PAK signalling in neuronal physiology

Genome-wide analysis implicates microRNAs and their target genes in the development of bipolar disorder

Bipolar disorder (BD) is a severe and highly heritable neuropsychiatric disorder with a lifetime prevalence of 1%. Molecular genetic studies have identified the first BD susceptibility genes. However, the disease pathways remain largely unknown. Accumulating evidence suggests that microRNAs, a class of small noncoding RNAs, contribute to basic mechanisms underlying brain development and plasticity, suggesting their possible involvement in the pathogenesis of several psychiatric disorders, including BD. In the present study, gene-based analyses were performed for all known autosomal microRNAs using the largest genome-wide association data set of BD to date (9747 patients and 14 278 controls). Associated and brain-expressed microRNAs were then investigated in target gene and pathway analyses. Functional analyses of miR-499 and miR-708 were performed in rat hippocampal neurons. Ninety-eight of the six hundred nine investigated microRNAs showed nominally significant P-values, suggesting that BD-associated microRNAs might be enriched within known microRNA loci. After correction for multiple testing, nine microRNAs showed a significant association with BD. The most promising were miR-499, miR-708 and miR-1908. Target gene and pathway analyses revealed 18 significant canonical pathways, including brain development and neuron projection. For miR-499, four Bonferroni-corrected significant target genes were identified, including the genome-wide risk gene for psychiatric disorder CACNB2. First results of functional analyses in rat hippocampal neurons neither revealed nor excluded a major contribution of miR-499 or miR-708 to dendritic spine morphogenesis. The present results suggest that research is warranted to elucidate the precise involvement of microRNAs and their downstream pathways in BD.

Regulation of AMPA receptor subunit GluA1 surface expression by PAK3 phosphorylation

AMPA receptors (AMPARs) are the major excitatory receptors of the brain and are fundamental to synaptic plasticity, memory, and cognition. Dynamic recycling of AMPARs in neurons is regulated through several types of posttranslational modification, including phosphorylation. Here, we identify a previously unidentified signal transduction cascade that modulates phosphorylation of serine residue 863 (S863) in the GluA1 AMPAR subunit and controls surface trafficking of GluA1 in neurons. Activation of the EphR-Ephrin signal transduction pathway enhances S863 phosphorylation. Further, EphB2 can interact with Zizimin1, a guanine-nucleotide exchange factor that activates Cdc42 and stimulates S863 phosphorylation in neurons. Among the numerous targets downstream of Cdc42, we determined that the p21-activated kinase-3 (PAK3) phosphorylates S863 in vitro. Moreover, specific loss of PAK3 expression and pharmacological inhibition of PAK both disrupt activity-dependent phosphorylation of S863 in cortical neurons. EphB2, Cdc42, and PAKs are broadly capable of controlling dendritic spine formation and synaptic plasticity and are implicated in multiple cognitive disorders. Collectively, these data delineate a novel signal cascade regulating AMPAR trafficking that may contribute to the molecular mechanisms that govern learning and cognition.

PAK1 and CtBP1 Regulate the Coupling of Neuronal Activity to Muscle Chromatin and Gene Expression

Acetylcholine receptor (AChR) expression in innervated muscle is limited to the synaptic region. Neuron-induced electrical activity participates in this compartmentalization by promoting the repression of AChR expression in the extrasynaptic regions. Here, we show that the corepressor CtBP1 (C-terminal binding protein 1) is present on the myogenin promoter together with repressive histone marks. shRNA-mediated downregulation of CtBP1 expression is sufficient to derepress myogenin and AChR expression in innervated muscle. Upon denervation, CtBP1 is displaced from the myogenin promoter and relocates to the cytoplasm, while repressive histone marks are replaced by activating ones concomitantly to the activation of myogenin expression. We also observed that upon denervation the p21-activated kinase 1 (PAK1) expression is upregulated, suggesting that phosphorylation by PAK1 may be involved in the relocation of CtBP1. Indeed, preventing CtBP1 Ser158 phosphorylation induces CtBP1 accumulation in the nuclei and abrogates the activation of myogenin and AChR expression. Altogether, these findings reveal a molecular mechanism to account for the coordinated control of chromatin modifications and muscle gene expression by presynaptic neurons via a PAK1/CtBP1 pathway.

Dietary magnesium restriction reduces amygdala-hypothalamic GluN1 receptor complex levels in mice

Reduced daily intake of magnesium (Mg(2+)) is suggested to contribute to depression. Indeed, preclinical studies show dietary magnesium restriction (MgR) elicits enhanced depression-like behaviour establishing a causal relationship. Amongst other mechanisms, Mg(2+) gates the activity of N-methyl-D-asparte (NMDA) receptors; however, it is not known whether reduced dietary Mg(2+) intake can indeed affect brain NMDA receptor complexes. Thus, the aim of the current study was to reveal whether MgR induces changes in brain NMDA receptor subunit composition that would indicate altered NMDA receptor regulation. The results revealed that enhanced depression-like behaviour elicited by MgR was associated with reduced amygdala-hypothalamic protein levels of GluN1-containing NMDA complexes. No change in GluN1 mRNA levels was observed indicating posttranslational changes were induced by dietary Mg(2+) restriction. To reveal possible protein interaction partners, GluN1 immunoprecipitation and proximity ligation assays were carried out revealing the expected GluN1 subunit association with GluN2A, GluN2B, but also novel interactions with GluA1, GluA2 in addition to known downstream signalling proteins. Chronic paroxetine treatment in MgR mice normalized enhanced depression-like behaviour, but did not alter protein levels of GluN1-containing NMDA receptors, indicating targets downstream of the NMDA receptor. Collectively, present data demonstrate that dietary MgR alters brain levels of GluN1-containing NMDA receptor complexes, containing GluN2A, GluN2B, AMPA receptors GluA1, GluA2 and several protein kinases. These data indicate that the modulation of dietary Mg(2+) intake may alter the function and signalling of this receptor complex indicating its involvement in the enhanced depression-like behaviour elicited by MgR.

Inhibition of invasion by glycogen synthase kinase-3 beta inhibitors through dysregulation of actin re-organisation via down-regulation of WAVE2

Cancer cell invasion is a critical phenomenon in cancer pathogenesis. Glycogen synthase kinase-3β (GSK-3β) has been reported to regulate cancer cell invasion both negatively and positively. Thus, the net effect of GSK-3β on invasion is unclear. In this report, we showed that GSK-3β inhibitors induced dysregulation of the actin cytoskeleton and functional insufficiency of focal adhesion, which resulted in suppressed invasion. In addition, WAVE2, an essential molecule for actin fibre branching, was down-regulated after GSK-3β inhibition. Collectively, we propose that the WAVE2-actin cytoskeleton axis is an important target of GSK-3β inhibitors in cancer cell invasion.

PAK1 regulates cortical development via promoting neuronal migration and progenitor cell proliferation

Background

p21-activated kinase 1 (PAK1) is a serine/threonine kinase known to be activated by the Rho family small GTPases and to play a key role in cytoskeletal reorganization, spine morphology and synaptic plasticity. PAK1 is also implicated in a number of neurodevelopmental and neurodegenerative diseases, including autism, intellectual disability and Alzheimer’s disease. However, the role of PAK1 in early brain development remains unknown.

Results

In this study, we employed genetic manipulations to investigate the role of PAK1 in the cerebral cortical development in mice. We showed that compared to the wild type littermates, PAK1 knockout mice have a reduction in the number of pyramidal neurons in several layers of the cerebral cortex, which is associated with a smaller pool of neural progenitor cells and impaired neuronal migration.

Conclusion

These results suggest that PAK1 regulates cortical development by promoting the proliferation of neural progenitor cells and facilitating the migration of these neurons to specific regions of the cortex.

Transcriptome sequencing and genome-wide association analyses reveal lysosomal function and actin cytoskeleton remodeling in schizophrenia and bipolar disorder

Schizophrenia (SCZ) and bipolar disorder (BPD) are severe mental disorders with high heritability. Clinicians have long noticed the similarities of clinic symptoms between these disorders. In recent years, accumulating evidence indicates some shared genetic liabilities. However, what is shared remains elusive. In this study, we conducted whole transcriptome analysis of post-mortem brain tissues (cingulate cortex) from SCZ, BPD and control subjects, and identified differentially expressed genes in these disorders. We found 105 and 153 genes differentially expressed in SCZ and BPD, respectively. By comparing the t-test scores, we found that many of the genes differentially expressed in SCZ and BPD are concordant in their expression level (q⩽0.01, 53 genes; q⩽0.05, 213 genes; q⩽0.1, 885 genes). Using genome-wide association data from the Psychiatric Genomics Consortium, we found that these differentially and concordantly expressed genes were enriched in association signals for both SCZ (P<10(-7)) and BPD (P=0.029). To our knowledge, this is the first time that a substantially large number of genes show concordant expression and association for both SCZ and BPD. Pathway analyses of these genes indicated that they are involved in the lysosome, Fc gamma receptor-mediated phagocytosis, regulation of actin cytoskeleton pathways, along with several cancer pathways. Functional analyses of these genes revealed an interconnected pathway network centered on lysosomal function and the regulation of actin cytoskeleton. These pathways and their interacting network were principally confirmed by an independent transcriptome sequencing data set of the hippocampus. Dysregulation of lysosomal function and cytoskeleton remodeling has direct impacts on endocytosis, phagocytosis, exocytosis, vesicle trafficking, neuronal maturation and migration, neurite outgrowth and synaptic density and plasticity, and different aspects of these processes have been implicated in SCZ and BPD.

Comparative Meta-Analysis of Transcriptomics Data during Cellular Senescence and In Vivo Tissue Ageing

Several studies have employed DNA microarrays to identify gene expression signatures that mark human ageing; yet the features underlying this complicated phenomenon remain elusive. We thus conducted a bioinformatics meta-analysis on transcriptomics data from human cell- and biopsy-based microarrays experiments studying cellular senescence or in vivo tissue ageing, respectively. We report that coregulated genes in the postmitotic muscle and nervous tissues are classified into pathways involved in cancer, focal adhesion, actin cytoskeleton, MAPK signalling, and metabolism regulation. Genes that are differentially regulated during cellular senescence refer to pathways involved in neurodegeneration, focal adhesion, actin cytoskeleton, proteasome, cell cycle, DNA replication, and oxidative phosphorylation. Finally, we revealed genes and pathways (referring to cancer, Huntington's disease, MAPK signalling, focal adhesion, actin cytoskeleton, oxidative phosphorylation, and metabolic signalling) that are coregulated during cellular senescence and in vivo tissue ageing. The molecular commonalities between cellular senescence and tissue ageing are also highlighted by the fact that pathways that were overrepresented exclusively in the biopsy- or cell-based datasets are modules either of the same reference pathway (e.g., metabolism) or of closely interrelated pathways (e.g., thyroid cancer and melanoma). Our reported meta-analysis has revealed novel age-related genes, setting thus the basis for more detailed future functional studies.

Regulators of G-protein-signaling proteins: negative modulators of G-protein-coupled receptor signaling

Regulators of G-protein-signaling (RGS) proteins are a category of intracellular proteins that have an inhibitory effect on the intracellular signaling produced by G-protein-coupled receptors (GPCRs). RGS along with RGS-like proteins switch on through direct contact G-alpha subunits providing a variety of intracellular functions through intracellular signaling. RGS proteins have a common RGS domain that binds to G alpha. RGS proteins accelerate GTPase and thus enhance guanosine triphosphate hydrolysis through the alpha subunit of heterotrimeric G proteins. As a result, they inactivate the G protein and quickly turn off GPCR signaling thus terminating the resulting downstream signals. Activity and subcellular localization of RGS proteins can be changed through covalent molecular changes to the enzyme, differential gene splicing, and processing of the protein. Other roles of RGS proteins have shown them to not be solely committed to being inhibitors but behave more as modulators and integrators of signaling. RGS proteins modulate the duration and kinetics of slow calcium oscillations and rapid phototransduction and ion signaling events. In other cases, RGS proteins integrate G proteins with signaling pathways linked to such diverse cellular responses as cell growth and differentiation, cell motility, and intracellular trafficking. Human and animal studies have revealed that RGS proteins play a vital role in physiology and can be ideal targets for diseases such as those related to addiction where receptor signaling seems continuously switched on.

Targeted pharmacological treatment of autism spectrum disorders: fragile X and Rett syndromes

Autism spectrum disorders (ASDs) are genetically and clinically heterogeneous and lack effective medications to treat their core symptoms. Studies of syndromic ASDs caused by single gene mutations have provided insights into the pathophysiology of autism. Fragile X and Rett syndromes belong to the syndromic ASDs in which preclinical studies have identified rational targets for drug therapies focused on correcting underlying neural dysfunction. These preclinical discoveries are increasingly translating into exciting human clinical trials. Since there are significant molecular and neurobiological overlaps among ASDs, targeted treatments developed for fragile X and Rett syndromes may be helpful for autism of different etiologies. Here, we review the targeted pharmacological treatment of fragile X and Rett syndromes and discuss related issues in both preclinical studies and clinical trials of potential therapies for the diseases.

Mouse models of PAK function

p21-activated kinases are a family of highly conserved protein serine/threonine kinases that are increasingly recognized as playing essential roles in a variety of key signaling processes. Genetic analyses in mice, using constitutive or regulated gene disruption, have provided important new insights into PAK function. In this paper, we review the genetic analysis of all six PAK genes in mice. These data address the singular and redundant functions of the various PAK genes and suggest therapeutic possibilities for small molecule PAK inhibitors or activators.

PAK family kinases: Physiological roles and regulation

The p21-activated kinases (PAKs) are a family of Ser/Thr protein kinases that are represented by six genes in humans (PAK 1-6), and are found in all eukaryotes sequenced to date. Genetic and knockdown experiments in frogs, fish and mice indicate group I PAKs are widely expressed, required for multiple tissue development, and particularly important for immune and nervous system function in the adult. The group II PAKs (human PAKs 4-6) are more enigmatic, but their restriction to metazoans and presence at cell-cell junctions suggests these kinases emerged to regulate junctional signaling. Studies of protozoa and fungal PAKs show that they regulate cell shape and polarity through phosphorylation of multiple cytoskeletal proteins, including microtubule binding proteins, myosins and septins. This chapter discusses what we know about the regulation of PAKs and their physiological role in different model organisms, based primarily on gene knockout studies.

Roles for DSCAM and DSCAML1 in central nervous system development and disease

DSCAMs (Down syndrome cell adhesion molecules) are a group of immunoglobulin-like transmembrane proteins that contain fibronectin III domains. The founding member of the family was isolated in a positional cloning study that sought to identify genes located on chromosome 21 at the locus 21q22.2-q22.3 that is implicated in the neurological and cardiac phenotypes associated with Down's syndrome. In Drosophila, Dscam proteins are involved in neuronal wiring, while in vertebrates, the role of these cell adhesion molecules in neurogenesis, dendritogenesis, axonal outgrowth, synaptogenesis, and synaptic plasticity is only just beginning to be understood. In this chapter, we will review the functions ascribed to the two paralogous proteins found in humans, DSCAM and DSCAML1 (DSCAM-like 1), based on findings in knockout mice. The signaling pathways downstream of DSCAM activation and the role of DSCAM miss-expression in disease will be also discussed, particularly with regard to the intellectual disability in Down's syndrome.

GIT1 and βPIX are essential for GABA(A) receptor synaptic stability and inhibitory neurotransmission

Effective inhibitory synaptic transmission requires efficient stabilization of GABA_A receptors (GABA_ARs) at synapses, which is essential for maintaining the correct excitatory-inhibitory balance in the brain. However, the signaling mechanisms that locally regulate synaptic GABA_AR membrane dynamics remain poorly understood. Using a combination of molecular, imaging, and electrophysiological approaches, we delineate a GIT1/βPIX/Rac1/PAK signaling pathway that modulates F-actin and is important for maintaining surface GABA_AR levels, inhibitory synapse integrity, and synapse strength. We show that GIT1 and βPIX are required for synaptic GABA_AR surface stability through the activity of the GTPase Rac1 and downstream effector PAK. Manipulating this pathway using RNAi, dominant-negative and pharmacological approaches leads to a disruption of GABA_AR clustering and decrease in the strength of synaptic inhibition. Thus, the GIT1/βPIX/Rac1/PAK pathway plays a crucial role in regulating GABA_AR synaptic stability and hence inhibitory synaptic transmission with important implications for inhibitory plasticity and information processing in the brain.

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GIT1 and βPIX are present at inhibitory synapses and complex with GABA_ARs

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GIT1 and βPIX are important for GABA_AR clustering and inhibitory transmission

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Rac1 and PAK activity is required for stabilization of GABA_ARs at synapses

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A GIT1/βPIX/Rac1/PAK pathway is required for inhibitory synaptic transmission

Participation of group I p21-activated kinases in neuroplasticity

PAKs are a family of serine/threonine protein kinases activated by small GTPases of the Rho family, including Rac and Cdc42, and are categorized into group I (isoforms 1, 2 and 3) and group II (isoforms 4, 5 and 6). PAK1 and PAK3 are critically involved in biological mechanisms associated with neurodevelopment, neuroplasticity and maturation of the nervous system, and changes in their activity have been detected in pathological disorders, such as Alzheimer's disease, Huntington's disease and mental retardation. The group I PAKs have been associated with neurological processes due to their involvement in intracellular mechanisms that result in molecular and cellular morphological alterations that promote cytoskeletal outgrowth, increasing the efficiency of synaptic transmission. Their substrates in these processes include other intracellular signaling molecules, such as Raf, Mek and LIMK, as well as other components of the cytoskeleton, such as MLC and FLNa. In this review, we describe the characteristics of group I PAKs, such as their molecular structure, mechanisms of activation and importance in the neurobiological processes involved in synaptic plasticity.

Loss of Cdc42 leads to defects in synaptic plasticity and remote memory recall

Cdc42 is a signaling protein important for reorganization of actin cytoskeleton and morphogenesis of cells. However, the functional role of Cdc42 in synaptic plasticity and in behaviors such as learning and memory are not well understood. Here we report that postnatal forebrain deletion of Cdc42 leads to deficits in synaptic plasticity and in remote memory recall using conditional knockout of Cdc42. We found that deletion of Cdc42 impaired LTP in the Schaffer collateral synapses and postsynaptic structural plasticity of dendritic spines in CA1 pyramidal neurons in the hippocampus. Additionally, loss of Cdc42 did not affect memory acquisition, but instead significantly impaired remote memory recall. Together these results indicate that the postnatal functions of Cdc42 may be crucial for the synaptic plasticity in hippocampal neurons, which contribute to the capacity for remote memory recall.

Cerebral palsy, epilepsy, and severe intellectual disability in a patient with 3q29 microduplication syndrome

Interstitial microduplication of 3q29 has been recently described. Individuals with this syndrome have widely variable phenotypes. We describe the first clinical case with a 1.607 Mb duplication at 3q29 (chr3: 195,731,956-197,339,329), accompanied by severe intellectual disability, epilepsy, and cerebral palsy. This duplication involves 22 genes; PAK2, DLG1, BDH1, and FBXO45 are implicated in neuronal development and synaptic function and could play an important role in this syndrome. We propose considering genetic studies, particularly array comparative genomic hybridization, in patients with epilepsy and/or cerebral palsy of unknown etiology when dysmorphic features are present.

p21-Activated protein kinases and their emerging roles in glucose homeostasis

p21-Activated protein kinases (PAKs) are centrally involved in a plethora of cellular processes and functions. Their function as effectors of small GTPases Rac1 and Cdc42 has been extensively studied during the past two decades, particularly in the realms of cell proliferation, apoptosis, and hence tumorigenesis, as well as cytoskeletal remodeling and related cellular events in health and disease. In recent years, a large number of studies have shed light onto the fundamental role of group I PAKs, most notably PAK1, in metabolic homeostasis. In skeletal muscle, PAK1 was shown to mediate the function of insulin on stimulating GLUT4 translocation and glucose uptake, while in pancreatic β-cells, PAK1 participates in insulin granule localization and vesicle release. Furthermore, we demonstrated that PAK1 mediates the cross talk between insulin and Wnt/β-catenin signaling pathways and hence regulates gut proglucagon gene expression and the production of the incretin hormone glucagon-like peptide-1 (GLP-1). The utilization of chemical inhibitors of PAK and the characterization of Pak1(-/-) mice enabled us to gain mechanistic insights as well as to assess the overall contribution of PAKs in metabolic homeostasis. This review summarizes our current understanding of PAKs, with an emphasis on the emerging roles of PAK1 in glucose homeostasis.

Parental binge alcohol abuse alters F1 generation hypothalamic gene expression in the absence of direct fetal alcohol exposure

Adolescent binge alcohol exposure has long-lasting effects on the expression of hypothalamic genes that regulate the stress response, even in the absence of subsequent adult alcohol exposure. This suggests that alcohol can induce permanent gene expression changes, potentially through epigenetic modifications to specific genes. Epigenetic modifications can be transmitted to future generations therefore, and in these studies we investigated the effects of adolescent binge alcohol exposure on hypothalamic gene expression patterns in the F1 generation offspring. It has been well documented that maternal alcohol exposure during fetal development can have devastating neurological consequences. However, less is known about the consequences of maternal and/or paternal alcohol exposure outside of the gestational time frame. Here, we exposed adolescent male and female rats to a repeated binge EtOH exposure paradigm and then mated them in adulthood. Hypothalamic samples were taken from the offspring of these animals at postnatal day (PND) 7 and subjected to a genome-wide microarray analysis followed by qRT-PCR for selected genes. Importantly, the parents were not intoxicated at the time of mating and were not exposed to EtOH at any time during gestation therefore the offspring were never directly exposed to EtOH. Our results showed that the offspring of alcohol-exposed parents had significant differences compared to offspring from alcohol-naïve parents. Specifically, major differences were observed in the expression of genes that mediate neurogenesis and synaptic plasticity during neurodevelopment, genes important for directing chromatin remodeling, posttranslational modifications or transcription regulation, as well as genes involved in regulation of obesity and reproductive function. These data demonstrate that repeated binge alcohol exposure during pubertal development can potentially have detrimental effects on future offspring even in the absence of direct fetal alcohol exposure.

Pak3 promotes cell cycle exit and differentiation of β-cells in the embryonic pancreas and is necessary to maintain glucose homeostasis in adult mice

The transcription factor neurogenin3 (Ngn3) triggers islet cell differentiation in the developing pancreas. However, little is known about the molecular mechanisms coupling cell cycle exit and differentiation in Ngn3(+) islet progenitors. We identified a novel effector of Ngn3 endocrinogenic function, the p21 protein-activated kinase Pak3, known to control neuronal differentiation and implicated in X-linked intellectual disability in humans. We show that Pak3 expression is initiated in Ngn3(+) endocrine progenitor cells and next maintained in maturing hormone-expressing cells during pancreas development as well as in adult islet cells. In Pak3-deficient embryos, the proliferation of Ngn3(+) progenitors and β-cells is transiently increased concomitantly with an upregulation of Ccnd1. β-Cell differentiation is impaired at E15.5 but resumes at later stages. Pak3-deficient mice do not develop overt diabetes but are glucose intolerant under high-fat diet (HFD). In the intestine, Pak3 is expressed in enteroendocrine cells but is not necessary for their differentiation. Our results indicate that Pak3 is a novel regulator of β-cell differentiation and function. Pak3 acts downstream of Ngn3 to promote cell cycle exit and differentiation in the embryo by a mechanism that might involve repression of Ccnd1. In the adult, Pak3 is required for the proper control of glucose homeostasis under challenging HFD.

Advancing avian behavioral neuroendocrinology through genomics

Genome technologies are transforming all areas of biology, including the study of hormones, brain and behavior. Annotated reference genome assemblies are rapidly being produced for many avian species. Here we briefly review the basic concepts and tools used in genomics. We then consider how these are informing the study of avian behavioral neuroendocrinology, focusing in particular on lessons from the study of songbirds. We discuss the impact of having a complete "parts list" for an organism; the transformational potential of studying large sets of genes at once instead one gene at a time; the growing recognition that environmental and behavioral signals trigger massive shifts in gene expression in the brain; and the prospects for using comparative genomics to uncover the genetic roots of behavioral variation. Throughout, we identify promising new directions for bolstering the application of genomic information to further advance the study of avian brain and behavior.

Shank3 deficiency induces NMDA receptor hypofunction via an actin-dependent mechanism

Shank3, which encodes a scaffolding protein at glutamatergic synapses, is a genetic risk factor for autism. In this study, we examined the impact of Shank3 deficiency on the NMDA-type glutamate receptor, a key player in cognition and mental illnesses. We found that knockdown of Shank3 with a small interfering RNA (siRNA) caused a significant reduction of NMDAR-mediated ionic or synaptic current, as well as the surface expression of NR1 subunits, in rat cortical cultures. The effect of Shank3 siRNA on NMDAR currents was blocked by an actin stabilizer, and was occluded by an actin destabilizer, suggesting the involvement of actin cytoskeleton. Since actin dynamics is regulated by the GTPase Rac1 and downstream effector p21-activated kinase (PAK), we further examined Shank3 regulation of NMDARs when Rac1 or PAK was manipulated. We found that the reducing effect of Shank3 siRNA on NMDAR currents was mimicked and occluded by specific inhibitors for Rac1 or PAK, and was blocked by constitutively active Rac1 or PAK. Immunocytochemical data showed a strong reduction of F-actin clusters after Shank3 knockdown, which was occluded by a PAK inhibitor. Inhibiting cofilin, the primary downstream target of PAK and a major actin depolymerizing factor, prevented Shank3 siRNA from reducing NMDAR currents and F-actin clusters. Together, these results suggest that Shank3 deficiency induces NMDAR hypofunction by interfering with the Rac1/PAK/cofilin/actin signaling, leading to the loss of NMDAR membrane delivery or stability. It provides a potential mechanism for the role of Shank3 in cognitive deficit in autism.

p21-Activated kinase (PAK) is required for Bone Morphogenetic Protein (BMP)-induced dendritogenesis in cortical neurons

Bone Morphogenetic Proteins (BMPs) are crucial for many aspects of the development and differentiation of the nervous system and are important in controlling cytoskeletal remodeling during neuronal morphogenesis. BMPs are TGFβ superfamily members that signal through a heteromeric complex of type I and type II BMP receptors. The BMPRII receptor is particularly important in mediating remodeling of the neuronal cytoskeleton through the activation of BMPRII-bound cytoskeletal regulators, such as LIM Kinase (LIMK). Here, we show that PAK1, a key regulator of diverse neuronal processes and an upstream activator of LIMK, binds to the BMP type I receptor, ALK2. Although, PAK1 is dispensable for activation of the Smad transcriptional mediators, abrogation of PAK1 expression or inhibition of PAK1 activity prevents BMP-induced neurite outgrowth in cultured neuroblastoma cell lines. Moreover, in primary murine embryonic cortical neurons, inhibition of PAK activity blocks BMP7-induced cofilin phosphorylation, prevents remodeling of the actin cytoskeleton and thereby blocks BMP7-induced dendrite formation. Thus, we propose a model in which BMP7 signaling leads to the recruitment of ALK2-bound PAK1 to BMPRII, which binds a downstream regulator of the actin cytoskeleton, LIMK1, and that the BMP receptor complex thereby acts as a scaffold to localize and coordinate actin cytoskeletal remodeling. We propose that this scaffold plays a key role in mediating BMP7-dependent dendritogenesis in primary cortical neurons.

Maturin is a novel protein required for differentiation during primary neurogenesis

Proliferation and differentiation are tightly controlled during neural development. In the embryonic neural plate, primary neurogenesis is driven by the proneural pathway. Here we report the characterization of Maturin, a novel, evolutionarily conserved protein that is required for normal primary neurogenesis. Maturin is detected throughout the early nervous system, yet it is most strongly expressed in differentiating neurons of the embryonic fish, frog and mouse nervous systems. Maturin expression can be induced by the proneural transcription factors Neurog2, Neurod1, and Ebf3. Maturin overexpression promotes neurogenesis, while loss-of-function inhibits the differentiation of neuronal progenitors, resulting in neural plate expansion. Maturin knockdown blocks the ability of Neurog2, Neurod1, and Ebf3 to drive ectopic neurogenesis. Maturin and Pak3, are both required for, and can synergize to promote differentiation of the primary neurons in vivo. Together, our results suggest that Maturin functions during primary neurogenesis and is required for the proneural pathway to regulate neural differentiation.

Kalirin-7 mediates cocaine-induced AMPA receptor and spine plasticity, enabling incentive sensitization

It is well established that behavioral sensitization to cocaine is accompanied by increased spine density and AMPA receptor (AMPAR) transmission in the nucleus accumbens (NAc), but two major questions remain unanswered. Are these adaptations mechanistically coupled? And, given that they can be dissociated from locomotor sensitization, what is their functional significance? We tested the hypothesis that the guanine-nucleotide exchange factor Kalirin-7 (Kal-7) couples cocaine-induced AMPAR and spine upregulation and that these adaptations underlie sensitization of cocaine's incentive-motivational properties-the properties that make it "wanted." Rats received eight daily injections of saline or cocaine. On withdrawal day 14, we found that Kal-7 levels and activation of its downstream effectors Rac-1 and PAK were increased in the NAc of cocaine-sensitized rats. Furthermore, AMPAR surface expression and spine density were increased, as expected. To determine whether these changes require Kal-7, a lentiviral vector expressing Kal-7 shRNA was injected into the NAc core before cocaine exposure. Knocking down Kal-7 abolished the AMPAR and spine upregulation normally seen during cocaine withdrawal. Despite the absence of these adaptations, rats with reduced Kal-7 levels developed locomotor sensitization. However, incentive sensitization, which was assessed by how rapidly rats learned to self-administer a threshold dose of cocaine, was severely impaired. These results identify a signaling pathway coordinating AMPAR and spine upregulation during cocaine withdrawal, demonstrate that locomotor and incentive sensitization involve divergent mechanisms, and link enhanced excitatory transmission in the NAc to incentive sensitization.

Nonautonomous regulation of neuronal migration by insulin signaling, DAF-16/FOXO, and PAK-1

Neuronal migration is essential for nervous system development in all organisms and is regulated in the nematode, C. elegans, by signaling pathways that are conserved in humans. Here, we demonstrate that the insulin/IGF-1-PI3K signaling pathway modulates the activity of the DAF-16/FOXO transcription factor to regulate the anterior migrations of the hermaphrodite-specific neurons (HSNs) during embryogenesis of C. elegans. When signaling is reduced, DAF-16 is activated and promotes migration; conversely, when signaling is enhanced, DAF-16 is inactivated, and migration is inhibited. We show that DAF-16 acts nonautonomously in the hypodermis to promote HSN migration. Furthermore, we identify PAK-1, a p21-activated kinase, as a downstream mediator of insulin/IGF-1-DAF-16 signaling in the nonautonomous control of HSN migration. Because a FOXO-Pak1 pathway was recently shown to regulate mammalian neuronal polarity, our findings indicate that the roles of FOXO and Pak1 in neuronal migration are most likely conserved from C. elegans to higher organisms.

PAK inactivation impairs social recognition in 3xTg-AD Mice without increasing brain deposition of tau and Aβ

Defects in p21-activated kinase (PAK) are suspected to play a role in cognitive symptoms of Alzheimer's disease (AD). Dysfunction in PAK leads to cofilin activation, drebrin displacement from its actin-binding site, actin depolymerization/severing, and, ultimately, defects in spine dynamics and cognitive impairment in mice. To determine the role of PAK in AD, we first quantified PAK by immunoblotting in homogenates from the parietal neocortex of subjects with a clinical diagnosis of no cognitive impairment (n = 12), mild cognitive impairment (n = 12), or AD (n = 12). A loss of total PAK, detected in the cortex of AD patients (-39% versus controls), was correlated with cognitive impairment (r(2) = 0.148, p = 0.027) and deposition of total and phosphorylated tau (r(2) = 0.235 and r(2) = 0.206, respectively), but not with Aβ42 (r(2) = 0.056). Accordingly, we found a decrease of total PAK in the cortex of 12- and 20-month-old 3xTg-AD mice, an animal model of AD-like Aβ and tau neuropathologies. To determine whether PAK dysfunction aggravates AD phenotype, 3xTg-AD mice were crossed with dominant-negative PAK mice. PAK inactivation led to obliteration of social recognition in old 3xTg-AD mice, which was associated with a decrease in cortical drebrin (-25%), but without enhancement of Aβ/tau pathology or any clear electrophysiological signature. Overall, our data suggest that PAK decrease is a consequence of AD neuropathology and that therapeutic activation of PAK may exert symptomatic benefits on high brain function.

The p21-activated kinase Mbt is a component of the apical protein complex in central brain neuroblasts and controls cell proliferation

The final size of the central nervous system is determined by precisely controlled generation, proliferation and death of neural stem cells. We show here that the Drosophila PAK protein Mushroom bodies tiny (Mbt) is expressed in central brain progenitor cells (neuroblasts) and becomes enriched to the apical cortex of neuroblasts in a cell cycle- and Cdc42-dependent manner. Using mushroom body neuroblasts as a model system, we demonstrate that in the absence of Mbt function, neuroblasts and their progeny are correctly specified and are able to generate different neuron subclasses as in the wild type, but are impaired in their proliferation activity throughout development. In general, loss of Mbt function does not interfere with establishment or maintenance of cell polarity, orientation of the mitotic spindle and organization of the actin or tubulin cytoskeleton in central brain neuroblasts. However, we show that mbt mutant neuroblasts are significantly reduced in cell size during different stages of development, which is most pronounced for mushroom body neuroblasts. This phenotype correlates with reduced mitotic activity throughout development. Additionally, postembryonic neuroblasts are lost prematurely owing to apoptosis. Yet, preventing apoptosis did not rescue the loss of neurons seen in the adult mushroom body of mbt mutants. From these results, we conclude that Mbt is part of a regulatory network that is required for neuroblast growth and thereby allows proper proliferation of neuroblasts throughout development.

Rac1 selective activation improves retina ganglion cell survival and regeneration

In adult mammals, after optic nerve injury, retinal ganglion cells (RGCs) do not regenerate their axons and most of them die by apoptosis within a few days. Recently, several strategies that activate neuronal intracellular pathways were proposed to prevent such degenerative processes. The rho-related small GTPase Rac1 is part of a complex, still not fully understood, intracellular signaling network, mediating in neurons many effects, including axon growth and cell survival. However, its role in neuronal survival and regeneration in vivo has not yet been properly investigated. To address this point we intravitreally injected selective cell-penetrating Rac1 mutants after optic nerve crush and studied the effect on RGC survival and axonal regeneration. We injected two well-characterized L61 constitutively active Tat-Rac1 fusion protein mutants, in which a second F37A or Y40C mutation confers selectivity in downstream signaling pathways. Results showed that, 15 days after crush, both mutants were able to improve survival and to prevent dendrite degeneration, while the one harboring the F37A mutation also improved axonal regeneration. The treatment with F37A mutant for one month did not improve the axonal elongation respect to 15 days. Furthermore, we found an increase of Pak1 T212 phosphorylation and ERK1/2 expression in RGCs after F37A treatment, whereas ERK1/2 was more activated in glial cells after Y40C administration. Our data suggest that the selective activation of distinct Rac1-dependent pathways could represent a therapeutic strategy to counteract neuronal degenerative processes in the retina.

Postsynaptic density scaffold SAP102 regulates cortical synapse development through EphB and PAK signaling pathway

Membrane-associated guanylate kinases (MAGUKs), including SAP102, PSD-95, PSD-93, and SAP97, are scaffolding proteins for ionotropic glutamate receptors at excitatory synapses. MAGUKs play critical roles in synaptic plasticity; however, details of signaling roles for each MAGUK remain largely unknown. Here we report that SAP102 regulates cortical synapse development through the EphB and PAK signaling pathways. Using lentivirus-delivered shRNAs, we found that SAP102 and PSD-95, but not PSD-93, are necessary for excitatory synapse formation and synaptic AMPA receptor (AMPAR) localization in developing mouse cortical neurons. SAP102 knockdown (KD) increased numbers of elongated dendritic filopodia, which is often observed in mouse models and human patients with mental retardation. Further analysis revealed that SAP102 coimmunoprecipitated the receptor tyrosine kinase EphB2 and RacGEF Kalirin-7 in neonatal cortex, and SAP102 KD reduced surface expression and dendritic localization of EphB. Moreover, SAP102 KD prevented reorganization of actin filaments, synapse formation, and synaptic AMPAR trafficking in response to EphB activation triggered by its ligand ephrinB. Last, p21-activated kinases (PAKs) were downregulated in SAP102 KD neurons. These results demonstrate that SAP102 has unique roles in cortical synapse development by mediating EphB and its downstream PAK signaling pathway. Both SAP102 and PAKs are associated with X-linked mental retardation in humans; thus, synapse formation mediated by EphB/SAP102/PAK signaling in the early postnatal brain may be crucial for cognitive development.

miR-23b regulates cytoskeletal remodeling, motility and metastasis by directly targeting multiple transcripts

Uncontrolled cell proliferation and cytoskeletal remodeling are responsible for tumor development and ultimately metastasis. A number of studies have implicated microRNAs in the regulation of cancer cell invasion and migration. Here, we show that miR-23b regulates focal adhesion, cell spreading, cell-cell junctions and the formation of lamellipodia in breast cancer (BC), implicating a central role for it in cytoskeletal dynamics. Inhibition of miR-23b, using a specific sponge construct, leads to an increase of cell migration and metastatic spread in vivo, indicating it as a metastatic suppressor microRNA. Clinically, low miR-23b expression correlates with the development of metastases in BC patients. Mechanistically, miR-23b is able to directly inhibit a number of genes implicated in cytoskeletal remodeling in BC cells. Through intracellular signal transduction, growth factors activate the transcription factor AP-1, and we show that this in turn reduces miR-23b levels by direct binding to its promoter, releasing the pro-invasive genes from translational inhibition. In aggregate, miR-23b expression invokes a sophisticated interaction network that co-ordinates a wide range of cellular responses required to alter the cytoskeleton during cancer cell motility.

The neural cell adhesion molecule (NCAM) associates with and signals through p21-activated kinase 1 (Pak1)

The Neural cell adhesion molecule (NCAM) plays an important role in regulation of nervous system development. To expand our understanding of the molecular mechanisms via which NCAM influences differentiation of neurons, we used a yeast two-hybrid screening to search for new binding partners of NCAM and identified p21-activated kinase 1 (Pak1). We show that NCAM interacts with Pak1 in growth cones of neurons. The autophosphorylation and activity of Pak1 were enhanced when isolated growth cones were incubated with NCAM function triggering antibodies, which mimic the interaction between NCAM and its extracellular ligands. The association of Pak1 with cell membranes, the efficiency of Pak1 binding to its activators, and Pak1 activity were inhibited in brains of NCAM-deficient mice. NCAM-dependent Pak1 activation was abolished after lipid raft disruption, suggesting that NCAM promotes Pak1 activation in the lipid raft environment. Phosphorylation of the downstream Pak1 effectors LIMK1 and cofilin was reduced in growth cones from NCAM-deficient neurons, which was accompanied by decreased levels of filamentous actin and inhibited filopodium mobility in the growth cones. Dominant-negative Pak1 inhibited and constitutively active Pak1 enhanced the ability of neurons to increase neurite outgrowth in response to the extracellular ligands of NCAM. Our combined observations thus indicate that NCAM activates Pak1 to drive actin polymerization to promote neuronal differentiation.

PAK-PIX interactions regulate adhesion dynamics and membrane protrusion to control neurite outgrowth

The roles of P21-activated kinase (PAK) in the regulation of axon outgrowth downstream of extracellular matrix (ECM) proteins are poorly understood. Here we show that PAK1-3 and PIX are expressed in the developing spinal cord and differentially localize to point contacts and filopodial tips within motile growth cones. Using a specific interfering peptide called PAK18, we found that axon outgrowth is robustly stimulated on laminin by partial inhibition of PAK-PIX interactions and PAK function, whereas complete inhibition of PAK function stalls axon outgrowth. Furthermore, modest inhibition of PAK-PIX stimulates the assembly and turnover of growth cone point contacts, whereas strong inhibition over-stabilizes adhesions. Point mutations within PAK confirm the importance of PIX binding. Together our data suggest that regulation of PAK-PIX interactions in growth cones controls neurite outgrowth by influencing the activity of several important mediators of actin filament polymerization and retrograde flow, as well as integrin-dependent adhesion to laminin.

TIPE2 protein serves as a negative regulator of phagocytosis and oxidative burst during infection

Phagocytosis and oxidative burst are two major effector arms of innate immunity. Although it is known that both are activated by Toll-like receptors (TLRs) and Rac GTPases, how their strengths are controlled in quiescent and TLR-activated cells is not clear. We report here that TIPE2 (TNFAIP8L2) serves as a negative regulator of innate immunity by linking TLRs to Rac. TLRs control the expression levels of TIPE2, which in turn dictates the strengths of phagocytosis and oxidative burst by binding to and blocking Rac GTPases. Consequently, TIPE2 knockout cells have enhanced phagocytic and bactericidal activities and TIPE2 knockout mice are resistant to bacterial infection. Thus, TIPE2 sets the strengths of phagocytosis and oxidative burst and may be targeted to effectively control infections.

A cell-based fascin bioassay identifies compounds with potential anti-metastasis or cognition-enhancing functions

The actin-bundling protein fascin is a key mediator of tumor invasion and metastasis and its activity drives filopodia formation, cell-shape changes and cell migration. Small-molecule inhibitors of fascin block tumor metastasis in animal models. Conversely, fascin deficiency might underlie the pathogenesis of some developmental brain disorders. To identify fascin-pathway modulators we devised a cell-based assay for fascin function and used it in a bidirectional drug screen. The screen utilized cultured fascin-deficient mutant Drosophila neurons, whose neurite arbors manifest the 'filagree' phenotype. Taking a repurposing approach, we screened a library of 1040 known compounds, many of them FDA-approved drugs, for filagree modifiers. Based on scaffold distribution, molecular-fingerprint similarities, and chemical-space distribution, this library has high structural diversity, supporting its utility as a screening tool. We identified 34 fascin-pathway blockers (with potential anti-metastasis activity) and 48 fascin-pathway enhancers (with potential cognitive-enhancer activity). The structural diversity of the active compounds suggests multiple molecular targets. Comparisons of active and inactive compounds provided preliminary structure-activity relationship information. The screen also revealed diverse neurotoxic effects of other drugs, notably the 'beads-on-a-string' defect, which is induced solely by statins. Statin-induced neurotoxicity is enhanced by fascin deficiency. In summary, we provide evidence that primary neuron culture using a genetic model organism can be valuable for early-stage drug discovery and developmental neurotoxicity testing. Furthermore, we propose that, given an appropriate assay for target-pathway function, bidirectional screening for brain-development disorders and invasive cancers represents an efficient, multipurpose strategy for drug discovery.

The p21-activated kinase PAK3 forms heterodimers with PAK1 in brain implementing trans-regulation of PAK3 activity

p21-activated kinase 1 (PAK1) and PAK3 belong to group I of the PAK family and control cell movement and division. They also regulate dendritic spine formation and maturation in the brain, and play a role in synaptic transmission and synaptic plasticity. PAK3, in particular, is known for its implication in X-linked intellectual disability. The pak3 gene is expressed in neurons as a GTPase-regulated PAK3a protein and also as three splice variants which display constitutive kinase activity. PAK1 regulation is based on its homodimerization, forming an inactive complex. Here, we analyze the PAK3 capacity to dimerize and show that although PAK3a is able to homodimerize, it is more likely to form heterodimeric complexes with PAK1. We further show that two intellectual disability mutations impair dimerization with PAK1. The b and c inserts present in the regulatory domain of PAK3 splice variants decrease the dimerization but retain the capacity to form heterodimers with PAK1. PAK1 and PAK3 are co-expressed in neurons, are colocalized within dendritic spines, co-purify with post-synaptic densities, and co-immunoprecipitate in brain lysates. Using kinase assays, we demonstrate that PAK1 inhibits the activity of PAK3a but not of the splice variant PAK3b in a trans-regulatory manner. Altogether, these results show that PAK3 and PAK1 signaling may be coordinated by heterodimerization.

Methods for treating neurological conditions (WO2011159945)

This patent application claims that inhibition of p21-activated kinases (PAK) reverses, partially reverses or delays clinical signs in neurological conditions (main claim for Huntington's disease (HD), substance abuse and addiction, Parkinson's disease, depression, bipolar disorder, anxiety disorder, posttraumatic stress disorder and neurofibromatosis). Several compounds with a pyrido-[2,3-d]pyrimidine-7(8H)-one core and high affinity to the catalytic domain of PAK1-4 are described in the patent. These PAK inhibitors are hypothesized to exert beneficial effects on clinical symptoms via modulation of dendritic spine morphology and/or synaptic function. Preliminary preclinical data suggest that PAK inhibition may be an interesting approach for the treatment of HD, neurofibromatosis and fragile X syndrome, while data for other neurological conditions are missing. Current limitations call for a comprehensive characterization of the role of PAK dysfunction in neurological disorders before further testing the effect of PAK inhibitors in relevant preclinical models. If ever, it will probably take many years before the most promising compounds will head to the clinic for further assessment in patients with neurological disorders.

Synapses of amphids defective (SAD-A) kinase promotes glucose-stimulated insulin secretion through activation of p21-activated kinase (PAK1) in pancreatic β-Cells

The p21-activated kinase-1 (PAK1) is implicated in regulation of insulin exocytosis as an effector of Rho GTPases. PAK1 is activated by the onset of glucose-stimulated insulin secretion (GSIS) through phosphorylation of Thr-423, a major activation site by Cdc42 and Rac1. However, the kinase(s) that phosphorylates PAK1 at Thr-423 in islet β-cells remains elusive. The present studies identified SAD-A (synapses of amphids defective), a member of AMP-activated protein kinase-related kinases exclusively expressed in brain and pancreas, as a key regulator of GSIS through activation of PAK1. We show that SAD-A directly binds to PAK1 through its kinase domain. The interaction is mediated by the p21-binding domain (PBD) of PAK1 and requires both kinases in an active conformation. The binding leads to direct phosphorylation of PAK1 at Thr-423 by SAD-A, triggering the onset of GSIS from islet β-cells. Consequently, ablation of PAK1 kinase activity or depletion of PAK1 expression completely abolishes the potentiating effect of SAD-A on GSIS. Consistent with its role in regulating GSIS, overexpression of SAD-A in MIN6 islet β-cells significantly stimulated cytoskeletal remodeling, which is required for insulin exocytosis. Together, the present studies identified a critical role of SAD-A in the activation of PAK1 during the onset of insulin exocytosis.

Epstein-Barr virus-encoded LMP1 interacts with FGD4 to activate Cdc42 and thereby promote migration of nasopharyngeal carcinoma cells

Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC), a human malignancy notorious for its highly metastatic nature. Among EBV-encoded genes, latent membrane protein 1 (LMP1) is expressed in most NPC tissues and exerts oncogenicity by engaging multiple signaling pathways in a ligand-independent manner. LMP1 expression also results in actin cytoskeleton reorganization, which modulates cell morphology and cell motility— cellular process regulated by RhoGTPases, such as Cdc42. Despite the prominent association of Cdc42 activation with tumorigenesis, the molecular basis of Cdc42 activation by LMP1 in NPC cells remains to be elucidated. Here using GST-CBD (active Cdc42-binding domain) as bait in GST pull-down assays to precipitate active Cdc42 from cell lysates, we demonstrated that LMP1 acts through its transmembrane domains to preferentially induce Cdc42 activation in various types of epithelial cells, including NPC cells. Using RNA interference combined with re-introduction experiments, we identified FGD4 (FYVE, RhoGEF and PH domain containing 4) as the GEF (guanine nucleotide exchange factor) responsible for the activation of Cdc42 by LMP1. Serial deletion experiments and co-immunoprecipitation assays further revealed that ectopically expressed FGD4 modulated LMP1-mediated Cdc42 activation by interacting with LMP1. Moreover, LMP1, through its transmembrane domains, directly bound FGD4 and enhanced FGD4 activity toward Cdc42, leading to actin cytoskeleton rearrangement and increased motility of NPC cells. Depletion of FGD4 or Cdc42 significantly reduced (∼50%) the LMP1-stimulated cell motility, an effect that was partially reversed by expression of a constitutively active mutant of Cdc42. Finally, quantitative RT-PCR and immunohistochemistry analyses showed that FGD4 and LMP1 were expressed in NPC tissues, supporting the potential physiologically relevance of this mechanism in NPC. Collectively, our results not only uncover a novel mechanism underlying LMP1-mediated Cdc42 activation, namely LMP1 interaction with FGD4, but also functionally link FGD4 to NPC tumorigenesis.

Epstein-Barr virus (EBV) is closely associated with human malignancies, including nasopharyngeal carcinoma (NPC). Among EBV-expressed genes, latent membrane protein 1 (LMP1) has been detected in most NPC tissues and has the ability to transform cell growth and drive cell migration, both of which are highly associated with tumorigenesis and tumor progression. Previous reports have demonstrated that cell migration primarily involves cytoskeleton rearrangement, and the RhoGTPase Cdc42 is known to actively mediate such rearrangement processes. Using LMP1-expressing NPC cells, we discovered that LMP1 induces Cdc42 activation by directly binding to FGD4, a positive regulator of Cdc42, thereby promoting motility of NPC cells. The observed correlation between FGD4 and LMP1 expression in NPC tissues provides support of physiological relevance. Notably, FGD4 has recently been shown to be responsible for a type of inherited neural disease. Our findings not only provide a novel insight into EBV pathogenesis, but also suggest a role for FGD4 in tumorigenesis.

p21-Activated kinase inhibitors: a patent review

INTRODUCTION

The p21-activated kinase (PAK) family of serine/threonine protein kinases is activated by binding to the small (p21) GTP-binding proteins Cdc42 and Rac. The PAK family plays important roles in cytoskeletal organisation, cellular morphogenesis and survival, and members of this family have been implicated in a wide range of diseases including cancer, infectious diseases, neurological disorders and arthritis.

AREAS COVERED

The present review seeks to summarise recent (up to 2011) reports of small-molecule inhibitors of p21-activated kinases. Where patent applications describe activity against a broad range of kinases and no information was provided specifically on PAK inhibition, these are excluded from this review. In patents considered to be relevant, exemplary compounds were selected and highlighted based on their representation of the chemical matter claimed, potencies, structural features and subsequent disclosure of their properties. Selected information from non-patent literature was also included.

EXPERT OPINION

A considerable amount of research has been devoted over the past 15 years to exploring the role of PAKs in a wide range of diseases, with a focus on oncology. Published PAK inhibitors are still comparatively rare and few exhibit satisfactory kinase selectivity and 'drug-like' properties. A key question is which profile, pan-PAK, group selective or isoform selective, holds the most promise from both therapeutic and safety standpoints. To investigate this question, isoform-selective, as well as kinome-selective, PAK inhibitor tool compounds will be needed. Pfizer was the first company to progress a PAK inhibitor (pan-PAK) to clinical development; it is expected that, despite the difficulties, other PAK inhibitors will soon follow.

Identification of neuronal substrates implicates Pak5 in synaptic vesicle trafficking

Synaptic transmission is mediated by a complex set of molecular events that must be coordinated in time and space. While many proteins that function at the synapse have been identified, the signaling pathways regulating these molecules are poorly understood. Pak5 (p21-activated kinase 5) is a brain-specific isoform of the group II Pak kinases whose substrates and roles within the central nervous system are largely unknown. To gain insight into the physiological roles of Pak5, we engineered a Pak5 mutant to selectively radiolabel its substrates in murine brain extract. Using this approach, we identified two novel Pak5 substrates, Pacsin1 and Synaptojanin1, proteins that directly interact with one another to regulate synaptic vesicle endocytosis and recycling. Pacsin1 and Synaptojanin1 were phosphorylated by Pak5 and the other group II Paks in vitro, and Pak5 phosphorylation promoted Pacsin1-Synaptojanin1 binding both in vitro and in vivo. These results implicate Pak5 in Pacsin1- and Synaptojanin1-mediated synaptic vesicle trafficking and may partially account for the cognitive and behavioral deficits observed in group II Pak-deficient mice.

Heparin/heparan sulfate/CD44-v3 enhances cell migration in term placenta-derived immortalized human trophoblast cells

The function of CD44-v3 and heparin/heparan sulfate (HS) signaling was investigated during trophoblast cell migration to identify their role in the renewal of syncytial layer damage caused by increased hemodynamic turbulence in the intervillous space and maintenance of syncytial integrity in pre-eclampsia. We evaluated the effect of heparin/HS/CD44-v3-mediated processes during scratch wound closure in monolayer immortalized human trophoblast cells derived from term placenta (TCL-1 cells). Western blot analysis showed that these cultured human trophoblast cells express the epidermal growth factor receptor and CD44-v3 but do not express syndecan 4. An in vitro scratch wound healing assay showed enhanced migration of trophoblast cells in a dose-dependent manner in the presence of heparin compared with controls when cultured under serum-free conditions. Conversely, an anti-CD44 function-blocking antibody and CD44 siRNA suppressed the migration of trophoblast cells in the presence of heparin in a similar scratch assay. Furthermore, both heparin treatment and in vitro scratch wounding induced the phosphorylation of p21-activated kinase 1 (PAK1), whereas the anti-CD44-v3 antibody suppressed the heparin-induced phosphorylation of PAK1 in trophoblast cells. These results indicate that heparin/HS/CD44-v3-mediated signaling, in the absence of growth factor networks, enhances the direct repair of the damaged trophoblast layer through the migration of trophoblast cells. This renewed cell coverage may lead to the maintenance of syncytiotrophoblast cell function and an associated reduction in pathogenic soluble factors derived from the damaged trophoblast cells.