Khita O. Mechanisms of expression regulation of nuclear genes encoded mitochondrial proteins in U87 glioma cells under IRE1 inhibition

Expression of genes encoding mitochondrial enzymes of citric acid cycle and factors which controll mitochondrial transcription and translation and regulate bioenergetic status, proliferation and apoptosis was studied in this work. The expression level of these genes was investigated in glioma cell line U87 with full and partial inhibition of IRE1 functional activity, which is the main sensor enzyme of endoplasmic reticulum stress. Also influence of hypoxia and deprivation of glutamine and glucose on genes expression is investigated to assess the role of these genes in ERN1-mediated control of glioma cells proliferation, as well as under hypoxic condition and deficiency of glucose or glutamine. Present study has clarified the possible role of these genes in IRE1-mediated suppression of glioma cells proliferation. For the first time it have been shown that inhibition of IRE1-mediated ER stress signalling pathway affects the expression level of all studied nuclear genes of mitochondrial proteins in gene specific manner and thus possibly contributes to slower glioma growth. It was found that observed changes in genes expression was mediated by both kinase and endoribonuclease activities of IRE1. Furthermore, the blockade of IRE1 function modifies the effects of hypoxia and glucose or glutamine deprivation on the expression levels of almost all studied genes. Differential changes of the expression level of nuclear genes encoding mitochnodrial enzymes and factors in glioma cells under inhibition of IRE1 clearly demonstrate the phenomenon of ER stress-dependent functional reprogramming of mitochondria under these experimental conditions. The obtained results strongly suggest an important role of nuclear genes of mitochondrial proteins in glioma cell proliferation with blockade of IRE1 enzyme function and partly clarify molecular mechanisms of hypoxia and nutrient deprivation influence on the expression level of these genes. Keywords: glioma, gene expression, IRE1 inhibition, endoplasmic reticulum stress, mitochondrial proteins, reprogramming of mitochondria, hypoxia, glucose deprivation, glutamine deprivation.