Article

Sorcin regulates excitation-contraction coupling in the heart

The Ohio State University, Columbus, Ohio, United States
Journal of Biological Chemistry (Impact Factor: 4.6). 09/2003; 278(31):28865-71. DOI: 10.1074/jbc.M302009200
Source: PubMed

ABSTRACT Sorcin is a penta-EF hand Ca2+-binding protein that associates with both cardiac ryanodine receptors and L-type Ca2+ channels and has been implicated in the regulation of intracellular Ca2+ cycling. To better define the function of sorcin, we characterized transgenic mice in which sorcin was overexpressed in the heart. Transgenic mice developed normally with no evidence of cardiac hypertrophy and no change in expression of other calcium regulatory proteins. In vivo hemodynamics revealed significant reductions in global indices of contraction and relaxation. Contractile abnormalities were also observed in isolated adult transgenic myocytes, along with significant depression of Ca2+ transient amplitudes. Whole cell ICa density and the time course of activation were normal in transgenic myocytes, but the rate of inactivation was significantly accelerated. These effects of sorcin on L-type Ca2+ currents were confirmed in Xenopus oocyte expression studies. Finally, we examined the expression of sorcin in normal and failing hearts from spontaneous hypertensive heart failure rats. In normal myocardium, sorcin extensively co-localized with ryanodine receptors at the Z-lines, whereas in myopathic hearts the degree of co-localization was markedly disrupted. Together, these data indicate that sorcin modulates intracellular Ca2+ cycling and Ca2+ influx pathways in the heart.

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    • "By interacting with these targets, sorcin modifies excitation– contraction (E–C) coupling by increasing NCX activity and reducing RyR2 activity (Meyers et al. 2003; Seidler et al. 2003). Sorcin is also implicated in the regulation of both Ca 2+ -dependent and voltage-dependent inactivation mechanisms of L-type Ca 2+ current (I Ca,L ; CDI and VDI), which regulates Ca 2+ influx into the cell (Meyers et al. 2003). Meyers and co-workers (1998) describe the binding of sorcin to the C−terminus of the LTCC, but the mechanism by which sorcin modulates Ca 2+ influx via I Ca,L activity, particularly via current inactivation, is not clearly understood. "
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    ABSTRACT: We examined the modulation of the cardiac L-type Ca(2+) channel (LTCC) by the regulatory protein sorcin and tested the hypothesis that modulation occurred by direct interaction. Whole-cell patch-clamp recordings were made on native rabbit ventricular myocytes and HEK 293 cells expressing cardiac alpha(1C) subunits. In ventricular cells, sorcin increased peak current when using either Ca(2+) or Ba(2+) as charge carriers. In HEK 293 cells, sorcin increased peak current density when using Ba(2+) as a charge carrier but not when using Ca(2+). In ventricular myocytes, current inactivation (tau(fast), in ms) was slowed by sorcin with Ca(2+) as the charge carrier, whilst in the presence of Ba(2+) it was enhanced. In HEK 293 cells, sorcin significantly enhanced tau(fast), but no significant change was observed with Ba(2+). This trend was mimicked by the truncated peptide, sorcin Ca(2+)-binding domain, which lacks the N-terminal domain. These data suggest that sorcin interacts with LTCC via its C-terminal domain, which alters current magnitude and tau(fast). These effects appear to be influenced by the prevailing experimental conditions.
    Experimental Physiology 08/2008; 93(12):1233-8. DOI:10.1113/expphysiol.2008.043497 · 2.87 Impact Factor
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    • "High-affinity EF hands usually contain, in the coordination position defined as –Z, a glutamic acid residue required for establishing a bidentate interaction with the metal (Blumenschein and Reinach, 2000). PEF proteins are stabilized by homo-and heterodimerization through the odd EF5 hand, and contribute to transduction of a variety of Ca coupling and, in particular, contributes to terminating cardiac contraction (Zamparelli et al., 2000; Meyers et al., 2003; Farrell et al., 2004). Indeed, transgenic mice carrying the F112L missense mutation in the critical D helix–EF3 loop calcium binding region display defective excitation–contraction coupling in the heart (Collis et al., 2007). "
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    ABSTRACT: Penta-EF-hand (PEF) proteins bind calcium and participate in a variety of calcium-dependent processes in vertebrates. In yeast, intracellular cations regulate processes like cell division and polarized growth. This study reports the identification of a unique PEF protein in Saccharomyces cerevisiae encoded by the uncharacterized open reading frame YGR058w. Pef1p has a long and unstructured N-terminal domain conserved in ascomycetes, and a highly conserved C-terminal calcium binding domain homologous to human ALG-2 and sorcin. Pef1p binds calcium and zinc and homodimerizes in vitro and in vivo like vertebrate homologues. Disruption of PEF1 induces defective growth in SDS and cation depletion conditions. Significantly, a critical substitution in the second EF hand (E218A) lowers the in vitro affinity for zinc and phenocopies growth defects. The dissection of protein-protein interactions and the cellular localization of Pef1p analogous to that of RAM pathway components controlling daughter-specific gene expression at the site of bud emergence bring out the importance of this novel protein. Our data suggest that cation homeostasis is involved in the control of polarized growth and in stress response in budding yeast.
    Molecular Microbiology 09/2007; 65(4):1122-38. DOI:10.1111/j.1365-2958.2007.05852.x · 5.03 Impact Factor
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    • "Sorcin (soluble resistance-related calcium binding protein) is a penta-EF hand Ca 2+ -binding protein that in the heart regulates intracellular Ca 2+ homeostasis by interacting with proteins involved in excitation– contraction (E-C) coupling such as RyRs (Meyers et al. 1995b, 2003; Lokuta et al. 1997; Farrell et al. 2003) and the Na + –Ca 2+ exchanger (Seidler et al. 2003). Other protein targets continue to emerge (Meyers et al. 2003; Suarez et al. 2004; Matsumoto et al. 2005; Frank et al. 2005), placing sorcin as an important molecular switchboard that links Ca 2+ signals with effector proteins. In all tissues where it is expressed, sorcin is largely soluble at low [Ca 2+ ] (< 1 μm) and supposedly inactive, but at high [Ca 2+ ] i it undergoes conformational changes that expose hydrophobic residues and trigger binding to membrane-embedded protein targets (Meyers et al. 1995a; Farrell et al. 2003). "
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    ABSTRACT: Spontaneous, local Ca(2+) release events or Ca(2+) sparks by ryanodine receptors (RyRs) are important determinants of vascular tone and arteriolar resistance, but the mechanisms that modulate their properties in smooth muscle are poorly understood. Sorcin, a Ca(2+)-binding protein that associates with cardiac RyRs and quickly stops Ca(2+) release in the heart, provides a potential mechanism to modulate Ca(2+) sparks in vascular smooth muscle, but little is known about the functional role of sorcin in this tissue. In this work, we characterized the expression and intracellular location of sorcin in aorta and cerebral artery and gained mechanistic insights into its functional role as a modulator of Ca(2+) sparks. Sorcin is present in endothelial and smooth muscle cells, as assessed by immunocytochemical and Western blot analyses. Smooth muscle sorcin translocates from cytosolic to membranous compartments in a Ca(2+)-dependent manner and associates with RyRs, as shown by coimmunoprecipitation and immunostaining experiments. Ca(2+) sparks recorded in saponin-permeabilized vascular myocytes have increased frequency, duration and spatial spread but reduced amplitude with respect to Ca(2+) sparks in intact cells, suggesting that permeabilization disrupts the normal organization of RyRs and releases diffusible substances that control Ca(2+) spark properties. Perfusion of 2 mum sorcin onto permeabilized myocytes reduced the amplitude, duration and spatial spread of Ca(2+) sparks, demonstrating that sorcin effectively regulates Ca(2+) signalling in vascular smooth muscle. Together with a dense distribution in the perimeter of the cell along a pool of RyRs, these properties make sorcin a viable candidate to modulate vascular tone in smooth muscle.
    The Journal of Physiology 12/2006; 576(Pt 3):887-901. DOI:10.1113/jphysiol.2006.113951 · 4.54 Impact Factor
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