Inositol-requiring enzyme 1α is a key regulator of angiogenesis and invasion in malignant glioma

Abstract

Inositol-requiring enzyme 1 (IRE1) is a proximal endoplasmic reticulum (ER) stress sensor and a central mediator of the unfolded protein response. In a human glioma model, inhibition of IRE1α correlated with down-regulation of prevalent proangiogenic factors such as VEGF-A, IL-1β, IL-6, and IL-8. Significant up-regulation of antiangiogenic gene transcripts was also apparent. These transcripts encode SPARC, decorin, thrombospondin-1, and other matrix proteins functionally linked to mesenchymal differentiation and glioma invasiveness. In vivo, using both the chick chorio-allantoic membrane assay and a mouse orthotopic brain model, we observed in tumors underexpressing IRE1: (i) reduction of angiogenesis and blood perfusion, (ii) a decreased growth rate, and (iii) extensive invasiveness and blood vessel cooption. This phenotypic change was consistently associated with increased overall survival in glioma-implanted recipient mice. Ectopic expression of IL-6 in IRE1-deficient tumors restored angiogenesis and neutralized vessel cooption but did not reverse the mesenchymal/infiltrative cell phenotype. The ischemiaresponsive IRE1 protein is thus identified as a key regulator of tumor neovascularization and invasiveness.tumor ischemia | unfolded protein response | mesenchymal drift

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

“…Multiple studies have clarified the link between can cer and endoplasmic reticulum stress, which con trols diffe rent processes including cell proliferation and surviving as well as circadian rhythms [32,35]. Furthermore, the inhibition of IRE1 as a central me diator of the unfolded protein response leads to sup pression of tumor growth through downregulation of key proangiogenic and proproliferative factors and upregulation of tumor suppressor genes as well as through modification of hypoxic regulation of these genes [4,6]. However, the executive mecha nisms of the exhibited anti-proliferative effects of IRE1 inhibition are not yet known.…”

“…This untreated subline of glioma cells (control glioma cells) was used in the study of the effect of hypoxia on the expression level of G6PD, tkt, TALDO1, PGLS, rPIA, and GPI genes. The second subline was obtained by selection of sta ble transfected clone with overexpression of IRE1 dominant/negative construct (dnIRE1) and conse quent inhibition of both protein kinase and endori bonuclease activities of this signaling enzyme of en doplasmic reticulum stress [6]. Effect of hypoxia on the expression levels of studied genes in these two sublines of glioma cells were compared with corre sponding levels in cells, transfected by vector or by dnIRE1.…”

“…The IRE1as sociated protein kinase autophosphorylates and di merizes this enzyme in the endoplasmic reticulum membrane, leading to the activation of its endoribo nuclease domain, and has some additional functions [7]. Endoribonuclease activity is responsible for deg radation of a specific subset of mRNA and initiation of the preXBP1 (Xbox binding protein 1) mRNA splicing that stimulates the expression of more than five hundreds of unfolded protein response-specific genes [6,30,31]. It is possible that this activation of the ERN1 endoribonuclease is a result of its interac tion with other sensorsignalling systems of endo plasmic reticulum stress.…”

“…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/endoplasmic reticulum stress, which controls numerous processes including proliferation [6,29]. The signa ling enzyme IRE1 has two distinct catalytic domains: serine/thre onine kinase and endoribonuclease.…”

“…Effect of hypoxia on the expression levels of studied genes in these two sublines of glioma cells were compared with corre sponding levels in cells, transfected by vector or by dnIRE1. The efficiency of IRE1 suppression in this glioma cell subline was estimated previously [6,7] by determining the expression level of spliced XBP1, a key transcription factor in the IRE1 signaling, and the level of the phosphorylated IRE1 isoform in cells treated by tunicamycin (0.01 mg/ml during 2 h).…”