Dysregulation of a potassium channel, THIK-1, targeted by caspase-8 accelerates cell shrinkage
Kazuhiro Sakamaki1, Takahiro M Ishii2, Toshiya Sakata3
1Department of Animal Development and Physiology, Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan.
Abstract:
Activation of caspases is crucial for the execution of apoptosis. Although the caspase cascade associated with activation of the initiator caspase-8 (CASP8) has been investigated in molecular and biochemical detail, the physiological role of CASP8 is not fully understood. Here, we identified a two-pore domain potassium channel, tandem-pore domain halothane-inhibited K+ channel 1 (THIK-1), as a novel CASP8 substrate. The intracellular region of THIK-1 was cleaved by CASP8 in apoptotic cells. Overexpression of THIK-1, but not its mutant lacking the CASP8-target sequence in the intracellular portion, accelerated cell shrinkage in response to apoptotic stimuli. In contrast, knockdown of endogenous THIK-1 by RNA interference resulted in delayed shrinkage and potassium efflux. Furthermore, a truncated THIK-1 mutant lacking the intracellular region, which mimics the form cleaved by CASP8, led to a decrease of cell volume of cultured cells without apoptotic stimulation and excessively promoted irregular development of Xenopus embryos. Taken together, these results indicate that THIK-1 is involved in the acceleration of cell shrinkage. Thus, we have demonstrated a novel physiological role of CASP8: creating a cascade that advances the cell to the next stage in the apoptotic process.
Insights
Caspase-8 (CASP8) cleaves the THIK-1 potassium channel during apoptosis, accelerating cell shrinkage. This reveals a new role for CASP8 in advancing the apoptotic process.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Caspase activation is essential for apoptosis execution.
- The precise physiological role of initiator caspase-8 (CASP8) remains incompletely understood.
- Two-pore domain potassium channels are involved in cellular processes.
Purpose of the Study:
- To identify novel substrates of caspase-8 (CASP8).
- To elucidate the role of THIK-1 in apoptosis.
- To understand the physiological function of CASP8 in the apoptotic cascade.
Main Methods:
- Identification of THIK-1 as a CASP8 substrate.
- Analysis of THIK-1 cleavage by CASP8 in apoptotic cells.
- Overexpression and knockdown studies of THIK-1 using RNA interference.
- Investigation of THIK-1 function in cell shrinkage and potassium efflux.
- Functional analysis of a truncated THIK-1 mutant in cell volume regulation and Xenopus development.
Main Results:
- THIK-1 was identified as a novel substrate cleaved by CASP8 in its intracellular region during apoptosis.
- Overexpression of THIK-1 accelerated apoptotic cell shrinkage, while THIK-1 knockdown delayed it and reduced potassium efflux.
- A truncated THIK-1 mutant mimicked CASP8 cleavage, inducing cell volume decrease without apoptosis and causing developmental abnormalities in Xenopus embryos.
- THIK-1 is demonstrated to accelerate cell shrinkage during apoptosis.
Conclusions:
- THIK-1 is a direct substrate of CASP8 and plays a critical role in accelerating cell shrinkage during apoptosis.
- CASP8-mediated cleavage of THIK-1 is a key event in advancing the apoptotic process.
- This study uncovers a novel physiological role for CASP8 in regulating cell volume and promoting subsequent stages of apoptosis.
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