Hydrocortisone interacts with endoplasmic reticulum stress in hypoxic regulation of phosphoserine aminotransferase 1 gene expression differently in normal human astrocytes and glioblastoma cells.

Abstract

Objective. Endoplasmic reticulum (ER) stress and hypoxia are key factors for the effective growth of malignant tumors, including glioblastoma. The phosphoserine aminotransferase 1 (PSAT1) is an ER stress-responsive enzyme responsible for serine synthesis and necessary for tumor cell proliferation. The present study aims to investigate the regulation of the PSAT1 gene expression in U87MG glioblastoma cells and normal human astrocytes by ER stress and hypoxia depending on hydrocortisone, a native stress hormone used for co-treatment of glioblastoma and other malignant tumors. Methods. The U87MG glioblastoma cells and normal human astrocytes were used. Hypoxia was introduced by dimethyloxalylglycine. Tunicamycin was used for the induction of ER stress. Further, the cells were treated with hydrocortisone. RNA was extracted from cells after 4 h exposure to hydrocortisone, tunicamycin, and hypoxia. The expression level of the PSAT1 gene was studied by quantitative RT-PCR and normalized to ACTB mRNA. Results. We found that treatment of normal human astrocytes with hydrocortisone resulted in a decreased expression of the PSAT1 gene, but its expression in glioblastoma cells was resistant to this hormone action. However, hypoxia did not significantly change the expression of the PSAT1 gene in normal astrocytes, but strongly modified the effect of hydrocortisone on this gene expression. At the same time, hypoxia increased the expression of the PSAT1 gene in glioblastoma cells independently of hydrocortisone. Tunicamycin decreased the expression of this gene in normal astrocytes, but increased it in glioblastoma cells. In addition, the impact of tunicamycin on PSAT1 gene expression was suppressed by hypoxia in both normal astrocytes and glioblastoma cells and by hydrocortisone only in normal astrocytes. At the same time, the combined effect of hypoxia and hydrocortisone greatly enhanced the expression of the PSAT1 gene in tunicamycin-treated normal astrocytes and especially glioblastoma cells. Conclusion. The results of this study showed that hydrocortisone differentially controls the regulation of PSAT1 gene expression by ER stress and hypoxia in normal astrocytes and glioblastoma cells and that the combined effect of hydrocortisone and hypoxia greatly enhanced PSAT1 gene expression in tunicamycin-treated cells.