Inhibition of IRE1 modifies hypoxic regulation of G6PD, GPI, TKT, TALDO1, PGLS and RPIA genes expression in U87 glioma cells.

O H Minchenko,D O Minchenko,I A Garmash, ,Bohomolets National Medical University, Kyiv, Ukraine

doi:10.15407/ubj89.01.038

Abstract

We have studied the effect of hypoxia on the expression level of mRNA of the basic enzymes of pentose-phosphate cycle (G6PD, TKT, TALDO1, PGLS and RPIA) and glucose-6-phosphate isomerase (GPI) in U87 glioma cells in relation to inhibition of IRE1 (inositol requiring enzyme 1). It was shown that hypoxia leads to up-regulation of the expression of GPI and PGLS genes and to down-regulation of TALDO1 and RPIA genes in control glioma cells. Changes for GPI gene were more significant than for other genes. At the same time, inhibition of IRE1 modified the effect of hypoxia on the expression of all studied genes. In particular, it increased sensitivity to hypoxia of G6PD and TKT genes expression and suppressed the effect of hypoxia on the expression of GPI and RPIA genes. Additionally, inhibition of IRE1 eliminated hypoxic regulation of PGLS gene and did not change significantly effect of hypoxia on the expression of TALDO1 gene in glioma cells. Present study demonstrated that hypoxia, which often contributes to tumor growth, affects the expression of most studied genes and inhibition of IRE1 modified the hypoxic regulation of pentose-phosphate cycle gene expressions in a gene specific manner and thus possibly contributes to slower glioma growth, but several aspects of this regulation warrant further investigation.

Highlights

Pentose phosphate pathway of glucose metabo lism plays an important role in the regula tion of various processes both in normal and pathological conditions, especially in glioma growth, and depends on endoplasmic reticulum stress, which is obligate component of cancer growth [1,2,3,4]
To determine if hypoxia affects the expression of a subset of genes encoding pentose phosphate pathway enzymes, such as G6PD, TKT, TAL DO1, PGLS (6-phosphoglucolacto nase), and RPIA, as well as glucose-6-phosphate isomerase (GPI) through the IRE1 branch of endoplasmic reticulum stress response, we investigated the effect of hypoxia on the expression level of these genes in control glioma cells and cells without both enzymatic activities of this signaling enzyme
To in vestigate a possible role of endoplasmic reticulum stress signaling mediated by IRE1 enzyme in regu lation of the expression of GPI gene by hypoxia, we investigated the effect of hypoxic condition on this gene expression in glioma cells without enzymatic activities of this signaling enzyme

Summary

Introduction

Pentose phosphate pathway of glucose metabo lism plays an important role in the regula tion of various processes both in normal and pathological conditions, especially in glioma growth, and depends on endoplasmic reticulum stress, which is obligate component of cancer growth [1,2,3,4]. Pentose phosphate pathway genes such as G6PD (glucose-6-phosphate dehydrogenase), TKT (transketolase), TALDO1 (transaldolase 1), PGLS (6-phosphoglucolactonase) та RPIA (ribose-5-phos phate isomerase) as well as GPI (glucose phosphate isomerase) gene play an important role in malignant tumor growth [2,3,4]. Transaldolase is a key enzyme of the nonoxi dative pentose phosphate pathway providing ribose5-phosphate for nucleic acid synthesis and NADPH for lipid biosynthesis [18] This enzyme as well as TKT are important for the balance of metabolites in the pentose-phosphate pathway and involved in mitochondrial homoeostasis, oxidative stress, apop tosis, multiple sclerosis, and cancer [2, 18,19,20]. AMF/PGI may contribute to HER2-mediated breast cancer progression [28]

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