EN
Inhibition of IRE1 (inositol requiring enzyme-1),
the major signaling pathway of endoplasmic reticulum
stress, significantly decreases tumor growth and
proliferation of glioma cells. To elucidate the role of IRE1-
mediated glioma growth, we studied the expression of a
subset genes encoding for TNF (tumor necrosis factor)-
related factors and receptors and their hypoxic regulation
in U87 glioma cells overexpressing dominant-negative
IRE1 (dnIRE1). We demonstrated that the expression of
TNFAIP1, TNFRSF10D, TNFRSF21, TNFRSF11B, TNFSF7,
and LITAF genes is increased in glioma cells with modified
IRE1; however, TNFRSF10B, TRADD, and TNFAIP3 is
down-regulated in these cells as compared to their control
counterparts. We did not find TNFRSF1A gene expression
to change significantly under this experimental condition.
In control glioma cells, hypoxia leads to the up-regulated
expression of TNFAIP1, TNFAIP3, TRADD, and TNFRSF10D
genes and the concomitant down-regulation of TNFRSF21,
TNFRSF11B, and LITAF genes; while, TNFRSF10B and
TNFRSF1A genes are resistant to hypoxic treatment.
However, inhibition of IRE1 modifies the hypoxic
regulation of LITAF, TNFRSF21, TNFRSF11B, and TRADD
genes and introduces hypoxia-induced sensitivity to TNFRSF10B, TNFRSF1A, and TNFSF7 gene expressions.
Furthermore, knockdown by siRNA of TNFRSF21 mRNA
modifies the hypoxic effect on the IRE1-dependent rate
of proliferation and cell death in U87 glioma cells. The
present study demonstrates that fine-tuned manipulation
of the expression of TNF-related factors and receptors
directly relating to cell death and proliferation, is mediated
by an effector of endoplasmic reticulum stress, IRE1,
as well as by hypoxia in a gene-specific manner. Thus,
inhibition of the kinase and endoribonuclease activities
of IRE1 correlates with deregulation of TNF-related factors
and receptors in a manner that is gene specific and thus
slows tumor growth.