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Journal of Biochemistry Advance Access published online on November 2, 2009
Journal of Biochemistry, doi:10.1093/jb/mvp176
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© The authors 2009. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Calcium-dependent cleavage of the Na+/Ca2+ exchanger by m-calpain in isolated endoplasmic reticulum

Krishna Samanta, Pulak Kar, Tapati Chakraborti and Sajal Chakraborti*

Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India

* Address correspondences: Prof. Sajal Chakraborti, Ph.D, D.Sc Department of Biochemistry and Biophysics University of Kalyani, Kalyani 741235, India E. mail: sajal_chakraborti{at}yahoo.com

Received August 7, 2009; Accepted September 28, 2009


  Abstract

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+/Ca2+ exchanger (NCX) in the ER. Treatment of the ER with Ca2+ (5 mM) dissociates m-calpain-calpastatin association leading to the activation of m-calpain, which subsequently cleaves the ER integral trans-membrane protein NCX1 (116 kDa) to an 82 kDa fragment. Pretreatment of the ER with calpain inhibitors, calpeptin (10 µM) or MDL28170 (10 µM); or Ca2+ 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 Ca2+ overload in the smooth muscle, which could be important for the manifestation of pulmonary hypertension.

Key Words: Calpastatin, endoplasmic reticulum, m-calpain, Na+/Ca2+ exchanger, pulmonary smooth muscle


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