ERN1 dependent impact of glucose and glutamine deprivations on PBX3, PBXIP1, PAX6, MEIS1, and MEIS2 genes expression in U87 glioma cells

Abstract

Objective. Homeobox genes play a fundamental role in the embryogenesis, but some of them have been linked to oncogenesis. The present study is aimed to investigate the impact of glucose and glutamine deprivations on the expression of homeobox genes such as PAX6 (paired box 6), PBX3 (PBX homeobox 3), PBXIP1 (PBX homeobox interacting protein 1), MEIS1 (MEIS homeobox 1), and MEIS2 in ERN1 knockdown U87 glioma cells with the intent to reveal the role of ERN1 (endoplasmic reticulum to nucleus signaling 1) signaling pathway on the endoplasmic reticulum stress dependent regulation of homeobox genes. Methods. The control (transfected by empty vector) and ERN1 knockdown (transfected by dominant-negative ERN1) U87 glioma cells were exposed to glucose and glutamine deprivations for 24 h. The cells RNA was extracted and reverse transcribed. The expression level of PAX6, PBX3, PBXIP1, MEIS1, and MEIS2 genes was evaluated by a real-time quantitative polymerase chain reaction analysis and normalized to ACTB. Results. It was found that glucose deprivation down-regulated the expression level of PAX6, MEIS1, and MEIS2 genes in control glioma cells, but did not significantly alter PBX3 and PBXIP1 genes expression. At the same time, ERN1 knockdown significantly modified the sensitivity of all studied genes to glucose deprivation. Other changes in gene expression were detected in control glioma cells under the glutamine deprivation. The expression of PBX3 and MEIS2 genes was down- while PAX6 and PBXIP1 genes up-regulated. Furthermore, ERN1 knockdown significantly modified the effect of glutamine deprivation on the majority of studied genes expression in U87 glioma cells. Conclusion. The results of the present study demonstrate that the exposure of U87 glioma cells under glucose and glutamine deprivations affected the expression of the majority of the studied homeobox genes and that the sensitivity of PAX6, PBX3, PBXIP1, MEIS1, and MEIS2 genes expression under these experimental conditions is mediated by ERN1, the major pathway of the endoplasmic reticulum stress signaling.