Reversal by 5-azacytidine of the S-adenosyl-l-methionine-induced inhibition of the development of putative preneoplastic foci in rat liver carcinogenesis

doi:10.1016/0304-3835(91)90011-6

Cancer Letters

Volume 56, Issue 3, March 1991, Pages 259-265

https://doi.org/10.1016/0304-3835(91)90011-6 Get rights and content

Abstract

The development of γ-glutamyltranspeptidase (GGT)-positive foci, in Wistar rats, initiated with diethylnitrosamine and subjected to selection according to ‘resistant hepatocyte’ protocol, was coupled, 7 weeks after initiation, with liver DNA hypomethylation and with a fall in S-adenosylmethionine/S-adenosylhomocysteine ( $SAM SAH$ ) ratio, and in 5-methylthio-adenosine (MTA) content. A 15-day treatment with SAM, started 1 week after selection, caused a dose-dependent decrease in the development of GGT-positive foci, recovery of liver $SAM SAH$ ratio and MTA level, and liver DNA methylation. A 12-day treatment with 20 μmol/kg per day of 5-azacytidine (AzaC), starting 1 week after selection, enhanced growth of GGT-positive foci, caused strong DNA hypomethylation, and partially counteracted the inhibition of GGT-positive foci growth, without affecting recovery of $SAM SAH$ ratio and MTA level, induced by SAM. These results suggest a role of DNA methylation in the antipromoting effect of SAM.

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Cited by (31)

Pleiotropic effects of methionine adenosyltransferases deregulation as determinants of liver cancer progression and prognosis
2013, Journal of Hepatology
Citation Excerpt :
The observation that stable transfectants of HuH7 cells overexpressing MAT1A exhibit higher SAM levels and no change in 5′-MTA content, and are less tumorigenic in vivo than control cells [50], strongly supports an anti-tumorigenic effect of SAM independent of 5′-MTA. Furthermore, SAM deficiency during hepatocarcinogenesis is associated with global DNA hypomethylation [37] that is not reversed by 5′-MTA, whereas SAM-induced inhibition of the development of preneoplastic foci in rat liver carcinogenesis is associated with complete recovery of DNA hypomethylation [41], and is prevented by the hypomethylating agent 5-azacytidine [82]. Global DNA hypomethylation induces GI during hepatocarcinogenesis [83].
Downregulation of liver-specific MAT1A gene, encoding S-adenosylmethionine (SAM) synthesizing isozymes MATI/III, and upregulation of widely expressed MAT2A, encoding MATII isozyme, known as MAT1A:MAT2A switch, occurs in hepatocellular carcinoma (HCC). Being inhibited by its reaction product, MATII isoform upregulation cannot compensate for MATI/III decrease. Therefore, MAT1A:MAT2A switch contributes to decrease in SAM level in rodent and human hepatocarcinogenesis. SAM administration to carcinogen-treated rats prevents hepatocarcinogenesis, whereas MAT1A-KO mice, characterized by chronic SAM deficiency, exhibit macrovesicular steatosis, mononuclear cell infiltration in periportal areas, and HCC development. This review focuses upon the pleiotropic changes, induced by MAT1A/MAT2A switch, associated with HCC development. Epigenetic control of MATs expression occurs at transcriptional and post-transcriptional levels. In HCC cells, MAT1A/MAT2A switch is associated with global DNA hypomethylation, decrease in DNA repair, genomic instability, and signaling deregulation including c-MYC overexpression, rise in polyamine synthesis, upregulation of RAS/ERK, IKK/NF-kB, PI3K/AKT, and LKB1/AMPK axis. Furthermore, decrease in MAT1A expression and SAM levels results in increased HCC cell proliferation, cell survival, and microvascularization. All of these changes are reversed by SAM treatment in vivo or forced MAT1A overexpression or MAT2A inhibition in cultured HCC cells. In human HCC, MAT1A:MAT2A and MATI/III:MATII ratios correlate negatively with cell proliferation and genomic instability, and positively with apoptosis and global DNA methylation. This suggests that SAM decrease and MATs deregulation represent potential therapeutic targets for HCC. Finally, MATI/III:MATII ratio strongly predicts patients’ survival length suggesting that MAT1A:MAT2A expression ratio is a putative prognostic marker for human HCC.
Diet and the epigenetic (re)programming of phenotypic differences in behavior
2008, Brain Research
Citation Excerpt :
Dietary methionine is converted by methionine adenosyltransferase into SAM (Cantoni, 1975; Mudd and Cantoni, 1958), which serves as the donor of methyl groups for DNA methylation. SAM was shown to inhibit active demethylation (Detich et al., 2003b) and to stimulate methylation (Pascale et al., 1991). Importantly, the synthesis of SAM is dependent on the local availability of methionine (Cooney, 1993).
Phenotypic diversity is shaped by both genetic and epigenetic mechanisms that program tissue specific patterns of gene expression. Cells, including neurons, undergo massive epigenetic reprogramming during development through modifications to chromatin structure, and by covalent modifications of the DNA through methylation. There is evidence that these changes are sensitive to environmental influences such as maternal behavior and diet, leading to sustained differences in phenotype. For example, natural variations in maternal behavior in the rat that influence stress reactivity in offspring induce long-term changes in gene expression, including in the glucocorticoid receptor, that are associated with altered histone acetylation, DNA methylation, and NGFI-A transcription factor binding. These effects can be reversed by early postnatal cross-fostering, and by pharmacological manipulations in adulthood, including Trichostatin A (TSA) and l-methionine administration, that influence the epigenetic status of critical loci in the brain. Because levels of methionine are influenced by diet, these effects suggest that diet could contribute significantly to this behavioral plasticity. Recent data suggest that similar mechanisms could influence human behavior and mental health. Epidemiological data suggest indeed that dietary changes in methyl contents could affect DNA methylation and gene expression programming. Nutritional restriction during gestation could affect epigenetic programming in the brain. These findings provide evidence for a stable yet dynamic epigenome capable of regulating phenotypic plasticity through epigenetic programming.
Epigenetic changes and liver carcinogenesis
2006, Gastroenterologie Clinique et Biologique
Les mécanismes moléculaires impliqués dans la carcinogenèse hépatique restent mal connus. Durant la dernière décennie, les anomalies épigénétiques (méthylation de l’ADN) ont fait l’objet d’une attention particulière en raison de leur possible implication dans le développement du carcinome hépato-cellulaire. Le niveau de méthylation de l’ADN est influencé par des facteurs environnementaux (apports en folates et méthionine) et génétiques (polymorphismes de la méthylènetétrahydrofolate réductase/MTHFR). Ces données pourraient permettre une meilleure compréhension de la carcinogénèse hépatique. Des études d’intervention sont maintenant requises afin de déterminer l’intérêt d’une supplémentation en folates pour prévenir le développement de tumeurs hépatiques dans une population cible.
The molecular mechanisms involved in liver carcinogenesis are poorly understood. Over the past decade, epigenetic changes (DNA methylation) have received increasing attention for their potential involvement in the development of hepatocarcinoma. The DNA methylation level is influenced by environmental factors (folate and methionine diet), as well as by genetic factors (methylenetetrahydrofolate reductase/MTHFR polymorphisms). These findings provide new insight into the understanding of liver carcinogenesis. Interventional studies are now required to determine the role of folate supplementation in the development of liver tumors in targeted patients.
Targeting DNA methylation in cancer
2003, Ageing Research Reviews
There is overwhelming evidence that DNA methylation patterns are altered in cancer. Methylation of CG-rich islands in regulatory regions of genes marks them for transcriptional silencing. Multiple genes, which confer selective advantage upon cancer cells such as tumor suppressors, adhesion molecules, inhibitors of angiogenesis and repair enzymes are silenced. In parallel, tumor cell genomes are globally less methylated than their normal counterparts. In contrast to regional hypermethylation, this loss of methylation in cancer cells occurs in sparsely distributed CG sequences. We now understand that DNA methylation machineries might include a number of DNA methyltransferases, proteins that direct DNA methyltransferases to specific promoters, chromatin modifying enzymes as well as demethylases. There is also data to suggest that pharmacological down regulation of some members of the DNA methylation machinery could inhibit cancer in vitro, in vivo and in clinical trials. Understanding which functions of DNA methylation machinery are critical for cancer is essential for the design of inhibitors of the DNA methylation machinery as anticancer agents. This review discusses the possible role of DNA methyltranferases and demethylases in tumorigenesis and the possible pharmacological and therapeutic implications of the DNA methylation machinery.
The methyl donor S-Adenosylmethionine inhibits active demethylation of DNA. A candidate novel mechanism for the pharmacological effects of S-Adenosylmethionine
2003, Journal of Biological Chemistry
Citation Excerpt :
The percent demethylation (C/(C + mC)) was calculated per each sample and then normalized to the value obtained for the demethylase reaction in the absence of inhibitor (0 mm AdoMet/AdoHcy). AdoMet Inhibits TSA-induced Active Demethylation of Ectopically Methylated and Transiently Transfected CMV-GFP in a Dose-dependent Manner—There have been several reports demonstrating that exogenous administration of AdoMet leads to DNA hypermethylation (19, 21, 35). Similarly, other studies have shown that a decrease in dietary folate, or a depletion of intracellular AdoMet, results in DNA hypomethylation (6, 12, 36, 37).
S-Adenosylmethionine (AdoMet) is the methyl donor of numerous methylation reactions. The current model is that an increased concentration of AdoMet stimulates DNA methyltransferase reactions, triggering hypermethylation and protecting the genome against global hypomethylation, a hallmark of cancer. Using an assay of active demethylation in HEK 293 cells, we show that AdoMet inhibits active demethylation and expression of an ectopically methylated CMV-GFP (green fluorescent protein) plasmid in a dose-dependent manner. The inhibition of GFP expression is specific to methylated GFP; AdoMet does not inhibit an identical but unmethylated CMV-GFP plasmid. S-Adenosylhomocysteine (AdoHcy), the product of methyltransferase reactions utilizing AdoMet does not inhibit demethylation or expression of CMV-GFP. In vitro, AdoMet but not AdoHcy inhibits methylated DNA-binding protein 2/DNA demethylase as well as endogenous demethylase activity extracted from HEK 293, suggesting that AdoMet directly inhibits demethylase activity, and that the methyl residue on AdoMet is required for its interaction with demethylase. Taken together, our data support an alternative mechanism of action for AdoMet as an inhibitor of intracellular demethylase activity, which results in hypermethylation of DNA.
Chemoprevention of hepatocarcinogenesis: S-adenosyl-L-methionine
2002, Alcohol
Accumulation of genetic changes characterizes the progression of cells, initiated by carcinogens, to full malignancy. Various epigenetic mechanisms, such as high polyamine synthesis, aberrant DNA methylation, and production of reactive oxygen species, may favor this process by stimulating growth and inducing DNA damage. We observed a decrease in S-adenosyl-l-methionine (SAM) content in the liver, associated with DNA hypomethylation in rat liver, during the development of preneoplastic foci, and in neoplastic nodules and hepatocellular carcinomas, induced in diethylnitrosamine-initiated rats by “resistant hepatocyte” (RH) protocol. Reconstitution of the methyl donor level in the liver by SAM administration inhibits growth and induces phenotypic reversion and apoptosis of preneoplastic cells. A 6-month SAM treatment results in a sharp and persistent decrease in development of neoplastic nodules, suggesting a long duration of SAM chemopreventive effect. Various observations support the suggestion of a role of DNA methylation in chemoprevention by SAM: (1) Exogenous SAM reconstitutes the SAM pool in preneoplastic and neoplastic liver lesions. (2) DNA methylation is positively correlated with SAM:S-adenosylhomocysteine (SAH) ratio in these lesions. (3) 5-Azacytidine, a DNA methyltransferase inhibitor, inhibits chemoprevention by SAM. (4) c-Ha-ras, c-Ki-ras, and c-myc are hypomethylated and overexpressed in preneoplastic liver. Their expression is inversely correlated with SAM:SAH ratio in SAM-treated rats. (5) S-Adenosyl-l-methionine treatment results in overall DNA methylation and partial methylation of these genes. Other possible mechanisms of SAM treatment include inhibition of polyamine synthesis, linked to partial transformation of SAM into 5′-methylthioadenosine (MTA), and antioxidant and antifibrogenic activities of both SAM and MTA.

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Cancer Letters

Abstract

References (29)

Cellular differentiation, cytidine analogs, and DNA methylation

Cell

Inhibition of DNA methyltransferase and induction of Friend erythmleukemia cell differentiation by 5-azacytidine and 5-aza-2′-deoxycytidine

J. Biol. Chem.

Azapyrimidine nucleosides: metabolism and mechanisms

Adv. Enz. Regul.

Inhibition by ethanol of rat liver plasma membrane (Na⁺0K+)ATPase: Protective effect of S-adenosyl-l-methionine, l-methionine, and N-acetylcysteine

Toxicol. Appl. Pharmacol.

DNA hypomethylation in ethionine-induced rat preneoplastic hepatocyte nodules

Biochem. Biophys. Res. Commun.

The specificity of 5-adenosylmethionine derivatives in methyl transfer reactions

J. Biol. Chem.

Perturbation of biochemical transmethylations by 3-deazaadenosine in vivo

Biochem. Pharmacol.

5-Azacytidine carcinogenesis in $Balb c$ mice

Cancer Lett.

Gene expression during the mammalian cell cycle

Biochim. Biophys. Acta

Early stimulation of polyamine biosynthesis during promotion by phenobarbital of diethylnitrosamine-induced rat liver carcinogenesis. The effects of variations of the S-adenosyl-l-methionine cellular pool

Carcinogenesis

The variations of S-adenosyl-l-methionine content modulate hepatocyte growth during phenobarbital promotion of diethylnitrosamine-induced rat liver carcinogenesis

Toxicol. Pathol.

Variations of ornithine decarboxylase activity and S-adenosyl-l-methionine and 5-methylthioadenosine contents during the development of diethylnitrosamine-induced liver hyperplastic nodules and hepatocellular carcinomas

Carcinogenesis

Mechanism of the inhibition of liver hepatocarcinogenesis promotion by S-adenosyl-l-methionine

S-adenosylmethionine antipromotion and antiprogression effect in hepatocarcinogenesis. Its association with DNA methylation and inhibition of gene expression

Cited by (31)

Pleiotropic effects of methionine adenosyltransferases deregulation as determinants of liver cancer progression and prognosis

Diet and the epigenetic (re)programming of phenotypic differences in behavior

Epigenetic changes and liver carcinogenesis

Targeting DNA methylation in cancer

The methyl donor S-Adenosylmethionine inhibits active demethylation of DNA. A candidate novel mechanism for the pharmacological effects of S-Adenosylmethionine

Chemoprevention of hepatocarcinogenesis: S-adenosyl-L-methionine