Necrosis-like death can engage multiple pro-apoptotic Bcl-2 protein family members

Abstract

Necroptosis is a physiologically relevant mode of cell death with some well-described initiating events, but largely unknown executioners. Here we investigated necrostatin-1 (Nec-1) sensitive death elicited by different necroptosis stimuli in L929 mouse fibrosarcoma cells, mouse embryonic fibroblasts (MEF) and bone marrow-derived macrophages. We found that TNFα-or zVADinduced necroptosis occurs independently of the recently implicated executioners Bmf or PARP-2, but can involve the Bcl-2 family proteins Bid and Bak. Furthermore, this type of necroptosis is associated with mitochondrial cytochrome c release and partly sensitive to cyclosporine A inhibition, suggesting a cross talk with the mitochondrial permeability transition pore. Necroptosis triggered by cadmium (Cd) exposure caused fully Nec-1-sensitive and caspase-independent death in L929 cells that was associated with autocrine TNFα-mediated feed-forward signalling. In MEF Cd-exposure elicited a mixed mode of cell death that was to some extent Nec-1-sensitive but also displayed features of apoptosis. It was partly dependent on Bmf and Bax/Bak, proteins typically considered to act pro-apoptotic, but ultimately insensitive to caspase inhibition. Overall, our study indicates that inducers of "extrinsic" and "intrinsic" necroptosis can both trigger TNF-receptor signalling. Further, necroptosis may depend on mitochondrial changes engaging proteins considered critical for MOMP during apoptosis that ultimately contribute to caspase-independent necrotic cell death.

The Role of BCL-2 Family Members in Acute Kidney Injury

“…BCL-2 proteins are unlikely to be innocent even in necroptosis, however, because several laboratories have reported that bid and bax are active participants in this form of cell death. [111][112][113][114] Although it is tempting to ascribe three modes of cell death (apoptosis, necrosis, and necroptosis) to the dose and duration of cisplatin exposure, or to cell type or rodent species variation, growing evidence shows that this cisplatin is a facile killer. Given the possibility that apoptosis, necrosis, and necroptosis each mediate renal cell death, manipulation of BCL-2 family members may be a rational approach for inhibiting them all.…”

“…Although morphologically distinct, apoptosis and necrosis appear to share similar biologic processes including membrane pore transition on the mitochondria surface, and therefore are susceptible to regulation by BCL-2 proteins. 19,114,[146][147][148] Curiously, inhibition of apoptosis (eg, by a pancaspase inhibitor), forces cells to die by necrosis, suggesting a continuum between these two forms of cell death. The early prediction that apoptosis and necrosis might be the "kissing cousins of cell death" has come to fruition with the realization that under some circumstances, MPT regulates both apoptosis and necrosis.…”

“…130 It appears likely that specific intracellular events (eg, intracellular oxidants) could act as a cellular switch between apoptosis and necrosis in a single cell, 150 with the mitochondrion as their mutual undertaker. 113,114 Cell death is more likely to be a series of interrelated events rather than a single catastrophic one. In addition, it now is appreciated that renal cell death is not a simultaneous acute event but rather occurs in waves separated by hours and even several days after an insult has occurred.…”

“…153 Both forms of cell death and release of proinflammatory mediators including TNF, damage-associated molecular patterns, F-actin, interleukins, cytokines, RNA and DNA, and others. 49,113,114,154 Thus, cell death by apoptosis and necrosis could represent the "first cell death wave" that precipitates alternative forms of death within the kidney and elsewhere that may share regulation by BCL-2 proteins. Finally, necroptosis, membrane pore transition-regulated necrosis, and perhaps pyroptosis all interface with mitochondrial membrane pore transition, 112,155,156 the "ancient temple" of BCL-2 effects, creating pathway overlap between seemingly distinct forms of cell death.…”

Interrogating the relevance of mitochondrial apoptosis for vertebrate development and postnatal tissue homeostasis

“…Recently, a structural contribution of BAX and BAK that differs from their pore-forming potential driving MOMP has been proposed to be required for programmed necrosis upon MTP opening, e.g., in response to H 2 O 2 , Ca 2+ overload, or heavy-metal poisoning (Tischner et al 2012;Karch et al 2013). Most strikingly, MEFs and liver mitochondria isolated from Bax/Bak DKO mice showed clear deficits in MTP activity and codeletion of Bax/Bak in the heart (αMHC-Cre) protected from coronary artery ligation-induced myocardial infarction, an insult usually associated with rapid ATP depletion converting apoptotic death into necrosis involving MTP (Karch et al 2013).…”