Related Experiment Videos
Differential regulation and ATP requirement for caspase-8 and caspase-3 activation during CD95- and anticancer
D Ferrari1, A Stepczynska, M Los
1Department of Internal Medicine I, Eberhard-Karls University, D-72076 Tübingen, Germany.
Abstract:
Apoptosis is induced by different stimuli, among them triggering of the death receptor CD95, staurosporine, and chemotherapeutic drugs. In all cases, apoptosis is mediated by caspases, although it is unclear how these diverse apoptotic stimuli cause protease activation. Two regulatory pathways have been recently identified, but it remains unknown whether they are functionally independent or linked to each other. One is mediated by recruitment of the proximal regulator caspase-8 to the death receptor complex. The other pathway is controlled by the release of cytochrome c from mitochondria and the subsequent ATP-dependent activation of the death regulator apoptotic protease-activating factor 1 (Apaf-1). Here, we report that both pathways can be dissected by depletion of intracellular ATP. Prevention of ATP production completely inhibited caspase activation and apoptosis in response to chemotherapeutic drugs and staurosporine. Interestingly, caspase-8, whose function appeared to be restricted to death receptors, was also activated by these drugs under normal conditions, but not after ATP depletion. In contrast, inhibition of ATP production did not affect caspase activation after triggering of CD95. These results suggest that chemotherapeutic drug-induced caspase activation is entirely controlled by a receptor-independent mitochondrial pathway, whereas CD95-induced apoptosis can be regulated by a separate pathway not requiring Apaf-1 function.
Insights
Cellular ATP levels regulate apoptosis. Depleting ATP blocks caspase activation from chemotherapy and staurosporine, but not CD95 receptor triggering, revealing distinct apoptotic pathways.
Area of Science:
- Cellular biology
- Biochemistry
- Molecular biology
Background:
- Apoptosis, or programmed cell death, is crucial for development and homeostasis.
- Diverse stimuli, including death receptors (e.g., CD95), staurosporine, and chemotherapy, induce apoptosis.
- Caspase activation is the central mechanism, but the upstream regulation by different stimuli is not fully understood.
- Two pathways exist: one involving caspase-8 at death receptors, and another via mitochondrial cytochrome c release and Apaf-1 activation.
Purpose of the Study:
- To investigate the functional relationship between the two identified apoptotic pathways.
- To determine the role of intracellular ATP in mediating caspase activation by different apoptotic stimuli.
- To elucidate the distinct mechanisms of apoptosis induction by chemotherapeutic drugs versus CD95 receptor triggering.
Main Methods:
- Manipulating intracellular ATP levels through depletion.
- Assessing caspase activation and apoptosis induction in response to various stimuli (CD95, staurosporine, chemotherapeutic drugs) under normal and ATP-depleted conditions.
- Analyzing the involvement of caspase-8 and the mitochondrial pathway (cytochrome c/Apaf-1).
Main Results:
- Complete inhibition of caspase activation and apoptosis by chemotherapeutic drugs and staurosporine upon ATP depletion.
- Caspase-8 activation by these drugs occurred under normal conditions but was abolished with ATP depletion.
- CD95-induced caspase activation remained unaffected by ATP depletion, indicating independence from the mitochondrial pathway.
- Chemotherapeutic drug-induced apoptosis relies on a receptor-independent mitochondrial pathway dependent on ATP.
Conclusions:
- Intracellular ATP is essential for chemotherapeutic drug- and staurosporine-induced apoptosis, primarily through the mitochondrial pathway.
- CD95-mediated apoptosis utilizes a distinct, ATP- and Apaf-1-independent pathway.
- These findings reveal the differential regulation of apoptosis based on the initiating stimulus, highlighting the critical role of ATP and mitochondrial integrity.