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EN
Inhibition of IRE1 (inositol requiring enzyme-1), the major signaling pathway of endoplasmic reticulum stress, significantly decreases tumor growth and proliferation of glioma cells. To elucidate the role of IRE1- mediated glioma growth, we studied the expression of a subset genes encoding for TNF (tumor necrosis factor)- related factors and receptors and their hypoxic regulation in U87 glioma cells overexpressing dominant-negative IRE1 (dnIRE1). We demonstrated that the expression of TNFAIP1, TNFRSF10D, TNFRSF21, TNFRSF11B, TNFSF7, and LITAF genes is increased in glioma cells with modified IRE1; however, TNFRSF10B, TRADD, and TNFAIP3 is down-regulated in these cells as compared to their control counterparts. We did not find TNFRSF1A gene expression to change significantly under this experimental condition. In control glioma cells, hypoxia leads to the up-regulated expression of TNFAIP1, TNFAIP3, TRADD, and TNFRSF10D genes and the concomitant down-regulation of TNFRSF21, TNFRSF11B, and LITAF genes; while, TNFRSF10B and TNFRSF1A genes are resistant to hypoxic treatment. However, inhibition of IRE1 modifies the hypoxic regulation of LITAF, TNFRSF21, TNFRSF11B, and TRADD genes and introduces hypoxia-induced sensitivity to TNFRSF10B, TNFRSF1A, and TNFSF7 gene expressions. Furthermore, knockdown by siRNA of TNFRSF21 mRNA modifies the hypoxic effect on the IRE1-dependent rate of proliferation and cell death in U87 glioma cells. The present study demonstrates that fine-tuned manipulation of the expression of TNF-related factors and receptors directly relating to cell death and proliferation, is mediated by an effector of endoplasmic reticulum stress, IRE1, as well as by hypoxia in a gene-specific manner. Thus, inhibition of the kinase and endoribonuclease activities of IRE1 correlates with deregulation of TNF-related factors and receptors in a manner that is gene specific and thus slows tumor growth.
EN
Inhibition of ERN1 (endoplasmic reticulum to nuclei 1), the major signalling pathway of endoplasmic reticulum stress, significantly decreases tumor growth. We have studied the expression of tumor protein 53 (TP53)- related genes such as TOPORS (topoisomerase I binding, arginine/serine-rich, E3 ubiquitin protein ligase), TP53BP1 (TP53 binding protein 1), TP53BP2, SESN1 (sestrin 1), NME6 (non-metastatic cells 6), and ZMAT3 (zinc finger, Matrin-type 3) in glioma cells expressing dominantnegative ERN1 under baseline and hypoxic conditions. We demonstrated that inhibition of ERN1 function in U87 glioma cells resulted in increased expression of RYBP, TP53BP2, and SESN1 genes, but decreased expression of TP53BP1, TOPORS, NME6, and ZMAT3 genes. Moreover, inhibition of ERN1 affected hypoxia-mediated changes in expression of TP53-related genes and their magnitude. Indeed, hypoxia has no effect on expression of TP53BP1 and SESN1 in control cells, while resulted in increased expression of these genes in cells with inhibited ERN1 function. Magnitude of hypoxia-mediated changes in expression levels of RYBP and TP53BP2 was gene specific and more robust in the case of TP53BP2. Hypoxiamediated decrease in expression levels of TOPORS was more prominent if ERN1 was inhibited. Present study demonstrates that fine-tuning of the expression of TP53- associated genes depends upon endoplasmic reticulum stress signaling under normal and hypoxic conditions. Inhibition of ERN1 branch of endoplasmic reticulum stress response correlates with deregulation of p53 signaling and slower tumor growth.
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