Protein kinase CK2 links extracellular growth factor signaling with the control of p27(Kip1) stability in the heart

Macrophage migration inhibitory factor antagonizes pressure overload-induced cardiac hypertrophy

Macrophage migration inhibitory factor (MIF) functions as a proinflammatory cytokine when secreted from the cell, but it also exhibits antioxidant properties by virtue of its intrinsic oxidoreductase activity. Since increased production of ROS is implicated in the development of left ventricular hypertrophy, we hypothesized that the redox activity of MIF protects the myocardium when exposed to hemodynamic stress. In a mouse model of myocardial hypertrophy induced by transverse aortic coarctation (TAC) for 10 days, we showed that growth of the MIF-deficient heart was significantly greater by 32% compared with wild-type (WT) TAC hearts and that fibrosis was increased by fourfold (2.62 ± 0.2% vs. 0.6 ± 0.1%). Circulating MIF was increased in TAC animals, and expression of MIF receptor, CD74, was increased in the hypertrophic myocardium. Gene expression analysis showed a 10-fold increase (P < 0.01) in ROS-generating mitochondrial NADPH oxidase and 2- to 3-fold reductions (P < 0.01) in mitochondrial SOD2 and mitochondrial aconitase activities, indicating enhanced oxidative injury in the hypertrophied MIF-deficient ventricle. Hypertrophic signaling pathways showed that phosphorylation of cytosolic glycogen synthase kinase-3α was greater (P < 0.05) at baseline in MIF-deficient hearts than in WT hearts and remained elevated after 10-day TAC. In the hemodynamically stressed MIF-deficient heart, nuclear p21(CIP1) increased sevenfold (P < 0.01), and the cytosolic increase of phospho-p21(CIP1) was significantly greater than in WT TAC hearts. We conclude that MIF antagonizes myocardial hypertrophy and fibrosis in response to hemodynamic stress by maintaining a redox homeostatic phenotype and attenuating stress-induced activation of hypertrophic signaling pathways.

MiR-221 promotes cardiac hypertrophy in vitro through the modulation of p27 expression

Cardiac hypertrophy has been known as an independent predictor for cardiovascular morbidity and mortality. Molecular mechanisms underlying the development of heart failure remain elusive. Recently, microRNAs (miRs) have been established as important regulators in cardiac hypertrophy. Here, we reported miR-221 was up-regulated in both transverse aortic constricted mice and patients with hypertrophic cardiomyopathy (HCM). Forced expression of miR-221 by transfection of miR-221 mimics increased myocyte cell size and induced the re-expression of fetal genes, which were inhibited by the knockdown of endogenous miR-221 in cardiomyocytes. The TargetScan algorithm-based prediction identified that p27, a cardiac hypertrophic suppressor, is the putative target of miR-221, which was confirmed by luciferase assay and Western blotting. In conclusion, our results demonstrated that miR-221 regulated cardiomyocyte hypertrophy probably through down-regulation of p27, suggesting that miR-221 may be a new intervention target for cardiac hypertrophy.

Anti-apoptotic function of the E2F transcription factor 4 (E2F4)/p130, a member of retinoblastoma gene family in cardiac myocytes

The E2F4-p130 transcriptional repressor complex is a cell-cycle inhibitor in mitotic cells. However, the role of E2F4/p130 in differentiated cells is largely unknown. We investigated the role of E2F4/p130 in the regulation of apoptosis in postmitotic cardiomyocytes. Here we demonstrate that E2F4 can inhibit hypoxia-induced cell death in isolated ventricular cardiomyocytes. As analyzed by chromatin immunoprecipitation, the E2F4-p130-repressor directly blocks transcription of essential apoptosis-related genes, E2F1, Apaf-1, and p73α through recruitment of histone deacetylase 1 (HDAC1). In contrast, diminution of the E2F4-p130-HDAC1-repressor and recruitment of E2F1 and histone acetylase activity to these E2F-regulated promoters is required for the execution of cell death. Expression of kinase-dead HDAC1.H141A or HDAC-binding deficient p130ΔHDAC1 abolishes the antiapoptotic effect of E2F4. Moreover, histological examination of E2F4(-/-) hearts revealed a markedly enhanced degree of cardiomyocyte apoptosis. Taken together, our genetic and biochemical data delineate an essential negative function of E2F4 in cardiac myocyte apoptosis.

Post-myocardial infarct p27 fusion protein intravenous delivery averts adverse remodelling and improves heart function and survival in rodents

AIMS

P27Kip1 (p27) blocks cell proliferation through the inhibition of cyclin-dependent kinase 2 (cdk-2). Despite robust expression in the heart, little is known about the regulation and function of p27 in this terminally differentiated tissue. Previously, we demonstrated that p27 exerts anti-apoptotic and growth-inhibitory effects through interaction with casein kinase 2 (ck2) in neonatal rat cardiomyocytes. Here, we test the hypothesis that delivery of a transactivator of transcription (TAT)-p27 fusion protein (TAT.p27) will improve cardiac function and survival in a rat model of myocardial infarction (MI).

METHODS AND RESULTS

Fisher rats underwent permanent left anterior descending ligation-induced MI followed by iv injection of TAT.p27 or TAT.LacZ (20 mg/kg) on Days 1 and 7 post-MI. Delivery of TAT.p27 was evaluated by western blot (WB) and immunofluorescence microscopy. Heart function was assessed by echocardiography and pressure-volume catheter. Apoptosis, hypertrophy, and fibrosis were detected by histochemistry and morphometry. WB confirmed gradual reduction in endogenous cardiac p27 levels following MI, with immunohistochemistry demonstrating successful delivery of TAT.p27 to the heart. At 48 h post-MI, cardiac apoptosis was decreased in rats treated with TAT.p27 when compared with saline- and TAT.LacZ-treated controls. At 28 days post-MI, rats treated with TAT.p27 manifested less cardiomyocyte hypertrophy and fibrosis, less diminished cardiac function, and greater survival. Additionally, p27KO mice undergoing experimental MI suffered an early increase in apoptosis with a larger infarct size and markedly reduced survival when compared with wild-type (WT) controls.

CONCLUSION

These gain- and loss-of-function studies reveal a critical role for p27 in cardiac remodelling post-MI.

p27(Kip1) controls cytokinesis via the regulation of citron kinase activation

p27(Kip1) (p27) acts as a tumor suppressor by inhibiting cyclin-cyclin-dependent kinase (cyclin-CDK) activity. However, mice expressing a form of p27 that is unable to bind or inhibit cyclin-CDK complexes (p27(CK-)) have increased incidence of tumor development as compared with wild-type and p27(-/-) mice, revealing an oncogenic role for p27. Here, we identified a phenotype of multinucleation and polyploidy in p27(CK-) mice not present in p27(-/-) animals, suggesting a role for p27 in G2/M that is independent of cyclin-CDK regulation. Further analysis revealed that p27(CK-) expression caused a cytokinesis and abscission defect in mouse embryonic fibroblasts. We identified the Rho effector citron kinase (citron-K) as a p27-interacting protein in vitro and in vivo and found that p27 and citron-K colocalized at the contractile ring and mid-body during telophase and cytokinesis. Moreover, overexpression of the minimal p27-binding domain of citron-K was sufficient to rescue the phenotype caused by p27(CK-). Conversely, expression of a mutant p27(CK-) unable to bind citron-K did not induce multinucleation. Finally, by binding to citron-K, p27 prevented the interaction of citron-K with its activator RhoA. Taken together, these data suggest a role for p27 during cytokinesis via the regulation of citron-K activity.

SUMO2/3 conjugation is an endogenous neuroprotective mechanism

Small ubiquitin-like modifier (SUMO)2/3 but not SUMO1 conjugation is activated after transient cerebral ischemia. To investigate its function, we blocked neuronal SUMO2/3 translation through lentiviral microRNA delivery in primary cortical neurons. Viability was unaffected by SUMO2/3 silencing unless neurons were stressed by transient oxygen-glucose deprivation (OGD). Both 15 and 45 minutes of OGD were tolerated by control microRNA-expressing neurons but damaged >60% of neurons expressing SUMO2/3 microRNA. Damaging OGD (75 minutes) increased neuronal loss to 54% (control microRNA) and to 99% (SUMO2/3 microRNA). This suggests that activation of SUMO2/3 conjugation is an endogenous neuroprotective stress response.

Up-regulation of p27(kip1) contributes to Nrf2-mediated protection against angiotensin II-induced cardiac hypertrophy

AIMS

Nuclear factor erythroid-2-related factor 2 (Nrf2) appears to be a negative regulator of maladaptive cardiac remodelling and dysfunction; however, a potential of the Nrf2-mediated cardiac protection in diverse pathological settings remains to be determined. This study was aimed to explore the role of Nrf2 in angiotensin II (Ang II)-induced cardiac hypertrophy.

METHODS AND RESULTS

Littermate wild-type (WT) and Nrf2 knockout (Nrf2(-/-)) mice were administered Ang II via osmotic mini-pumps for 2 weeks to induce cardiac hypertrophy. Elevation of blood pressure by the continuous Ang II infusion was comparable between WT and Nrf2(-/-) mice. Relative to WT mice, however, Nrf2(-/-) mice exhibited exaggerated myocardial oxidative stress with an impaired induction of a group of antioxidant genes and increased cardiac hypertrophy in response to the sustained Ang II stimulation. In cultured cardiomyocytes, adenoviral overexpression of Nrf2 shRNA enhanced Ang II-induced reactive oxygen species (ROS) production and protein synthesis, whereas adenoviral overexpression of Nrf2 exerted opposite effects. Moreover, Nrf2 deficiency exacerbated Ang II-induced down-regulation of p27(kip1) expression in the heart via a mechanism of post-transcriptional regulation. In contrast, adenoviral overexpression of Nrf2 increased p27(kip1) protein but not mRNA expression and reversed Ang II-induced down-regulation of p27(kip1) protein expression in cultured cardiomyocytes by suppressing ROS formation. Finally, the enhancement of Ang II-induced hypertrophic growth due to the Nrf2 deficiency was negated by overexpressing p27(kip1) in cultured cardiomyocytes.

CONCLUSION

The Nrf2-p27(kip1) pathway serves as a novel negative feedback mechanism in Ang II-induced pathogenesis of cardiac hypertrophy, independent of changes in blood pressure.

The impact of PTEN regulation by CK2 on PI3K-dependent signaling and leukemia cell survival

Gene alterations affecting elements of PI3K signaling pathway do not appear to be sufficient to explain the extremely high frequency of PI3K signaling hyperactivation in leukemia. It has been known for long that PTEN phosphorylation at the C-terminal tail, in particular by CK2, contributes to the stabilization and simultaneous inhibition of this critical tumor suppressor. However, direct evidence of the involvement of this mechanism in cancer has been gathered only recently. It is now known that CK2-mediated posttranslational, non-deleting, inactivation of PTEN occurs in T-ALL, CLL and probably other leukemias and solid tumors. To explore this knowledge for therapeutic purposes remains one of the challenges ahead.

How druggable is protein kinase CK2?

CK2 is a pleiotropic, ubiquitous, and constitutively active protein kinase (PK), with both cytosolic and nuclear localization in most mammalian cells. The holoenzyme is generally composed of two catalytic (alpha and/or alpha') and two regulatory (beta) subunits, but the free alpha/alpha' subunits are catalytically active by themselves and can be present in cells under some circumstances. CK2 catalyzes the phosphorylation of more than 300 substrates characterized by multiple acidic residues surrounding the phosphor-acceptor amino acid, and, consequently, it plays a key role in several physiological and pathological processes. But how can one kinase orchestrate all these tasks faithfully? How is it possible that one kinase can, despite all pleiotropic characteristics of PKs in general, be involved in so many different biochemical events? Is CK2 a druggable target? Several questions are still to be clearly answered, and this review is an occasion for a fruitful discussion.

c-FLIPL enhances anti-apoptotic Akt functions by modulation of Gsk3β activity

Akt is a serine-threonine kinase that has an important role in transducing survival signals. Akt also regulates a number of proteins involved in the apoptotic process. To find new Akt interactors, we performed a two-hybrid screening in yeast using full-length Akt cDNA as bait and a human cDNA heart library as prey. Among 200 clones obtained, two of them were identified as coding for the c-FLIP(L) protein. c-FLIP(L) is an endogenous inhibitor of death receptor-induced apoptosis through the caspase-8 pathway. Using co-immunoprecipitation experiments of either transfected or endogenous proteins, we confirmed the interaction between Akt and c-FLIP(L). Furthermore, we observed that c-FLIP(L) overexpression interferes with Gsk3-β phosphorylation levels. Moreover, through its effects on Gsk3β, c-FLIP(L) overexpression in cancer cells induced resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). This effect was mediated by the regulation of p27(Kip1) and caspase-3 expression. These results indicate the existence of a new mechanism of resistance to TRAIL in cancer cells, and unexpected functions of c-FLIP(L).

Novel markers of left ventricular hypertrophy in uremia

AIMS

Left ventricular hypertrophy (LVH) is the most frequent cardiac complication in chronic renal disease. Previous studies implicate elevated serum phosphorus as a risk factor for LVH.

METHODS

We treated 5/6 nephrectomized rats with enalapril or enalapril + sevelamer carbonate for 4 months to determine if sevelamer carbonate had an additional beneficial effect on the development of LVH and uremia-induced left ventricle (LV) remodeling.

RESULTS

Uremia increased LV weight and cardiomyocyte size. Enalapril and enalapril + sevelamer blunted the increase in left ventricular weight. Only enalapril + sevelamer diminished the increase in cardiomyocyte size. Uremia increased cyclin D2 and PCNA and decreased p27 protein expression in the heart. Enalapril + sevelamer diminished the decrease in p27 expression caused by uremia. Uremia increased Ki67-positive and phosphohistone H(3)-positive interstitial cells. This was not seen in cardiomyocytes. Multivariable regression analysis showed that increased phosphorus was an independent risk factor for both increased LV weight and cardiomyocyte size.

CONCLUSIONS

These data suggest left ventricular remodeling consists of cardiomyocyte hypertrophy and interstitial cell proliferation, but not cardiomyocyte proliferation. p27 and cyclin D2 may play important roles in the development of LVH. In addition, phosphorus can be an independent risk factor for the development of LVH.

SUMO--a post-translational modification with therapeutic potential?

Sumoylation is a covalent modification, which is mediated by small ubiquitin-like modifier (SUMO) polypeptides. A growing body of evidence has shown that sumoylation affects the functional properties of many substrates in the regulation of cellular processes. Recent reports indicate the crucial role of sumoylation in human diseases including familial dilated cardiomyopathy, suggesting that targeting of sumoylation would be of considerable interest for novel therapies. Even though hundreds of SUMO substrates have been identified, their pathophysiological roles remain to be determined. Among them, ERK5-sumoylation has recently been linked to diabetes and implicated in endothelial dysfunction and cardiomyocyte apoptosis in vivo. These findings support the idea that ERK5-sumoylation is a novel therapeutic target for the treatment of diabetes-related cardiovascular diseases.

Proliferation signal inhibitors and cardiac allograft vasculopathy

PURPOSE OF REVIEW

Cardiac allograft vasculopathy (CAV) is the leading cause of late morbidity and mortality in heart transplant patients and limits long-term survival. Immunosuppression following cardiac transplantation has traditionally comprised a calcineurin inhibitor in combination with mycophenolate mofetil or azathioprine and corticosteroids. This combination provides effective immunosuppression but does not prevent subsequent development of CAV. Proliferation signal inhibitors (such as sirolimus and everolimus), a new class of immunosuppressants, have recently been shown to be effective in attenuating the development of CAV following cardiac transplantation.

RECENT FINDINGS

In addition to immunosuppressive properties, proliferation signal inhibitors have important antiproliferative effects outside the immune system. Several ex-vivo and preclinical studies on animal models have demonstrated control of the vascular manifestations after cardiac transplantation. In clinical trials, proliferation signal inhibitors used as secondary immunosuppressive agents in place of azathioprine or mycophenolate prevented CAV progression and reduced the incidence of clinically significant cardiac events. Proliferation signal inhibitors are also effective as primary immunosuppressants, and, after complete calcineurin inhibitor withdrawal, mitigate the progression of CAV, improve calcineurin inhibitor-induced nephropathy and hypertension.

SUMMARY

Proliferation signal inhibitors are powerful immunosuppressive agents with antiproliferative properties that attenuate CAV and have the potential to improve long-term survival following cardiac transplantation.

p66Shc links alpha1-adrenergic receptors to a reactive oxygen species-dependent AKT-FOXO3A phosphorylation pathway in cardiomyocytes

p66Shc is an adapter protein that is induced by hypertrophic stimuli and has been implicated as a major regulator of reactive oxygen species (ROS) production and cardiovascular oxidative stress responses. This study implicates p66Shc in an alpha(1)-adrenergtic receptor (alpha(1)-AR) pathway that requires the cooperative effects of protein kinase (PK)Cepsilon and PKCdelta and leads to AKT-FOXO3a phosphorylation in cardiomyocytes. alpha(1)-ARs promote p66Shc-YY(239/240) phosphorylation via a ROS-dependent mechanism that is localized to caveolae and requires epidermal growth factor receptor (EGFR) and PKCepsilon activity. alpha(1)-ARs also increase p66Shc-S(36) phosphorylation via an EGFR transactivation pathway involving PKCdelta. p66Shc links alpha(1)-ARs to an AKT signaling pathway that selectively phosphorylates/inactivates FOXO transcription factors and downregulates the ROS-scavenging protein manganese superoxide dismutase (MnSOD); the alpha(1)-AR-p66Shc-dependent pathway involving AKT does not regulate GSK3. Additional studies show that RNA interference-mediated downregulation of endogenous p66Shc leads to the derepression of FOXO3a-regulated genes such as MnSOD, p27Kip1, and BIM-1. p66Shc downregulation also increases proliferating cell nuclear antigen expression and induces cardiomyocyte hypertrophy, suggesting that p66Shc exerts an antihypertrophic action in neonatal cardiomyocytes. The novel alpha(1)-AR- and ROS-dependent pathway involving p66Shc identified in this study is likely to contribute to cardiomyocyte remodeling and the evolution of heart failure.

Sirolimus affects cardiomyocytes to reduce left ventricular mass in heart transplant recipients

AIMS

The cellular mechanisms underlying cardiac hypertrophy may result from changes in cardiac myocyte growth and differentiation. We tested whether sirolimus, an immunosuppressive agent that inhibits mTOR, a protein that regulates cell division and differentiation, might modify cardiac hypertrophy after cardiac transplantation.

METHODS AND RESULTS

Fifty-eight cardiac transplant recipients were withdrawn from treatment with calcineurin inhibitors (CNIs) and treated with sirolimus. Eighty-three control subjects were maintained on CNIs. After 12 months, left ventricular (LV) mass decreased from 196.15 +/- 48.28 to 182.21 +/- 43.56 g (P = 0.05) and LV mass index from 99.25 +/- 20.08 to 93.82 +/- 20.22 g/m(2) (P = 0.031) in sirolimus-treated subjects but did not change in controls. The left atrial volume index of sirolimus-treated subjects decreased from 52.44 +/- 17.22 to 48.40 +/- 15.14 cc/m(2) (P = 0.008) and increased from 52.07 +/- 19.45 to 57.03 +/- 19.93 cc/m(2) (P = 0.0012) in controls. The difference between the groups was independent of blood pressure. The number of cells in myocardial biopsies positive for p27Kip1, a protein induced by mTOR inhibition, increased in sirolimus-treated subjects (P = 0.0005) and did not change in controls (P = 0.54) suggesting sirolimus acted directly on myocardium.

CONCLUSION

Sirolimus may inhibit adverse ventricular remodelling resulting in cardiac hypertrophy and have potential in the treatment of conditions in which severe hypertrophy compromises cardiac function.

The Cdk inhibitor p27 in human cancer: prognostic potential and relevance to anticancer therapy

The cyclin-dependent kinase (Cdk) inhibitor p27 (also known as KIP1) regulates cell proliferation, cell motility and apoptosis. Interestingly, the protein can exert both positive and negative functions on these processes. Diverse post-translational modifications determine the physiological role of p27. Phosphorylation regulates p27 binding to and inhibition of cyclin-Cdk complexes, its localization and its ubiquitin-mediated proteolysis. In cancers, p27 is inactivated through impaired synthesis, accelerated degradation and by mislocalization. Moreover, studies in several tumour types indicate that p27 expression levels have both prognostic and therapeutic implications.