The slingshot family of phosphatases mediates Rac1 regulation of cofilin phosphorylation, laminin-332 organization, and motility behavior of keratinocytes

Tonic repression of Collagen I by the Bradykinin receptor 2 in skin fibroblasts

Imbalance of collagen I expression results in severe pathologies. Apart from activation by the TGFβ-receptor/Smad pathway, control of collagen I expression remains poorly understood. Here, we used human dermal fibroblasts expressing a mCherry fluorescent protein driven by endogenous COL1A1 promoter to functionally screen the kinome and phosphatome. We identify 8 negative regulators, revealing that collagen is under tonic repression. The cell surface receptor BDKRB2 represses collagen I and other pro-fibrotic genes. Interestingly, it also promotes other basal membrane ECM genes. This function is independent of the natural ligand, bradykinin, and of SMAD2/3 factors, instead requiring constant ERK1/2 repression. TGFβ stimulation induces rapid BDKRB2 transcriptional downregulation. Human fibrotic fibroblasts have reduced BDKRB2 levels and enhancing its expression in keloid fibroblasts represses COL1A1. We propose that tonic signalling by BDKRB2 prevents collagen overproduction in skin fibroblasts.

A meta-analysis indicates that the regulation of cell motility is a non-intrinsic function of chemoattractant receptors that is governed independently of directional sensing

Chemoattraction, defined as the migration of a cell toward a source of a chemical gradient, is controlled by chemoattractant receptors. Chemoattraction involves two basic activities, namely, directional sensing, a molecular mechanism that detects the direction of a source of chemoattractant, and actin-based motility, which allows the migration of a cell towards it. Current models assume first, that chemoattractant receptors govern both directional sensing and motility (most commonly inducing an increase in the migratory speed of the cells, i.e. chemokinesis), and, second, that the signaling pathways controlling both activities are intertwined. We performed a meta-analysis to reassess these two points. From this study emerge two main findings. First, although many chemoattractant receptors govern directional sensing, there are also receptors that do not regulate cell motility, suggesting that is the ability to control directional sensing, not motility, that best defines a chemoattractant receptor. Second, multiple experimental data suggest that receptor-controlled directional sensing and motility can be controlled independently. We hypothesize that this independence may be based on the existence of separated signalling modules that selectively govern directional sensing and motility in chemotactic cells. Together, the information gathered can be useful to update current models representing the signalling from chemoattractant receptors. The new models may facilitate the development of strategies for a more effective pharmacological modulation of chemoattractant receptor-controlled chemoattraction in health and disease.

Galectin-3 (MAC-2) controls phagocytosis and macropinocytosis through intracellular and extracellular mechanisms

Galectin-3 (Gal-3; formally named MAC-2) is a β-galactoside-binding lectin. Various cell types produce Gal-3 under either normal conditions and/or pathological conditions. Gal-3 can be present in cells' nuclei and cytoplasm, secreted from producing cells, and associated with cells' plasma membranes. This review focuses on how Gal-3 controls phagocytosis and macropinocytosis. Intracellular and extracellular Gal-3 promotes the phagocytosis of phagocytic targets/cargo (e.g., tissue debris and apoptotic cells) in “professional phagocytes” (e.g., microglia and macrophages) and “non-professional phagocytes” (e.g., Schwann cells and astrocytes). Intracellularly, Gal-3 promotes phagocytosis by controlling the “eat me” signaling pathways that phagocytic receptors generate, directing the cytoskeleton to produce the mechanical forces that drive the structural changes on which phagocytosis depends, protrusion and then retraction of filopodia and lamellipodia as they, respectively, engulf and then internalize phagocytic targets. Extracellularly, Gal-3 promotes phagocytosis by functioning as an opsonin, linking phagocytic targets to phagocytic receptors, activating them to generate the “eat me” signaling pathways. Macropinocytosis is a non-selective endocytic mechanism that various cells use to internalize the bulk of extracellular fluid and included materials/cargo (e.g., dissolved nutrients, proteins, and pathogens). Extracellular and intracellular Gal-3 control macropinocytosis in some types of cancer. Phagocytosed and macropinocytosed targets/cargo that reach lysosomes for degradation may rupture lysosomal membranes. Damaged lysosomal membranes undergo either repair or removal by selective autophagy (i.e., lysophagy) that intracellular Gal-3 controls.

Concomitant novel ALK-SSH2, EML4-ALK and ARID2-ALK, EML4-ALK double-fusion variants and confer sensitivity to crizotinib in two lung adenocarcinoma patients, respectively

Introduction

Anaplastic lymphoma kinase (ALK) gene rearrangements, have been identified in approximately 2-7% of patients with lung adenocarcinoma (LUAD). However, co-occurrence of double ALK fusions in one patient was rare. Herein, we reported two Chinese female LUAD patients with confirmed double ALK fusion variants by next generation sequencing.

Case presentation

Case 1, a 38-year-old female was diagnosed as peripheral LUAD in left upper lobe with synchronous multiple intrapulmonary metastases (pT2N0M1b, stage IVa). And case 2, a 58-year-old female had left lower lobe primary LUAD and synchronous multiple lung metastases (pT4N2M1b, stage IVa). In both patients, tumor cells displayed strong expression of ALK protein. Genetic profiling by next generation sequencing showed both patients concurrently harbored two types of ALK rearrangements. Case 1 had an unreported ALK-SSH2/EML4-ALK double fusions, and case 2 had an another novel ARID2-ALK/EML4‐ALK double fusions. Both of these patients responded to ALK inhibitor crizotinib.

Conclusions

Our study reported two novel ALK fusion partners never reported, which expands the knowledge of ALK fusion spectrum and provides insight into therapeutic options for patients with double ALK fusions.

Metabolites of Cannabis Induce Cardiac Toxicity and Morphological Alterations in Cardiac Myocytes

Cannabis is one of the most commonly used recreational drugs worldwide. Rrecent epidemiology studies have linked increased cardiac complications to cannabis use. However, this literature is predominantly based on case incidents and post-mortem investigations. This study elucidates the molecular mechanism of Δ9-tetrahydrocannabinol (THC), and its primary metabolites 11-Hydroxy-Δ9-THC (THC-OH) and 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol (THC-COOH). Treatment of cardiac myocytes with THC-OH and THC-COOH increased cell migration and proliferation (p < 0.05), with no effect on cell adhesion, with higher doses (250–100 ng/mL) resulting in increased cell death and significant deterioration in cellular architecture. Conversely, no changes in cell morphology or viability were observed in response to THC. Expression of key ECM proteins α-SMA and collagen were up-regulated in response to THC-OH and THC-COOH treatments with concomitant modulation of PI3K and MAPK signalling. Investigations in the planarian animal model Polycelis nigra demonstrated that treatments with cannabinoid metabolites resulted in increased protein deposition at transection sites while higher doses resulted in significant lethality and decline in regeneration. These results highlight that the key metabolites of cannabis elicit toxic effects independent of the parent and psychoactive compound, with implications for cardiotoxicity relating to hypertrophy and fibrogenesis.

Rac-maninoff and Rho-vel: The symphony of Rho-GTPase signaling at excitatory synapses

Synaptic connections between neurons are essential for every facet of human cognition and are thus regulated with extreme precision. Rho-family GTPases, molecular switches that cycle between an active GTP-bound state and an inactive GDP-bound state, comprise a critical feature of synaptic regulation. Rho-GTPases are exquisitely controlled by an extensive suite of activators (GEFs) and inhibitors (GAPs and GDIs) and interact with many different signalling pathways to fulfill their roles in orchestrating the development, maintenance, and plasticity of excitatory synapses of the central nervous system. Among the mechanisms that control Rho-GTPase activity and signalling are cell surface receptors, GEF/GAP complexes that tightly regulate single Rho-GTPase dynamics, GEF/GAP and GEF/GEF functional complexes that coordinate multiple Rho-family GTPase activities, effector positive feedback loops, and mutual antagonism of opposing Rho-GTPase pathways. These complex regulatory mechanisms are employed by the cells of the nervous system in almost every step of development, and prominently figure into the processes of synaptic plasticity that underlie learning and memory. Finally, misregulation of Rho-GTPases plays critical roles in responses to neuronal injury, such as traumatic brain injury and neuropathic pain, and in neurodevelopmental and neurodegenerative disorders, including intellectual disability, autism spectrum disorder, schizophrenia, and Alzheimer's Disease. Thus, decoding the mechanisms of Rho-GTPase regulation and function at excitatory synapses has great potential for combatting many of the biggest current challenges in mental health.

Cocaine Induces Cytoskeletal Changes in Cardiac Myocytes: Implications for Cardiac Morphology

Cocaine is one of the most widely abused illicit drugs worldwide and has long been recognised as an agent of cardiac dysfunction in numerous cases of drug overdose. Cocaine has previously been shown to up-regulate cytoskeletal rearrangements and morphological changes in numerous tissues; however, previous literature observes such changes primarily in clinical case reports and addiction studies. An investigation into the fundamental cytoskeletal parameters of migration, adhesion and proliferation were studied to determine the cytoskeletal and cytotoxic basis of cocaine in cardiac cells. Treatment of cardiac myocytes with cocaine increased cell migration and adhesion (p < 0.05), with no effect on cell proliferation, except with higher doses eliciting (1–10 μg/mL) its diminution and increase in cell death. Cocaine downregulated phosphorylation of cofilin, decreased expression of adhesion modulators (integrin-β3) and increased expression of ezirin within three hours of 1 μg/mL treatments. These functional responses were associated with changes in cellular morphology, including alterations in membrane stability and a stellate-like phenotype with less compaction between cells. Higher dose treatments of cocaine (5–10 μg/mL) were associated with significant cardiomyocyte cell death (p < 0.05) and loss of cellular architecture. These results highlight the importance of cocaine in mediating cardiomyocyte function and cytotoxicity associated with the possible loss of intercellular contacts required to maintain normal cell viability, with implications for cardiotoxicity relating to hypertrophy and fibrogenesis.

Dual-specificity phosphatases in mental and neurological disorders

The dual-specificity phosphatase (DUSP) family includes a heterogeneous group of protein phosphatases that dephosphorylate both phospho-tyrosine and phospho-serine/phospho-threonine residues within a single substrate. These protein phosphatases have many substrates and modulate diverse neural functions, such as neurogenesis, differentiation, and apoptosis. DUSP genes have furthermore been associated with mental disorders such as depression and neurological disorders such as Alzheimer's disease. Herein, we review the current literature on the DUSP family of genes concerning mental and neurological disorders. This review i) outlines the structure and general functions of DUSP genes, and ii) overviews the literature on DUSP genes concerning mental and neurological disorders, including model systems, while furthermore providing perspectives for future research.

Cofilin-1-induced actin reorganization in stored platelets

BACKGROUND

During platelet storage, there are extensive changes in cytoskeleton and phosphatidylserine exposure. The intrinsic mitochondrial pathway of apoptosis, activated in stored platelets, is a major mediator these changes. Cofilin-1 is an effector of actin reorganization. We examined the effect of cofilin-1 deficiency on cytoskeleton and phosphatidylserine exposure during storage and following activation of apoptosis.

METHODS AND RESULTS

We assessed actin filaments by Alexa-647-phalloidin and phosphatidylserine exposure by fluorescein isothiocyanate-lactadherin by fluorescence microscopy. In fresh platelets, actin filaments are distributed in the subcortical region, and they do not express phosphatidylserine in the outer surface. In stored platelets, there is retraction of actin filaments from the subcortical region with increased phosphatidylserine expression. These changes are seen in 20% of platelets of 6 days old and increases further with storage. Treatment with ABT-737, which activates the mitochondrial apoptosis, induces similar cytoskeletal changes in actin filaments with increased phosphatidylserine. Cofilin-1 is activated in stored platelets as well as in ABT-737 treated platelets by dephosphorylation. In cofilin-1 deficient murine platelets actin filaments are abnormal and ABT-737 induces less phosphatidylserine. Despite these changes in vitro, platelet survival of cofilin-1 deficient platelets in mice was not significantly different from their wild-type controls.

CONCLUSION

These results show that cofilin-1 plays a role in apoptosis-induced actin rearrangement and phosphatidylserine exposure during storage. Despite the defects in platelet cytoskeleton and phosphatidylserine exposure in cofilin-1-deficient platelets, the in vivo life span of platelets is similar to littermate controls, indicating multiple redundant pathways for the clearance of platelets in vivo.

miR-194 Inhibits the Proliferation of SW620 Colon Cancer Stem Cells Through Downregulation of SSH2 Expression

Purpose

Colorectal cancer (CRC) stem cells are tumorigenic, capable of self-renewal, and resistant to therapy. Although the expression pattern and functions of micro RNA (miR)-194 in CRC cells have been widely investigated, little is known about its role in CRC stem cells. Therefore, the aim of this study was to investigate the potential role of miR-194 in CRC stem cells.

Materials and methods

CRC stem cells were isolated from the SW620 colon cancer cell line using microbeads. The expression levels of miR-194 and slingshot 2 (SSH2) in CRC stem cells were detected by RT-PCR and Western blot. A luciferase reporter assay was performed to confirm that miR-194 directly targets SSH2. Proliferation of CRC stem cells was examined by colony formation and MTT assays. Apoptosis in CRC stem cells was detected by cell cycle and apoptosis assays. The role of miR-194 in tumor growth was determined in vivo.

Results

Cells positive for CD44 and CD133 accounted for approximately 88.7% of the isolated population after microbead isolation. We reveal for the first time that miR-194 expression is decreased in CRC stem cells. Specifically, miR-194 is involved in inhibiting the proliferation of CRC stem cells and promoting CRC stem cell apoptosis by directly targeting SSH2. Furthermore, overexpression of miR-194 resulted in blocking the G1/S transition, the induction of cellular apoptotic process, thereby suppressing the malignant behaviors of CRC stem cells.

Conclusion

This study represents a novel characterization of miR-194 function in CRC stem cells, which may aid in the development of promising therapeutic strategies targeting CRC.

Rho GTPases-Emerging Regulators of Glucose Homeostasis and Metabolic Health

Rho guanosine triphosphatases (GTPases) are key regulators in a number of cellular functions, including actin cytoskeleton remodeling and vesicle traffic. Traditionally, Rho GTPases are studied because of their function in cell migration and cancer, while their roles in metabolism are less documented. However, emerging evidence implicates Rho GTPases as regulators of processes of crucial importance for maintaining metabolic homeostasis. Thus, the time is now ripe for reviewing Rho GTPases in the context of metabolic health. Rho GTPase-mediated key processes include the release of insulin from pancreatic β cells, glucose uptake into skeletal muscle and adipose tissue, and muscle mass regulation. Through the current review, we cast light on the important roles of Rho GTPases in skeletal muscle, adipose tissue, and the pancreas and discuss the proposed mechanisms by which Rho GTPases act to regulate glucose metabolism in health and disease. We also describe challenges and goals for future research.

Hemidesmosomes and Focal Adhesions Treadmill as Separate but Linked Entities during Keratinocyte Migration

Hemidesmosomes anchor the epidermal keratin filament cytoskeleton to the extracellular matrix. They are crucial for the mechanical integrity of skin. Their role in keratinocyte migration, however, remains unclear. Examining migrating primary human keratinocytes, we find that hemidesmosomes cluster as ordered arrays consisting of multiple chevrons that are flanked by actin-associated focal adhesions. These hemidesmosomal arrays with intercalated focal adhesions extend from the cell rear to the cell front. New hemidesmosomal chevrons form subsequent to focal adhesion assembly at the cell's leading front, whereas chevrons and associated focal adhesions disassemble at the cell rear in reverse order. The bulk of the hemidesmosome-focal adhesion composite, however, remains attached to the substratum during cell translocation. Similar hemidesmosome-focal adhesion patterns emerge on X-shaped fibronectin-coated micropatterns, during cell spreading and in leader cells during collective cell migration. We further find that hemidesmosomes and focal adhesions affect each other's distribution. We propose that both junctions are separate but linked entities, which treadmill coordinately to support efficient directed cell migration and cooperate to coordinate the dynamic interplay between the keratin and actin cytoskeleton.

Cofilin and profilin: partners in cancer aggressiveness

This review covers aspects of cofilin and profilin regulations and their influence on actin polymerisation responsible for cell motility and metastasis. The regulation of their activity by phosphorylation and nitration, miRs, PI(4,5)P₂ binding, pH, oxidative stress and post-translational modification is described. In this review, we have highlighted selected similarities, complementarities and differences between the two proteins and how their interplay affects actin filament dynamics.

Chronophin activation is necessary in Doxorubicin-induced actin cytoskeleton alteration

Although doxorubicin (Dox)-induced oxidative stress is known to be associated with cytotoxicity, the precise mechanism remains unclear. Genotoxic stress not only generates free radicals, but also affects actin cytoskeleton stability. We showed that Dox-induced RhoA signaling stimulated actin cytoskeleton alterations, resulting in central stress fiber disruption at early time points and cell periphery cortical actin formation at a later stage, in HeLa cells. Interestingly, activation of a cofilin phosphatase, chronophin (CIN), was initially evoked by Dox-induced RhoA signaling, resulting in a rapid phosphorylated cofilin turnover leading to actin cytoskeleton remodeling. In addition, a novel interaction between CIN and 14-3-3ζ was detected in the absence of Dox treatment. We demonstrated that CIN activity is quite contrary to 14-3-3ζ binding, and the interaction leads to enhanced phosphorylated cofilin levels. Therefore, initial CIN activation regulation could be critical in Dox-induced actin cytoskeleton remodeling through RhoA/cofilin signaling. [BMB Reports 2017; 50(6): 335-340].

A hemidesmosomal protein regulates actin dynamics and traction forces in motile keratinocytes

During wound healing of the skin, keratinocytes disassemble hemidesmosomes and reorganize their actin cytoskeletons in order to exert traction forces on and move directionally over the dermis. Nonetheless, the transmembrane hemidesmosome component collagen XVII (ColXVII) is found in actin-rich lamella, situated behind the lamellipodium. A set of actin bundles, along which ColXVII colocalizes with actinin4, is present at each lamella. Knockdown of either ColXVII or actinin4 not only inhibits directed migration of keratinocytes but also relieves constraints on actin bundle retrograde movement at the site of lamella, such that actin bundle movement is enhanced more than 5-fold. Moreover, whereas control keratinocytes move in a stepwise fashion over a substrate by generating alternating traction forces, of up to 1.4 kPa, at each flank of the lamellipodium, ColXVII knockdown keratinocytes fail to do so. In summary, our data indicate that ColXVII-actinin4 complexes at the lamella of a moving keratinocyte regulate actin dynamics, thereby determining the direction of cell movement.-Hiroyasu, S., Colburn, Z. T., Jones, J. C. R. A hemidesmosomal protein regulates actin dynamics and traction forces in motile keratinocytes.

Potential crosstalk between cofilin-1 and EGFR pathways in cisplatin resistance of non-small-cell lung cancer

Current challenge in oncology is to establish the concept of personalized medicine in clinical practice. In this context, non-small-cell lung cancer (NSCLC) presents clinical, histological and molecular heterogeneity, being one of the most genomically diverse of all cancers. Recent advances added Epidermal Growth Factor Receptor (EGFR) as a predictive biomarker for patients with advanced NSCLC. In tumors with activating EGFR mutations, tyrosine kinase inhibitors (TKI) are indicated as first-line treatment, although restricted to a very small target population. In this context, cofilin-1 (a cytosolic protein involved with actin dynamics) has been widely studied as a biomarker of an aggressive phenotype in tumors, and overexpression of cofilin-1 is associated with cisplatin resistance and poor prognosis in NSCLC. Here, we gather information about the predictive potential of cofilin-1 and reviewed the crosstalk between cofilin-1/EGFR pathways. We aimed to highlight new perspectives of how these interactions might affect cisplatin resistance in NSCLC. We propose that cofilin-1 quantification in clinical samples in combination with presence/absence of EGFR mutation could be used to select patients that would benefit from TKI's treatment. This information is of paramount importance and could result in a possibility of guiding more effective treatments to NSCLC patients.

Caspase-11 and caspase-1 differentially modulate actin polymerization via RhoA and Slingshot proteins to promote bacterial clearance

Inflammasomes are multiprotein complexes that include members of the NOD-like receptor family and caspase-1. Caspase-1 is required for the fusion of the Legionella vacuole with lysosomes. Caspase-11, independently of the inflammasome, also promotes phagolysosomal fusion. However, it is unclear how these proteases alter intracellular trafficking. Here, we show that caspase-11 and caspase-1 function in opposing manners to phosphorylate and dephosphorylate cofilin, respectively upon infection with Legionella. Caspase-11 targets cofilin via the RhoA GTPase, whereas caspase-1 engages the Slingshot phosphatase. The absence of either caspase-11 or caspase-1 maintains actin in the polymerized or depolymerized form, respectively and averts the fusion of pathogen-containing vacuoles with lysosomes. Therefore, caspase-11 and caspase-1 converge on the actin machinery with opposing effects to promote vesicular trafficking.

Cofilin phosphorylation is elevated after F-actin disassembly induced by Rac1 depletion

Cytoskeletal reorganization is essential to keratinocyte function. Rac1 regulates cytoskeletal reorganization through signaling pathways such as the cofilin cascade. Cofilin severs actin filaments after activation by dephosphorylation. Rac1 was knocked out in mouse keratinocytes and it was found that actin filaments disassembled. In the epidermis of mice in which Rac1 was knocked out only in keratinocytes, cofilin phosphorylation was aberrantly elevated, corresponding to repression of the phosphatase slingshot1 (SSH1). These effects were independent of the signaling pathways for p21-activated kinase/LIM kinase (Pak/LIMK), protein kinase C, or protein kinase D or generation of reactive oxygen species. Similarly, when actin polymerization was specifically inhibited or Rac1 was knocked down, cofilin phosphorylation was enhanced and SSH1 was repressed. Repression of SSH1 partially blocked actin depolymerization induced by Rac1 depletion. Therefore, aberrant cofilin phosphorylation that induces actin polymerization might be a consequence of actin disassembly induced by the absence of Rac1.

A Drosophila-centric view of protein tyrosine phosphatases

Most of our knowledge on protein tyrosine phosphatases (PTPs) is derived from human pathologies and mouse knockout models. These models largely correlate well with human disease phenotypes, but can be ambiguous due to compensatory mechanisms introduced by paralogous genes. Here we present the analysis of the PTP complement of the fruit fly and the complementary view that PTP studies in Drosophila will accelerate our understanding of PTPs in physiological and pathological conditions. With only 44 PTP genes, Drosophila represents a streamlined version of the human complement. Our integrated analysis places the Drosophila PTPs into evolutionary and functional contexts, thereby providing a platform for the exploitation of the fly for PTP research and the transfer of knowledge onto other model systems.

The NAV2 homolog Sickie regulates F-actin-mediated axonal growth in Drosophila mushroom body neurons via the non-canonical Rac-Cofilin pathway

The Rac-Cofilin pathway is essential for cytoskeletal remodeling to control axonal development. Rac signals through the canonical Rac-Pak-LIMK pathway to suppress Cofilin-dependent axonal growth and through a Pak-independent non-canonical pathway to promote outgrowth. Whether this non-canonical pathway converges to promote Cofilin-dependent F-actin reorganization in axonal growth remains elusive. We demonstrate that Sickie, a homolog of the human microtubule-associated protein neuron navigator 2, cell-autonomously regulates axonal growth of Drosophila mushroom body (MB) neurons via the non-canonical pathway. Sickie was prominently expressed in the newborn F-actin-rich axons of MB neurons. A sickie mutant exhibited axonal growth defects, and its phenotypes were rescued by exogenous expression of Sickie. We observed phenotypic similarities and genetic interactions among sickie and Rac-Cofilin signaling components. Using the MARCM technique, distinct F-actin and phospho-Cofilin patterns were detected in developing axons mutant for sickie and Rac-Cofilin signaling regulators. The upregulation of Cofilin function alleviated the axonal defect of the sickie mutant. Epistasis analyses revealed that Sickie suppresses the LIMK overexpression phenotype and is required for Pak-independent Rac1 and Slingshot phosphatase to counteract LIMK. We propose that Sickie regulates F-actin-mediated axonal growth via the non-canonical Rac-Cofilin pathway in a Slingshot-dependent manner.

Kinome-wide functional analysis highlights the role of cytoskeletal remodeling in somatic cell reprogramming

The creation of induced pluripotent stem cells (iPSCs) from somatic cells by ectopic expression of transcription factors has galvanized the fields of regenerative medicine and developmental biology. Here, we report a kinome-wide RNAi-based analysis to identify kinases that regulate somatic cell reprogramming to iPSCs. We prepared 3,686 small hairpin RNA (shRNA) lentiviruses targeting 734 kinase genes covering the entire mouse kinome and individually examined their effects on iPSC generation. We identified 59 kinases as barriers to iPSC generation and characterized seven of them further. We found that shRNA-mediated knockdown of the serine/threonine kinases TESK1 or LIMK2 promoted mesenchymal-to-epithelial transition, decreased COFILIN phosphorylation, and disrupted Actin filament structures during reprogramming of mouse embryonic fibroblasts. Similarly, knockdown of TESK1 in human fibroblasts also promoted reprogramming to iPSCs. Our study reveals the breadth of kinase networks regulating pluripotency and identifies a role for cytoskeletal remodeling in modulating the somatic cell reprogramming process.

Pctaire1/Cdk16 promotes skeletal myogenesis by inducing myoblast migration and fusion

The Cdk-related protein kinase Pctaire1/Cdk16 is abundantly expressed in brain, testis and skeletal muscle. Functional roles of Pctaire1 such as regulation of neuron migration and neurite outgrowth thus far have been mainly elucidated in the field of nervous system development. Although these regulations based on cytoskeletal rearrangements evoke a possible role of Pctaire1 in the development of skeletal muscle, little is known in this regard. In this study, we demonstrated that myogenic differentiation and subsequent fusion is promoted in Pctaire1 overexpressing cells, and conversely, is inhibited in the knockdown cells. Furthermore, our findings suggest that Pctaire1 exerts promyogenic effects by regulating myoblast migration and process formation during skeletal myogenesis.

βArrestin1 regulates the guanine nucleotide exchange factor RasGRF2 expression and the small GTPase Rac-mediated formation of membrane protrusion and cell motility

βArrestin proteins shuttle between the cytosol and nucleus and have been shown to regulate G protein-coupled receptor signaling, actin remodeling, and gene expression. Here, we tested the hypothesis that βarrestin1 regulates actin remodeling and cell migration through the small GTPase Rac. Depletion of βarrestin1 promotes Rac activation, leading to the formation of multipolar protrusions and increased cell circularity, and overexpression of a dominant negative form of Rac reverses these morphological changes. Small interfering RNA library screen identifies RasGRF2 as a target of βarrestin1. RasGRF2 gene and protein expression levels are elevated following depletion of βarrestin1, and the consequent activation of Rac results in dephosphorylation of cofilin that can promote actin polymerization and formation of multipolar protrusions, thereby retarding cell migration and invasion. Together, these results suggest that βarrestin1 regulates rasgrf2 gene expression and Rac activation to affect membrane protrusion and cell migration and invasion.

Focal Contact and Hemidesmosomal Proteins in Keratinocyte Migration and Wound Repair

Significance: During wound healing of the skin, keratinocytes should move over while still adhering to their underlying matrix. Thus, mechanistic insights into the wound-healing process require an understanding of the forms and functions of keratinocyte matrix adhesions, specifically focal contacts and hemidesmosomes, and their components. Recent Advances: Although the structure and composition of focal contacts and hemidesmosomes are relatively well defined, the functions of their components are only now being delineated using mouse genetic models and knockdown approaches in cell culture systems. Remarkably, both focal contact and hemidesmosomal proteins appear involved in determining the speed and directional migration of epidermal cells by modulating several signal transduction pathways. Critical Issues: Although many publications are centered on focal contacts, their existence in tissues such as the skin is controversial. Nonetheless, focal contact proteins are central to mechanisms that regulate skin cell motility. Conversely, hemidesmosomes have been identified in intact skin but whether hemidesmosomal components play a positive regulatory function in keratinocyte motility remains debated in the field. Future Directions: Defective wound healing is a developing problem in the aged, hospitalized and diabetic populations. Hence, deriving new insights into the molecular roles of matrix adhesion proteins in wound healing is a prerequisite to the development of novel therapeutics to enhance tissue repair and regeneration.

Type VII collagen regulates expression of OATP1B3, promotes front-to-rear polarity and increases structural organisation in 3D spheroid cultures of RDEB tumour keratinocytes

Type VII collagen is the main component of anchoring fibrils, structures that are integral to basement membrane homeostasis in skin. Mutations in the gene encoding type VII collagen COL7A1 cause recessive dystrophic epidermolysis bullosa (RDEB) an inherited skin blistering condition complicated by frequent aggressive cutaneous squamous cell carcinoma (cSCC). OATP1B3, which is encoded by the gene SLCO1B3, is a member of the OATP (organic anion transporting polypeptide) superfamily responsible for transporting a wide range of endogenous and xenobiotic compounds. OATP1B3 expression is limited to the liver in healthy tissues, but is frequently detected in multiple cancer types and is reported to be associated with differing clinical outcome. The mechanism and functional significance of tumour-specific expression of OATP1B3 has yet to be determined. Here, we identify SLCO1B3 expression in tumour keratinocytes isolated from RDEB and UV-induced cSCC and demonstrate that SLCO1B3 expression and promoter activity are modulated by type VII collagen. We show that reduction of SLCO1B3 expression upon expression of full-length type VII collagen in RDEB cSCC coincides with acquisition of front-to-rear polarity and increased organisation of 3D spheroid cultures. In addition, we show that type VII collagen positively regulates the abundance of markers implicated in cellular polarity, namely ELMO2, PAR3, E-cadherin, B-catenin, ITGA6 and Ln332.

Laminin-332 and α3β1 integrin-supported migration of bronchial epithelial cells is modulated by fibronectin

The repair of the bronchiolar epithelium damaged by cell-mediated, physical, or chemical insult requires epithelial cell migration over a provisional matrix composed of complexes of extracellular matrix molecules, including fibronectin and laminin. These matrix molecules support migration and enhance cell adhesion. When cells adhere too tightly to their matrix they fail to move; but if they adhere too little, they are unable to develop the traction force necessary for motility. Thus, we investigated the relative contributions of laminin and fibronectin to bronchiolar cell adhesion and migration using the immortalized bronchial lung epithelial cell line (BEP2D) and normal human bronchial epithelial (NHBE) cells, both of which assemble a laminin α3β3γ2 (LM332)/fibronectin-rich matrix. Intriguingly, BEP2D and NHBE cells migrate significantly faster on an LM332-rich matrix than on fibronectin. Moreover, addition of fibronectin to LM332 matrix suppresses motility of both cell types. Finally, fibronectin enhances the adhesion of both BEP2D and NHBE cells to LM332-coated surfaces. These results suggest that fibronectin fine tunes LM332-mediated migration by boosting bronchiolar cell adhesion to substrate. We suggest that, during epithelial wound healing of the injured airway, fibronectin plays an important adhesive role for laminin-driven epithelial cell motility by promoting a stable cellular interaction with the provisional matrix.

Collagen VII plays a dual role in wound healing

Although a host of intracellular signals is known to contribute to wound healing, the role of the cell microenvironment in tissue repair remains elusive. Here we employed 2 different mouse models of genetic skin fragility to assess the role of the basement membrane protein collagen VII (COL7A1) in wound healing. COL7A1 secures the attachment of the epidermis to the dermis, and its mutations cause a human skin fragility disorder coined recessive dystrophic epidermolysis bullosa (RDEB) that is associated with a constant wound burden. We show that COL7A1 is instrumental for skin wound closure by 2 interconnected mechanisms. First, COL7A1 was required for re-epithelialization through organization of laminin-332 at the dermal-epidermal junction. Its loss perturbs laminin-332 organization during wound healing, which in turn abrogates strictly polarized expression of integrin α6β4 in basal keratinocytes and negatively impacts the laminin-332/integrin α6β4 signaling axis guiding keratinocyte migration. Second, COL7A1 supported dermal fibroblast migration and regulates their cytokine production in the granulation tissue. These findings, which were validated in human wounds, identify COL7A1 as a critical player in physiological wound healing in humans and mice and may facilitate development of therapeutic strategies not only for RDEB, but also for other chronic wounds.

Activation of ADF/cofilin by phosphorylation-regulated Slingshot phosphatase is required for the meiotic spindle assembly in Xenopus laevis oocytes

We identify Xenopus ADF/cofilin (XAC) and its activator, Slingshot phosphatase (XSSH), as key regulators of actin dynamics essential for spindle microtubule assembly during Xenopus oocyte maturation. Phosphorylation of XSSH at multiple sites within the tail domain occurs just after germinal vesicle breakdown (GVBD) and is accompanied by dephosphorylation of XAC, which was mostly phosphorylated in immature oocytes. This XAC dephosphorylation after GVBD is completely suppressed by latrunculin B, an actin monomer-sequestering drug. On the other hand, jasplakinolide, an F-actin-stabilizing drug, induces dephosphorylation of XAC. Effects of latrunculin B and jasplakinolide are reconstituted in cytostatic factor-arrested extracts (CSF extracts), and XAC dephosphorylation is abolished by depletion of XSSH from CSF extracts, suggesting that XSSH functions as an actin filament sensor to facilitate actin filament dynamics via XAC activation. Injection of anti-XSSH antibody, which blocks full phosphorylation of XSSH after GVBD, inhibits both meiotic spindle formation and XAC dephosphorylation. Coinjection of constitutively active XAC with the antibody suppresses this phenotype. Treatment of oocytes with jasplakinolide also impairs spindle formation. These results strongly suggest that elevation of actin dynamics by XAC activation through XSSH phosphorylation is required for meiotic spindle assembly in Xenopus laevis.

Patent Highlights

A snapshot of recent key developments in the patent literature of relevance to the advancement of pharmaceutical and medical R&D

Proteomic approaches identify members of cofilin pathway involved in oral tumorigenesis

The prediction of tumor behavior for patients with oral carcinomas remains a challenge for clinicians. The presence of lymph node metastasis is the most important prognostic factor but it is limited in predicting local relapse or survival. This highlights the need for identifying biomarkers that may effectively contribute to prediction of recurrence and tumor spread. In this study, we used one- and two-dimensional gel electrophoresis, mass spectrometry and immunodetection methods to analyze protein expression in oral squamous cell carcinomas. Using a refinement for classifying oral carcinomas in regard to prognosis, we analyzed small but lymph node metastasis-positive versus large, lymph node metastasis-negative tumors in order to contribute to the molecular characterization of subgroups with risk of dissemination. Specific protein patterns favoring metastasis were observed in the “more-aggressive” group defined by the present study. This group displayed upregulation of proteins involved in migration, adhesion, angiogenesis, cell cycle regulation, anti-apoptosis and epithelial to mesenchymal transition, whereas the “less-aggressive” group was engaged in keratinocyte differentiation, epidermis development, inflammation and immune response. Besides the identification of several proteins not yet described as deregulated in oral carcinomas, the present study demonstrated for the first time the role of cofilin-1 in modulating cell invasion in oral carcinomas.

Signaling mechanisms and functional roles of cofilin phosphorylation and dephosphorylation

Cofilin and actin-depolymerizing factor (ADF) are actin-binding proteins that play an essential role in regulating actin filament dynamics and reorganization by stimulating the severance and depolymerization of actin filaments. Cofilin/ADF are inactivated by phosphorylation at the serine residue at position 3 by LIM-kinases (LIMKs) and testicular protein kinases (TESKs) and are reactivated by dephosphorylation by the slingshot (SSH) family of protein phosphatases and chronophin. This review describes recent advances in our understanding of the signaling mechanisms regulating LIMKs and SSHs and the functional roles of cofilin phospho-regulation in cell migration, tumor invasion, mitosis, neuronal development, and synaptic plasticity. Accumulating evidence demonstrates that the phospho-regulation of cofilin/ADF is a key convergence point of cell signaling networks that link extracellular stimuli to actin cytoskeletal dynamics and that spatiotemporal control of cofilin/ADF activity by LIMKs and SSHs plays a crucial role in a diverse array of cellular and physiological processes. Perturbations in the normal control of cofilin/ADF activity underlie many pathological conditions, including cancer metastasis and neurological and cardiovascular disorders.

Actinin-4 in keratinocytes regulates motility via an effect on lamellipodia stability and matrix adhesions

During wound repair, epidermal cells at the edge of an injury establish front-rear polarity through orchestrated changes in their cytoskeleton and adhesion structures. The polarity and directed migration of such cells is determined by the assembly, extension, and stabilization of a lamellipodium. Actinin-4 associates with lamellipodia and has been implicated in regulating lamellipodial structure, function and assembly. To study the functions of actinin-4 in human keratinocytes, we used shRNA to generate knockdown cells and compared their motility behavior and matrix adhesion assembly to scrambled shRNA treated control keratinocytes. Actinin-4 knockdown keratinocytes lack polarity, assemble multiple lamellipodia with a 2× increased area over controls, display reduced activity of the actin remodeling protein cofilin, and fail to migrate in a directional manner. This motility defect is rescued by plating knockdown cells on preformed laminin-332 matrix. In actinin-4-knockdown keratinocytes, focal contact area is increased by 25%, and hemidesmosome proteins are mislocalized. Specifically, α6β4 integrin localizes to large lamellipodial extensions, displays reduced dynamics, and fails to recruit its bullous pemphigoid antigen binding partners. Together, our data indicate a role for actinin-4 in regulating the steering mechanism of keratinocytes via profound effects on their matrix adhesion sites.

The 5-phosphatase OCRL mediates retrograde transport of the mannose 6-phosphate receptor by regulating a Rac1-cofilin signalling module

Mutations in the OCRL gene encoding the phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) 5-phosphatase OCRL cause Lowe syndrome (LS), which is characterized by intellectual disability, cataracts and selective proximal tubulopathy. OCRL localizes membrane-bound compartments and is implicated in intracellular transport. Comprehensive analysis of clathrin-mediated endocytosis in fibroblasts of patients with LS did not reveal any difference in trafficking of epidermal growth factor, low density lipoprotein or transferrin, compared with normal fibroblasts. However, LS fibroblasts displayed reduced mannose 6-phosphate receptor (MPR)-mediated re-uptake of the lysosomal enzyme arylsulfatase B. In addition, endosome-to-trans Golgi network (TGN) transport of MPRs was decreased significantly, leading to higher levels of cell surface MPRs and their enrichment in enlarged, retromer-positive endosomes in OCRL-depleted HeLa cells. In line with the higher steady-state concentration of MPRs in the endosomal compartment in equilibrium with the cell surface, anterograde transport of the lysosomal enzyme, cathepsin D was impaired. Wild-type OCRL counteracted accumulation of MPR in endosomes in an activity-dependent manner, suggesting that PI(4,5)P(2) modulates the activity state of proteins regulated by this phosphoinositide. Indeed, we detected an increased amount of the inactive, phosphorylated form of cofilin and lower levels of the active form of PAK3 upon OCRL depletion. Levels of active Rac1 and RhoA were reduced or enhanced, respectively. Overexpression of Rac1 rescued both enhanced levels of phosphorylated cofilin and MPR accumulation in enlarged endosomes. Our data suggest that PI(4,5)P(2) dephosphorylation through OCRL regulates a Rac1-cofilin signalling cascade implicated in MPR trafficking from endosomes to the TGN.

Caenorhabditis elegans screen reveals role of PAR-5 in RAB-11-recycling endosome positioning and apicobasal cell polarity

Apically enriched Rab11-positive recycling endosomes (Rab11-REs) are important for establishing and maintaining epithelial polarity. Yet, little is known about the molecules controlling trafficking of Rab11-REs in an epithelium in vivo. Here, we report a genome-wide, image-based RNA interference screen for regulators of Rab11-RE positioning and transport of an apical membrane protein (PEPT-1) in C. elegans intestine. Among the 356 screen hits was the 14-3-3 and partitioning defective protein PAR-5, which we found to be specifically required for Rab11-RE positioning and apicobasal polarity maintenance. Depletion of PAR-5 induced abnormal clustering of Rab11-REs to ectopic sites at the basolateral cortex containing F-actin and other apical domain components. This phenotype required key regulators of F-actin dynamics and polarity, such as Rho GTPases (RHO-1 and the Rac1 orthologue CED-10) and apical PAR proteins. Our data suggest that PAR-5 acts as a regulatory hub for a polarity-maintaining network required for apicobasal asymmetry of F-actin and proper Rab11-RE positioning.

α6β4 integrin, a master regulator of expression of integrins in human keratinocytes

Three major laminin and collagen-binding integrins in skin (α6β4, α3β1, and α2β1) are involved in keratinocyte adhesion to the dermis and dissemination of skin cells during wound healing and/or tumorigenesis. Knockdown of α6 integrin in keratinocytes not only results in motility defects but also leads to decreased surface expression of the α2, α3, and β4 integrin subunits. Whereas α2 integrin mRNA levels are decreased in α6 integrin knockdown cells, α3 and β4 integrin mRNAs levels are unaffected. Expression of either α6 or α3 integrin in α6 integrin knockdown cells restores α2 integrin mRNA levels. Moreover, re-expression of α6 integrin increases β4 integrin protein at the cell surface, which results in an increase in α3 integrin expression via activation of initiation factor 4E-binding protein 1. Our data indicate that the α6β4 integrin is a master regulator of transcription and translation of other integrin subunits and underscore its pivotal role in wound healing and cancer.

Cofilin weakly interacts with 14-3-3 and therefore can only indirectly participate in regulation of cell motility by small heat shock protein HspB6 (Hsp20)

It has been previously reported that phosphorylated cofilin interacted with 14-3-3ζ protein to generate a sub-micromolar K(d) binary complex. Here we challenge this hypothesis by analyzing the direct association of recombinant cofilin with 14-3-3ζ using different in vitro biochemical methods. Phosphorylated cofilin at high concentration binds to 14-3-3 immobilized on nitrocellulose, however no complex formation was detected by means of native gel electrophoresis or chemical crosslinking. Intact dimeric or mutant monomeric 14-3-3 was unable to form stable complexes with phosphorylated or unphosphorylated cofilin detected by size-exclusion chromatography. In co-sedimentation assay 14-3-3 did not affect interaction of cofilin with F-actin. The data of native gel electrophoresis indicate that 14-3-3 did not affect interaction of cofilin with G-actin. Thus, cofilin only weakly interacts with 14-3-3 and therefore cannot directly compete with phosphorylated small heat shock protein HspB6 for its binding to 14-3-3. It is hypothesized that phosphorylated HspB6 might affect interaction of 14-3-3 with protein phosphatases (and/or protein kinases) involved in dephosphorylation (or phosphorylation) of cofilin and by this means regulate cofilin-dependent reorganization of cytoskeleton.

Small RNA sequencing reveals microRNAs that modulate angiotensin II effects in vascular smooth muscle cells

Angiotensin II (Ang II)-mediated vascular smooth muscle cell dysfunction plays a critical role in cardiovascular diseases. However, the role of microRNAs (miRNAs) in this process is unclear. We used small RNA deep sequencing to profile Ang II-regulated miRNAs in rat vascular smooth muscle cells (VSMC) and evaluated their role in VSMC dysfunction. Sequencing results revealed several Ang II-responsive miRNAs, and bioinformatics analysis showed that their predicted targets can modulate biological processes relevant to cardiovascular diseases. Further studies with the most highly induced miR-132 and miR-212 cluster (miR-132/212) showed time- and dose-dependent up-regulation of miR-132/212 by Ang II through the Ang II Type 1 receptor. We identified phosphatase and tensin homolog (PTEN) as a novel target of miR-132 and demonstrated that miR-132 induces monocyte chemoattractant protein-1 at least in part via PTEN repression in rat VSMC. Moreover, miR-132 overexpression enhanced cyclic AMP-response element-binding protein (CREB) phosphorylation via RASA1 (p120 Ras GTPase-activating protein 1) down-regulation, whereas miR-132 inhibition attenuated Ang II-induced CREB activation. Furthermore, miR-132 up-regulation by Ang II required CREB activation, demonstrating a positive feedback loop. Notably, aortas from Ang II-infused mice displayed similar up-regulation of miR-132/212 and monocyte chemoattractant protein-1, supporting in vivo relevance. In addition, microarray analysis and reverse transcriptase-quantitative PCR validation revealed additional novel miR-132 targets among Ang II-down-regulated genes implicated in cell cycle, motility, and cardiovascular functions. These results suggest that miR132/212 can serve as a novel cellular node to fine-tune and amplify Ang II actions in VSMC.

Slingshot isoform-specific regulation of cofilin-mediated vascular smooth muscle cell migration and neointima formation

OBJECTIVE

We hypothesized that cofilin activation by members of the slingshot (SSH) phosphatase family is a key mechanism regulating vascular smooth muscle cell (VSMC) migration and neoinitima formation following vascular injury.

METHODS AND RESULTS

Scratch wound and modified Boyden chamber assays were used to assess VSMC migration following downregulation of the expression of cofilin and each SSH phosphatase isoform (SSH1, SSH2, and SSH3) by small interfering RNA (siRNA), respectively. Cofilin siRNA greatly attenuated the ability of VSMC migration into the "wound," and platelet-derived growth factor (PDGF)-induced migration was virtually eliminated versus a 3.5-fold increase in nontreated VSMCs, establishing a critical role for cofilin in VSMC migration. Cofilin activation (dephosphorylation) was increased in PDGF-stimulated VSMCs. Thus, we assessed the role of the SSH family of phosphatases on cofilin activation and VSMC migration. Treatment with either SSH1 or SSH2 siRNA attenuated cofilin activation, whereas SSH3 siRNA had no effect. Only SSH1 siRNA significantly reduced wound healing and PDGF-induced VSMC migration. Both SSH1 expression (4.7-fold) and cofilin expression (3.9-fold) were increased in balloon injured versus noninjured carotid arteries, and expression was prevalent in the neointima.

CONCLUSION

These studies demonstrate that the regulation of VSMC migration by cofilin is SSH1 dependent and that this mechanism potentially contributes to neointima formation following vascular injury in vivo.

The ADF/Cofilin-Pathway and Actin Dynamics in Podocyte Injury

ADF/cofilins are the major regulators of actin dynamics in mammalian cells. The activation of ADF/cofilins is controlled by a variety of regulatory mechanisms. Dysregulation of ADF/cofilin may result in loss of a precisely organized actin cytoskeletal architecture and can reduce podocyte migration and motility. Recent studies suggest that cofilin-1 can be regulated through several extracellular signals and slit diaphragm proteins. Cofilin knockdown and knockout animal models show dysfunction of glomerular barrier and filtration with foot process effacement and loss of secondary foot processes. This indicates that cofilin-1 is necessary for modulating actin dynamics in podocytes. Podocyte alterations in actin architecture may initiate or aid the progression of a large variety of glomerular diseases, and cofilin activity is required for reorganization of an intact filtration barrier. Since almost all proteinuric diseases result from a similar phenotype with effacement of the foot processes, we propose that cofilin-1 is at the centre stage of the development of proteinuria and thus may be an attractive drug target for antiproteinuric treatment strategies.

Laminin 511 partners with laminin 332 to mediate directional migration of Madin-Darby canine kidney epithelial cells

Sustained directional migration of epithelial cells is essential for regeneration of injured epithelia. Front-rear polarity of migrating cells is determined by local activation of a signaling network involving Cdc42 and other factors in response to spatial cues from the environment, the nature of which are obscure. We examined the roles of laminin (LM)-511 and LM-332, two structurally different laminin isoforms, in the migration of Madin-Darby canine kidney cells by suppressing expression of their α subunits using RNA interference. We determined that knockdown of LM-511 inhibits directional migration and destabilizes cell-cell contacts, in part by disturbing the localization and activity of the polarization machinery. Suppression of integrin α3, a laminin receptor subunit, in cells synthesizing normal amounts of both laminins has a similar effect as knockdown of LM-511. Surprisingly, simultaneous suppression of both laminin α5 and laminin α3 restores directional migration and cell-cell contact stability, suggesting that cells recognize a haptotactic gradient formed by a combination of laminins.

Recruitment of actin modifiers to TrkA endosomes governs retrograde NGF signaling and survival

The neurotrophins NGF and NT3 collaborate to support development of sympathetic neurons. Although both promote axonal extension via the TrkA receptor, only NGF activates retrograde transport of TrkA endosomes to support neuronal survival. Here, we report that actin depolymerization is essential for initiation of NGF/TrkA endosome trafficking and that a Rac1-cofilin signaling module associated with TrkA early endosomes supports their maturation to retrograde transport-competent endosomes. These actin-regulatory endosomal components are absent from NT3/TrkA endosomes, explaining the failure of NT3 to support retrograde TrkA transport and survival. The inability of NT3 to activate Rac1-GTP-cofilin signaling is likely due to the labile nature of NT3/TrkA complexes within the acidic environment of TrkA early endosomes. Thus, TrkA endosomes associate with actin-modulatory proteins to promote F-actin disassembly, enabling their maturation into transport-competent signaling endosomes. Differential control of this process explains how NGF but not NT3 supports retrograde survival of sympathetic neurons.

14-3-3 proteins and regulation of cytoskeleton

The proteins of the 14-3-3 family are universal adapters participating in multiple processes running in the cell. We describe the structure, isoform composition, and distribution of 14-3-3 proteins in different tissues. Different elements of 14-3-3 structure important for dimer formation and recognition of protein targets are analyzed in detail. Special attention is paid to analysis of posttranslational modifications playing important roles in regulation of 14-3-3 function. The data of the literature concerning participation of 14-3-3 in regulation of intercellular contacts and different elements of cytoskeleton formed by microfilaments are analyzed. We also describe participation of 14-3-3 in regulation of small G-proteins and protein kinases important for proper functioning of cytoskeleton. The data on the interaction of 14-3-3 with different components of microtubules are presented, and the probable role of 14-3-3 in developing of certain neurodegenerative diseases is discussed. The data of the literature concerning the role of 14-3-3 in formation and normal functioning of intermediate filaments are also reviewed. It is concluded that due to its adapter properties 14-3-3 plays an important role in cytoskeleton regulation. The cytoskeletal proteins that are abundant in the cell might compete with the other protein targets of 14-3-3 and therefore can indirectly regulate many intracellular processes that are dependent on 14-3-3.

Platelet-derived growth factor (PDGF) regulates Slingshot phosphatase activity via Nox1-dependent auto-dephosphorylation of serine 834 in vascular smooth muscle cells

Migration of vascular smooth muscle cells (VSMCs) contributes to vascular pathology. PDGF induces VSMC migration by a Nox1-based NADPH oxidase mediated mechanism. We have previously shown that PDGF-induced migration in VSMCs requires Slingshot-1L (SSH1L) phosphatase activity. In the present work, the mechanism of SSH1L activation by PDGF is further investigated. We identified a 14-3-3 consensus binding motif encompassing Ser-834 in SSH1L that is constitutively phosphorylated. PDGF induces SSH1L auto-dephosphorylation at Ser-834 in wild type (wt), but not in Nox1(-/y) cells. A SSH1L-S834A phospho-deficient mutant has significantly lower binding capacity for 14-3-3 when compared with the phospho-mimetic SSH1L-S834D mutant, and acts as a constitutively active phosphatase, lacking of PDGF-mediated regulation. Given that Nox1 produces reactive oxygen species, we evaluated their participation in this SSH1L activation mechanism. We found that H(2)O(2) activates SSH1L and this is accompanied by SSH1L/14-3-3 complex disruption and 14-3-3 oxidation in wt, but not in Nox1(-/y) cells. Together, these data demonstrate that PDGF activates SSH1L in VSMC by a mechanism that involves Nox1-mediated oxidation of 14-3-3 and Ser-834 SSH1L auto-dephosphorylation.

Cofilin and slingshot localization in the epithelium of uterine endometrium changes during the menstrual cycle and in endometriosis

Regulation of the actin cytoskeleton is essential for epithelial cell polarity and protein trafficking within human uterine epithelium. The actin-binding protein cofilin is involved in regulation of actin dynamics by promoting actin branching and cytoskeleton reorganization. Dual immunohistochemical staining of cofilin and G-actin (represented by DNAse I staining) revealed cofilin-G-actin colocalization in the apical side of luminal epithelial cells of human uterine endometrium during the proliferative phase of the menstrual cycle. Interestingly, during the secretory phase of the menstrual cycle, cofilin was only present on the basolateral side. To determine whether the disease endometriosis causes a different pattern of actin remodeling, we investigated an established baboon model of induced endometriosis. The cofilin pattern in the secretory phase of baboons with endometriosis was similar to the proliferative phase in normal animals; cofilin was observed in the apical parts of luminal and glandular epithelium. A phosphatase regulating the activity of cofilin, slingshot (SSH1), revealed a similar staining pattern within these tissues. These patterns were confirmed through quantitative image analysis. Quantification of messenger RNA (mRNA) detected upregulated SSH1 and suggested a progesterone resistance-related pattern of nuclear steroid hormone receptors, but no change in membrane progesterone receptors (mPR alpha or mPR beta) was observed in endometriosis. Our data indicate that the severe dyssynchrony during menstrual cycle phases in endometriosis is connected with improper cytoskeleton rearrangements. We suggest that cofilin-mediated actin reorganization in uterine epithelial cells might be important in preparation for blastocyst implantation; dysregulation of this reorganization may lead to decreased fertility in endometriosis.