Regulation of Ryanodine Receptors via Macromolecular Complexes: A Novel Role for Leucine/Isoleucine Zippers

doi:10.1016/S1050-1738(02)00156-1

Trends in Cardiovascular Medicine

Volume 12, Issue 4, May 2002, Pages 166-170

https://doi.org/10.1016/S1050-1738(02)00156-1 Get rights and content

Abstract

Defective calcium (Ca²⁺) signaling, manifest as a loss of excitation–contraction (EC) coupling gain in cardiac muscle, likely plays an important role in the pathophysiology of human heart failure. The mechanism underlying this loss of cardiac EC coupling gain involves altered regulation of the cardiac ryanodine receptor (RyR2), the major sarcoplasmic reticulum Ca²⁺ release channel in the heart. This altered regulation of RyR2 is due, in part, to hyperphosphorylation of the channel by cyclic adenosine monophosphate-dependent protein kinase A (PKA). PKA phosphorylation of RyR2 is controlled by a macromolecular signaling complex that targets PKA and two phosphatases (PP1 and PP2A) to the channel. The targeting of PKA, PP1, and PP2A to RyR2 is dependent on the binding of targeting proteins to the channel via highly conserved leucine/isoleucine zippers (LIZs). Formation of an ion channel macromolecular signaling complex is a novel role of LIZs. Recognition of this new function for LIZ motifs has provided a road map for rapidly identifying components of the RyR2 macromolecular signaling complex that play a key role in regulating normal cardiac physiology as part of the “fight or flight” response. The components of the RyR2 macromolecular signaling complex are also novel targets for heart failure and cardiac arrhythmia therapeutics. (Trends Cardiovascular Med 2002;12:166–170).

Section snippets

FKBP12.6 Regulates RyR2

In 1989, Marks et al. (1989) identified a 12-kDa protein, originally identified as a peptide KC7 that co-purifies with RyR1, that was subsequently shown to be the FK506 binding protein (FKBP12), a cytosolic receptor for the immunosuppressant drugs FK506 and rapamycin (Schreiber 1991). FKBP12 is expressed at high levels in all types of muscle (Jayaraman et al. 1992). FKBP12 and a highly homologous protein 12.6-kDa protein (FKBP12.6) are cis–trans peptidyl–prolyl isomerases that are members of

PKA Phosphorylation of RyR2 Dissociates FKBP12.6 from the Channel

The RyR2 macromolecular complex includes FKBP12.6, PKA and its targeting protein mAKAP, PP1 and its targeting protein spinophilin, and PP2A with its targeting protein PR130 Marx et al. 2000, Marx et al. 2001b. Binding of FKBP12.6 to RyR2 is physiologically regulated by PKA phosphorylation of the channel that dissociates FKBP12.6 from RyR2 (Marx et al. 2000) resulting in increased activity (increased Po) of RyR2. Similarly, PKA phosphorylation of RyR1 also regulates FKBP12 binding (Marks et al.,

Acknowledgements

The authors thank members of the Marks laboratory for helpful discussions and comments on the manuscript. This work was supported by grante to A.R.M. from the NIH, the AHA, and the Richard and Lynne Kaiser Family Foundation, and the Whitaker Foundation (S.R.). A.R.M. is a Doris Duke Foundation Distinguished Clinical Scientist.

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Reversible phosphorylation of ion channels and calcium-handling proteins provides precise post-translational regulation of cardiac excitation and contractility. Serine/threonine phosphatases govern dephosphorylation of the majority of cardiac proteins. Accordingly, dysfunction of this regulation contributes to the development and progression of heart failure and atrial fibrillation. On the molecular level, these changes include alterations in the expression level and phosphorylation status of Ca²⁺ handling and excitation-contraction coupling proteins provoked by dysregulation of phosphatases. The serine/threonine protein phosphatase PP1 is one a major player in the regulation of cardiac excitation-contraction coupling. PP1 essentially impacts on cardiac physiology and pathophysiology via interactions with the cardiac ion channels Cav1.2, NKA, NCX and KCNQ1, sarcoplasmic reticulum-bound Ca²⁺ handling proteins such as RyR2, SERCA and PLB as well as the contractile proteins MLC2, TnI and MyBP-C. PP1 itself but also PP1-regulatory proteins like inhibitor-1, inhibitor-2 and heat-shock protein 20 are dysregulated in cardiac disease. Therefore, they represent interesting targets to gain more insights in heart pathophysiology and to identify new treatment strategies for patients with heart failure or atrial fibrillation. We describe the genetic and holoenzymatic structure of PP1 and review its role in the heart and cardiac disease. Finally, we highlight the importance of the PP1 regulatory proteins for disease manifestation, provide an overview of genetic models to study the role of PP1 for the development of heart failure and atrial fibrillation and discuss possibilities of pharmacological interventions.
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Citation Excerpt :
Blocking RyR immediately after SCI has been shown to be neuro-/axoprotective (Orem et al., 2017). RyRs are homotetrameric macromolecular protein complexes (Marks et al., 2002; Marx et al., 2000), whereby the calstabin subunit (FKBP12) is of particular interest because it stabilizes the channel in an state of reduced activity and as a result preventing a pathological release of calcium (Brillantes et al., 1994). Modifications of RyRs leading to a loss of calstabin from the channel macromolecular complex play an important role in neuropathology (Dridi et al., 2020; Lacampagne et al., 2017; Reiken et al., 2021).
Calcium homeostasis is essential for neuronal cell survival/differentiation. Imbalance of the Ca²⁺ homeostasis due to excessive Ca²⁺ overload is essential for spinal cord injury (SCI). The overload resulted from Ca²⁺ flux across the plasma membrane and from internal Ca²⁺ store release (mitochondria, endoplasmic reticulum, ER). Inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) are involved in releasing Ca²⁺ from ER contributing to axonal degeneration following SCI. In turn, block of both receptors is axoprotective. The calstabin RyR subunit, stabilizing the channel in a state of reduced activity, prevents pathological Ca²⁺ release too.
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Citation Excerpt :
Co-immunoprecipitation studies have revealed that the RyR macromolecular complex consists of (FKBP) calstabin, catalytic subunit of PKA (PKA), regulatory subunit of PKA (RII), protein phosphatases 1 (PP1) and 2A (PP2A), and an anchoring protein mAKAP [30]. Targeting of PKA, PP1, and PP2A to RyR is mediated by the binding of anchoring proteins to leucine/isoleucine zipper (LZ) motifs [31]. PP1 interaction with RyR2 is mediated by spinophilin binding to an LZ domain located between amino acids 530–704 [32].
Regulation of intracellular calcium (Ca²⁺) is critical in all cell types. The ryanodine receptor (RyR), an intracellular Ca²⁺ release channel located on the sarco/endoplasmic reticulum (SR/ER), releases Ca²⁺ from intracellular stores to activate critical functions including muscle contraction and neurotransmitter release. Dysfunctional RyR-mediated Ca²⁺ handling has been implicated in the pathogenesis of inherited and non-inherited conditions including heart failure, cardiac arrhythmias, skeletal myopathies, diabetes, and neurodegenerative diseases. Here we have reviewed the evidence linking human disorders to RyR dysfunction and describe novel approaches to RyR-targeted therapeutics.

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Brief reviewRegulation of Ryanodine Receptors via Macromolecular Complexes: A Novel Role for Leucine/Isoleucine Zippers

Abstract

Section snippets

FKBP12.6 Regulates RyR2

PKA Phosphorylation of RyR2 Dissociates FKBP12.6 from the Channel

Acknowledgements

Biophys J

Cell

Biophys J

J Biol Chem

J Biol Chem

J Mol Cell Cardiol

Cell

Biochem Biophys Res Comm

Biochem Biophys Res Comm

J Biol Chem

Biophys J

Excitation-Contraction Coupling and Cardiac Contractile Force

Bastadin 10 stabilizes the open conformation of the ryanodine-sensitive Ca(2+) channel in an FKBP12-dependent manner

J Biol Chem

Calcium and cardiac excitation–contraction coupling

Annu Rev Physiol

After depolarizations and triggered activity

Basic Res Cardiol

FKBP12 binding modulates ryanodine receptor channel gating

J Biol Chem

Phosphorylation of the purified cardiac ryanodine receptor by exogenous and endogenous protein kinases

Biochem J

Effects of rapamycin on ryanodine receptor/ Ca2+-release channels from cardiac muscle

Circ Res

The leucine zippera hypothetical structure common to a new class of DNA binding proteins

Science

Brief review
Regulation of Ryanodine Receptors via Macromolecular Complexes: A Novel Role for Leucine/Isoleucine Zippers

Effects of rapamycin on ryanodine receptor/ Ca²⁺-release channels from cardiac muscle