No abstract

Elevated expression of enhancer of zeste homolog 2 (EZH2), a histone H3K27 methyltransferase, was observed in gliomas harboring telomerase reverse transcriptase (TERT) promoter mutations. Given the known involvement of TERT and EZH2 in glioma progression, the correlation between the two and subsequently its involvement in metabolic programming was investigated. Inhibition of human telomerase reverse transcriptase either pharmacologically or through genetic manipulation not only decreased EZH2 expression, but also (i) abrogated FASN levels, (ii) decreased de novo fatty acid accumulation, and (iii) increased ataxia-telangiectasia-mutated (ATM) phosphorylation levels. Conversely, diminished TERT and FASN levels upon siRNA-mediated EZH2 knockdown indicated a positive correlation between TERT and EZH2. Interestingly, ATM kinase inhibitor rescued TERT inhibition-mediated decrease in FASN and EZH2 levels. Importantly, TERT promoter mutant tumors exhibited greater microsatellite instability, heightened FASN levels and lipid accumulation. Coherent with in vitro findings, pharmacological inhibition of TERT by costunolide decreased lipid accumulation and elevated ATM expression in heterotypic xenograft glioma mouse model. By bringing TERT-EZH2 network at the forefront as driver of dysregulated metabolism, our findings highlight the non-canonical but distinct role of TERT in metabolic reprogramming and DNA damage responses in glioblastoma.

A dynamic network of metabolic adaptations, inflammatory responses and redox homeostasis is known to drive tumor progression. A considerable overlap between these processes exists, but several of their key regulators remain unknown. To this end, here we investigated the role of the proinflammatory cytokine IL-1β in connecting these processes in glioma cells. We found that glucose starvation sensitizes glioma cells to IL-1β-induced apoptosis in a manner that depended on reactive oxygen species (ROS).Although IL-1β-induced JNK had no effect on cell viability under glucose deprivation, it mediated nuclear translocation of hexokinase 2 (HK2). This event was accompanied by increases in the levels of sirtuin 6 (SIRT6), nuclear factor erythroid 2-related factor 2 (Nrf2), and xanthine oxidoreductase (XOR).

De-synchronized circadian rhythm in tumors is coincident with aberrant inflammation and dysregulated metabolism. As their inter-relationship in cancer etiology is largely unknown, we investigated the link between the three in glioma. Tumor metabolite lactate- mediated increase in pro-inflammatory cytokine IL-1β was concomitant with elevated levels of core circadian regulators Clock and Bmal1. siRNA mediated knockdown of Bmal1 and Clock decreased (i) LDHA and IL-1β levels and (ii) release of lactate and pro-inflammatory cytokines. Lactate mediated deacetylation of Bmal1 and its interaction with Clock, regulate IL-1β levels and vice versa. Site-directed mutagenesis and luciferase reporter assay indicated the functionality of E-box sites on LDHA and IL-1β promoters. ChIP-re-ChIP revealed that lactate-IL-1β crosstalk positively affects co-recruitment of Clock-Bmal1 to these E-box sites. Clock-Bmal1 enrichment was accompanied by decreased H3K9me3, and increased H3K9ac and RNA pol II occupancy. Lactate-IL-1β-Clock (LIC) loop positively regulated expression of genes associated with cell cycle, DNA damage and cytoskeletal organization involved in glioma progression. TCGA data analysis suggested the presence of lactate- IL-1β-crosstalk in other cancers. The responsiveness of stomach and cervical cancer cells to lactate inhibition followed the same trend exhibited by glioma cells. In addition, components of LIC loop were found to be correlated with (i) patient survival, (ii) clinically actionable genes, and (iii) anti-cancer drug sensitivity. Our findings provide evidence for a potential cancer-specific axis wiring of IL-1β and LDHA through Clock -Bmal1, the outcome of which is to fuel an IL-1β-lactate autocrine loop that drives pro-inflammatory and oncogenic signals.

A gain-of-function mutation in isocitrate dehydrogenase 1 (IDH1) affects immune surveillance in gliomas. As elevated CD47 levels are associated with immune evasion in cancers, its status in gliomas harboring mutant IDH1 (IDH1-MT cells) was investigated. Decreased CD47 expression in IDH1-R132H-overexpressing cells was accompanied by diminished nuclear β-catenin, pyruvate kinase isoform M2 (PKM2), and TCF4 levels compared to those in cells harboring wild-type IDH1 (IDH1-WT cells). The inhibition of β-catenin in IDH1-WT cells abrogated CD47 expression, β-catenin-TCF4 interaction, and the transactivational activity of β-catenin/TCF4. The reverse effect was observed in IDH1-MT cells upon the pharmacological elevation of nuclear β-catenin levels. Genetic and pharmacological manipulation of nuclear PKM2 levels in IDH1-WT and IDH1-MT cells suggested that PKM2 is a positive regulator of the β-catenin-TCF4 interaction. The Cancer Genome Atlas (TCGA) data sets indicated diminished CD47, PKM2, and β-catenin levels in IDH1-MT gliomas compared to IDH1-WT gliomas. Also, elevated BRG1 levels with mutations in the ATP-dependent chromatin-remodeling site were observed in IDH1-MT glioma. The ectopic expression of ATPase-deficient BRG1 diminished CD47 expression as well as TCF4 occupancy on its promoter. Sequential chromatin immunoprecipitation (ChIP-re-ChIP) revealed the recruitment of the PKM2-β-catenin-BRG1-TCF4 complex to the TCF4 site on the CD47 promoter. This occupancy translated into CD47 transcription, as a diminished recruitment of this complex was observed in glioma cells bearing IDH1-R132H. In addition to its involvement in CD47 transcriptional regulation, PKM2-β-catenin-BRG1 cross talk affected the phagocytosis of IDH1-MT cells by microglia.