Calcium binding of ARC mediates regulation of caspase 8 and cell death

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Apoptosis repressor with CARD (ARC) regulates both caspase-dependent and caspase-independent cell death pathways.
• The precise mechanisms by which ARC modulates these distinct cell death routes remain incompletely understood.

Purpose of the Study:

• To investigate the role of calcium ions (Ca2+) in ARC-mediated regulation of cell death.
• To elucidate the molecular mechanisms underlying ARC's function in response to calcium signaling.

Main Methods:

• Ca2+ overlay assays and Stains-all assays to determine Ca2+ binding to ARC.
• Experiments using calcium ionophores (thapsigargin, A23187, ionomycin) to assess ARC's role in Ca2+-mediated cell death.
• Co-immunoprecipitation and binding analyses to study ARC-caspase 8 interactions under varying Ca2+ concentrations.
• CRISPR/Cas9 or siRNA to interfere with endogenous ARC synthesis.

Main Results:

• ARC protein directly binds Ca2+ through its C-terminal proline/glutamate-rich (P/E-rich) domain.
• ARC expression significantly reduced cytosolic Ca2+ transients and protected against Ca2+-mediated cytotoxicity.
• Increased Ca2+ concentration weakened the interaction between ARC and caspase 8, promoting caspase 8 activation.
• Interference with endogenous ARC synthesis potentiated Ca2+-induced cell death.

Conclusions:

• Calcium binding is a critical mechanism by which ARC regulates both caspase-dependent and caspase-independent cell death.
• ARC acts as a Ca2+-dependent molecular switch, modulating caspase 8 activity and cellular responses to calcium signaling.
• These findings reveal a novel regulatory role for calcium in ARC's function during apoptosis.