Calcium-dependent cleavage of the Na(+)/Ca(2+) exchanger by m-calpain in isolated endoplasmic reticulum

• Published in: Journal of biochemistry (Tokyo) 2010-02, Vol.147 (2), p.225-235
• Main Authors: Samanta, Krishna, Kar, Pulak, Chakraborti, Tapati, Chakraborti, Sajal
• Format: Article
• Language: English
• Subjects: Animals; Blotting, Western; Calcium - metabolism; Calcium-Binding Proteins - metabolism; Calpain - antagonists & inhibitors; Calpain - metabolism; Cattle; Dipeptides - pharmacology; Egtazic Acid - pharmacology; Electrophoresis, Polyacrylamide Gel; Endoplasmic Reticulum - metabolism; Immunoprecipitation; In Vitro Techniques; Muscle, Smooth - drug effects; Muscle, Smooth - metabolism; Protein Binding; Pulmonary Artery - cytology; Sodium-Calcium Exchanger - metabolism
• ISSN: 1756-2651
• DOI: 10.1093/jb/mvp176

We have recently demonstrated the localization of associated m-calpain and calpastatin in the endoplasmic reticulum (ER) of bovine pulmonary artery smooth muscle. Herein, we sought to determine the role of m-calpain on calcium-dependent proteolytic cleavage of Na(+)/Ca(2+) exchanger (NCX) in the ER. Treatment of the ER with Ca(2+) (5 mM) dissociates m-calpain-calpastatin association leading to the activation of m-calpain, which subsequently cleaves the ER integral transmembrane protein NCX1 (116 kDa) to an 82 kDa fragment. Pre-treatment of the ER with calpain inhibitors, calpeptin (10 microM) or MDL28170 (10 microM), or Ca(2+) chelator, EGTA (10 mM) does not cleave NCX1. In vitro cleavage of the ER purified NCX1 by the ER purified m-calpain also supports our finding. Cleavage of NCX1 by m-calpain in the ER may be interpreted as the main cause of intracellular Ca(2+) overload in the smooth muscle, which could be important for the manifestation of pulmonary hypertension.