RESUMEN
Epstein-Barr virus (EBV) is an important cause of human lymphomas, including Burkitt lymphoma (BL). EBV+ BLs are driven by Myc translocation and have stringent forms of viral latency that do not express either of the two major EBV oncoproteins, EBNA2 (which mimics Notch signaling) and LMP1 (which activates NF-κB signaling). Suppression of Myc-induced apoptosis, often through mutation of the TP53 (p53) gene or inhibition of pro-apoptotic BCL2L11 (BIM) gene expression, is required for development of Myc-driven BLs. EBV+ BLs contain fewer cellular mutations in apoptotic pathways compared to EBV-negative BLs, suggesting that latent EBV infection inhibits Myc-induced apoptosis. Here we use an EBNA2-deleted EBV virus (ΔEBNA2 EBV) to create the first in vivo model for EBV+ BL-like lymphomas derived from primary human B cells. We show that cord blood B cells infected with both ΔEBNA2 EBV and a Myc-expressing vector proliferate indefinitely on a CD40L/IL21 expressing feeder layer in vitro and cause rapid onset EBV+ BL-like tumors in NSG mice. These LMP1/EBNA2-negative Myc-driven lymphomas have wild type p53 and very low BIM, and express numerous germinal center B cell proteins (including TCF3, BACH2, Myb, CD10, CCDN3, and GCSAM) in the absence of BCL6 expression. Myc-induced activation of Myb mediates expression of many of these BL-associated proteins. We demonstrate that Myc blocks LMP1 expression both by inhibiting expression of cellular factors (STAT3 and Src) that activate LMP1 transcription and by increasing expression of proteins (DNMT3B and UHRF1) known to enhance DNA methylation of the LMP1 promoters in human BLs. These results show that latent EBV infection collaborates with Myc over-expression to induce BL-like human B-cell lymphomas in mice. As NF-κB signaling retards the growth of EBV-negative BLs, Myc-mediated repression of LMP1 may be essential for latent EBV infection and Myc translocation to collaboratively induce human BLs.
Asunto(s)
Linfocitos B , Linfoma de Burkitt , Infecciones por Virus de Epstein-Barr , Herpesvirus Humano 4 , Proteínas Proto-Oncogénicas c-myc , Latencia del Virus , Animales , Linfoma de Burkitt/virología , Linfoma de Burkitt/metabolismo , Linfoma de Burkitt/patología , Linfoma de Burkitt/genética , Humanos , Ratones , Infecciones por Virus de Epstein-Barr/virología , Infecciones por Virus de Epstein-Barr/metabolismo , Infecciones por Virus de Epstein-Barr/complicaciones , Infecciones por Virus de Epstein-Barr/genética , Herpesvirus Humano 4/genética , Proteínas Proto-Oncogénicas c-myc/metabolismo , Proteínas Proto-Oncogénicas c-myc/genética , Linfocitos B/virología , Linfocitos B/metabolismo , Antígenos Nucleares del Virus de Epstein-Barr/metabolismo , Antígenos Nucleares del Virus de Epstein-Barr/genética , Apoptosis , Proteínas Virales/metabolismo , Proteínas Virales/genéticaRESUMEN
Latent Epstein-Barr virus (EBV) infection promotes undifferentiated nasopharyngeal carcinomas (NPCs) in humans, but the mechanism(s) for this effect has been difficult to study because EBV cannot transform normal epithelial cells in vitro and the EBV genome is often lost when NPC cells are grown in culture. Here we show that the latent EBV protein, LMP1 (Latent membrane protein 1), induces cellular proliferation and inhibits spontaneous differentiation of telomerase-immortalized normal oral keratinocytes (NOKs) in growth factor-deficient conditions by increasing the activity of the Hippo pathway effectors, YAP (Yes-associated protein) and TAZ (Transcriptional coactivator with PDZ-binding motif). We demonstrate that LMP1 enhances YAP and TAZ activity in NOKs both by decreasing Hippo pathway-mediated serine phosphorylation of YAP and TAZ and increasing Src kinase-mediated Y357 phosphorylation of YAP. Furthermore, knockdown of YAP and TAZ is sufficient to reduce proliferation and promote differentiation in EBV-infected NOKs. We find that YAP and TAZ are also required for LMP1-induced epithelial-to-mesenchymal transition. Importantly, we demonstrate that ibrutinib (an FDA-approved BTK inhibitor that blocks YAP and TAZ activity through an off-target effect) restores spontaneous differentiation and inhibits proliferation of EBV-infected NOKs at clinically relevant doses. These results suggest that LMP1-induced YAP and TAZ activity contributes to the development of NPC.
Asunto(s)
Infecciones por Virus de Epstein-Barr , Neoplasias Nasofaríngeas , Humanos , Diferenciación Celular , Proliferación Celular , Células Epiteliales/metabolismo , Herpesvirus Humano 4/genética , Neoplasias Nasofaríngeas/genética , Proteínas de la Matriz Viral/genética , Proteínas de la Matriz Viral/metabolismo , Proteínas Señalizadoras YAPRESUMEN
Differentiated epithelial cells are an important source of infectious EBV virions in human saliva, and latent Epstein-Barr virus (EBV) infection is strongly associated with the epithelial cell tumor, nasopharyngeal carcinoma (NPC). However, it has been difficult to model how EBV contributes to NPC, since EBV has not been shown to enhance proliferation of epithelial cells in monolayer culture in vitro and is not stably maintained in epithelial cells without antibiotic selection. In addition, although there are two major types of EBV (type 1 (T1) and type 2 (T2)), it is currently unknown whether T1 and T2 EBV behave differently in epithelial cells. Here we inserted a G418 resistance gene into the T2 EBV strain, AG876, allowing us to compare the phenotypes of T1 Akata virus versus T2 AG876 virus in a telomerase-immortalized normal oral keratinocyte cell line (NOKs) using a variety of different methods, including RNA-seq analysis, proliferation assays, immunoblot analyses, and air-liquid interface culture. We show that both T1 Akata virus infection and T2 AG876 virus infection of NOKs induce cellular proliferation, and inhibit spontaneous differentiation, in comparison to the uninfected cells when cells are grown without supplemental growth factors in monolayer culture. T1 EBV and T2 EBV also have a similar ability to induce epithelial-to-mesenchymal (EMT) transition and activate canonical and non-canonical NF-κB signaling in infected NOKs. In contrast to our recent results in EBV-infected lymphoblastoid cells (in which T2 EBV infection is much more lytic than T1 EBV infection), we find that NOKs infected with T1 and T2 EBV respond similarly to lytic inducing agents such as TPA treatment or differentiation. These results suggest that T1 and T2 EBV have similar phenotypes in infected epithelial cells, with both EBV types enhancing cellular proliferation and inhibiting differentiation when growth factors are limiting.
Asunto(s)
Infecciones por Virus de Epstein-Barr , Neoplasias Nasofaríngeas , Telomerasa , Antibacterianos/metabolismo , Proliferación Celular , Herpesvirus Humano 4/metabolismo , Humanos , Queratinocitos , FN-kappa B/metabolismo , Carcinoma Nasofaríngeo/metabolismo , Telomerasa/genética , Activación ViralRESUMEN
The Metabotropic glutamate receptor 2 (mGluR2) is involved in several neurological and psychiatric disorders and is an attractive drug target. It is believed to form a strict dimer and the dimeric assembly is necessary for glutamate induced activation. Although many studies have focused on glutamate induced conformational changes, the dimerization propensity of mGluR2 with and without glutamate has never been investigated. Also, the role of the unstructured loop in dimerization of mGluR2 is not clear. Here, using Forster Resonance Energy Transfer (FRET) based assay in live cells we show that mGluR2 does not form a "strict dimer" rather it exists in a dynamic monomer-dimer equilibrium. The unstructured loop moderately destabilizes the dimers. Furthermore, binding of glutamate to mGluR2 induces conformational change that promotes monomerization of mGluR2. In the absence of an unstructured loop, mGluR2 neither undergoes conformational change nor monomerizes upon binding to glutamate.
Asunto(s)
Ácido Glutámico/metabolismo , Ácido Glutámico/farmacología , Multimerización de Proteína/efectos de los fármacos , Receptores de Glutamato Metabotrópico/química , Receptores de Glutamato Metabotrópico/metabolismo , Células HEK293 , Humanos , Ligandos , Unión Proteica , Estructura Cuaternaria de ProteínaRESUMEN
Metabotropic Glutamate Receptors (mGluRs) are Class C G-protein coupled receptors (GPCRs) that are expressed throughout the central nervous system and are involved in several neurological and psychiatric disorders. Although, many studies focused on Glutamate induced activation of mGluR2, however, the role of unstructured loop (or "BC loop") in activation of metabotropic Glutamate receptors is currently unknown. Here, using Förster Resonance Energy Transfer (FRET) based assay in live cells we show that unstructured loop is required for Glutamate induced conformation and hence the activation of the receptor.
Asunto(s)
Ácido Glutámico/metabolismo , Receptores de Glutamato Metabotrópico/metabolismo , Línea Celular , Transferencia Resonante de Energía de Fluorescencia , Humanos , Modelos Moleculares , Conformación Proteica , Receptores de Glutamato Metabotrópico/químicaRESUMEN
All members of the Eph receptor family of tyrosine kinases contain a SAM domain near the C terminus, which has been proposed to play a role in receptor homotypic interactions and/or interactions with binding partners. The SAM domain of EphA2 is known to be important for receptor function, but its contribution to EphA2 lateral interactions in the plasma membrane has not been determined. Here we use a FRET-based approach to directly measure the effect of the SAM domain on the stability of EphA2 dimers on the cell surface in the absence of ligand binding. We also investigate the functional consequences of EphA2 SAM domain deletion. Surprisingly, we find that the EphA2 SAM domain inhibits receptor dimerization and decreases EphA2 tyrosine phosphorylation. This role is dramatically different from the role of the SAM domain of the related EphA3 receptor, which we previously found to stabilize EphA3 dimers and increase EphA3 tyrosine phosphorylation in cells in the absence of ligand. Thus, the EphA2 SAM domain likely contributes to a unique mode of EphA2 interaction that leads to distinct signaling outputs.
Asunto(s)
Secuencia de Aminoácidos , Membrana Celular/metabolismo , Efrina-A1/metabolismo , Receptor EphA2/metabolismo , Eliminación de Secuencia , Motivo alfa Estéril , Membrana Celular/química , Movimiento Celular , Efrina-A1/genética , Transferencia Resonante de Energía de Fluorescencia , Expresión Génica , Células HEK293 , Humanos , Cinética , Fosforilación , Unión Proteica , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Multimerización de Proteína , Receptor EphA2/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Tirosina/metabolismoRESUMEN
BACKGROUND: The EphA2 receptor tyrosine kinase is known to promote cancer cell malignancy in the absence of activation by ephrin ligands. This behavior depends on high EphA2 phosphorylation on Ser897 and low tyrosine phosphorylation, resulting in increased cell migration and invasiveness. We have previously shown that EphA2 forms dimers in the absence of ephrin ligand binding, and that dimerization of unliganded EphA2 can decrease EphA2 Ser897 phosphorylation. We have also identified a small peptide called YSA, which binds EphA2 and competes with the naturally occurring ephrin ligands. METHODS: Here, we investigate the effect of YSA on EphA2 dimer stability and EphA2 function using quantitative FRET techniques, Western blotting, and cell motility assays. RESULTS: We find that the YSA peptide stabilizes the EphA2 dimer, increases EphA2 Tyr phosphorylation, and decreases both Ser897 phosphorylation and cell migration. CONCLUSIONS: The experiments demonstrate that the small peptide ligand YSA reduces EphA2 Ser897 pro-tumorigenic signaling by stabilizing the EphA2 dimer. GENERAL SIGNIFICANCE: This work is a proof-of-principle demonstration that EphA2 homointeractions in the plasma membrane can be pharmacologically modulated to decrease the pro-tumorigenic signaling of the receptor.
Asunto(s)
Efrina-A2/metabolismo , Péptidos/metabolismo , Multimerización de Proteína/fisiología , Transducción de Señal/fisiología , Línea Celular , Movimiento Celular/fisiología , Efrinas/metabolismo , Células HEK293 , Humanos , Ligandos , Fosforilación/fisiología , Unión Proteica/fisiología , Receptor EphA2/metabolismoRESUMEN
The EphA2 receptor tyrosine kinase promotes cell migration and cancer malignancy through a ligand- and kinase-independent distinctive mechanism that has been linked to high Ser-897 phosphorylation and low tyrosine phosphorylation. Here, we demonstrate that EphA2 forms dimers in the plasma membrane of HEK293T cells in the absence of ephrin ligand binding, suggesting that the current seeding mechanism model of EphA2 activation is incomplete. We also characterize a dimerization-deficient EphA2 mutant that shows enhanced ability to promote cell migration, concomitant with increased Ser-897 phosphorylation and decreased tyrosine phosphorylation compared with EphA2 wild type. Our data reveal a correlation between unliganded dimerization and tumorigenic signaling and suggest that EphA2 pro-tumorigenic activity is mediated by the EphA2 monomer. Thus, a therapeutic strategy that aims at the stabilization of EphA2 dimers may be beneficial for the treatment of cancers linked to EphA2 overexpression.
Asunto(s)
Receptor EphA2/química , Receptor EphA2/metabolismo , Sustitución de Aminoácidos , Movimiento Celular , Células HEK293 , Humanos , Ligandos , Mutagénesis Sitio-Dirigida , Proteínas Oncogénicas/química , Proteínas Oncogénicas/genética , Proteínas Oncogénicas/metabolismo , Presión Osmótica , Fosforilación , Dominios y Motivos de Interacción de Proteínas , Multimerización de Proteína , Estabilidad Proteica , Estructura Cuaternaria de Proteína , Receptor EphA2/genética , Transducción de SeñalRESUMEN
The erythropoietin-producing hepatocellular carcinoma A3 (EphA3) receptor tyrosine kinase (RTK) regulates morphogenesis during development and is overexpressed and mutated in a variety of cancers. EphA3 activation is believed to follow a 'seeding mechanism' model, in which ligand binding to the monomeric receptor acts as a trigger for signal-productive receptor clustering. We study EphA3 lateral interactions on the surface of live cells and we demonstrate that EphA3 forms dimers in the absence of ligand binding. We further show that these dimers are stabilized by interactions involving the EphA3 sterile α-motif (SAM) domain. The discovery of unliganded EphA3 dimers challenges the current understanding of the chain of EphA3 activation events and suggests that EphA3 may follow the 'pre-formed dimer' model of activation known to be relevant for other receptor tyrosine kinases. The present work also establishes a new role for the SAM domain in promoting Eph receptor lateral interactions and signalling on the cell surface.
Asunto(s)
Multimerización de Proteína/fisiología , Proteínas Tirosina Quinasas Receptoras/metabolismo , Transducción de Señal/fisiología , Secuencias de Aminoácidos , Células HEK293 , Humanos , Estructura Terciaria de Proteína , Proteínas Tirosina Quinasas Receptoras/genética , Receptor EphA3RESUMEN
The sigma-1 receptor (S1R) is a 223-amino-acid membrane protein that resides in the endoplasmic reticulum and the plasma membrane of some mammalian cells. The S1R is regulated by various synthetic molecules including (+)-pentazocine, cocaine and haloperidol and endogenous molecules such as sphingosine, dimethyltryptamine and dehydroepiandrosterone. Ligand-regulated protein chaperone functions linked to oxidative stress and neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS) and neuropathic pain have been attributed to the S1R. Several client proteins that interact with S1R have been identified including various types of ion channels and G-protein coupled receptors (GPCRs). When S1R constructs containing C-terminal monomeric GFP2 and YFP fusions were co-expressed in COS-7 cells and subjected to FRET spectrometry analysis, monomers, dimers and higher oligomeric forms of S1R were identified under non-liganded conditions. In the presence of the prototypic S1R agonist, (+)-pentazocine, however, monomers and dimers were the prevailing forms of S1R. The prototypic antagonist, haloperidol, on the other hand, favoured higher order S1R oligomers. These data, in sum, indicate that heterologously expressed S1Rs occur in vivo in COS-7 cells in multiple oligomeric forms and that S1R ligands alter these oligomeric structures. We suggest that the S1R oligomerization states may regulate its function(s).
Asunto(s)
Membrana Celular/metabolismo , Retículo Endoplásmico/metabolismo , Modelos Moleculares , Receptores sigma/química , Sustitución de Aminoácidos , Analgésicos Opioides/química , Analgésicos Opioides/farmacología , Animales , Células COS , Membrana Celular/efectos de los fármacos , Chlorocebus aethiops , Dimerización , Retículo Endoplásmico/efectos de los fármacos , Haloperidol/química , Haloperidol/farmacología , Humanos , Ligandos , Proteínas Luminiscentes/química , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Antagonistas de Narcóticos/química , Antagonistas de Narcóticos/farmacología , Pentazocina/química , Pentazocina/farmacología , Mutación Puntual , Agregado de Proteínas/efectos de los fármacos , Estabilidad Proteica/efectos de los fármacos , Receptores sigma/agonistas , Receptores sigma/genética , Receptores sigma/metabolismo , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/metabolismo , Receptor Sigma-1RESUMEN
Förster resonance energy transfer (FRET) is an exquisitely sensitive method for detection of molecular interactions and conformational changes in living cells. The recent advent of fluorescence imaging technology with single-molecule (or molecular-complex) sensitivity, together with refinements in the kinetic theory of FRET, provide the necessary tool kits for determining the stoichiometry and relative disposition of the protomers within protein complexes (i.e., quaternary structure) of membrane receptors and transporters in living cells. In contrast to standard average-based methods, this method relies on the analysis of distributions of apparent FRET efficiencies, E(app), across the image pixels of individual cells expressing proteins of interest. The most probable quaternary structure of the complex is identified from the number of peaks in the E(app) distribution and their dependence on a single parameter, termed pairwise FRET efficiency. Such peaks collectively create a unique FRET spectrum corresponding to each oligomeric configuration of the protein. Therefore, FRET could quite literally become a spectrometric method--akin to that of mass spectrometry--for sorting protein complexes according to their size and shape.
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Transferencia Resonante de Energía de Fluorescencia , Estructura Cuaternaria de Proteína , Proteínas/química , Supervivencia Celular , Saccharomyces cerevisiae/citologíaRESUMEN
Current methods for analysis of data from studies of protein-protein interactions using fluorescence resonance energy transfer (FRET) emerged from several decades of research using wide-field microscopes and spectrofluorometers to measure fluorescence from individual cells or cell populations. Inherent to most measurements is an averaging of the distributions of FRET efficiencies over large populations of protein complexes, which washes out information regarding the stoichiometry and structure of protein complexes. Although the introduction of laser-scanning microscopes in principle could facilitate quantification of the distributions of FRET efficiencies in live cells, only comparatively recently did this potential fully materialize, through development of spectral- or lifetime-based approaches. To exploit this new opportunity in molecular imaging, it is necessary to further develop theoretical models and methods of data analysis. Using Monte Carlo simulations, we investigated FRET in homogenous and inhomogeneous spatial distributions of molecules. Our results indicate that an analysis based on distributions of FRET efficiencies presents significant advantages over the average-based approach, which include allowing for proper identification of biologically relevant FRET. This study provides insights into the effect of molecular crowding on FRET, and it offers a basis for information extraction from distributions of FRET efficiencies using simulations-based data fitting.
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Proteínas Bacterianas/metabolismo , Células/metabolismo , Transferencia Resonante de Energía de Fluorescencia/métodos , Proteínas/metabolismo , Espectrometría de Fluorescencia/métodos , Fluorescencia , Colorantes Fluorescentes , Microscopía Confocal , Microscopía Fluorescente/métodos , Imagen MolecularRESUMEN
EGFR is a receptor tyrosine kinase that plays a critical role in cell proliferation, differentiation, survival and migration. Its activating ligand, EGF, has long been believed to stabilize the EGFR dimer. Two research studies aimed at quantitative measurements of EGFR dimerization, however, have led to contradicting conclusions and have questioned this view. Given the controversy, here we sought to measure the dimerization of EGFR in the absence and in the presence of saturating EGF concentrations, and to tease out the effect of ligand on dimer stability, using a FRET-based quantitative method. Our measurements show that the dissociation constant is decreased ~150 times due to ligand binding, indicative of significant dimer stabilization. In addition, our measurements demonstrate that EGF binding induces a conformational change in the EGFR dimer.
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Factor de Crecimiento Epidérmico/farmacología , Receptores ErbB/química , Receptores ErbB/efectos de los fármacos , Transferencia Resonante de Energía de Fluorescencia , Humanos , Conformación Proteica/efectos de los fármacos , Multimerización de Proteína/efectos de los fármacos , Estabilidad Proteica/efectos de los fármacosRESUMEN
The eight metabotropic glutamate receptors (mGluRs) serve critical modulatory roles throughout the nervous system. The molecular diversity of mGluRs is thought to be further expanded by the formation of heterodimers, but the co-expression of mGluR subtypes at the cellular level and the relative propensities of heterodimer formation are not well known. Here, we analyze single-cell RNA sequencing data and find that cortical pyramidal cells express multiple mGluR subtypes with distinct profiles for different receptor combinations. We then develop quantitative, fluorescence-based assays to define the relative homo- and heterodimer propensities across group-I, -II, and -III mGluRs. We find a strong preference for heterodimerization in a number of cases, including mGluR2 with mGluR3, which we confirm in frontal cortex using in situ RNA hybridization and co-immunoprecipitation. Together, our findings support the biological relevance of mGluR heterodimerization and highlight the complex landscape of mGluR populations in the brain.
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Encéfalo/metabolismo , Células Piramidales/metabolismo , Receptores de Glutamato Metabotrópico/metabolismo , Animales , Corteza Cerebral/metabolismo , HumanosRESUMEN
The recently-discovered single-span transmembrane proteins endoregulin (ELN), dwarf open reading frame (DWORF), myoregulin (MLN), and another-regulin (ALN) are reported to bind to the SERCA calcium pump in a manner similar to that of known regulators of SERCA activity, phospholamban (PLB) and sarcolipin (SLN). To determine how micropeptide assembly into oligomers affects the availability of the micropeptide to bind to SERCA in a regulatory complex, we used co-immunoprecipitation and fluorescence resonance energy transfer (FRET) to quantify micropeptide oligomerization and SERCA-binding. Micropeptides formed avid homo-oligomers with high-order stoichiometry (nâ¯>â¯2 protomers per homo-oligomer), but it was the monomeric form of all micropeptides that interacted with SERCA. In view of these two alternative binding interactions, we evaluated the possibility that oligomerization occurs at the expense of SERCA-binding. However, even the most avidly oligomeric micropeptide species still showed robust FRET with SERCA, and there was a surprising positive correlation between oligomerization affinity and SERCA-binding. This comparison of micropeptide family members suggests that the same structural determinants that support oligomerization are also important for binding to SERCA. Moreover, the unique oligomerization/SERCA-binding profile of DWORF is in harmony with its distinct role as a PLB-competing SERCA activator, in contrast to the inhibitory function of the other SERCA-binding micropeptides.
Asunto(s)
Péptidos/química , Péptidos/metabolismo , ATPasas Transportadoras de Calcio del Retículo Sarcoplásmico/química , ATPasas Transportadoras de Calcio del Retículo Sarcoplásmico/metabolismo , Señalización del Calcio/genética , Señalización del Calcio/fisiología , Proteínas de Unión al Calcio/metabolismo , Línea Celular , Transferencia Resonante de Energía de Fluorescencia , Humanos , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Sistemas de Lectura Abierta/genética , Unión Proteica , Multimerización de Proteína/genética , Multimerización de Proteína/fisiología , Proteolípidos/metabolismo , ATPasas Transportadoras de Calcio del Retículo Sarcoplásmico/genéticaRESUMEN
The EphA2 receptor tyrosine kinase is capable of activating multiple diverse signaling pathways with roles in processes such as tissue homeostasis and cancer. EphA2 is known to form activated oligomers in the presence of ephrin-A ligands. Here, we characterize the lateral interactions between full-length EphA2 molecules in the plasma membrane in the presence of three types of ligands (dimeric ephrinA1-Fc, monomeric ephrinA1, and an engineered peptide ligand) as well as in the absence of ligand, using a quantitative FRET technique. The data show that EphA2 forms higher-order oligomers and two different types of dimers that all lead to increased EphA2 tyrosine phosphorylation, which is indicative of increased kinase-dependent signaling. We find that different ligands stabilize conformationally distinct oligomers that are assembled through two different interfaces. Our results suggest that these different oligomeric assemblies could have distinct signaling properties, contributing to the diverse activities of the EphA2 receptor.
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[This corrects the article DOI: 10.1038/s42003-018-0017-7.].
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Epithelial cadherin (Ecadherin) is responsible for the intercellular cohesion of epithelial tissues. It forms lateral clusters within adherens cell-cell junctions, but its association state outside these clusters is unknown. Here, we use a quantitative Forster resonance energy transfer (FRET) approach to show that Ecadherin forms constitutive dimers and that these dimers exist independently of the actin cytoskeleton or cytoplasmic proteins. The dimers are stabilized by intermolecular contacts that occur along the entire length of Ecadherin, with the intracellular domains having a surprisingly strong favorable contribution. We further show that Ecadherin mutations and calcium depletion induce structural alterations that propagate from the N terminus all the way to the C terminus, without destabilizing the dimeric state. These findings provide context for the interpretation of Ecadherin adhesion experiments. They also suggest that early events of adherens junction assembly involve interactions between from preformed Ecadherin dimers.
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Cadherinas/análisis , Membrana Celular/química , Multimerización de Proteína , Cadherinas/genética , Calcio/metabolismo , Línea Celular , Análisis Mutacional de ADN , Transferencia Resonante de Energía de Fluorescencia , HumanosRESUMEN
Pseudomonas aeruginosa is a pathogenic Gram-negative bacterium that affects patients with cystic fibrosis and immunocompromised individuals. This bacterium coexpresses two unique forms of lipopolysaccharides (LPSs) on its surface, the A- and B-band LPS, which are among the main virulence factors that contribute to its pathogenicity. The polysaccharides in A-band LPSs are synthesized in the cytoplasm and translocated into the periplasm via an ATP-binding cassette (ABC) transporter consisting of a transmembrane protein, Wzm, and a cytoplasmic nucleotide-binding protein, Wzt. Most of the biochemical studies of A-band PSs in Pseudomonas aeruginosa are focused on the stages of the synthesis and ligation of PS, leaving the export stage involving the ABC transporter mostly unexplored. This difficulty is compounded by the fact that the subunit composition and structure of this bi-component ABC transporter are still unknown. Here we propose a simple but powerful method, based on Förster Resonance Energy Transfer (FRET) and optical micro-spectroscopy technology, to probe the structure of dynamic (as opposed to static) protein complexes in living cells. We use this method to determine the association stoichiometry and quaternary structure of the Wzm-Wzt complex in living cells. It is found that Wzt forms a rhombus-shaped homo-tetramer which becomes a square upon co-expression with Wzm, and that Wzm forms a square-shaped homo-tetramer both in the presence and absence of Wzt. Based on these results, we propose a structural model for the double-tetramer complex formed by the bi-component ABC transporter in living cells. An understanding of the structure and behavior of this ABC transporter will help develop antibiotics targeting the biosynthesis of the A-band LPS endotoxin.