NDRG2 Is a Novel p53-Associated Regulator of Apoptosis in C6-Originated Astrocytes Exposed to Oxygen-Glucose Deprivation

Abstract

N-myc downstream-regulated gene 2 (NDRG2) has been documented to be a pro-differentiative and anti-proliferative gene in cancer research. Our previous study found a significant NDRG2 up-regulation in reactive astrocytes of penumbra after transient focal cerebral ischemia, which was parallel to the enhancement of TUNEL-positive signals. However, it is still uncertain whether NDRG2 participates in cellular apoptosis induced by ischemia-reperfusion injury in brain. In this study, we investigated the role of NDRG2 in cellular apoptosis induced by oxygen-glucose deprivation (OGD) in IL-6-differentiated C6 glioma cells. The results showed that NDRG2 was up-regulated and translocated from the cytoplasm to the nucleus after OGD exposure. NDRG2 over-expression exhibited an anti-proliferative effect and increased the Bax/Bcl-2 ratio after OGD exposure, while NDRG2 silencing promoted the cellular proliferation and attenuated the up-regulation of Bax/Bcl-2 ratio. The pro-apoptotic effect of p53 was verified by the results in which p53 silencing greatly reduced the percentage of OGD-induced apoptotic cells. p53 silencing also reduced the OGD-induced NDRG2 up-regulation. However, over-expression of p53 did not further improve the NDRG2 up-regulation. In conclusion, NDRG2 is a p53-associated regulator of apoptosis in C6-originated astrocytes after OGD exposure. These findings bring insight to the roles of NDRG2 in ischemic-hypoxic injury and provide potential targets for future clinical therapies on stroke.

Gliopreventive effects of guanosine against glucose deprivation in vitro

“…Astrocytes take up glucose and characteristically display a high glycolytic rate [52,53]. C6 astroglial cells metabolize glucose in relation to their sensitivity to the changes in extracellular glucose levels [54][55][56][57].…”

N-myc downstream-regulated gene 2 in the nervous system: from expression pattern to function

“…Intriguingly, the expression of NDRG2 was not obviously elevated in N-myc knockout embryos [33]. To date, glucocorticoids [16,31], p53 [26], and estrogen [34] have been demonstrated to regulate NDRG2 transcription in the nervous system. After adrenalectomy, the transcription of NDRG2 was obviously increased in the hippocampus with glucocorticoid treatment compared with sham-operated rats.…”

“…Bioinformatics analysis predicted that there are several binding sequences of NDRG2 in different transcription factors [2], including p53 [26,28], hypoxia-induced factor-1α (HIF-1α) [27], Wilms' tumor gene 1 (WT1) protein [14], estrogen [29], androgens [30], aldosterone [6,16], and glucocorticoids [16,31], and all these binding sequences were verified by subsequent experimental studies. An increased C-myc mRNA level was found to be associated with reduced NDRG2 mRNA in some human glioblastoma tissues and cell lines Table 1.…”

“…[26] [12], and it has been reported that the expression of human NDRG2 is down-regulated by C-myc via transcriptional inhibition in HeLa and HEK 293 cells [32]. Intriguingly, the expression of NDRG2 was not obviously elevated in N-myc knockout embryos [33].…”

“…In addition, subcellular localization studies showed that NDRG2 protein is mainly expressed in the cytoplasm [12,17,20,23] and some cell surface membranes [21,24,25]. NDRG2 protein was also found in nuclei or was transferred into nuclei from the cytoplasm under certain cell stress conditions [15,23,24,26] (Table 1). A middle fragment of the NDRG2 protein (101-178 amino acids) was demonstrated to be responsible for its nuclear translocation, but no nuclear localization signal sequence was identified in this protein [27].…”