Inhibition of IRE1 modifies the hypoxic regulation of GADD family gene expressions in U87 glioma cells.

O H Minchenko,I V Kryvdiuk,О O Riabovol

doi:10.15407/ubj88.02.025

Abstract

We have studied hypoxic regulation of the expression of genes encoded GADD (growth arrest and DNA damage) family proteins in U87 glioma cells in relation to inhibition of IRE1 (inositol requiring enzyme-1), which controls cell proliferation and tumor growth as a central mediator of endoplasmic reticulum stress. We have shown that hypoxia up-regulates the expression of GADD34, GADD45A, GADD45B, and GADD153 genes, which are related to cell proliferation and apoptosis, in control (transfected by empty vector) glioma cells in gene specific manner. At the same time, the expression level of EIF2AK 1 (eukaryotic translation initiation factor 2-alpha kinase 1) and AI FM1 (apoptosis inducing factor, mitochondria associated 1) genes in these cells is down-regulated upon hypoxic condition. It was also shown that inhibition of ІRE1 signaling enzyme function in U87 glioma cells enhances the effect of hypoxia on these genes expression, except EIF2AK 1 and AI FM1 genes. Furthermore, the expression of all studied genes in ІRE1 knockdown cells is significantly decreased upon normoxic condition, except GADD45B gene, which expression level is strongly up-regulated. Therefore, the expression level of genes encoding GADD34, GADD45A, GADD45B, GADD153, EIF2AK 1, and AI FM1 is affected by hypoxia and by inhibition of IRE1-mediated endoplasmic reticulum stress signaling in gene specific manner and correlates with suppression of glioma cell proliferation upon inhibition of the IRE1 enzyme function.

Highlights

Endoplasmic reticulum stress and hypoxia are necessary components of malignant tumors growth [1,2,3]
IRE1-associated endoribonuclease activity is involved in the degradation of a specific subset of mRNA and initiates the cytosolic splicing of the pre-XBP1 alternative splice variant (XBP1s) (Xbox binding protein 1) mRNA whose mature transcript encodes a transcription factor that stimulates the expression of unfolded protein response specific genes [2, 10]
The aim of this study was investigation the effect of hypoxia on the expression of growth arrest and DNA-damage-inducible 34 (GADD34), growth arrest and DNA-damage-inducible 45A (GADD45A), growth arrest and DNA-damage-inducible 45B (GADD45B), growth arrest and DNA-damage-inducible 153 (GADD153), and Eukaryotic translation initiation factor 2-alpha kinase 1 (EIF2AK1) genes, which related to cell proliferation and apoptosis, in glioma cells in relation to inhibition of signa ling enzyme IRE1

Summary

Introduction

Endoplasmic reticulum stress and hypoxia are necessary components of malignant tumors growth [1,2,3]. The GADD153, known as DDIT3 (DNA damage-inducible transcript 3), is a member of the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors (CHOP) and is activated by endoplasmic reticulum stress in carcinomas [20]. It plays an important role in the regulation of prolife ration and promotes endoplasmic reticulum stressmediated apoptosis through affecting the expression of TNFRSF10A and TNFRSF10B in human lung cancer cells [21, 22]. Eukaryotic translation initiation factor 2-alpha kinase 1 (EIF2AK1), an heme-controlled repressor, acts at the level of translation initiation to downregulate protein synthesis in response to various stress conditions, including endoplasmic reticulum stress through the phosphorylation of EIF2S1, preventing its recycling. Its level in carcinomas is significantly higher than in normal tissues [26]

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