EFFECT OF HYPOXIA ON THE EXPRESSION OF GENES THAT ENCODE SOME IGFBP AND CCN PROTEINS IN U87 GLIOMA CELLS DEPENDS ON IRE1 SIGNALING.

O H Minchenko, ,D O Minchenko,L L Karbovskyi,A P Kharkova,Bohomolets National Medical University, Kyiv, Ukraine

doi:10.15407/ubj87.06.052

Abstract

We have studied hypoxic regulation of the expression of different insulin-like growth factor binding protein genes in U87 glioma cells in relation to inhibition of IRE1 (inositol requiring enzyme-1), a central mediator of endoplasmic reticulum stress, which controls cell proliferation and tumor growth. We have demonstrated that hypoxia leads to up-regulation of the expression of IGFBP6, IGFBP7, IGFBP10/CYR61, WISP1, and WISP2 genes and down-regulation--of IGFBP9/NOV gene at the mRNA level in control glioma cells, being more signifcant changes for IGFBP10/CYR61 and WISP2 genes. At the same time, inhibition of IRE1 modifies the effect of hypoxia on the expression of all studied genes: eliminates sensitivity to hypoxia the expression of IGFBP7 and IGFBP9/NOV genes, suppresses effect of hypoxia on IGFBP6, IGFBP10/CYR61, and WISP2 genes, and slightly enhances hypoxic regulation of WISP1 gene expression in glioma cells. We have also demonstrated that the expression of all studied genes in glioma cells is regulated by IRE1 signaling enzyme upon normoxic condition, because inhibition of IRE1 significantly up-regulates IGFBP7, IGFBP10/CYR61, WISP1, and WISP2 genes and down-regulates IGFBP6 and IGFBP9/NOV genes as compared to control glioma cells. The present study demonstrates that hypoxia, which contributes to tumor growth, affects all studied IGFBP and WISP gene expressions and that inhibition of IRE1 preferentially abolishes or suppresses the hypoxic regulation of these gene expressions and thus possibly contributes to slower glioma growth. Moreover, inhibition of IRE1, which correlates with suppression of cell proliferation and glioma growth, is down-regulated expression of pro-proliferative IGFBP genes, attesting to the fact that endoplasmic reticulum stress is a necessary component of malignant tumor growth.

Highlights

Insulin-like growth factor binding proteins (IGFBPs) contain insulin-like growth factor (IGF) binding domain and play an important role in the regulation of numerous metabolic and proliferative processes mainly through interaction with IGF1 and IGF2, their cell surface receptors as well as insulin receptor, alter the half-life of the IGFs, modifying their biological activity
To determine if hypoxia affects the expression of a subset of genes encoding for different insulinlike growth factor binding proteins through the IRE1 branch of endoplasmic reticulum stress response, we investigated the effect of hypoxic condition on mRNA expression levels of different members of IGFBP and CCN families, which can participate in the regulation of glioma growth through insulinlike growth factor receptors as well as through other signaling pathways and mechanisms
To investigate a possible role of endoplasmic reticulum stress signaling mediated by signaling enzyme IRE1 in the expression of insulin-like growth factor binding protein gene IGFBP6 and its sensitivity to hypoxia we studied the effect of hypoxic condition on this gene expression in glioma cells with functional IRE1 and cells without both enzymatic activities of this signaling enzyme

Summary

Introduction

Insulin-like growth factor binding proteins (IGFBPs) contain insulin-like growth factor (IGF) binding domain and play an important role in the regulation of numerous metabolic and proliferative processes mainly through interaction with IGF1 and IGF2, their cell surface receptors as well as insulin receptor, alter the half-life of the IGFs, modifying their biological activity. The IGFBPs have different affinity for insulin-like growth factors They bind and regulate the availability of both insulin-like growth factors and inhibit or stimulate the growth promoting effects of the IGFs through IGF/INS receptors and through other signaling pathways and regulate cell proliferation and survival as well as angiogenesis and cancer. IGFBPs function in the cells and extracellular matrix to regulate cell proliferation and survival and are involved in tumor development, progression and resistance to treatment Because they interact with many proteins, in addition to their canonical ligands (IGF1 and IGF2), they play an important role in the regulation of various processes including transcription [6, 7]. IGFBP7 has diverse biological functions, regulating cell proliferation, apoptosis and senescence; it may play a key role in vascular biology [6] It elicits its biological effects by both insulin/ IGF-dependent and -independent mechanisms. The ele vated levels of WISP1/CCN4 and CYR61/CCN1 in primary breast cancers were associated with more advanced features [15]

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