No abstract

Kv7.1 (KCNQ1) coassembles with KCNE1 to generate the cardiac IKs-channel. Gain- and loss-of-function mutations in KCNQ1 are associated with cardiac arrhthymias, highlighting the importance of modulating IKs activity for cardiac function. Here, we report proteolysis of Kv7.1 as an irreversible posttranslational modification. The identification of two C-terminal fragments of Kv7.1 led us to identify an aspartate critical for the generation of one of the fragments and caspases as responsible for mediating proteolysis. Activating caspases reduces Kv7.1/KCNE1 currents, which is abrogated in cells expressing caspase-resistant channels. Enhanced cleavage of Kv7.1 can be detected for the LQT mutation G460S, which is located adjacent to the cleavage site, whereas a calmodulin-binding-deficient mutation impairs cleavage. Application of apoptotic stimuli or doxorubicin-induced cardiotoxicity provokes caspase-mediated cleavage of endogenous IKs in human cardiomyocytes. In summary, caspases are novel regulatory components of IKs channels that may have important implications for the molecular mechanism of doxorubicin-induced cardiotoxicity.

The voltage-gated potassium channel Kv7.1 (KCNQ1) co-assembles with KCNE1 to generate the cardiac potassium current IKs. Gain- and loss-of-function mutations in KCNQ1 are associated with atrial fibrillation and long-QT (LQT) syndrome, respectively, highlighting the importance of modulating IKS activity for proper cardiac function. On a post-translational level, IKS can be regulated by phosphorylation, ubiquitination and sumoylation. Here, we report proteolysis of Kv7.1 as a novel, irreversible posttranslational modification. The identification of two C-terminal fragments (CTF1 and CTF2) of Kv7.1 led us to identify an aspartate critical for the generation of CTF2 and caspases as responsible for mediating Kv7.1 proteolysis. Activating caspases by apoptotic stimuli significantly reduced Kv7.1/KCNE1 currents, which was abrogated in cells expressing caspase-resistant Kv7.1 D459A/KCNE1 channels. An increase in cleavage of Kv7.1 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 Kv7.1 in human cardiomyocytes. In summary, our findings establish caspases as novel regulatory components for modulating Kv7.1 activity which may have important implications for the molecular mechanism of doxorubicin-induced cardiotoxicity.Non-standard Abbreviations and AcronymsCamcalmodulinEBCequilibrium buffer contentLQT syndromelong QT syndromeNRVMNeonatal rat ventricular cardiomyocyteshiPSC-CMshuman induced pluripotent stem cell-derived cardiomyocytes