CHIP has a protective role against oxidative stress-induced cell death through specific regulation of Endonuclease G

Abstract

Oxidative stress is implicated in carcinogenesis, aging, and neurodegenerative diseases. The E3 ligase C terminus of Hsc-70 interacting protein (CHIP) has a protective role against various stresses by targeting damaged proteins for proteasomal degradation, and thus maintains protein quality control. However, the detailed mechanism by which CHIP protects cells from oxidative stress has not been demonstrated. Here, we show that depletion of CHIP led to elevated Endonuclease G (EndoG) levels and enhanced cell death upon oxidative stress. In contrast, CHIP overexpression reduced EndoG levels, and resulted in reduced or no oxidative stress-induced cell death in cancer cells and primary rat cortical neurons. Under normal conditions Hsp70 mediated the interaction between EndoG and CHIP, downregulating EndoG levels in a Hsp70/proteasome-dependent manner. However, under oxidative stress Hsp70 no longer interacted with EndoG, and the stabilized EndoG translocated to the nucleus and degraded chromosomal DNA. Our data suggest that regulation of the level of EndoG by CHIP in normal conditions may determine the sensitivity to cell death upon oxidative stress. Indeed, injection of H2O2 into the rat brain markedly increased cell death in aged mice compared with young mice, which correlated with elevated levels of EndoG and concurrent downregulation of CHIP in aged mice. Taken together, our findings demonstrate a novel protective mechanism of CHIP against oxidative stress through regulation of EndoG, and provide an opportunity to modulate oxidative stress-induced cell death in cancer and aging.

Cellular Inhibitor of Apoptosis Protein 1 ubiquitinates endonuclease G but does not affect endonuclease G-mediated cell death

“…Depletion of EndoG expression by siEndoG reduced cell death approximately 50% compared with scrambled (sc)RNA-expressing control cells (Fig. 4B, left and middle) as reported [16]. WB analysis demonstrated a similarly reduced level of EndoG expression (Fig.…”

“…4A), indicating that DIAP1 does not suppress EndoG-mediated cell death in S2 cells. Previously, we showed that oxidative stress triggers EndoGmediated cell death in human cells [16]. Therefore, we investigated whether cIAP1 affected EndoG-mediated cell death of human cells treated with H 2 O 2 .…”

“…EndoG expression triggers cell death in Caenorhabditis elegans, mouse, or human cell lines [13,14,16]. However, this role has yet to be investigated in insect cells.…”

“…EndoG expression correlates with the sensitivity of cells to chemical-or oxidative stress-induced cell death in cancer cells [15,16] [17], and Parkinson's disease [18]. However, studies on endoG knock-out mice have shown contradictory results.…”

“…EndoG has been shown to be ubiquitinated for proteasomal degradation [25], and we have reported that the co-chaperone E3 ligase CHIP is involved in regulating EndoG expression levels [16]. Considering that the activities of multifunctional proteins are controlled via different modifications, EndoG is likely modified in various ways.…”