Nrf2-driven TERT regulates pentose phosphate pathway in glioblastoma

Abstract

Given the involvement of telomerase activation and dysregulated metabolism in glioma progression, the connection between these two critical players was investigated. Pharmacological inhibition of human Telomerase reverse transcriptase (hTERT) by Costunolide induced glioma cell apoptosis in a reactive oxygen species (ROS)-dependent manner. Costunolide induced an ROS-dependent increase in p53 abrogated telomerase activity. Costunolide decreased Nrf2 level; and ectopic Nrf2 expression decreased Costunolide-induced ROS generation. While TERT knock-down abrogated Nrf2 levels, overexpression of Nrf2 increased TERT expression. Inhibition of hTERT either by Costunolide, or by siRNA or dominant-negative hTERT (DN-hTERT) abrogated (i) expression of Glucose-6-phosphate dehydrogenase (G6PD) and Transketolase (TKT) – two major nodes in the pentose phosphate (PPP) pathway; and (ii) phosphorylation of glycogen synthase (GS). hTERT knock-down decreased TKT activity and increased glycogen accumulation. Interestingly, siRNA-mediated knock-down of TKT elevated glycogen accumulation. Coherent with the in vitro findings, Costunolide reduced tumor burden in heterotypic xenograft glioma mouse model. Costunolide-treated tumors exhibited diminished TKT activity, heightened glycogen accumulation, and increased senescence. Importantly, glioblastoma multiforme (GBM) patient tumors bearing TERT promoter mutations (C228T and C250T) known to be associated with increased telomerase activity; exhibited elevated Nrf2 and TKT expression and decreased glycogen accumulation. Taken together, our findings highlight the previously unknown (i) role of telomerase in the regulation of PPP and glycogen accumulation and (ii) the involvement of Nrf2-TERT loop in maintaining oxidative defense responses in glioma cells.

Mutant Isocitrate Dehydrogenase 1 Disrupts PKM2–β-Catenin–BRG1 Transcriptional Network-Driven CD47 Expression

“…To analyze the endogenous IDH1 mRNA levels in IDH1-WT and IDH1-MT cells, RNA was isolated by using an RNeasy kit (Qiagen, Hilden, Germany), and cDNA was synthesized by using a High Capacity cDNA reverse transcription kit (Applied Biosystems Inc., Foster City, CA) on a Veriti thermal cycler (Applied Biosystems Inc.). Real-time PCR was performed as described previously (49), using a ViiA7 real-time thermocycler (Applied Biosystems Inc.), and results were plotted as fold changes over the values for the control (empty vector) for the IDH1 mRNA transcript. Values for all samples were normalized to their respective 18S rRNA threshold cycle (C T ) values.…”

Targeting immunometabolism as an anti-inflammatory strategy

“…32 In addition, Nrf2-driven expression of telomerase reverse transcriptase is required for the expression of glucose-6phosphate dehydrogenase (G6PD) and transketolase of the pentose phosphate pathway in glioblastoma. 33 In the context of hypercholesterolemia, Nrf2-deficient macrophages displayed downregulated expression of several genes of the pentose phosphate pathway, including 6-phosphogluconate dehydrogenase. 31 Somewhat surprising therefore, in human erythrocytes, DMF has been shown to inhibit G6PD, the rate-limiting enzyme of the oxidative branch of the pentose phosphate pathway, resulting in modulation of NADPHdependent glutathione reductase activity, as well as induction of eryptosis and cell shrinkage.…”

Metabolic reprogramming in the pathogenesis of glioma: Update

“…The altered metabolic landscape in IDH ‐mutant gliomas also affects phospholipid, energy, and oxidative stress pathways . Further, IDH mutations can indirectly reactivate telomerase reverse transcriptase (TERT), which regulates a part of metabolic pathways in GBM …”

“…16 Further, IDH mutations can indirectly reactivate telomerase reverse transcriptase (TERT), 17,18 which regulates a part of metabolic pathways in GBM. 19,20 Hypoxia promotes metabolic reprogramming in IDH wildtype gliomas Primary GBM (GBM, IDH wild-type) and IDH-wild-type…”