Lymphocyte activation; Signal transduction; Membrane-cytoskeletal dynamics; Lymphoma/Leukemia; Autoimmunity.
Antigen receptor signaling at the membrane-cytoskeletal interface in B cells.
OVERVIEW OF RESEARCH
The B cell antigen receptor (BCR) serves key roles in directing the activation of B cells that make antibodies reactive to foreign agents such as pathogens, tumors and transplants, and also in preventing B cells from making antibodies reactive to its own self. Underactive or overactive B cells are often associated with immunodeficiency, cancer and autoimmune disorders. B cell immune response involves communication of signals from the cell’s surface to its core, the nucleus, where gene expression occurs. Simultaneous rearrangement of the B cell membrane and the underlying actin cytoskeleton facilitates dynamic recruitment of key signaling components into signalosomes at the cell surface. An understanding of the molecular mechanisms of antigen receptor signaling are critical for design of better vaccines against infectious agents as well as identification of therapeutic targets in autoimmunity and cancer. In order to probe the molecular mechanisms of B cell activation, we employ a mixture of cutting edge technologies including high definition live cell imaging, intravital in situ imaging, quantitative proteomics, transgenic/knockout mice, as well as standard biochemistry and molecular biology methods.
We have demonstrated that BCR cross-linking induces fusion of nanoscale membrane raft units to generate patches that ultimately coalesce into stable, micron-sized rafts. Using systems biology and live cell imaging, we identified ezrin, a member of the ezrin-radixin-moesin (ERM) family, as a regulator of antigen-induced lipid raft coalescence via a conformational switch in its structure. The conformational inactivation occurs upon antigen-induced dephosphorylation of ezrin at the conserved threonine residue in its actin-binding domain.
Using scanning electron microscopy and total internal reflection microscopy (TIRF), we have further shown that a transient switch in the conformation of ezrin from active to dormant is a critical trigger that initiates morphological changes associated with cell polarization, and regulates B cell migration.
Ezrin can also potentially participate in signal transduction via an adaptor function. We have observed that BCR stimulation induces phosphorylation of ezrin on unconserved tyrosine residues, and that mutation of these residues impairs specific signaling pathways in B cell activation. Our data suggest that ezrin has a unique role in antigen-induced signal transduction.
ONGOING RESEARCH DIRECTIONS
We are currently engaged in structure-function analysis of ezrin through in vitro biochemistry and transgenic mouse modeling, as well as high definition live cell imaging. We are also interested in exploring the role of unconventional myosins in B cell development and activation.
Neetha Parameswaran, Ph.D., Postdoctoral Fellow
Debasis Pore, Ph.D., Postdoctoral Fellow
Gospel Enyindah-Asonye, Molecular Medicine Graduate Student
Andrea McClatchey, Ph.D., Harvard University
Sarah Veatch, Ph.D., University of Michigan
Bernd Wollscheid, Ph.D., Swiss Federal Research Institute, Zurich
Alex Huang, M.D., Ph.D., Case Western Reserve University
Parameswaran, N., Matsui, K., and Gupta, N.
2011. Conformational switching in ezrin regulates chemokine-induced morphological
and cytoskeletal changes required for B cell migration. J. Immunol.
186:4088-4097 . PMCID: PMC3106416
Matsui, K., Parameswaran, N., Bagheri, N., Willard, B.,
and Gupta, N. 2011. Proteomics analysis of the ezrin
interactome in B cells reveals a novel association with Myo18a a . J.
Proteome Res. 10:3983-3992 . PMCID: PMC3181492
1. Gupta, N., and DeFranco AL. 2007. Review:
Lipid rafts and B cell signaling. Semin. Cell Dev. Biol. 18:616-626
2. Viola, A., and Gupta, N. 2007. Review:
Tether and Trap: Regulation of membrane raft dynamics by actin-binding
proteins. Nat. Rev. Immunol. 7:889-896.
Neetu Gupta, Anthony L. DeFranco, and
Arthur Weiss. Signal transduction by T and B lymphocyte antigen receptors.
In Primary Immunodeficiency Diseases, a Molecular and Genetic Approach,
2nd Edition, H. D. Ochs, C. I. E. Smith, and J. Puck, eds ., Oxford
Press, Oxford, UK. 2007 .
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