Dependence of fibroblast migration on actin severing activity of gelsolin

Exogenous extracellular matrix proteins decrease cardiac fibroblast activation in stiffening microenvironment through CAPG

Controlling fibrosis is an essential part of regenerating the post-ischemic heart. In the post-ischemic heart, fibroblasts differentiate to myofibroblasts that produce collagen-rich matrix to physically stabilize the infarct area. Infarct models in adult mice result in permanent scarring unlike newborn animals which fully regenerate. Decellularized extracellular matrix (dECM) hydrogels derived from early-aged hearts have been shown to be a transplantable therapy that preserves heart function and stimulates cardiomyocyte proliferation and vascularization. In this study, we investigate the anti-fibrotic effects of injectable dECM hydrogels in a cardiac explant model in the context of age-associated tissue compliance. Treatments with adult and fetal dECM hydrogels were tested for molecular effects on cardiac fibroblast activation and fibrosis. Altered sensitivity of fibroblasts to the mechanosignaling of the remodeling microenvironment was evaluated by manipulating the native extracellular matrix in explants and also with elastomeric substrates in the presence of dECM hydrogels. The injectable fetal dECM hydrogel treatment decreases fibroblast activation and contractility and lowers the stiffness-mediated increases in fibroblast activation observed in stiffened explants. The anti-fibrotic effect of dECM hydrogel is most observable at highest stiffness. Experiments with primary cells on elastomeric substrates with dECM treatment support this phenomenon. Transcriptome analysis indicated that dECM hydrogels affect cytoskeleton related signaling including Macrophage capping protein (CAPG) and Leupaxin (LPXN). CAPG was down-regulated by the fetal dECM hydrogel. LPXN expression was decreased by stiffening the explants; however, this effect was reversed by dECM hydrogel treatment. Pharmacological disruption of cytoskeleton polymerization lowered fibroblast activation and CAPG levels. Knocking down CAPG expression with siRNA inhibited fibroblast activation and collagen deposition. Collectively, fibroblast activation is dependent on cooperative action of extracellular molecular signals and mechanosignaling by cytoskeletal integrity.

Gelsolin is an important mediator of Angiotensin II-induced activation of cardiac fibroblasts and fibrosis

Myocardial fibrosis is a characteristic of various cardiomyopathies, and myocardial fibroblasts play a central role in this process. Gelsolin (GSN) is an actin severing and capping protein that regulates actin assembly and may be involved in fibroblast activation. While the role of GSN in mechanical stress-mediated cardiac fibrosis has been explored, its role in myocardial fibrosis in the absence of mechanical stress is not defined. In this study, we investigated the role of GSN in myocardial fibrosis induced by Angiotensin II (Ang II), a profibrotic hormone that is elevated in cardiovascular disease. We utilized mice lacking GSN (Gsn^-/- ) and cultured primary adult cardiac fibroblasts (cFB). In vivo, Ang II infusion in mice resulted in significantly less severe myocardial fibrosis in Gsn^-/- compared with Gsn^+/+ mice, along with diminished activation of the TGFβ1-Smad2/3 pathway, and reduced expression of cardiac extracellular matrix proteins (collagen, fibronectin, periostin). Moreover, Gsn-deficient hearts exhibited suppressed activity of the AMPK pathway and its downstream effectors, mTOR and P70S6Kinase, which could contribute to the suppressed TGFβ1 activity. In vitro, the Ang II-induced activation of cFBs was reduced in Gsn-deficient fibroblasts evident from decreased expression of αSMA and periostin, diminished actin filament turnover; which also exhibited reduced activity of the AMPK-mTOR pathway, and P70S6K phosphorylation. AMPK inhibition compensated for the loss of GSN, restored the levels of G-actin in Gsn^-/- cFBs and promoted activation to myofibroblasts by increasing αSMA and periostin levels. This study reveals a novel role for GSN in mediating myocardial fibrosis by regulating the AMPK-mTOR-P70S6K pathway in cFB activation independent from mechanical stress-induced factors.

Reduced allergic lung inflammation and airway responsiveness in mice lacking the cytoskeletal protein gelsolin

Airway smooth muscle hyperresponsiveness associated with chronic airway inflammation leads to the typical symptoms of asthma including bronchoconstriction and wheezing. Asthma severity is associated with airway inflammation; therefore reducing airway inflammation is an important therapeutic target. Gelsolin is an actin capping and severing protein that has been reported to be involved in modulation of the inflammatory response. Using mice genetically lacking gelsolin, we evaluated the role of gelsolin in the establishment of house dust mite (HDM) antigen-induced allergic lung inflammation. The genetic absence of gelsolin was found to be protective against HDM sensitization, resulting in reduced lung inflammation, inflammatory cytokines and Muc5AC protein in bronchoalveolar lavage (BAL) fluid. The number of eosinophils, lymphocytes and interstitial macrophages in the BAL were increased after HDM sensitization in wild type mice, but were attenuated in gelsolin null mice. The observed attenuation of inflammation may be partly due to delayed migration of immune cells, because the reduced eosinophils in the BALs from gelsolin null mice compared to controls occurred despite similar amounts of the chemoattractant eotaxin. Splenic T cells demonstrated similar proliferation rates, but ex vivo alveolar macrophage migration was delayed in gelsolin null mice. In vivo, the reduced lung inflammation after HDM sensitization in gelsolin null mice was associated with significantly diminished airway resistance to inhaled methacholine compared with HDM-treated wild type mice. Our results suggest that modulation of gelsolin expression or function in selective inflammatory cell types that modulate allergic lung inflammation could be a therapeutic approach for asthma.

The scaffold-protein IQGAP1 enhances and spatially restricts the actin-nucleating activity of Diaphanous-related formin 1 (DIAPH1)

The actin cytoskeleton is a dynamic array of filaments that undergoes rapid remodeling to drive many cellular processes. An essential feature of filament remodeling is the spatio-temporal regulation of actin filament nucleation. One family of actin filament nucleators, the Diaphanous-related formins, is activated by the binding of small G-proteins such as RhoA. However, RhoA only partially activates formins, suggesting that additional factors are required to fully activate the formin. Here we identify one such factor, IQ motif containing GTPase activating protein-1 (IQGAP1), which enhances RhoA-mediated activation of the Diaphanous-related formin (DIAPH1) and targets DIAPH1 to the plasma membrane. We find that the inhibitory intramolecular interaction within DIAPH1 is disrupted by the sequential binding of RhoA and IQGAP1. Binding of RhoA and IQGAP1 robustly stimulates DIAPH1-mediated actin filament nucleation in vitro In contrast, the actin capping protein Flightless-I, in conjunction with RhoA, only weakly stimulates DIAPH1 activity. IQGAP1, but not Flightless-I, is required to recruit DIAPH1 to the plasma membrane where actin filaments are generated. These results indicate that IQGAP1 enhances RhoA-mediated activation of DIAPH1 in vivo Collectively these data support a model where the combined action of RhoA and an enhancer ensures the spatio-temporal regulation of actin nucleation to stimulate robust and localized actin filament production in vivo.

PI3Kα-regulated gelsolin activity is a critical determinant of cardiac cytoskeletal remodeling and heart disease

Biomechanical stress and cytoskeletal remodeling are key determinants of cellular homeostasis and tissue responses to mechanical stimuli and injury. Here we document the increased activity of gelsolin, an actin filament severing and capping protein, in failing human hearts. Deletion of gelsolin prevents biomechanical stress-induced adverse cytoskeletal remodeling and heart failure in mice. We show that phosphatidylinositol (3,4,5)-triphosphate (PIP3) lipid suppresses gelsolin actin-severing and capping activities. Accordingly, loss of PI3Kα, the key PIP3-producing enzyme in the heart, increases gelsolin-mediated actin-severing activities in the myocardium in vivo, resulting in dilated cardiomyopathy in response to pressure-overload. Mechanical stretching of adult PI3Kα-deficient cardiomyocytes disrupts the actin cytoskeleton, which is prevented by reconstituting cells with PIP3. The actin severing and capping activities of recombinant gelsolin are effectively suppressed by PIP3. Our data identify the role of gelsolin-driven cytoskeletal remodeling in heart failure in which PI3Kα/PIP3 act as negative regulators of gelsolin activity.

Cytokinesis requires localized β-actin filament production by an actin isoform specific nucleator

Cytokinesis is initiated by the localized assembly of the contractile ring, a dynamic actomyosin structure that generates a membrane furrow between the segregating chromosomal masses to divide a cell into two. Here we show that the stabilization and organization of the cytokinetic furrow is specifically dependent on localized β-actin filament assembly at the site of cytokinesis. β-actin filaments are assembled directly at the furrow by an anillin-dependent pathway that enhances RhoA-dependent activation of the formin DIAPH3, an actin nucleator. DIAPH3 specifically generates homopolymeric filaments of β-actin in vitro. By employing enhancers and activators, cells can achieve acute spatio-temporal control over isoform-specific actin arrays that are required for distinct cellular functions.

Cytokinesis is initiated by the localized assembly of the contractile ring. Here the authors show that the stabilization and organization of the cytokinetic furrow requires localized β-actin filament assembly at the site of cytokinesis by an actin isoform specific nucleator.

Progressive cranial nerve involvement and grading of facial paralysis in gelsolin amyloidosis

INTRODUCTION

Hereditary gelsolin amyloidosis (GA) is a rare condition caused by the gelsolin gene mutation. The diagnostic triad includes corneal lattice dystrophy (type 2), progressive bilateral facial paralysis, and cutis laxa. Detailed information on facial paralysis in GA and the extent of cranial nerve injury is lacking.

METHODS

29 GA patients undergoing facial corrective surgery were interviewed, examined, and studied electroneurophysiologically.

RESULTS

All showed dysfunction of facial (VII) and trigeminal (V) nerves, two-thirds of oculomotor (III) and hypoglossal (XII) nerves, and half of vestibulocochlear (acoustic) (VIII) nerve. Clinical involvement of frontal, zygomatic, and buccal facial nerve branches was seen in 97%, 83%, and 52% of patients, respectively. Electromyography showed marked motor unit potential loss in facial musculature.

CONCLUSIONS

Cranial nerve involvement in GA is more widespread than previously described, and correlates with age, severity of facial paralysis, and electromyographic findings. We describe a grading method for bilateral facial paralysis in GA, which is essential for evaluation of disease progression and the need for treatment.

The biochemistry of blister fluid from pediatric burn injuries: proteomics and metabolomics aspects

Burn injury is a prevalent and traumatic event for pediatric patients. At present, the diagnosis of burn injury severity is subjective and lacks a clinically relevant quantitative measure. This is due in part to a lack of knowledge surrounding the biochemistry of burn injuries and that of blister fluid. A more complete understanding of the blister fluid biochemistry may open new avenues for diagnostic and prognostic development. Burn insult induces a highly complex network of signaling processes and numerous changes within various biochemical systems, which can ultimately be examined using proteome and metabolome measurements. This review reports on the current understanding of burn wound biochemistry and outlines a technical approach for 'omics' profiling of blister fluid from burn wounds of differing severity.

Mechanisms of pyruvate kinase M2 isoform inhibits cell motility in hepatocellular carcinoma cells

AIM

To investigate biological mechanisms underlying pyruvate kinase M2 isoform (PKM2) regulation of cell migration and invasion in hepatocellular carcinoma cells.

METHODS

HepG2 and Huh-7 hepatocellular carcinoma cell lines were stably transfected and cultured in DMEM (HyClone, Logan, UT, United States). To investigate the effects of PKM2 on cellular proliferation, hepatocellular carcinoma cells were subjected to the Cell Counting Kit-8 (Dojindo, Kamimashiki-gun, Kumamoto, Japan). And investigate the effects of PKM2 on cell signal pathway related with migration and invasion, Western immunoblotting were used to find out the differential proteins. All the antibody used was purchaseed from Cell Signal Technology. In order to explore cell motility used Transwell invasion and wound healing assays. The transwell plate with 0.5 mg/mL collagen type I (BD Bioscience, San Jose, CA)-coated filters. The wound-healing assay was performed in 6-well plates. Total RNA was extracted using TRIzol reagent (Invitrogen, CA, United States) and then reverse transcription was conducted. Quantitative reverse transcription-polymerase chain reaction (PCR) analysis was performed with the ABI 7500 real-time PCR system (Applied Biosystems). We further use digital gene expression tag profiling and identification of differentially expressed genes.

RESULTS

The cells seeded in four 96-well plates were measured OD450 by conducted Cell Counting Kit-8. From this conduction we observed that both HepG2 and Huh-7 hepatocellular carcinoma cells with silenced PKM2 turn on a proliferate inhibition; however, cell migration and invasion were enhanced compared with the control upon stimulation with epidermal growth factor (EGF). Our results indicate that the knockdown of PKM2 decreased the expression of E-cadherin and enhanced the activity of the EGF/EGFR signaling pathway, furthermore up-regulate the subsequent signal molecular the PLCγ1 and extracellular signal-regulated kinase 1/2 expression in the hepatocellular carcinoma cell lines HepG2 and Huh-7, which regulates cell motility. These variations we observed were due to the activation of the transforming growth factor beta (TGFβ) signaling pathway after PKM2 knockdown. We also found that the expression of TGFBRI was increased and the phosphorylation of Smad2 was enhanced. Taken together, our findings demonstrate that PKM2 can regulate cell motility through the EGF/EGFR and TGFβ/TGFR signaling pathways in hepatocellular carcinoma cells.

CONCLUSION

PKM2 play different roles in modulating the proliferation and metastasis of hepatocellular carcinoma cells, and this finding could help to guide the future targeted therapies.

Cell adhesion proteins: roles in periodontal physiology and discovery by proteomics

Adhesion molecules expressed by periodontal connective tissue cells are involved in cell migration, matrix remodeling and inflammatory responses to infection. Currently, the processes by which the biologic activity of these molecules are appropriately regulated in time and space to preserve tissue homeostasis, and to control inflammatory responses and tissue regeneration, are not defined. As cell adhesions are heterogeneous, dynamic, contain a complex group of interacting molecules and are strongly influenced by the type of substrate to which they adhere, we focus on how cell adhesions in periodontal connective tissues contribute to information generation and processing that regulate periodontal structure and function. We also consider how proteomic methods can be applied to discover novel cell-adhesion proteins that could potentially contribute to the form and function of periodontal tissues.

The interaction of gelsolin with tropomyosin modulates actin dynamics

We have investigated the interactions between the actin-binding proteins gelsolin and tropomyosin, with special respect to any effects on the functional properties of gelsolin. Limited proteolysis indicated that the loop connecting the gelsolin domains G3 and G4 is involved in tropomyosin binding. Under nonpolymerizing conditions, binding of tropomyosin neither prevented the formation of a 2: 1actin-gelsolin complex, nor did it affect the nucleating activity of gelsolin in actin polymerization, likely as a result of competitive displacement of tropomyosin from gelsolin. To evaluate the effect of tropomyosin on the actin filament severing activity of gelsolin, we measured both filamentous actin (F-actin) viscosity and the relative number concentrations of filaments after fragmentation, either by gelsolin alone or by gelsolin-tropomyosin complexes. The interaction of gelsolin with tropomyosin caused a reduction in F-actin severing activity of up to 80% compared to gelsolin alone. Thus, being bound to gelsolin, tropomyosin prevented gelsolin from severing actin filaments. By contrast, the severing activity of gelsolin for F-actin/tropomyosin was similar to that for F-actin alone even at a tropomyosin : actin saturation ratio of 1: 7. Thus, when bound to actin filaments, tropomyosin did not significantly inhibit the severing of filaments by gelsolin. The interaction between gelsolin and tropomyosin was largely independent of the muscle actin and tropomyosin isoforms investigated. The results obtained in the present study suggest that tropomyosin is involved in the modulation of actin dynamics not via the protection of filaments against severing, but rather by binding gelsolin in solution to prevent it from severing and to promote the formation of new actin filaments.

Pyruvate kinase M2 plays a dual role on regulation of the EGF/EGFR signaling via E-cadherin-dependent manner in gastric cancer cells

BACKGROUND AND AIMS

EGFR activation and PKM2 expression are instrumental in tumorigenesis. EGFR activation regulates PKM2 functions in a subcellular compartment-dependent manner and promotes gene transcription and tumor growth. In addition, PKM2 is upregulated in EGFR-induced pathways in glioma malignancies. However, we found that PKM2 could also regulate the activity of the EGF/EGFR signaling pathway in gastric cancer cells. We aimed to define the biological mechanisms for PKM2 in regulating the cell motility and invasion.

METHODS

We employed stable transfection with short hairpin RNA to stably silence the expression of PKM2 in the BGC823, SGC7901 and AGS gastric cancer cell lines. The effects of PKM2 in vitro were determined by assessing cell migration and invasion. Immunohistochemical analysis was used to explore the relationship among PKM2 and other proteins.

RESULTS

Our results indicate that the knockdown of PKM2 decreased the activity of E-cadherin and enhanced the EGF/EGFR signaling pathway in the gastric cell lines BGC823 and SGC7901 that were positive for E-cadherin expression. However, in the undifferentiated gastric carcinoma cell line AGS, which lacks E-cadherin expression, PKM2 promoted cell migration and invasion. Immunohistochemical analyses showed that the levels of E-cadherin expression, ERK1/2 phosphorylation, and cytoplasmic PKM2 expression were correlated with each other.

CONCLUSION

PKM2 may play different roles in differently differentiated gastric cancer cell types, and this finding would be consistent with the previous clinical research. The results of our study reveal an important link between PKM2 and E-cadherin during EGFR-stimulated gastric cancer cell motility and invasion.

Identification of fibronectin as a major factor in human serum to recruit subchondral mesenchymal progenitor cells

Human serum has the potential for mesenchymal progenitor cell recruitment in repair of articular cartilage lesions. It is unclear which factor(s) in serum mediate this migratory effect. Our goal was to identify cell recruiting factors in human serum fractions obtained by ion exchange chromatography. The recruiting activity of serum fractions on human subchondral mesenchymal progenitor cells was analyzed using 96-well chemotaxis assays. Protein composition of recruiting serum fractions were analyzed by mass spectrometry and showed 58 potential candidates. Fibronectin, gelsolin, lumican, thrombospondin-1 and WNT-9a were identified as key candidates for progenitor cell recruitment. Only human plasma derived and recombinant fibronectin showed significant recruiting activity on progenitors reaching 50-90% of the recruiting activity of normal human serum. Presence of fibronectin in all human serum fractions with recruiting activity was verified by Western blot analysis. This study shows that fibronectin is a key factor in human serum to recruit mesenchymal progenitor cells and might be involved in subchondral mesenchymal progenitor cell migration into cartilage defects after microfracture.

Gelsolin induces colorectal tumor cell invasion via modulation of the urokinase-type plasminogen activator cascade

Gelsolin is a cytoskeletal protein which participates in actin filament dynamics and promotes cell motility and plasticity. Although initially regarded as a tumor suppressor, gelsolin expression in certain tumors correlates with poor prognosis and therapy-resistance. In vitro, gelsolin has anti-apoptotic and pro-migratory functions and is critical for invasion of some types of tumor cells. We found that gelsolin was highly expressed at tumor borders infiltrating into adjacent liver tissues, as examined by immunohistochemistry. Although gelsolin contributes to lamellipodia formation in migrating cells, the mechanisms by which it induces tumor invasion are unclear. Gelsolin's influence on the invasive activity of colorectal cancer cells was investigated using overexpression and small interfering RNA knockdown. We show that gelsolin is required for invasion of colorectal cancer cells through matrigel. Microarray analysis and quantitative PCR indicate that gelsolin overexpression induces the upregulation of invasion-promoting genes in colorectal cancer cells, including the matrix-degrading urokinase-type plasminogen activator (uPA). Conversely, gelsolin knockdown reduces uPA levels, as well as uPA secretion. The enhanced invasiveness of gelsolin-overexpressing cells was attenuated by treatment with function-blocking antibodies to either uPA or its receptor uPAR, indicating that uPA/uPAR activity is crucial for gelsolin-dependent invasion. In summary, our data reveals novel functions of gelsolin in colorectal tumor cell invasion through its modulation of the uPA/uPAR cascade, with potentially important roles in colorectal tumor dissemination to metastatic sites.

Familial amyloidotic polyneuropathy type IV--gelsolin amyloidosis

Familial amyloidotic polyneuropathy type IV, or Gelsolin amyloidosis (GA), is a rare condition caused by G654A or G654T mutation in gelsolin gene at 9q32-34. Gelsolin seems essential in many processes, including inflammation, cell motility, neural recovery, apoptosis and even carcinogenesis. So far reported from many European countries, USA, Japan, Iran and Brazil, GA is probably still underdiagnosed. The typical diagnostic triad includes corneal lattice dystrophy, progressive bilateral facial paralysis and cutis laxa. Patients present with progressive cranial and peripheral neuropathy, eye symptoms, usually mild proteinuria, and cardiac conductive disturbances with age. Central nervous system symptoms are rare. Gelsolin amyloid collection in tissues is widespread. To date, treatment is symptomatic. Regular check-ups with ophthalmologist are recommended. Plastic surgery relieves the functional symptoms caused by facial paralysis and loose, hanging facial skin.

Flightless I is a focal adhesion-associated actin-capping protein that regulates cell migration

The role of adhesion-associated actin-binding proteins in cell migration is not well defined. In mouse fibroblasts we screened for focal adhesion-associated proteins that were isolated with collagen-coated beads and detected by tandem mass spectrometry. We identified flightless I (FliI) as an actin-binding protein in focal adhesion fractions, which was verified by immunoblotting. By confocal microscopy most FliI was distributed throughout the cytosol and in focal adhesions. By sedimentation assays and in vitro binding assays, we found that FliI associates with actin filaments and actin monomers. Assays using purified proteins showed that FliI inhibits actin polymerization and caps but does not sever actin filaments. Cells with FliI knockdown or cells overexpressing FliI migrated more or less rapidly, respectively, than wild-type controls. Compared with controls, cells with FliI knockdown were less adherent than wild-type cells, exhibited reduced numbers of focal adhesions containing activated β1 integrins and vinculin, and exhibited increased incorporation of actin monomers into nascent filaments at focal adhesions. These data indicate that FliI regulates cell migration through its localization to focal adhesions and its ability to cap actin filaments, which collectively affect focal adhesion maturation.

Involvement of epidermal growth factor receptor overexpression in the promotion of breast cancer brain metastasis

BACKGROUND

Brain-metastatic breast cancer (BMBC) is increasing and poses a severe clinical problem because of the lack of effective treatments and because the underlying molecular mechanisms are largely unknown. Recent work has demonstrated that deregulation of epidermal growth factor receptor (EGFR) may correlate with BMBC progression. However, the exact contribution that EGFR makes to BMBC remains unclear.

METHODS

The role of EGFR in BMBC was explored by serial analyses in a brain-trophic clone of human MDA-MB-231 breast carcinoma cells (231-BR cells). EGFR expression was inhibited by stable short-hairpin RNA transfection or by the kinase inhibitor erlotinib, and it was activated by heparin-binding epidermal growth factor-like growth factor (HB-EGF). Cell growth and invasion activities also were analyzed in vitro and in vivo.

RESULTS

EGFR inhibition or activation strongly affected 231-BR cell migration/invasion activities as assessed by an adhesion assay, a wound-healing assay, a Boyden chamber invasion assay, and cytoskeleton staining. Also, EGFR inhibition significantly decreased brain metastases of 231-BR cells in vivo. Surprisingly, changes to EGFR expression affected cell proliferation activities less significantly as determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, an anchorage-independent growth assay, and cell cycle analysis. Immunoblot analysis suggested that EGFR drives cells' invasiveness capability mainly through phosphoinositide 3-kinase/protein kinase B and phospholipase C γ downstream pathways. In addition, EGFR was involved less in proliferation because of the insensitivity of the downstream mitogen-activated protein kinase pathway.

CONCLUSIONS

The current results indicated that EGFR plays more important roles in cell migration and invasion to the brain than in cell proliferation progression on 231-BR cells, providing new evidence of the potential value of EGFR inhibition in treating BMBC.

BCL2 inhibits cell adhesion, spreading, and motility by enhancing actin polymerization

BCL2 is best known as a multifunctional anti-apoptotic protein. However, little is known about its role in cell-adhesive and motility events. Here, we show that BCL2 may play a role in the regulation of cell adhesion, spreading, and motility. When BCL2 was overexpressed in cultured murine and human cell lines, cell spreading, adhesion, and motility were impaired. Consistent with these results, the loss of Bcl2 resulted in higher motility observed in Bcl2-null mouse embryonic fibroblast (MEF) cells compared to wild type. The mechanism of BCL2 regulation of cell adhesion and motility may involve formation of a complex containing BCL2, actin, and gelsolin, which appears to functionally decrease the severing activity of gelsolin. We have observed that the lysate from MCF-7 and NIH3T3 cells that overexpressed BCL2 enhanced actin polymerization in cell-free in vitro assays. Confocal immunofluorescent localization of BCL2 and F-actin during spreading consistently showed that increased expression of BCL2 resulted in increased F-actin polymerization. Thus, the formation of BCL2 and gelsolin complexes (which possibly contain other proteins) appears to play a critical role in the regulation of cell adhesion and migration. Given the established correlation of cell motility with cancer metastasis, this result may explain why the expression of BCL2 in some tumor cell types reduces the potential for metastasis and is associated with improved patient prognosis.

FAK, PIP5KIγ and gelsolin cooperatively mediate force-induced expression of α-smooth muscle actin

During the development of pressure-induced cardiac hypertrophy, fibroblasts are activated to become myofibroblasts, which exhibit actin-cytoskeletal remodeling and express α-smooth muscle actin (SMA; encoded by ACTA2). Currently, the mechanosensing signaling pathways that regulate SMA expression are not defined. Because focal-adhesion complexes are putative mechanosensing organelles, we examined the role of focal adhesion kinase (FAK) and its interaction with gelsolin in the regulation of SMA expression. We subjected NIH3T3 cells to tensile forces (0.65 pN/μm2) by using collagen-coated magnetite beads attached to integrins. After stimulation by mechanical force, FAK and gelsolin were recruited to magnetite beads and there was increased phosphorylation of Tyr397FAK. Mechanical force enhanced SMA promoter activity by twofold; this increased activity was blocked by FAK knockdown using siRNA and by deletion of gelsolin. Force-induced nuclear translocation of MRTF-A, a transcriptional co-activator of SMA that is regulated by actin filaments, was also reduced by FAK knockdown. Phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P2], which uncaps gelsolin from actin filaments, was enriched at sites of force application. Type-I phosphatidylinositol 4-phosphate 5 kinase-γ (PIP5KIγ), which generates PtdIns(4,5)P2, associated with FAK and was required for force-mediated SMA-promoter activity and actin assembly. Catalytically inactive PIP5KIγ inhibited force-induced phosphorylation of FAK at Tyr397. These data suggest a novel pathway in which mechanosensing by FAK regulates actin assembly via gelsolin and the activity of PIP5KIγ; actin assembly in turn controls SMA expression via MRTF-A.

Proteomic analysis of circulating monocytes in Chinese premenopausal females with extremely discordant bone mineral density

Osteoporosis (OP) is a major public health problem, mainly characterized by low bone mineral density (BMD). Circulating monocytes (CMCs) may serve as progenitors of osteoclasts and produce a wide variety of factors important to bone metabolism. However, the specific action mechanism of CMCs in the pathogenesis of OP is far from clear. We performed a comparative protein expression profiling study of CMCs in Chinese premenopausal females with extremely discordant BMD, identified a total of 38 differentially expressed proteins, and confirmed with Western blotting five proteins: ras suppressor protein1 (RSU1), gelsolin (GSN), manganese-containing superoxide dismutase (SOD2), glutathione peroxidase 1(GPX1), and prolyl 4-hydroxylase beta subunit (P4HB). These proteins might affect CMCs' trans-endothelium, differentiation, and/or downstream osteoclast functions, thus contribute to differential osteoclastogenesis and finally lead to BMD variation. The findings promote our understanding of the role of CMCs in BMD determination, and provide an insight into the pathogenesis of human OP.

Vesicular egress of non-enveloped lytic parvoviruses depends on gelsolin functioning

The autonomous parvovirus Minute Virus of Mice (MVM) induces specific changes in the cytoskeleton filaments of infected permissive cells, causing in particular the degradation of actin fibers and the generation of “actin patches.” This is attributed to a virus-induced imbalance between the polymerization factor N-WASP (Wiscott-Aldrich syndrome protein) and gelsolin, a multifunctional protein cleaving actin filaments. Here, the focus is on the involvement of gelsolin in parvovirus propagation and virus-induced actin processing. Gelsolin activity was knocked-down, and consequences thereof were determined for virus replication and egress and for actin network integrity. Though not required for virus replication or progeny particle assembly, gelsolin was found to control MVM (and related H1-PV) transport from the nucleus to the cell periphery and release into the culture medium. Gelsolin-dependent actin degradation and progeny virus release were both controlled by (NS1)/CKIIα, a recently identified complex between a cellular protein kinase and a MVM non-structural protein. Furthermore, the export of newly synthesized virions through the cytoplasm appeared to be mediated by (virus-modified) lysomal/late endosomal vesicles. By showing that MVM release, like entry, is guided by the cytoskeleton and mediated by vesicles, these results challenge the current view that egress of non-enveloped lytic viruses is a passive process.

Rodent parvoviruses are non-enveloped lytic viruses that are thought excellent tools for a virotherapy of cancer because of their strong natural oncolytic potential and low pathogenicity in humans. Egress of non-enveloped lytic viruses is commonly thought to occur as a virus burst after cell disintegration. Indeed, we showed in the past that autonomous parvoviruses induce severe cytopathic effects to the host cell, manifested in restructuring and degradation of cytoskeletal filaments, thereby supporting such mode of virus spread. Here, we focus on the impact of virus-induced actin degradation, and particularly the functioning of the actin-severing protein gelsolin. Although not required for DNA replication or progeny particle production, gelsolin appears to facilitate a regulated virus egress from the nucleus to the cell periphery via (virus modified) lysosomal/late endosomal vesicles. These results challenge the current view that lytic virus egress is just a passive process at the end of infection and suggests that these pathogens are endowed with the ability to efficiently spread from cell to cell potentially in solid (tumor) tissue.

TRPC1 channels regulate directionality of migrating cells

Cell migration depends on the generation of structural asymmetry and on different steps: protrusion and adhesion at the front and traction and detachment at the rear part of the cell. The activity of Ca(2+) channels coordinate these steps by arranging intracellular Ca(2+) signals along the axis of movement. Here, we investigated the role of the putative mechanosensitive canonical transient receptor potential channel 1 (TRPC1) in cell migration. We analyzed its function in transformed renal epithelial (Madin-Darby canine kidney-focus) cells with variation of TRPC1 expression. As shown by time lapse video microscopy, TRPC1 knockdown cells have partially lost their polarity and the ability to persistently migrate into a given direction. This failure is linked to the suppression of a local Ca(2+) gradient at the front of migrating TRPC1 knockdown cells, whereas TRPC1 overexpression leads to steeper Ca(2+) gradients. We propose that the Ca(2+) signaling events regulated by TRPC1 within the lamellipodium determine polarity and directed cell migration.

Induced expression of the transcription of tropomodulin 1 by Wnt5a and characterization of the tropomodulin 1 promoter

Microarray analysis was carried out to identify novel downstream target genes regulated by non-canonical Wnt signaling. We found that Tmod1, known as an actin-capping protein, is up-regulated by Wnt5a, while gelsolin, known as an actin-severing protein, is down-regulated by Wnt5a. As expected from the roles of genes regulated by Wnt5a, L929 cells expressing Wnt5a show abnormal cell shape and a reduced migration rate. Cloning and analysis of the putative promoter show that two conserved sequences, one in the 5'-end of the first exon and the other in the intron next to the first exon, are necessary for the basal promoter activity.

MscCa Regulation of Tumor Cell Migration and Metastasis

The acquisition of cell motility is a required step in order for a cancer cell to migrate from the primary tumor and spread to secondary sites (metastasize). For this reason, blocking tumor cell migration is considered a promising approach for preventing the spread of cancer. However, cancer cells just as normal cells can migrate by several different modes referred to as "amoeboid," "mesenchymal," and "collective cell." Under appropriate conditions, a single cell can switch between modes. A consequence of this plasticity is that a tumor cell may be able to avoid the effects of an agent that targets only one mode by switching modes. Therefore, a preferred strategy would be to target mechanisms that are shared by all modes. This chapter reviews the evidence that Ca(2+) influx via the mechanosensitive Ca(2+)-permeable channel (MscCa) is a critical regulator of all modes of cell migration and therefore represents a very good therapeutic target to block metastasis.

Mechanism of depolymerization and severing of actin filaments and its significance in cytoskeletal dynamics

The actin cytoskeleton is one of the major structural components of the cell. It often undergoes rapid reorganization and plays crucial roles in a number of dynamic cellular processes, including cell migration, cytokinesis, membrane trafficking, and morphogenesis. Actin monomers are polymerized into filaments under physiological conditions, but spontaneous depolymerization is too slow to maintain the fast actin filament dynamics observed in vivo. Gelsolin, actin-depolymerizing factor (ADF)/cofilin, and several other actin-severing/depolymerizing proteins can enhance disassembly of actin filaments and promote reorganization of the actin cytoskeleton. This review presents advances as well as a historical overview of studies on the biochemical activities and cellular functions of actin-severing/depolymerizing proteins.

Interaction of phospholipase C-gamma1 with villin regulates epithelial cell migration

Tyrosine-phosphorylated villin regulates actin dynamics, cell morphology, and cell migration. Previously, we identified four tyrosine phosphorylation sites in the amino-terminal domain of villin. In this study we report six new sites in the carboxyl-terminal region of the villin core. With this study we document all phosphorylatable tyrosine residues in villin and map them to functions of villin. In this study, we identify for the first time the functional relevance of the carboxyl-terminal domains of the villin core. Expression of the carboxyl-terminal phosphorylation site mutant, as well as the villin truncation mutant S1-S3, inhibited cell migration in HeLa and Madin-Darby canine kidney Tet-Off cells, confirming the role of the carboxyl-terminal phosphorylation sites in villin-induced cell migration. The carboxyl-terminal phosphorylation sites were found to be critical for the interaction of villin with its ligand phospholipase C-gamma1 and for its localization to the developing lamellipodia in a motile cell. The results presented here elucidate the molecular basis for tyrosine-phosphorylated villin-induced changes in cell motility.

Role of p38 in stress activation of Sp1

Cell stressors such as physical forces can activate Sp1-dependent genes but the regulatory mechanisms are not defined. We determined if the stress-induced MAP kinase, p38, can phosphorylate Sp1 and thereby regulate the Sp1 target gene FLNA. We used Rat-2 cells and human gingival fibroblasts to examine stress-induced activation of an Sp1-dependent gene and SL2 cells, an Sp1-deficient model system, to facilitate interaction studies of transfected Sp1 with regulatory factors. Mechanical stress applied to Rat-2 cells increased promoter activity of the Sp1 target gene filamin A by >5-fold; activation was blocked by mutations to Sp1 binding sites in the filamin A promoter. Transfection experiments in SL2 cells with Sp1 expression vectors showed that when co-transfected with constitutively active p38, wild-type Sp1 but not an Sp1 binding mutant, increased promoter activity of the Sp1 target gene, filamin A, and enhanced binding of nuclear extracts to a filamin A promoter oligonucleotide. Filamin A promoter activity was blocked by dominant negative p38. Sp1 that was phosphorylated at Thr453 and Thr739 by constitutively active p38 bound to the filamin A promoter more effectively than un-phosphorylated Sp1. Recombinant active p38 phosphorylated wild-type Sp1 in vitro while the Sp1 Thr453Thr739 double mutant protein showed >3-fold reduction of phosphorylation. We conclude that stress activation of p38 phosphorylates Sp1 at specific threonine residues, modifications which in turn enhance the expression of Sp1-dependent genes.

siRNA gelsolin knockdown induces epithelial-mesenchymal transition with a cadherin switch in human mammary epithelial cells

Epithelial-mesenchymal transition (EMT) describes a process occurring during development and oncogenesis by which epithelial cells obtain fibroblast-like properties and show reduced cell adhesion and increased motility. In this report, we demonstrated typical EMT in human mammary epithelial MCF10A small interfering (si)RNA gelsolin-knockdown cells. EMT was characterized by fibroblastic morphology, loss of contact inhibition and focus formation in monolayer growth, enhanced motility and invasiveness in vitro, increased actin filaments, overexpression of RAC, activation of both extracellular signal-regulated kinase and AKT, inactivation of glycogen synthase kinase-3, conversion of cadherin from the E- to N-type and induction of the transcription factor Snail. These results suggested that gelsolin functions as a switch that controls E- and N-cadherin conversion via Snail, and demonstrated that its knockdown leads to EMT in human mammary epithelial cells and possibly to the development of human mammary tumors.

Lesion-induced gelsolin upregulation in the hippocampus following entorhinal deafferentation

Gelsolin is an actin-binding protein that regulates actin filament-severing and capping activity in the various processes of cell motilities. Here, we report the expression of gelsolin mRNA and protein in the hippocampus following transections of the entorhinal afferents. Northern blot analysis showed that transcript of gelsolin was upregulated in a transient manner in the deafferented hippocampus by 1.3-, 2.1-, 1.7-, and 1.1- folds of controls, respectively, at 1, 3, 7, and 15 days postlesion (dpl). In situ hybridization and immunohistochemistry confirmed the temporal expression of gelsolin specifically in the entorhinally denervated zones: the stratum lacunosum-molecular (SLM) of the hippocampus and the outer molecular layer (OML) of the dentate gyrus (DG), which initiated as early as at 1 dpl, reached the maximum at 3 dpl, remained prominently elevated by 7 dpl, and discernibly higher at 15 dpl than that of controls. Double labeling of either gelsolin mRNA or protein with markers of glial cells (Griffonia simplicifolia IB4 and CD11b for microglial cells, GFAP for astroglial cells) revealed that gelsolin was highly expressed by both activated microglia and astrocytes. The results suggest that the spatiotemporal upregulation of gelsolin in the hippocampus is induced by entorhinal deafferentation, and that gelsolin would participate in the activation processes of both microglial and astroglial cells and thereby, indirectly play important roles in the subsequent lesion-induced neural reorganization in the hippocampus following entorhinal deafferentation.

Involvement of gelsolin in cadmium-induced disruption of the mesangial cell cytoskeleton

Cadmium (Cd2+) is known to cause a selective disruption of the filamentous actin cytoskeleton in the smooth muscle-like renal mesangial cell. We examined the effect of Cd2+ on the distribution of the actin-severing protein, gelsolin. Over 8 h, CdCl2 (10 microM) caused a progressive shift of gelsolin from a diffuse perinuclear and cytoplasmic distribution to a pattern decorating F-actin filaments. Over this time filaments were decreased in number in many cells, and membrane ruffling was initiated. Western blotting and 125I-F-actin gel overlays demonstrated an increase in actin-binding gelsolin activity in the cytoskeletal fraction of cell extracts following Cd2+ treatment. In in vitro polymerization assays, gelsolin acted as a nucleating factor and increased the rate of polymerization. Cytosolic extracts also increased the polymerization rate. Addition of Cd2+ together with gelsolin further increased the rate of polymerization. Gelsolin enhanced depolymerization of purified actin, and Cd2+ partially suppressed this effect. However, cytoskeletal extracts from Cd2+-treated cells also markedly increased depolymerization, suggesting further that Cd2+ may activate cellular component(s) such as gelsolin for actin binding. We conclude that a major effect of Cd2+ on the mesangial cell cytoskeleton is manifest through activating the association of gelsolin with actin, with gelsolin's severing properties predominating under conditions found in Cd2+-treated cells.

Biochemistry and biomechanics of cell motility

Cell motility is an essential cellular process for a variety of biological events. The process of cell migration requires the integration and coordination of complex biochemical and biomechanical signals. The protrusion force at the leading edge of a cell is generated by the cytoskeleton, and this force generation is controlled by multiple signaling cascades. The formation of new adhesions at the front and the release of adhesions at the rear involve the outside-in and inside-out signaling mediated by integrins and other adhesion receptors. The traction force generated by the cell on the extracellular matrix (ECM) regulates cell-ECM adhesions, and the counter force exerted by ECM on the cell drives the migration. The polarity of cell migration can be amplified and maintained by the feedback loop between the cytoskeleton and cell-ECM adhesions. Cell migration in three-dimensional ECM has characteristics distinct from that on two-dimensional ECM. The migration of cells is initiated and modulated by external chemical and mechanical factors, such as chemoattractants and the mechanical forces acting on the cells and ECM, as well as the surface density, distribution, topography, and rigidity of the ECM.

Smooth muscle actin determines mechanical force-induced p38 activation

The mitogen-activated protein kinase p38 is activated by mechanical force, but the cellular elements that mediate force-induced p38 phosphorylation are not defined. As alpha-smooth muscle actin (SMA) is an actin isoform associated with force generation in fibroblasts, we asked if SMA participates in the activation of p38 by force. Tensile forces (0.65 pn/mum(2)) generated by magnetic fields were applied to collagen-coated magnetite beads bound to Rat-2 cells. Immunoblotting showed that p38alpha was the predominant p38 isoform. Analysis of bead-associated proteins demonstrated that SMA enrichment of collagen receptor complexes required the alpha2beta1 integrin. SMA was present almost entirely as filaments. Swinholide depolymerized SMA filaments and blocked force-induced p38 phosphorylation and force-induced increases of SMA. Knockdown of SMA (70% reduction) using RNA interference did not affect beta-actin but inhibited force-induced p38 phosphorylation by 50%. Inhibition of Rho kinase blocked SMA filament assembly, force-induced increases of SMA, and force-induced p38 activation. Force application increased SMA content and enhanced the association of phosphorylated p38 with SMA filaments. Blockade of p38 phosphorylation by SB203586 abrogated force-induced increases of SMA. In cells transfected with SMA promoter-beta-galactosidase fusion constructs, co-transfection with constitutively active p38 or MKK6 increased SMA promoter activity by 2.5-3-fold. Dominant negative p38 blocked force-induced activation of the SMA promoter. In SMA negative cells, there was no force-induced p38 phosphorylation. We conclude that force-induced p38 phosphorylation is dependent on an SMA filament-dependent pathway that uses a feed-forward amplification loop to synergize force-induced SMA expression with p38 activation.

Regulation of cell motility by tyrosine phosphorylated villin

Temporal and spatial regulation of the actin cytoskeleton is vital for cell migration. Here, we show that an epithelial cell actin-binding protein, villin, plays a crucial role in this process. Overexpression of villin in doxycyline-regulated HeLa cells enhanced cell migration. Villin-induced cell migration was modestly augmented by growth factors. In contrast, tyrosine phosphorylation of villin and villin-induced cell migration was significantly inhibited by the src kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) as well as by overexpression of a dominant negative mutant of c-src. These data suggest that phosphorylation of villin by c-src is involved in the actin cytoskeleton remodeling necessary for cell migration. We have previously shown that villin is tyrosine phosphorylated at four major sites. To further investigate the role of tyrosine phosphorylated villin in cell migration, we used phosphorylation site mutants (tyrosine to phenylalanine or tyrosine to glutamic acid) in HeLa cells. We determined that tyrosine phosphorylation at residues 60, 81, and 256 of human villin played an essential role in cell migration as well as in the reorganization of the actin cytoskeleton. Collectively, these studies define how biophysical events such as cell migration are actuated by biochemical signaling pathways involving tyrosine phosphorylation of actin binding proteins, in this case villin.

Regulation of intercellular adhesion strength in fibroblasts

The regulation of adherens junction formation in cells of mesenchymal lineage is of critical importance in tumorigenesis but is poorly characterized. As actin filaments are crucial components of adherens junction assembly, we studied the role of gelsolin, a calcium-dependent, actin severing protein, in the formation of N-cadherin-mediated intercellular adhesions. With a homotypic, donor-acceptor cell model and plates or beads coated with recombinant N-cadherin-Fc chimeric protein, we found that gelsolin spatially co-localizes to, and is transiently associated with, cadherin adhesion complexes. Fibroblasts from gelsolin-null mice exhibited marked reductions in kinetics and strengthening of N-cadherin-dependent junctions when compared with wild-type cells. Experiments with lanthanum chloride (250 microm) showed that adhesion strength was dependent on entry of calcium ions subsequent to N-cadherin ligation. Cadherin-associated gelsolin severing activity was required for localized actin assembly as determined by rhodamine actin monomer incorporation onto actin barbed ends at intercellular adhesion sites. Scanning electron microscopy showed that gelsolin was an important determinant of actin filament architecture of adherens junctions at nascent N-cadherin-mediated contacts. These data indicate that increased actin barbed end generation by the severing activity of gelsolin associated with N-cadherin regulates intercellular adhesion strength.

Polyphosphoinositides-dependent regulation of the osteoclast actin cytoskeleton and bone resorption

BACKGROUND

Gelsolin, an actin capping protein of osteoclast podosomes, has a unique function in regulating assembly and disassembly of the podosome actin filament. Previously, we have reported that osteopontin (OPN) binding to integrin alphavbeta3 increased the levels of gelsolin-associated polyphosphoinositides, podosome assembly/disassembly, and actin filament formation. The present study was undertaken to identify the possible role of polyphosphoinositides and phosphoinositides binding domains (PBDs) of gelsolin in the osteoclast cytoskeletal structural organization and osteoclast function.

RESULTS

Transduction of TAT/full-length gelsolin and PBDs containing gelsolin peptides into osteoclasts demonstrated: 1) F-actin enriched patches; 2) disruption of actin ring; 3) an increase in the association polyphosphoinositides (PPIs) with the transduced peptides containing PBDs. The above-mentioned effects were more pronounced with gelsolin peptide containing 2 tandem repeats of PBDs (PBD (2)). Binding of PPIs to the transduced peptides has resulted in reduced levels of PPIs association with the endogenous gelsolin, and thereby disrupted the actin remodeling processes in terms of podosome organization in the clear zone area and actin ring formation. These peptides also exhibited a dominant negative effect in the formation of WASP-Arp2/3 complex indicating the role of phosphoinositides in WASP activation. The TAT-PBD gelsolin peptides transduced osteoclasts are functionally defective in terms of motility and bone resorption.

CONCLUSIONS

Taken together, these data demonstrate that transduction of PBD gelsolin peptides into osteoclasts produced a dominant negative effect on actin assembly, motility, and bone resorption. These findings indicate that phosphoinositide-mediated signaling mechanisms regulate osteoclast cytoskeleton, podosome assembly/disassembly, actin ring formation and bone resorption activity of osteoclasts.

Regulation of Tension-induced Mechanotranscriptional Signals by the Microtubule Network in Fibroblasts

Mechanical loading of connective tissues induces the expression of extracellular matrix and cytoskeletal genes that are involved in matrix remodeling. These processes depend in part on force transmission through beta1 integrins and actin filaments, but the role of microtubules in regulating mechanotranscriptional responses is not well defined. We assessed the involvement of microtubules in the mechanotranscriptional regulation of filamin A, an actin-cross-linking protein that protects cells against force-induced apoptosis by stabilizing cell membranes. Collagen-coated magnetite beads and magnetic fields were used to apply tensile forces to cultured fibroblasts at focal adhesions. Force enhanced recruitment of alpha-tubulin and the plus end microtubule-binding protein cytoplasmic linker protein-170 (CLIP-170) at focal adhesions. Immunoprecipitation studies demonstrated no direct binding of tubulin to actin or filamin A, but CLIP-170 interacted with tubulin, filamin A, and beta-actin. The association of CLIP-170 with beta-actin was enhanced by force. Force activated the p38 mitogen-activated protein kinase, increased filamin A expression, and induced the relocation of p38 and filamin A to focal adhesions. Disruption of microtubules with nocodazole, independent of force application, enhanced filamin A expression and Sp1-mediated filamin A promoter activity, while stabilization of microtubules with Taxol inhibited force induction of both filamin A mRNA and protein. We conclude that in response to tensile forces applied through beta1 integrins and actin the microtubule network modulates mechanotranscriptional coupling of filamin A.

Differential effect of wounding on actin and its associated proteins, paxillin and gelsolin, in fetal skin explants

Skin from the embryonic day 17 rat retains the ability to epithelialize an excisional wound when isolated in serum-supplemented suspension culture. This ability is lost by embryonic day 19. We have investigated this effect of gestational age on fetal epithelial wound closure by correlating the involvement of filamentous actin (F-actin) and its associated proteins, paxillin and gelsolin, in the wound margins of embryonic day 17 and 19 rat skins, with the ability to close a full thickness excisional wound. Using fluorescent-phalloidin histochemistry and scanning confocal microscopy, actin polymerization was observed some five to six cells back from the margin of wounds in the embryonic day 17 skin as early as 3 h postwounding. As the wounds closed over the following 48-72 h, the actin further condensed around the epithelial margin before dispersing after wound closure. In contrast, no organization of actin was seen in the epithelial margin of wounds in skin from the embryonic day 19 embryos. Instead, actin filaments were observed surrounding the dermal wound margins. Chemical or mechanical disruption of the actin in wounded embryonic day 17 skins prevented epithelial closure, although wound repair was independent of cell division. In particular, incising the wound margin 24 h after wounding resulted in the "springing-open" of the embryonic day 17 wound but not the embryonic day 19 wound, reflecting the development of tension in the embryonic day 17 wound margin. Expression of paxillin mRNA was upregulated following wounding at embryonic day 17 but not at embryonic day 19. Paxillin was also observed to colocalize with actin in embryonic day 17 wounds, but not embryonic day 19 wounds, indicating a potential role for paxillin in epithelial repair of the fetal wound. In contrast, gelsolin mRNA was upregulated in embryonic day 19 fetal skin but not at embryonic day 17 and gelsolin protein was observed surrounding actin filaments at embryonic day 19 but not embryonic day 17. These results demonstrate a change in the mechanism of wound epithelialization at the same gestational age that fetal wounds change from scar-free to scar-forming wound repair.

Interaction of p38 and Sp1 in a mechanical force-induced, beta 1 integrin-mediated transcriptional circuit that regulates the actin-binding protein filamin-A

Connective tissue cells in mechanically active environments survive applied physical forces by modifying actin cytoskeletal structures that stabilize cell membranes. In fibroblasts, tensile forces induce the expression of filamin-A, a mechanoprotective actin-binding protein, but the mechanisms and protein interactions by which force activates filamin-A transcription are not defined. We found that in fibroblasts, application of tensile forces through collagen-coated magnetite beads to cell surface beta(1) integrins induced filamin-A expression. This induction required actin filaments and selective activation of the p38 mitogen-activated protein kinase. Force promoted the redistribution of p38 to the integrin/bead locus and the nucleus as well as enhanced binding of the transcription factor Sp1 to proximal, regulatory domains of the filamin-A promoter. Force application increased association of Sp1 with p38 and phosphorylation of Sp1. Transcriptional activation of filamin-A in force-treated fibroblasts was subsequently mediated by Sp1-binding sites on the filamin-A promoter. These results provide evidence for a mechanically coupled transcriptional circuit that originates at the magnetite bead/integrin locus, activates p38, tethers p38 to actin filaments, promotes binding of p38 to Sp1 in the nucleus, and induces filamin-A expression.

Signal processing in migrating T24 human bladder carcinoma cells: role of the autocrine interleukin-8 loop

T24 human bladder carcinoma cells reveal a high locomotor activity (70% locomoting cells) within a 3-dimensional collagen matrix. This high migratory activity is induced by an autocrine engagement of the interleukin-8 receptor A, as was shown by antibodies neutralizing the secreted interleukin-8. Treatment of the cells with these specific antibodies reduced the locomotor activity by half. The intracellular signal transduction underlying the interleukin-8-induced T24 locomotion involves the activity of protein tyrosine kinases (PTKs), the phospholipase Cgamma (PLCgamma) and the protein kinase C (PKC), as proven by the use of specific enzyme inhibitors. These results suggest the following model for the regulatory signal transduction of interleukin-8-induced human T24 bladder carcinoma cell migration: The engagement of the interleukin-8-receptor, a receptor of the serpentine family, leads to the beta-arrestin-mediated activation of PTKs. These kinases phosphorylate the PLCgamma, which generates the second messengers diacylglycerol (DAG) and inositol-1,4,5-trisphosphate (IP(3)). DAG activates the PKC, whereas IP(3) mediates the release of calcium from the endoplasmatic reticulum. By means of confocal laser microscopy, we observed an oscillation of the cytosolic calcium concentration in migrating T24 cells, which were loaded with the calcium-dye fluo-3/AM. Here, we report on a new autocrine function of secreted interleukin-8 and the intracellular signal transduction leading to the regulation of cytosolic calcium and to a migratory tumor cell phenotype.

Mechanisms of tumour invasion and metastasis: emerging targets for therapy

The progression of a tumour from one of benign and delimited growth to one that is invasive and metastatic is the major cause of poor clinical outcome in cancer patients. The invasion and metastasis of tumours is a highly complex and multistep process that requires a tumour cell to modulate its ability to adhere, degrade the surrounding extracellular matrix, migrate, proliferate at a secondary site and stimulate angiogenesis. Knowledge of the process has greatly increased and this has resulted in the identification of a number of molecules that are fundamental to the process. The involvement of these molecules has been shown to relate not only to the survival and proliferation of the tumour cell but, also to the processes of tumour cell adhesion, migration, and the tumour cells ability to degrade and escape the primary site as well as play a role in angiogenesis. These molecules may provide important therapeutic targets that represent the ability to target specific steps in the process of invasion and metastasis and provide additional therapies. The review focuses on representative key targets in each of these processes and summarises the state of play in each case.

Binding of gelsolin domain 2 to actin. An actin interface distinct from that of gelsolin domain 1 and from ADF/cofilin

It is generally assumed that of the six domains that comprise gelsolin, domain 2 is primarily responsible for the initial contact with the actin filament that will ultimately result in the filament being severed. Other actin-binding regions within domains 1 and 4 are involved in gelsolin's severing and subsequent capping activity. The overall fold of all gelsolin repeated domains are similar to the actin depolymerizing factor (ADF)/cofilin family of actin-binding proteins and it has been proposed that there is a similarity in the actin-binding interface. Gelsolin domains 1 and 4 bind G-actin in a similar manner and compete with each other, whereas domain 2 binds F-actin at physiological salt concentrations, and does not compete with domain 1. Here we investigate the domain 2 : actin interface and compare this to our recent studies of the cofilin : actin interface. We conclude that important differences exist between the interfaces of actin with gelsolin domains 1 and 2, and with ADF/cofilin. We present a model for F-actin binding of domain 2 with respect to the F-actin severing and capping activity of the whole gelsolin molecule.

Gelsolin functions as a metastasis suppressor in B16-BL6 mouse melanoma cells and requirement of the carboxyl-terminus for its effect

Gelsolin, an actin-binding protein, is implicated as a critical regulator in cell motility. In addition, we have reported that cellular levels of gelsolin are decreased in various tumor cells, and overexpression of gelsolin by gene transfer suppresses tumorigenicity. We sought to assess the effects of gelsolin overexpression on metastasis and to determine the importance of a carboxyl-terminus that confers Ca(2+) dependency on gelsolin for effects of its overexpression. Expression vectors with cDNA encoding either full-length wild-type or His321 mutant form, isolated from a flat revertant of Ras-transformed cells and a carboxyl-terminal truncate, C-del of gelsolin, were transfected into a highly metastatic murine melanoma cell line, B16-BL6. Expression of introduced cDNA in transfectants was confirmed using Western blotting, 2-dimensional gel electrophoresis and reverse transcription-polymerase chain reaction (RT-PCR). We characterized phenotypes of transfectants, such as growth rate, colony formation in soft agar, cell motility and metastasis formation in vivo. Transfectants expressing the wild-type, His321 mutant and C-del gelsolin exhibited reduced growth ability in soft agar. Although expression of integrin beta1 or alpha4 on the cell surface of transfectants was not changed, wild-type and His321 mutant gelsolin, except for C-del gelsolin, exhibited retardation of cell spreading, reduced chemotatic migration to fibronectin and suppressed lung colonization in spontaneous metastasis assay. Gelsolin may function as a metastasis suppressor as well as a tumor suppressor gene. The carboxyl-terminus of gelsolin is important for retardation of cell spreading, reduced chemotasis and metastasis suppression.

Serum withdrawal induces a redistribution of intracellular gelsolin towards F-actin in NIH 3T3 fibroblasts preceding apoptotic cell death

The intracellular distribution of gelsolin in NIH 3T3 cells was examined by immunostaining using affinity-purified polyclonal gelsolin antibodies before and after induction of apoptosis by serum withdrawal. Serum deprivation induced detachment of an increasing number of NIH 3T3 cells, but also apoptosis in attached cells as verified morphologically by chromatin condensation, nuclear fragmentation and labelling of their periphery by FITC-annexin V. Ongoing apoptosis was also demonstrated by activation of caspase-3 activity and chromatin cleavage into high-molecular-mass fragments, although no internucleosomal chromatin degradation (DNA-ladder formation) was detected. When cells were maintained in the presence of 10% foetal calf serum, gelsolin immunoreactivity was evenly distributed in the cytoplasm. No obvious co-localisation of gelsolin and the actin-containing stress fibres was detected under these conditions. At day one after serum withdrawal, a redistribution of gelsolin to actin filaments was detected within a few attached cells by double fluorescence staining. The number of cells exhibiting this redistribution increased at days two to four. In addition, the stress fibres increased in thickness and their length was continuously reduced. At day four, many cells contained shortened stress fibres, which had lost their longitudinal orientation. Additionally, the cytoplasm of a number of attached cells was highly condensed around their nuclei and a homogenous distribution of both gelsolin and actin was detected in the remaining cytoplasmic rim. Up to day two, these effects were reversible after re-addition of serum to attached cells. A similar redistribution of gelsolin immunore-activity was observed after induction of apoptosis by cycloheximide, but not after initiation of necrosis by hydrogen peroxide. In NIH 3T3 cells no alteration in the expression of gelsolin at the level of protein (Western blot) or specific mRNA (Northern blot) was observed after serum withdrawal. Using Western blotting, no proteolysis of gelsolin was detected up to day 4, although caspase-3 activity was found to have increased fivefold after serum withdrawal. These results suggested that in these cells F-actin severing might occur in the absence or advance of gelsolin cleavage by caspases. Intact gelsolin on its own may be sufficient for the dissolution of the microfilaments, since micro-injection of gelsolin into primary bovine lens cells led to a transient disappearance of the stress fibres and to a reduction of their attachment area to the substratum. In NIH 3T3 cells similar effects of micro-injected gelsolin were only observed at day one after serum withdrawal.

Stress fiber formation is required for matrix reorganization in a corneal myofibroblast cell line

Corneal wound healing fibroblasts (myofibroblasts) develop a muscle-like contractile apparatus composed of prominent microfilament bundles (stress fibers) and express alpha-smooth muscle actin (alpha-SMA). In this study, gelsolin, an actin filament-severing protein, was overexpressed in a alpha-SMA-expressing corneal myofibroblast cell line (TRK43) to assess whether intact stress fibers are required for in vitro matrix organization and wound contraction. Stably integrated gelsolin was introduced by electroporation of an expression construct (pREPCG8) into cultured cells. Thirty-seven clones were isolated with half of the clones showing a fibroblastic phenotype while the remaining half appeared epithelioid. One fibroblastic clone, GS56, and one epithelioid clone, GS44, were selected for detailed characterization. The GS56 cells appeared highly elongated and spindle-shaped and had prominent stress fibers and focal adhesions. GS44 cells showed disruption of stress fibers and a cortical f-actin organization as well as the down regulation of alpha-SMA expression by immunocytochemistry and Western blotting. Both phenotypes showed enhanced gelsolin expression; however, fractionation of cell extracts demonstrated differences in the subcellular distribution of gelsolin with GS44 cells having markedly reduced and GS56 cells having markedly increased cytoskeletal gelsolin. In an in vitro wound contraction assay, epithelioid GS44 cells showed a significantly impaired ability to contract a collagen matrix compared to that of TRK43 cells, CT9 or GS56 transfectants. Loss of stress fibers in GS44 cells also correlated with enhanced cell motility. Together, these results demonstrate that the ability to form microfilament bundles or stress fibers is required for matrix organization and contraction by corneal myofibroblasts. Although no clear explanation is available, we suspect that differences in gene insertion of the gelsolin overexpression vector may have led to differential intercellular localization of gelsolin and its effect on stress fiber formation in the two cell lines.

The flightless I protein colocalizes with actin- and microtubule-based structures in motile Swiss 3T3 fibroblasts: evidence for the involvement of PI 3-kinase and Ras-related small GTPases

The flightless I protein contains an actin-binding domain with homology to the gelsolin family and is likely to be involved in actin cytoskeletal rearrangements. It has been suggested that this protein is involved in linking the cytoskeletal network with signal transduction pathways. We have developed antibodies directed toward the leucine rich repeat and gelsolin-like domains of the human and mouse homologues of flightless I that specifically recognize expressed and endogenous forms of the protein. We have also constructed a flightless I-enhanced green fluorescent fusion vector and used this to examine the localization of the expressed protein in Swiss 3T3 fibroblasts. The flightless I protein localizes predominantly to the nucleus and translocates to the cytoplasm following serum stimulation. In cells stimulated to migrate, the flightless I protein colocalizes with beta-tubulin- and actin-based structures. Members of the small GTPase family, also implicated in cytoskeletal control, were found to colocalize with flightless I in migrating Swiss 3T3 fibroblasts. LY294002, a specific inhibitor of PI 3-kinase, inhibits the translocation of flightless I to actin-based structures. Our results suggest that PI 3-kinase and the small GTPases, Ras, RhoA and Cdc42 may be part of a common functional pathway involved in Fliih-mediated cytoskeletal regulation. Functionally, we suggest that flightless I may act to prepare actin filaments or provide factors required for cytoskeletal rearrangements necessary for cell migration and/or adhesion.

The mouse mammary gland requires the actin-binding protein gelsolin for proper ductal morphogenesis

Gelsolin is an actin-binding/severing protein expressed in intracellular and secreted forms. It is a major regulator of the form and function of the actin cytoskeleton in most all cells. Here we demonstrate that female mice with a targeted deletion of the gelsolin gene (Gsn-/-) have defects in mammary gland morphogenesis. Two distinct defects were identified in the gelsolin-null mammary gland. First, the mammary anlage from Gsn-/- mice failed to elongate at the onset of puberty and remained rudimentary until approximately 9 weeks of age, early block (Gsn-/-(EB)). Second, after the mammary epithelium had filled the mammary fat pad, a complete lack of terminal branching, or late block, was observed (Gsn-/-(LB)). The Gsn-/-(EB) was seen in 70% of Gsn-/- mice and appeared to be dependent on a modifier gene(s) in addition to the loss of gelsolin. Gsn-/-(LB) was observed in all Gsn-/- mice. Terminal end buds (TEBs) were not evident in the mammary anlage from Gsn-/-(EB) mice until approximately 9 weeks of age. Cellular proliferation in the terminal ductal regions of Gsn-/-(EB) females was detected by bromodeoxyuridine incorporation, but was less than that found in the TEBs of age-matched controls. In mice deficient for gelsolin, mammary gland architecture was unaltered at the histological level. Lobuloalveolar development was delayed in response to pregnancy in mammary glands of Gsn-/- mice but was otherwise normal. Lactation and involution in the gelsolin-null animals were similar to those of wild-type mice. Transplantation of epithelium devoid of gelsolin into a wild-type (GsnWT) mammary fat pad resulted in proper arborization of the ductal tree. Transplantation of GsnWT epithelium into the Gsn-/- fat pad recapitulated the lack of terminal branching seen in Gsn-/- females. These results indicate that gelsolin is required in the mammary stroma for proper ductal morphogenesis. Our results provide the first evidence of an actin regulatory protein affecting mammary ductal growth through stromal-epithelial communication.