Calsequestrin Accumulation in Rough Endoplasmic Reticulum Promotes Perinuclear Ca2+ Release

Guo, Ang; Cala, Steven E.; Song, Long‐Sheng

doi:10.1074/jbc.m112.340927

Cited by 29 publications

(25 citation statements)

References 40 publications

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“…4B, white arrowheads ), suggesting that the initial highly fluorescent jSR puncta were yet distal to the actual sites of biosynthesis. To further investigate the sites of jSR protein biosynthesis, we compared early JCT dog and TRD dog sites of accumulation with the bright red DsRed fluorescence that accompanies accumulation and concentration of CSQ2-DsRed in rough ER [18, 28]. …”

Section: Resultsmentioning

confidence: 99%

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Transitions of protein traffic from cardiac ER to junctional SR

Sleiman

McFarland

Jones

et al. 2015

Journal of Molecular and Cellular Cardiology

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The junctional sarcoplasmic reticulum (jSR) is an important and unique ER subdomain in the adult myocyte that concentrates resident proteins to regulate Ca2+ release. To investigate cellular mechanisms for sorting and trafficking proteins to jSR, we overexpressed canine forms of junctin (JCT) or triadin (TRD) in adult rat cardiomyocytes. Protein accumulation over time was visualized by confocal fluorescence microscopy using species-specific antibodies. Newly synthesized JCTdog and TRDdog appeared by 12-24 h as bright fluorescent puncta close to the nuclear surface, decreasing in intensity with increasing radial distance. With increasing time (24-48 h), fluorescent puncta appeared at further radial distances from the nuclear surface, eventually populating jSR similar to steady-state patterns. CSQ2-DsRed, a form of CSQ that polymerizes ectopically in rough ER, prevented anterograde traffic of newly made TRDdog and JCTdog, demonstrating common pathways of intracellular trafficking as well as in situ binding to CSQ2 in juxtanuclear rough ER. Reversal of CSQD-sRed interactions occurred when a form of TRDdog was used in which CSQ2-binding sites are removed (delTRD). With increasing levels of expression, CSQ2-DsRed revealed a novel smooth ER network that surrounds nuclei and connects the nuclear axis. TRDdog was retained in smooth ER by binding to CSQ2-DsRed, but escaped to populate jSR puncta. TRDdog and del TRD were therefore able to elucidate areas of ER-SR transition. High levels of CSQ2-DsRed in the ER led to loss of jSR puncta labeling, suggesting a plasticity of ER-SR transition sites. We propose a model of ER and SR protein traffic along microtubules, with prominent transverse/radial ER trafficking of JCT and TRD along Z-lines to populate jSR, and an abundant longitudinal/axial smooth ER between and encircling myonuclei, from which jSR proteins traffic.

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Section: Resultsmentioning

confidence: 99%

“…This shift in the ER-to-SR transition was consistently observed by 48 h of CSQ2-DsRed expression. It is interesting to speculate that changes in ER-jSR transition are driven by the same changes in intraluminal Ca 2+ that were shown to generate spontaneous ryanodine receptor-dependent Ca 2+ release in cultured cardiomyocytes [28]. …”

Section: Discussionmentioning

confidence: 99%

Transitions of protein traffic from cardiac ER to junctional SR

Sleiman

McFarland

Jones

et al. 2015

Journal of Molecular and Cellular Cardiology

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“…Likewise, the apoptosis-linked gene 2, a Ca 2+ -binding protein that serves as a Ca 2+ sensor, is dependant of the COPII vesicle formation process and components [33]. Hence, the role of Sar1b in Ca 2+ trafficking can explain its high level of expression not only in the skeletal muscle, but also in the heart, in view of Ca 2+ signaling and trafficking in cardiomyocytes [34,35]. Accordingly, it was reported that patients with chylomicron retention disease suffer from myolysis, cardiac abnormalities and elevated creatine kinase levels [16].…”

Section: Resultsmentioning

confidence: 99%

Tissue Distribution and Regulation of the Small Sar1b GTPase in Mice

Marcil

Seidman

Sinnett

et al. 2014

Cell Physiol Biochem

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Background/Aims: Sar1b GTPase (Sar1b) represents an obligatory component of COPII vesicles that bud from the endoplasmic reticulum to transport proteins to the Golgi apparatus. Its genetic mutations lead to a severe disorder known as chylomicron retention disease. Despite growing knowledge on Sar1b, little is known about it tissue distribution and regulation, which constitute the aims of the present study. We aimed to determine the Sar1b tissue distribution and modulation by a high-fat diet and gene forcing using transgenic mice in comparison to wild-type mice. Methods: The expression pattern of Sar1b was studied in different organs of wild-type and Sar1b transgenic mice by qRT-PCR and Western blot. The effect of transgenesis and insulin resistance induced by a 12-week high-fat diet on Sar1b gene expression was also assessed by qRT-PCR. Results: Evaluation of Sar1b mRNA revealed the skeletal muscle as the tissue with the highest Sar1b expression, followed by the heart and liver, the organs composing the digestive tract, the brain and finally the lung and the adipose tissue. Sar1b protein expression levels follow a similar pattern among the organs, except for its lower expression in the heart. While the high-fat diet did not exert any significant alterations, Sar1b transgenic mice displayed higher gene expression in the liver, ileum, jejunum, proximal and distal colon compared to wild-type mice. Conclusion: Our study supports the importance of Sar1b in organs involved in lipid transport and/or calcium trafficking such as the liver, intestine, skeletal muscle and heart.

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“…Isolation and culture of cardiomyocytes were performed as described previously (24). Adenoviruses were applied at a multiplicity of infection of 100, which resulted in transfection of almost all cells, as confirmed by immunostaining of epitope tags.…”

Section: Methodsmentioning

confidence: 99%

Molecular Determinants of Calpain-dependent Cleavage of Junctophilin-2 Protein in Cardiomyocytes

Guo

Hall

Zhang

et al. 2015

Journal of Biological Chemistry

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Background: Down-regulation of junctophilin-2 is associated with a variety of cardiac diseases. Results: Junctophilin-2 is cleaved by calpain at multiple sites, resulting in dysfunctional junctophilin-2 truncations. Conclusion: Calpain-mediated proteolysis contributes to posttranslational down-regulation of junctophilin-2. Significance: These data reveal, for the first time, the detailed molecular determinants responsible for calpain proteolysis of junctophilin-2.Junctophilin-2 (JP2), a membrane-binding protein that provides a structural bridge between the plasmalemma and sarcoplasmic reticulum, is essential for precise Ca 2؉ -induced Ca 2؉release during excitation-contraction coupling in cardiomyocytes. In animal and human failing hearts, expression of JP2 is decreased markedly, but the molecular mechanisms underlying JP2 down-regulation remain incompletely defined. In mouse hearts, ischemia/reperfusion injury resulted in acute JP2 downregulation, which was attenuated by pretreatment with the calpain inhibitor MDL-28170 or by transgenic overexpression of calpastatin, an endogenous calpain inhibitor. Using a combination of computational analysis to predict calpain cleavage sites and in vitro calpain proteolysis reactions, we identified four putative calpain cleavage sites within JP2 with three N-terminal and one C-terminal cleavage sites. Mutagenesis defined the C-terminal region of JP2 as the predominant calpain cleavage site. Exogenous expression of putative JP2 cleavage fragments was not sufficient to rescue Ca 2؉ handling in JP2-deficient cardiomyocytes, indicating that cleaved JP2 is non-functional for normal Ca 2؉ -induced Ca 2؉ release. These data provide new molecular insights into the posttranslational regulatory mechanisms of JP2 in cardiac diseases.Myocardial infarction, one of the most common causes of heart failure, is characterized by defects in cardiac excitationcontraction (E-C) 2 coupling (1, 2). In a normal cardiomyocyte, release from the sarcoplasmic reticulum (SR) via type 2 ryanodine receptors (RyR2) (3, 4). L-type Ca 2ϩ channels and RyR2s are physically and functionally organized into a tightly regulated structure known as the Ca 2ϩ release unit, which provides the structural basis for Ca 2ϩ -induced Ca 2ϩ release (4, 5). The integrity of the Ca 2ϩ release unit is maintained by the structural protein junctophilin-2 (JP2) that bridges the T-tubule membrane and the SR (6 -8). Disruption of the fine architecture of the E-C coupling machinery impairs Ca 2ϩ -induced Ca 2ϩ release, thereby leading to loss of contractility and heart failure (9). JP2, the major junctophilin isoform expressed in the heart, contains eight N-terminal membrane occupation and recognition nexus (MORN) domains that mediate interactions with the plasmalemma, a space-spanning ␣ helix, and a C-terminal transmembrane (TM) domain that anchors JP2 to the SR membrane (6). Consistent with a critical role for JP2 in E-C coupling, conditional silencing of JP2 in cardiomyocytes results in contractile dysfunction, abnormal Ca 2ϩ hand...

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Calsequestrin Accumulation in Rough Endoplasmic Reticulum Promotes Perinuclear Ca2+ Release

Cited by 29 publications

References 40 publications

Transitions of protein traffic from cardiac ER to junctional SR

Transitions of protein traffic from cardiac ER to junctional SR

Tissue Distribution and Regulation of the Small Sar1b GTPase in Mice

Molecular Determinants of Calpain-dependent Cleavage of Junctophilin-2 Protein in Cardiomyocytes

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