Cardiac Troponin I-interacting kinase (TNNI3K) is a cardiac specific kinase whose biological function remains largely unknown. We have recently shown that TNNI3K expression greatly accelerates cardiac dysfunction in mouse models of cardiomyopathy, indicating an important role in modulating disease progression. To further investigate TNNI3K kinase activity in vivo, we have generated transgenic mice expressing both wild-type and kinase-dead versions of the human TNNI3K protein. Importantly, we show that the increased TNNI3K kinase activity induces mouse cardiac hypertrophy, and the kinase activity is required to accelerate disease progression in a left-ventricular pressure overload model of mouse cardiomyopathy. We demonstrate the clinical relevance of these observations by identifying two potential missense mutations near the kinase activation loop of TNNI3K in idiopathic dilated cardiomyopathy (DCM) human patients. Using an in vitro kinase assay and proteomics analysis, we show that TNNI3K is a dual-function kinase with Tyr and Ser/Thr kinase activity. Using antisera to TNNI3K, we show that TNNI3K protein is located at the sarcomere Z disc. These combined data suggest that TNNI3K mediates cell signaling to modulate cardiac response to stress. The essential role of the kinase activity makes TNNI3K a strong potential pharmaceutical target of kinase inhibitors for heart disease.
Cellular Proliferative Response to Cardiac Troponin-I in Patients with Idiopathic Dilated Cardiomyopathy