Inhibition of signaling protein ERN1 increases the sensitivity of serine synthesis gene expressions to glucose and glutamine deprivations in U87MG glioblastoma cells

Objective. Glucose and glutamine supply as well as serine synthesis and endoplasmic reticulum (ER) stress are important factors of glioblastoma growth. Previous studies showed that the knockdown of ERN1 (ER to nucleus signaling 1) suppressed glioblastoma cell proliferation and modified the sensitivity of numerous gene expressions to nutrient deprivations. The present study is aimed to investigate the impact of glucose and glutamine deprivations on the expression of serine synthesis genes in U87MG glioblastoma cells in relation to ERN1 knockdown with the intent to reveal the role of ERN1 signaling pathway on the ER stress-dependent regulation of these gene expressions. Clarification of the regulatory mechanisms of serine synthesis is a great significance for glioblastoma therapy. Methods. The control U87MG glioblastoma cells (transfected by empty vector) and ERN1 knockdown cells (transfected by dominant-negative ERN1) were exposed under glucose and glutamine deprivation conditions for 16 h. RNA was extracted from cells and reverse transcribed. The expression level of PHGDH (phosphoglycerate dehydrogenase), PSAT1 (phosphoserine amino-transferase 1), PSPH (phosphoserine phosphatase), ATF4 (activating transcription factor 4), and SHMT1 (serine hydroxymethyltransferase 1) genes was studied by real-time qPCR and normalized to ACTB. Results. It was found that the expression level of genes responsible for serine synthesis such as PHGDH, PSAT1, PSPH, and transcription factor ATF4 was up-regulated in U87MG glioblastoma cells under glucose and glutamine deprivations. Furthermore, inhibition of ERN1 significantly enhances the impact of glucose and especially glutamine deprivations on these gene expressions. At the same time, the expression of the SHMT1 gene, which is responsible for serine conversion to glycine, was down-regulated in both nutrient deprivation conditions with more significant changes in ERN1 knockdown glioblastoma cells. Conclusion. Taken together, the results of present study indicate that the expression of genes responsible for serine synthesis is sensitive to glucose and glutamine deprivations in gene-specific manner and that suppression of ERN1 signaling significantly modifies the impact of both glucose and glutamine deprivations on PHGDH, PSAT1, PSPH, ATF4, and SHMT1 gene expressions and reflects the ERN1-mediated genome reprograming introduced by nutrient deprivation condition.

Cortisol controls endoplasmic reticulum stress and hypoxia dependent regulation of insulin receptor and related genes expression in HEK293 cells

Objective. Glucocorticoids are important stress-responsive regulators of insulin-dependent metabolic processes realized through specific changes in genome function. The aim of this study was to investigate the impact of cortisol on insulin receptor and related genes expression in HEK293 cells upon induction the endoplasmic reticulum (ER) stress by tunicamycin and hypoxia. Methods. The human embryonic kidney cell line HEK293 was used. Cells were exposed to cortisol (10 µM) as well as inducers of hypoxia (dimethyloxalylglycine, DMOG; 0.5 mM) and ER stress (tunicamycin; 0.2 µg/ml) for 4 h. The RNA from these cells was extracted and reverse transcribed. The expression level of INSR, IRS2, and INSIG2 and some ER stress responsive genes encoding XBP1n, non-spliced variant, XBP1s, alternatively spliced variant of XBP1, and DNAJB9 proteins, was measured by quantitative polymerase chain reaction and normalized to ACTB. Results. We showed that exposure of HEK293 cells to cortisol elicited up-regulation in the expression of INSR and DNAJB9 genes and down-regulation of XBP1s, XBP1n, IRS2, and INSIG2 mRNA levels. At the same time, induction of hypoxia by DMOG led to an up-regulation of the expression level of most studied mRNAs: XBP1s and XBP1n, IRS2 and INSIG2, but did not change significantly INSR and DNAJB9 gene expression. We also showed that combined impact of cortisol and hypoxia introduced the up-regulation of INSR and suppressed XBP1n mRNA expression levels. Furthermore, the exposure of HEK293 cells to tunicamycin affected the expression of IRS2 gene and increased the level of XBP1n mRNA. At the same time, the combined treatment of these cells with cortisol and inductor of ER stress had much stronger impact on the expression of all the tested genes: strongly increased the mRNA level of ER stress dependent factors XBP1s and DNAJB9 as well as INSR and INSIG2, but down-regulated IRS2 and XBP1n. Conclusion. Taken together, the present study indicates that cortisol may interact with ER stress and hypoxia in the regulation of ER stress dependent XBP1 and DNAJB9 mRNA expression as well as INSR and its signaling and that this corticosteroid hormone modified the impact of hypoxia and especially tunicamycin on the expression of most studied genes in HEK293 cells. These data demonstrate molecular mechanisms of glucocorticoids interaction with ER stress and insulin signaling at the cellular level.

Hypoxia controls the expression of genes responsible for serine synthesis in U87MG cells on ERN1-dependent manner

Objective. Serine synthesis as well as endoplasmic reticulum stress and hypoxia are important factors of malignant tumor growth including glioblastoma. Previous studies have shown that the knockdown of ERN1 (endoplasmic reticulum to nucleus signaling) significantly suppressed the glioblastoma cell proliferation and modified the hypoxia regulation. The present study is aimed to investigate the impact of hypoxia on the expression of PHGDH (phosphoglycerate dehydrogenase), PSAT1 (phosphoserine aminotransferase 1), PSPH (phosphoserine phosphatase), ATF4 (activating transcription factor 4), and SHMT1 (serine hydroxymethyltransferase 1) in U87MG glioblastoma cells in relation to knockdown of ERN1 with the intent to reveal the role of ERN1 signaling pathway on the endoplasmic reticulum stress-dependent regulation of expression of these genes. Methods. The control U87MG glioblastoma cells (transfected by empty vector) and ERN1 knockdown cells (transfected by dominant-negative ERN1) were exposed to hypoxia introduced by dimethyloxalylglycine for 4 h. RNA was extracted from cells and reverse transcribed. The expression level of PHGDH, PSAT1, PDPH, SHMT1, and ATF4 genes was studied by real-time qPCR and normalized to ACTB. Results. It was found that hypoxia up-regulated the expression level of PHGDH, PSAT1, and ATF4 genes in control U87MG cells, but PSPH and SHMT1 genes expression was down-regulated. The expression of PHGDH, PSAT1, and ATF4 genes in glioblastoma cells with knockdown of ERN1 signaling protein was more sensitive to hypoxia, especially PSAT1 gene. At the same time, the expression of PSPH gene in ERN1 knockdown cells was resistant to hypoxia. The expression of SHMT1 gene, encoding the enzyme responsible for conversion of serine to glycine, showed similar negative sensitivity to hypoxia in both control and ERN1 knockdown glioblastoma cells. Conclusion. The results of the present study demonstrate that the expression of genes responsible for serine synthesis is sensitive to hypoxia in gene-specific manner and that ERN1 knockdown significantly modifies the impact of hypoxia on the expression of PHGDH, PSAT1, PSPH, and ATF4 genes in glioblastoma cells and reflects the ERN1-mediated reprograming of hypoxic regulation at gene expression level.

The low doses of SWCNTs affect the expression of proliferation and apoptosis related genes in normal human astrocytes

The unique properties of single-walled carbon nanotubes (SWCNTs) make them viable candidates for versatile implementation in the biomedical devices. They are able to cross the blood-brain barrier, enter cells and accumulate in cell nuclei. We studied the effect of these carbon nanoparticles on the expression of genes associated with endoplasmic reticulum stress and proliferation, cell viability and cancerogenesis as well as microRNAs in normal human astrocytes. We have shown that treatment of normal human astrocytes by small doses of SWCNTs (2 and 8 ng/ml of medium for 24 hrs) affect the expression of DNAJB9, IGFBP3, IGFBP6, CLU, ZNF395, KRT18, GJA1, HILPDA, and MEST mRNAs as well as several miRNAs, which have binding sites at 3'-UTR of these mRNAs. These changes in the expression profile of individual mRNAs introduced by SWCNTs are dissimilar in magnitude and direction and are the result of both transcriptional and posttranscriptional mechanisms of regulation. It is possible that these changes in gene expressions are mediated by the endoplasmic reticulum stress introduced by carbon nanotubes and reflect the disturbance of the genome stability. In conclusion, the low doses of SWCNTs disrupt the functional integrity of the genome and possibly exhibit a genotoxic effect.