HECT‐Type Ubiquitin E3 Ligase ITCH Interacts With Thioredoxin‐Interacting Protein and Ameliorates Reactive Oxygen Species–Induced Cardiotoxicity

<jats:sec xml:lang="en"> <jats:title>Background</jats:title> <jats:p xml:lang="en"> The <jats:styled-content style="fixed-case">homologous to the E6‐AP carboxyl terminus (HECT)</jats:styled-content> –type ubiquitin E3 ligase <jats:styled-content style="fixed-case">ITCH</jats:styled-content> is an enzyme that plays a pivotal role in posttranslational modification by ubiquitin proteasomal protein degradation. Thioredoxin‐interacting protein ( <jats:styled-content style="fixed-case">TXNIP</jats:styled-content> ) is a negative regulator of the thioredoxin system and an endogenous reactive oxygen species scavenger. In the present study, we focused on the functional role of ubiquitin E3 ligase <jats:styled-content style="fixed-case">ITCH</jats:styled-content> and its interaction with <jats:styled-content style="fixed-case">TXNIP</jats:styled-content> to elucidate the mechanism of cardiotoxicity induced by <jats:styled-content style="fixed-case">reactive oxygen species</jats:styled-content> , such as doxorubicin and hydrogen peroxide. </jats:p> </jats:sec> <jats:sec xml:lang="en"> <jats:title>Methods and Results</jats:title> <jats:p xml:lang="en"> Protein interaction between <jats:styled-content style="fixed-case">TXNIP</jats:styled-content> and <jats:styled-content style="fixed-case">ITCH</jats:styled-content> in cardiomyocyte was confirmed by immunoprecipitation assays. Overexpression of <jats:styled-content style="fixed-case">ITCH</jats:styled-content> increased proteasomal <jats:styled-content style="fixed-case">TXNIP</jats:styled-content> degradation and augmented thioredoxin activity, leading to inhibition of <jats:styled-content style="fixed-case">reactive oxygen species</jats:styled-content> generation, p38 <jats:styled-content style="fixed-case">MAPK</jats:styled-content> , p53, and subsequent intrinsic pathway cardiomyocyte apoptosis in <jats:styled-content style="fixed-case">reactive oxygen species</jats:styled-content> –induced cardiotoxicity. Conversely, knockdown of <jats:styled-content style="fixed-case">ITCH</jats:styled-content> using small interfering <jats:styled-content style="fixed-case">RNA</jats:styled-content> inhibited <jats:styled-content style="fixed-case">TXNIP</jats:styled-content> degradation and resulted in a subsequent increase in cardiomyocyte apoptosis. Next, we generated a transgenic mouse with cardiac‐specific overexpression of <jats:styled-content style="fixed-case">ITCH</jats:styled-content> , called the <jats:styled-content style="fixed-case">ITCH</jats:styled-content> ‐Tg mouse. The expression level of <jats:styled-content style="fixed-case">TXNIP</jats:styled-content> in the myocardium in <jats:styled-content style="fixed-case">ITCH</jats:styled-content> ‐Tg mice was significantly lower than WT littermates. In <jats:styled-content style="fixed-case">ITCH</jats:styled-content> ‐Tg mice, cardiac dysfunction and remodeling were restored compared with WT littermates after doxorubicin injection and myocardial infarction surgery. Kaplan–Meier analysis revealed that <jats:styled-content style="fixed-case">ITCH</jats:styled-content> ‐Tg mice had a higher survival rate than WT littermates after doxorubicin injection and myocardial infarction surgery. </jats:p> </jats:sec> <jats:sec xml:lang="en"> <jats:title>Conclusion</jats:title> <jats:p xml:lang="en"> We demonstrated, for the first time, that <jats:styled-content style="fixed-case">ITCH</jats:styled-content> targets <jats:styled-content style="fixed-case">TXNIP</jats:styled-content> for ubiquitin‐proteasome degradation in cardiomyocytes and ameliorates <jats:styled-content style="fixed-case">reactive oxygen species</jats:styled-content> –induced cardiotoxicity through the thioredoxin system. </jats:p> </jats:sec>