https://www. jbc. org/cgi/doi/10.1074/jbc. RA120. 015216 The latest version is at

摘要: The QT interval is a recording of cardiac electrical activity. Previous genome-wide association studies (GWAS) identified genetic variants that modify the QT interval upstream of LITAF(lipopolysaccharide-induced tumor necrosis factor-alpha factor), a protein encoding a regulator of endosomal trafficking. However, it was not clear how LITAF might impact cardiac excitation. We investigated the effect of LITAF on the voltage-gated sodium channel Nav1. 5, which is critical for cardiac depolarization. We show that overexpressed LITAF resulted in a significant increase in the density of Nav1. 5-generated voltage-gated sodium current INa and Nav1. 5 surface protein levels in rabbit cardiomyocytes and in HEK cells stably expressing Nav1. 5. Proximity ligation assays showed co-localization of endogenous LITAF and Nav1. 5 in cardiomyocytes, while coimmunoprecipitations confirmed they are in the same complex when overexpressed in HEK cells. In vitro data suggests LITAF interacts with the ubiquitin ligase NEDD4-2, a regulator of Nav1. 5. LITAF overexpression downregulated NEDD4-2 in cardiomyocytes and HEK cells. In HEK cells, LITAF increased ubiquitination and proteasomal degradation of co-expressed NEDD4-2 and significantly blunted the negative effect of NEDD4-2 on INa. We conclude that LITAF controls cardiac excitability by promoting degradation of NEDD4-2, which is essential for removal of surface Nav1. 5. LITAF-knockout zebrafish showed increased variation in and a non-significant 15% prolongation of action potential duration (APD). Computer simulations using a rabbit-cardiomyocyte model demonstrated that changes in Ca2 …