Angiotensin II‐induced phosphorylation of CHK1 at serine‐280 drives cardiac remodelling by direct phosphorylation of JAK1, thus activating JAK1‐STAT signalling in murine cardiomyocytes

Background and Purpose Cardiac remodelling is a common pathological process of heart disease. Checkpoint kinase 1 (CHK1), a key regulator of the DNA damage response and cell cycle, is well‐studied in oncology, but its role in pathological cardiac remodelling remains unclear. Here, we investigated the activation of CHK1 and its effects in mouse models of cardiac remodelling induced by angiotensin II. Experimental Approach We used co‐immunoprecipitation and mass spectrometry (Co‐IP/MS) to identify the substrate kinase of CHK1. Cardiac remodelling in C57BL/6 mice and hypertrophy in primary neonatal rat cardiomyocytes (NRCMs) was induced with angiotensin II. These models were treated with the CHK1 selective inhibitor CCT245737 or the JAK1 inhibitor upadacitinib. Key Results In vitro and in vivo, angiotensin II selectively activated phosphorylation of CHK1 at serine‐280 (S280), but not at S345, in cardiomyocytes, without altering levels of CHK1 protein. Inhibition of CHK1 with CCT245737 suppressed angiotensin II‐induced hypertrophy in NRCMs. Such hypertrophy was enhanced by the phospho‐mimetic CHK1 S280E mutant but was attenuated by the inactivating CHK1 S280A mutant. Co‐IP/MS revealed that, in cardiomyocytes, JAK1 is the substrate protein of CHK1. Angiotensin II promoted CHK1 interaction with JAK1 to induce JAK1 phosphorylation and activation of JAK1‐STAT3 signalling. In mice, both CCT245737 and upadacitinib reversed angiotensin II‐induced cardiac remodelling and dysfunction. Conclusions and Implications Cardiomyocyte CHK1 S280 phosphorylation is a key step in angiotensin II‐induced cardiac remodelling, through activation of the JAK1‐STAT3 pathway. Pharmacological inhibition of CHK1 could be a potential therapeutic strategy for hypertensive heart failure.