Rough endoplasmic reticulum to junctional sarcoplasmic reticulum trafficking of calsequestrin in adult cardiomyocytes

Abstract Cardiac calsequestrin (CSQ) is synthesized on rough endoplasmic reticulum (ER), but concentrates within the junctional sarcoplasmic reticulum (SR) lumen where it becomes part of the Ca2+ -release protein complex. To investigate CSQ trafficking through biosynthetic/secretory compartments of...

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Bibliographic Details
Published in:Journal of molecular and cellular cardiology 2010-10, Vol.49 (4), p.556-564
Main Authors: McFarland, Timothy P, Milstein, Michelle L, Cala, Steven E
Format: Article
Language:English
Subjects:
Animals
Arrhythmias, Cardiac - metabolism
Calsequestrin
Calsequestrin - metabolism
Cardiomyocytes
Cardiovascular
Cells, Cultured
DsRed
Electrophoresis, Polyacrylamide Gel
Endoplasmic Reticulum, Rough - metabolism
Fluorescence microscopy
Immunoblotting
Junctional sarcoplasmic reticulum
Localization
Microscopy, Confocal
Microscopy, Fluorescence
Myocytes, Cardiac - metabolism
Polymerization
Rats
Rough endoplasmic secretory pathway
Sarcoplasmic Reticulum - metabolism
Trafficking
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Summary:Abstract Cardiac calsequestrin (CSQ) is synthesized on rough endoplasmic reticulum (ER), but concentrates within the junctional sarcoplasmic reticulum (SR) lumen where it becomes part of the Ca2+ -release protein complex. To investigate CSQ trafficking through biosynthetic/secretory compartments of adult cardiomyocytes, CSQ-DsRed was overexpressed in cultured cells and examined using confocal fluorescence microscopy. By 48 h of adenovirus treatment, CSQ-DsRed fluorescence had specifically accumulated in perinuclear cisternae, where it co-localized with markers of rough ER. From rough ER, CSQ-DsRed appeared to traffic directly to junctional SR along a transverse (Z-line) pathway along which sec 23-positive (ER-exit) sites were enriched. In contrast to DsRed direct fluorescence that presumably reflected DsRed tetramer formation, both anti-DsRed and anti-CSQ immunofluorescence did not detect the perinuclear CSQ-DsRed protein, but labeled only junctional SR puncta. These putative CSQ-DsRed monomers, but not the fluorescent tetramers, were observed to traffic anterogradely over the course of a 48 h overexpression from rough ER towards the cell periphery. We propose a new model of CSQ and junctional SR protein traffic in the adult cardiomyocyte, wherein CSQ traffics from perinuclear cisternae, along contiguous ER/SR lumens in cardiomyocytes as a mobile monomer, but is retained in junctional SR as a polymer.
ISSN:0022-2828
1095-8584
DOI:10.1016/j.yjmcc.2010.05.012