Glucose-regulated protein 75 overexpression attenuates ionizing radiation-mediated injury in PC12 cells by inducing the expression of topoisomerase IIα

Abstract

Abstract. Glucose-regulated protein 75 (Grp75), also known as mortalin/mthsp70/PBP74, is a member of the heat-shock protein 70 (HSP70) family. Grp75 is known to protect cells from stress-induced injury. Previous studies have shown that the expression of Grp75 is upregulated by a low dose of ionizing radiation (IR). To evaluate the protective role of Grp75 on cell proliferation in response to IR, Grp75 was overexpressed in a rat adrenal pheochromocytoma cell line (PC12). It was revealed that Grp75 overexpression desensitized PC12 cells to IR-mediated cell injury. In addition, the expression of topoisomerase IIα (Topo IIα) was downregulated in PC12 cells following γ-ray IR. The effect of Grp75 overexpression on Topo IIα expression was examined. It was revealed that Grp75 overexpression reversed the inhibitory effect of IR on Topo IIα expression. In conclusion, the data indicated that Grp75 overexpression attenuates IR-induced injury in PC12 cells by maintaining the expression of Topo IIα. IntroductionIonizing radiation (IR) induces a variety of cellular responses at clinically relevant doses. MCF-7 cells were arrested at the G1 and G2 phases of the cell cycle and MDA-MB231 cells were arrested at the G2 phase in response to IR (1,2). It has been demonstrated that X-rays at extremely low doses, between 1-5 cGy, stimulate cell proliferation, whereas at doses >1 Gy, IR is lethal to cells (3). Topoisomerase IIα (Topo IIα), a nuclear enzyme involved in a number of cellular processes, is necessary for eukaryotic survival. Topo IIα is significant in the replication and repair of DNA and takes part in chromosome condensation and segregation during mitosis (4). Previous studies have demonstrated that DNA Topo IIα expression levels correlate with chromatid radiosensitivity (5). Topo IIα has also been shown to play a significant role in male mouse meiosis and its activity is required at the metaphase-anaphase transition of the two meiotic divisions for proper chromosome disjunction (6,7). The expression of Topo IIα changes periodically during cell growth and therefore, Topo IIα is thought to be a marker of cell proliferation (8-10). Topo IIα expression is affected by numerous environmental factors, including heat-shock and IR. It has been reported that, if the activity of Topo IIα is restrained or the distribution of Topo IIα in cells changes as the result of genetic mutations, the aneuploid ratio of the cells increases (11,12).Grp75, a member of the HSP70 family, is involved in multiple functions that are required to maintain cell metabolism, including the stress response, cell proliferation and differentiation (13). Previous studies have demonstrated that Grp75 levels appear to correlate with mitochondrial activity and biogenesis (14) and that Grp75 expression is induced by cerebral ischemia (15), glucose deprivation (16) and low doses of IR (17). The gene expression of Grp75 in HT29 and MCF-7 cells was upregulated following exposure to IR (17,18). To investigate the potential link between the expression of Grp75 and Topo I...

Glucose-regulated protein 75 determines ER–mitochondrial coupling and sensitivity to oxidative stress in neuronal cells

“…In previous studies, GRP75 overexpression was associated with protection against cell death in cancer cells exposed to lethal cellular stress such as UV irradiation or in cultured astrocytes exposed to oxygen-glucose deprivation. 49 , 50 Here, we showed that GRP75 was involved in pro-death rather than pro-survival signaling in neuronal HT22 cells. We found that glutamate-induced cell death was prevented in GRP75 knockdown and KO cells, whereas GRP75 overexpression enhanced the sensitivity of neuronal cells to the oxidative insult.…”

“…The discrepancy between our findings and the aforementioned studies might be attributed to the various cellular functions of GRP75 which seem to be different in different cell types. Besides its role in ER–mitochondrial coupling, GRP75 is also a major component of the mitochondrial import machinery, being identified as a regulator of MAPK (Akt/Erk)-dependent pro-survival signaling, 49 , 52 and being linked to the regulation of p53. Moreover, the cell death or disease model seems to influence the outcome of GRP75 modulation.…”

Impaired endoplasmic reticulum-mitochondrial signaling in ataxia-telangiectasia

“…Interaction between GRP75 and IP3R1 has been demonstrated to increase upon axonal injury, contributing to increased ER-mitochondrial tethering, elevated mitochondrial Ca 2+ , and enhanced ATP generation to promote axonal regrowth (Lee et al, 2019). GRP75 overexpression is also associated with protection against cell death after exposure to cellular stress such as radiation and in astrocytes exposed to oxygen-glucose deprivation (Guo et al, 2012;Voloboueva et al, 2008). Overexpression studies also give rise to both mitochondrial stress response and protection against stress-induced ROS formation and loss of mitochondrial membrane potential in different cell types (Jin et al, 2006;Burbulla et al, 2014).…”

One protein, different cell fate: the differential outcome of depleting GRP75 during oxidative stress in neurons

“…GRP75 is a chaperone interacting with other proteins to regulate mitochondrial protein import, and to activate pro-survival signaling pathways through MAPK activation or pro-apoptotic p53-dependent signaling cascades 8 , 9 . In hepatocellular carcinoma cells, GRP75 inhibition substantially enhanced cell death which was linked to an increase in the nucleo-cytoplasmic shuttling of the tumor suppressor p53, thereby driving apoptosis 10 .…”