory subunit beta that modulates the activity of the MAT2A-encoded isoenzyme MATII. We reported that MAT2A and MAT2beta genes are required for liver cancer cell growth that is induced by the profibrogenic factor leptin. Also, MAT2beta regulates leptin signaling. The strong association of MAT genes with proliferation and leptin signaling in liver cells led us to examine the role of these genes during HSC activation. MAT2A and MAT2beta are induced in culture-activated primary rat HSCs and HSCs from 10-day bile duct ligated (BDL) rat livers. HSC activation led to a decline in intracellular SAMe and MTA levels, a drop in the SAMe/SAH ratio, and global DNA hypomethylation. The decrease in SAMe levels was associated with lower MATII activity during activation. MAT2A silencing in primary HSCs and MAT2A or MAT2beta silencing in the human stellate cell line LX-2 resulted in decreased collagen and alpha-smooth muscle actin (alpha-SMA) expression and cell growth and increased apoptosis. MAT2A knockdown decreased intracellular SAMe levels in LX-2 cells. Activation of extracellular signal-regulated kinase and phosphatidylinositol-3-kinase signaling in LX-2 cells required the expression of MAT2beta but not that of MAT2A. MAT2A and MAT2beta genes are induced during HSC activation and are essential for this process. The SAMe level falls, resulting in global DNA hypomethylation.

Oxidative stress-induced regulation of the methionine metabolic pathway in human lung epithelial-like (A549) cells

The effects of low, moderate and severe oxidative stress on the steady-state levels of the metabolites involved in the transmethylation/transsulfuration pathway were studied in lung epithelial (A549) cells. When cells were exposed to low (0.1 mM) or moderate (1.0 mM) concentrations of hydrogen peroxide (H 2O 2) or tert-butylhydroperoxide (t-butOOH), intracellular levels of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) were significantly decreased, while the SAM/SAH ratio remained the same or elevated. Likewise, extracellular levels of SAM and SAH metabolites remained steady or elevated. Both intracellular and extracellular levels of homocyst(e)ine and cyst(e)ine were decreased. Cell contents of serine, cystathionine and methionine were also decreased. Total intracellular glutathione content was decreased only by moderate t-butOOH exposure. When cells were exposed to high concentrations (10 mM) of either of the peroxides, extracellular levels of methionine, cystathionine, and total cyst(e)ine were depleted, mostly due to direct oxidation of sulfur amino acids by peroxides, as indicated by oxidative treatment of culture media alone. Similar to low and moderate oxidative conditions, the levels of SAM, SAH, and sulfur amino acids were decreased, while cell SAM/SAH ratio increased. Paradoxically, under high peroxide exposure, extracellular concentrations of SAM, SAH, and cyst(e)ine were increased, indicating cellular release, despite the severe methionine depletion. Intracellular total glutathione was also decreased. The results indicate that lung epithelial cells release high levels of SAM, probably as an adaptive response to increased oxidative stress, even when the substrate for SAM formation, methionine, is critically depleted.

Overexpression of yeast S-adenosylmethionine synthetase metK in Streptomyces actuosus leads to increased production of nosiheptide

S-Adenosylmethionine (SAM) is synthesized via the metabolic reaction involving adenosine triphosphate and L-methionine that is catalyzed by the enzyme S-adenosyl-L-methionine synthetase (SAM-s) and encoded by the gene metK. In the present study, metK with the absence of introns from Saccharomyces cerevisiae was introduced into Streptomyces actuosus, a nosiheptide (Nsh) producer. Intracellular SAM levels were determined by high-pressure liquid chromatography. Through optimizing the nutrient content of the medium, it was shown that increased SAM production induced by the overexpression of SAM-s leads to an increase in the intracellular cysteine pool and overproduction of Nsh in S. actuosus. This investigation shows that increased SAM promotes the elevated production of the non-ribosomal thiopeptide Nsh in Streptomyces sp.

Selective Diminution of Leukemic Cell Growth by shRNA‐Mediated Targeting of S‐Adenosylmethionine (SAMe) Metabolism

Leukemic cells require significantly higher amount, than normal lymphocytes, of S‐adenosylmethionine (SAMe). We exploited these differences to modulate the kinetics of methionine adenosyltransferase (MAT) that catalyzes SAMe synthesis from ATP and methionine using shRNA technology to silence the expression of MAT regulatory subunit, consequently reducing intracellular SAMe levels and diminishing leukemic cell growth in physiologic levels of methionine, both in vitro and in vivo. These cells also showed significantly higher apoptosis than control cells even at high methionine levels. Whereas control transduced Jurkat cells showed heightened engraftment in a hyper‐immunodeficient mouse model, leukemic cells where gene expression was ablated failed to engraft for up to 5 weeks. We predict that it may be possible, via dietary control of methionine intake; to adjust methionine levels in a way that would rescue normal cells while selectively induce death and apoptosis of leukemic cells that do not express MAT regulatory subunit.

Ethanol inhibits methionine adenosyltransferase II activity and S-adenosylmethionine biosynthesis and enhances caspase-3-dependent cell death in T lymphocytes: relevance to alcohol-induced immunosuppression

An important aspect in alcohol abuse-associated immune suppression is the loss of T helper CD4 + lymphocytes, leading to impairment of multiple immune functions. Our work has shown that ethanol can sensitize CD4 + T lymphocytes to caspase-3-dependent activation-induced cell death (AICD). It has been demonstrated that the formation of S-adenosylmethionine (SAMe) catalyzed by methionine adenosyltransferase (MAT) II is essential for CD4 + T-cell activation and proliferation. Since ethanol is known to affect SAMe metabolism in hepatocytes, we investigated the effect of ethanol on MAT II activity/expression, SAMe biosynthesis and cell survival in CD4 + T lymphocytes. We demonstrate for the first time that ethanol at a physiologically relevant concentration (25 mM) substantially decreased the enzymatic activity of MAT II in T lymphocytes. Ethanol was observed to decrease the transcription of MAT2A, which encodes the catalytic subunit of MAT II and is vital for MAT II activity and SAMe biosynthesis. Furthermore, correspondent to its effect on MAT II, ethanol decreased intracellular SAMe levels and enhanced caspase-3-dependent AICD. Importantly, restoration of intracellular SAMe levels by exogenous SAMe supplementation considerably decreased both caspase-3 activity and apoptotic death in T lymphocytes. In conclusion, our data show that MAT II and SAMe are critical molecular components essential for CD4 + T-cell survival that are affected by ethanol, leading to enhanced AICD. Furthermore, these studies provide a clinical paradigm for the development of much needed therapy using SAMe supplementation in the treatment of immune dysfunction induced by alcohol abuse.