Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P21817 (RyR1)
 1,154 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Intracellular Ca2+-release channels on the sarcoplasmic reticulum of striated muscle [ryanodine receptors (RyRs)] and on the endoplasmic reticulum of almost all types of cells [inositol 1,4,5-trisphosphate receptors (IP3Rs)] comprise a unique family of molecules that are structurally and functionally distinct from all other known ion channels. These channels play crucial roles in Ca2+-mediated signaling that triggers excitation-contraction coupling, T-lymphocyte activation, fertilization, and many other cellular functions. Three forms of RyR have been identified: RyR1, expressed predominantly in skeletal muscle; RyR2, expressed predominantly in cardiac muscle; and RyR3, expressed in specialized muscles and nonmuscle tissues including the brain. RyR channels are tetramers composed of four subunits each with a molecular mass of approximately 560,000 Da. The tetrameric structures of RyR1 and RyR2 are stabilized by a channel-associated protein known as the FK506 binding protein (FKBP). FKBP is the cytosolic receptor for the immunosuppressant drugs FK506 and rapamycin that inhibit the prolyl isomerase activity of FKBP and can dissociate FKBP from RyRs. Rapamycin and FK506 increase the sensitivity of RyRs to agonists such as caffeine and could be a cause of cardiac dysfunction associated with high-dose immunosuppressant therapy by promoting leakage of Ca2+ from the sarcoplasmic reticulum. The role of prolyl isomerase activity of FKBP in regulating RyR function remains uncertain, and several models have been proposed that could explain how the channel is modulated by its association with FKBP. Three forms of IP3Rs (types 1, 2 and 3) have been characterized by cDNA cloning. Most cells have at least one form of IP3R, and many express all three types. Like RyRs, the IP3R channels are tetramers composed of four subunits (approximately 300,000 Da each). IP3R1 function is regulated by at least two major cellular signaling pathways: the second messenger IP3 activates the channel, and phosphorylation by nonreceptor protein tyrosine kinases (e.g., Fyn) increase its open probability. During end-stage human heart failure, RyR2 mRNA and protein are downregulated, whereas IP3R1 is upregulated, suggesting that altered Ca2+-release channel levels may contribute to defects in Ca2+ homeostasis. Cells that are deficient in IP3R1 exhibit defective T cell-receptor signaling and thus cannot be activated by T cell-receptor stimulation. IP3R1-deficient cells are also resistant to induced apoptosis. Thus RyRs and IP3Rs play critical roles in fundamental and diverse signaling phenomena that include excitation-contraction coupling, T-cell activation, and programmed cell death.
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PMID:Intracellular calcium-release channels: regulators of cell life and death. 912 14

The cardiac ryanodine receptor (RyR2), the major calcium release channel on the sarcoplasmic reticulum (SR) in cardiomyocytes, has recently been shown to be involved in at least two forms of sudden cardiac death (SCD): (1) Catecholaminergic polymorphic ventricular tachycardia (CPVT) or familial polymorphic VT (FPVT); and (2) Arrhythmogenic right ventricular dysplasia type 2 (ARVD2). Eleven RyR2 missense mutations have been linked to these diseases. All eleven RyR2 mutations cluster into 3 regions of RyR2 that are homologous to the three malignant hyperthermia (MH)/central core disease (CCD) mutation regions of the skeletal muscle ryanodine receptor/calcium release channel RyR1. MH/CCD RyR1 mutations have been shown to alter calcium-induced calcium release. Sympathetic nervous system stimulation leads to phosphorylation of RyR2 by protein kinase A (PKA). PKA phosphorylation of RyR2 activates the channel. In conditions associated with high rates of SCD such as heart failure RyR2 is PKA hyperphosphorylated resulting in "leaky" channels. SR calcium leak during diastole can generate "delayed after depolarizations" that can trigger fatal cardiac arrhythmias (e.g., VT). We propose that RyR2 mutations linked to genetic forms of catecholaminergic-induced SCD may alter the regulation of the channel resulting in increased SR calcium leak during sympathetic stimulation.
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PMID:Involvement of the cardiac ryanodine receptor/calcium release channel in catecholaminergic polymorphic ventricular tachycardia. 1180 5

The type 1 ryanodine receptor (RyR1) on the sarcoplasmic reticulum (SR) is the major calcium (Ca2+) release channel required for skeletal muscle excitation-contraction (EC) coupling. RyR1 function is modulated by proteins that bind to its large cytoplasmic scaffold domain, including the FK506 binding protein (FKBP12) and PKA. PKA is activated during sympathetic nervous system (SNS) stimulation. We show that PKA phosphorylation of RyR1 at Ser2843 activates the channel by releasing FKBP12. When FKB12 is bound to RyR1, it inhibits the channel by stabilizing its closed state. RyR1 in skeletal muscle from animals with heart failure (HF), a chronic hyperadrenergic state, were PKA hyperphosphorylated, depleted of FKBP12, and exhibited increased activity, suggesting that the channels are "leaky." RyR1 PKA hyperphosphorylation correlated with impaired SR Ca2+ release and early fatigue in HF skeletal muscle. These findings identify a novel mechanism that regulates RyR1 function via PKA phosphorylation in response to SNS stimulation. PKA hyperphosphorylation of RyR1 may contribute to impaired skeletal muscle function in HF, suggesting that a generalized EC coupling myopathy may play a role in HF.
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PMID:PKA phosphorylation activates the calcium release channel (ryanodine receptor) in skeletal muscle: defective regulation in heart failure. 1262 52

Phosphorylation of the skeletal muscle (RyR1) and cardiac muscle (RyR2) ryanodine receptors has been reported to modulate channel activity. Abnormally high phosphorylation levels (hyperphosphorylation) at Ser-2843 in RyR1 and Ser-2809 in RyR2 and dissociation of FK506-binding proteins from the receptors have been implicated as one of the causes of altered calcium homeostasis observed during human heart failure. Using site-directed mutagenesis, we prepared recombinant RyR1 and RyR2 mutant receptors mimicking constitutively phosphorylated and dephosphorylated channels carrying a Ser/Asp (RyR1-S2843D and RyR2-S2809D) and Ser/Ala (RyR1-S2843A and RyR2-S2809A) substitution, respectively. Following transient expression in human embryonic kidney 293 cells, the effects of Ca2+, Mg2+, and ATP on channel function were determined using single channel and [3H]ryanodine binding measurements. In both assays, neither the skeletal nor cardiac mutants showed significant differences compared with wild type. Similarly essentially identical caffeine responses were observed in Ca2+ imaging measurements. Co-immunoprecipitation and Western blot analysis showed comparable binding of FK506-binding proteins to wild type and mutant receptors. Finally metabolic labeling experiments showed that the cardiac ryanodine receptor was phosphorylated at additional sites. Taken together, the results did not support the view that phosphorylation of a single site (RyR1-Ser-2843 and RyR2-Ser-2809) substantially changes RyR1 and RyR2 channel function.
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PMID:Characterization of recombinant skeletal muscle (Ser-2843) and cardiac muscle (Ser-2809) ryanodine receptor phosphorylation mutants. 1453 76

Ryanodine receptors (RyRs) are the major sarcoplasmic reticulum calcium-release channels required for excitation-contraction coupling in skeletal and cardiac muscle. Mutations in RyRs have been linked to several human diseases. Mutations in the cardiac isoform of RyR2 are associated with catecholaminergic polymorphic ventricular arrhythmias (CPVT), and arrhythmogenic right ventricular dysplasia type 2 (ARVD2), whereas mutations in the skeletal muscle isoform (RyR1) are linked to malignant hyperthermia (MH) and central core disease (CCD). RyRs are modulated by several other proteins, including the FK506 binding proteins (FKBPs), FKBP12 and FKBP12.6. These immunophilins appear to stabilize a closed state of the channel and are important for cooperative interactions among the subunits of RyRs. This review discusses the regulation of RyRs by FKBPs and the possibility that defective modulation of RyR2 by FKBP12.6 could play a role in heart failure, CPVT, and ARVD2. Also discussed are the consequences of FKBP12 depletion to skeletal muscle and the possibility of FKBP12 involvement in certain forms of MH or CCD.
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PMID:Regulation of ryanodine receptors by FK506 binding proteins. 1545 14

The biological activity of nitric oxide (NO) and NO-donors has been extensively investigated yet few studies have examined those of nitroxyl (HNO) species even though both exist in chemical equilibrium but oxidize thiols by different reaction mechanisms: S-nitrosation versus disulfide bond formation. Here, sodium trioxodinitrate (Na2N2O3; Angeli's salt; ANGS) was used as an HNO donor to investigate its effects on skeletal (RyR1) and cardiac (RyR2) ryanodine receptors. At steady-state concentrations of nanomoles/L, HNO induced a rapid Ca2+ release from sarcoplasmic reticulum (SR) vesicles then the reducing agent dithiothreitol (DTT) reversed the oxidation by HNO resulting in Ca2+ re-uptake by SR vesicles. With RyR1 channel proteins reconstituted in planar bilayers, HNO added to the cis-side increased the open probability (Po) from 0.056+/-0.026 to 0.270+/-0.102 (P<0.005, n=4) then DTT (3 mM) reduced Po to 0.096+/-0.040 (P<0.01, n=4). In parallel experiments, the time course of HNO production from ANGS was monitored by EPR and UV spectroscopy and compared with the rate of SR Ca2+ release indicating that picomolar concentrations of HNO triggered SR Ca2+ release. Controls showed that the hydroxyl radical scavenger, phenol did not alter ANGS-induced SR Ca2+ release, indicating that hydroxyl radical production from ANGS did not account for Ca2+ release from the SR. The findings indicate that HNO is a more potent activator of RyR1 than NO and that HNO activation of RyRs may contribute to NO's activation of RyRs and to the therapeutic effects of HNO-releasing prodrugs in heart failure.
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PMID:Nitroxyl triggers Ca2+ release from skeletal and cardiac sarcoplasmic reticulum by oxidizing ryanodine receptors. 1554 67

The ryanodine receptor-calcium release channel complex (RyR) plays a pivotal role in excitation-contraction coupling in skeletal and cardiac muscle. RyR channel activity is modulated by interaction with FK506-binding protein (FKBP), and disruption of the RyR-FKBP association has been implicated in cardiomyopathy, cardiac hypertrophy, and heart failure. Evidence for an interaction between RyR and FKBP is well documented, both in skeletal muscle (RyR1-FKBP12) and in cardiac muscle (RyR2-FKBP12.6), however definition of the FKBP-binding site remains elusive. Early reports proposed interaction of a short RyR central domain with FKBP12/12.6, however this site has been questioned, and recently an alternative FKBP12.6 interaction site has been identified within the N-terminal half of RyR2. In this study, we report evidence for the human RyR2 C-terminal domain as a novel FKBP12.6-binding site. Using competition binding assays, we find that short C-terminal RyR2 fragments can displace bound FKBP12.6 from the native RyR2, although they are unable to exclusively support interaction with FKBP12.6. However, expression of a large RyR2 C-terminal construct in mammalian cells encompassing the pore-forming transmembrane domains exhibits rapamycin-sensitive binding specifically to FKBP12.6 but not to FKBP12. We also obtained some evidence for involvement of the RyR2 N-terminal, but not the central domain, in FKBP12.6 interaction. Our studies suggest that a novel interaction site for FKBP12.6 may be present at the RyR2 C terminus, proximal to the channel pore, a sterically appropriate location that would enable this protein to play a central role in the modulation of this critical ion channel.
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PMID:Interaction of FKBP12.6 with the cardiac ryanodine receptor C-terminal domain. 1559 Oct 45

Abnormalities in intracellular calcium release and reuptake are responsible for decreased contractility in heart failure (HF). We have previously shown that cardiac ryanodine receptors (RyRs) are protein kinase A-hyperphosphorylated and depleted of the regulatory subunit calstabin-2 in HF. Moreover, similar alterations in skeletal muscle RyR have been linked to increased fatigability in HF. To determine whether restoration of calstabin binding to RyR may ameliorate cardiac and skeletal muscle dysfunction in HF, we treated WT and calstabin-2-/- mice subjected to myocardial infarction (MI) with JTV519. JTV519, a 1,4-benzothiazepine, is a member of a class of drugs known as calcium channel stabilizers, previously shown to increase calstabin binding to RyR. Echocardiography at 21 days after MI demonstrated a significant increase in ejection fraction in WT mice treated with JTV519 (45.8 +/- 5.1%) compared with placebo (31.1 +/- 3.1%; P < 0.05). Coimmunoprecipitation experiments revealed increased amounts of calstabin-2 bound to the RyR2 channel in JTV519-treated WT mice. However, JTV519 did not show any of these beneficial effects in calstabin-2-/- mice with MI. Additionally, JTV519 improved skeletal muscle fatigue in WT and calstabin-2-/- mice with HF by increasing the binding of calstabin-1 to RyR1. The observation that treatment with JTV519 improved cardiac function in WT but not calstabin-2-/- mice indicates that calstabin-2 binding to RyR2 is required for the beneficial effects in failing hearts. We conclude that JTV519 may provide a specific way to treat the cardiac and skeletal muscle myopathy in HF by increasing calstabin binding to RyR.
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PMID:Enhancing calstabin binding to ryanodine receptors improves cardiac and skeletal muscle function in heart failure. 1597 11

The cardiac isoform of the ryanodine receptor (RyR2) from dog binds predominantly a 12.6-kDa isoform of the FK506-binding protein (FKBP12.6), whereas RyR2 from other species binds both FKBP12.6 and the closely related isoform FKBP12. The role played by FKBP12.6 in modulating calcium release by RyR2 is unclear at present. We have used cryoelectron microscopy and three-dimensional (3D) reconstruction techniques to determine the binding position of FKBP12.6 on the surface of canine RyR2. Buffer conditions that should favor the "open" state of RyR2 were used. Quantitative comparison of 3D reconstructions of RyR2 in the presence and absence of FKBP12.6 reveals that FKBP12.6 binds along the sides of the square-shaped cytoplasmic region of the receptor, adjacent to domain 9, which forms part of the four clamp (corner-forming) structures. The location of the FKBP12.6 binding site on "open" RyR2 appears similar, but slightly displaced (by 1-2 nm) from that found previously for FKBP12 binding to the skeletal muscle ryanodine receptor that was in the buffer that favors the "closed" state. The conformation of RyR2 containing bound FKBP12.6 differs considerably from that depleted of FKBP12.6, particularly in the transmembrane region and in the clamp structures. The x-ray structure of FKBP12.6 was docked into the region of the 3D reconstruction that is attributable to bound FKBP12.6, to show the relative orientations of amino acid residues (Gln-31, Asn-32, Phe-59) that have been implicated as being critical in interactions with RyR2. A thorough understanding of the structural basis of RyR2-FKBP12.6 interaction should aid in understanding the roles that have been proposed for FKBP12.6 in heart failure and in certain forms of sudden cardiac death.
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PMID:Three-dimensional visualization of FKBP12.6 binding to an open conformation of cardiac ryanodine receptor. 1621 74

Heart rate recovery is the difference in heart rate at peak exercise and at a specific time interval following the onset of recovery. Attenuated heart rate recovery is an independent predictor of mortality in patients with a history of coronary artery disease. The aim of the present study was to evaluate the effect of a statin on heart rate recovery, particularly in patients with ischemic heart failure and hyperlipidemia. Twenty-nine consecutive hyperlipidemic, stable coronary artery disease patients with heart failure and 19 healthy subjects were enrolled. Heart rate recovery values at the 1st and 3rd minutes and lipid profiles of the patients were evaluated at baseline and following 3 months of treatment with fluvastatin. Compared with healthy subjects, the heart rate recovery values were significantly lower in the heart failure patients in both the 1st and 3rd minutes, respectively (31 +/- 6 versus 19 +/- 7, P < 0.0001; 66 +/- 7 versus 47 +/- 8, P < 0.0001). Heart rate recovery in the 1st and 3rd minutes increased from 19 +/- 7 to 24 +/- 9 and 47 +/- 8 to 57 +/- 11, respectively, following treatment (P < 0.001, P < 0.001). There were no significant correlations among the changes in lipid parameters or HRR in the first and third minutes in the recovery period. The results revealed an improvement in heart rate recovery in heart failure patients by fluvastatin treatment. If this association can be confirmed by other studies, it would be interesting to perform further studies into the mechanism underlying this finding.
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PMID:Decreased heart rate recovery in patients with heart failure: effect of fluvastatin therapy. 1627 75


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