Expression of phosphoribosyl pyrophosphate synthetase genes in U87 glioma cells with ERN1 knockdown: effect of hypoxia and endoplasmic reticulum stress

O H Minchenko

doi:10.15407/ubj86.06.074

Abstract

Activation of pentose phosphate pathway is an important factor of enhanced cell proliferation and tumor growth. Phosphoribosyl pyrophosphate synthetase (PRPS) is a key enzyme of this pathway and plays a central role in the synthesis of purines and pyrimidines. Hypoxia as well as ERN1 (from endoplasmic reticulum to nuclei-1) mediated endoplasmic reticulum stress response-signalling pathway is linked to the proliferation because the blockade of ERN1 suppresses tumor growth, including glioma. We studied the expression of different PRPS genes in glioma cells with ERN1 knockdown under hypoxic condition. It was shown that hypoxia decreases the expression of PRPS1 and PRPS2 genes in both types of glioma cells, being more pronounced in cells without ERN1 function, but PRPSAP1 and PRPSAP2 gene expressions are suppressed by hypoxia only in glioma cells with blockade of ERN1. Moreover, the blockade of endoribonuclease activity of ERN1 does not affect the expression of PRPS1 and PRPS2 as well as PPRS-associated protein genes in U87 glioma cells. At the same time, the induction of endoplasmic reticulum stress by tunicamycin in glioma cells with suppressed activity of ERN1 endoribonuclease decreases the expression level of PRPS1 and PRPS2 genes only. Results of this investigation clearly demonstrated that the expression of different genes encoding subunits of PRPS enzyme is affected by hypoxia in U87 glioma cells, but the effect of hypoxia is modified by suppression of endoplasmic reticulum stress signaling enzyme ERN1.

Highlights

M alignant gliomas are highly aggressive tumors and are characterized by marked angiogenesis and extensive tumor cell invasion into the normal brain parenchyma, and to date there is no efficient treatment available
We studied the expression of four different genes which encoded phosphoribosyl pyrophosphate synthetase, which exists as heterotetramer and contains two catalytic subunits (PRPS1 and PRPS2) and two associated proteins (PRPSAP1 and PRPSAP2) in U87 glioma cells under hypoxia and under complete blockade of ERN1 signaling enzyme function as well as in cells with mutation in ERN1 endoribonuclease active center
We have shown that the induction of endoplasmic reticulum stress by tunicamycin in glioma cells with suppressed endoribonuclease activity of ERN1 signaling enzyme leads to a significant decrease of both catalytic subunits of PRPS (Fig. 1 and 2)

Summary

Introduction

M alignant gliomas are highly aggressive tumors and are characterized by marked angiogenesis and extensive tumor cell invasion into the normal brain parenchyma, and to date there is no efficient treatment available. The endoplasmic reticulum is a key organelle in the cellular response to hypoxia and some chemicals which activate a complex set of signaling pathways named the unfolded protein response. ERN1 is the dominant sensor of the unfolded protein response to the accumulation of misfolded proteins and represents a key regulator of life and death processes [6,7,8,9,10]. As such, it participates in the early cellular response to the accumulation of misfolded proteins in the lumen of the endoplasmic reticulum [11, 12]. The malignant tumors use the endoplasmic reticulum stress and ischemia for activation of proliferation, because the endoplasmic reticulum stress response-signalling IRE-1 pathway is linked with the apoptosis as well as cell death processes and suppression of IRE-1 gene function significantly decreases the tumour growth [6, 16,17,18]

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