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Ally or traitor: the dual role of p62 in caspase-2 regulation
Pavel I Volik1,2, Alexey V Zamaraev1,2, Aleksandra Y Egorshina1
1Engelhardt Institute of Molecular Biology, RAS, Moscow, Russia.
Abstract:
Caspase-2 is a unique and conserved cysteine protease that is involved in several cellular processes, including different forms of cell death, maintenance of genomic stability, and the response to reactive oxygen species. Despite advances in caspase-2 research in recent years, the mechanisms underlying its activation remain largely unclear. Although caspase-2 is activated in the PIDDosome complex, its processing could occur even in the absence of PIDD1 and/or RAIDD, suggesting the existence of an alternative platform for caspase-2 activation. Here, we show that caspase-2 undergoes ubiquitination and interacts with scaffolding protein p62/sequestosome-1 (SQSTM1) under normal conditions and in response to DNA damage. p62 promotes proteasomal but not autophagic caspase-2 degradation as well as its dimerization and activation that triggers the caspase cascade and, subsequently, cell death. Inhibition of p62 expression attenuates cisplatin-induced caspase-2 processing and apoptosis. Notably, the ZZ domain of p62 is critical for caspase-2 binding, whereas the UBA domain is seemingly required to stabilize the p62-caspase-2 complex. Thus, we have uncovered the dual role of p62 in regulating caspase-2 activity: it can foster the degradation of caspase-2 in the proteasome or facilitate its activation by acting as a scaffold platform.
Insights
Scaffolding protein p62/sequestosome-1 (SQSTM1) regulates caspase-2 activity by promoting its degradation or facilitating its activation and dimerization. Inhibition of p62 attenuates cisplatin-induced apoptosis, revealing its dual role in cell death pathways.
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- Caspase-2 is a cysteine protease involved in cell death and genomic stability.
- Mechanisms of caspase-2 activation are not fully understood, with potential alternative platforms beyond the PIDDosome complex.
Purpose of the Study:
- To investigate the role of scaffolding protein p62/sequestosome-1 (SQSTM1) in caspase-2 regulation.
- To elucidate the mechanisms by which p62 influences caspase-2 activity and cell death.
Main Methods:
- Western blotting to detect protein ubiquitination and interactions.
- Co-immunoprecipitation to study protein complex formation.
- Gene silencing (siRNA) to inhibit p62 expression.
- Caspase activity assays and apoptosis detection.
Main Results:
- Caspase-2 undergoes ubiquitination and interacts with p62 under normal and DNA-damaged conditions.
- p62 promotes proteasomal degradation, dimerization, and activation of caspase-2.
- Inhibition of p62 reduces caspase-2 processing and cisplatin-induced apoptosis.
- p62's ZZ domain binds caspase-2, while the UBA domain stabilizes the complex.
Conclusions:
- p62 acts as a scaffold, modulating caspase-2 activity through dual mechanisms: promoting degradation or facilitating activation.
- p62 plays a critical role in initiating the caspase cascade and subsequent apoptosis.
- Targeting the p62-caspase-2 interaction could offer therapeutic strategies for controlling cell death.
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