Actin-binding Protein Gelsolin Research Articles

Coupled Electrostatic and Hydrophobic Destabilisation of the Gelsolin-Actin Complex Enables Facile Detection of Ovarian Cancer Biomarker Lysophosphatidic Acid.

Lysophosphatidic acid (LPA) is a promising biomarker candidate to screen for ovarian cancer (OC) and potentially stratify and treat patients according to disease stage. LPA is known to target the actin-binding protein gelsolin which is a key regulator of actin filament assembly. Previous studies have shown that the phosphate headgroup of LPA alone is inadequate to bind to the short chain of amino acids in gelsolin known as the PIP2-binding domain. Thus, the molecular-level detail of the mechanism of LPA binding is poorly understood. Here, we model LPA binding to the PIP2-binding domain of gelsolin in the gelsolin-actin complex through extensive ten-microsecond atomistic molecular dynamics (MD) simulations. We predict that LPA binding causes a local conformational rearrangement due to LPA interactions with both gelsolin and actin residues. These conformational changes are a result of the amphipathic nature of LPA, where the anionic phosphate, polar glycerol and ester groups, and lipophilic aliphatic tail mediate LPA binding via charged electrostatic, hydrogen bonding, and van der Waals interactions. The negatively-charged LPA headgroup binds to the PIP2-binding domain of gelsolin-actin while its hydrophobic tail is inserted into actin, creating a strong LPA-insertion pocket that weakens the gelsolin-actin interface. The computed structure, dynamics, and energetics of the ternary gelsolin-LPA-actin complex confirms that a quantitative OC assay is possible based on LPA-triggered actin release from the gelsolin-actin complex.

Physical Interaction between HPV16E7 and the Actin-Binding Protein Gelsolin Regulates Epithelial-Mesenchymal Transition via HIPPO-YAP Axis.

Simple SummaryHuman papilloma viruses cause benign or malignant hyper-proliferative lesions in cervical, anogenital and oropharyngeal tissues. Our previous studies revealed that HPV16 E7 alters actin cytoskeleton mainly by binding to and inhibiting Gelsolin. We suggest that the physical interaction E7/Gelsolin in HPV positive tumor cell, and the resulting epithelial to mesenchymal transition process, induce HIPPO signaling cascade by promoting YAP inactivation and favoring HPV-induced cell transformation, cancer motility and aggressiveness. The results of this study provide new insights into the oncogenic transformation mechanisms elicited by HPV in the infected cells and may suggest a repertoire of targets for therapeutic purposes.Human papillomavirus 16 (HPV16) exhibits a strong oncogenic potential mainly in cervical, anogenital and oropharyngeal cancers. The E6 and E7 viral oncoproteins, acting via specific interactions with host cellular targets, are required for cell transformation and maintenance of the transformed phenotype as well. We previously demonstrated that HPV16E7 interacts with the actin-binding protein gelsolin, involved in cytoskeletal F-actin dynamics. Herein, we provide evidence that the E7/gelsolin interaction promotes the cytoskeleton rearrangement leading to epithelial-mesenchymal transition-linked morphological and transcriptional changes. E7-mediated cytoskeletal actin remodeling induces the HIPPO pathway by promoting the cytoplasmic retention of inactive P-YAP. These results suggest that YAP could play a role in the “de-differentiation” process underlying the acquisition of a more aggressive phenotype in HPV16-transformed cells. A deeper comprehension of the multifaceted mechanisms elicited by the HPV infection is vital for providing novel strategies to block the biological and clinical features of virus-related cancers.

Attenuation of murine and human airway contraction by a peptide fragment of the cytoskeleton regulatory protein gelsolin.

We have previously reported that mice genetically deficient in the actin binding protein gelsolin exhibit impaired airway smooth muscle (ASM) relaxation. Primary cultured ASM cells from these mice demonstrate enhanced inositol triphosphate (IP3) synthesis and increased intracellular calcium in response to Gq-coupled agonists. We hypothesized that this was due to increased intracellular availability of unbound phosphatidylinositol 4,5-bisphosphate (PIP2), based on the fact that gelsolin contains a short peptide region that binds PIP2, presumably making it a less available substrate. We now questioned whether a peptide that corresponds to the PIP2 binding region of gelsolin could modulate ASM signaling and contraction. The 10 amino acid sequence of the gelsolin peptide within the PIP2-binding region was incubated with primary cultures of human ASM cells, and IP3 synthesis was measured in response to a Gq-coupled agonist. Gelsolin peptide-treated cells generated less IP3 under basal and bradykinin or acetylcholine (Gq-coupled) conditions. Acetylcholine-induced contractile force measured in isolated tracheal rings from mice and human tracheal muscle strips in organ baths was attenuated in the presence of the gelsolin peptide. The gelsolin peptide also attenuated methacholine-induced airway constriction in murine precision-cut lung slices. Furthermore, this peptide fragment delivered to the respiratory system of mice via nebulization attenuated subsequent methacholine-induced increases in airway resistance in vivo. The current study demonstrates that introduction of this small gelsolin peptide into the airway may be a novel therapeutic option in bronchoconstrictive diseases.

Hepatoprotective effects of capping protein gelsolin against hyperoxia-induced hepatotoxicity, oxidative stress and DNA damage in neonatal rats

Tissues and organs get exposed to high oxygen (O2) supply in hyperoxia conditions. The goal of this research was to investigate the protective effect of actin binding protein gelsolin on hyperoxia-induced hepatotoxicity through histopathology and measurement of oxidative stress parameters and DNA damage in a neonatal Wistar albino rats. The pups were randomly separated to four equal groups such as: normoxia control group (NC), normoxia plus gelsolin group (NG, 10 ng/kg bw/day gelsolin), hyperoxia (≥85% O2) group (HC), hyperoxia plus gelsolin group (HG, ≥85% O2; 10 ng/kg bw/day gelsolin). Histopathological changes of pups in hyperoxia condition were revealed in the form of severe leukocyte infiltration, vascular congestion, necrosis, vacuolar degeneration, binucleated hepatocytes and hemorrhage in the liver tissue. SOD, CAT, GPx and GST activities decreased and MDA level increased in the hyperoxia-induced group in liver tissue (P < 0.05). Tail DNA%, tail length and moment indicating DNA damage statistically increased in hyperoxia treatment groups when compared to controls. Treatment of rats with hyperoxia plus gelsolin prevented hyperoxia-induced changes in tissue structure, antioxidant enzyme activities and MDA level, mean tail DNA% and length. Based on these findings, gelsolin restored these changing to near normal levels but it does not protect completely in the hyperoxia conditions.

Structure, regulation and related diseases of the actin-binding protein gelsolin.

Gelsolin (GSN), one of the most abundant actin-binding proteins, is involved in cell motility, shape and metabolism. As a member of the GSN superfamily, GSN is a highly structured protein in eukaryotic cells that can be regulated by calcium concentration, intracellular pH, temperature and phosphatidylinositol-4,5-bisphosphate. GSN plays an important role in cellular mechanisms as well as in different cellular interactions. Because of its participation in immunologic processes and its interaction with different cells of the immune system, GSN is a potential candidate for various therapeutic applications. In this review, we summarise the structure of GSN as well as its regulating and functional roles, focusing on distinct diseases such as Alzheimer's disease, rheumatoid arthritis and cancer. A short overview of GSN as a therapeutic target in today's medicine is also provided.

Validation of an automated immune turbidimetric assay for serum gelsolin and its possible clinical utility in sepsis.

Studies showing the potential predictive value of the actin-binding protein gelsolin, in critically ill patients are scarce. Moreover, even up to now a rapid automated measurement of gelsolin has still remained a challenge. Therefore, we developed and validated an automated serum gelsolin immune turbidimetric assay for possible clinical use. Validation of serum gelsolin assay was performed on a Cobas 8000/c502 analyzer (Roche) according to the second edition of Eurachem guidelines. Furthermore, we also studied the diagnostic value of serum gelsolin in sepsis when investigating sera of septic (n=25), systemic inflammatory response syndrome (SIRS; n=8) and control patients (n=14). We compared our previously published Western blot data with those of the new turbidimetric assay. The sample volume was 7μL and the assay time was 10minutes. The detection limit was 0.72mg/L, intra- and inter-assay imprecision remained in most cases less than 5% expressed as CV. Recovery was found to be 84.56%-93.52% and linearity study gave an appropriate correlation coefficient by linear regression analysis (r2 =.998). Septic patients exhibited lower (P=.015) first-day serum gelsolin levels than SIRS patients, which confirmed our previous Western blot results. The determined cut-off point for serum gelsolin was 14.05mg/L (sensitivity: 75%; specificity: 60%) when investigating its diagnostic value in sepsis. Based on the results, our immune turbidimetric measurement offers a rapid and accurate quantitation of gelsolin in human serum samples. Serum gelsolin seems a promising additional diagnostic marker of sepsis which has to be further investigated.

Impaired Relaxation of Airway Smooth Muscle in Mice Lacking the Actin-Binding Protein Gelsolin.

Diverse classes of ligands have recently been discovered that relax airway smooth muscle (ASM) despite a transient increase in intracellular calcium concentrations ([Ca2+]i). However, the cellular mechanisms are not well understood. Gelsolin is a calcium-activated actin-severing and -capping protein found in many cell types, including ASM cells. Gelsolin also binds to phosphatidylinositol 4,5-bisphosphate, making this substrate less available for phospholipase Cβ-mediated hydrolysis to inositol triphosphate and diacylglycerol. We hypothesized that gelsolin plays a critical role in ASM relaxation and mechanistically accounts for relaxation by ligands that transiently increase [Ca2+]i. Isolated tracheal rings from gelsolin knockout (KO) mice showed impaired relaxation to both a β-agonist and chloroquine, a bitter taste receptor agonist, which relaxes ASM, despite inducing transiently increased [Ca2+]i. A single inhalation of methacholine increased lung resistance to a similar extent in wild-type and gelsolin KO mice, but the subsequent spontaneous relaxation was less in gelsolin KO mice. In ASM cells derived from gelsolin KO mice, serotonin-induced Gq-coupled activation increased both [Ca2+]i and inositol triphosphate synthesis to a greater extent compared to cells from wild-type mice, possibly due to the absence of gelsolin binding to phosphatidylinositol 4,5-bisphosphate. Single-cell analysis showed higher filamentous:globular actin ratio at baseline and slower cytoskeletal remodeling dynamics in gelsolin KO cells. Gelsolin KO ASM cells also showed an attenuated decrease in cell stiffness to chloroquine and flufenamic acid. These findings suggest that gelsolin plays a critical role in ASM relaxation and that activation of gelsolin may contribute to relaxation induced by ligands that relax ASM despite a transient increase in [Ca2+]i.

Abstract 1444: Docosahexaenoic acid reduces cancer cell migration may link with actin binding proteins and miRNA 17-92 cluster expressions changes

Abstract Metastasis and progression, reflected by higher migration and longer cell survival, are major contributing factors in making cancers the leading cause of death worldwide. Cancer cells exhibit higher migration rates and greater cell viability facilitated by actin binding protein-mediated cytoskeletal remodeling and secondary messengers (cAMP and/or cGMP) signaling. Studies have shown that docosahexaenoic acid (DHA), a poly unsaturated fatty acid, inhibits cancer cell metastatic phenotype. Moreover, miRNA-17∼92 cluster has been reported to be highly expressed in metastasis. Therefore, we put forward a hypothesis that DHA will induce changes in actin binding protein dynamics and miRNA-17∼92 cluster expression to inhibit cancer cell migration and viability. Non-cance (MLE12) and cancer (A549) cells were treated with 8-Br-cAMP and/or DHA for 30 min, 3h, 6h and 24h. Actin binding proteins (profilin, cofilin, vimentin and gelsolin) and miRNA-17∼92 cluster expression were analyzed by western blot and qRT PCR respectively. Cell migration was estimated by wound assay and transwell apparatus. F-actin content and actin binding proteins were measured using confocal microscopy at the leading edges of wound. Proliferation and cell viability were estimated by flow cytometer, IF using ki-67, and cleaved-caspase-3 antibodies. F-actin content, cell migration and proliferation were increased while cell viability was decreased by cAMP. DHA treatment reverses the increase in actin content and cell migration in cancer cells but not in non-cancer cells. These findings correlate with changes in actin binding protein content and miRNA 17∼92 cluster expression. Thus, DHA specifically inhibits cancer cell migration, proliferation, and viability and this effect correlates with decreases in actin binding protein levels and miRNA-17∼92 cluster expression. In conclusion, DHA supplementation suppresses cellular changes related to metastatic potential in cancer cells and could provide therapeutic potential against cancer cell metastasis. Moreover, actin binding proteins and miRNA-17∼92 cluster expression could serve as innovative therapeutic targets and biomarkers for cancer progression. Citation Format: Mehboob Ali, Kathryn M. Heyob, Lynette K. Rogers. Docosahexaenoic acid reduces cancer cell migration may link with actin binding proteins and miRNA 17-92 cluster expressions changes. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1444. doi:10.1158/1538-7445.AM2015-1444

Single-molecule force spectroscopy reveals force-enhanced binding of calcium ions by gelsolin.

Force is increasingly recognized as an important element in controlling biological processes. Forces can deform native protein conformations leading to protein-specific effects. Protein–protein binding affinities may be decreased, or novel protein–protein interaction sites may be revealed, on mechanically stressing one or more components. Here we demonstrate that the calcium-binding affinity of the sixth domain of the actin-binding protein gelsolin (G6) can be enhanced by mechanical force. Our kinetic model suggests that the calcium-binding affinity of G6 increases exponentially with force, up to the point of G6 unfolding. This implies that gelsolin may be activated at lower calcium ion levels when subjected to tensile forces. The demonstration that cation–protein binding affinities can be force-dependent provides a new understanding of the complex behaviour of cation-regulated proteins in stressful cellular environments, such as those found in the cytoskeleton-rich leading edge and at cell adhesions.

The Actin-Binding Proteins Eps8 and Gelsolin Have Complementary Roles in Regulating the Growth and Stability of Mechanosensory Hair Bundles of Mammalian Cochlear Outer Hair Cells

Sound transduction depends upon mechanosensitive channels localized on the hair-like bundles that project from the apical surface of cochlear hair cells. Hair bundles show a stair-case structure composed of rows of stereocilia, and each stereocilium contains a core of tightly-packed and uniformly-polarized actin filaments. The growth and maintenance of the stereociliary actin core are dynamically regulated. Recently, it was shown that the actin-binding protein gelsolin is expressed in the stereocilia of outer hair cells (OHCs) and in its absence they become long and straggly. Gelsolin is part of a whirlin scaffolding protein complex at the stereocilia tip, which has been shown to interact with other actin regulatory molecules such as Eps8. Here we investigated the physiological effects associated with the absence of gelsolin and its possible overlapping role with Eps8. We found that, in contrast to Eps8, gelsolin does not affect mechanoelectrical transduction during immature stages of development. Moreover, OHCs from gelsolin knockout mice were able to mature into fully functional sensory receptors as judged by the normal resting membrane potential and basolateral membrane currents. Mechanoelectrical transducer current in gelsolin-Eps8 double knockout mice showed a profile similar to that observed in the single mutants for Eps8. We propose that gelsolin has a non-overlapping role with Eps8. While Eps8 is mainly involved in the initial growth of stereocilia in both inner hair cells (IHCs) and OHCs, gelsolin is required for the maintenance of mature hair bundles of low-frequency OHCs after the onset of hearing.

Single Molecule Force Spectroscopy Reveals Force-Enhanced Binding of Calcium Ions by Gelsolin

Force is increasingly recognized as an important element in controlling biological processes. Forces are able to deform native protein conformations leading to protein-specific effects. Although in a few cases, the exposure of novel protein binding sites by force has been reported, mechanical stress generally leads to the decrease of protein-protein binding affinities. In this paper, we demonstrate that the calcium-binding affinity of the actin-binding protein gelsolin domain G6 is enhanced, rather than decreased, by mechanical force. Using a recently developed single molecule-binding assay based on atomic force microscopy, we establish that the calcium-binding affinity of G6 increases exponentially with the applied force, up to the point of G6 unfolding. This implies that gelsolin will be activated at lower calcium ion levels when subjected to tensile forces and suggests a basis for enhanced cooperativity during multi-cation induced activation. This is, to our knowledge, the first experimental verification of the force-amplified ligand binding concept at the molecular level. Such force-amplified ligand binding is fundamentally different from the widely accepted ideas of "catch bond" and force activated binding. The demonstration that cation-protein binding affinities can be force-dependent provides a new paradigm in understanding the complex interactions of cation-regulated proteins in stressful cellular environments, such as those found in the cytoskeleton-rich leading edge and at cell adhesions.

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.

The human papillomavirus-16 E7 oncoprotein exerts antiapoptotic effects via its physical interaction with the actin-binding protein gelsolin

The oncoprotein E7 from human papillomavirus-16 (HPV-16 E7) plays a pivotal role in HPV postinfective carcinogenesis, and its physical interaction with host cell targets is essential to its activity. We identified a novel cellular partner for the viral oncoprotein: the actin-binding protein gelsolin (GSN), a key regulator of actin filament assembly and disassembly. In fact, biochemical analyses, generation of a 3D molecular interaction model and the use of specific HPV-16 E7 mutants provided clear cut evidence supporting the crucial role of HPV-16 E7 in affecting GSN integrity and function in human immortalized keratinocytes. Accordingly, functional analyses clearly suggested that stable HPV-16 E7 expression induced an imbalance between polymeric and monomeric actin in favor of the former. These events also lead to changes of cell cycle (increased S phase), to the inhibition of apoptosis and to the increase of cell survival. These results provide support to the hypotheses generated from the 3D molecular interaction model and encourage the design of small molecules hindering HPV-induced host cell reprogramming by specifically targeting HPV-16 E7-expressing cells.

Gelsolin co-occurs with Lewy bodies in vivo and accelerates α-synuclein aggregation in vitro

Deposition of fibrillar α-synuclein as Lewy bodies is the neuropathological hallmark of Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). Apart from α-synuclein, these intraneuronal inclusions contain over 250 different proteins. The actin binding protein gelsolin, has previously been suggested to be part of the Lewy body, but its potential role in α-synuclein aggregation remains unknown. Here, we studied the association between gelsolin and α-synuclein in brain tissue from PD and DLB patients as well as in a cell model for α-synuclein aggregation. Moreover, the potential effect of gelsolin on α-synuclein fibrillization was also investigated. Our data demonstrate that gelsolin co-occured with α-synuclein in Lewy bodies from affected human brain as well as with Lewy body-like inclusions in α-synuclein over expressing cells. Furthermore, in the presence of calcium chloride, gelsolin was found to enhance the aggregation rate of α-synuclein in vitro. Moreover, no apparent structural differences could be observed between fibrils formed in the presence or absence of gelsolin. Further studies on gelsolin and other Lewy body associated proteins are warranted to learn more about their potential role in the α-synuclein aggregation process.

Abstract 4753: The interaction of two metastasis suppressor genes, Nm23-H1 and Gelsolin, results in synergistic phenotypes

Abstract Metastasis Suppressor Genes (MSGs) are able to inhibit metastasis without reducing primary tumor size. Nm23 was the first MSGs to be identified. The biochemical basis for the anti-metastatic effect of Nm23 has been subject of many studies but remains unresolved. We performed co-immunoprecipitation assays using flag-tagged constructs of both the human and murine forms of Nm23 (Nm23-H1 and Nm23-M1, respectively) over-expressed in the mouse mammary carcinoma cell line 4T1. Co-immunoprecipitation assays were also performed on tissue extracts of primary tumors and metastases obtained from Balb/C mice injected with these cell lines. Using Mass-Spectrometry, new binding partners were identified including the actin-binding protein Gelsolin. Gelsolin is an actin regulatory protein that modulates actin assembly and disassembly, and is believed to regulate cell motility in vivo through modulation of the actin network. Recently, Gelsolin has been added to the list of MSGs. An interaction between Gelsolin and Nm23 was validated in a murine cell line (4T1- Nm23-H1/M1 clones) and in a human breast carcinoma cell lines (MCF-7). In the low- metastatic cells MCF-7 an interaction between endogenous Nm23-H1 and Gelsolin was observed. However, in the highly metastatic MDA-MB-435 and MDA-MB-231 cell lines the interaction was observed only after the over-expression of Nm23-H1. These results suggest that an Nm23-Gelsolin interaction may only take place when relatively high levels of Nm23 are expressed. We conclude that the interaction between Nm23-H1 and Gelsolin occurs in the non-metastatic state, where high levels of both proteins are present, and this interaction can contribute to the anti-metastatic property associated to Nm23. Using cultures of MDA-MB-231 stably overexpressing Gelsolin, Nm23-H1 or both proteins, the biological role of this interaction was analyzed. The two metastasis suppressors, Nm23-H1 and Gelsolin, when overexpressed in the single stable clone did not affect the cell growth; however they cooperated in decreasing the cell growth. This is the first time overexpression of Nm23-H1 has decreased cell proliferatioin and suggests that combinations of MSGs may have distinct phenotypic effects. Moreover, overexpression of both Nm23-H1 and Gelsolin in MDA-MB-231 cells reduced cell migration and cell invasion compared to the clone overexpressing the empty vector or single suppressor genes. In summary, Nm23-H1 has been demonstrated to bind another Metastasis Suppressor, Gelsolin. Additive and synergistic effects of multiple Metastasis Suppressors were identified. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4753. doi:10.1158/1538-7445.AM2011-4753

Cytochrome P450 2B1 Mediates Complement-dependent Sublytic Injury in a Model of Membranous Nephropathy

Membranous nephropathy is a disease that affects the filtering units of the kidney, the glomeruli, and results in proteinuria accompanied by loss of kidney function. Passive Heymann nephritis is an experimental model that mimics membranous nephropathy in humans, wherein the glomerular epithelial cell (GEC) injury induced by complement C5b-9 leads to proteinuria. We examined the role of cytochrome P450 2B1 (CYP2B1) in this complement-mediated sublytic injury. Overexpression of CYP2B1 in GECs significantly increased the formation of reactive oxygen species, cytotoxicity, and collapse of the actin cytoskeleton following treatment with anti-tubular brush-border antiserum (anti-Fx1A). In contrast, silencing of CYP2B1 markedly attenuated anti-Fx1A-induced reactive oxygen species generation and cytotoxicity with preservation of the actin cytoskeleton. Gelsolin, which maintains an organized actin cytoskeleton, was significantly decreased by complement C5b-9-mediated injury but was preserved in CYP2B1-silenced cells. In rats injected with anti-Fx1A, the cytochrome P450 inhibitor cimetidine blocked an increase in catalytic iron and ROS generation, reduced the formation of malondialdehyde adducts, maintained a normal distribution of nephrin in the glomeruli, and provided significant protection at the onset of proteinuria. Thus, GEC CYP2B1 contributes to complement C5b-9-mediated injury and plays an important role in the pathogenesis of passive Heymann nephritis.

Abstract 5125: The identification of Gelsolin as a potential binding partner of Nm23

Abstract Nm23 was the first metastasis suppressor gene to be identified. To better understand the biological mechanism leading to its anti-metastatic properties, we have investigated new potential binding-proteins of Nm23. Using Mass-spectrometry, we analyzed proteins obtained with co-immunoprecipitation of Nm23 in a mouse mammary cancer cell line overexpressing the human and murine forms of Nm23 (4T1-Nm23H1-flag and 4T1-Nm23M1-flag). Co-immunoprecipitations were also performed from primary tumors and liver metastases obtained from injection of these cell lines into Balb/C mice. Several proteins were found to bind Nm23, both in vitro and in vivo specimens. In addition to previously published Nm23 interacting proteins, we identified new binding partners including the actin-binding protein Gelsolin. Using immunoprecipitation assays, the interaction between Gelsolin and Nm23 was validated in a murine cell line (4T1- Nm23H1/M1 clones) and then in human breast carcinoma cell lines with low (MCF-7) and high metastatic potentials (MDA-MB-435, MDA-MB-231). In the highly metastatic MDA-MB-231 cell line, the interaction was observed only after the overexpression of Nm23 in the system. These results suggest that a Nm23-gelsolin interaction may only take place when relatively high levels of Nm23 are expressed. Moreover, we observed that this interaction involves not only the native form of Gelsolin but also Gelsolin-fragments, NH2-terminal and COOH-terminal, which are generated by the action of caspase-3 cleavage. Full-length Gelsolin binds and severs actin polymers in a Ca2+-dependent manner, whereas caspase-3-cleaved Gelsolin severs actin polymers independent of Ca2+. The overexpression of the NH2-terminal fragment has been shown to induce apoptosis, whereas the COOH Terminal fragment has been shown to have an anti-apoptotic effect. We are therefore interested in exploring which Gelsolin-fragment may be specifically binding to Nm23, in order to determine the biological function regulated by this interaction. Our results show a novel Nm23 binding partner, Gelsolin, which is involved in the actin-cytoskeleton regulation and may, in part, explain the motility inhibitory activity of Nm23. The exact interactions between Nm23 and Gelsolin are currently being explored. In particular we are evaluating the role of this interaction in the anti-metastatic effects of Nm23, both human and murine. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5125.

Mass Spectrometric Analyses of Peptides and Proteins in Human Gingival Crevicular Fluid

Gingival crevicular fluid (GCF) is a pathophysiological fluid that flows into the oral cavity. Human GCF was collected using sterile glass microcapillary tubes from inflamed periodontal sites in patients who had a history of periodontal disease and were in the maintenance phase of treatment. Samples from individual sites were analyzed using MS techniques both before and following HPLC. GCF samples were also pooled and subjected to SDS-PAGE, in-gel digestion and MS analyses using both MALDI-TOF/TOF MS and nanoLC-ESI-MS/MS. MS spectra were used to search human protein sequence databases for protein identification. With these approaches, 33 peptides and 66 proteins were positively identified in human GCF. All of the peptides discovered in this study are reported in GCF here for the first time. Forty-three of the identified proteins, such as actin and the actin binding proteins profilin, cofilin and gelsolin, have not been reported in GCF before.

In colon carcinogenesis, the cytoskeletal protein gelsolin is down-regulated during the transition from adenoma to carcinoma

The actin-binding protein gelsolin is involved in cell motility via the regulation of actin cytoskeleton, and its expression is modified in several human cancers. However, the potential implication of this protein in colorectal carcinogenesis is debated. By using immunohistochemistry, we studied gelsolin expression in 69 cases of colon adenocarcinomas and in 72 lesions representative of the different stages of colonic tumorigenesis. In addition, we performed Northern blot analysis of gelsolin messenger RNA in 12 paired samples of human colon cancer and normal corresponding mucosa. Gelsolin protein and messenger RNA expressions were severely down-regulated in all adenocarcinomas tested. Moreover, gelsolin protein was down-regulated in a large proportion of high-grade adenomas (14/16) before the acquisition of invasive properties but in only a small proportion of low grade adenomas and serrated adenomas (2/30) and in none of the 9 cases of nonneoplastic hyperplastic polyps tested. Our results therefore demonstrate that gelsolin down-regulation is an early and almost constant event in colon carcinogenesis and is associated with the transition from adenoma to carcinoma.

Phosphatidylinositol-4,5 Bisphosphate Produced by PIP5KIγ Regulates Gelsolin, Actin Assembly, and Adhesion Strength of N-Cadherin Junctions

Phosphoinositides regulate several actin-binding proteins but their role at intercellular adhesions has not been defined. We found that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) was generated at sites of N-cadherin-mediated intercellular adhesion and was a critical regulator of intercellular adhesion strength. Immunostaining for PI(4,5)P2 or transfection with GFP-PH-PLCdelta showed that PI(4,5)P2 was enriched at sites of N-cadherin adhesions and this enrichment required activated Rac1. Isoform-specific immunostaining for type I phosphatidylinositol 4-phosphate 5 kinase (PIP5KI) showed that PIP5KIgamma was spatially associated with N-cadherin-Fc beads. Association of PIP5KIgamma with N-cadherin adhesions was in part dependent on the activation of RhoA. Transfection with catalytically inactive PIP5KIgamma blocked the enrichment of PI(4,5)P2 around beads. Catalytically inactive PIP5KIgamma or a cell-permeant peptide that mimics and competes for the PI(4,5)P2-binding region of the actin-binding protein gelsolin inhibited incorporation of actin monomers in response to N-cadherin ligation and reduced intercellular adhesion strength by more than twofold. Gelsolin null fibroblasts transfected with a gelsolin severing mutant containing an intact PI(4,5)P2 binding region, demonstrated intercellular adhesion strength similar to wild-type transfected controls. We conclude that PIP5KIgamma-mediated generation of PI(4,5)P2 at sites of N-cadherin contacts regulates intercellular adhesion strength, an effect due in part to PI(4,5)P2-mediated regulation of gelsolin.