Ahmad F, Dixit D, Sharma V, Kumar A, Joshi S D, Sarkar C, Sen E
National Brain Research Centre, Department of Molecular and Cellular Neuroscience Division, Manesar, Gurgaon, Haryana 122051, India.
All India Institute of Medical Sciences, Department of Pathology, Ansari Nagar East, New Delhi 110029, India.
Cell Death Dis. 2016 May 5;7(5):e2213. doi: 10.1038/cddis.2016.117.
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.
鉴于端粒酶激活和代谢失调在胶质瘤进展中的作用，对这两个关键因素之间的联系进行了研究。木香内酯对人端粒酶逆转录酶（hTERT）的药理学抑制以活性氧（ROS）依赖的方式诱导胶质瘤细胞凋亡。木香内酯诱导ROS依赖的p53增加，从而消除端粒酶活性。木香内酯降低Nrf2水平；异位表达Nrf2可减少木香内酯诱导的ROS生成。虽然敲低TERT可消除Nrf2水平，但Nrf2的过表达会增加TERT的表达。用木香内酯、siRNA或显性负性hTERT（DN-hTERT）抑制hTERT可消除：（i）葡萄糖-6-磷酸脱氢酶（G6PD）和转酮醇酶（TKT）的表达，这是磷酸戊糖途径（PPP）中的两个主要节点；以及（ii）糖原合酶（GS）的磷酸化。敲低hTERT会降低TKT活性并增加糖原积累。有趣的是，siRNA介导的TKT敲低会增加糖原积累。与体外研究结果一致，木香内酯可减轻异型异种移植胶质瘤小鼠模型中的肿瘤负担。经木香内酯处理的肿瘤表现出TKT活性降低、糖原积累增加和衰老增加。重要的是，多形性胶质母细胞瘤（GBM）患者中携带已知与端粒酶活性增加相关的TERT启动子突变（C228T和C250T）的肿瘤，表现出Nrf2和TKT表达升高以及糖原积累减少。综上所述，我们的研究结果突出了端粒酶在调节PPP和糖原积累中以前未知的作用，以及Nrf2-TERT环在维持胶质瘤细胞氧化防御反应中的作用。
