title: A congenital activating mutant of WASp causes altered plasma membrane topography and adhesion under flow in lymphocytes.
abstract: Leukocytes rely on dynamic actin-dependent changes in cell shape to pass through blood vessels, which is fundamental to immune surveillance. Wiskott-Aldrich Syndrome protein (WASp) is a hematopoietic cell-restricted cytoskeletal regulator important for modulating cell shape through Arp2/3-mediated actin polymerization. A recently identified WASp(I294T) mutation was shown to render WASp constitutively active in vivo, causing increased filamentous (F)-actin polymerization, high podosome turnover in macrophages, and myelodysplasia. The aim of this study was to determine the effect of WASp(I294T) expression in lymphocytes. Here, we report that lymphocytes isolated from a patient with WASp(I294T), and in a cellular model of WASp(I294T), displayed abnormal microvillar architecture, associated with an increase in total cellular F-actin. Microvillus function was additionally altered as lymphocytes bearing the WASp(I294T) mutation failed to roll normally on L-selectin ligand under flow. This was not because of defects in L-selectin expression, shedding, cytoskeletal anchorage, or membranal positioning; however, under static conditions of adhesion, WASp(I294T)-expressing lymphocytes exhibited altered dynamic interaction with L-selectin ligand, with a significantly reduced rate of adhesion turnover. Together, our results demonstrate that WASp(I294T) significantly affects lymphocyte membrane topography and L-selectin-dependent adhesion, which may be linked to defective hematopoiesis and leukocyte function in affected patients.
authors.affiliation: Molecular Immunology Unit, Centre for Immunodeficiency, Institute of Child Health, University College London, London, UK.
authors.forename: Siobhan O
authors.initials: SO
authors.lastname: Burns
authors.forename: David J
authors.initials: DJ
authors.lastname: Killock
authors.forename: Dale A
authors.initials: DA
authors.lastname: Moulding
authors.forename: Joao
authors.initials: J
authors.lastname: Metelo
authors.forename: Joao
authors.initials: J
authors.lastname: Nunes
authors.forename: Ruth R
authors.initials: RR
authors.lastname: Taylor
authors.forename: Andrew
authors.initials: A
authors.lastname: Forge
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Thrasher
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Ivetic
mesh_terms: D000199:Actins / Q000378:metabolism; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000648:ultrastructure; D002478:Cells, Cultured; D015870:Gene Expression; D040181:Genetic Diseases, X-Linked / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D019041:L-Selectin / Q000235:genetics / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000166:cytology; D007970:Leukopenia / Q000235:genetics* / Q000378:metabolism; D008214:Lymphocytes / Q000166:cytology* / Q000378:metabolism; D008871:Microvilli / Q000648:ultrastructure*; D009154:Mutation; D051316:Wiskott-Aldrich Syndrome Protein / Q000235:genetics* / Q000378:metabolism
chemical_list: D000199:Actins; D051316:Wiskott-Aldrich Syndrome Protein; D019041:L-Selectin