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Cathepsin B launches an apoptotic exit effort upon cell death-associated disruption of lysosomes.

ABSTRACT: The release of cathepsin proteases from disrupted lysosomes results in lethal cellular autodigestion. Lysosomal disruption-related cell death is highly variable, showing both apoptotic and necrotic outcomes. As the substrate spectrum of lysosomal proteases encompasses the apoptosis-regulating proteins of the Bcl-2 family, their degradation could influence the cell death outcome upon lysosomal disruption. We used Förster resonance energy transfer (FRET)-based biosensors to image the real-time degradation of the Bcl-2-family members, Bcl-xl, Bax and Bid, in living cells undergoing lysosomal lysis and identified an early chain of proteolytic events, initiated by the release of cathepsin B, which directs cells toward apoptosis. In this apoptotic exit strategy, cathepsin B's proteolytic activity results in apoptosis-inducing Bid and removes apoptosis-preventing Bcl-xl. Cathepsin B furthermore appears to degrade a cystein protease that would otherwise have eliminated apoptosis-supporting Bax, indirectly keeping cellular levels of the Bax protein up. The concerted effort of these three early events shifts the balance of cell fate away from necrosis and toward apoptosis.

SUBMITTER: de Castro MA

PROVIDER: S-EPMC4979493 | biostudies-other | 2016

REPOSITORIES: biostudies-other

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Cathepsin B launches an apoptotic exit effort upon cell death-associated disruption of lysosomes.

de Castro M A G MA Bunt G G Wouters F S FS

Cell death discovery 20160229

The release of cathepsin proteases from disrupted lysosomes results in lethal cellular autodigestion. Lysosomal disruption-related cell death is highly variable, showing both apoptotic and necrotic outcomes. As the substrate spectrum of lysosomal proteases encompasses the apoptosis-regulating proteins of the Bcl-2 family, their degradation could influence the cell death outcome upon lysosomal disruption. We used Förster resonance energy transfer (FRET)-based biosensors to image the real-time deg ...[more]

PMID: 27551506

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Project description:A number of studies, mostly performed ex vivo, suggest that lysosomes are involved in apoptosis as a result of a release of their cathepsins into the cytosol. These enzymes could then contribute to the permeabilization of the outer mitochondrial membrane; they could also activate effector caspases. The present study aims at testing whether the membrane of liver lysosomes is disrupted during Fas-mediated cell death of hepatocytes in vivo, a process implicated in several liver pathologies. Apoptosis was induced by injecting mice with aFas (anti-Fas antibody). The state of lysosomes was assessed by determining the proportion of lysosomal enzymes (beta-galactosidase, beta-glucuronidase, cathepsin C and cathepsin B) present in homogenate supernatants, devoid of intact lysosomes, and by analysing the behaviour in differential and isopycnic centrifugation of beta-galactosidase. Apoptosis was monitored by measuring caspase 3 activity (DEVDase) and the release of sulfite cytochrome c reductase, an enzyme located in the mitochondrial intermembrane space. Results show that an injection of 10 microg of aFas causes a rapid and large increase in DEVDase activity and in unsedimentable sulfite cytochrome c reductase. This modifies neither the proportion of unsedimentable lysosomal enzyme in the homogenates nor the behaviour of lysosomes in centrifugation. Experiments performed with a lower dose of aFas (5 microg) indicate that unsedimentable lysosomal hydrolase activity increases in the homogenate after injection but with a marked delay with respect to the increase in DEVDase activity and in unsedimentable sulfite cytochrome c reductase. Comparative experiments ex vivo performed with Jurkat cells show an increase in unsedimentable lysosomal hydrolases, but much later than caspase 3 activation, and a release of dipeptidyl peptidase III and DEVDase into culture medium. It is proposed that the weakening of lysosomes observed after aFas treatment in vivo and ex vivo results from a necrotic process that takes place late after initiation of apoptosis.

Project description:A sigma-2 receptor agonist siramesine has been shown to trigger cell death of cancer cells and to exhibit a potent anticancer activity in vivo. However, its mechanism of action is still poorly understood. We show that siramesine can induce rapid cell death in a number of cell lines at concentrations above 20 ?M. In HaCaT cells, cell death was accompanied by caspase activation, rapid loss of mitochondrial membrane potential (MMP), cytochrome c release, cardiolipin peroxidation and typical apoptotic morphology, whereas in U-87MG cells most apoptotic hallmarks were not notable, although MMP was rapidly lost. In contrast to the rapid loss of MMP above 20 ?M siramesine, a rapid increase in lysosomal pH was observed at all concentrations tested (5-40 ?M); however, it was not accompanied by lysosomal membrane permeabilisation (LMP) and the release of lysosomal enzymes into the cytosol. Increased lysosomal pH reduced the lysosomal degradation potential as indicated by the accumulation of immature forms of cysteine cathepsins. The lipophilic antioxidant ?-tocopherol, but not the hydrophilic antioxidant N-acetyl-cysteine, considerably reduced cell death and destabilisation of mitochondrial membranes, but did not prevent the increase in lysosomal pH. At concentrations below 15 ?M, siramesine triggered cell death after 2 days or later, which seems to be associated with a general metabolic and energy imbalance due to defects in the endocytic pathway, intracellular trafficking and energy production, and not by a specific molecular event. Overall, we show that cell death in siramesine-treated cells is induced by destabilisation of mitochondria and is independent of LMP and the release of cathepsins into the cytosol. Moreover, it is unlikely that siramesine acts exclusively through sigma-2 receptors, but rather through multiple molecular targets inside the cell. Our findings are therefore of significant importance in designing the next generation of siramesine analogues with high anticancer potential.

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Cathepsin B launches an apoptotic exit effort upon cell death-associated disruption of lysosomes.

Publications

Cathepsin B launches an apoptotic exit effort upon cell death-associated disruption of lysosomes.

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