A thermostable archaeal S-adenosylmethionine synthetase: a promising tool to improve the synthesis of adenosylmethionine analogs of biotechnological interest

S-Adenosylmethionine, a Promising Antitumor Agent in Oral and Laryngeal Cancer

Squamous cell carcinoma of the head and neck (HNSCC), which includes cancers of the oral cavity and larynx, is one of the most common and highly aggressive malignancies worldwide, despite significant efforts committed in recent decades in its detection, prevention, and treatment. The intrinsic or acquired drug resistance during treatment is the main limitation to chemotherapy, increasing mortality and cancer recurrence. Therefore, there is a growing scientific interest in identifying and developing adjuvant chemotherapies able to improve currently available treatments. S-Adenosylmethionine (AdoMet), a safe and nontoxic natural cofactor with pleiotropic effects on multiple cellular processes and the main biological methyl donor in transmethylation reactions, has been considerably studied as a therapeutic compound. Its application, alone or in combination with other drugs, is emerging as a potentially effective strategy for cancer treatment and for chemoprevention. This review summarizes the structural, pharmacological, and clinical aspects of AdoMet and provides an overview of the recent results highlighting its anticancer activity in the treatment of oral and laryngeal cancer, with particular emphasis on its molecular mechanisms and the promising chemoprotective and synergistic effects exerted in combination with cisplatin and specific microRNAs.

Mutual Correlation between Non-Coding RNA and S-Adenosylmethionine in Human Cancer: Roles and Therapeutic Opportunities

Simple Summary

Non-coding RNAs and S-adenosylmethionine, the methyl donor required in all epigenetic methylation reactions, have emerged in recent years as crucial players in the modulation of gene expression in different types of human cancers. This review summarizes the most recent findings on reciprocal regulation between AdoMet and non-coding RNAs. AdoMet was found to exert anticancer activity through epigenetic regulation of non-coding RNAs, including microRNAs, long non-coding RNAs and circular RNAs. On the other hand, several microRNAs and long non-coding RNAs have been reported to display regulatory effects on the expression of genes involved in AdoMet synthesis and metabolism. Increasing knowledge on the relationship between AdoMet and non-coding RNAs will provide insights for further development of diagnostic and therapeutic strategies for cancer treatments.

Abstract

Epigenetics includes modifications in DNA methylation, histone and chromatin structure, and expression of non-coding RNAs (ncRNAs), especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Knowledge of the relationships between S-adenosylmethionine (AdoMet or SAM), the universal methyl donor for all epigenetic methylation reactions and miRNAs or lncRNAs in human cancer may provide helpful insights for the development of new end more effective anticancer therapeutic approaches. In recent literature, a complex network of mutual interconnections between AdoMet and miRNAs or lncRNAs has been reported and discussed. Indeed, ncRNAs expression may be regulated by epigenetic mechanisms such as DNA and RNA methylation and histone modifications. On the other hand, miRNAs or lncRNAs may influence the epigenetic apparatus by modulating the expression of its enzymatic components at the post-transcriptional level. Understanding epigenetic mechanisms, such as dysregulation of miRNAs/lncRNAs and DNA methylation, has become of central importance in modern research. This review summarizes the recent findings on the mechanisms by which AdoMet and miRNA/lncRNA exert their bioactivity, providing new insights to develop innovative and more efficient anticancer strategies based on the interactions between these epigenetic modulators.

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.

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.

AdoMet triggers apoptosis in head and neck squamous cancer by inducing ER stress and potentiates cell sensitivity to cisplatin

S-Adenosyl-l-methionine (AdoMet) is a naturally and widely occurring sulfonium compound that plays a primary role in cell metabolism and acts as the principal methyl donor in many methylation reactions. AdoMet also exhibits antiproliferative and proapoptotic activities in different cancer cells. However, the molecular mechanisms underlying the effects exerted by AdoMet have only been partially studied. In the current study, we evaluated the antiproliferative effect of AdoMet on Cal-33 oral and JHU-SCC-011 laryngeal squamous cancer cells to define the underlying mechanisms. We demonstrated that AdoMet induced apoptosis in Cal-33 and JHU-SCC-011 cells, involving a caspase-dependent mechanism paralleled by an increased Bax/Bcl-2 ratio. Moreover, we showed, for the first time, that AdoMet induced ER-stress in Cal-33 cells and activated the unfolded protein response, which can be responsible for apoptosis induction through the activation of CHOP and JNK. In addition, AdoMet-induced ER-stress was followed by autophagy with a consistent increase in the levels of the autophagic marker LC3B-II, which was indeed potentiated by the autophago-lysosome inhibitor chloroquine. As both escape from apoptosis and decreased activation of JNK are mechanisms of resistance to cisplatin (cDPP), an agent usually used in cancer therapy, we have evaluated the effects of AdoMet in combination with cDPP on Cal-33 cells. Our data showed that the combined treatment resulted in a strong synergism in inhibiting cell proliferation and in enhancing apoptosis via intrinsic mechanism. These results demonstrate that AdoMet has ER-stress-mediated antiproliferative activity and synergizes with cDDP on cell growth inhibition, thus providing the basis for its use in new anticancer strategies.

S-Adenosylmethionine regulates apoptosis and autophagy in MCF-7 breast cancer cells through the modulation of specific microRNAs

Background

To get insight into the molecular mechanisms underlying the anti-tumor activity of S-adenosyl-l-methionine (AdoMet), we analyzed AdoMet-induced modulation of microRNAs (miRNAs) expression profile in MCF-7 breast cell line and its correlation with cancer-related biological pathways.

Methods

MiRNA expression profiling was performed using a TaqMan MiRNA Array, following 500 µM AdoMet-treatment. The results were confirmed by Quantitative real-time PCR analysis. MCF-7 were transfected with miR-34a, miR-34c and miR-486-5p, mimics and inhibitors in presence or not of 500 µM AdoMet for 72 h. Apoptosis and autophagy were analyzed by flow cytometry and the modulation of the main antiproliferative signaling pathways were evaluated by Western blotting. The potential mRNA targets for each miRNA were identified by the TargetScan miRNA target prediction software.

Results

Twenty-eight microRNAs resulted differentially expressed in AdoMet-treated MCF-7 cells compared to control cells. Among them, miRNA-34a and miRNA-34c were up-regulated while miRNA-486-5p was down-regulated. Moreover, we confirmed the ability of AdoMet to regulate these miRNAs in MDA-MB 231 breast cancer cell line. We demonstrate that, in MCF7 cells, the combination of either miR-34a or miR-34c mimic with AdoMet greatly potentiated the pro-apoptotic effect of AdoMet, by a caspase-dependent mechanism and activates p53 acetylation by inhibiting SIRT1 and HDAC1 expression. We also showed that miR-486-5p inhibitor induces autophagy and enhances AdoMet-induced autophagic process by increasing PTEN expression and by inhibiting AKT signaling.

Conclusions

Our findings provide the first evidence that AdoMet can regulate miRNA expression in MCF-7 increasing our knowledge on the molecular basis of the antitumor effect of the sulfonium compound and suggest the use of AdoMet as an attractive miRNA-mediated chemopreventive and therapeutic strategy in breast cancer.

Structure of a thermostable methionine adenosyltransferase from Thermus thermophilus HB27 reveals a novel fold of the flexible loop

Methionine adenosyltransferases (MATs) are the family of enzymes which synthesize S-adenosylmethionine (AdoMet), the major biological methyl donor.