Control of actin dynamics by p38 MAP kinase – Hsp27 distribution in the lamellipodium of smooth muscle cells

A combined proteomic and transcriptomic approach shows diverging molecular mechanisms in thoracic aortic aneurysm development in patients with tricuspid- and bicuspid aortic valve

Thoracic aortic aneurysm is a pathological local dilatation of the aorta, potentially leading to aortic rupture or dissection. The disease is a common complication of patients with bicuspid aortic valve, a congenital disorder present in 1-2% of the population. Using two dimensional fluorescence difference gel electrophoresis proteomics followed by mRNA expression, and alternative splicing analysis of the identified proteins, differences in dilated and nondilated aorta tissues between 44 patients with bicuspid and tricuspid valves was examined. The pattern of protein expression was successfully validated with LC-MS/MS. A multivariate analysis of protein expression data revealed diverging protein expression fingerprints in patients with tricuspid compared with the patients with bicuspid aortic valves. From 302 protein spots included in the analysis, 69 and 38 spots were differentially expressed between dilated and nondilated aorta specifically in patients with tricuspid and bicuspid aortic valve, respectively. 92 protein spots were differentially expressed between dilated and nondilated aorta in both phenotypes. Similarly, mRNA expression together with alternative splicing analysis of the identified proteins also showed diverging fingerprints in the two patient groups. Differential splicing was abundant but the expression levels of differentially spliced mRNA transcripts were low compared with the wild type transcript and there was no correlation between splicing and the number of spots. Therefore, the different spots are likely to represent post-translational modifications. The identification of differentially expressed proteins suggests that dilatation in patients with a tricuspid aortic valve involves inflammatory processes whereas aortic aneurysm in patients with BAV may be the consequence of impaired repair capacity. The results imply that aortic aneurysm formation in patients with bicuspid and tricuspid aortic valves involve different biological pathways leading to the same phenotype.

AMP-18 facilitates assembly and stabilization of tight junctions to protect the colonic mucosal barrier

BACKGROUND

Inflammatory bowel disease (IBD) is characterized by an injured epithelium. Development of agents that could enhance mucosal healing is a major goal in IBD therapeutics. The 18-kDa antrum mucosal protein (AMP-18) and a 21-mer peptide derived from AMP-18 stimulate accumulation of tight junction (TJ) proteins in cultured epithelial cells and mouse colonic mucosa to protect the mucosal barrier, suggesting it might be a useful agent to treat IBD.

METHODS

We searched for molecular mechanisms by which AMP peptide or recombinant AMP-18 act on TJs in intact cell monolayers, or those disrupted by low-calcium medium. Roles of the p38 mitogen-activated protein kinase (MAPK) / heat shock protein (hsp)25 pathway and PKCζ were investigated by immunoblotting and confocal microscopy.

RESULTS

AMP peptide activated p38 MAPK, which subsequently phosphorylated hsp25. Accumulated phospho-hsp25 was associated with perijunctional actin. AMP-18 also induced rapid phosphorylation of PKCζ and its colocalization with perijunctional actin in Caco2/bbe cells, which was accompanied by translocation and formation of complexes of "polarity proteins" in the TJ-containing detergent-insoluble fraction. Treatment with AMP-18 also stimulated accumulation of ZO-1, ZO-2, and JAM-A in nascent TJs known to associate with the multimeric p-PKCζ/Par6/ Cdc42/ECT2·GTP/Par3 polarity protein complex.

CONCLUSIONS

AMP-18 facilitates translocation and assembly of multiple proteins into TJs and their association with and subsequent stabilization of the actin filament network. We speculate that improved barrier function induced by AMP-18 is mediated by enhanced TJ assembly. Thus, AMP-18 may provide a promising lead to develop agents effective in healing injured colonic epithelium in IBD.

Reactive oxygen species regulate protrusion efficiency by controlling actin dynamics

Productive protrusions allowing motile cells to sense and migrate toward a chemotactic gradient of reactive oxygen species (ROS) require a tight control of the actin cytoskeleton. However, the mechanisms of how ROS affect cell protrusion and actin dynamics are not well elucidated yet. We show here that ROS induce the formation of a persistent protrusion. In migrating epithelial cells, protrusion of the leading edge requires the precise regulation of the lamellipodium and lamella F-actin networks. Using fluorescent speckle microscopy, we showed that, upon ROS stimulation, the F-actin retrograde flow is enhanced in the lamellipodium. This event coincides with an increase of cofilin activity, free barbed ends formation, Arp2/3 recruitment, and ERK activity at the cell edge. In addition, we observed an acceleration of the F-actin flow in the lamella of ROS-stimulated cells, which correlates with an enhancement of the cell contractility. Thus, this study demonstrates that ROS modulate both the lamellipodium and the lamella networks to control protrusion efficiency.

Absence of a human DnaJ protein hTid-1S correlates with aberrant actin cytoskeleton organization in lesional psoriatic skin

The biochemical mechanism by which the human tumorous imaginal disc1(S) (hTid-1(S)) interferes with actin cytoskeleton organization in keratinocytes of human skin epidermis was investigated. We found that hTid-1, specifically hTid-1(S), interacts with MK5, a p38-regulated/activated protein kinase, and inhibits the protein kinase activity of MK5 that phosphorylates heat shock protein HSP27 in cultured HeLa cells. Thus, hTid-1(S) expression inhibits the phosphorylation of HSP27 known to play important roles in F-actin polymerization and actin cytoskeleton organization. The interplay between MK5/HSP27 signaling and hTid-1(S) expression was supported by the inhibition of HSP27 phosphorylation and MK5 activity in HeLa cells in response to hypoxia during which hTid-1(S) expression was down-regulated. We also found that overexpression of hTid-1(S) results in the inhibition of HSP27 phosphorylation, F-actin polymerization, and actin cytoskeleton organization in transduced HaCaT keratinocytes. This study further proposes that the loss of hTid-1(S) expression in the basal layer of skin epidermis correlates with the enhanced HSP27 phosphorylation, keratinocyte hyperproliferation, and excess actin cytoskeleton organization in lesional psoriatic skin.

Neutrophils Promote Mycobacterial Trehalose Dimycolate-Induced Lung Inflammation via the Mincle Pathway

Trehalose 6,6'-dimycolate (TDM), a cord factor of Mycobacterium tuberculosis (Mtb), is an important regulator of immune responses during Mtb infections. Macrophages recognize TDM through the Mincle receptor and initiate TDM-induced inflammatory responses, leading to lung granuloma formation. Although various immune cells are recruited to lung granulomas, the roles of other immune cells, especially during the initial process of TDM-induced inflammation, are not clear. In this study, Mincle signaling on neutrophils played an important role in TDM-induced lung inflammation by promoting adhesion and innate immune responses. Neutrophils were recruited during the early stage of lung inflammation following TDM-induced granuloma formation. Mincle expression on neutrophils was required for infiltration of TDM-challenged sites in a granuloma model induced by TDM-coated-beads. TDM-induced Mincle signaling on neutrophils increased cell adherence by enhancing F-actin polymerization and CD11b/CD18 surface expression. The TDM-induced effects were dependent on Src, Syk, and MAPK/ERK kinases (MEK). Moreover, coactivation of the Mincle and TLR2 pathways by TDM and Pam3CSK4 treatment synergistically induced CD11b/CD18 surface expression, reactive oxygen species, and TNFα production by neutrophils. These synergistically-enhanced immune responses correlated with the degree of Mincle expression on neutrophil surfaces. The physiological relevance of the Mincle-mediated anti-TDM immune response was confirmed by defective immune responses in Mincle⁻/⁻ mice upon aerosol infections with Mtb. Mincle-mutant mice had higher inflammation levels and mycobacterial loads than WT mice. Neutrophil depletion with anti-Ly6G antibody caused a reduction in IL-6 and monocyte chemotactic protein-1 expression upon TDM treatment, and reduced levels of immune cell recruitment during the initial stage of infection. These findings suggest a new role of Mincle signaling on neutrophils during anti-mycobacterial responses.

Charcot-Marie-Tooth disease and intracellular traffic

Mutations of genes whose primary function is the regulation of membrane traffic are increasingly being identified as the underlying causes of various important human disorders. Intriguingly, mutations in ubiquitously expressed membrane traffic genes often lead to cell type- or organ-specific disorders. This is particularly true for neuronal diseases, identifying the nervous system as the most sensitive tissue to alterations of membrane traffic. Charcot-Marie-Tooth (CMT) disease is one of the most common inherited peripheral neuropathies. It is also known as hereditary motor and sensory neuropathy (HMSN), which comprises a group of disorders specifically affecting peripheral nerves. This peripheral neuropathy, highly heterogeneous both clinically and genetically, is characterized by a slowly progressive degeneration of the muscle of the foot, lower leg, hand and forearm, accompanied by sensory loss in the toes, fingers and limbs. More than 30 genes have been identified as targets of mutations that cause CMT neuropathy. A number of these genes encode proteins directly or indirectly involved in the regulation of intracellular traffic. Indeed, the list of genes linked to CMT disease includes genes important for vesicle formation, phosphoinositide metabolism, lysosomal degradation, mitochondrial fission and fusion, and also genes encoding endosomal and cytoskeletal proteins. This review focuses on the link between intracellular transport and CMT disease, highlighting the molecular mechanisms that underlie the different forms of this peripheral neuropathy and discussing the pathophysiological impact of membrane transport genetic defects as well as possible future ways to counteract these defects.

Deletion of the SPARC acidic domain or EGF-like module reduces SPARC-induced migration and signaling through p38 MAPK/HSP27 in glioma

We previously demonstrated that secreted protein acidic and rich in cysteine (SPARC) increases heat shock protein 27 (HSP27) expression and phosphorylation and promotes glioma cell migration through the p38 mitogen-activated protein kinase (MAPK)/HSP27 signaling pathway. As different regions of the SPARC protein mediate different SPARC functions, elucidating which SPARC domains regulate HSP27 expression, signaling and migration might provide potential therapeutic strategies to target these functions. To investigate the roles of specific domains, we used an SPARC-green fluorescent protein (GFP) fusion protein and constructs of SPARC-GFP with deletions of either the acidic domain (ΔAcidic) or the epidermal growth factor (EGF)-like module (ΔEGF). GFP, SPARC-GFP and the two deletion mutants were expressed in U87MG glioma cells. Characterization of the derived stable clones by confocal imaging and western blotting suggests proper folding, processing and secretion of the deletion constructs. Uptake of the constructs by naive cells suggests enhanced internalization of ΔAcidic and reduced internalization of ΔEGF. Wound and transwell migration assays and western blot analysis confirm our previous results and indicate that ΔAcidic reduces SPARC-induced migration and p38 MAPK/HSP27 signaling and ΔEGF decreases SPARC-induced migration and dramatically decreases the expression and phosphorylation of HSP27 but is poorly internalized. Loss of the EGF-like module suppresses the enhanced HSP27 protein stability conferred by SPARC. In conclusion, deletions of the acidic domain and EGF-like module have differential effects on cell surface binding and HSP27 protein stability; however, both regions regulate SPARC-induced migration and signaling through HSP27. Our data link the domains of SPARC with different functions and suggest one or both of the constructs as potential therapeutic agents to inhibit SPARC-induced migration.

Hsp27-actin interaction

Hsp27 oligomer is reported to interact with F-actin as a barbed-end-capping protein. The present study determined the binding strength and stoichiometry of the interaction using fluorescence of probes attached to Hsp27 cysteine-137. The fluorescence of acrylodan attached to Hsp27 increased 4-5-fold upon interaction with F-actin. Titration of the fluorescence with F-actin yielded a weak binding constant (K_D^app = 5.3 μM) with an actin/Hsp27 stoichiometry between < 1 and 6. This stoichiometry is inconsistent with an F-actin end-capping protein. Pyrene attached to Hsp27 exhibited a large excimer fluorescence, in agreement with the known proximity of the cysteine-137's in the Hsp27 oligomer. Upon interaction with F-actin the pyrene-Hsp27 excimer fluorescence was largely lost, suggesting that Hsp27 interacts with F-actin as a monomer, consistent with the acrylodan-Hsp27 results. EM images of F-actin-Hsp27 demonstrated that Hsp27 is not a strong G-actin sequester. Thus, Hsp27, in vitro, is a weak F-actin side-binding protein.

Accelerating axonal growth promotes motor recovery after peripheral nerve injury in mice

Although peripheral nerves can regenerate after injury, proximal nerve injury in humans results in minimal restoration of motor function. One possible explanation for this is that injury-induced axonal growth is too slow. Heat shock protein 27 (Hsp27) is a regeneration-associated protein that accelerates axonal growth in vitro. Here, we have shown that it can also do this in mice after peripheral nerve injury. While rapid motor and sensory recovery occurred in mice after a sciatic nerve crush injury, there was little return of motor function after sciatic nerve transection, because of the delay in motor axons reaching their target. This was not due to a failure of axonal growth, because injured motor axons eventually fully re-extended into muscles and sensory function returned; rather, it resulted from a lack of motor end plate reinnervation. Tg mice expressing high levels of Hsp27 demonstrated enhanced restoration of motor function after nerve transection/resuture by enabling motor synapse reinnervation, but only within 5 weeks of injury. In humans with peripheral nerve injuries, shorter wait times to decompression surgery led to improved functional recovery, and, while a return of sensation occurred in all patients, motor recovery was limited. Thus, absence of motor recovery after nerve damage may result from a failure of synapse reformation after prolonged denervation rather than a failure of axonal growth.

β-arrestin-dependent actin reorganization: bringing the right players together at the leading edge

First identified as mediators of G-protein-coupled receptor desensitization and internalization and later as signaling platforms, β-arrestins play a requisite role in chemotaxis and reorganization of the actin cytoskeleton, downstream of multiple receptors. However, the precise molecular mechanisms underlying their involvement have remained elusive. Initial interest in β-arrestins as facilitators of cell migration and actin reorganization stemmed from the known interplay between receptor endocytosis and actin filament formation, because disruption of the actin cytoskeleton inhibits these β-arrestin-dependent events. With growing interest in the mechanisms by which cells can sense a gradient of agonist during cell migration, investigators began to hypothesize that β-arrestins may contribute to directed migration by controlling chemotactic receptor turnover at the plasma membrane. Finally, increasing evidence emerged that β-arrestins are more than just clathrin adaptor proteins involved in turning off receptor signals; they are actually capable of generating their own signals by scaffolding signaling molecules and controlling the activity of multiple cellular enzymes. This new role of β-arrestins as signaling scaffolds has led to the hypothesis that they can facilitate cell migration by sequestering actin assembly activities and upstream regulators of actin assembly at the leading edge. This Minireview discusses recent advances in our understanding of how β-arrestin scaffolds contribute to cell migration, focusing on recently identified β-arrestin interacting proteins and phosphorylation targets that have known roles in actin reorganization.

Rapid Disruption of Cellular Integrity of Zinc-treated Astroglia Is Regulated by p38 MAPK and Ca-dependent Mechanisms

Cultured cortical primary astroglia treated with zinc died while rapidly detached from culture plates, a distinct part of zinc-treated astroglia. In the present study, we investigated the mechanism underlying the rapid change in the morphologic integrity of zinc-treated astroglia. Among the early cellular events occurring in zinc-treated astroglia, strong activation of p38 MAPK and JNK was evident. Although inhibitors of p38 (SB203580 and SB202190) or JNK (SP600125) did not protect zinc-insulted astroglia from cell death, the p38 inhibitors, but not the JNK inhibitor, suppressed actin filament and cell morphology disruption. The Ca(2+) ionophore, A23187, also suppressed actin filament and cell morphology disruption, but not cell death, of zinc-insulted astroglia. However, A23187 did not inhibit p38 MAPK activation in zinc-treated astroglia. Together these results suggest that zinc influx in astroglia results in rapid loss of the morphologic integrity via mechanisms regulated by p38 kinase and/or Ca(2+) signaling.

The p38/MK2/Hsp25 pathway is required for BMP-2-induced cell migration

Background

Bone morphogenetic proteins (BMPs) have been shown to participate in the patterning and specification of several tissues and organs during development and to regulate cell growth, differentiation and migration in different cell types. BMP-mediated cell migration requires activation of the small GTPase Cdc42 and LIMK1 activities. In our earlier report we showed that activation of LIMK1 also requires the activation of PAKs through Cdc42 and PI3K. However, the requirement of additional signaling is not clearly known.

Methodology/Principal Findings

Activation of p38 MAPK has been shown to be relevant for a number of BMP-2′s physiological effects. We report here that BMP-2 regulation of cell migration and actin cytoskeleton remodelling are dependent on p38 activity. BMP-2 treatment of mesenchymal cells results in activation of the p38/MK2/Hsp25 signaling pathway downstream from the BMP receptors. Moreover, chemical inhibition of p38 signaling or genetic ablation of either p38α or MK2 blocks the ability to activate the downstream effectors of the pathway and abolishes BMP-2-induction of cell migration. These signaling effects on p38/MK2/Hsp25 do not require the activity of either Cdc42 or PAK, whereas p38/MK2 activities do not significantly modify the BMP-2-dependent activation of LIMK1, measured by either kinase activity or with an antibody raised against phospho-threonine 508 at its activation loop. Finally, phosphorylated Hsp25 colocalizes with the BMP receptor complexes in lamellipodia and overexpression of a phosphorylation mutant form of Hsp25 is able to abolish the migration of cells in response to BMP-2.

Conclusions

These results indicate that Cdc42/PAK/LIMK1 and p38/MK2/Hsp25 pathways, acting in parallel and modulating specific actin regulatory proteins, play a critical role in integrating responses during BMP-induced actin reorganization and cell migration.

Anti-inflammatory cytokine interleukin-19 inhibits smooth muscle cell migration and activation of cytoskeletal regulators of VSMC motility

Vascular smooth muscle cell (VSMC) migration is an important cellular event in multiple vascular diseases, including atherosclerosis, restenosis, and transplant vasculopathy. Little is known regarding the effects of anti-inflammatory interleukins on VSMC migration. This study tested the hypothesis that an anti-inflammatory Th2 interleukin, interleukin-19 (IL-19), could decrease VSMC motility. IL-19 significantly decreased platelet-derived growth factor (PDGF)-stimulated VSMC chemotaxis in Boyden chambers and migration in scratch wound assays. IL-19 significantly decreased VSMC spreading in response to PDGF. To determine the molecular mechanism(s) for these cellular effects, we examined the effect of IL-19 on activation of proteins that regulate VSMC cytoskeletal dynamics and locomotion. IL-19 decreased PDGF-driven activation of several cytoskeletal regulatory proteins that play an important role in smooth muscle cell motility, including heat shock protein-27 (HSP27), myosin light chain (MLC), and cofilin. IL-19 decreased PDGF activation of the Rac1 and RhoA GTPases, important integrators of migratory signals. IL-19 was unable to inhibit VSMC migration nor was able to inhibit activation of cytoskeletal regulatory proteins in VSMC transduced with a constitutively active Rac1 mutant (RacV14), suggesting that IL-19 inhibits events proximal to Rac1 activation. Together, these data are the first to indicate that IL-19 can have important inhibitory effects on VSMC motility and activation of cytoskeletal regulatory proteins. This has important implications for the use of anti-inflammatory cytokines in the treatment of vascular occlusive disease.

Structure-functions of HspB1 (Hsp27)

Human HspB1 (also denoted Hsp27) is a well-known member, together with alphaB-crystallin, of the small heat-shock (or stress) proteins (sHsps) (20-40 kDa). In this chapter, I describe procedures for testing the oligomeric and phosphorylation patterns of HspB1 as well as its interaction with specific partner/client polypeptides using tissue culture cells genetically modified to express different levels of this protein. The procedures have been developed in my laboratory and could be used in any well-established cellular laboratory. In addition, the different procedures presented here could be extended to test the nine other human sHsp members as well as sHsps from other species.

HMGB1 induces human lung endothelial cell cytoskeletal rearrangement and barrier disruption

Acute lung injury (ALI) results from loss of alveolar-capillary barrier integrity and the evolution of high-permeability pulmonary edema resulting in alveolar flooding and significant morbidity and mortality. HMGB1 is a late mediator of sepsis which uniquely participates in the evolution of sepsis and sepsis-induced ALI. The molecular events by which HMGB1 contributes to ALI remain poorly characterized. We characterized the role of HMGB1 in endothelial cell (EC) cytoskeletal rearrangement and vascular permeability, events essential to paracellular gap formation and barrier dysfunction characteristic of ALI. Initial experiments demonstrated HMGB1-mediated dose-dependent (5-20 μg/ml) decreases in transendothelial cell electrical resistance (TER) in the human pulmonary artery EC, a reflection of loss of barrier integrity. Furthermore, HMGB1 produced dose-dependent increases in paracellular gap formation in concert with loss of peripheral organized actin fibers, dissociation of cell-cell junctional cadherins, and the development of central stress fibers, a phenotypic change associated with increased contractile activity and increased EC permeability. Using siRNA strategies directed against known HMGB1 receptors (RAGE, TLR2, TLR4), we systematically determined that the receptor for advanced glycation end products (RAGE) is the primary receptor signaling HMGB1-induced TER decreases and paracellular gap formation via p38 MAP kinase activation and phosphorylation of the actin-binding protein, Hsp27. These studies add to the understanding of HMGB1-induced inflammatory events and vascular barrier disruption and offer the potential for clinical intervention in sepsis-induced ALI.

Curcumin activates the p38MPAK-HSP25 pathway in vitro but fails to attenuate diabetic nephropathy in DBA2J mice despite urinary clearance documented by HPLC

BACKGROUND

Curcumin has anti-inflammatory, anti-oxidant, and anti-proliferative properties, and depending upon the experimental circumstances, may be pro- or anti-apoptotic. Many of these biological actions could ameliorate diabetic nephropathy.

METHODS/DESIGN

Mouse podocytes, cultured in basal or high glucose conditions, underwent acute exposure to curcumin. Western blots for p38-MAPK, COX-2 and cleaved caspase-3; isoelectric focusing for HSP25 phosphorylation; and DNase I assays for F- to G- actin cleavage were performed for in vitro analyses. In vivo studies examined the effects of dietary curcumin on the development of diabetic nephropathy in streptozotocin (Stz)-induced diabetes in DBA2J mice. Urinary albumin to creatinine ratios were obtained, high performance liquid chromatography was performed for urinary curcuminoid measurements, and Western blots for p38-MAPK and total HSP25 were performed.

RESULTS

Curcumin enhanced the phosphorylation of both p38MAPK and downstream HSP25; inhibited COX-2; induced a trend towards attenuation of F- to G-actin cleavage; and dramatically inhibited the activation of caspase-3 in vitro. In curcumin-treated DBA2J mice with Stz-diabetes, HPLC measurements confirmed the presence of urinary curcuminoid. Nevertheless, dietary provision of curcumin either before or after the induction of diabetes failed to attenuate albuminuria.

CONCLUSIONS

Apart from species, strain, early differences in glycemic control, and/or dosing effects, the failure to modulate albuminuria may have been due to a decrement in renal HSP25 or stimulation of the 12/15 lipoxygenase pathway in DBA2J mice fed curcumin. In addition, these studies suggest that timed urine collections may be useful for monitoring curcumin dosing and renal pharmacodynamic effects.

Modulation of mammary cancer cell migration by 15-deoxy-delta(12,14)-prostaglandin J(2): implications for anti-metastatic therapy

Recently, a number of steps in the progression of metastatic disease have been shown to be regulated by redox signalling. Electrophilic lipids affect redox signalling through the post-translational modification of critical cysteine residues in proteins. However, the therapeutic potential as well as the precise mechanisms of action of electrophilic lipids in cancer cells is poorly understood. In the present study, we investigate the effect of the electrophilic prostaglandin 15d-PGJ2 (15-deoxy-Delta12,14-prostaglandin J2) on metastatic properties of breast cancer cells. 15d-PGJ2 was shown to decrease migration, stimulate focal-adhesion disassembly and cause extensive F-actin (filamentous actin) reorganization at low concentrations (0.03-0.3 microM). Importantly, these effects seem to be independent of PPARgamma (peroxisome-proliferator-activated receptor gamma) and modification of actin or Keap1 (Kelch-like ECH-associated protein 1), which are known protein targets of 15d-PGJ2 at higher concentrations. Interestingly, the p38 inhibitor SB203580 was able to prevent both 15d-PGJ2-induced F-actin reorganization and focal-adhesion disassembly. Taken together, the results of the present study suggest that electrophiles such as 15d-PGJ2 are potential anti-metastatic agents which exhibit specificity for migration and adhesion pathways at low concentrations where there are no observed effects on Keap1 or cytotoxicity.

HSPB1, actin filament dynamics, and aging cells

Investigations into the possible roles of human HSPB1 in aging have focused on its role as a molecular chaperone protecting partially folded or unfolded proteins, particularly during oxidative stress. A thorough analysis of potential roles of HSPB1 in aging cells has been hampered by a limited knowledge of its functions in living cells. Most studies have employed cell-free extracts and purified proteins. For example, HSPB1 is known to bind actin in vitro, and this observation led to the hypothesis that HSPB1 regulates actin filament dynamics. In the study summarized herein, the role of HSPB1 in regulating actin filament dynamics was further investigated by using cultured human cells. These results show that HSPB1 and actin form a complex in vivo and that HSPB1 is important for cell motility. A model for HSPB1 as a regulator of actin filament dynamics is presented, and evidence from the literature on cytoskeletal alterations in aging cells is discussed.

Protective effect of phosphorylated Hsp27 in coronary arteries through actin stabilization

There is evidence for an inverse association between cellular expression of Hsp27 and vascular disease with carotid plaques, endarterectomy specimens, and cardiac biopsies investigated to date. Here we compare non-diseased coronary arteries from human heart transplant donors and patients with dilated cardiomyopathy (DCM) with no evidence of coronary artery disease, to coronary arteries from patients with ischemic heart disease (IHD) in order to determine abundance of phosphorylated Hsp27 (phospho-Hsp27) in plaque-free diseased vessels and elucidate how this protective effect is brought about through protein regulation. Western blotting identified phospho-Hsp27, phosphorylated on Ser82, Ser78, and Ser15, to be specifically decreased in IHD, but not DCM, compared to non-diseased vessels. Immunohistochemistry confirmed these results and revealed phospho-Hsp27 was located within both smooth muscle and endothelial cells. Disease-free coronary arteries and from patients with IHD were then subjected to 2-Dimensional Difference Gel Electrophoresis (2D-DIGE) analysis to detect proteins with altered abundance, which were subsequently identified by mass spectrometry. Hsp27 showed decreased abundance in ischemic vessels as expected. The expression of cytoskeletal proteins, namely vimentin was significantly reduced, while transgelin and tropomyosin showed significantly increased abundance in vessels with IHD. Immunohistochemistry studies suggested an increase in G-actin abundance to be present within IHD vessels. The results are consistent with the hypothesis that phospho-Hsp27 protects against vascular disease possibly by stabilizing the actin cytoskeleton within endothelial and/or smooth muscle cells.

Dynamic processes that reflect anti-apoptotic strategies set up by HspB1 (Hsp27)

Human HspB1 (also denoted Hsp27) is an oligomeric anti-apoptotic protein that has tumorigenic and metastatic roles. To approach the structural organizations of HspB1 that are active in response to apoptosis inducers acting through different pathways, we have analyzed the relative protective efficiency induced by this protein as well its localization, oligomerization and phosphorylation. HeLa cells, that constitutively express high levels of HspB1 were treated with either etoposide, Fas agonist antibody, staurosporine or cytochalasin D. Variability in HspB1 efficiency to interfere with the different apoptotic transduction pathways induced by these agents were detected. Moreover, inducer-specific dynamic changes in HspB1 localization, native size and phosphorylation were observed, that differed from those observed after heat shock. Etoposide and Fas treatments gradually shifted HspB1 towards large but differently phosphorylated oligomeric structures. In contrast, staurosporine and cytochalasin D induced the rapid but transient formation of small oligomers before large structures were formed. These events correlated with inducer-specific phosphorylations of HspB1. Of interest, the formation of small oligomers in response to staurosporine and cytochalasin D was time correlated with the rapid disruption of F-actin. The subsequent, or gradual in the case of etoposide and Fas, formation of large oligomeric structures was a later event concomitant with the early phase of caspase activation. These observations support the hypothesis that HspB1 has the ability, through specific changes in its structural organization, to adapt and interfere at several levels with challenges triggered by different signal transduction pathways upstream of the execution phase of apoptosis.

Thiolutin inhibits endothelial cell adhesion by perturbing Hsp27 interactions with components of the actin and intermediate filament cytoskeleton

Thiolutin is a dithiole synthesized by Streptomyces sp. that inhibits endothelial cell adhesion and tumor growth. We show here that thiolutin potently inhibits developmental angiogenesis in zebrafish and vascular outgrowth from tissue explants in 3D cultures. Thiolutin is a potent and selective inhibitor of endothelial cell adhesion accompanied by rapid induction of HSPB1 (Hsp27) phosphorylation. The inhibitory effects of thiolutin on endothelial cell adhesion are transient, potentially due to a compensatory increase in Hsp27 protein levels. Accordingly, heat shock induction of Hsp27 limits the anti-adhesive activity of thiolutin. Thiolutin treatment results in loss of actin stress fibers, increased cortical actin as cells retract, and decreased cellular F-actin. Mass spectrometric analysis of Hsp27 binding partners following immunoaffinity purification identified several regulatory components of the actin cytoskeleton that associate with Hsp27 in a thiolutin-sensitive manner including several components of the Arp2/3 complex. Among these, ArpC1a is a direct binding partner of Hsp27. Thiolutin treatment induces peripheral localization of phosphorylated Hsp27 and Arp2/3. Hsp27 also associates with the intermediate filament components vimentin and nestin. Thiolutin treatment specifically ablates Hsp27 interaction with nestin and collapses nestin filaments. These results provide new mechanistic insights into regulation of cell adhesion and cytoskeletal dynamics by Hsp27.

Molecular regulators of leucocyte chemotaxis during inflammation

A fundamental feature of any immune response is the movement of leucocytes from one site in the body to another to provide effector functions. Therefore, elucidating the molecular mechanisms underlying the migration of leucocytes from the blood to tissues is critical to our understanding of immune function during inflammation. The classic steps of leucocyte trafficking involve leucocyte tethering and rolling on vessel walls of the vasculature, followed by firm adhesion to the endothelium. Recent evidence suggests that upon adhering, leucocytes crawl within the vessels before transmigrating across vessel walls and crawling into targeted tissues. The directed nature of the crawling events is orchestrated by a complex array of soluble factors and molecular regulators in combination with the local intravascular and extracellular environment. In fact, this process is known as chemotaxis and orientates cell movement in relation to the ligand gradient. Several signalling pathways have been proposed to be involved in this gradient-sensing and amplification process, but the best studied, discussed in detail here, is the phosphatidylinositol 3-kinase pathway. Substantial progress has been made in understanding how cells roll and adhere in blood vessels; however, how cells crawl in blood vessels, emigrate, and then crawl in tissues has received much less attention. Therefore, the focus of this review is to provide recent insights into molecular mechanisms and cellular processes that mediate leucocyte crawling in blood vessels and tissues during the inflammatory response.

The role of Hsp27 and actin in the regulation of movement in human cancer cells responding to heat shock

Human heat shock 27-kDa protein 1 (HSPB1)/heat shock protein (Hsp) 27 is a small heat shock protein which is thought to have several roles within the cell. One of these roles includes regulating actin filament dynamics in cell movement, since Hsp27 has previously been found to inhibit actin polymerization in vitro. In this study, the role of Hsp27 in regulating actin filament dynamics is further investigated. Hsp27 protein levels were reduced using siRNA in SW480 cells, a human colon cancer cell line. An in vitro wound closure assay showed that cells with knocked down Hsp27 levels were unable to close wounds, indicating that this protein is involved in regulating cell motility. Immunoprecipitation pull down assays were done, to observe if and when Hsp27 and actin are in the same complex within the cell, before and after heat shock. At all time points tested, Hsp27 and actin were present in the same cell lysate fraction. Lastly, indirect immunostaining was done before and after heat shock to evaluate Hsp27 and actin interaction in cells. Hsp27 and actin showed colocalization before heat shock, little association 3 h after heat shock, and increased association 24 h after heat shock. Cytoprotection was observed as early as 3 h after heat shock, yet cells were still able to move. These results show that Hsp27 and actin are in the same complex in cells and that Hsp27 is important for cell motility.

Hsp-27 expression at diagnosis predicts poor clinical outcome in prostate cancer independent of ETS-gene rearrangement

BACKGROUND

This study was performed to test the hypothesis that expression of small heat shock protein Hsp-27 is, at diagnosis, a reliable predictive biomarker of clinically aggressive prostate cancer.

METHODS

A panel of tissue microarrays constructed from a well-characterised cohort of 553 men with conservatively managed prostate cancer was stained immunohistochemically to detect Hsp-27 protein. Hsp-27 expression was compared with a series of pathological and clinical parameters, including outcome.

RESULTS

Hsp-27 staining was indicative of higher Gleason score (P<0.001). In tissue cores having a Gleason score >7, the presence of Hsp-27 retained its power to independently predict poor clinical outcome (P<0.002). Higher levels of Hsp-27 staining were almost entirely restricted to cancers lacking ERG rearrangements (chi2 trend=31.4, P<0.001), although this distribution did not have prognostic significance.

INTERPRETATION

This study has confirmed that, in prostate cancers managed conservatively over a period of more than 15 years, expression of Hsp-27 is an accurate and independent predictive biomarker of aggressive disease with poor clinical outcome (P<0.001). These findings suggest that apoptotic and cell-migration pathways modulated by Hsp-27 may contain targets susceptible to the development of biologically appropriate chemotherapeutic agents that are likely to prove effective in treating aggressive prostate cancers.

Role of actin cytoskeleton in LPS-induced NF-kappaB activation and nitric oxide production in murine macrophages

Lipopolysaccharide (LPS) is a major cell wall component of Gram-negative bacteria and is known to cause actin cytoskeleton reorganization in a variety of cells including macrophages. Actin cytoskeleton dynamics influence many cell signaling pathways including the NF-kappaB pathway. LPS is also known to induce the expression of many pro-inflammatory genes via the NF-kappaB pathway. Here, we have investigated the role of actin cytoskeleton in LPS-induced NF-kappaB activation and signaling leading to the expression of iNOS and nitric oxide production. Using murine macrophages, we show that disruption of actin cytoskeleton by either cytochalasin D (CytD) or latrunculin B (LanB) does not affect LPS-induced NF-kappaB activation and the expression of iNOS, a NF-kappaB target gene. However, disruption of actin cytoskeleton caused significant reduction in LPS-induced nitric oxide production indicating a role of actin cytoskeleton in the post-translational regulation of iNOS.

Hindlimb unweighting induces changes in the p38MAPK contractile pathway of the rat abdominal aorta

Hindlimb unweighting (HLU) of rats is a model used to mimic the cephalic fluid shift potentially involved in the orthostatic intolerance experienced by astronauts. Certain arteries in these rats exhibit a decreased contractile response to adrenergic agonists. It was shown previously that this may be caused by changes in thick filament regulation (Summers et al., Vascul Pharmacol 48: 208-214, 2008). In the present study, it was hypothesized that HLU also modifies thin filament regulation by effects on p38(MAPK) and ERK. Abdominal aorta rings from 20-day HLU rats and untreated controls were subjected to phenylephrine and phorbol 12,13-dibutyrate (PDBU) concentration response curves in the presence and absence of two inhibitors: the p38(MAPK) inhibitor SB-203580 and the MEK inhibitor U-0126. SB-203580 decreased control sensitivity to both agonists, but HLU sensitivity was not significantly affected. U-0126, which blocks enzymes immediately upstream of ERK, affected sensitivity to both agonists equally between control and HLU. Western blot analysis revealed no change in total levels of p38(MAPK) and its downstream target heat shock protein 27 but did reveal a decrease in phosphorylated levels of both after stimulation with PDBU and phenylephrine after HLU treatment. Neither total ERK nor phosphorylated levels after stimulation were affected by HLU. Total levels of caldesmon, a molecule downstream of both pathways, were decreased, but phosphorylated levels after stimulation were decreased by roughly twice as much. The results of this study demonstrate that HLU downregulates p38(MAPK), but not ERK, signaling. In turn, this may decrease actin availability for contraction.

Peripheral sensory axon growth: from receptor binding to cellular signaling

Regeneration following axonal injury of the adult peripheral sensory nervous system is heavily influenced by factors located in a neuron's extracellular environment. These factors include neurotrophins, such as Nerve Growth Factor (NGF) and the extracellular matrix, such as laminin. The presence of these molecules in the peripheral nervous system (PNS) is a major contributing factor for the dichotomy between regenerative capacities of central vs. peripheral neurons. Although PNS neurons are capable of spontaneous regeneration, this response is critically dependent on many different factors including the type, location and severity of the injury. In this article, we will focus on the plasticity of adult dorsal root ganglion (DRG) sensory neurons and how trophic factors and the extracellular environment stimulate the activation of intracellular signaling cascades that promote axonal growth in adult dorsal root ganglion neurons.

A novel role for MAPKAPK2 in morphogenesis during zebrafish development

One of the earliest morphogenetic processes in the development of many animals is epiboly. In the zebrafish, epiboly ensues when the animally localized blastoderm cells spread, thin over, and enclose the vegetally localized yolk. Only a few factors are known to function in this fundamental process. We identified a maternal-effect mutant, betty boop (bbp), which displays a novel defect in epiboly, wherein the blastoderm margin constricts dramatically, precisely when half of the yolk cell is covered by the blastoderm, causing the yolk cell to burst. Whole-blastoderm transplants and mRNA microinjection rescue demonstrate that Bbp functions in the yolk cell to regulate epiboly. We positionally cloned the maternal-effect bbp mutant gene and identified it as the zebrafish homolog of the serine-threonine kinase Mitogen Activated Protein Kinase Activated Protein Kinase 2, or MAPKAPK2, which was not previously known to function in embryonic development. We show that the regulation of MAPKAPK2 is conserved and p38 MAP kinase functions upstream of MAPKAPK2 in regulating epiboly in the zebrafish embryo. Dramatic alterations in calcium dynamics, together with the massive marginal constrictive force observed in bbp mutants, indicate precocious constriction of an F-actin network within the yolk cell, which first forms at 50% epiboly and regulates epiboly progression. We show that MAPKAPK2 activity and its regulator p38 MAPK function in the yolk cell to regulate the process of epiboly, identifying a new pathway regulating this cell movement process. We postulate that a p38 MAPKAPK2 kinase cascade modulates the activity of F-actin at the yolk cell margin circumference allowing the gradual closure of the blastopore as epiboly progresses.

One of the earliest cell movement processes in the development of many animals is epiboly. In the zebrafish, epiboly ensues when the blastoderm cells spread over and enclose the yolk cell. Only a few factors are known to function in this fundamental process. We identified a maternal-effect mutant, betty boop (bbp), which displays a novel defect in epiboly, wherein the blastoderm margin constricts dramatically, precisely when half of the yolk cell is covered by the blastoderm, causing the yolk cell to burst. We demonstrate that Bbp functions in the yolk cell to regulate epiboly. We positionally cloned the bbp mutant gene and identified it as the serine-threonine kinase Mitogen Activated Protein Kinase Activated Protein Kinase 2, or MAPKAPK2, which was not previously known to function in embryonic development. We show that the regulation of MAPKAPK2 is conserved within a p38 MAP kinase pathway, thus identifying a new pathway in the regulation of this fundamental cell movement process. We postulate that a p38 MAPKAPK2 kinase cascade modulates F-actin contraction at the yolk cell margin circumference, allowing the gradual closure of the cells over the yolk cell as epiboly progresses.

Triamcinolone acetonide prevents oxidative stress-induced tight junction disruption of retinal pigment epithelial cells

PURPOSE

Oxidative stress is known to disrupt the integrity of retinal pigment epithelium (RPE) tight junctions. The goal of this study is to evaluate the effect of triamcinolone acetonide (TA) on the junctional integrity of RPE under oxidative stress and to identify the underlying mechanisms.

METHODS

Second passage porcine RPE cells were cultured on 6-well membrane inserts until 4 weeks after reaching confluence. Cells were incubated with TA (10(-5) M) for 30 min. FITC-containing medium was added to the upper chamber (cell's apical side). The cells were then challenged with 1 mM Hydrogen Peroxide (H(2)O(2)). After 5 h, the fluorescence intensity of the medium from lower chamber (cell's basolateral side) was measured using a fluorescence spectrofluorophotometer. This transepithelial flux of FITC-dextran was measured until the 21st day. The immunolocalization of occludin and F-actin was examined with fluorescence microscope. Reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio was determined by a colorimetric assay kit.

RESULTS

Non-lethal oxidative stress by H(2)O(2) increased transepithelial flux of FITC-dextran significantly. TA inhibited this increase and preserved the lower flux through the whole experimental period. This permeability change by H(2)O(2) was reversible and recovered to the normal level within 3 weeks. In immunohistological study, H(2)O(2) reduced linear occludin staining at the cell border and increased actin stress fibers. TA prevented H(2)O(2)-induced disruption of junctional assembly of occludin and F-actin. Glutathione assay demonstrated that intracellular GSH/GSSG ratio decreased significantly with H(2)O(2), while TA preserved this ratio by up-regulating GSH synthesis.

CONCLUSIONS

TA has a protective effect against oxidative stress-induced disruption of RPE tight junction by preserving cellular redox state.

PKA-induced F-actin rearrangement requires phosphorylation of Hsp27 by the MAPKAP kinase MK5

Mitogen-activated protein kinase (MAPK) pathways can play a role in F-actin dynamics. In particular, the p38 MAPK/MAPK-activated protein kinase 2 (MK2)/heat shock protein 27 (Hsp27) pathway is involved in F-actin alternations. Previously, we showed that MK5 is implicated in F-actin rearrangement induced by the cAMP/cAMP-dependent protein kinase pathway in PC12 cells, while others found Hsp27 to be a good in vitro MK5 substrate. Here we demonstrate that MK5 can specifically interact with Hsp27 in vivo and can induce phosphorylation at serine residues 78 and 82 in cells. siRNA-mediated depletion of Hsp27 protein levels, as well as overexpression of the non-phosphorylatable Hsp27-3A mutant prevented forskolin-induced F-actin reorganization. While ectopic expression of a constitutive active MK5 mutant was sufficient to induce F-actin rearrangement in PC12 cells, co-expression of Hsp27-3A could ablate this process. Our results imply that MK5 is involved in Hsp27-controlled F-actin dynamics in response to activation of the cAMP-dependent protein kinase pathway. These findings render the MK5/Hsp27 connection into a putative therapeutic target for conditions with aberrant Hsp27 phosphorylation such as metastasis, cardiovascular diseases, muscle atrophy, autoimmune skin disease and neuropathology.

Hyperosmotic stress induces Rho/Rho kinase/LIM kinase-mediated cofilin phosphorylation in tubular cells: key role in the osmotically triggered F-actin response

Hyperosmotic stress induces cytoskeleton reorganization and a net increase in cellular F-actin, but the underlying mechanisms are incompletely understood. Whereas de novo F-actin polymerization likely contributes to the actin response, the role of F-actin severing is unknown. To address this problem, we investigated whether hyperosmolarity regulates cofilin, a key actin-severing protein, the activity of which is inhibited by phosphorylation. Since the small GTPases Rho and Rac are sensitive to cell volume changes and can regulate cofilin phosphorylation, we also asked whether they might link osmostress to cofilin. Here we show that hyperosmolarity induced rapid, sustained, and reversible phosphorylation of cofilin in kidney tubular (LLC-PK1 and Madin-Darby canine kidney) cells. Hyperosmolarity-provoked cofilin phosphorylation was mediated by the Rho/Rho kinase (ROCK)/LIM kinase (LIMK) but not the Rac/PAK/LIMK pathway, because 1) dominant negative (DN) Rho and DN-ROCK but not DN-Rac and DN-PAK inhibited cofilin phosphorylation; 2) constitutively active (CA) Rho and CA-ROCK but not CA-Rac and CA-PAK induced cofilin phosphorylation; 3) hyperosmolarity induced LIMK-2 phosphorylation, and 4) inhibition of ROCK by Y-27632 suppressed the hypertonicity-triggered LIMK-2 and cofilin phosphorylation.We thenexamined whether cofilin and its phosphorylation play a role in the hypertonicity-triggered F-actin changes. Downregulation of cofilin by small interfering RNA increased the resting F-actin level and eliminated any further rise upon hypertonic treatment. Inhibition of cofilin phosphorylation by Y-27632 prevented the hyperosmolarity-provoked F-actin increase. Taken together, cofilin is necessary for maintaining the osmotic responsiveness of the cytoskeleton in tubular cells, and the Rho/ROCK/LIMK-mediated cofilin phosphorylation is a key mechanism in the hyperosmotic stress-induced F-actin increase.

Mitogen-activated protein kinases in hemostasis and thrombosis

The mitogen-activated protein (MAP) kinases ERK2, p38 and JNK1 are present in platelets and are activated by various stimuli, such as thrombin, collagen, von Willebrand factor (VWF) and ADP. Until recently, MAP kinases were only studied in the conventional model of agonist-induced platelet aggregation mediated by fibrinogen and integrin alphaIIbbeta3. However, this approach is likely to be too limited for a physiological understanding of platelet MAP kinases and their signaling pathways. Recent studies with varying blood-flow conditions and animal models of thrombosis have provided deeper insight into the role of MAP kinases in thrombus formation and the dependence of these kinases on shear conditions. This review summarizes and discusses the physiological functions of these kinases in hemostasis and thrombosis as revealed by various technical approaches.

Amifostine reduces lung vascular permeability via suppression of inflammatory signalling

Despite an encouraging outcome of antioxidant therapy in animal models of acute lung injury, effective antioxidant agents for clinical application remain to be developed. The present study investigated the effect of pre-treatment with amifostine, a thiol antioxidant compound, on lung endothelial barrier dysfunction induced by Gram-negative bacteria wall-lipopolysaccharide (LPS). Endothelial permeability was monitored by changes in transendothelial electrical resistance. Cytoskeletal remodelling and reactive oxygen species (ROS) production was examined by immunofluorescence. Cell signalling was assessed by Western blot. Measurements of Evans blue extravasation, cell count and protein content in bronchoalveolar lavage fluid were used as in vivo parameters of lung vascular permeability. Hydrogen peroxide, LPS and interleukin-6 caused cytoskeletal reorganisation and increased permeability in the pulmonary endothelial cells, reflecting endothelial barrier dysfunction. These disruptive effects were inhibited by pre-treatment with amifostine and linked to the amifostine-mediated abrogation of ROS production and redox-sensitive signalling cascades, including p38, extracellular signal regulated kinase 1/2, mitogen-activated protein kinases and the nuclear factor-kappaB pathway. In vivo, concurrent amifostine administration inhibited LPS-induced oxidative stress and p38 mitogen-activated protein kinase activation, which was associated with reduced vascular leak and neutrophil recruitment to the lungs. The present study demonstrates, for the first time, protective effects of amifostine against lipopolysaccharide-induced lung vascular leak in vitro and in animal models of lipopolysaccharide-induced acute lung injury.

A novel protein kinase A-independent, beta-arrestin-1-dependent signaling pathway for p38 mitogen-activated protein kinase activation by beta2-adrenergic receptors

A growing body of evidence has demonstrated that p38 mitogen-activated protein kinase (MAPK) has a crucial role in various physiological and pathological processes mediated by beta(2)-adrenergic receptors (beta(2)-ARs). However, the detailed mechanism of beta(2)-ARs-induced p38 MAPK activation has not yet been fully defined. The present study demonstrates a novel kinetic model of p38 MAPK activation induced by beta(2)-ARs in human embryonic kidney 293A cells. The beta(2)-AR agonist isoproterenol induced a time-dependent biphasic phosphorylation of p38 MAPK: the early phase peaked at 10 min, and was followed by a delayed phase that appeared at 90 min and was sustained for 6 h. Interestingly, inhibition of the cAMP/protein kinase A (PKA) pathway failed to affect the early phosphorylation but abolished the delayed activation. By contrast, silencing of beta-arrestin-1 expression by small interfering RNA inhibited the early phase activation of p38 MAPK. Furthermore, the NADPH oxidase complex is a downstream target of beta-arrestin-1, as evidenced by the fact that isoproterenol-induced Rac1 activation was also suppressed by beta-arrestin-1 knockdown. In addition, early phase activation of p38 MAPK was prevented by inactivation of Rac1 and NADPH oxidase by pharmacological inhibitors, overexpression of a dominant negative mutant of Rac1, and p47(phox) knockdown by RNA interference. Of note, we demonstrated that only early activation of p38 MAPK is involved in isoproterenol-induced F-actin rearrangement. Collectively, these data suggest that the classic cAMP/PKA pathway is responsible for the delayed activation, whereas a beta-arrestin-1/Rac1/NADPH oxidase-dependent signaling is a heretofore unrecognized mechanism for beta(2)-AR-mediated early activation of p38 MAPK.

Comprehensive characterization of heat shock protein 27 phosphorylation in human endothelial cells stimulated by the microbial dithiole thiolutin

Thiolutin is a sulfur-based microbial compound with known activity as an angiogenesis inhibitor. Relative to previously studied angiogenesis inhibitors, thiolutin is a remarkably potent inducer of heat shock protein 27 (Hsp27) phosphorylation. This phosphorylation requires p38 kinase but is independent of increased p38 phosphorylation. To elucidate how thiolutin regulates Hsp27 phosphorylation and ultimately angiogenesis, Hsp27 was immunoprecipitated using nonphosphorylated and phospho-Ser78 specific antibodies from lysates of thiolutin treated and untreated human umbilical vein endothelial cells and analyzed by LC-MS. Separate LC-MS analyses of Lys-C, Lys-C plus trypsin, and Lys-C plus Glu-C digests provided 100% sequence coverage, including the identification of a very large 13 kDa Lys-C fragment using a special sample handling procedure (4 M guanidine HCl) prior to the LC-MS analysis to improve the large peptide recovery. The analysis revealed a novel post-translational modification of Hsp27 involving truncation of the N-terminal Met and acetylation of the penultimate Thr. Analysis of a Glu-C fragment containing two phosphorylation sites, Ser78 and Ser82, and a tryptic fragment containing the other phosphorylation site, Ser15, enabled quantitative stoichiometry of Hsp27 phosphorylation by LC-MS. The strategy revealed details of Hsp27 phosphorylation, including significant di-phosphorylation at both Ser78 and Ser82, that would be difficult to obtain by traditional approaches because oligomerization of the hydrophobic N-terminal region of the molecule prevents efficient enzymatic cleavage. The combination of Western blotting, immunoprecipation, and LC-MS provides a quantitative analysis of thiolutin-stimulated Hsp27 phosphorylation and further defines the role of Hsp27 in the antiangiogenic activities of thiolutin and related dithiolethiones.

PI3K accelerates, but is not required for, neutrophil chemotaxis to fMLP

PI3K activity, resulting in the accumulation of PIP(3) along the leading edge of a chemotaxing cell, has been proposed to be an indispensable signaling event that is required for cells to undergo chemotaxis to endogenous and exogenous chemoattractants. Some studies have suggested that this might be the case for chemoattractants such as IL8, whereas chemotaxis to other stimuli, such as the bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP), might occur normally in the absence of PI3K activity. Herein, we systematically analyze the role of PI3K in mediating chemotaxis to fMLP, both in vitro and in vivo. Using short- and long-term in vitro assays, as well as an in vivo chemotaxis assay, we investigated the importance of PI3K in response to the prototypic chemoattractant fMLP. Exposure of neutrophils to fMLP induced an immediate polarization, which resulted in directional migration towards fMLP within 2-3 minutes. PI3K-inhibited cells also polarized and migrated in a directional fashion towards fMLP; however, this process was delayed by approximately 15 minutes, demonstrating that PI3K accelerates the initial response to fMLP, but an alternative pathway replaces PI3K over time. By contrast, p38-MAPK-inhibited cells, or cells lacking MK2, were unable to polarize in response to fMLP. Long-term chemotaxis assays using a pan-PI3K inhibitor, a PI3Kdelta-specific inhibitor or PI3Kgamma-knockout neutrophils, demonstrated no role for PI3K in mediating chemotaxis to fMLP, regardless of the steepness of the fMLP gradient. Similar results were observed in vivo, with PI3Kgamma(-/-) cells displaying a delayed, but otherwise normal, chemotactic response to gradients of fMLP. Together, these data demonstrate that, although PI3K can enhance early responses to the bacterial chemoattractant fMLP, it is not required for migration towards this chemoattractant.

HSP27 regulates cell adhesion and invasion via modulation of focal adhesion kinase and MMP-2 expression

Heat-shock protein 27 (HSP27), a member of the small heat-shock protein family, is a molecule involved in cellular protection in response to a variety of stresses such as heat shock, toxicants, and oxidative stress. HSP27 is also known to modulate cell functions via interaction with the actin cytoskeleton. To elucidate the functions of HSP27 in adhesion and invasion in more detail, we examined NIH3T3 cells overexpressing HSP27. HSP27 overexpression affected FAK phosphorylation and focal adhesion formation, depending on integrin-mediated actin cytoskeleton polymerization. In addition, the HSP27-overexpressing cells showed a retarded cell migration and invasion in wound-healing assays. Such HSP27-mediated retarded wound healing was correlated with reduced matrix metalloproteinase-2 (MMP-2) expression. The transcription factor for MMP-2 expression, signal transducer and activator or transcription 3 (STAT3), was correspondingly less phosphorylated. When a phosphomimetic form of HSP27 was transiently transfected, migration and invasion were similarly decreased via the regulation of the FAK/STAT3/MMP-2 signaling pathway, whereas a non-phosphorylatable form of HSP27 blocked HSP27-mediated phenotypes probably due to a dominant-negative effect on phosphorylation of endogenous HSP27. Altogether, our results suggest that HSP27 can enhance cell adhesion and modulate cell migration and invasion via the coordination of FAK-dependent actin organization and STAT3-dependent MMP-2 expression, and that phosphorylation of HSP27 is indispensable to regulate this signal pathway.

Cyclic strain-induced HSP27 phosphorylation modulates actin filaments in airway smooth muscle cells

Mechanical stress (cyclic deformational strain) increases proteins of cytoskeletal and contractile domains in airway smooth muscle (ASM) cells in a manner that increases cell contractility. Here we studied the role of HSP27 in strain-induced microfilament formation and stability. Cultured ASM cells showed rapid phosphorylation of HSP27 upon cyclic strain within a few minutes that continued for 30 to 40 minutes. Such increases in HSP27 phosphorylation were abolished with SB 202190, a specific inhibitor of p38 mitogen-activated protein kinase (MAPK), but not by PD 98059 (an inhibitor of extracellular regulated kinase), GF109203X (an inhibitor of protein kinase C), or Y27632 (an inhibitor of Rho kinase). Direct activation of RhoA by GTPgammaS did not alter the level of HSP27 phosphorylation. Confocal microscopy revealed that cells pre-incubated with SB 202190, and/or Y27632 resulted in disorganization of stress fibers upon strain, unlike PD 98059 and GF 1092030X, suggesting that both p38 MAPK and Rho kinase were necessary for strain-induced microfilament formation. To determine the relationship between HSP27 and RhoA in strain-induced microfilament formation, cells were transfected with various isoforms of HSP27 and RhoA before strain. Co-expression of inactive HSP27 (3A-HSP27) with constitutively active EGF-RhoA (RhoV14) caused diminution of microfilaments compared with constitutive active EGFP-RhoA (RhoV14) alone, suggesting that HSP27 is necessary for microfilament stability. Similarly, expression of phosphomimicking HSP27 (3D-HSP27) was sufficient for retaining microfilament formation even when co-expressed with the dominant-negative RhoA (EGFP-RhoN17). Thus, HSP27 activation is necessary for microfilament stability independently of RhoA activation.

Regulation of contractility by Hsp27 and Hic-5 in rat mesenteric small arteries

The regulation of small artery contractility by vasoconstrictors is important for vascular function, and actin cytoskeleton remodeling is required for contraction. p38 MAPK and tyrosine kinases are implicated in actin polymerization and contraction through heat shock protein 27 (Hsp27) and the cytoskeletal protein paxillin, respectively. We evaluated the roles of downstream targets of p38 MAPK and tyrosine kinases in cytoskeletal reorganization and contraction and whether the two signaling pathways regulate contraction independent of each other. We identified the expression of the paxillin homologue hydrogen peroxide-inducible clone-5 (Hic-5) and showed its activation by norepinephrine (NE) in a Src-dependent manner. Furthermore, we demonstrated a NE-induced interaction of proline-rich tyrosine kinase-2 (PYK2) but not Src or p125 focal adhesion kinase with Hic-5. This interaction was Src dependent, suggesting that Hic-5 was a substrate for PYK2 downstream from Src. The activation of Hic-5 induced its relocalization to the cytosol. The parallel activation of Hsp27 by NE was p38 MAPK dependent and led to its dissociation from actin filaments and translocation from membrane to cytosol and increased actin polymerization. Both Hsp27 and Hic-5 activation resulted in their association within the same time frame as NE-induced contraction, and the inhibition of either p38 MAPK or Src inhibited the interaction between Hsp27 and Hic-5 and the contractile response. Furthermore, combined p38 MAPK and Src inhibition had no greater effect on contraction than individual inhibition, suggesting that the two pathways act through a common mechanism. These data show that NE-induced activation and the association of Hsp27 and Hic-5 are required for the reorganization of the actin cytoskeleton and force development in small arteries.

Modulation of F-actin rearrangement by the cyclic AMP/cAMP-dependent protein kinase (PKA) pathway is mediated by MAPK-activated protein kinase 5 and requires PKA-induced nuclear export of MK5

The MAPK-activated protein kinases belong to the Ca2+/calmodulin-dependent protein kinases. Within this group, MK2, MK3, and MK5 constitute three structurally related enzymes with distinct functions. Few genuine substrates for MK5 have been identified, and the only known biological role is in ras-induced senescence and in tumor suppression. Here we demonstrate that activation of cAMP-dependent protein kinase (PKA) or ectopic expression of the catalytic subunit Calpha in PC12 cells results in transient nuclear export of MK5, which requires the kinase activity of both Calpha and MK5 and the ability of Calpha to enter the nucleus. Calpha and MK5, but not MK2, interact in vivo, and Calpha increases the kinase activity of MK5. Moreover, Calpha augments MK5 phosphorylation, but not MK2, whereas MK5 does not seem to phosphorylate Calpha. Activation of PKA can induce actin filament accumulation at the plasma membrane and formation of actin-based filopodia. We demonstrate that small interfering RNA-triggered depletion of MK5 interferes with PKA-induced F-actin rearrangement. Moreover, cytoplasmic expression of an activated MK5 variant is sufficient to mimic PKA-provoked F-actin remodeling. Our results describe a novel interaction between the PKA pathway and MAPK signaling cascades and suggest that MK5, but not MK2, is implicated in PKA-induced microfilament rearrangement.

14-3-3epsilon inhibits MK5-mediated cell migration by disrupting F-actin polymerization

The signal pathway by which 14-3-3epsilon inhibits cell migration induced by MAPK-activated protein kinase 5 (MK5) was investigated in cultured HeLa cells. Both in vivo and in vitro analyses have revealed that 14-3-3epsilon interacts with MK5. 14-3-3epsilon bound to MK5 inhibits the phosphorylation of HSP27, a known substrate of MK5. Disturbance of actin cytoskeleton organization by 14-3-3epsilon was shown in transfected cells transiently expressing 14-3-3epsilon as well as established cells stably expressing 14-3-3epsilon. Moreover, overexpression of 14-3-3epsilon resulted in the inhibition of cell migration induced by MK5 overexpression or TNFalpha treatment. Our results suggest that 14-3-3epsilon bound to MK5 inhibits cell migration by inhibiting the phosphorylation of HSP27 whose phosphorylation regulates F-actin polymerization, actin cytoskeleton organization and subsequent actinfilament dynamics.

Phorbol 12-myristate 13-acetate (PMA)-induced migration of glioblastoma cells is mediated via p38MAPK/Hsp27 pathway

We investigated the mechanism of phorbol 12-myristate 13-acetate (PMA)-induced migration of glioblastoma cells focusing on the p38 mitogen-activated protein kinase (MAPK)/heat shock protein 27 (Hsp27) pathway. PMA-induced cell migration and activation of p38MAPK in A172 glioblastoma cells. PMA-induced formation of lamellipodia and focal complexes was blocked by inhibiting p38MAPK with SB203580 or small interfering RNA (siRNA). Furthermore, activation of p38MAPK resulted in phosphorylation of an F-actin polymerization regulator, Hsp27. Immunohistochemical analysis showed that upon PMA stimulation, both unphosphorylated and phosphorylated Hsp27 were translocated to the lamellipodia. SB203580 or p38MAPK siRNA blocked these phenomena, indicating that Hsp27 phosphorylation and translocation from cytosol to membrane were mediated by p38MAPK. To address the question of whether endogenous Hsp27 participates in PMA-induced migration, we inhibited the expression of Hsp27 using Hsp27 siRNA. Although knockdown of Hsp27 by siRNA had little effect on p38MAPK activation, lamellipodia and focal complex formation was markedly inhibited. Migration was also abolished in Hsp27 siRNA-transfected cells. In conclusion, p38MAPK activation followed by Hsp27 phosphorylation was required for PMA-induced migration. Furthermore, Hsp27 itself played critical roles in PMA-induced migration. Our data provide substantial evidence for a model elucidating the molecular mechanisms of regulation of actin dynamics and migration by PMA-activated protein kinase C in glioblastoma cells.

MAPK and heat shock protein 27 activation are associated with respiratory syncytial virus induction of human bronchial epithelial monolayer disruption

Respiratory syncytial virus (RSV) is the major cause of bronchiolitis in infants, and a common feature of RSV infections is increased lung permeability. The accumulation of fluid in the infected lungs is caused by changes in the endothelial and epithelial membrane integrity. However, the exact mechanisms of viral-induced fluid extravasation remain unclear. Here, we report that infection of human epithelial cells with RSV results in significant epithelial membrane barrier disruption as assessed by a decrease in transepithelial electrical resistance (TEpR). This decrease in TEpR, which indicates changes in paracellular permeability, was mediated by marked cellular cytoskeletal rearrangement. Importantly, the decrease in TEpR was attenuated by using p38 MAPK inhibitors (SB-203580) but was partially affected by JNK inhibitor SP-600125. Interestingly, treatment of A549 cells with MEK1/2 inhibitor (U-0126) led to a decrease in TEpR in the absence of RSV infection. The changes in TEpR were concomitant with an increase in heat shock protein 27 (Hsp27) phosphorylation and with actin microfilament rearrangement. Thus our data suggest that p38 MAPK and Hsp27 are required for RSV induction of human epithelial membrane permeability.

Anthrax lethal toxin paralyzes actin-based motility by blocking Hsp27 phosphorylation

Inhalation of anthrax causes fatal bacteremia, indicating a meager host immune response. We previously showed that anthrax lethal toxin (LT) paralyzes neutrophils, a major component of innate immunity. Here, we have found that LT also inhibits actin-based motility of the intracellular pathogen Listeria monocytogenes. LT inhibition of actin assembly is mediated by blockade of Hsp27 phosphorylation, and can be reproduced by treating cells with the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580. Nonphosphorylated Hsp27 inhibits Listeria actin-based motility in cell extracts, and binds to and sequesters purified actin monomers. Phosphorylation of Hsp27 reverses these effects. RNA interference knockdown of Hsp27 blocks LT inhibition of Listeria actin-based motility. Rescue with wild-type Hsp27 accelerates Listeria speed in knockdown cells, whereas introduction of Hsp27 mutants incapable of phosphorylation or dephosphorylation causes slowing down. We propose that Hsp27 facilitates actin-based motility through a phosphorylation cycle that shuttles actin monomers to regions of new actin filament assembly. Our findings provide a previously unappreciated mechanism for LT virulence, and emphasize a central role for p38 MAP kinase-mediated phosphorylation of Hsp27 in actin-based motility and innate immunity.