ERN1 knockdown modifies the hypoxic regulation of TP53, MDM2, USP7 and PERP gene expressions in U87 glioma cells.

Endoplasmic reticulum stress and hypoxia are necessary components of malignant tumors growth and suppression of ERN1 (from endoplasmic reticulum to nuclei-1) signalling pathway, which is linked to the apoptosis and cell death processes, significantly decreases proliferative processes. Glioma cells with ERN1 knockdown were used in order to investigate the effect of ERNI blockade on the expression of TP53, MDM2, PERP, and USP7 genes and its hypoxic regulation. We have studied the expression of TP53 (tumor protein 53), MDM2 (TP53 E3 ubiquitin protein ligase homolog), PERP (TP53 apoptosis effector), and USP7 (ubiquitin specific peptidase 7) genes, which are related to cell proliferation and apoptosis, in glioma cells with ERN1 knockdown under hypoxic condition. It was shown that blockade of ERNI gene function in U87 glioma cells intensified the expression of TP53 and USP7 genes, but decreased the expression ofMDM2 and PERP genes. Thus, an enhanced expression of TP53 gene in ERN1 knockdown glioma cells correlates with the decreased level of ubiquitin ligase MDM2 and increased expression level of USP7 which deubiquitinates TP53 and MDM2 and induces TP53-dependent cell growth repression and apoptosis. At the same time, the expression levels of TP53, MDM2, and USP7 genes do not change significantly in glioma cells with suppression of endoribonuclease activity only, but PERP gene expression is strongly increased. Moreover, the expression of TP53 and UPS7 genes is decreased in hypoxic conditions in control glioma cells only; however, MDM2 and PERP gene expressions are increased in both cell types, being more significant in ERN1 knockdown cells. Thus, the expression of genes encoding TP53 and related to TP53 factors depends upon the endoplasmic reticulum stress signaling as well as on hypoxia, and correlates with suppression of glioma growth under ERN1 knockdown.