Review ArticleProtein kinase Cα as a heart failure therapeutic target
Research Highlights
► Multiple papers have shown that PKCa regulates cardiac contractility. ► Deletion or genetic inhibition of PKCa increases cardiac function and protects from failure. ► Pharmacologic inhibition of PKCa protects from heart failure after injury. ► PKCa inhibitory drugs are promising therapeutics for human heart failure.
Introduction
The protein kinase C (PKC) family of Ca2+ and/or lipid-activated serine/threonine kinases function downstream of many membrane-associated signal transduction pathways [1]. Approximately 10 different isozymes comprise the PKC family, which are broadly classified by their activation characteristics. The conventional PKC isozymes (α, βI, βII, and γ) are Ca2+- and lipid-activated, while the novel isozymes (ε, θ, η, and δ) and atypical isozymes (ζ and λ) are Ca2+-independent but activated by distinct lipids [1]. PKC family members contain N-terminal regulatory and C-terminal catalytic domains separated by a flexible hinge region. In the absence of activating cofactors, the catalytic domain is subject to autoinhibition by the regulatory domain mediated, in part, by a pseudosubstrate sequence motif that resembles the consensus sequence for phosphorylation by PKC [2]. For the classical PKC isozymes, binding of Ca2+ and phosphatidylserine to the C2 domain leads to increased membrane association. Binding of diacylglycerol (DAG) to the zinc finger region of the C1 domain causes a conformational change, further enabling activation of the enzyme [3]. For all PKC isoforms, membrane translocation provides a mechanism to regulate substrate access through docking complexes such as RACKs, although PKC isoforms may also function when unbound and free in the cytosol or nucleus [4]. In addition to changes in phosphorylation and translocation of PKC, alterations in PKC levels can also affect activity and signaling, such as during cardiac development and with pathological events. For example, PKCα, β, ε, and ζ expression are high in fetal and neonatal hearts but decrease in adult hearts [5]. Select PKC isoforms also increase during transition to heart failure in humans, suggesting a reversion back to a neonatal phenotype [3].
With respect to the conventional isoforms, PKCα is the predominant subtype expressed in the mouse, human, and rabbit hearts, while PKCβ and PKCγ are detectable but expressed at substantially lower levels [6], [7], [8]. Numerous reports have also associated PKCα activation or an increase in PKCα expression with hypertrophy, dilated cardiomyopathy, ischemic injury, or mitogen stimulation [1]. For example, hemodynamic pressure overload in rodents promotes translocation and presumed activation of PKCα during the hypertrophic phase or during the later stages of heart failure [9], [10], [11], [12], [13]. Increased expression of PKCα was also observed following myocardial infarction [14], [15]. Human heart failure has also been associated with increased activation of conventional PKC isoforms, including PKCα [15], [16]. Thus, PKCα fits an important criterion as a therapeutic target; its expression and activity are increased during heart disease.
Section snippets
PKCα gene-deleted mice
We and others have shown that PKCα functions as a fundamental regulator of cardiac contractility [17], [18]. PKCα−/− mice showed an increase in cardiac contractile performance in multiple experimental systems. For example, closed-chest invasive hemodynamic assessment showed a 15%–20% increase in maximum dP/dt at baseline, with a corresponding parallel increase in performance after β-adrenergic receptor stimulation. An ex vivo working heart preparation, which shows the intrinsic function of the
Molecular mechanisms of action
A number of independent molecular mechanisms have been associated with the known protection from heart failure by PKCα inhibition, although all of these mechanisms have so far been associated with modulation of cardiac contractility (Fig. 1). The first identified mechanism whereby PKCα inhibition enhances cardiac contractility is through SR Ca2+ loading [17]. Specifically, PKCα phosphorylates inhibitor 1 (I-1) at Ser67, resulting in greater protein phosphatase 1 activity, leading to greater
PKCα inhibitory drugs protect the rodent heart (translational data)
The results in genetically modified animal models and in isolated adult myocytes clearly show a cardioprotective effect with PKCα inhibition. Such results suggested that a nontoxic and tissue available pharmacological inhibitor with selectivity toward PKCα might be of significant therapeutic value. Thus, we and others carefully examined the effects of cPKC inhibitors of the bisindolylmaleimide class, such as ruboxistaurin (LY333531), Ro-32-0432, or Ro-31-8220, in different rodent heart failure
Important future considerations for bringing this to the clinic
Based on genetic experiments and various pharmacological studies discussed above, a more selective PKCα inhibitor would serve as a better therapeutic agent compared with existing cPKC inhibitors. For example, while the non-selective cPKC inhibitor ruboxistaurin also targets PKCβ and γ, inhibiting PKCα clearly predominates in providing protection to the heart [19]. Thus, a PKCα selective inhibitor would greatly reduce potential adverse effects and achieve greater efficacy, especially since PKCβγ
Disclosure Statement
None declared.
Acknowledgments
This work was supported by grants from the National Institutes of Health (NIH), the Fondation Leducq, and the Howard Hughes Medical Institute (J. D. M.). Q. L. was supported by a K99/R00 award from the NIH.
References (43)
- et al.
Tissue-specific developmental regulation of protein kinase C isoforms
Biochem Pharmacol
(1996) - et al.
Calcineurin promotes protein kinase C and c-Jun NH2-terminal kinase activation in the heart. Cross-talk between cardiac hypertrophic signaling pathways
J Biol Chem
(2000) - et al.
Identification of a functionally critical protein kinase C phosphorylation residue of cardiac troponin T
J Biol Chem
(2003) - et al.
PKC-betaII sensitizes cardiac myofilaments to Ca2+ by phosphorylating troponin I on threonine-144
J Mol Cell Cardiol
(2006) - et al.
Inhibition of protein kinase C reduces left ventricular fibrosis and dysfunction following myocardial infarction
J Mol Cell Cardiol
(2005) - et al.
Chronic heart failure: contemporary diagnosis and management
Mayo Clin Proc
(2010) - et al.
Protein kinase cascades in the regulation of cardiac hypertrophy
J Clin Invest
(2005) - et al.
Protein kinase C contains a pseudosubstrate prototope in its regulatory domain
Science
(1987) - et al.
PKC isozymes in chronic cardiac disease: possible therapeutic targets?
Annu Rev Pharmacol Toxicol
(2008) - et al.
Protein kinase C isoform-selective signals that lead to cardiac hypertrophy and the progression of heart failure
Mol Cell Biochem
(2003)
Pharmacological- and gene therapy-based inhibition of protein kinase Calpha/beta enhances cardiac contractility and attenuates heart failure
Circulation
Enhanced PKC beta II translocation and PKC beta II-RACK1 interactions in PKC epsilon-induced heart failure: a role for RACK1
Am J Physiol Heart Circ Physiol
Ischemic preconditioning induces selective translocation of protein kinase C isoforms epsilon and eta in the heart of conscious rabbits without subcellular redistribution of total protein kinase C activity
Circ Res
Increased protein kinase C and isozyme redistribution in pressure-overload cardiac hypertrophy in the rat
Circ Res
PKC translocation without changes in Galphaq and PLC-beta protein abundance in cardiac hypertrophy and failure
Am J Physiol Heart Circ Physiol
Alterations in protein kinase C isoenzyme expression and autophosphorylation during progression of pressure overload-induced left ventricular hypertrophy
Mol Cell Biochem
Differential regulation of cardiac protein kinase C isozyme expression after aortic banding in rat
Cardiovasc Res
Convergence of protein kinase C and JAK-STAT signaling on transcription factor GATA-4
Mol Cell Biol
Protein kinase C in the human heart: differential regulation of the isoforms in aortic stenosis or dilated cardiomyopathy
Mol Cell Biochem
Increased protein kinase C activity and expression of Ca2+-sensitive isoforms in the failing human heart
Circulation
PKC-alpha regulates cardiac contractility and propensity toward heart failure
Nat Med
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