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

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.

Cysteine‑ and glycine‑rich protein 2: A vital regulator that inhibits necroptosis glioma cell by activating the JAK‑STAT1 pathways

Cysteine‑ and glycine‑rich protein 2 (CSRP2) are closely associated with tumor invasion and metastasis. CSRP2 is significantly upregulated in glioma tissues and is associated with the clinical stage of the tumor. Overexpression of CSRP2 in glioma cells promotes the proliferation and metastasis of cancer cells, whereas CSRP2 knockdown inhibits the biological functions of tumor cells. Transcriptome sequencing of CSRP2‑knockdown U251M cells revealed that silencing of CSRP2 inhibited the JAK‑STAT1 signaling pathway, and differentially expressed genes were significantly enriched in cell processes related to necroptosis. Experiments on necroptosis in glioma cells using flow cytometry, Hoechst 33342/PI dual staining and transmission electron microscopy indicated that CSRP2 overexpression inhibited necroptosis in glioma cells. Western blotting results showed that overexpression of CSRP2 activated the JAK‑STAT1 signaling pathway, while the addition of the pathway inhibitor ruxolitinib promoted the phosphorylation of necroptosis proteins RIPK1, RIPK3 and MLKL. Therefore, it was hypothesized that CSRP2 maintains JAK‑STAT1 activation by inhibiting the protein inhibitor of activated STAT1, which then inhibits the necrotizing apoptosis of glioma cells.