title: L-plastin regulates polarization and migration in chemokine-stimulated human T lymphocytes.
abstract: Chemokines such as SDF-1α play a crucial role in orchestrating T lymphocyte polarity and migration via polymerization and reorganization of the F-actin cytoskeleton, but the role of actin-associated proteins in this process is not well characterized. In this study, we have investigated a role for L-plastin, a leukocyte-specific F-actin-bundling protein, in SDF-1α-stimulated human T lymphocyte polarization and migration. We found that L-plastin colocalized with F-actin at the leading edge of SDF-1α-stimulated T lymphocytes and was also phosphorylated at Ser(5), a site that when phosphorylated regulates the ability of L-plastin to bundle F-actin. L-plastin phosphorylation was sensitive to pharmacological inhibitors of protein kinase C (PKC), and several PKC isoforms colocalized with L-plastin at the leading edge of SDF-1α-stimulated lymphocytes. However, PKC ζ, an established regulator of cell polarity, was the only isoform that regulated L-plastin phosphorylation. Knockdown of L-plastin expression with small interfering RNAs demonstrated that this protein regulated the localization of F-actin at the leading edge of chemokine-stimulated cells and was also required for polarization, lamellipodia formation, and chemotaxis. Knockdown of L-plastin expression also impaired the Rac1 activation cycle and Akt phosphorylation in response to SDF-1α stimulation. Furthermore, L-plastin also regulated SDF-1α-mediated lymphocyte migration on the integrin ligand ICAM-1 by influencing velocity and persistence, but in a manner that was independent of LFA-1 integrin activation or adhesion. This study, therefore, demonstrates an important role for L-plastin and the signaling pathways that regulate its phosphorylation in response to chemokines and adds L-plastin to a growing list of proteins implicated in T lymphocyte polarity and migration.
authors.affiliation: Department of Clinical Medicine, Institute of Molecular Medicine, Trinity College Dublin, Dublin 2, Ireland. freeleym@tcd.ie
authors.forename: Michael
authors.initials: M
authors.lastname: Freeley
authors.forename: Francis
authors.initials: F
authors.lastname: O'Dowd
authors.forename: Toby
authors.initials: T
authors.lastname: Paul
authors.forename: Dmitry
authors.initials: D
authors.lastname: Kashanin
authors.forename: Anthony
authors.initials: A
authors.lastname: Davies
authors.forename: Dermot
authors.initials: D
authors.lastname: Kelleher
authors.forename: Aideen
authors.initials: A
authors.lastname: Long
mesh_terms: D000199:Actins / Q000276:immunology / Q000378:metabolism; D015153:Blotting, Western; D016764:Cell Polarity / Q000276:immunology*; D018925:Chemokines / Q000276:immunology / Q000378:metabolism; D002634:Chemotaxis, Leukocyte / Q000276:immunology*; D003599:Cytoskeleton / Q000276:immunology / Q000378:metabolism; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D055785:Gene Knockdown Techniques; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology; D008562:Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*; D008840:Microfilament Proteins / Q000276:immunology / Q000378:metabolism*; D010766:Phosphorylation; D034741:RNA, Small Interfering; D015398:Signal Transduction / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism*
chemical_list: D000199:Actins; D018925:Chemokines; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D034741:RNA, Small Interfering; C026742:plastin