Doxorubicin induces caspase-mediated proteolysis of KV7.1

Area of Science:

• Molecular biology
• Cardiovascular research
• Biochemistry

Background:

• K_v7.1 (KCNQ1) and KCNE1 form the cardiac I_Ks channel, crucial for heart rhythm.
• Mutations in KCNQ1 are linked to cardiac arrhythmias, underscoring the need to understand I_Ks regulation.

Purpose of the Study:

• To investigate the role of proteolysis in K_v7.1 regulation.
• To identify the enzymes responsible for K_v7.1 cleavage and their functional consequences.

Main Methods:

• Identification of K_v7.1 C-terminal fragments.
• Site-directed mutagenesis to identify critical residues (e.g., aspartate) and caspase-resistant mutants.
• Electrophysiological recordings of K_v7.1/KCNE1 currents.
• Analysis of K_v7.1 cleavage in response to apoptotic stimuli and doxorubicin in human cardiomyocytes.

Main Results:

• Proteolysis of K_v7.1 was identified as an irreversible posttranslational modification.
• Caspases were identified as the enzymes responsible for K_v7.1 cleavage.
• Caspase activation reduced K_v7.1/KCNE1 currents, an effect blocked by caspase-resistant channels.
• Enhanced K_v7.1 cleavage was observed with the LQT mutation G460S and impaired with a calmodulin-binding-deficient mutation.
• Caspase-mediated cleavage of endogenous I_Ks occurred in human cardiomyocytes under apoptotic or doxorubicin-induced cardiotoxicity conditions.

Conclusions:

• Caspases represent novel regulators of cardiac I_Ks channels.
• K_v7.1 proteolysis by caspases may contribute to the molecular mechanisms underlying doxorubicin-induced cardiotoxicity.
• Understanding this cleavage pathway offers insights into cardiac arrhythmia pathogenesis and drug-induced cardiac dysfunction.