Excessive autophagic degradation of MYLK3 causes sunitinib-induced cardiotoxicity

Sunitinib is a receptor tyrosine kinase inhibitor used for the treatment of renal cell carcinoma and imatinib-resistant gastrointestinal stromal tumors. Clinical data have shown that patients receiving sunitinib develop reduced cardiac function, arrhythmia and heart failure, thereby largely limiting its clinical use. However, the molecular mechanisms underlying sunitinib-induced arrhythmogenesis remain unclear. Here, utilizing the human induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) model, we found that sunitinib caused a variety of deleterious phenotypes, including cardiomyocyte death, sarcomeric disorganization, irregular Ca²⁺ transients, impaired ATP2A2a/SERCA2a (ATPase sarcoplasmic/endoplasmic reticulum Ca²⁺ transporting 2a) activity, arrhythmia, and excessive macroautophagy/autophagy. Mechanistically, SQSTM1/p62 (sequestosome 1) interacts with MYLK3 (myosin light chain kinase 3) and drives excessive autophagic degradation of MYLK3 in sunitinib-treated iPSC-CMs. Downregulation of MYLK3 suppresses the phosphorylation of CAMK2/CAMKII (calcium/calmodulin dependent protein kinase II), thereby reducing the phosphorylation level of its downstream substrate PLN (phospholamban), leading to impaired ATP2A2a/SERCA2a activity and subsequent Ca²⁺ dyshomeostasis and arrhythmia. Moreover, pharmacological intervention of the cardiac myosin activator omecamtiv mecarbil (OM) or overexpression of MYLK3 significantly restored the expression of MYLK3 and reversed pathogenic phenotypes in sunitinib-treated iPSC-CMs. Nanoparticle delivery of OM effectively prevented sunitinib-induced cardiac dysfunction in mice. Our findings suggest that sunitinib-induced MYLK3 degradation causes the inhibition of the CAMK2-PLN-ATP2A2a signaling pathway and leads to sunitinib-induced arrhythmogenesis, and that MYLK3 can act as a novel cardioprotective target for sunitinib-induced cardiotoxicity. <b>Abbreviation</b>: ACTN:actinin alpha;APD:action potential duration; ATG:autophagy related;ATP2A2a/SERCA2a:ATPase sarcoplasmic/endoplasmicreticulum Ca2+ transporting 2a;BafA1:bafilomycin A₁;Caff: caffine; CAMK2/CAMKII:calcium/calmodulin dependent protein kinase II;CASP3:caspase 3;CQ, chloroquine;DADs:delayed afterdepolarizations; EAD:early afterdepolarization; ECG: electrocardiogram; EF: ejectionfraction; FS: fractional shortening; iPSC:inducedpluripotent stem cell;iPSC-CM: inducedpluripotent stem-cell-derived cardiomyocyte;ISO: isoprenaline; LVIDs: left ventricular end systolic diameter;LVIDd: left ventricular end diastolic diameter;MAP1LC3/LC3:microtubuleassociatedprotein 1 light chain 3;MYL2v/MLC2v:myosin light chain 2 v;MYLK3:myosin light chain kinase 3;OE: overexpression; OM:omecamtiv mecarbil; PLN: phospholamban;SIC:sunitinib-induced cardiotoxicity; SR:sarcoplasmic reticulum; TUNEL:TdT-mediated dUTP nick end labeling.