Inhibition of IRE1 signaling affects the expression of genes encoded glucocorticoid receptor and some related factors and their hypoxic regulation in U87 glioma cells

Abstract Objective. The aim of the present investigation was to examine the effect of inhibition of endoplasmic reticulum stress signaling, mediated by IRE1 (inositol requiring enzyme 1), which is a central mediator of the unfolded protein response on the expression of genes encoding glucocorticoid receptor (NR3C1) and some related proteins (SGK1, SGK3, NCOA1, NCOA2, ARHGAP35, NNT) and their hypoxic regulation in U87 glioma cells for evaluation of their possible significance in the control of the glioma growth. Methods. The expression of NR3C1,SGK1,SGK3, NCOA1, NCOA2, ARHGAP35, and NNT genes in U87 glioma cells, transfected by empty vector pcDNA3.1 (control) and cells without IRE1 signaling enzyme function (transfected by dnIRE1) upon hypoxia, was studied by quantitative polymerase chain reaction. Results. Inhibition of IRE1 signaling enzyme function up-regulates the expression of NR3C1, SGK1, NCOA1, NCOA2, ARHGAP35, and NNT genes in U87 glioma cells in comparison with the control glioma cells, with more significant changes for NR3C1, SGK1, and NNT genes. At the same time, the expression of SGK3 gene is strongly down-regulated in glioma cells upon inhibition of IRE1. We have also shown that hypoxia increases the expression of NR3C1, SGK1, NCOA2, ARHGAP35, and NNT genes but decreases SGK3 and NCOA1 genes expression in control glioma cells. Moreover, the inhibition of both enzymatic activities (kinase and endoribonuclease) of IRE1 in U87 glioma cells enhances the eff ect of hypoxia on the expression of SGK1, SGK3, and NNT genes, but decreases the sensitivity of NR3C1 gene to hypoxic condition. Furthermore, the expression of NCOA1 gene is resistant to hypoxia in control glioma cells, but NCOA2 and ARHGAP35 genes are resistant to this condition in glioma cells without functional activity of IRE1 signaling enzyme. Conclusions. Results of this investigation demonstrate that inhibition of IRE1 signaling enzyme function affects the expression of NR3C1, SGK1, SGK3, NCOA1, NCOA2, ARHGAP35, and NNT genes in U87 glioma cells in gene specific manner and that all these genes are regulated by hypoxia preferentially through IRE1 signaling pathway of the endoplasmic reticulum stress.