The cardiac sarcoplasmic reticulum phospholamban kinase is a distinct delta-CaM kinase isozyme

The function of LncRNA-H19 in cardiac hypertrophy

Cardiac hypertrophy, characterized by the enlargement of cardiomyocytes, is initially an adaptive response to physiological and pathological stimuli. Decompensated cardiac hypertrophy is related to fibrosis, inflammatory cytokine, maladaptive remodeling, and heart failure. Although pathological myocardial hypertrophy is the main cause of hypertrophy-related morbidity and mortality, our understanding of its mechanism is still poor. Long noncoding RNAs (lncRNAs) are noncoding RNAs that regulate various physiological and pathological processes through multiple molecular mechanisms. Recently, accumulating evidence has indicated that lncRNA-H19 is a potent regulator of the progression of cardiac hypertrophy. For the first time, this review summarizes the current studies about the role of lncRNA-H19 in cardiac hypertrophy, including its pathophysiological processes and underlying pathological mechanism, including calcium regulation, fibrosis, apoptosis, angiogenesis, inflammation, and methylation. The context within which lncRNA-H19 might be developed as a target for cardiac hypertrophy treatment is then discussed to gain better insight into the possible biological functions of lncRNA-H19 in cardiac hypertrophy.

Chronic CaMKII inhibition reverses cardiac function and cardiac reserve in HF mice

AIMS

The present study was to explore the impact of KN93 - a specific inhibitor of CaMKII - on cardiac function and cardiac reserve in HF mice.

MAIN METHODS

We have generated pressure-overload HF mice using modified transverse aortic constriction (TAC) method. For acute inhibition (AI) experiment, HF mice were randomly divided into HF group, HF + KN93 AI group and HF + KN92 AI group, using sham mice as control. Mice in HF + KN93 AI group and HF + KN92 AI group were injected with CaMKII inhibitor KN93 or its inactive analogue KN92 on post-TAC day 15, while mice in HF group and Sham group were treated with saline. For chronic inhibition (CI) experiment, mice were injected daily with KN93, KN92 or saline for one week. At baseline and after isoproterenol (Iso) injection, in vivo cardiac function was assessed by echocardiography and left ventricular pressure-volume catheter.

KEY FINDINGS

Acute inhibition of CaMKII leads to decreased -dP/dtmin, increased EF, FS, longitudinal strain, longitudinal strain rate, ESPVR, dP/dtmax-EDV, PRSW, Tau and EDPVR, and unaltered reactivity to Iso in HF mice. Chronic inhibition results in increased EF, FS, longitudinal strain, longitudinal strain rate, ESPVR, dP/dtmax-EDV and PRSW, without alteration in -dP/dtmin, Tau and EDPVR. In addition, chronic inhibition reverses the effect of Iso on HF mice.

SIGNIFICANCE

Although acute CaMKII inhibition can repair systolic function in HF mice, it also exacerbates the diastolic function, whereas chronic inhibition improves both systolic function and cardiac reserve to β-adrenergic stimulation without impairing diastolic function.

Effect of ganglioside GT1b on the in vitro maturation of porcine oocytes and embryonic development

Ganglioside is an acidic glycosphingolipid with sialic acids residues. This study was performed to investigate the effect and mechanism of ganglioside GT1b in porcine oocytes in the process of in vitro maturation (IVM) and preimplantation development. Metaphase II (MII) rates were significantly (P < 0.05) different between the control group and the 5 nM GT1b treatment group. Intracellular glutathione (GSH) levels in oocytes matured with 5 nM and 20 nM and GT1b decreased significantly (P < 0.05). The 10 nM group showed a significant (P < 0.05) decrease in intracellular reactive oxygen species (ROS) levels compared with the control group. Subsequently, the level of intracellular Ca(2+) in oocytes treated with different concentrations of GT1b was measured. Intracellular Ca(2+) was significantly (P < 0.05) increased with a higher concentration of GT1b in a dose-dependent manner. Real-time PCR was performed and showed that the expression of bradykinin 2 receptor (B2R) and calcium/calmodulin-dependent protein kinase II delta (CaMKIIδ) in cumulus cells was significantly (P < 0.05) decreased in the 20 nM GT1b treatment group. Treatment with 5 nM GT1b significantly (P < 0.05) decreased the expression of CaMKIIδ. In oocytes, treatment with 5 nM GT1b significantly (P < 0.05) decreased CaMKIIγ and POU5F1 (POU domain, class 5, transcription factor 1). However, treatment with 20 nM GT1b significantly (P < 0.05) increased the expression of POU5F1. Finally, embryonic developmental data showed no significant differences in the two experiments (parthenogenesis and in vitro fertilization). In conclusion, the results of the present study indicated that GT1b plays an important role in increasing the nuclear maturation rate and decreasing the intracellular ROS levels during IVM. However, GT1b inhibited maturation of the cytoplasm by maintaining intracellular Ca(2+) in the process of oocyte maturation regardless of the cell cycle stage. Therefore, GT1b is thought to act on another mechanism that controls intracellular Ca(2+).

Targeting the CaMKII/ERK Interaction in the Heart Prevents Cardiac Hypertrophy

Aims

Activation of Ca²⁺/Calmodulin protein kinase II (CaMKII) is an important step in signaling of cardiac hypertrophy. The molecular mechanisms by which CaMKII integrates with other pathways in the heart are incompletely understood. We hypothesize that CaMKII association with extracellular regulated kinase (ERK), promotes cardiac hypertrophy through ERK nuclear localization.

Methods and Results

In H9C2 cardiomyoblasts, the selective CaMKII peptide inhibitor AntCaNtide, its penetratin conjugated minimal inhibitory sequence analog tat-CN17β, and the MEK/ERK inhibitor UO126 all reduce phenylephrine (PE)-mediated ERK and CaMKII activation and their interaction. Moreover, AntCaNtide or tat-CN17β pretreatment prevented PE induced CaMKII and ERK nuclear accumulation in H9C2s and reduced the hypertrophy responses. To determine the role of CaMKII in cardiac hypertrophy in vivo, spontaneously hypertensive rats were subjected to intramyocardial injections of AntCaNtide or tat-CN17β. Left ventricular hypertrophy was evaluated weekly for 3 weeks by cardiac ultrasounds. We observed that the treatment with CaMKII inhibitors induced similar but significant reduction of cardiac size, left ventricular mass, and thickness of cardiac wall. The treatment with CaMKII inhibitors caused a significant reduction of CaMKII and ERK phosphorylation levels and their nuclear localization in the heart.

Conclusion

These results indicate that CaMKII and ERK interact to promote activation in hypertrophy; the inhibition of CaMKII-ERK interaction offers a novel therapeutic approach to limit cardiac hypertrophy.

Ca2+/Calmodulin-dependent protein kinase II δ mediates myocardial ischemia/reperfusion injury through nuclear factor-κB

RATIONALE

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) has been implicated as a maladaptive mediator of cardiac ischemic injury. We hypothesized that the inflammatory response associated with in vivo ischemia/reperfusion (I/R) is initiated through CaMKII signaling.

OBJECTIVE

To assess the contribution of CaMKIIδ to the development of inflammation, infarct, and ventricular dysfunction after in vivo I/R and define early cardiomyocyte-autonomous events regulated by CaMKIIδ using cardiac-specific knockout mice.

METHODS AND RESULTS

Wild-type and CaMKIIδ knockout mice were subjected to in vivo I/R by occlusion of the left anterior descending artery for 1 hour followed by reperfusion for various times. CaMKIIδ deletion protected the heart against I/R damage as evidenced by decreased infarct size, attenuated apoptosis, and improved functional recovery. CaMKIIδ deletion also attenuated I/R-induced inflammation and upregulation of nuclear factor-κB (NF-κB) target genes. Further studies demonstrated that I/R rapidly increases CaMKII activity, leading to NF-κB activation within minutes of reperfusion. Experiments using cyclosporine A and cardiac-specific CaMKIIδ knockout mice indicate that NF-κB activation is initiated independent of necrosis and within cardiomyocytes. Expression of activated CaMKII in cardiomyocytes leads to IκB kinase phosphorylation and concomitant increases in nuclear p65. Experiments using an IκB kinase inhibitor support the conclusion that this is a proximal site of CaMKII-mediated NF-κB activation.

CONCLUSIONS

This is the first study demonstrating that CaMKIIδ mediates NF-κB activation in cardiomyocytes after in vivo I/R and suggests that CaMKIIδ serves to trigger, as well as to sustain subsequent changes in inflammatory gene expression that contribute to myocardial I/R damage.

Alterations of L-type calcium current and cardiac function in CaMKII{delta} knockout mice

RATIONALE

Recent studies have highlighted important roles of CaMKII in regulating Ca(2+) handling and excitation-contraction coupling. However, the cardiac effect of chronic CaMKII inhibition has not been well understood.

OBJECTIVE

We have tested the alterations of L-type calcium current (I(Ca)) and cardiac function in CaMKIIdelta knockout (KO) mouse left ventricle (LV).

METHODS AND RESULTS

We used the patch-clamp method to record I(Ca) in ventricular myocytes and found that in KO LV, basal I(Ca) was significantly increased without changing the transmural gradient of I(Ca) distribution. Substitution of Ba(2+) for Ca(2+) showed similar increase in I(Ba). There was no change in the voltage dependence of I(Ca) activation and inactivation. I(Ca) recovery from inactivation, however, was significantly slowed. In KO LV, the Ca(2+)-dependent I(Ca) facilitation (CDF) and I(Ca) response to isoproterenol (ISO) were significantly reduced. However, ISO response was reversed by beta2-adrenergic receptor (AR) inhibition. Western blots showed a decrease in beta1-AR and an increase in Ca(v)1.2, beta2-AR, and Galphai3 protein levels. Ca(2+) transient and sarcomere shortening in KO myocytes were unchanged at 1-Hz but reduced at 3-Hz stimulation. Echocardiography in conscious mice revealed an increased basal contractility in KO mice. However, cardiac reserve to work load and beta-adrenergic stimulation was reduced. Surprisingly, KO mice showed a reduced heart rate in response to work load or beta-adrenergic stimulation.

CONCLUSIONS

Our results implicate physiological CaMKII activity in maintaining normal I(Ca), Ca(2+) handling, excitation-contraction coupling, and the in vivo heart function in response to cardiac stress.

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Inhibition of calcium-calmodulin-dependent kinase II suppresses cardiac fibroblast proliferation and extracellular matrix secretion

Calcium-calmodulin-dependent protein kinase II (CaMKII) is one of the main protein kinases mediating intracellular Ca changes. It is also involved in the process of cardiac diseases, such as cardiac hypertrophy, but its effects on myocardial fibrosis remain unclear. The present study investigates whether CaMKII is involved in cardiac fibroblast proliferation and extracellular matrix (ECM) secretion induced by angiotensin II (AngII) or electrical field stimulation (EFS) in cultured neonatal rat cardiac fibroblasts. Cardiac fibroblast proliferation was assessed by a cell survival assay (MTT) and manual cell enumeration. Cellular matrix production was demonstrated by matrix metalloproteinases (MMP) 1, 2, 9, and collagen I/III messenger RNA expression, MMP-2, 9 protein expression, and secretion of transforming growth factor beta1 and tumor necrosis factor alpha. Either AngII or EFS promoted cardiac fibroblast proliferation and ECM secretion, while also up-regulating expression of CaMKII deltaB and deltaC. More importantly, CaMKII inhibitors, autocamtide-2-related inhibitory peptide (AIP 5 microM) or KN93 (0.5 microM), suppressed cardiac fibroblast proliferation, inhibited the excretion of transforming growth factor beta1 and tumor necrosis factor alpha, decreased the messenger RNA expression of MMP-1, 2, 9 and collagen I/III, and decreased the protein expression of MMP-2, 9. These results suggest that CaMKII mediates cardiac fibroblast proliferation and ECM secretion induced by either AngII or EFS.

Proteome changes in CaMKIIδC-overexpressing cardiac myocytes

Recent studies have demonstrated that the expression as well as the activity of Ca/calmodulin-dependent protein kinase IIδ(C) (CaMKIIδ(C)) is increased in heart failure. Transgenic overexpression of CaMKIIδ(C) in mouse hearts results in severe dilated cardiomyopathy. So far, little is known about CaMKIIδ(C)-induced changes in gene expression and proteome alteration. We hypothesize that proteome changes similar to those found in advanced heart failure can be assessed even after short term overexpression of CaMKIIδ(C) in an in vitro culture model. Thus, we designed a study using a proteomic approach combined with adenovirus-mediated gene transfer of CaMKIIδ(C) to identify early CaMKIIδ(C)-induced changes in cardiac myocyte phenotype on proteome level. CaMKIIδ(C) was overexpressed by adenovirus-mediated gene transfer in isolated cardiac myocytes of adult rabbits for 48 h. Proteome changes were analyzed by two-dimensional gel electrophoresis and mass spectrometry (MS). Overexpression of CaMKIIδ(C) resulted in a decreased expression of 21 proteins (at least twofold change of expression, P<.05, n=10). Using in-gel digest and MS, we identified 13 out of these 21 proteins. CaMKIIδ(C) overexpression leads to a reduced abundance of NADH dehydrogenase, lactate dehydrogenase, pyruvate kinase, dihydrolipoamide succinyltransferase, creatine kinase M, heat shock protein 70, elongation factor Tu, and superoxide dismutase. The profile of the proteome changes induced by CaMKIIδ(C) overexpression after 48 h displayed striking alterations of metabolic proteins, cell-protecting proteins including antioxidants, and proteins involved in protein synthesis. Interestingly, the observed proteome changes are in common with the phenotype of failing cardiac myocytes on the protein level. These altered proteins may act individually as contributors to heart failure, which is observed after overexpression of CaMKIIδ(C) in genetically altered mice.

Cardioprotection by CaMKII-deltaB is mediated by phosphorylation of heat shock factor 1 and subsequent expression of inducible heat shock protein 70

RATIONALE

Ca2+/calmodulin-dependent protein kinase (CaMK)II is a multifunctional kinase involved in vital cellular processes such as Ca(2+) handling and cell fate regulation. In mammalian heart, 2 primary CaMKII isoforms, deltaB and deltaC, localize in nuclear and cytosolic compartments, respectively. Although previous studies have established an essential role of CaMKII-deltaC in cardiomyocyte apoptosis, the functional role of the more abundant isoform, CaMKII-deltaB, remains elusive.

OBJECTIVE

Here, we determined the potential role of CaMKII-deltaB in regulating cardiomyocyte viability and explored the underlying mechanism.

METHODS AND RESULTS

In cultured neonatal rat cardiomyocytes, the expression of CaMKII-deltaB and CaMKII-deltaC was inversely regulated in response to H2O2-induced oxidative stress with a profound reduction of the former and an increase of the later. Similarly, in vivo ischemia/reperfusion (IR) led to an opposite regulation of these CaMKII isoforms in a rat myocardial IR model. Notably, overexpression of CaMKII-deltaB protected cardiomyocytes against oxidative stress-, hypoxia-, and angiotensin II-induced apoptosis, whereas overexpression of its cytosolic counterpart promoted apoptosis. Using cDNA microarray, real-time PCR and Western blotting, we demonstrated that overexpression of CaMKII-deltaB but not CaMKII-deltaC elevated expression of heat shock protein (HSP)70 family members, including inducible (i)HSP70 and its homolog (Hst70). Moreover, overexpression of CaMKII-deltaB led to phosphorylation and activation of heat shock factor (HSF)1, the primary transcription factor responsible for HSP70 gene regulation. Importantly, gene silencing of iHSP70, but not Hst70, abolished CaMKII-deltaB-mediated protective effect, indicating that only iHSP70 was required for CaMKII-deltaB elicited antiapoptotic signaling.

CONCLUSIONS

We conclude that cardiac CaMKII-deltaB and CaMKII-deltaC were inversely regulated in response to oxidative stress and IR injury, and that in contrast to CaMKII-deltaC, CaMKII-deltaB serves as a potent suppressor of cardiomyocyte apoptosis triggered by multiple death-inducing stimuli via phosphorylation of HSF1 and subsequent induction of iHSP70, marking both CaMKII-delta isoforms as promising therapeutic targets for the treatment of ischemic heart disease.

Critical role of nuclear calcium/calmodulin-dependent protein kinase IIdeltaB in cardiomyocyte survival in cardiomyopathy

Calcium/calmodulin-dependent protein kinase II (CaMKII) plays a central role in cardiac contractility and heart disease. However, the specific role of alternatively spliced variants of CaMKII in cardiac disease and apoptosis remains poorly explored. Here we report that the deltaB subunit of CaMKII (CaMKIIdeltaB), which is the predominant nuclear isoform of calcium/calmodulin-dependent protein kinases in heart muscle, acts as an anti-apoptotic factor and is a novel target of the antineoplastic and cardiomyopathic drug doxorubicin (Dox (adriamycin)). Hearts of rats that develop cardiomyopathy following chronic treatment with Dox also show down-regulation of CaMKIIdeltaB mRNA, which correlates with decreased cardiac function in vivo, reduced expression of sarcomeric proteins, and increased tissue damage associated with Dox cardiotoxicity. Overexpression of CaMKIIdeltaB in primary cardiac cells inhibits Dox-mediated apoptosis and prevents the loss of the anti-apoptotic protein Bcl-2. Specific silencing of CaMKIIdeltaB by small interfering RNA prevents the formation of organized sarcomeres and decreases the expression of Bcl-2, which all mimic the effect of Dox. CaMKIIdeltaB is required for GATA-4-mediated co-activation and binding to the Bcl-2 promoter. These results reveal that CaMKIIdeltaB plays an essential role in cardiomyocyte survival and provide a mechanism for the protective role of CaMKIIdeltaB. These results suggest that selective targeting of CaMKII in the nuclear compartment might represent a strategy to regulate cardiac apoptosis and to reduce Dox-mediated cardiotoxicity.

Requirement for Ca2+/calmodulin-dependent kinase II in the transition from pressure overload-induced cardiac hypertrophy to heart failure in mice

Ca2+/calmodulin-dependent kinase II (CaMKII) has been implicated in cardiac hypertrophy and heart failure. We generated mice in which the predominant cardiac isoform, CaMKIIdelta, was genetically deleted (KO mice), and found that these mice showed no gross baseline changes in ventricular structure or function. In WT and KO mice, transverse aortic constriction (TAC) induced comparable increases in relative heart weight, cell size, HDAC5 phosphorylation, and hypertrophic gene expression. Strikingly, while KO mice showed preserved hypertrophy after 6-week TAC, CaMKIIdelta deficiency significantly ameliorated phenotypic changes associated with the transition to heart failure, such as chamber dilation, ventricular dysfunction, lung edema, cardiac fibrosis, and apoptosis. The ratio of IP3R2 to ryanodine receptor 2 (RyR2) and the fraction of RyR2 phosphorylated at the CaMKII site increased significantly during development of heart failure in WT mice, but not KO mice, and this was associated with enhanced Ca2+ spark frequency only in WT mice. We suggest that CaMKIIdelta contributes to cardiac decompensation by enhancing RyR2-mediated sarcoplasmic reticulum Ca2+ leak and that attenuating CaMKIIdelta activation can limit the progression to heart failure.

CaMKIIdelta isoforms differentially affect calcium handling but similarly regulate HDAC/MEF2 transcriptional responses

The delta(B) and delta(C) splice variants of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), which differ by the presence of a nuclear localization sequence, are both expressed in cardiomyocytes. We used transgenic (TG) mice and CaMKII expression in cardiomyocytes to test the hypothesis that the CaMKIIdelta(C) isoform regulates cytosolic Ca(2+) handling and the delta(B) isoform, which localizes to the nucleus, regulates gene transcription. Phosphorylation of CaMKII sites on the ryanodine receptor (RyR) and on phospholamban (PLB) were increased in CaMKIIdelta(C) TG. This was associated with markedly enhanced sarcoplasmic reticulum (SR) Ca(2+) spark frequency and decreased SR Ca(2+) content in cardiomyocytes. None of these parameters were altered in TG mice expressing the nuclear-targeted CaMKIIdelta(B). In contrast, cardiac expression of either CaMKIIdelta(B) or delta(C) induced transactivation of myocyte enhancer factor 2 (MEF2) gene expression and up-regulated hypertrophic marker genes. Studies using rat ventricular cardiomyocytes confirmed that CaMKIIdelta(B) and delta(C) both regulate MEF2-luciferase gene expression, increase histone deacetylase 4 (HDAC4) association with 14-3-3, and induce HDAC4 translocation from nucleus to cytoplasm, indicating that either isoform can stimulate HDAC4 phosphorylation. Finally, HDAC4 kinase activity was shown to be increased in cardiac homogenates from either CaMKIIdelta(B) or delta(C) TG mice. Thus CaMKIIdelta isoforms have similar effects on hypertrophic gene expression but disparate effects on Ca(2+) handling, suggesting distinct roles for CaMKIIdelta isoform activation in the pathogenesis of cardiac hypertrophy versus heart failure.

Differential expression of CaMK-II genes during early zebrafish embryogenesis

CaMK-II is a highly conserved Ca(2+)/calmodulin-dependent protein kinase expressed throughout the lifespan of all vertebrates. During early development, CaMK-II regulates cell cycle progression and "non-canonical" Wnt-dependent convergent extension. In the zebrafish, Danio rerio, CaMK-II activity rises within 2 hr after fertilization. At the time of somite formation, zygotic expression from six genes (camk2a1, camk2b1, camk2g1, camk2g2, camk2d1, camk2d2) results in a second phase of increased activity. Zebrafish CaMK-II genes are 92-95% identical to their human counterparts in the non-variable regions. During the first three days of development, alternative splicing yields at least 20 splice variants, many of which are unique. Whole-mount in situ hybridization reveals that camk2g1 comprises the majority of maternal expression. All six genes are expressed strongly in ventral regions at the 18-somite stage. Later, camk2a1 is expressed in anterior somites, heart, and then forebrain. Camk2b1 is expressed in somites, mid- and forebrain, gut, retina, and pectoral fins. Camk2g1 appears strongly along the midline and then in brain, gut, and pectoral fins. Camk2g2 is expressed early in the midbrain and trunk and exhibits the earliest retinal expression. Camk2d1 is elevated early at somite boundaries, then epidermal tissue, while camk2d2 is expressed in discrete anterior locations, steadily increasing along either side of the dorsal midline and then throughout the brain, including the retina. These findings reveal a complex pattern of CaMK-II gene expression consistent with pleiotropic roles during development.

Activation of CaMKIIδC Is a Common Intermediate of Diverse Death Stimuli-induced Heart Muscle Cell Apoptosis

Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is expressed in many mammalian cells, with the delta isoform predominantly expressed in cardiomyocytes. Previous studies have shown that inhibition of CaMKII protects cardiomyocytes against beta(1)-adrenergic receptor-mediated apoptosis. However, it is unclear whether activation of CaMKII is sufficient to cause cardiomyocyte apoptosis and whether CaMKII signaling is important in heart muscle cell apoptosis mediated by other stimuli. Here, we specifically enhanced or suppressed CaMKII activity using adenoviral gene transfer of constitutively active (CA-CaMKII(deltaC)) or dominant negative (DN-CaMKII(deltaC)) mutants of CaMKII(deltaC) in cultured adult rat cardiomyocytes. Expression of CA-CaMKII(deltaC) promoted cardiomyocyte apoptosis that was associated with increased mitochondrial cytochrome c release and attenuated by co-expression of Bcl-X(L). Importantly, isoform-specific suppression of CaMKII(deltaC) with the DN-CaMKII(deltaC) mutant similar to nonselective CaMKII inhibition by the pharmacological inhibitors (KN-93 or AIP) not only prevented CA-CaMKII(deltaC)-mediated apoptosis but also protected cells from multiple death-inducing stimuli. Thus, activation of CaMKII(deltaC) constitutes a common intermediate by which various death-inducing stimuli trigger cardiomyocyte apoptosis via the primary mitochondrial death pathway.

Nuclear calcium/calmodulin-dependent protein kinase IIdelta preferentially transmits signals to histone deacetylase 4 in cardiac cells

Class II histone deacetylases (HDACs) act as repressors of cardiac hypertrophy, an adaptative response of the heart characterized by a reprogramming of fetal cardiac genes. Prolonged hypertrophy often leads to dilated cardiomyopathy and heart failure. Upstream endogenous regulators of class II HDACs that regulate hypertrophic growth are just beginning to emerge. Here we demonstrate that the delta B isoform of calcium/calmodulin-dependent protein kinase II (CaMKIIdeltaB), known to promote cardiac hypertrophy, transmits signals specifically to HDAC4 but not other class II HDACs. CaMKIIdeltaB efficiently phosphorylates both a glutathione S-transferase (GST)-HDAC4 fragment spanning amino acids 207-311 and full-length FLAG-HDAC4 but not the equivalents in HDAC5. Although previous studies in skeletal muscle cells have shown that HDAC4 lacking serine 246 cannot be phosphorylated by CaMKI/IV, a similar mutant is still phosphorylated by CaMKIIdeltaB. Importantly, mutation of serine 210 to alanine totally abolishes phosphorylation of the GST fragment and significantly reduces phosphorylation of full-length HDAC by CaMKIIdeltaB. RNA interference knockdown of CaMKIIdeltaB prevents the effects of hypertrophic stimuli. Overexpression of CaMKIIdeltaB in primary neonatal cardiomyocytes increases the activity of the Mef2 transcription factor and completely rescues HDAC4-mediated repression of MEF2 but only partially rescues inhibition by HDAC5 or the HDAC4 S210A mutant. CaMKIIdeltaB strongly interacts with HDAC4 in cells but not with HDAC5. These results demonstrate that CaMKIIdeltaB preferentially targets HDAC4, and this involves serine 210. These findings identify HDAC4 as a specific downstream substrate of CaMKIIdeltaB in cardiac cells and have broad applications for the signaling pathways leading to cardiac hypertrophy and heart failure.

Sarcoplasmic reticulum and cardiac oxidative stress: an emerging target for heart disease

The sarcoplasmic reticulum (SR) is a major player in maintaining cardiac function, as it is intimately involved in the regulation of Ca2+-movements on a beat-to-beat basis. SR dysfunction due to abnormalities in SR protein content has been reported in different cardiac diseases such as ischaemic heart disease, myocardial infarction, congestive heart failure and various cardiomyopathies; thus the genes expressing the SR Ca2+-pump, Ca2+-channels, calsequestrin, phospholamban and other regulatory proteins are considered important targets for drug development. In our experience, ischaemic preconditioning (IP) and pharmacological therapies, such as anti-oxidants, beta-adrenergic receptor blockers, angiotensin receptor (AT-1) blockers, angiotensin converting enzyme inhibitors (ACE-I) and angiotensin receptor blockers are effective therapies that improve cardiac performance in the failing heart by improving SR function. Accordingly, this paper is intended to shed light on the knowledge in the field of cardiac therapy targeted to improve and protect SR function.

Calcium/calmodulin-dependent protein kinase IIdelta associates with the ryanodine receptor complex and regulates channel function in rabbit heart

Cardiac ryanodine receptors (RyR2s) play a critical role in excitation-contraction coupling by providing a pathway for the release of Ca(2+) from the sarcoplasmic reticulum into the cytosol. RyR2s exist as macromolecular complexes that are regulated via binding of Ca(2+) and protein phosphorylation/dephosphorylation. The present study examined the association of endogenous CaMKII (calcium/calmodulin-dependent protein kinase II) with the RyR2 complex and whether this enzyme could modulate RyR2 function in isolated rabbit ventricular myocardium. Endogenous phosphorylation of RyR2 was verified using phosphorylation site-specific antibodies. Co-immunoprecipitation studies established that RyR2 was physically associated with CaMKIIdelta. Quantitative assessment of RyR2 protein was performed by [(3)H]ryanodine binding to RyR2 immunoprecipitates. Parallel kinase assays allowed the endogenous CaMKII activity associated with these immunoprecipitates to be expressed relative to the amount of RyR2. The activity of RyR2 in isolated cardiac myocytes was measured in two ways: (i) RyR2-mediated Ca(2+) release (Ca(2+) sparks) using confocal microscopy and (ii) Ca(2+)-sensitive [(3)H]ryanodine binding. These studies were performed in the presence and absence of AIP (autocamtide-2-related inhibitory peptide), a highly specific inhibitor of CaMKII. At 1 microM AIP Ca(2+) spark duration, frequency and width were decreased significantly. Similarly, 1 microM AIP decreased [(3)H]ryanodine binding. At 5 microM AIP, a more profound inhibition of Ca(2+) sparks and a decrease in [(3)H]ryanodine binding was observed. Separate measurements showed that AIP (1-5 microM) did not affect sarcoplasmic reticulum Ca(2+)-ATPase-mediated Ca(2+) uptake. These results suggest the existence of an endogenous CaMKIIdelta that associates directly with RyR2 and specifically modulates RyR2 activity.

Reduced cell adhesion during mitosis by threonine phosphorylation of beta1 integrin

Cell shape and adhesion of cultured mammalian cells change dramatically during mitosis, however, how cell cycle-dependent alterations in cell adhesion are regulated remain to be elucidated. We show here that normal human mammary epithelial (HME) cells which became less adhesive and adopted the rounded morphology during the G(2)/M phase of the cell cycle significantly reduced their dependence on beta1 integrin-mediated adhesion to laminin, by using function blocking antibody to beta1 integrin. In G(2)/M cells, both total and cell surface expressions of beta1 integrin were comparable with those in G(1) cells but it was phosphorylated at threonines 788-789 within its cytoplasmic domain and coimmunoprecipitated Ca(2+)/calmodulin-dependent protein kinase (CaMK) II. The threonine phosphorylated beta1 integrin significantly reduced its intracellular linkage with actin, with no significant reduction in the actin expression. In contrast, beta1 integrin in G(1) cells was not threonine phosphorylated but formed a link with actin and coimmunoprecipitated the core enzyme of the serine/threonine protein phosphatase (PP) 2A. The results suggest that reduced beta1 integrin-mediated cell adhesion of HME cells to the substratum during mitosis may be induced by beta1 integrin phosphorylation at threonines 788-789 and its reduced ability to link with the actin cytoskeleton.

Involvement of calcium/calmodulin-dependent protein kinase II (CaMKII) in meiotic maturation and activation of pig oocytes

Calcium signal is important for the regulation of meiotic cell cycle in oocytes, but its downstream mechanism is not well known. The functional roles of calcium/calmodulin-dependent protein kinase II (CaMKII) in meiotic maturation and activation of pig oocytes were studied by drug treatment, Western blot analysis, kinase activity assay, indirect immunostaining, and confocal microscopy. The results indicated that meiotic resumption of both cumulus-enclosed and denuded oocytes was prevented by CaMKII inhibitor KN-93, Ant-AIP-II, or CaM antagonist W7 in a dose-dependent manner, but only germinal vesicle breakdown (GVBD) of denuded oocytes was inhibited by membrane permeable Ca2+ chelator BAPTA-AM. When the oocytes were treated with KN-93, W7, or BAPTA-AM after GVBD, the first polar body emission was inhibited. A quick elevation of CaMKII activity was detected after electrical activation of mature pig oocytes, which could be prevented by the pretreatment of CaMKII inhibitors. Treatment of oocytes with KN-93 or W7 resulted in the inhibition of pronuclear formation. The possible regulation of CaMKII on maturation promoting factor (MPF), mitogen-activated protein kinase (MAPK), and ribosome S6 protein kinase (p90rsk) during meiotic cell cycles of pig oocytes was also studied. KN-93 and W7 prevented the accumulation of cyclin B and the full phosphorylation of MAPK and p90rsk during meiotic maturation. When CaMKII activity was inhibited during parthenogenetic activation, cyclin B, the regulatory subunit of MPF, failed to be degraded, but MAPK and p90rsk were quickly dephosphorylated and degraded. Confocal microscopy revealed that CaM and CaMKII were localized to the nucleus and the periphery of the GV stage oocytes. Both proteins were concentrated to the condensed chromosomes after GVBD. In oocytes at the meiotic metaphase MI or MII stage, CaM distributed on the whole spindle, but CaMKII was localized only on the spindle poles. After transition into anaphase, both proteins were translocated to the area between separating chromosomes. All these results suggest that CaMKII is a multifunctional regulator of meiotic cell cycle and spindle assembly and that it may exert its effect via regulation of MPF and MAPK/p90rsk activity during the meiotic maturation and activation of pig oocytes.

The deltaC isoform of CaMKII is activated in cardiac hypertrophy and induces dilated cardiomyopathy and heart failure

Recent studies have demonstrated that transgenic (TG) expression of either Ca2+/calmodulin-dependent protein kinase IV (CaMKIV) or CaMKIIdeltaB, both of which localize to the nucleus, induces cardiac hypertrophy. However, CaMKIV is not present in heart, and cardiomyocytes express not only the nuclear CaMKIIdeltaB but also a cytoplasmic isoform, CaMKIIdeltaC. In the present study, we demonstrate that expression of the deltaC isoform of CaMKII is selectively increased and its phosphorylation elevated as early as 2 days and continuously for up to 7 days after pressure overload. To determine whether enhanced activity of this cytoplasmic deltaC isoform of CaMKII can lead to phosphorylation of Ca2+ regulatory proteins and induce hypertrophy, we generated TG mice that expressed the deltaC isoform of CaMKII. Immunocytochemical staining demonstrated that the expressed transgene is confined to the cytoplasm of cardiomyocytes isolated from these mice. These mice develop a dilated cardiomyopathy with up to a 65% decrease in fractional shortening and die prematurely. Isolated myocytes are enlarged and exhibit reduced contractility and altered Ca2+ handling. Phosphorylation of the ryanodine receptor (RyR) at a CaMKII site is increased even before development of heart failure, and CaMKII is found associated with the RyR in immunoprecipitates from the CaMKII TG mice. Phosphorylation of phospholamban is also increased specifically at the CaMKII but not at the PKA phosphorylation site. These findings are the first to demonstrate that CaMKIIdeltaC can mediate phosphorylation of Ca2+ regulatory proteins in vivo and provide evidence for the involvement of CaMKIIdeltaC activation in the pathogenesis of dilated cardiomyopathy and heart failure.

The cardiac-specific nuclear delta(B) isoform of Ca2+/calmodulin-dependent protein kinase II induces hypertrophy and dilated cardiomyopathy associated with increased protein phosphatase 2A activity

The delta isoform of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) predominates in the heart. To investigate the role of CaMKII in cardiac function, we made transgenic (TG) mice that express the nuclear delta(B) isoform of CaMKII. The expressed CaMKIIdelta(B) transgene was restricted to the myocardium and highly concentrated in the nucleus. Cardiac hypertrophy was evidenced by an increased left ventricle to body weight ratio and up-regulation of embryonic and contractile protein genes including atrial natriuretic factor, beta-myosin heavy chain, and alpha-skeletal actin. Echocardiography revealed ventricular dilation and decreased cardiac function, which was also observed in hemodynamic measurements from CaMKIIdelta(B) TG mice. Surprisingly, phosphorylation of phospholamban at both Thr(17) and Ser(16) was significantly decreased in the basal state as well as upon adrenergic stimulation. This was associated with diminished sarcoplasmic reticulum Ca(2+) uptake in vitro and altered relaxation properties in vivo. The activity and expression of protein phosphatase 2A were both found to be increased in CaMKII TG mice, and immunoprecipitation studies indicated that protein phosphatase 2A directly associates with CaMKII. Our findings are the first to demonstrate that CaMKII can induce hypertrophy and dilation in vivo and indicate that compensatory increases in phosphatase activity contribute to the resultant phenotype.

Depressed levels of Ca2+-cycling proteins may underlie sarcoplasmic reticulum dysfunction in the diabetic heart

In view of the depressed sarcoplasmic reticulum (SR) Ca2+-pump and Ca2+-release activities in the diabetic heart and the critical role of phosphorylation in regulating the SR function, we examined the status of Ca2+-calmodulin-dependent protein kinase (CaMK) and cAMP-dependent protein kinase (PKA)-mediated phosphorylations in the diabetic heart. Diabetes was induced in male Sprague-Dawley rats by an injection of streptozotocin (65 mg/kg i.v.), and the animals were killed 6 weeks later for assessment of the ventricular SR function. Depressed cardiac performance and SR Ca2+-uptake and -release activities in diabetic animals were accompanied by a significant decrease in the level of SR Ca2+-cycling proteins, such as ryanodine receptor, Ca2+-pump ATPase, and phospholamban. On the other hand, the CaMK- and PKA-mediated phosphorylations of these Ca2+-cycling proteins, the endogenous SR CaMK and PKA activities, and the endogenous SR and cytosolic phosphatase activities were increased in the diabetic heart. Treatment of 3-week diabetic animals with insulin partially or fully prevented the diabetes-induced changes in cardiac performance, SR Ca2+-uptake and -release activites, and SR protein content, whereas the diabetes-induced changes in SR CaMK- and PKA-mediated phosphorylations and activities, as well as phosphatase activities, were not significantly affected. These results suggest that the reduced content of the Ca2+-cycling proteins, unlike alterations in PKA and phosphatase activities, appear to be the major defect underlying SR dysfunction in the diabetic heart.

Glucocorticoid modulation of protein phosphorylation and sarcoplasmic reticulum function in rat myocardium

To decipher the mechanism(s) underlying glucocorticoid action on cardiac contractile function, this study investigated the effects of adrenalectomy and dexamethasone treatment on the contents of sarcoplasmic reticulum (SR) Ca(2+)-cycling proteins, their phosphorylation by endogenous Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II), and SR Ca(2+) sequestration in the rat myocardium. Cardiac SR vesicles from adrenalectomized rats displayed significantly diminished rates of ATP-energized Ca(2+) uptake in vitro compared with cardiac SR vesicles from control rats; in vivo administration of dexamethasone to adrenalectomized rats prevented the decline in SR function. Western immunoblotting analysis showed that the relative protein amounts of ryanodine receptor/Ca(2+)-release channel, Ca(2+)-ATPase, calsequestrin, and phospholamban were neither diminished significantly by adrenalectomy nor elevated by dexamethasone treatment. However, the relative amount of SR-associated CaM kinase II protein was increased 2.5- to 4-fold in dexamethasone-treated rats compared with control and adrenalectomized rats. Endogenous CaM kinase II activity, as judged from phosphorylation of ryanodine receptor, Ca(2+)-ATPase, and phospholamban protein, was also significantly higher (50--80% increase) in the dexamethasone-treated rats. The stimulatory effect of CaM kinase II activation on Ca(2+) uptake activity of SR was significantly depressed after adrenalectomy and greatly enhanced after dexamethasone treatment. These findings identify the SR as a major target for glucocorticoid actions in the heart and implicate modification of the SR CaM kinase II system as a component of the mechanisms by which dexamethasone influences SR Ca(2+)-cycling and myocardial contraction.

Expression of Ca2+/calmodulin-dependent protein kinase II delta-subunit isoforms in rats with hypertensive cardiac hypertrophy

Myocardial hypertrophy is characterized by abnormal intracellular Ca2+ handling and decreased contractile performance. Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylates numerous Ca2+ handling proteins and thus can regulate intracellular Ca2+ homeostasis directly. We therefore investigated whether differential expression of CaMKII isoforms occurs with cardiac hypertrophy which might promote an abnormal intracellular Ca2+ homeostasis. We further investigated the potential influence of angiotensin (Ang) II on CaMKII expression levels. Hearts from adult Spontaneously Hypertensive Rats (SHR) and hearts from two transgenic rat models with Ang II-dependent hypertension were studied. The expression of the cardiac CaMKII isoforms delta2, delta3, delta4 and delta9 was determined by RT-PCR and immunoblot methods. Rats transgenic for the mouse Ren-2 gene (mrTGR), SHR and controls were studied at the age of 6 months and rats transgenic for the human renin-angiotensin system (hrTGR) from postnatal day 1 to week 8. SHR and mrTGR had an increased heart/body weight ratio (26 and 25%) compared with controls (p < 0.05). SHR hearts showed significantly increased mRNA levels of delta4 and delta9 (p < 0.05) with no change for delta2 and delta3. mrTGR hearts had a significantly increased delta4 and a significantly decreased delta3 transcript level (p < 0.05) with no change for delta2 and delta9. hrTGR hearts developed severe hypertrophy (42%) after postnatal day 14. The neonatal delta2, delta3 and delta4 isoform expression levels were higher (30-100%) compared with SD controls. The levels decreased with increasing age and equalized to controls at week 8, except for delta4 which started to increase after week 4 (p < 0.05). CaMKIIdelta protein levels of all cardiac hypertrophy models were increased in sarcoplasmic reticulum preparations (50-120%) compared with controls (p < 0.05) while the cytosolic levels remained unchanged. Thus, CaMKIIdelta isoforms are differentially expressed in cardiac hypertrophy. The fetal delta4 isoform was constantly expressed. CaMKIIdelta adopts the fetal phenotype independent of the type of hypertrophic stimulus. The observed alterations of CaMKIIdelta isoform patterns may affect intracellular Ca2+ homeostasis and thus contribute to the abnormal contractile phenotype of cardiac hypertrophy.

Phosphorylation of phospholamban at threonine-17 in the absence and presence of beta-adrenergic stimulation in neonatal rat cardiomyocytes

The site-specific phospholamban phosphorylation was studied with respect to the interplay of cAMP- and Ca(2+)signaling in neonatal rat cardiomyocytes. To elucidate the signal pathway(s) for the activation of Ca(2+)/calmodulin-dependent protein kinase (CaMKII) we studied Thr17 phosphorylation of phospholamban in dependence of Ca(2+)channel activation by S(-)-Bay K8644 and in dependence of the depletion of the sarcoplasmic reticulum Ca(2+)stores by ryanodine or thapsigargin in the absence or presence of beta -adrenergic stimulation. The isoproterenol (0.1 microM)-induced Thr17 phosphorylation was potentiated 2.5-fold in presence of 1 microM S(-)-Bay K8644. Interestingly, S(-)-Bay K8644 alone was also able to induce Thr17 phosphorylation in a dose- and time-dependent fashion. Ryanodine (1.0 microM) reduced both the isoproterenol (0.1 microM) and S(-)-Bay K8644-(1 microM) mediated Thr17 phosphorylation by about 90%. Thapsigargin (1 microM) diminished the S(-)-Bay K8644 and isoproterenol-associated Thr17 phosphorylation by 53.5+/-6.3% and 92. 5+/-11.1%, respectively. Ser16 phosphorylation was not affected under these conditions. KN-93 reduced the Thr17 phosphorylation by S(-)-Bay K8644 and isoproterenol to levels of 1.1+/-0.3% and 8.6+/-2. 1%, respectively. However, the effect of KN-93 was attenuated (47. 8+/-3.6%) in isoproterenol prestimulated cells. Protein phosphatase inhibition by okadaic acid increased exclusively the Ser16 phosphorylation. In summary, our results reflect a cross-talk between beta -adrenoceptor stimulation and intracellular Ca(2+)at the level of CaMKII-mediated phospholamban phosphorylation in neonatal rat cardiomyocytes. We report conditions which exclusively produce Thr17 or Ser16 phosphorylation. We postulate that Ca(2+)transport systems of the sarcoplasmic reticulum are critical determinants for the activation of CaMKII that catalyzes phosphorylation of phospholamban.

Ischemic preconditioning prevents I/R-induced alterations in SR calcium-calmodulin protein kinase II

Although Ca(2+)/calmodulin-dependent protein kinase II (CaMK II) is known to modulate the function of cardiac sarcoplasmic reticulum (SR) under physiological conditions, the status of SR CaMK II in ischemic preconditioning (IP) of the heart is not known. IP was induced by subjecting the isolated perfused rat hearts to three cycles of brief ischemia-reperfusion (I/R; 5 min ischemia and 5 min reperfusion), whereas the control hearts were perfused for 30 min with oxygenated medium. Sustained I/R in control and IP groups was induced by 30 min of global ischemia followed by 30 min of reperfusion. The left ventricular developed pressure, rate of the left ventricular pressure, as well as SR Ca(2+)-uptake activity and SR Ca(2+)-pump ATPase activity were depressed in the control I/R hearts; these changes were prevented upon subjecting the hearts to IP. The beneficial effects of IP on the I/R-induced changes in contractile activity and SR Ca(2+) pump were lost upon treating the hearts with KN-93, a specific CaMK II inhibitor. IP also prevented the I/R-induced depression in Ca(2+)/calmodulin-dependent SR Ca(2+)-uptake activity and the I/R-induced decrease in the SR CaMK II activity; these effects of IP were blocked by KN-93. The results indicate that IP may prevent the I/R-induced alterations in SR Ca(2+) handling abilities by preserving the SR CaMK II activity, and it is suggested that CaMK II may play a role in mediating the beneficial effects of IP on heart function.

Sarcoplasmic reticulum Ca(2+)/Calmodulin-dependent protein kinase is altered in heart failure

Although Ca(2+)/calmodulin-dependent protein kinase-II (CaMK) is known to phosphorylate different Ca(2+) cycling proteins in the cardiac sarcoplasmic reticulum (SR) and regulate its function, the status of CaMK in heart failure has not been investigated previously. In this study, we examined the hypothesis that changes in the CaMK-mediated phosphorylation of the SR Ca(2+) cycling proteins are associated with heart failure. For this purpose, heart failure in rats was induced by occluding the coronary artery for 8 weeks, and animals with >30% infarct of the left ventricle wall plus septum mass were used. Noninfarcted left ventricle was used for biochemical assessment; sham-operated animals served as control. A significant depression in SR Ca(2+) uptake and release activities was associated with a decrease in SR CaMK phosphorylation of the SR proteins, ryanodine receptor (RyR), Ca(2+) pump ATPase (SR/endoplasmic reticulum Ca(2+) ATPase [SERCA2a]), and phospholamban (PLB) in the failing heart. The SR protein contents for RyR, SERCA2a, and PLB were decreased in the failing hearts. Although the SR Ca(2+)/calmodulin-dependent CaMK activity, CaMK content, and CaMK autophosphorylation were depressed, the SR phosphatase activity was enhanced in the failing heart. On the other hand, the cAMP-dependent protein kinase-mediated phosphorylation of RyR and PLB was not affected in the failing heart. On the basis of these results, we conclude that alterations in SR CaMK-mediated phosphorylation may be partly responsible for impaired SR function in heart failure.

Regulation of the transient outward K(+) current by Ca(2+)/calmodulin-dependent protein kinases II in human atrial myocytes

Ca(2+)/calmodulin-dependent protein kinases II (CaMKII) have important functions in regulating cardiac excitability and contractility. In the present study, we examined whether CaMKII regulated the transient outward K(+) current (I(to)) in whole-cell patch-clamped human atrial myocytes. We found that a specific CaMKII inhibitor, KN-93 (20 micromol/L), but not its inactive analog, KN-92, accelerated the inactivation of I(to) (tau(fast): 66.9+/-4.4 versus 43.0+/-4.4 ms, n=35; P<0.0001) and inhibited its maintained component (at +60 mV, 4.9+/-0.4 versus 2.8+/-0.4 pA/pF, n = 35; P<0. 0001), leading to an increase in the extent of its inactivation. Similar effects were observed by dialyzing cells with a peptide corresponding to CaMKII residues 281 to 309 or with autocamtide-2-related inhibitory peptide and by external application of the calmodulin inhibitor calmidazolium, which also suppressed the effects of KN-93. Furthermore, the phosphatase inhibitor okadaic acid (500 nmol/L) slowed I(to) inactivation, increased I(sus), and inhibited the effects of KN-93. Changes in [Ca(2+)](i) by dialyzing cells with approximately 30 nmol/L Ca(2+) or by using the fast Ca(2+) buffer BAPTA had opposite effects on I(to). In BAPTA-loaded myocytes, I(to) was less sensitive to KN-93. In myocytes from patients in chronic atrial fibrillation, characterized by a prominent I(sus), KN-93 still increased the extent of inactivation of I(to). Western blot analysis of atrial samples showed that delta-CaMKII expression was enhanced during chronic atrial fibrillation. In conclusion, CaMKII control the extent of inactivation of I(to) in human atrial myocytes, a process that could contribute to I(to) alterations observed during chronic atrial fibrillation.

Downregulation of delta CaM kinase II in human tumor cells

Over two dozen alternative splice variants of CaMK-II, the type II Ca(2+)/CaM-dependent protein kinase, are encoded from four genes (alpha, beta, gamma and delta) in mammalian cells. Isozymes of alpha and beta CaMK-II are well characterized in brain; however, an understanding of the relative endogenous levels of CaMK-II isozymes in a wide variety of non-neuronal cells has not yet been described. In this study, we have demonstrated that CaMK-II consists primarily of the 54 kDa delta CaMK-II (delta(2) or delta(C)) isozyme in rodent fibroblasts. beta and gamma CaMK-II isozymes are minor and alpha CaMK-II was not expressed. The primary delta CaMK-II in human fibroblasts and the MCF10A mammary epithelial cell line was the 52 kDa delta(4) CaMK-II, an isozyme identical to delta(2) except for a missing 21-amino-acid C-terminal tail. delta CaMK-II levels were diminished in both human and rodent fibroblasts after SV40 transformation and in the mammary adenocarcinoma MCF7 cell line when compared to MCF10A cells. In fact, most tumor cells exhibited CaMK-II specific activities which were two- to tenfold lower than in untransformed fibroblasts. We conducted complementary CaMK-II studies on the NGF-induced differentiation of rat PC-12 cells. Although no new synthesis of CaMK-II occurs, neurite outgrowth in these cells is accompanied by a preferential activation of delta CaMK-II. Endogenous delta CaMK-II has a perinuclear distribution in fibroblasts and extends along neurites in PC-12 cells. These findings point to a role for delta CaMK-II isozymes in cellular differentiation.

Calcium/calmodulin-dependent protein kinase II activity is increased in sarcoplasmic reticulum from coronary artery ligated rabbit hearts

A protein kinase activity intrinsic to the sarcoplasmic reticulum was studied in normal and hypertrophied rabbit hearts. The relationship between this kinase activity and phospholamban phosphorylation was examined. Calmodulin-dependent kinase II activity was found to be increased in sarcoplasmic reticulum preparations from hypertrophied hearts compared with normal. This was evident by measuring the phosphotransferase activity of the kinase and also by examining phospholamban phosphorylation by electrophoretic band shift analysis. Increased phospholamban phosphorylation by Calmodulin-dependent protein kinase II was dependent on prior phosphorylation by cAMP-dependent protein kinase, indicating potential crosstalk. Specific immunoblot analysis of the rabbit sarcoplasmic reticulum identified the presence of the delta form of calmodulin dependent protein kinase II and showed it to be up-regulated in hypertrophied hearts.

Status of Ca2+/calmodulin protein kinase phosphorylation of cardiac SR proteins in ischemia-reperfusion

Although the sarcoplasmic reticulum (SR) is known to regulate the intracellular concentration of Ca2+ and the SR function has been shown to become abnormal during ischemia-reperfusion in the heart, the mechanisms for this defect are not fully understood. Because phosphorylation of SR proteins plays a crucial role in the regulation of SR function, we investigated the status of endogenous Ca2+/calmodulin-dependent protein kinase (CaMK) and exogenous cAMP-dependent protein kinase (PKA) phosphorylation of the SR proteins in control, ischemic (I), and ischemia-reperfused (I/R) hearts treated or not treated with superoxide dismutase (SOD) plus catalase (CAT). SR and cytosolic fractions were isolated from control, I, and I/R hearts treated or not treated with SOD plus CAT, and the SR protein phosphorylation by CaMK and PKA, the CaMK- and PKA-stimulated Ca2+ uptake, and the CaMK, PKA, and phosphatase activities were studied. The SR CaMK and CaMK-stimulated Ca2+ uptake activities, as well as CaMK phosphorylation of Ca2+ pump ATPase (SERCA2a) and phospholamban (PLB), were significantly decreased in both I and I/R hearts. The PKA phosphorylation of PLB and PKA-stimulated Ca2+ uptake were reduced significantly in the I/R hearts only. Cytosolic CaMK and PKA activities were unaltered, whereas SR phosphatase activity in the I and I/R hearts was depressed. SOD plus CAT treatment prevented the observed alterations in SR CaMK and phosphatase activities, CaMK and PKA phosphorylations, and CaMK- and PKA-stimulated Ca2+ uptake. These results indicate that depressed CaMK phosphorylation and CaMK-stimulated Ca2+ uptake in I/R hearts may be due to a depression in the SR CaMK activity. Furthermore, prevention of the I/R-induced alterations in SR protein phosphorylation by SOD plus CAT treatment is consistent with the role of oxidative stress during ischemia-reperfusion injury in the heart.

Ser16 prevails over Thr17 phospholamban phosphorylation in the beta-adrenergic regulation of cardiac relaxation

Phospholamban is a critical regulator of sarcoplasmic reticulum Ca2+-ATPase and myocardial contractility. To determine the extent of cross signaling between Ca2+ and cAMP pathways, we have investigated the beta-adrenergic-induced phosphorylation of Ser16 and Thr17 of phospholamban in perfused rat hearts using antibodies recognizing phospholamban phosphorylated at either position. Isoproterenol caused the dose-dependent phosphorylation of Ser16 and Thr17 with strikingly different half-maximal values (EC50 = 4.5 +/- 1.6 and 28. 2 +/- 1.4 nmol/l, respectively). The phosphorylation of Ser16 induced by isoproterenol, forskolin, or 3-isobutyl-1-methylxanthine correlated to increased cardiac relaxation (r = 0.96), whereas phosphorylation of Thr17 did not. Elevation of extracellular Ca2+ did not induce phosphorylation at Thr17; only in the presence of a submaximal dose of isoproterenol, phosphorylation at Thr17 increased eightfold without additional effects on relaxation rate. Thr17 phosphorylation was partially affected by ryanodine and was completely abolished in the presence of 1 micromol/l verapamil or nifedipine. The data indicate that 1) phosphorylation of phospholamban at Ser16 by cAMP-dependent protein kinase is the main regulator of beta-adrenergic-induced cardiac relaxation definitely preceding Thr17 phosphorylation and 2) the beta-adrenergic-mediated phosphorylation of Thr17 by Ca2+-calmodulin-dependent protein kinase required influx of Ca2+ through the L-type Ca2+ channel.

Identification and expression of delta-isoforms of the multifunctional Ca2+/calmodulin-dependent protein kinase in failing and nonfailing human myocardium

Despite its importance for the regulation of heart function, little is known about the isoform expression of the multifunctional Ca2+/calmodulin-dependent protein kinase (CaMKII) in human myocardium. In this study, we investigated the spectrum of CaMKII isoforms delta2, delta3, delta4, delta8, and delta9 in human striated muscle tissue. Isoform delta3 is characteristically expressed in cardiac muscle. In skeletal muscle, specific expression of a new isoform termed delta11 is demonstrated. Complete sequencing of human delta2 cDNA, representing all common features of the investigated CaMKII subclass, revealed its high homology to the corresponding rat cDNA. Comparative semiquantitative reverse transcription-polymerase chain reaction analyses from left ventricular tissues of normal hearts and from patients suffering from dilated cardiomyopathy showed a significant increase in transcript levels of isoform delta3 relative to the expression of glyceraldehyde-3-phosphate dehydrogenase in diseased hearts (101. 6+/-11.0% versus 64.9+/-9.9% in the nonfailing group; P<0.05, n=6). Transcript levels of the other investigated cardiac CaMKII isoforms remained unchanged. At the protein level, by using a subclass-specific antibody, we observed a similar increase of a delta-CaMKII-specific signal (7.2+/-1.0 versus 3.8+/-0.7 optical density units in the nonfailing group; P<0.05, n=4 through 6). The diseased state of the failing hearts was confirmed by a significant increase in transcript levels for atrial natriuretic peptide (292. 9+/-76.4% versus 40.1+/-3.2% in the nonfailing group; P<0.05, n=3 through 6). Our data characterize for the first time the delta-CaMKII isoform expression pattern in human hearts and demonstrate changes in this expression pattern in heart failure.

Immunohistochemical localization of Ca2+/Calmodulin-dependent protein kinase IV in outer hair cells

A smooth membrane system consisting of subsurface cisternae (SSC) underlies the lateral plasmalemma of auditory outer hair cells (OHCs). The SSC contain Ca-ATPase and are regarded as an intracellular Ca2+ reservoir like the sarcoplasmic reticulum of myocytes. Recently, it has been demonstrated that Ca-ATPase activity in sarcoplasmic reticulum is regulated by Ca2+/calmodulin-dependent protein kinases (CaM kinases). Here we investigated the presence of CaM kinases in OHCs and their possible association with the SSC. Inner ears collected from adult gerbils and from neonates at 2-day intervals between 0 and 20 days after birth were immunostained with antibodies specific for different CaM kinases. A polyclonal antiserum against CaM kinase IV yielded a strong immunostaining reaction along the lateral wall of OHCs. The staining appeared after the tenth postnatal day and continued into adulthood. No other site in the inner ear, including cochlear inner hair cells and vestibular hair cells, was reactive. The kinase's apparent association with the SSC strongly supports its involvement in intracellular Ca2+ homeostasis and suggests a role in regulating the OHCs' slow motile responses.

Effects of aging on sarcoplasmic reticulum Ca2+-cycling proteins and their phosphorylation in rat myocardium

Diminished Ca2+-sequestering activity of the sarcoplasmic reticulum (SR) is implicated in the age-associated slowing of cardiac muscle relaxation. In attempting to further define the underlying mechanisms, the present study investigated the impact of aging on the contents of major SR Ca2+-cycling proteins and SR protein phosphorylation by endogenous Ca2+/calmodulin-dependent protein kinase (CaM kinase). The studies were performed using homogenates and SR vesicles derived from the ventricular myocardium of adult (6-8 mo old) and aged (26-28 mo old) Fischer 344 rats. Western immunoblotting analysis showed no significant age-related difference in the relative amounts of ryanodine receptor-Ca2+-release channel (RyR-CRC), the Ca2+-storage protein calsequestrin, Ca2+-pumping ATPase (Ca2+-ATPase), and Ca2+-ATPase-regulatory protein phospholamban (PLB) in SR or homogenate. On the other hand, the relative amount of immunoreactive CaM kinase II (delta-isoform) was approximately 50% lower in the aged heart. CaM kinase-mediated phosphorylation of RyR-CRC, Ca2+-ATPase, and PLB was reduced significantly ( approximately 25-40%) in the aged compared with adult rat. ATP-dependent Ca2+-uptake activity of SR and the stimulatory effect of calmodulin on Ca2+ uptake were also reduced significantly with aging. Treatment of SR vesicles with anti-PLB antibody (PLBab) invoked relatively less stimulation of Ca2+ uptake in the aged (</=26%) compared with the adult (</=65%) rat. Ca2+-ATPase but not PLB underwent phosphorylation by CaM kinase in PLBab-treated SR with resultant stimulation of Ca2+ uptake. The rates of Ca2+ uptake by PLBab-treated SR were significantly lower (45-55%) in the aged compared with adult rat in the absence and presence of calmodulin. These findings imply that changes in the intrinsic functional properties of SR Ca2+-cycling proteins and/or their phosphorylation-dependent regulation contribute to impaired SR function in the aging heart.

Modification of ischemia-reperfusion-induced changes in cardiac sarcoplasmic reticulum by preconditioning

To examine the effects of ischemic preconditioning on ischemia-reperfusion-induced changes in the sarcoplasmic reticulum (SR) function, isolated rat hearts were either perfused with a control medium for 30 min or preconditioned with three episodes of 5-min ischemia and 5-min reperfusion before sustained ischemia for 30 min followed by reperfusion for 30 min was induced. Preconditioning itself depressed cardiac function (left ventricular developed pressure, peak rate of contraction, and peak rate of relaxation) and SR Ca2+-release and -uptake activities as well as protein content and Ca2+/calmodulin-dependent protein kinase (CaMK) phosphorylation of Ca2+-release channels by 25-60%. Global ischemia for 30 min produced marked depressions in SR Ca2+-release and -uptake activities as well as SR Ca2+-pump protein content in control hearts; these changes were significantly attenuated by preconditioning. Compared with the control preparations, preconditioning improved the recovery of cardiac function and SR Ca2+-release and -uptake activities as well as Ca2+-release channel and Ca2+-pump protein contents in the ischemic-reperfused hearts. Unlike the protein kinase A-mediated phosphorylation in SR membranes, the CaMK-mediated phosphorylations at Ca2+-release channels, Ca2+ pump, and phospholamban were depressed in the ischemic hearts; these changes were prevented by preconditioning. These results indicate that ischemic preconditioning may exert beneficial effects on ischemia-reperfusion-induced alterations in SR function by preventing changes in Ca2+-release channel and Ca2+-pump protein contents in the SR membrane.

CaMK-II inhibition reduces cyclin D1 levels and enhances the association of p27kip1 with Cdk2 to cause G1 arrest in NIH 3T3 cells

The calmodulin-dependent protein kinase-II (CaMK-II) inhibitor KN-93 has been shown to reversibly arrest mouse and human cells in the G1 phase of the cell cycle [Tombes, R. M., Westin, E., Grant. S., and Krystal, G. (1995) Cell Growth Differ. 6, 1073-1070; Rasmussen, G., and Rasmussen, C. (1995) Biochem. Cell Biol. 71, 201-207]. The stimulation of Ca(2+)-independent (autonomous) CaMK-II enzymatic activity, a barometer of in situ activated CaMK-II, was prevented by the same KN-93 concentrations that cause G1 phase arrest. KN-93 caused the retinoblastoma protein pRB to become dephosphorylated and the activity of both cdk2 and cdk4, two potential pRb kinases, to decrease. Neither the activity of p42MAP kinase, an early response G1 signaling molecule, nor the phosphorylation status or DNA-binding capability of the transcription factors serum response factor and cAMP responsive element-binding protein was altered during this G1 arrest. The protein levels of cyclin-dependent kinase 2 (cdk2) and cdk4 were unaffected during this G1 arrest and the total cellular levels of the cdk inhibitors p21cip1 and p27kip1 were not increased. Instead, the cdk4 activity decreases resulting from KN-93 were the result of a 75% decrease in cyclin D1 levels. In contrast, cyclin A and E levels were relatively constant. Cdk2 activity decreases were primarily the result of enhanced p27kip1 association with cdk2/cyclin E. All of these phenomena were unaffected by KN-93's inactive analog, KN-92, and were reversible upon KN-93 washout. The kinetics of recovery from cell cycle arrest were similar to those reported for other G1 phase blockers. These results suggest a mechanism by which G1 Ca2+ signals could be linked via calmodulin-dependent phosphorylations to the cell cycle-controlling machinery through cyclins and cdk inhibitors.

The endogenous cardiac sarcoplasmic reticulum Ca2+/calmodulin-dependent kinase is activated in response to beta-adrenergic stimulation and becomes Ca2+-independent in intact beating hearts

We investigated the effects of beta-adrenergic stimulation on the activity of the endogenous cardiac sarcoplasmic reticulum Ca2+/calmodulin-dependent protein kinase (SRCaM kinase) in Langendorff-perfused rat hearts. We found that isoproterenol induced generation of autonomous (Ca2+-independent) SRCaM kinase activity to 28 +/- 4.4% of the total activity. Moreover, dephosphorylation of the autonomous SRCaM kinase with protein phosphatase 2A resulted in an enzyme that was again dependent on Ca2+ and calmodulin for its activity. Activation of SRCaM kinase was coupled to phospholamban phosphorylation and activation of the cAMP-signaling system. Our results suggest that the cardiac SRCaM kinase is activated in response to beta-adrenoceptor stimulation. This activation stimulates autophosphorylation at its regulatory domain and converts it to an active Ca2+-independent species that may be the basis for potentiation of Ca2+ transients in the heart.

Effects of zinc on phospholamban phosphorylation

The effects of zinc on the phosphorylation of phospholamban (PLB) were studied in sarcoplasmic reticulum (SR) membranes prepared from swine ventricular muscle. Zinc produced a dose dependent inhibition of PLB phosphorylation. With the use of phosphorylation site specific antibodies, it was shown that this inhibition was specific for the PLB phosphorylation at Thr-17. Since phosphorylation of this site is known to be mediated by the Ca2+/calmodulin-dependent protein kinase endogenous to the cardiac SR (SRCaM kinase), the action of zinc on SRCaM kinase was investigated. It was found that (i) zinc inhibited the activity of SRCaM kinase (IC50: 15 microM) and (ii) zinc concentrations, at the millimolar range, stimulated Ca(2+)-independent SRCaM kinase autophosphorylation. This ability of zinc to differentiate between autophosphorylation and substrate phosphorylation activities of SRCaM kinase raises the possibility that zinc mediated independent regulation of these processes can occur in the intact heart.

Site-specific phosphorylation of a phospholamban peptide by cyclic nucleotide- and Ca2+/calmodulin-dependent protein kinases of cardiac sarcoplasmic reticulum

Phospholamban (PLB), the regulator of the cardiac sarcoplasmic reticulum (SR) Ca2+ pump is specifically phosphorylated at Ser16 and Thr17 by cAMP-dependent protein kinase (PKA) and Ca2+/calmodulin-dependent protein kinase (CaMK), respectively. The regulation of this dual-site phosphorylation of amino acid residues in direct proximity is only poorly understood. In order to study the site-specific phosphorylation of PLB, we used a synthetic peptide (PLB-24) corresponding to the cytosolic part of the PLB monomer with the phosphorylation sites as a model substrate. PLB-24 possesses substrate properties as the native PLB as demonstrated by phosphorylation with exogenous, purified PKA, cGMP-dependent protein kinase (PKG) and a type II CaMK (CaMKII). In isolated vesicles of cardiac SR there was a rapid phosphorylation of the peptide by the endogenous PKA (SR-PKA) and CaMK (SR-CaMK), but not under conditions that activate PKG. Both SR-PKA and SR-CaMK incorporated the same amount of 32P into PLB-24, 0.60 +/- 0.01 nmol 32P/mg SR protein and 0.61 +/- 0.03 nmol 32P/mg SR protein, respectively. Phosphorylation by SR-PKA was abolished by the specific PKA inhibitor (IC50 = 0.2 microM), whereas SR-CaMK phosphorylation was inhibited by calmidazolium (IC50 = 1.6 microM) and a CaMKII-specific inhibitor peptide (IC50 = 2.5 microM). Phosphorylation by SR-PKA was exclusively at Ser, whereas SR-CaMK phosphorylated only Thr. After simultaneous activation of both SR-kinases 32P incorporation into PLB-24 was additive and occurred at Ser as well as at Thr. Sequential activation of SR-PKA and SR-CaMK also caused the additive phosphorylation of PLB-24 independently of which kinase was activated first. Thus, at the monomeric level of PLB the respective phosphorylation site appears to be accessible to its related SR protein kinase in vitro even when the adjacent site is phosphorylated.