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Resistance to caspase-independent cell death requires persistence of intact mitochondria.

ABSTRACT: During apoptosis, mitochondrial outer membrane permeabilization (MOMP) is often a point-of-no-return; death can proceed even if caspase activation is disrupted. However, under certain conditions, resistance to MOMP-dependent, caspase-independent cell death is observed. Mitochondrial recovery represents a key process in this survival. Live cell imaging revealed that during apoptosis not all mitochondria in a cell necessarily undergo MOMP. This incomplete MOMP (iMOMP) was observed in response to various stimuli and in different cell types regardless of caspase activity. Importantly, the presence of intact mitochondria correlated with cellular recovery following MOMP, provided that caspase activity was blocked. Such intact mitochondria underwent MOMP in response to treatment of cells with the Bcl-2 antagonist ABT-737, suggesting that the resistance of these mitochondria to MOMP lies at the point of Bax or Bak activation. Thus, iMOMP provides a critical source of intact mitochondria that permits cellular survival following MOMP.

SUBMITTER: Tait SW

PROVIDER: S-EPMC3004027 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature

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Resistance to caspase-independent cell death requires persistence of intact mitochondria.

Tait Stephen W G SW Parsons Melissa J MJ Llambi Fabien F Bouchier-Hayes Lisa L Connell Samuel S Muñoz-Pinedo Cristina C Green Douglas R DR

Developmental cell 20100501 5

During apoptosis, mitochondrial outer membrane permeabilization (MOMP) is often a point-of-no-return; death can proceed even if caspase activation is disrupted. However, under certain conditions, resistance to MOMP-dependent, caspase-independent cell death is observed. Mitochondrial recovery represents a key process in this survival. Live cell imaging revealed that during apoptosis not all mitochondria in a cell necessarily undergo MOMP. This incomplete MOMP (iMOMP) was observed in response to v ...[more]

PMID: 20493813

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Project description:UnlabelledVirus-induced apoptosis is thought to be the primary mechanism of cell death following reovirus infection. Induction of cell death following reovirus infection is initiated by the incoming viral capsid proteins during cell entry and occurs via NF-?B-dependent activation of classical apoptotic pathways. Prototype reovirus strain T3D displays a higher cell-killing potential than strain T1L. To investigate how signaling pathways initiated by T3D and T1L differ, we methodically analyzed cell death pathways activated by these two viruses in L929 cells. We found that T3D activates NF-?B, initiator caspases, and effector caspases to a significantly greater extent than T1L. Surprisingly, blockade of NF-?B or caspases did not affect T3D-induced cell death. Cell death following T3D infection resulted in a reduction in cellular ATP levels and was sensitive to inhibition of the kinase activity of receptor interacting protein 1 (RIP1). Furthermore, membranes of T3D-infected cells were compromised. Based on the dispensability of caspases, a requirement for RIP1 kinase function, and the physiological status of infected cells, we conclude that reovirus can also induce an alternate, necrotic form of cell death described as necroptosis. We also found that induction of necroptosis requires synthesis of viral RNA or proteins, a step distinct from that necessary for the induction of apoptosis. Thus, our studies reveal that two different events in the reovirus replication cycle can injure host cells by distinct mechanisms.ImportanceVirus-induced cell death is a determinant of pathogenesis. Mammalian reovirus is a versatile experimental model for identifying viral and host intermediaries that contribute to cell death and for examining how these factors influence viral disease. In this study, we identified that in addition to apoptosis, a regulated form of cell death, reovirus is capable of inducing an alternate form of controlled cell death known as necroptosis. Death by this pathway perturbs the integrity of host membranes and likely triggers inflammation. We also found that apoptosis and necroptosis following viral infection are activated by distinct mechanisms. Our results suggest that host cells can detect different stages of viral infection and attempt to limit viral replication through different forms of cellular suicide. While these death responses may aid in curbing viral spread, they can also exacerbate tissue injury and disease following infection.

Project description:BackgroundBone morphogenetic proteins (BMP) are evolutionarily conserved morphogens that are reactivated in lung carcinomas. In lung cancer cells, BMP signaling suppresses AMP activated kinase (AMPK) by inhibiting LKB1. AMPK is activated by mitochondrial stress that inhibits ATP production, which is enhanced 100-fold when phosphorylated by LKB1. Activated AMPK can promote survival of cancer cells but its "hyperactivation" induces cell death. The studies here reveal novel cell death mechanisms induced by BMP inhibitors, together with agents targeting the mitochondria, which involves the "hyperactivation" of AMPK.MethodsThis study examines the synergistic effects of two BMP inhibitors together with mitochondrial targeting agents phenformin and Ym155, on cell death of lung cancer cells expressing LKB1 (H1299), LKB1 null (A549), and A549 cells transfected with LKB1 (A549-LKB1). Cell death mechanisms evaluated were the activation of caspases and the nuclear localization of apoptosis inducing factor (AIF). A769662 was used to allosterically activate AMPK. Knockdown of BMPR2 and LKB1 using siRNA was used to examine their effects on nuclear localization of AMPK. Validation studies were performed on five passage zero primary NSCLC.ResultsBoth BMP inhibitors synergistically suppressed growth when combined with Ym155 or phenformin in cells expressing LKB1. The combination of BMP inhibitors with mitochondrial targeting agents enhanced the activation of AMPK in lung cancer cells expressing LKB1. Allosteric activation of AMPK with A769662 induced cell death in both H1299 and A549 cells. Cell death induced by the combination of BMP inhibitors and mitochondrial-targeting agents did not activate caspases. The combination of drugs induced nuclear localization of AIF in cells expressing LKB1, which was attenuated by knockdown of LKB1. Knockdown of BMPR2 together with Ym155 increased nuclear localization of AIF. Combination therapy also enhanced cell death and AIF nuclear localization in primary NSCLC.ConclusionsThese studies demonstrate that inhibition of BMP signaling together with mitochondrial targeting agents induce AIF caspase-independent cell death, which involves the "hyperactivation" of AMPK. AIF caspase-independent cell death is an evolutionarily conserved cell death pathway that is infrequently studied in cancer. These studies provide novel insight into mechanisms inducing AIF caspase-independent cell death in cancer cells using BMP inhibitors. Video Abstract.

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Resistance to caspase-independent cell death requires persistence of intact mitochondria.

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Resistance to caspase-independent cell death requires persistence of intact mitochondria.

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