Cardiac Hypertrophy Causes Newly-Synthesized Calsequestrin to Remain Around the Nucleus in Rough Endoplasmic Reticulum

Abstract

Hypertrophy (LVH) leads to use of perinuclear Ca2+ distinct from junctional sarcoplasmic reticulum (jSR). Little is known about Ca2+-handling proteins associated with regulation of perinuclear Ca pools. Calsequestrin (CSQ), the Ca2+-binding protein of jSR, exists as a polymorphic collection of mass isoforms that results from actions of phosphatases and mannosidases following its biosynthesis in rough ER. To test the hypothesis that LVH triggers changes in CSQ structure by regulating its biosynthesis, we induced heart failure (LVEF <35%) in dogs by intracoronary microembolizations, resulting in increased cardiomyocyte cross-sectional area (60 ± 10%). Detergent-solubilized CSQ was purified from LV, and electrospray mass spectrometric analysis resolved individual CSQ protein structures in 3 failed and 3 normal hearts. In hypertrophic hearts, only higher mass CSQ structures were present, characteristic of perinuclear rough ER of cardiomyocytes (Figure). CSQ glycoforms and phosphoforms in LVH showed underprocessed structures characteristic of newly formed CSQ in rough ER that were more highly phosphorylated by CK2, a growth-activated kinase. These changes in CSQ processing in LVH may be part of a transformation from jSR Ca stores to perinuclear IP3-sensitive stores needed to maintain an altered phenotype.View Large Image | View Hi-Res Image | Download PowerPoint Slide