Characterization of junctate–SERCA2a interaction in murine cardiomyocyte

Junctate is a newly identified sarcoplasmic reticulum (SR) Ca2+ binding protein, but its function in cardiac muscle has remained unclear. Our previous study showed that chronic over-expression of junctate in transgenic mice led to altered SR functions and development of severe hypertrophy. In this study, we identified the interaction of junctate with SERCA2a by co-immunoprecipitation and GST-pull-down assay. This interaction was inhibited by higher Ca2+ concentration. Immunolocalization assays also showed that junctate and SERCA2a were co-localized in the SR of cardiomyocytes. Direct binding of the C-terminal region of junctate (amino acids 79–270) and luminal domain of SERCA2a (amino acids 70–89) was observed by deletion mutation experiments. Adenovirus-mediated transient over-expression of junctate in cardiomyocytes showed a reduced decay time of Ca2+ transients and increased oxalate-supported SERCA2 Ca2+ uptake, suggesting an increased activity of SERCA2a. Taken together, according to our data, junctate may play an important role in the regulation of SR Ca2+ cycling through the interaction with SERCA2a in the murine heart.