title: The chemotactic defect in wiskott-Aldrich syndrome macrophages is due to the reduced persistence of directional protrusions.
abstract: Wiskott-Aldrich syndrome protein (WASp) is an actin nucleation promoting factor that is required for macrophages to directionally migrate towards various chemoattractants. The chemotaxis defect of WASp-deficient cells and its activation by Cdc42 in vivo suggest that WASp plays a role in directional sensing, however, its precise role in macrophage chemotaxis is still unclear. Using shRNA-mediated downregulation of WASp in the murine monocyte/macrophage cell line RAW/LR5 (shWASp), we found that WASp was responsible for the initial wave of actin polymerization in response to global stimulation with CSF-1, which in Dictyostelium discoideum amoebae and carcinoma cells has been correlated with the ability to migrate towards chemoattractants. Real-time monitoring of shWASp cells, as well as WASp⁻/⁻ bone marrow-derived macrophages (BMMs), in response to a CSF-1 gradient revealed that the protrusions from WASp-deficient cells were directional, showing intact directional sensing. However, the protrusions from WASp-deficient cells demonstrated reduced persistence compared to their respective control shRNA and wild-type cells. Further examination showed that tyrosine phosphorylation of WASp was required for both the first wave of actin polymerization following global CSF-1 stimulation and proper directional responses towards CSF-1. Importantly, the PI3K, Rac1 and WAVE2 proteins were incorporated normally in CSF-1 - elicited protrusions in the absence of WASp, suggesting that membrane protrusion driven by the WAVE2 complex signaling is intact. Collectively, these results suggest that WASp and its phosphorylation play critical roles in coordinating the actin cytoskeleton rearrangements necessary for the persistence of protrusions required for directional migration of macrophages towards CSF-1.
authors.affiliation: Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America.
authors.forename: Dan
authors.initials: D
authors.lastname: Ishihara
authors.forename: Athanassios
authors.initials: A
authors.lastname: Dovas
authors.forename: Haein
authors.initials: H
authors.lastname: Park
authors.forename: Beth M
authors.initials: BM
authors.lastname: Isaac
authors.forename: Dianne
authors.initials: D
authors.lastname: Cox
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D002633:Chemotaxis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D057507:Mice, 129 Strain; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011554:Pseudopodia / Q000187:drug effects / Q000378:metabolism; D034622:RNA Interference; D013997:Time Factors; D014923:Wiskott-Aldrich Syndrome / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051316:Wiskott-Aldrich Syndrome Protein / Q000235:genetics / Q000378:metabolism*; D051300:Wiskott-Aldrich Syndrome Protein Family / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
chemical_list: D000199:Actins; C492303:Wasf2 protein, mouse; D051316:Wiskott-Aldrich Syndrome Protein; D051300:Wiskott-Aldrich Syndrome Protein Family; D016173:Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases; D020830:rac1 GTP-Binding Protein