Roles of the small GTPases RhoA and Rac1 in cell behavior

The Rho-family GTPases are proving to have a variety of biological functions apart from their well known effects on the cytoskeleton. Recent work indicates their involvement in signaling between the adhesion receptors integrin and syndecan, effects on the recruitment of beta-catenin to the nucleus, and potential roles in the nucleus as well as the cytoplasm

The actin crosslinking protein palladin modulates force generation and mechanosensitivity of tumor associated fibroblasts

Cells organize actin filaments into higher-order structures by regulating the composition, distribution and concentration of actin crosslinkers. Palladin is an actin crosslinker found in the lamellar actin network and stress fibers, which are critical for mechanosensing of the environment. Palladin also serves as a molecular scaffold for α-actinin, another key actin crosslinker. By virtue of its close interactions with actomyosin structures in the cell, palladin may play an important role in cell mechanics. However, the role of palladin in cellular force generation and mechanosensing has not been studied. Here, we investigate the role of palladin in regulating the plasticity of the actin cytoskeleton and cellular force generation in response to alterations in substrate stiffness. Traction force microscopy revealed that tumor-associated fibroblasts generate larger forces on substrates of increased stiffness. Contrary to expectations, knocking down palladin increased the forces generated by cells and inhibited their ability to sense substrate stiffness for very stiff gels. This was accompanied by significant differences in actin organization, adhesion dynamics and altered myosin organization in palladin knock-down cells. Our results suggest that actin crosslinkers such as palladin and myosin motors coordinate for optimal cell function and to prevent aberrant behavior as in cancer metastasis

The role of palladin in actin organization and cell motility

Palladin is a widely expressed protein found in stress fibers, focal adhesions, growth cones, Z-discs, and other actin-based subcellular structures. It belongs to a small gene family that includes the Z-disc proteins myopalladin and myotilin, all of which share similar Ig-like domains. Recent advances have shown that palladin shares with myotilin the ability to bind directly to F-actin, and to crosslink actin filaments into bundles, in vitro. Studies in a variety of cultured cells suggest that the actin-organizing activity of palladin plays a central role in promoting cell motility. Correlative evidence also supports this hypothesis, as palladin levels are typically upregulated in cells that are actively migrating: in developing vertebrate embryos, in cells along a wound edge, and in metastatic cancer cells. Recently, a mutation in the human palladin gene was implicated in an unusually penetrant form of inherited pancreatic cancer, which has stimulated new ideas about the role of palladin in invasive cancer

Predictores de eventos clínicos en una cohorte de pacientes con enfermedad de Fabry en tratamiento sustitutivo enzimático

Enfermedad de Fabry; Enfermedad renal crónica; Tratamiento enzimático sustitutivoFabry disease; Chronic kidney disease; Enzyme replacement therapyMalaltia de Fabry; Malaltia renal crònica; Tractament enzimàtic substitutiuFabry disease may be treated by enzyme replacement therapy (ERT), but the impact of chronic kidney disease (CKD) on the response to therapy remains unclear. The aim of the present study was to analyse the incidence and predictors of clinical events in patients on ERT. Study design: Multicentre retrospective observational analysis of patients diagnosed and treated with ERT for Fabry disease. The primary outcome was the first renal, neurological or cardiological events or death during a follow-up of 60 months (24-120). Results: In 69 patients (42 males, 27 females, mean age 44.6±13.7 years), at the end of follow-up, eGFR and the left ventricular septum thickness remained stable and the urinary albumin: creatinine ratio tended to decrease, but this decrease only approached significance in patients on agalsidase-beta (242-128mg/g (p=0.05). At the end of follow-up, 21 (30%) patients had suffered an incident clinical event: 6 renal, 2 neurological and 13 cardiological (including 3 deaths). Events were more frequent in patients with baseline eGFR≤60ml/min/1.73m2 (log Rank 12.423, p=0.001), and this remained significant even after excluding incident renal events (log Rank 4.086, p=0.043) and in males and in females. Lower baseline eGFR was associated with a 3- to 7-fold increase the risk of clinical events in different Cox models. Conclusions: GFR at the initiation of ERT is the main predictor of clinical events, both in males and in females, suggesting that start of ERT prior to the development of CKD is associated with better outcomes.El objetivo de este estudio es realizar un mapa del tratamiento actual de la enfermedad de Fabry en España, analizando el efecto de diferentes factores en el desarrollo de eventos clínicos a largo plazo. Diseño del estudio: Análisis observacional retrospectivo multicéntrico. Criterios de inclusión: pacientes diagnosticados y tratados de enfermedad de Fabry. Se recogieron datos generales en relación con el diagnóstico, síntomas y tipo mutación, tipo de tratamiento recibido, evolución renal y cardiológica. Durante un tiempo de seguimiento de 60 meses (24-120), se recogió el primer evento clínico tras el inicio de tratamiento sustitutivo enzimático definido como mortalidad, evento renal, cardiológico o neurológico. Resultados: Se incluyeron 69 pacientes (42 H, 27 M) con una edad media de 44,6 ± 13,7 años. A los cinco años de tratamiento, el FGe y la hipertrofia ventricular izquierda se mantuvieron estables, y la albuminuria tiende a disminuir, siendo este descenso más significativo en el grupo de pacientes tratados con beta-galactosidasa (de 242 a 128mg/g (p = 0,05). Veintiún pacientes sufrieron un evento clínico (30%): seis renales, dos neurológicos y 13 cardiológicos (incluidas tres muertes). Los pacientes con ERC (FGe < 60) antes del inicio de tratamiento tuvieron más eventos (log-rank 12.423, p = 0,001), manteniéndose la predicción si excluíamos los eventos renales (log-rank 4.086 (p = 0,043) en hombres y mujeres. La peor función renal al inicio del tratamiento aumentó entre tres y siete veces el riesgo de eventos clínicos en diferentes modelos de Cox ajustados. Conclusiones: La función renal al inicio de tratamiento sustitutivo enzimático es la principal predictora de desarrollo de eventos clínicos a largo plazo, tanto en hombres como mujeres. El inicio de tratamiento sustitutivo enzimático precoz antes del desarrollo de ERC mejoraría el pronóstico.MG, JT, AO, RT are supported by ISCIII RETIC REDINREN, RD016/009 and FEDER fund

Cytoplasmic Ig-domain proteins: Cytoskeletal regulators with a role in human disease

Immunoglobulin domains are found in a wide variety of functionally diverse transmembrane proteins, and also in a smaller number of cytoplasmic proteins. Members of this latter group are usually associated with the actin cytoskeleton, and most of them bind directly to either actin or myosin, or both. Recently, studies of inherited human disorders have identified disease-causing mutations in five cytoplasmic Ig-domain proteins: myosin-binding protein C, titin, myotilin, palladin, and myopalladin. Together with results obtained from cultured cells and mouse models, these clinical studies have yielded novel insights into the unexpected roles of Ig domain proteins in mechanotransduction and signaling to the nucleus. An emerging theme in this field is that cytoskeleton-associated Ig domain proteins are more than structural elements of the cell, and may have evolved to fill different needs in different cellular compartments

Low density lipoprotein receptor–related protein is a calreticulin coreceptor that signals focal adhesion disassembly

Thrombospondin (TSP) signals focal adhesion disassembly (the intermediate adhesive state) through interactions with cell surface calreticulin (CRT). TSP or a peptide (hep I) of the active site induces focal adhesion disassembly through binding to CRT, which activates phosphoinositide 3-kinase (PI3K) and extracellular signal–related kinase (ERK) through Gαi2 proteins. Because CRT is not a transmembrane protein, it is likely that CRT signals as part of a coreceptor complex. We now show that low density lipoprotein receptor–related protein (LRP) mediates focal adhesion disassembly initiated by TSP binding to CRT. LRP antagonists (antibodies, receptor-associated protein) block hep I/TSP-induced focal adhesion disassembly. LRP is necessary for TSP/hep I signaling because TSP/hep I is unable to stimulate focal adhesion disassembly or ERK or PI3K signaling in fibroblasts deficient in LRP. LRP is important in TSP–CRT signaling, as shown by the ability of hep I to stimulate association of Gαi2 with LRP. The isolated proteins LRP and CRT interact, and LRP and CRT are associated with hep I in molecular complexes extracted from cells. These data establish a mechanism of cell surface CRT signaling through its coreceptor, LRP, and suggest a novel function for LRP in regulating cell adhesion

FARP1, ARHGEF39, and TIAM2 are essential receptor tyrosine kinase effectors for Rac1-dependent cell motility in human lung adenocarcinoma

Despite the undisputable role of the small GTPase Rac1 in the regulation of actin cytoskeleton reorganization, the Rac guanine-nucleotide exchange factors (Rac-GEFs) involved in Rac1-mediated motility and invasion in human lung adenocarcinoma cells remain largely unknown. Here, we identify FARP1, ARHGEF39, and TIAM2 as essential Rac-GEFs responsible for Rac1-mediated lung cancer cell migration upon EGFR and c-Met activation. Noteworthily, these Rac-GEFs operate in a non-redundant manner by controlling distinctive aspects of ruffle dynamics formation. Mechanistic analysis reveals a leading role of the AXL-Gab1-PI3K axis in conferring pro-motility traits downstream of EGFR. Along with the positive association between the overexpression of Rac-GEFs and poor lung adenocarcinoma patient survival, we show that FARP1 and ARHGEF39 are upregulated in EpCam+ cells sorted from primary human lung adenocarcinomas. Overall, our study reveals fundamental insights into the complex intricacies underlying Rac-GEF-mediated cancer cell motility signaling, hence underscoring promising targets for metastatic lung cancer therapy.Fil: Cooke, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas; Argentina. University of Pennsylvania; Estados UnidosFil: Kreider Letterman, Gabriel. University Of Toledo (utoledo); Estados UnidosFil: Baker, Martin James. University of Pennsylvania; Estados UnidosFil: Zhang, Suli. University of Pennsylvania; Estados UnidosFil: Sullivan, Neil T.. University of Pennsylvania; Estados UnidosFil: Eruslanov, Evgeniy. University of Pennsylvania; Estados UnidosFil: Abba, Martín Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Médicas. Centro de Investigaciones Inmunológicas Básicas y Aplicadas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Goicoechea, Silvia M.. University Of Toledo (utoledo); Estados UnidosFil: Garcia Mata, Rafael. University Of Toledo (utoledo); Estados UnidosFil: Kazanietz, Marcelo Gabriel. University of Pennsylvania; Estados Unido

Structure and Function of Palladin's Actin Binding Domain

Here we report the NMR structure of the actin-binding domain contained in the cell adhesion protein palladin. Previously we demonstrated that one of the immunoglobulin domains of palladin (Ig3) is both necessary and sufficient for direct F-actin binding in vitro. In this study, we identify two basic patches on opposite faces of Ig3 that are critical for actin binding and crosslinking. Sedimentation equilibrium assays indicate that the Ig3 domain of palladin does not self-associate. These combined data are consistent with an actin crosslinking mechanism that involves concurrent attachment of two actin filaments by a single palladin molecule by an electrostatic mechanism. Palladin mutations that disrupt actin binding show altered cellular distributions and morphology of actin in cells, revealing a functional requirement for the interaction between palladin and actin in vivo

Predictors of outcome in a Spanish cohort of patients with Fabry disease on enzyme replacement therapy

Fabry disease may be treated by enzyme replacement therapy (ERT), but the impact of chronic kidney disease (CKD) on the response to therapy remains unclear. The aim of the present study was to analyse the incidence and predictors of clinical events in patients on ERT. Study design: Multicentre retrospective observational analysis of patients diagnosed and treated with ERT for Fabry disease. The primary outcome was the first renal, neurological or cardiological events or death during a follow-up of 60 months (24-120). Results: In 69 patients (42 males, 27 females, mean age 44.6±13.7 years), at the end of follow-up, eGFR and the left ventricular septum thickness remained stable and the urinary albumin: creatinine ratio tended to decrease, but this decrease only approached significance in patients on agalsidase-beta (242-128mg/g (p=0.05). At the end of follow-up, 21 (30%) patients had suffered an incident clinical event: 6 renal, 2 neurological and 13 cardiological (including 3 deaths). Events were more frequent in patients with baseline eGFR≤60ml/min/1.73m2 (log Rank 12.423, p=0.001), and this remained significant even after excluding incident renal events (log Rank 4.086, p=0.043) and in males and in females. Lower baseline eGFR was associated with a 3- to 7-fold increase the risk of clinical events in different Cox models. Conclusions: GFR at the initiation of ERT is the main predictor of clinical events, both in males and in females, suggesting that start of ERT prior to the development of CKD is associated with better outcomes