1
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Karl K, Del Piccolo N, Light T, Roy T, Dudeja P, Ursachi VC, Fafilek B, Krejci P, Hristova K. Ligand bias underlies differential signaling of multiple FGFs via FGFR1. eLife 2024; 12:RP88144. [PMID: 38568193 PMCID: PMC10990489 DOI: 10.7554/elife.88144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/05/2024] Open
Abstract
The differential signaling of multiple FGF ligands through a single fibroblast growth factor (FGF) receptor (FGFR) plays an important role in embryonic development. Here, we use quantitative biophysical tools to uncover the mechanism behind differences in FGFR1c signaling in response to FGF4, FGF8, and FGF9, a process which is relevant for limb bud outgrowth. We find that FGF8 preferentially induces FRS2 phosphorylation and extracellular matrix loss, while FGF4 and FGF9 preferentially induce FGFR1c phosphorylation and cell growth arrest. Thus, we demonstrate that FGF8 is a biased FGFR1c ligand, as compared to FGF4 and FGF9. Förster resonance energy transfer experiments reveal a correlation between biased signaling and the conformation of the FGFR1c transmembrane domain dimer. Our findings expand the mechanistic understanding of FGF signaling during development and bring the poorly understood concept of receptor tyrosine kinase ligand bias into the spotlight.
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Affiliation(s)
- Kelly Karl
- Department of Materials Science and Engineering, Institute for NanoBioTechnology, and Program in Molecular Biophysics, Johns Hopkins UniversityBaltimoreUnited States
| | - Nuala Del Piccolo
- Department of Materials Science and Engineering, Institute for NanoBioTechnology, and Program in Molecular Biophysics, Johns Hopkins UniversityBaltimoreUnited States
| | - Taylor Light
- Department of Materials Science and Engineering, Institute for NanoBioTechnology, and Program in Molecular Biophysics, Johns Hopkins UniversityBaltimoreUnited States
| | - Tanaya Roy
- Department of Materials Science and Engineering, Institute for NanoBioTechnology, and Program in Molecular Biophysics, Johns Hopkins UniversityBaltimoreUnited States
| | - Pooja Dudeja
- Department of Biology, Faculty of Medicine, Masaryk UniversityBrnoCzech Republic
- Institute of Animal Physiology and Genetics of the CASBrnoCzech Republic
| | - Vlad-Constantin Ursachi
- Department of Biology, Faculty of Medicine, Masaryk UniversityBrnoCzech Republic
- International Clinical Research Center, St. Anne's University HospitalBrnoCzech Republic
| | - Bohumil Fafilek
- Department of Biology, Faculty of Medicine, Masaryk UniversityBrnoCzech Republic
- Institute of Animal Physiology and Genetics of the CASBrnoCzech Republic
- International Clinical Research Center, St. Anne's University HospitalBrnoCzech Republic
| | - Pavel Krejci
- Department of Biology, Faculty of Medicine, Masaryk UniversityBrnoCzech Republic
- Institute of Animal Physiology and Genetics of the CASBrnoCzech Republic
- International Clinical Research Center, St. Anne's University HospitalBrnoCzech Republic
| | - Kalina Hristova
- Department of Materials Science and Engineering, Institute for NanoBioTechnology, and Program in Molecular Biophysics, Johns Hopkins UniversityBaltimoreUnited States
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2
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Girych M, Kulig W, Enkavi G, Vattulainen I. How Neuromembrane Lipids Modulate Membrane Proteins: Insights from G-Protein-Coupled Receptors (GPCRs) and Receptor Tyrosine Kinases (RTKs). Cold Spring Harb Perspect Biol 2023; 15:a041419. [PMID: 37487628 PMCID: PMC10547395 DOI: 10.1101/cshperspect.a041419] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/26/2023]
Abstract
Lipids play a diverse and critical role in cellular processes in all tissues. The unique lipid composition of nerve membranes is particularly interesting because it contains, among other things, polyunsaturated lipids, such as docosahexaenoic acid, which the body only gets through the diet. The crucial role of lipids in neurological processes, especially in receptor-mediated cell signaling, is emphasized by the fact that in many neuropathological diseases there are significant deviations in the lipid composition of nerve membranes compared to healthy individuals. The lipid composition of neuromembranes can significantly affect the function of receptors by regulating the physical properties of the membrane or by affecting specific interactions between receptors and lipids. In addition, it is worth noting that the ligand-binding pocket of many receptors is located inside the cell membrane, due to which lipids can even modulate the binding of ligands to their receptors. These mechanisms highlight the importance of lipids in the regulation of membrane receptor activation and function. In this article, we focus on two major protein families: G-protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs) and discuss how lipids affect their function in neuronal membranes, elucidating the basic mechanisms underlying neuronal function and dysfunction.
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Affiliation(s)
- Mykhailo Girych
- Department of Physics, University of Helsinki, FI-00014 Helsinki, Finland
| | - Waldemar Kulig
- Department of Physics, University of Helsinki, FI-00014 Helsinki, Finland
| | - Giray Enkavi
- Department of Physics, University of Helsinki, FI-00014 Helsinki, Finland
| | - Ilpo Vattulainen
- Department of Physics, University of Helsinki, FI-00014 Helsinki, Finland
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3
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Karl K, Rajagopal S, Hristova K. Quantitative assessment of ligand bias from bias plots: The bias coefficient "kappa". Biochim Biophys Acta Gen Subj 2023; 1867:130428. [PMID: 37488010 PMCID: PMC10528940 DOI: 10.1016/j.bbagen.2023.130428] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2023] [Revised: 06/15/2023] [Accepted: 07/16/2023] [Indexed: 07/26/2023]
Abstract
The current methods for quantifying ligand bias involve the construction of bias plots and the calculations of bias coefficients that can be compared using statistical methods. However, widely used bias coefficients can diverge in their abilities to identify ligand bias and can give false positives. As the empirical bias plots are considered the most reliable tools in bias identification, here we develop an analytical description of bias plot trajectories and introduce a bias coefficient, kappa, which is calculated from these trajectories. The new bias coefficient complements the tool-set in ligand bias identification in cell signaling research.
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Affiliation(s)
- Kelly Karl
- Institute for NanoBioTechnology, Department of Materials Science and Engineering, and Program in Molecular Biophysics, Johns Hopkins University, Baltimore, MD 21218, United States of America
| | - Sudarshan Rajagopal
- Division of Cardiology, Department of Medicine, Duke University School of Medicine, Durham, NC 27710, United States of America
| | - Kalina Hristova
- Institute for NanoBioTechnology, Department of Materials Science and Engineering, and Program in Molecular Biophysics, Johns Hopkins University, Baltimore, MD 21218, United States of America.
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4
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Stoneman MR, Raicu V. Fluorescence-Based Detection of Proteins and Their Interactions in Live Cells. J Phys Chem B 2023. [PMID: 37205844 DOI: 10.1021/acs.jpcb.3c01419] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Recent advances in fluorescence-based microscopy techniques, such as single molecule fluorescence, Förster resonance energy transfer (FRET), fluorescence intensity fluctuations analysis, and super-resolution microscopy have expanded our ability to study proteins in greater detail within their native cellular environment and to investigate the roles that protein interactions play in biological functions, such as inter- and intracellular signaling and cargo transport. In this Perspective, we provide an up-to-date overview of the current state of the art in fluorescence-based detection of proteins and their interactions in living cells with an emphasis on recent developments that have facilitated the characterization of the spatial and temporal organization of proteins into oligomeric complexes in the presence and absence of natural and artificial ligands. Further advancements in this field will only deepen our understanding of the underlying mechanisms of biological processes and help develop new therapeutic targets.
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Affiliation(s)
- Michael R Stoneman
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
| | - Valerică Raicu
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
- Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
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5
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Zapata-Mercado E, Biener G, McKenzie DM, Wimley WC, Pasquale EB, Raicu V, Hristova K. The efficacy of receptor tyrosine kinase EphA2 autophosphorylation increases with EphA2 oligomer size. J Biol Chem 2022; 298:102370. [PMID: 35970390 PMCID: PMC9512837 DOI: 10.1016/j.jbc.2022.102370] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Revised: 08/09/2022] [Accepted: 08/10/2022] [Indexed: 11/30/2022] Open
Abstract
The receptor tyrosine kinase (RTK) EphA2 is expressed in epithelial and endothelial cells and controls the assembly of cell-cell junctions. EphA2 has also been implicated in many diseases, including cancer. Unlike most RTKs, which signal predominantly as dimers, EphA2 readily forms high-order oligomers upon ligand binding. Here, we investigated if a correlation exists between EphA2 signaling properties and the size of the EphA2 oligomers induced by multiple ligands, including the widely used ephrinA1-Fc ligand, the soluble monomeric m-ephrinA1, and novel engineered peptide ligands. We used fluorescence intensity fluctuation (FIF) spectrometry to characterize the EphA2 oligomer populations induced by the different ligands. Interestingly, we found that different monomeric and dimeric ligands induce EphA2 oligomers with widely different size distributions. Our comparison of FIF brightness distribution parameters and EphA2 signaling parameters reveals that the efficacy of EphA2 phosphorylation on tyrosine 588, an autophosphorylation response contributing to EphA2 activation, correlates with EphA2 mean oligomer size. However, we found that other characteristics, such as the efficacy of AKT inhibition and ligand bias coefficients, appear to be independent of EphA2 oligomer size. Taken together, this work highlights the utility of FIF in RTK signaling research and demonstrates a quantitative correlation between the architecture of EphA2 signaling complexes and signaling features.
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Affiliation(s)
- Elmer Zapata-Mercado
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, USA
| | - Gabriel Biener
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin, USA
| | - Daniel M McKenzie
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, USA
| | - William C Wimley
- Tulane University School of Medicine, Department of Biochemistry and Molecular Biology, New Orleans, Louisiana, USA
| | - Elena B Pasquale
- Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, USA.
| | - Valerica Raicu
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin, USA; Department of Biological Sciences, University of Wisconsin, Milwaukee, Wisconsin, USA.
| | - Kalina Hristova
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, USA.
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6
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Killeen TD, Rahman S, Badu DN, Biener G, Stoneman MR, Raicu V. Fluorescence Intensity Fluctuation Analysis of Protein Oligomerization in Cell Membranes. Curr Protoc 2022; 2:e384. [PMID: 35312215 DOI: 10.1002/cpz1.384] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Fluorescence fluctuation spectroscopy (FFS) encompasses a bevy of techniques that involve analyzing fluorescence intensity fluctuations occurring due to fluorescently labeled molecules diffusing in and out of a microscope's focal region. Statistical analysis of these fluctuations may reveal the oligomerization (i.e., association) state of said molecules. We have recently developed a new FFS-based method, termed Two-Dimensional Fluorescence Intensity Fluctuation (2D FIF) spectrometry, which provides quantitative information on the size and stability of protein oligomers as a function of receptor concentration. This article describes protocols for employing FIF spectrometry to quantify the oligomerization of a membrane protein of interest, with specific instructions regarding cell preparation, image acquisition, and analysis of images given in detail. Application of the FIF Spectrometry Suite, a software package designed for applying FIF analysis on fluorescence images, is emphasized in the protocol. Also discussed in detail is the identification, removal, and/or analysis of inhomogeneous regions of the membrane that appear as bright spots. The 2D FIF approach is particularly suited to assess the effects of agonists and antagonists on the oligomeric size of membrane receptors of interest. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Preparation of live cells expressing protein constructs Basic Protocol 2: Image acquisition and noise correction Basic Protocol 3: Drawing and segmenting regions of interest Basic Protocol 4: Calculating the molecular brightness and concentration of individual image segments Basic Protocol 5: Combining data subsets using a manual procedure (Optional) Alternate Protocol 1: Combining data subsets using the advanced FIF spectrometry suite (Optional; alternative to Basic Protocol 5) Basic Protocol 6: Performing meta-analysis of brightness spectrograms Alternate Protocol 2: Performing meta-analysis of brightness spectrograms (alternative to Basic Protocol 6) Basic Protocol 7: Spot extraction and analysis using a manual procedure or by writing a program (Optional) Alternate Protocol 3: Automated spot extraction and analysis (Optional; alternative to Protocol 7) Support Protocol: Monomeric brightness determination.
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Affiliation(s)
- Tom D Killeen
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Sadia Rahman
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Dammar N Badu
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Gabriel Biener
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Michael R Stoneman
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Valerică Raicu
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.,Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
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7
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Adhikari DP, Biener G, Stoneman MR, Badu DN, Paprocki JD, Eis A, Park PSH, Popa I, Raicu V. Comparative photophysical properties of some widely used fluorescent proteins under two-photon excitation conditions. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2021; 262:120133. [PMID: 34243141 DOI: 10.1016/j.saa.2021.120133] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 06/17/2021] [Accepted: 06/28/2021] [Indexed: 06/13/2023]
Abstract
Understanding the photophysical properties of fluorescent proteins (FPs), such as emission and absorption spectra, molecular brightness, photostability, and photo-switching, is critical to the development of criteria for their selection as tags for fluorescent-based biological applications. While two-photon excitation imaging techniques have steadily gained popularity - due to comparatively deeper penetration depth, reduced out-of-focus photobleaching, and wide separation between emission spectra and two-photon excitation spectra -, most studies reporting on the photophysical properties of FPs tend to remain focused on single-photon excitation. Here, we report our investigation of the photophysical properties of several commonly used fluorescent proteins using two-photon microscopy with spectral resolution in both excitation and emission. Our measurements indicate that not only the excitation (and sometimes emission) spectra of FPs may be markedly different between single-photon and two-photon excitation, but also their relative brightness and their photo-stability. A good understanding of the photophysical properties of FPs under two-photon excitation is essential for choosing the right tag(s) for a desired experiment.
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Affiliation(s)
- Dhruba P Adhikari
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Gabriel Biener
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | | | - Dammar N Badu
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Joel D Paprocki
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Annie Eis
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Paul S-H Park
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Ionel Popa
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Valerică Raicu
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA; Department of Biological Sciences, University of Wisconsin-Milwaukee, WI 53211, USA.
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8
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Regulation of the EphA2 receptor intracellular region by phosphomimetic negative charges in the kinase-SAM linker. Nat Commun 2021; 12:7047. [PMID: 34857764 PMCID: PMC8639986 DOI: 10.1038/s41467-021-27343-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Accepted: 11/11/2021] [Indexed: 11/22/2022] Open
Abstract
Eph receptor tyrosine kinases play a key role in cell-cell communication. Lack of structural information on the entire multi-domain intracellular region of any Eph receptor has hindered understanding of their signaling mechanisms. Here, we use integrative structural biology to investigate the structure and dynamics of the EphA2 intracellular region. EphA2 promotes cancer malignancy through a poorly understood non-canonical form of signaling involving serine/threonine phosphorylation of the linker connecting its kinase and SAM domains. We show that accumulation of multiple linker negative charges, mimicking phosphorylation, induces cooperative changes in the EphA2 intracellular region from more closed to more extended conformations and perturbs the EphA2 juxtamembrane segment and kinase domain. In cells, linker negative charges promote EphA2 oligomerization. We also identify multiple kinases catalyzing linker phosphorylation. Our findings suggest multiple effects of linker phosphorylation on EphA2 signaling and imply that coordination of different kinases is necessary to promote EphA2 non-canonical signaling. Eph receptor tyrosine kinases and their ephrin ligands mediate cell-cell communication. Here, the authors assess the structure and dynamics of the EphA2 intracellular region and uncover complex effects of phosphorylation within the linker region between EphA2 kinase and SAM domains.
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9
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Light TP, Brun D, Guardado-Calvo P, Pederzoli R, Haouz A, Neipel F, Rey FA, Hristova K, Backovic M. Human herpesvirus 8 molecular mimicry of ephrin ligands facilitates cell entry and triggers EphA2 signaling. PLoS Biol 2021; 19:e3001392. [PMID: 34499637 PMCID: PMC8454987 DOI: 10.1371/journal.pbio.3001392] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Revised: 09/21/2021] [Accepted: 08/16/2021] [Indexed: 01/19/2023] Open
Abstract
Human herpesvirus 8 (HHV-8) is an oncogenic virus that enters cells by fusion of the viral and endosomal cellular membranes in a process mediated by viral surface glycoproteins. One of the cellular receptors hijacked by HHV-8 to gain access to cells is the EphA2 tyrosine kinase receptor, and the mechanistic basis of EphA2-mediated viral entry remains unclear. Using X-ray structure analysis, targeted mutagenesis, and binding studies, we here show that the HHV-8 envelope glycoprotein complex H and L (gH/gL) binds with subnanomolar affinity to EphA2 via molecular mimicry of the receptor’s cellular ligands, ephrins (Eph family receptor interacting proteins), revealing a pivotal role for the conserved gH residue E52 and the amino-terminal peptide of gL. Using FSI-FRET and cell contraction assays, we further demonstrate that the gH/gL complex also functionally mimics ephrin ligand by inducing EphA2 receptor association via its dimerization interface, thus triggering receptor signaling for cytoskeleton remodeling. These results now provide novel insight into the entry mechanism of HHV-8, opening avenues for the search of therapeutic agents that could interfere with HHV-8–related diseases. Herpesviruses are known to hijack cellular receptors to enter cells, but this study shows that human herpesvirus 8 takes this to another level by using its envelope glycoprotein complex gH/gL to mimic the EphA2 receptor’s natural ligands, ephrins.
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Affiliation(s)
- Taylor P Light
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America.,Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Delphine Brun
- Department of Virology, Structural Virology Unit, Institut Pasteur, Paris, France.,CNRS, UMR 3569, Paris, France
| | - Pablo Guardado-Calvo
- Department of Virology, Structural Virology Unit, Institut Pasteur, Paris, France.,CNRS, UMR 3569, Paris, France
| | - Riccardo Pederzoli
- Department of Virology, Structural Virology Unit, Institut Pasteur, Paris, France.,CNRS, UMR 3569, Paris, France
| | - Ahmed Haouz
- CNRS, UMR 3569, Paris, France.,Crystallography Platform C2RT, Institut Pasteur, Paris, France
| | - Frank Neipel
- Crystallography Platform C2RT, Institut Pasteur, Paris, France
| | - Félix A Rey
- Department of Virology, Structural Virology Unit, Institut Pasteur, Paris, France.,CNRS, UMR 3569, Paris, France
| | - Kalina Hristova
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America.,Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Marija Backovic
- Department of Virology, Structural Virology Unit, Institut Pasteur, Paris, France.,CNRS, UMR 3569, Paris, France
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10
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Light TP, Gomez-Soler M, Wang Z, Karl K, Zapata-Mercado E, Gehring MP, Lechtenberg BC, Pogorelov TV, Hristova K, Pasquale EB. A cancer mutation promotes EphA4 oligomerization and signaling by altering the conformation of the SAM domain. J Biol Chem 2021; 297:100876. [PMID: 34139238 PMCID: PMC8260879 DOI: 10.1016/j.jbc.2021.100876] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2021] [Revised: 05/20/2021] [Accepted: 06/13/2021] [Indexed: 12/24/2022] Open
Abstract
The Eph receptor tyrosine kinases and their ephrin ligands regulate many physiological and pathological processes. EphA4 plays important roles in nervous system development and adult homeostasis, while aberrant EphA4 signaling has been implicated in neurodegeneration. EphA4 may also affect cancer malignancy, but the regulation and effects of EphA4 signaling in cancer are poorly understood. A correlation between decreased patient survival and high EphA4 mRNA expression in melanoma tumors that also highly express ephrinA ligands suggests that enhanced EphA4 signaling may contribute to melanoma progression. A search for EphA4 gain-of-function mutations in melanoma uncovered a mutation of the highly conserved leucine 920 in the EphA4 sterile alpha motif (SAM) domain. We found that mutation of L920 to phenylalanine (L920F) potentiates EphA4 autophosphorylation and signaling, making it the first documented EphA4 cancer mutation that increases kinase activity. Quantitative Föster resonance energy transfer and fluorescence intensity fluctuation (FIF) analyses revealed that the L920F mutation induces a switch in EphA4 oligomer size, from a dimer to a trimer. We propose this switch in oligomer size as a novel mechanism underlying EphA4-linked tumorigenesis. Molecular dynamics simulations suggest that the L920F mutation alters EphA4 SAM domain conformation, leading to the formation of EphA4 trimers that assemble through two aberrant SAM domain interfaces. Accordingly, EphA4 wild-type and the L920F mutant are affected differently by the SAM domain and are differentially regulated by ephrin ligand stimulation. The increased EphA4 activation induced by the L920F mutation, through the novel mechanism we uncovered, supports a functional role for EphA4 in promoting pathogenesis.
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Affiliation(s)
- Taylor P Light
- Department of Materials Science and Engineering, Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland, USA
| | - Maricel Gomez-Soler
- Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, USA
| | - Zichen Wang
- Department of Chemistry, Center for Biophysics and Quantitative Biology, Beckman Institute for Advanced Science and Technology, and National Center for Supercomputing Applications, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Kelly Karl
- Program in Molecular Biophysics, Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland, USA
| | - Elmer Zapata-Mercado
- Program in Molecular Biophysics, Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland, USA
| | - Marina P Gehring
- Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, USA
| | - Bernhard C Lechtenberg
- Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, USA
| | - Taras V Pogorelov
- Department of Chemistry, Center for Biophysics and Quantitative Biology, Beckman Institute for Advanced Science and Technology, and National Center for Supercomputing Applications, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Kalina Hristova
- Department of Materials Science and Engineering, Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland, USA; Program in Molecular Biophysics, Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland, USA.
| | - Elena B Pasquale
- Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, USA.
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11
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Biener G, Stoneman MR, Raicu V. Fluorescence intensity fluctuation analysis of receptor oligomerization in membrane domains. Biophys J 2021; 120:3028-3039. [PMID: 34214533 DOI: 10.1016/j.bpj.2021.06.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 06/02/2021] [Accepted: 06/11/2021] [Indexed: 11/26/2022] Open
Abstract
Fluorescence micrographs of the plasma membrane of cells expressing fluorescently labeled G protein-coupled receptors (GPCRs) often exhibit small clusters of pixels (or puncta) with intensities that are higher than those of the surrounding pixels. Although studies of GPCR interactions in uniform membrane areas abound, understanding the details of the GPCR interactions within such puncta as well as the nature of the membrane formations underlying the puncta is hampered by the lack of adequate experimental techniques. Here, we introduce an enhancement of a recently developed method termed fluorescence intensity fluctuation spectrometry, which permits analysis of protein-protein interactions within the puncta in live cell membranes. We applied the novel fluorescence intensity fluctuation data analysis protocol to previously published data from cells expressing human secretin receptors and determined that the oligomer size increases with receptor concentration and duration of treatment with cognate ligand, not only within uniform regions of the membrane (in agreement with previous publications) but also within the puncta. In addition, we found that the number density and fractional area of the puncta increased after treatment with ligand. This method could be applied for probing the evolution in the time of the chain of events that begins with ligand binding and continues with coated pits formation and receptor internalization for other GPCRs and, indeed, other membrane receptors in living cells.
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Affiliation(s)
- Gabriel Biener
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Michael R Stoneman
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Valerică Raicu
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.
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12
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P120 catenin potentiates constitutive E-cadherin dimerization at the plasma membrane and regulates trans binding. Curr Biol 2021; 31:3017-3027.e7. [PMID: 34019823 DOI: 10.1016/j.cub.2021.04.061] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Revised: 11/09/2020] [Accepted: 04/26/2021] [Indexed: 11/23/2022]
Abstract
Cadherins are essential adhesion proteins that regulate tissue cohesion and paracellular permeability by assembling dense adhesion plaques at cell-to-cell contacts. Adherens junctions are central to a wide range of tissue functions; identifying protein interactions that potentiate their assembly and regulation has been the focus of research for over 2 decades. Here, we present evidence for a new, unexpected mechanism of cadherin oligomerization on cells. Fully quantified spectral imaging fluorescence resonance energy transfer (FSI-FRET) and fluorescence intensity fluctuation (FIF) measurements directly demonstrate that E-cadherin forms constitutive lateral (cis) dimers at the plasma membrane. Results further show that binding of the cytosolic protein p120ctn binding to the intracellular region is required for constitutive E-cadherin dimerization. This finding differs from a model that attributes lateral (cis) cadherin oligomerization solely to extracellular domain interactions. The present, novel findings are further supported by studies of E-cadherin mutants that uncouple p120ctn binding or with cells in which p120ctn was knocked out using CRISPR-Cas9. Quantitative affinity measurements further demonstrate that uncoupling p120ctn binding reduces the cadherin trans binding affinity and cell adhesion. These findings transform the current model of cadherin assembly at cell surfaces and identify the core building blocks of cadherin-mediated intercellular adhesions. They also identify a new role for p120ctn and reconcile findings that implicate both the extracellular and intracellular cadherin domains in cadherin clustering and intercellular cohesion.
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13
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Interactions between Ligand-Bound EGFR and VEGFR2. J Mol Biol 2021; 433:167006. [PMID: 33891904 DOI: 10.1016/j.jmb.2021.167006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 03/25/2021] [Accepted: 04/15/2021] [Indexed: 11/21/2022]
Abstract
In this work, we put forward the provocative hypothesis that the active, ligand-bound RTK dimers from unrelated subfamilies can associate into heterooligomers with novel signaling properties. This hypothesis is based on a quantitative FRET study that monitors the interactions between EGFR and VEGFR2 in the plasma membrane of live cells in the absence of ligand, in the presence of either EGF or VEGF, and in the presence of both ligands. We show that direct interactions occur between EGFR and VEGFR2 in the absence of ligand and in the presence of the two cognate ligands. However, there are not significant heterointeractions between EGFR and VEGFR2 when only one of the ligands is present. Since RTK dimers and RTK oligomers are believed to signal differently, this finding suggests a novel mechanism for signal diversification.
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