Endoplasmic reticulum–nuclei signaling enzyme-1 knockdown modulates effect of hypoxia and ischemia on the expression of circadian genes in glioma cells

The main molecular components of circadian clock system are proteins which play a significant role in the control of both metabolism and malignant tumor growth. Endoplasmic reticulum stress as well as hypoxia and ischemia are important factors for tumor neovascularization and growth. We have studied the expression of circadian genes in the glioma cell line U87 under knockdown of endoplasmic reticulum–nuclei-1 (ERN1) sensing and signaling enzyme. It was shown that blockade of ERN1 leads to increase in the expression levels of PER1, PER3 and CLOCK mRNA; but the CRY1, PER2, BMAL1, BMAL2 and DEC2 mRNA levels are decreased. Moreover, the expression levels of most of the studied genes are increased under glucose or glutamine deprivation conditions both in control and ERN1-deficient glioma cells; however knockdown of ERN1 modifies the effect of these ischemic conditions. Hypoxia has different effects on the expression levels of circadian genes and these effects are dependent on ERN1 function. Hypoxia induces the expression of PER1, BMAL1 and DEC2 and decreased – PER3, CLOCK, CRY1 and BMAL2 mRNA in control glioma cells, while in genetically modified cells it induces the expression of BMAL1 mRNA only. Thus, the expression of circadian genes is dependent on ERN1 signaling enzyme function in normal, hypoxic and ischaemic conditions.