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Phosphorylation by protein kinase CK2: a signaling switch for the caspase-inhibiting protein ARC
Pei-Feng Li1, Jincheng Li, Eva-Christina Müller
1Max-Delbrück-Center for Molecular Medicine, 13125 Berlin, Germany.
Abstract:
Caspases play a central role in apoptosis, but their activity is under the control of caspase-inhibiting proteins. A characteristic of caspase-inhibiting proteins is direct caspase binding. It is yet unknown how the localization of caspase-inhibiting proteins is regulated and whether there are upstream signals controlling their function. Here we report that the function of ARC is regulated by protein kinase CK2. ARC at threonine 149 is phosphorylated by CK2. This phosphorylation targets ARC to mitochondria. ARC is able to bind to caspase-8 only when it is localized to mitochondria but not to the cytoplasm. Our results reveal a molecular mechanism by which a caspase-inhibiting protein requires phosphorylation in order to prevent apoptosis.
Insights
The protein kinase CK2 phosphorylates ARC, targeting it to mitochondria. This mitochondrial localization enables ARC to inhibit caspase-8, revealing a new mechanism for controlling apoptosis.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- Caspases are key regulators of apoptosis.
- Caspase activity is controlled by inhibitory proteins.
- Regulation and upstream signals for caspase-inhibiting proteins remain unclear.
Purpose of the Study:
- Investigate the regulation of apoptosis inhibitor ARC.
- Determine the upstream signals controlling ARC function.
- Elucidate the mechanism by which ARC inhibits caspases.
Main Methods:
- Protein kinase assays to assess CK2 activity on ARC.
- Phosphorylation site mapping (Threonine 149).
- Subcellular localization studies (cytoplasmic vs. mitochondrial).
- Caspase-binding assays (ARC and caspase-8).
Main Results:
- Protein kinase CK2 phosphorylates ARC at Threonine 149.
- Phosphorylation by CK2 targets ARC to mitochondria.
- ARC binds to caspase-8 exclusively in the mitochondria, not the cytoplasm.
- This phosphorylation-dependent localization is crucial for ARC's apoptotic inhibitory function.
Conclusions:
- ARC's function as a caspase inhibitor is regulated by CK2-mediated phosphorylation.
- Phosphorylation directs ARC to mitochondria, enabling caspase-8 binding.
- This study reveals a novel phosphorylation-dependent mechanism controlling apoptosis via caspase inhibition.