The PXXP domain is critical for the protective effect of BAG 3 in cardiomyocytes

Summary Bcl‐2‐associated athanogene3( BAG 3) protects the heart and cardiomyocytes from ischaemia/reperfusion (I/R) injury. Although the anti‐apoptosis effect of BAG 3 has been demonstrated in multiple cell types, the structural domain of BAG 3, which is responsible for its anti‐apoptosis effect, is not well understood. BAG 3 protein consists of various characteristic amino acid motifs/regions that permit the interaction of BAG 3 with numerous proteins involved in many cellular key pathways. The purpose of this study is to determine whether the proline‐rich ( PXXP ) domain of BAG 3 is necessary for its cellular protection against hypoxia–reoxygenation (H/R) stress by binding to its chaperone, heat shock cognate 71 kD a protein ( HSC 70). Cell apoptosis induced by H/R was evaluated using propidium iodide ( PI ) staining, caspase 3/7 activation and TUNEL staining in cultured H9C2 cells. The expression levels of BAG 3 and HSC 70 were manipulated, where BAG 3 or its mutant, which lacked the PXXP domain, was overexpressed using a plasmid and adenovirus vector, and HSC 70 expression was silenced using si RNA . Co‐immunoprecipitation (co‐ IP ) followed by western blot was employed to define the complex of BAG 3 binding to its chaperones. The PXXP domain of BAG 3 was determined to be critical for BAG 3‐mediated attenuation of H9C2 cell apoptosis induced by H/R through the binding of PXXP with HSC 70. The abolished cellular protection of BAG 3 induced by the knockdown of HSC 70 is associated with reduced binding to HSC 70. Given that the structural domain PXXP of BAG 3 is necessary for the cellular protection of BAG 3 from I/R injury, the mechanism revealed in this study indicates that BAG 3 may be a therapeutic target in patients undergoing reperfusion after myocardial infarction.