Doxorubicin induces caspase-mediated proteolysis of K V 7.1

The voltage-gated potassium channel K v 7.1 (KCNQ1) co-assembles with KCNE1 to generate the cardiac potassium current I Ks . Gain- and loss-of-function mutations in KCNQ1 are associated with atrial fibrillation and long-QT (LQT) syndrome, respectively, highlighting the importance of modulating I KS activity for proper cardiac function. On a post-translational level, I KS can be regulated by phosphorylation, ubiquitination and sumoylation. Here, we report proteolysis of K v 7.1 as a novel, irreversible posttranslational modification. The identification of two C-terminal fragments (CTF1 and CTF2) of K v 7.1 led us to identify an aspartate critical for the generation of CTF2 and caspases as responsible for mediating K v 7.1 proteolysis. Activating caspases by apoptotic stimuli significantly reduced K v 7.1/KCNE1 currents, which was abrogated in cells expressing caspase-resistant K v 7.1 D459A/KCNE1 channels. An increase in cleavage of K v 7.1 could be detected in the case of LQT mutation G460S, which is located adjacent to the cleavage site. Application of apoptotic stimuli or doxorubicin-induced cardiotoxicity provoked caspase-mediated cleavage of endogenous K v 7.1 in human cardiomyocytes. In summary, our findings establish caspases as novel regulatory components for modulating K v 7.1 activity which may have important implications for the molecular mechanism of doxorubicin-induced cardiotoxicity. Non-standard Abbreviations and Acronyms Cam calmodulin EBC equilibrium buffer content LQT syndrome long QT syndrome NRVM Neonatal rat ventricular cardiomyocytes hiPSC-CMs human induced pluripotent stem cell-derived cardiomyocytes