Manganese Superoxide Dismutase (SOD2) Inhibits Radiation-Induced Apoptosis by Stabilization of the Mitochondrial Membrane

Abstract

To define the molecular pathways involved in radiation-induced apoptosis and the role of the mitochondria, 32D cl 3 hematopoietic cells and subclones overexpressing either the human manganese superoxide dismutase (SOD2) transgene (1F2 and 2C6) or BCL2L1 (also known as Bcl-xl) transgene (32D-Bcl-xl) were compared for their response to radiation at the subcellular level, comparing nuclear to mitochondrial localized pathways. All cell lines showed complete detectable DNA repair by 30 min after irradiation, and clearly delayed migration of BAX and active stress-activated protein (SAP) kinases MAPK1 (also known as p38) and MAPK8 (also known as JNK1) to the mitochondria at 3 h. Radioresistant clonal lines 1F2, 2C6 and 32D-Bcl-xl showed significant decreases in mitochondrial membrane permeability, cytochrome C release, caspase 3 and poly(adenosine diphosphate-ribose) polymerase (PARP) activation at 6-12 h, and in apoptosis at 24 h. Since the nuclear-to-cytoplasm events preceding the release of cytochrome C were similar in all cell lines, and increased expression of either the SOD2 or the BCL2L1 transgene provided radiation protection, we conclude that events at the level of the mitochondria are critically involved in radiation-induced apoptosis.

Delayed radioprotection by nuclear transcription factor κB -mediated induction of manganese superoxide dismutase in human microvascular endothelial cells after exposure to the free radical scavenger WR1065

“…MnSOD has been described by many investigators as being an effective endogenous antioxidant enzyme capable of conferring enhanced radiation resistance to cells [4,5,8,10]. Since maximal elevation of MnSOD occurs between 16 and 24 h following exposure of cells to WR1065, it was of interest to determine whether irradiation of cells at this time would result in an enhanced cellular resistance to the cytotoxic effects of ionizing radiation.…”

“…10). Elevation of cellular radiation resistance by MnSOD has historically been observed as an enhancement of the initial slope or α component of the survival curve [4,[8][9][10]23]. To facilitate a more quantitative analysis of the protective effects of MnSOD, protection enhancement ratios (PER), defined by the ratio of the α components of the radiation survival curves describing the survival responses of control and WR1065 treated HMEC, i.e., α C /α WR1065 , were determined and are listed in Table 1.…”

“…When elevated in cells, it is known to confer among other things an enhanced resistance against the cytotoxic effects of ionizing radiation [4,[8][9][10]23,24]. The MnSOD gene contains multiple transcription factor-binding motifs that include sites for AP1, AP2, Sp1, CREB, and NFκB [19][20][21][22].…”

“…Mitochondria have been demonstrated to play an important role in the apoptotic processes induced by ionizing radiation, including the release of cytochrome c and the activation of caspase 3 that leads to PARP cleavage and subsequent DNA strand breaks [4,6,7]. Consistent with the role of mitochondrial damage leading to cell death, overexpression of MnSOD in cells induced by tranfection of an MnSOD transgene gives rise to an enhanced radioresistance and to an inhibition of radiation-induced apoptosis [8][9][10]. Furthermore, it has been demonstrated that localization of superoxide dismutase within the mitochondria is a requirement for subsequent radioprotection against cellular damage [4].…”

The subcellular distribution of MnSOD alters during sodium selenite-induced apoptosis

“…In consistent with its cellular function, the MnSOD knockout mice die embryonically and are hypersensitive to apoptosis (4,5). Furthermore, the over-expression of MnSOD blocks apoptosis induced by praline oxidase, TNF-α, IL-3 withdrawal or ionizing irradiation (6)(7)(8)(9). During Fas-mediated apoptosis, MnSOD is inactivated by caspase-specific degradation (10).…”