Respiratory Syncytial Virus Matrix Protein Is Sufficient and Necessary to Remodel Host Mitochondria in Infection

Although respiratory syncytial virus (RSV) is the most common cause of respiratory infection in infants, immunosuppressed adults and the elderly worldwide, there is no licensed RSV vaccine or widely applicable antiviral therapeutics We previously reported a staged redistribution of mitochondria with compromised respiratory activities and increased reactive oxygen species (ROS) generation during RSV infection. Here, we show for the first time that the RSV matrix protein (M) is sufficient and necessary to induce these effects. Ectopically expressed M, but not other RSV proteins, was able to induce mitochondrial perinuclear clustering, inhibition of mitochondrial respiration, loss of mitochondrial membrane potential (Δψ_m), and enhanced generation of mitochondrial ROS (mtROS) in infection. Truncation and mutagenic analysis revealed that the central nucleic acid-binding domain of M is essential for the effects on host mitochondria, with arginine/lysine residues 170/172 being critically important. Recombinant RSV carrying the arginine/lysine mutations in M was unable to elicit effects on host mitochondria. Further, wild-type but not mutant RSV was found to inhibit the mRNA expression of genes encoding mitochondrial proteins, including Complex I subunits. Importantly, the RSV mutant was impaired in virus production, underlining the importance of M-dependent effects on mitochondria to RSV infection. Together, our results highlight M's unique ability to remodel host cell mitochondria and its critical role in RSV infection, representing a novel, potential target for future anti-RSV strategies.

Bimolecular Fluorescence Complementation: Quantitative Analysis of In Cell Interaction of Nuclear Transporter Importin α with Cargo Proteins

Bimolecular fluorescence complementation utilizes the ability of two complementary nonfluorescent fragments to reconstitute and emit fluorescence when brought together through specific interaction of attached protein fragments of interest. It has been used in several different contexts to study protein-protein interaction. Here we apply the method for the first time to study interaction of the nuclear transporter importin α and its cargoes in a cellular context. By using image analysis to quantify the extent of nuclear complexation, it is possible to gain insight into the strength of interaction in cells.

The ataxin-1 interactome reveals direct connection with multiple disrupted nuclear transport pathways

The expanded polyglutamine (polyQ) tract form of ataxin-1 drives disease progression in spinocerebellar ataxia type 1 (SCA1). Although known to form distinctive intranuclear bodies, the cellular pathways and processes that polyQ-ataxin-1 influences remain poorly understood. Here we identify the direct and proximal partners constituting the interactome of ataxin-1[85Q] in Neuro-2a cells, pathways analyses indicating a significant enrichment of essential nuclear transporters, pointing to disruptions in nuclear transport processes in the presence of elevated levels of ataxin-1. Our direct assessments of nuclear transporters and their cargoes confirm these observations, revealing disrupted trafficking often with relocalisation of transporters and/or cargoes to ataxin-1[85Q] nuclear bodies. Analogous changes in importin-β1, nucleoporin 98 and nucleoporin 62 nuclear rim staining are observed in Purkinje cells of ATXN1[82Q] mice. The results highlight a disruption of multiple essential nuclear protein trafficking pathways by polyQ-ataxin-1, a key contribution to furthering understanding of pathogenic mechanisms initiated by polyQ tract proteins.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

The broad spectrum antiviral ivermectin targets the host nuclear transport importin α/β1 heterodimer

Infection by RNA viruses such as human immunodeficiency virus (HIV)-1, influenza, and dengue virus (DENV) represent a major burden for human health worldwide. Although RNA viruses replicate in the infected host cell cytoplasm, the nucleus is central to key stages of the infectious cycle of HIV-1 and influenza, and an important target of DENV nonstructural protein 5 (NS5) in limiting the host antiviral response. We previously identified the small molecule ivermectin as an inhibitor of HIV-1 integrase nuclear entry, subsequently showing ivermectin could inhibit DENV NS5 nuclear import, as well as limit infection by viruses such as HIV-1 and DENV. We show here that ivermectin's broad spectrum antiviral activity relates to its ability to target the host importin (IMP) α/β1 nuclear transport proteins responsible for nuclear entry of cargoes such as integrase and NS5. We establish for the first time that ivermectin can dissociate the preformed IMPα/β1 heterodimer, as well as prevent its formation, through binding to the IMPα armadillo (ARM) repeat domain to impact IMPα thermal stability and α-helicity. We show that ivermectin inhibits NS5-IMPα interaction in a cell context using quantitative bimolecular fluorescence complementation. Finally, we show for the first time that ivermectin can limit infection by the DENV-related West Nile virus at low (μM) concentrations. Since it is FDA approved for parasitic indications, ivermectin merits closer consideration as a broad spectrum antiviral of interest.

Respiratory syncytial virus co-opts host mitochondrial function to favour infectious virus production

Although respiratory syncytial virus (RSV) is responsible for more human deaths each year than influenza, its pathogenic mechanisms are poorly understood. Here high-resolution quantitative imaging, bioenergetics measurements and mitochondrial membrane potential- and redox-sensitive dyes are used to define RSV’s impact on host mitochondria for the first time, delineating RSV-induced microtubule/dynein-dependent mitochondrial perinuclear clustering, and translocation towards the microtubule-organizing centre. These changes are concomitant with impaired mitochondrial respiration, loss of mitochondrial membrane potential and increased production of mitochondrial reactive oxygen species (ROS). Strikingly, agents that target microtubule integrity the dynein motor protein, or inhibit mitochondrial ROS production strongly suppresses RSV virus production, including in a mouse model with concomitantly reduced virus-induced lung inflammation. The results establish RSV’s unique ability to co-opt host cell mitochondria to facilitate viral infection, revealing the RSV-mitochondrial interface for the first time as a viable target for therapeutic intervention.

Oligonucleotide-directed STAT3 alternative splicing switch drives anti-tumorigenic outcomes in MCF10 human breast cancer cells

Signal transducer and activator of transcription 3 (STAT3), a transcription factor responsive to the activation of cytokine receptors, is known for its oncogenic actions. Whilst STAT3α is the predominant spliceform in most tissues, alternative splicing of the STAT3 gene can generate a shorter STAT3β spliceform. Redirecting splicing to enhance STAT3β levels can result in tumor suppression in vivo, and so we evaluated the cellular basis underlying the anti-tumorigenic properties of STAT3β. To investigate the impact of increased STAT3β levels in cancer cells, we implemented a Morpholino-based antisense oligonucleotide strategy to modulate STAT3 spliceform expression in the MCF10CA1h cancer cells of the MCF10 series of human breast cancer cells. We employed nonsense-mediated decay (NMD) oligonucleotides and STAT3α-to-β expression switching (SWI) oligonucleotides to successfully induce STAT3 knockdown and redirect alternative splicing to increase STAT3β levels in MCF10CA1h cells, respectively. Importantly, assessment of the impacts of STAT3 splicing modulation on tumor cell biology showed that the SWI treatment significantly reduced MCF10CA1h cell growth, viability, and migration, whereas NMD treatment was without significant impact, although neither NMD nor SWI oligonucleotides significantly inhibited MCF10CA1h cell invasion through a semi-solid matrix. In conclusion, our data demonstrate that reduced breast cancer cell growth, viability and migration, but not invasion, follow the redirection of STAT3α-to-β expression switching to favour STAT3β expression.

Doublecortin X (DCX) serine 28 phosphorylation is a regulatory switch, modulating association of DCX with microtubules and actin filaments

Doublecortin X (DCX) plays essential roles in neuronal development via its regulation of cytoskeleton dynamics. This is mediated through direct interactions between its doublecortin (DC) domains (DC1 and DC2) with microtubules (MTs) and indirect association with actin filaments (F-ACT). While the regulatory role of the DCX C-terminus following DC2 (i.e. DCX residues 275-366) has been established, less is known of the possible contributions made by the DCX N-terminus preceding DC1 (i.e. DCX residues 1-44). Here, we assessed the influence of DCX Ser28 within the DCX N-terminus, on the association of DCX with MTs and F-ACT. We compared the cytoskeletal interactions of the DCX S28E phosphomimetic and DCX S28A phospho-resistant mutants and wild-type DCX. Immunoprecipitation and colocalisation analyses indicated increased association of DCX S28E with F-ACT but decreased interaction with MTs, and conversely enhanced DCX S28A association with MTs but decreased association with F-ACT. To evaluate the impact of DCX mutants on cytoskeletal filaments we performed fluorescence recovery after photobleaching (FRAP) studies on SiR-tubulin and β-actin-mCherry and observed comparable tubulin and actin exchange rates in the presence of DCX WT and DCX S28A. However, we observed faster tubulin exchange rates but slower actin exchange rates in the presence of DCX S28E. Moreover, DCX S28E enhanced the association with the actin-binding protein spinophilin (Spn) suggesting the shift to favour association with both F-ACT and Spn in the presence of DCX S28E. Taken together, our results highlight a new role for DCX S28 as a regulatory switch for cytoskeletal organisation.

Complementary proteomics strategies capture an ataxin-1 interactome in Neuro-2a cells

Ataxin-1 mutation, arising from a polyglutamine (polyQ) tract expansion, is the underlying genetic cause of the late-onset neurodegenerative disease Spinocerebellar ataxia type 1 (SCA1). To identify protein partners of polyQ-ataxin-1 in neuronal cells under control or stress conditions, here we report our complementary proteomics strategies of proximity-dependent biotin identification (BioID) and affinity purification (via GFP-Trap pulldown) in Neuro-2a cells expressing epitope-tagged forms of ataxin-1[85Q]. These approaches allowed our enrichment of proximal proteins and interacting partners, respectively, with the subsequent protein identification performed by liquid chromatography-MS/MS. Background proteins, not dependent on the presence of the polyQ-ataxin-1 protein, were additionally defined by their endogenous biotinylation (for the BioID protocol) or by their non-specific interaction with GFP only (in the GFP-Trap protocol). All datasets were generated from biological replicates. Following the removal of the identified background proteins from the acquired protein lists, our experimental design has captured a comprehensive polyQ-ataxin-1 proximal and direct protein partners under normal and stress conditions. Data are available via ProteomeXchange, with identifier PXD010352.

TrawlerWeb: an online de novo motif discovery tool for next-generation sequencing datasets

Background

A strong focus of the post-genomic era is mining of the non-coding regulatory genome in order to unravel the function of regulatory elements that coordinate gene expression (Nat 489:57–74, 2012; Nat 507:462–70, 2014; Nat 507:455–61, 2014; Nat 518:317–30, 2015). Whole-genome approaches based on next-generation sequencing (NGS) have provided insight into the genomic location of regulatory elements throughout different cell types, organs and organisms. These technologies are now widespread and commonly used in laboratories from various fields of research. This highlights the need for fast and user-friendly software tools dedicated to extracting cis-regulatory information contained in these regulatory regions; for instance transcription factor binding site (TFBS) composition. Ideally, such tools should not require prior programming knowledge to ensure they are accessible for all users.

Results

We present TrawlerWeb, a web-based version of the Trawler_standalone tool (Nat Methods 4:563–5, 2007; Nat Protoc 5:323–34, 2010), to allow for the identification of enriched motifs in DNA sequences obtained from next-generation sequencing experiments in order to predict their TFBS composition. TrawlerWeb is designed for online queries with standard options common to web-based motif discovery tools. In addition, TrawlerWeb provides three unique new features: 1) TrawlerWeb allows the input of BED files directly generated from NGS experiments, 2) it automatically generates an input-matched biologically relevant background, and 3) it displays resulting conservation scores for each instance of the motif found in the input sequences, which assists the researcher in prioritising the motifs to validate experimentally. Finally, to date, this web-based version of Trawler_standalone remains the fastest online de novo motif discovery tool compared to other popular web-based software, while generating predictions with high accuracy.

Conclusions

TrawlerWeb provides users with a fast, simple and easy-to-use web interface for de novo motif discovery. This will assist in rapidly analysing NGS datasets that are now being routinely generated. TrawlerWeb is freely available and accessible at: http://trawler.erc.monash.edu.au.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4630-0) contains supplementary material, which is available to authorized users.

Aurora A phosphorylation of WD40-repeat protein 62 in mitotic spindle regulation

Mitotic spindle organization is regulated by centrosomal kinases that potentiate recruitment of spindle-associated proteins required for normal mitotic progress including the microcephaly protein WD40-repeat protein 62 (WDR62). WDR62 functions underlie normal brain development as autosomal recessive mutations and wdr62 loss cause microcephaly. Here we investigate the signaling interactions between WDR62 and the mitotic kinase Aurora A (AURKA) that has been recently shown to cooperate to control brain size in mice. The spindle recruitment of WDR62 is closely correlated with increased levels of AURKA following mitotic entry. We showed that depletion of TPX2 attenuated WDR62 localization at spindle poles indicating that TPX2 co-activation of AURKA is required to recruit WDR62 to the spindle. We demonstrated that AURKA activity contributed to the mitotic phosphorylation of WDR62 residues Ser49 and Thr50 and phosphorylation of WDR62 N-terminal residues was required for spindle organization and metaphase chromosome alignment. Our analysis of several MCPH-associated WDR62 mutants (V65M, R438H and V1314RfsX18) that are mislocalized in mitosis revealed that their interactions and phosphorylation by AURKA was substantially reduced consistent with the notion that AURKA is a key determinant of WDR62 spindle recruitment. Thus, our study highlights the role of AURKA signaling in the spatiotemporal control of WDR62 at spindle poles where it maintains spindle organization.

Opposing roles for JNK and Aurora A in regulating the association of WDR62 with spindle microtubules

WD40-repeat protein 62 (WDR62) is a spindle pole protein required for normal cell division and neuroprogenitor differentiation during brain development. Microcephaly-associated mutations in WDR62 lead to mitotic mislocalization, highlighting a crucial requirement for precise WDR62 spatiotemporal distribution, although the regulatory mechanisms are unknown. Here, we demonstrate that the WD40-repeat region of WDR62 is required for microtubule association, whereas the disordered C-terminal region regulates cell-cycle-dependent compartmentalization. In agreement with a functional requirement for the WDR62–JNK1 complex during neurogenesis, WDR62 specifically recruits JNK1 (also known as MAPK8), but not JNK2 (also known as MAPK9), to the spindle pole. However, JNK-mediated phosphorylation of WDR62 T1053 negatively regulated microtubule association, and loss of JNK signaling resulted in constitutive WDR62 localization to microtubules irrespective of cell cycle stage. In contrast, we identified that Aurora A kinase (AURKA) and WDR62 were in complex and that AURKA-mediated phosphorylation was required for the spindle localization of WDR62 during mitosis. Our studies highlight complex regulation of WDR62 localization, with opposing roles for JNK and AURKA in determining its spindle association.

Dual role of Src kinase in governing neuronal survival

BACKGROUND

Src-family kinases (SFKs) are involved in neuronal survival and their aberrant regulation contributes to neuronal death. However, how they control neuronal survival and death remains unclear.

OBJECTIVE

To define the effect of inhibition of Src activity and expression on neuronal survival.

RESULTS

In agreement with our previous findings, we demonstrated that Src was cleaved by calpain to form a 52-kDa truncated fragment in neurons undergoing excitotoxic cell death, and expression of the recombinant truncated Src fragment induced neuronal death. The data confirm that the neurotoxic signaling pathways are intact in the neurons we used for our study. To define the functional role of neuronal SFKs, we treated these neurons with SFK inhibitors and discovered that the treatment induced cell death, suggesting that the catalytic activity of one or more of the neuronal SFKs is critical to neuronal survival. Using small hairpin RNAs that suppress Src expression, we demonstrated that Src is indispensable to neuronal survival. Additionally, we found that neuronal death induced by expression of the neurotoxic truncated Src mutant, treatment of SFK inhibitors or knock-down of Src expression caused inhibition of the neuroprotective protein kinases Erk1/2, or Akt.

CONCLUSIONS

Src is critical to both neuronal survival and death. Intact Src sustains neuronal survival. However, in the excitotoxic condition, calpain cleavage of Src generates a neurotoxic truncated Src fragment. Both intact Src and the neurotoxic truncated Src fragment exert their biological actions by controlling the activities of neuroprotective protein kinases.

Cytokine-induced slowing of STAT3 nuclear import; faster basal trafficking of the STAT3β isoform

The STAT3 signal transducer and activator of transcription is a key mediator of gene transcription in response to cytokines such as oncostatin M (OSM). We performed direct live cell imaging of GFP-tagged STAT3 proteins for the first time, showing transient relocalization of STAT3α to the nucleus following OSM exposure, in contrast to sustained nuclear relocalization of the shorter STAT3β spliceform. To explore this further, we applied fluorescence recovery after photobleaching (FRAP) to determine the nuclear import kinetics of STAT3α and β, as well as of a C-terminal truncation derivative STAT3ΔC comprising only the sequence shared by the spliceforms, in the absence or presence of OSM. The rates of basal nuclear import for STAT3β and STAT3ΔC were significantly faster than those for STAT3α. Strikingly, OSM slowed the import rates of all the three STAT3 proteins, whereas the import rates of GFP alone or a classical importin-mediated cargo were unaffected, with analysis of Y705F mutant derivatives for all the three STAT3 constructs, or of a S727A mutant within the unique C-terminus of STAT3α, reinforcing the contribution of specific phosphorylation to the cytokine-stimulated changes. The results introduce a new paradigm where cytokine treatment prolongs nuclear retention simultaneous with decreasing rather than increasing the rate of nuclear import.

Oxidative stress impairs multiple regulatory events to drive persistent cytokine-stimulated STAT3 phosphorylation

Although cytokine-driven STAT3 phosphorylation and activation are often transient, persistent activation of STAT3 is a hallmark of a range of pathologies and underpins altered transcriptional responses. As triggers in disease frequently include combined increases in inflammatory cytokine and reactive oxygen species levels, we report here how oxidative stress impacts on cytokine-driven STAT3 signal transduction events. In the model system of murine embryonic fibroblasts (MEFs), combined treatment with the interleukin-6 family cytokine Leukemia Inhibitory Factor (LIF) and hydrogen peroxide (H2O2) drove persistent STAT3 phosphorylation whereas STAT3 phosphorylation increased only transiently in response to LIF alone and was not increased by H2O2 alone. Surprisingly, increases in transcript levels of the direct STAT3 gene target SOCS3 were delayed during the combined LIF + H2O2 treatment, leading us to probe the impact of oxidative stress on STAT3 regulatory events. Indeed, LIF + H2O2 prolonged JAK activation, delayed STAT3 nuclear localisation, and caused relocalisation of nuclear STAT3 phosphatase TC-PTP (TC45) to the cytoplasm. In exploring the nuclear import/ export pathways, we observed disruption of nuclear/cytoplasmic distributions of Ran and importin-alpha3 in cells exposed to H2O2 and the resultant reduced nuclear trafficking of Classical importin-alpha/3-dependent protein cargoes. CRM1-mediated nuclear export persisted despite the oxidative stress insult, with sustained STAT3 Y705 phosphorylation enhancing STAT3 nuclear residency. Our studies thus reveal for the first time the striking impact of oxidative stress to sustain STAT3 phosphorylation and nuclear retention following disruption of multiple regulatory events, with significant implications for STAT3 function.

Hyperosmotic stress sustains cytokine-stimulated phosphorylation of STAT3, but slows its nuclear trafficking and impairs STAT3-dependent transcription

Persistent STAT3 phosphorylation and nuclear retention are hallmarks of a range of pathologies suggesting the importance of STAT3 transcriptional responses in disease progression. Since hyperosmotic stress (HOS) is a hallmark of diseases such as diabetes and asthma, we analysed the impact of HOS on cytokine-stimulated STAT3 signalling. In contrast to transient STAT3 Y705 and S727 phosphorylation in murine embryonic fibroblasts (MEFs) stimulated by the interleukin-6 family cytokine, leukemia inhibitory factor (LIF), under non-stress conditions, HOS induced by sorbitol treatment increased STAT3 S727 but not Y705 phosphorylation. Strikingly, combined LIF+HOS treatment stimulated persistent STAT3 Y705 and S727 phosphorylation and nuclear localisation, but STAT3 nuclear accumulation was slowed during HOS, likely reflecting the mislocalisation of Ran and importin-α3 during HOS that also reduced the nuclear localisation of classical importin-α/β-recognised nuclear import cargoes. Strikingly, combined LIF+HOS exposure, even though stimulating STAT3 phosphorylation and nuclear accumulation did not elicit a transcriptional output, as demonstrated by qPCR analyses of its target genes SOCS3 and c-Fos. Our analysis thus shows for the first time that HOS can disconnect nuclear, phosphorylated STAT3 from transcriptional outcomes, and emphasizes the importance of assessing STAT3 target gene changes in addition to STAT3 phosphorylation status and localisation.

cAMP-dependent protein kinase and c-Jun N-terminal kinase mediate stathmin phosphorylation for the maintenance of interphase microtubules during osmotic stress

Dynamic microtubule changes after a cell stress challenge are required for cell survival and adaptation. Stathmin (STMN), a cytoplasmic microtubule-destabilizing phosphoprotein, regulates interphase microtubules during cell stress, but the signaling mechanisms involved are poorly defined. In this study ectopic expression of single alanine-substituted phospho-resistant mutants demonstrated that STMN Ser-38 and Ser-63 phosphorylation were specifically required to maintain interphase microtubules during hyperosmotic stress. STMN was phosphorylated on Ser-38 and Ser-63 in response to hyperosmolarity, heat shock, and arsenite treatment but rapidly dephosphorylated after oxidative stress treatment. Two-dimensional PAGE and Phos-tag gel analysis of stress-stimulated STMN phospho-isoforms revealed rapid STMN Ser-38 phosphorylation followed by subsequent Ser-25 and Ser-63 phosphorylation. Previously, we delineated stress-stimulated JNK targeting of STMN. Here, we identified cAMP-dependent protein kinase (PKA) signaling as responsible for stress-induced STMN Ser-63 phosphorylation. Increased cAMP levels induced by cholera toxin triggered potent STMN Ser-63 phosphorylation. Osmotic stress stimulated an increase in PKA activity and elevated STMN Ser-63 and CREB (cAMP-response element-binding protein) Ser-133 phosphorylation that was substantially attenuated by pretreatment with H-89, a PKA inhibitor. Interestingly, PKA activity and subsequent phosphorylation of STMN were augmented in the absence of JNK activation, indicating JNK and PKA pathway cross-talk during stress regulation of STMN. Taken together our study indicates that JNK- and PKA-mediated STMN Ser-38 and Ser-63 phosphorylation are required to preserve interphase microtubules in response to hyperosmotic stress.

Identification and characterization of bi-thiazole-2,2'-diamines as kinase inhibitory scaffolds

Based on bioinformatics interrogation of the genome, >500 mammalian protein kinases can be clustered within seven different groups. Of these kinases, the mitogen-activated protein kinase (MAPK) family forms part of the CMGC group of serine/threonine kinases that includes extracellular signal regulated kinases (ERKs), cJun N-terminal kinases (JNKs), and p38 MAPKs. With the JNKs considered attractive targets in the treatment of pathologies including diabetes and stroke, efforts have been directed to the discovery of new JNK inhibitory molecules that can be further developed as new therapeutics. Capitalizing on our biochemical understanding of JNK, we performed in silico screens of commercially available chemical databases to identify JNK1-interacting compounds and tested their in vitro JNK inhibitory activity. With in vitro and cell culture studies, we showed that the compound, 4'-methyl-N(2)-3-pyridinyl-4,5'-bi-1,3-thiazole-2,2'-diamine (JNK Docking (JD) compound 123, but not the related compound (4'-methyl-N~2~-(6-methyl-2-pyridinyl)-4,5'-bi-1,3-thiazole-2,2'-diamine (JD124), inhibited JNK1 activity towards a range of substrates. Molecular docking, saturation transfer difference NMR experiments and enzyme kinetic analyses revealed both ATP- and substrate-competitive inhibition of JNK by JD123. In characterizing JD123 further, we noted its ATP-competitive inhibition of the related p38-γ MAPK, but not ERK1, ERK2, or p38-α, p38-β or p38-δ. Further screening of a broad panel of kinases using 10μM JD123, identified inhibition of kinases including protein kinase Bβ (PKBβ/Aktβ). Appropriately modified thiazole diamines, as typified by JD123, thus provide a new chemical scaffold for development of inhibitors for the JNK and p38-γ MAPKs as well as other kinases that are also potential therapeutic targets such as PKBβ/Aktβ.

Endothelin-1-dependent signaling pathways in the myocardium

Endothelin-1 (ET-1) is a locally acting vasoactive peptide that also has profound effects on the contractile properties and growth of the cardiac myocyte. Binding of ET-1 to its transmembrane heptahelical receptors activates G proteins of the G(q) and G(i) classes. Activation of G(q) stimulates hydrolysis of phosphatidylinositol-4,5-bisphosphate, and the diacylglycerol thus formed stimulates protein kinase C. Subsequently, the protein kinase Raf is activated and this leads to activation of the extracellular signal-regulated protein kinase (ERK) subfamily of mitogen-activated protein kinases. Activation of G(i) counteracts β-adrenoceptor-mediated increases in cAMP concentrations. We have attempted to rationalize the established physiological consequences of ET-1 agonism in the cardiac myocyte (that is, on contraction and growth) in terms of activation of these signaling pathways.

WD40-repeat protein 62 is a JNK-phosphorylated spindle pole protein required for spindle maintenance and timely mitotic progression

The impact of aberrant centrosomes and/or spindles on asymmetric cell division in embryonic development indicates the tight regulation of bipolar spindle formation and positioning that is required for mitotic progression and cell fate determination. WD40-repeat protein 62 (WDR62) was recently identified as a spindle pole protein linked to the neurodevelopmental defect of microcephaly but its roles in mitosis have not been defined. We report here that the in utero electroporation of neuroprogenitor cells with WDR62 siRNAs induced their cell cycle exit and reduced their proliferative capacity. In cultured cells, we demonstrated cell-cycle-dependent accumulation of WDR62 at the spindle pole during mitotic entry that persisted until metaphase-anaphase transition. Utilizing siRNA depletion, we revealed WDR62 function in stabilizing the mitotic spindle specifically during metaphase. WDR62 loss resulted in spindle orientation defects, decreased the integrity of centrosomes displaced from the spindle pole and delayed mitotic progression. Additionally, we revealed JNK phosphorylation of WDR62 is required for maintaining metaphase spindle organization during mitosis. Our study provides the first functional characterization of WDR62 and has revealed requirements for JNK/WDR62 signaling in mitotic spindle regulation that may be involved in coordinating neurogenesis.

Phosphoinositide 3-Kinase p110α Is a Master Regulator of Exercise-Induced Cardioprotection and PI3K Gene Therapy Rescues Cardiac Dysfunction

Background—

Numerous molecular and biochemical changes have been linked with the cardioprotective effects of exercise, including increases in antioxidant enzymes, heat shock proteins, and regulators of cardiac myocyte proliferation. However, a master regulator of exercise-induced protection has yet to be identified. Here, we assess whether phosphoinositide 3-kinase (PI3K) p110α is essential for mediating exercise-induced cardioprotection, and if so, whether its activation independent of exercise can restore function of the failing heart.

Methods and Results—

Cardiac-specific transgenic (Tg) mice with elevated or reduced PI3K(p110α) activity (constitutively active PI3K [caPI3K] and dominant negative PI3K, respectively) and non-Tg controls were subjected to 4 weeks of exercise training followed by 1 week of pressure overload (aortic-banding) to induce pathological remodeling. Aortic-banding in untrained non-Tg controls led to pathological cardiac hypertrophy, depressed systolic function, and lung congestion. This phenotype was attenuated in non-Tg controls that had undergone exercise before aortic-banding. Banded caPI3K mice were protected from pathological remodeling independent of exercise status, whereas exercise provided no protection in banded dominant negative PI3K mice, suggesting that PI3K is necessary for exercise-induced cardioprotection. Tg overexpression of heat shock protein 70 could not rescue the phenotype of banded dominant negative PI3K mice, and deletion of heat shock protein 70 from banded caPI3K mice had no effect. Next, we used a gene therapy approach (recombinant adeno-associated viral vector 6) to deliver caPI3K expression cassettes to hearts of mice with established cardiac dysfunction caused by aortic-banding. Mice treated with recombinant adeno-associated viral 6-caPI3K vectors had improved heart function after 10 weeks.

Conclusions—

PI3K(p110α) is essential for exercise-induced cardioprotection and delivery of caPI3K vector can improve function of the failing heart.

C-Jun N-terminal kinase controls TDP-43 accumulation in stress granules induced by oxidative stress

BACKGROUND

TDP-43 proteinopathies are characterized by loss of nuclear TDP-43 expression and formation of C-terminal TDP-43 fragmentation and accumulation in the cytoplasm. Recent studies have shown that TDP-43 can accumulate in RNA stress granules (SGs) in response to cell stresses and this could be associated with subsequent formation of TDP-43 ubiquinated protein aggregates. However, the initial mechanisms controlling endogenous TDP-43 accumulation in SGs during chronic disease are not understood. In this study we investigated the mechanism of TDP-43 processing and accumulation in SGs in SH-SY5Y neuronal-like cells exposed to chronic oxidative stress. Cell cultures were treated overnight with the mitochondrial inhibitor paraquat and examined for TDP-43 and SG processing.

RESULTS

We found that mild stress induced by paraquat led to formation of TDP-43 and HuR-positive SGs, a proportion of which were ubiquitinated. The co-localization of TDP-43 with SGs could be fully prevented by inhibition of c-Jun N-terminal kinase (JNK). JNK inhibition did not prevent formation of HuR-positive SGs and did not prevent diffuse TDP-43 accumulation in the cytosol. In contrast, ERK or p38 inhibition prevented formation of both TDP-43 and HuR-positive SGs. JNK inhibition also inhibited TDP-43 SG localization in cells acutely treated with sodium arsenite and reduced the number of aggregates per cell in cultures transfected with C-terminal TDP-43 162-414 and 219-414 constructs.

CONCLUSIONS

Our studies are the first to demonstrate a critical role for kinase control of TDP-43 accumulation in SGs and may have important implications for development of treatments for FTD and ALS, targeting cell signal pathway control of TDP-43 aggregation.

Opposing actions of extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription 3 (STAT3) in regulating microtubule stabilization during cardiac hypertrophy

Excessive proliferation and stabilization of the microtubule (MT) array in cardiac myocytes can accompany pathological cardiac hypertrophy, but the molecular control of these changes remains poorly characterized. In this study, we examined MT stabilization in two independent murine models of heart failure and revealed increases in the levels of post-translationally modified stable MTs, which were closely associated with STAT3 activation. To explore the molecular signaling events contributing to control of the cardiac MT network, we stimulated cardiac myocytes with an α-adrenergic agonist phenylephrine (PE), and observed increased tubulin content without changes in detyrosinated (glu-tubulin) stable MTs. In contrast, the hypertrophic interleukin-6 (IL6) family cytokines increased both the glu-tubulin content and glu-MT density. When we examined a role for ERK in regulating cardiac MTs, we showed that the MEK/ERK-inhibitor U0126 increased glu-MT density in either control cardiac myocytes or following exposure to hypertrophic agents. Conversely, expression of an activated MEK1 mutant reduced glu-tubulin levels. Thus, ERK signaling antagonizes stabilization of the cardiac MT array. In contrast, inhibiting either JAK2 with AG490, or STAT3 signaling with Stattic or siRNA knockdown, blocked cytokine-stimulated increases in glu-MT density. Furthermore, the expression of a constitutively active STAT3 mutant triggered increased glu-MT density in the absence of hypertrophic stimulation. Thus, STAT3 activation contributes substantially to cytokine-stimulated glu-MT changes. Taken together, our results highlight the opposing actions of STAT3 and ERK pathways in the regulation of MT changes associated with cardiac myocyte hypertrophy.

c-Jun N-terminal kinase phosphorylation of stathmin confers protection against cellular stress

The cell stress response encompasses the range of intracellular events required for adaptation to stimuli detrimental to cell survival. Although the c-Jun N-terminal kinase (JNK) is a stress-activated kinase that can promote either cell survival or death in response to detrimental stimuli, the JNK-regulated mechanisms involved in survival are not fully characterized. Here we show that in response to hyperosmotic stress, JNK phosphorylates a key cytoplasmic microtubule regulatory protein, stathmin (STMN), on conserved Ser-25 and Ser-38 residues. In in vitro biochemical studies, we identified STMN Ser-38 as the critical residue required for efficient phosphorylation by JNK and identified a novel kinase interaction domain in STMN required for recognition by JNK. We revealed that JNK was required for microtubule stabilization in response to hyperosmotic stress. Importantly, we also demonstrated a novel cytoprotective function for STMN, as the knockdown of STMN levels by siRNA was sufficient to augment viability in response to hyperosmotic stress. Our findings show that JNK targeting of STMN represents a novel stress-activated cytoprotective mechanism involving microtubule network changes.

Severe heart failure and early mortality in a double-mutation mouse model of familial hypertrophic cardiomyopathy

BACKGROUND

Familial hypertrophic cardiomyopathy (FHC) is characterized by genetic and clinical heterogeneity. Five percent of FHC families have 2 FHC-causing mutations, which results in earlier disease onset, increased cardiac dysfunction, and a higher incidence of sudden death events. These observations suggest a relationship between the number of gene mutations and phenotype severity in FHC.

METHODS AND RESULTS

We sought to develop, characterize, and investigate the pathogenic mechanisms in a double-mutant murine model of FHC. This model (designated TnI-203/MHC-403) was generated by crossbreeding mice with the Gly203Ser cardiac troponin I (TnI-203) and Arg403Gln alpha-myosin heavy chain (MHC-403) FHC-causing mutations. The mortality rate in TnI-203/MHC-403 mice was 100% by age 21 days. At age 14 days, TnI-203/MHC-403 mice developed a significantly increased ratio of heart weight to body weight, marked interstitial myocardial fibrosis, and increased expression of atrial natriuretic factor and brain natriuretic peptide compared with nontransgenic, TnI-203, and MHC-403 littermates. By age 16 to 18 days, TnI-203/MHC-403 mice rapidly developed a severe dilated cardiomyopathy and heart failure, with inducibility of ventricular arrhythmias, which led to death by 21 days. Downregulation of mRNA levels of key regulators of Ca(2+) homeostasis in TnI-203/MHC-403 mice was observed. Increased levels of phosphorylated STAT3 were observed in TnI-203/MHC-403 mice and corresponded with the onset of disease, which suggests a possible cardioprotective response.

CONCLUSIONS

TnI-203/MHC-403 double-mutant mice develop a severe cardiac phenotype characterized by heart failure and early death. The presence of 2 disease-causing mutations may predispose individuals to a greater risk of developing severe heart failure than human FHC caused by a single gene mutation.

Myoseverin disrupts sarcomeric organization in myocytes: an effect independent of microtubule assembly inhibition

Although disruption of the microtubule (MT) array inhibits myogenesis in myocytes, the relationship between the assembly of microtubules (MT) and the organization of the contractile filaments is not clearly defined. We now report that the assembly of mature myofibrils in hypertrophic cardiac myocytes is disrupted by myoseverin, a compound previously shown to perturb the MT array in skeletal muscle cells. Myoseverin treated cardiac myocytes showed disruptions of the striated Z-bands containing alpha-actinin and desmin and the localization of tropomyosin, titin and myosin on mature sarcomeric filaments. In contrast, MT depolymerization by nocodazole did not perturb sarcomeric filaments. Similarly, expression of constitutively active stathmin as a non-chemical molecular method of MT depolymerization did not prevent sarcomere assembly. The extent of MT destabilization by myoseverin and nocodazole were comparable. Thus, the effect of myoseverin on sarcomere assembly was independent of its capacity for MT inhibition. Furthermore, we found that upon removal of myoseverin, sarcomeres reformed in the absence of an intact MT network. Sarcomere formation in cardiac myocytes therefore, does not appear to require an intact MT network and thus we conclude that a functional MT array appears to be dispensable for myofibrillogenesis.

Changes in the transcriptional profile of cardiac myocytes following green fluorescent protein expression

Green fluorescent protein (GFP) and its multiple forms, such as enhanced GFP (EGFP), have been widely used as marker proteins and for tracking purposes in many biological systems, including the heart and cardiac cell systems. Despite some concerns on its toxicity under certain circumstances, GFP remains amongst the most reliable and easy-to-use markers available. Using rat full genome DNA microarrays, we have investigated the broader consequences of adenoviral-driven GFP expression in cardiac myocytes. In our transcriptional profiling analysis, we set a threshold of a twofold change. We removed possible changes resulting from adenoviral infection by comparison with transcriptional profiles of cardiac myocytes with adenoviral-driven expression of an unrelated protein, the kinase MEK. Our analysis revealed changes in the expression of 212 genes. Of these genes, 174 were upregulated and 38 were downregulated following GFP expression. Many of these genes remain unannotated, but an evaluation of those with described functions for their resulting proteins indicated that many were involved in processes, including responses to stimuli/stress and signal transduction. Our analysis thus indicates the broader consequences of GFP expression in altering gene expression profiles in cardiac cells. Care should therefore be taken when using GFP expression as a control in gene expression studies.

Inhibitors of c-Jun N-terminal kinases: JuNK no more?

The c-Jun N-terminal kinases (JNKs) have been the subject of intense interest since their discovery in the early 1990s. Major research programs have been directed to the screening and/or design of JNK-selective inhibitors and testing their potential as drugs. We begin this review by considering the first commercially-available JNK ATP-competitive inhibitor, SP600125. We focus on recent studies that have evaluated the actions of SP600125 in lung, brain, kidney and liver following exposure to a range of stress insults including ischemia/reperfusion. In many but not all cases, SP600125 administration has proved beneficial. JNK activation can also follow infection, and we next consider recent examples that demonstrate the benefits of SP600125 administration in viral infection. Additional ATP-competitive JNK inhibitors have now been described following high throughput screening of small molecule libraries, but information on their use in biological systems remains limited and thus these inhibitors will require further evaluation. Peptide substrate-competitive ATP-non-competitive inhibitors of JNK have also now been described, and we discuss the recent advances in the use of JNK inhibitory peptides in the treatment of neuronal death, diabetes and viral infection. We conclude by raising a number of questions that should be considered in the quest for JNK-specific inhibitors.

A new paradigm for protein kinase inhibition: blocking phosphorylation without directly targeting ATP binding

Protein kinases are now recognised as an important class of drug targets. Whilst many protein kinase inhibitors directly interact with the ATP-binding site, Gleevec is a notable example from a new class of allosteric inhibitors that alter protein kinase conformation to block productive ATP binding. Recently, kinase inhibitors with different mechanisms of action have also been described. Some of these are allosteric inhibitors that alter kinase conformation and prevent protein substrate binding. Other inhibitors directly compete with protein substrate binding. These inhibitors promise exciting therapeutic opportunities by exploiting new mechanisms of action and may thus allow greater specificity in protein kinase inhibition with fewer off-target side effects.

Necrotic death of neurons following an excitotoxic insult is prevented by a peptide inhibitor of c-jun N-terminal kinase

Peptide inhibitors of c-Jun N-terminal kinase (JNK) have been shown to potently protect against cerebral ischemia. The protective effect has been ascribed to prevention of apoptosis, but cell death following cerebral ischemia is a consequence of both apoptotic and necrotic cell death. We evaluated whether a peptide inhibitor (TAT-TIJIP) of JNK could prevent necrotic cell death in an in vitro model of excitotoxic neuronal death. We find that TAT-TIJIP effectively prevented cell death by interfering with several processes which have been identified as leading to cell death by necrosis. In particular, reactive oxygen species production was reduced, as indicated by an 88% decrease in the rate of dihydroethidium fluorescence in the presence of TAT-TIJIP. Furthermore, TAT-TIJIP attenuated the increase in cytosolic calcium following the excitotoxic insult. The potent neuroprotective properties of JNK peptide inhibitors likely reflects their abilities to prevent cell death by necrosis as well as apoptosis.

The isoform-specific functions of the c-Jun N-terminal Kinases (JNKs): differences revealed by gene targeting

The c-Jun N-terminal kinases (JNKs) are members of the mitogen-activated protein kinase (MAPK) family. In mammalian genomes, three genes encode the JNK family. To evaluate JNK function, mice have been created with deletions in one or more of three Jnk genes. Initial studies on jnk1(-/-) or jnk2(-/-) mice have shown roles for these JNKs in the immune system whereas studies on jnk3(-/-) mice have highlighted roles for JNK3 in the nervous system. Further studies have highlighted the contributions of JNK1 and/or JNK2 to a range of biological and pathological processes. These include bone remodelling and joint disease, inflammatory and autoimmune diseases, obesity, diabetes, cardiovascular disease, liver disease and tumorigenesis in addition to effects in neurons. These results emphasise the differences in the roles played by JNK isoforms in vivo and suggest that the design of JNK inhibitors for subsequent therapeutic uses may benefit from selective inhibition of individual JNK isoforms.

Activation of mitogen-activated protein kinase pathways by the granulocyte colony-stimulating factor receptor: mechanisms and functional consequences

The cytokine Granulocyte Colony Stimulating Factor (G-CSF) promotes proliferation, differentiation, survival and functional maturation of cells within the neutrophilic granulocyte lineage. G-CSF binds to its cell-surface receptor (G-CSFR) causing activation via homodimerisation and subsequent phosphorylation on four tyrosine residues of the receptor intracellular domain. This initiates a range of intracellular signalling events including the activation of Mitogen-Activated Protein Kinase (MAPK) pathways. G-CSF stimulates activation of the ERK 1/2 pathway, as well as the stress-activated JNK and p38 pathways, and the less-characterised ERK5/Big MAPK 1 pathway. Receptor mutagenesis studies have aided in the identification of regions of the G-CSFR that mediate specific activation of these MAPK pathways. In addition, the activation of individual MAPK pathways appears to contribute to distinct biological outcomes. Thus, MAPK activation may be an important mediator of the actions of G-CSF.

Uses for JNK: the many and varied substrates of the c-Jun N-terminal kinases

The c-Jun N-terminal kinases (JNKs) are members of a larger group of serine/threonine (Ser/Thr) protein kinases from the mitogen-activated protein kinase family. JNKs were originally identified as stress-activated protein kinases in the livers of cycloheximide-challenged rats. Their subsequent purification, cloning, and naming as JNKs have emphasized their ability to phosphorylate and activate the transcription factor c-Jun. Studies of c-Jun and related transcription factor substrates have provided clues about both the preferred substrate phosphorylation sequences and additional docking domains recognized by JNK. There are now more than 50 proteins shown to be substrates for JNK. These include a range of nuclear substrates, including transcription factors and nuclear hormone receptors, heterogeneous nuclear ribonucleoprotein K, and the Pol I-specific transcription factor TIF-IA, which regulates ribosome synthesis. Many nonnuclear substrates have also been characterized, and these are involved in protein degradation (e.g., the E3 ligase Itch), signal transduction (e.g., adaptor and scaffold proteins and protein kinases), apoptotic cell death (e.g., mitochondrial Bcl2 family members), and cell movement (e.g., paxillin, DCX, microtubule-associated proteins, the stathmin family member SCG10, and the intermediate filament protein keratin 8). The range of JNK actions in the cell is therefore likely to be complex. Further characterization of the substrates of JNK should provide clearer explanations of the intracellular actions of the JNKs and may allow new avenues for targeting the JNK pathways with therapeutic agents downstream of JNK itself.

Necrotic death without mitochondrial dysfunction-delayed death of cardiac myocytes following oxidative stress

Oxidative stress has been implicated in cell death in range of disease states including ischemia/reperfusion injury of the heart and heart failure. Here we have investigated the mechanisms of cell death following chronic exposure of cardiac myocytes to oxidative stress initiated by hydrogen peroxide. This exposure induced a delayed form of cell death with ultrastructural changes typical of necrosis, and that was accompanied by the release of lactate dehydrogenase and increased lipid peroxidation. However, this delayed death was not accompanied by the loss of mitochondrial membrane potential or caspase-3 activation. Furthermore, we could demonstrate that this delayed necrosis was at least partially prevented by pre-treatment with the hypertrophic stimuli endothelin-1 or leukemic inhibitory factor. Our results suggest that this delayed form necrosis may also comprise an ordered series of events involving pathways amenable to therapeutic modulation.

Gene expression profiling reveals complex changes following MEK-EE expression in cardiac myocytes

The activation of the MEK/ERK pathway has been implicated in the proliferative growth of many tissues, however in the heart it has been linked with hypertrophic growth of the individual cardiac myocytes. We have explored the transcriptional consequences of prolonged ERK1/2 activation in cardiac myocytes following the adenoviral overexpression of a constitutively active form of MEK, MEK-EE. Analysis of microarray data obtained using full rat genome arrays showed >2000 gene expression changes in response to MEK-EE overexpression for 24h. We observed similar numbers of genes upregulated and downregulated. The genes were involved in diverse processes including cell structure, metabolism and intracellular signalling. There were also changes in the pro- and ani-apoptotic genes as well as downregulation of the antioxidant enzymes, Mn superoxide dismutase, catalase and thioredoxin 2. Our results reveal the complexity of transcriptional changes that follow the activation of the ERK signalling pathway in these cells and suggest that activation of this MAPK pathway impinges on diverse cellular functions.

Contrasting actions of prolonged mitogen-activated protein kinase activation on cell survival

Activation of the ERK mitogen-activated protein kinase pathway has been implicated in pro-survival and cellular protective mechanisms, so that chronic ERK activation may be a useful therapeutic strategy. Here, we further explored the consequences of prolonged ERK activation following expression of constitutively active form of MEK, MEK-EE, in cardiac myocytes. We confirmed that chronic MEK-EE overexpression halved myocyte death following glucose deprivation, but surprisingly this was not associated with preserved intracellular ATP levels. Whilst activities of a number of antioxidant enzymes were not altered upon MEK-EE expression, paradoxically Cu/Zn superoxide dismutase activity was almost halved upon MEK-EE expression. When we then exposed myocytes to the superoxide generator menadione, we observed significantly higher death of MEK-EE expressing myocytes. Pre-incubation with U0126 inhibited menadione-induced death. Our results are the first to show that MEK-ERK signalling can act to increase or decrease cell survival, the outcome depending on the form of stress stimulus encountered.

Peptide inhibitors of protein kinases-discovery, characterisation and use

Protein kinases are now the second largest group of drug targets, and most protein kinase inhibitors in clinical development are directed towards the ATP-binding site. However, these inhibitors must compete with high intracellular ATP concentrations and they must discriminate between the ATP-binding sites of all protein kinases as well the other proteins that also utilise ATP. It would therefore be beneficial to target sites on protein kinases other than the ATP-binding site. This review describes the discovery, characterisation and use of peptide inhibitors of protein kinases. In many cases, the development of these peptides has resulted from an understanding of the specific protein-binding partners for a particular protein kinase. In addition, novel peptide sequences have been discovered in library screening approaches and have provided new leads in the discovery and/or design of peptide inhibitors of protein kinases. These approaches are therefore providing exciting new opportunities in the development of ATP non-competitive inhibitors of protein kinases.

Proteomic Analysis Reveals Different Protein Changes during Endothelin-1- or Leukemic Inhibitory Factor-induced Hypertrophy of Cardiomyocytes in Vitro

Proteomic analyses are being increasingly used to identify protein changes accompanying changes in cellular function. An advantage of this approach is that it is largely unbiased by prior assumptions on the importance of each protein in the process under investigation. Here we have evaluated the protein changes that accompany the enlargement, or hypertrophy, of cardiomyocytes in culture. We have taken the additional step of comparing the changes that accompany a concentric hypertrophic phenotype stimulated by endothelin-1 exposure and an eccentric hypertrophic phenotype stimulated by leukemic inhibitory factor exposure. Following separation of the protein extracts by two-dimensional gel electrophoresis and staining with colloidal Coomassie Brilliant Blue, we identified 15 protein spots representing 12 proteins that changed in response to endothelin-1. In comparison, 17 protein spots representing 17 proteins changed in response to leukemic inhibitory factor, and 35 protein spots representing 28 proteins did not change under these conditions. Importantly the well established marker of cardiac pathology, atrial natriuretic factor, was identified as a protein up-regulated by both endothelin-1 and leukemic inhibitory factor (2.4+/-0.8- and 2.2+/-0.3-fold, respectively). However, nine of the observed protein changes occurred for only endothelin-1, whereas 11 of the changes occurred only with leukemic inhibitory factor exposure. These two different stimuli are therefore able to elicit unique changes in the protein expression profile of cardiac myocytes. This is consistent with the differences in morphologies noted as well as the different signaling pathways utilized by these different stimuli.

Therapeutic promise of JNK ATP-noncompetitive inhibitors

Protein kinases are being increasingly targeted in the quest for new therapeutics, and the c-Jun N-terminal kinases (JNKs) are no exception. Protein-kinase inhibitors are generally small molecules that show competitive inhibition with respect to ATP. However, a peptide has been developed that is an ATP-noncompetitive inhibitor of JNK. This article describes the use of this peptide in an increasing number of animal models of disease, including diabetes, stroke, neurotrauma, hearing loss and Alzheimer's disease. The efficacy of this peptide shows that JNK inhibition is an effective strategy for the treatment of these diseases and opens the possibility for testing whether JNK inhibition will be beneficial in other diseases, such as atherosclerosis, arthritis and a range of neurodegenerative diseases.

Small G-protein Rho is involved in the maintenance of cardiac myocyte morphology

The use of small membrane-permeable sequences or protein transduction domains (PTDs) can facilitate the transport of proteins into many cell types. In preliminary studies with the application of three PTDs (penetratin, modified penetratin, and the HIV TAT transduction domains) to cardiac myocytes, we found that the TAT and penetratin sequences showed high efficiency of uptake and low toxicity. Rho has been previously shown to be an important regulator of cytoskeletal organization and morphology in other non-cardiac cell types. To evaluate a role for Rho in cardiac myocyte morphology, we used the TAT-PTD to deliver a RhoA-specific inhibitor, the C3 exoenzyme, to cultured cardiac myocytes. We showed that this incubation with TAT-C3 abolished the basal levels of RhoA activity, demonstrating the efficacy of this treatment. Incubation with TAT-C3 also altered cardiac myocyte morphology so that TAT-C3-treated cells produced multiple projections from the major cell body. This was accompanied by a statistically significant increase in cell size, albeit to a lesser extent than the changes accompanying exposure to the hypertrophic agent, endothelin-1. Furthermore, the change in size of TAT-C3-treated cells was not accompanied by the induction of atrial natriuretic factor (ANF) expression that accompanies the hypertrophy of cardiac myocytes. These results reveal a role for RhoA in the maintenance of normal myocyte morphology.

Outer membrane protein 25-a mitochondrial anchor and inhibitor of stress-activated protein kinase-3

Stress-activated protein kinase-3 (SAPK3) is unique amongst the mitogen-activated protein kinase (MAPK) family with its C-terminal 5 amino acids directing interaction with the PDZ domain-containing substrates alpha1-Syntrophin and SAP90/PSD95. Here, we identify three additional PDZ domain-containing binding partners, Lin-7C, Scribble, and outer membrane protein 25 (OMP25). This latter protein is localised together with SAPK3 at the mitochondria but it is not a SAPK3 substrate. Instead, OMP25 inhibits SAPK3 activity towards PDZ domain-containing substrates such as alpha1-Syntrophin and substrates without PDZ domains such as the mitochondrial protein Sab. This is a new mechanism for the regulation of SAPK3 and suggests that its intracellular activity should not be solely assessed by its phosphorylation status.

Counting on mitogen-activated protein kinases—ERKs 3, 4, 5, 6, 7 and 8

Signal transduction pathways in eukaryotic cells integrate diverse extracellular signals, and regulate complex biological responses such as growth, differentiation and death. One group of proline-directed Ser/Thr protein kinases, the mitogen-activated protein kinases (MAPKs), plays a central role in these signalling pathways. Much attention has focused in recent years on three subfamilies of MAPKs, the extracellular signal regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs) and the p38 MAPKs. However, the ERK family is broader than the ERK1 and ERK2 proteins that have been the subject of most studies in this area. Here we overview the work on ERKs 3 to 8, emphasising where possible their biological activities as well as distinctive biochemical properties. It is clear from these studies that these additional ERKs show similarities to ERK1 and ERK2, but with some interesting differences that challenge the paradigm of the archetypical ERK1/2 MAPK pathway.

An update on the cardiac effects of erythropoietin cardioprotection by erythropoietin and the lessons learnt from studies in neuroprotection

Erythropoietin (Epo) was once thought to act exclusively in the formation of red blood cells. As recently reviewed by Smith et al. [Cardiovasc. Res. 59 (2003) 538-548], Epo can also act within the cardiovascular system with effects in thrombosis and hypertension as well as actions on platelets, vascular endothelium and smooth muscle, and myocytes of the heart. Here, the actions of Epo to protect neuronal cells of the brain are first evaluated and parallel actions of Epo in cardioprotection are then drawn. Thus, with recent reports of Epo receptor (EpoR) expression by cardiac myocytes, it could be predicted that Epo initiates direct protective signalling events. This is supported by five independent studies published in 2003 showing Epo protects cardiac myocytes following ischemia/reperfusion. Importantly, these protective actions have been observed in vitro and in vivo. The former suggests the direct actions of Epo to prevent myocyte death independently of its effects on red blood cell number or cells other than cardiac myocytes. The latter demonstrates the potential for Epo in the treatment of the heart post-infarction, decreasing the numbers of apoptotic myocytes, limiting infarct expansion and attenuating the post-infarct deterioration in haemodynamic function. These beneficial effects of Epo should stimulate further research into the actions of Epo.