title: Macrophage-enriched myristoylated alanine-rich C kinase substrate and its phosphorylation is required for the phorbol ester-stimulated diffusion of beta 2 integrin molecules.
abstract: An early event of beta(2) integrin activation is the increased diffusion rate of this molecule on the cell surface, thereby providing integrin molecules with a better chance to meet the ligands. The activation of protein kinase C (PKC) stimulates integrin diffusion by releasing the cytoskeletal constraint on integrin molecules. We report here that macrophage-enriched myristoylated alanine-rich C kinase substrate (MacMARCKS), a membrane-associated PKC substrate involved in integrin activation, is required for this PKC-stimulated diffusion of integrin molecules. Using the single-particle tracking technique, we observed that the activation of PKC stimulated an 11-fold increase in the diffusion rate of beta(2) integrins in wild type J774 macrophage cells but not in those expressing mutant MacMARCKS. Further evidence is provided from a MacMARCKS-deficient cell line in which phorbol esters failed to stimulate the diffusion of integrin. Transfection of wild type MacMARCKS into these cells restored the rapid diffusion rate of the beta(2) integrins. The phosphorylation of MacMARCKS is important because transfection of a nonphosphorylatable MacMARCKS mutant or the addition of staurosporine eliminates the rapid diffusion rate of integrin. Furthermore, adding cytochalasin D bypasses the MacMARCKS deficiency and stimulates beta(2) integrin diffusion, suggesting that MacMARCKS's involvement in integrin activation is prior or at the site of cytoskeleton. Therefore, we conclude that MacMARCKS is required for releasing the cytoskeletal constraint on integrin molecules during PKC-mediated integrin activation.
authors.affiliation: Department of Oral Biology, College of Dentistry and the Department of Microbiology and Immunology, College of Medicine, University of Illinois, Chicago, Illinois 60612, USA.
authors.forename: X
authors.initials: X
authors.lastname: Zhou
authors.forename: J
authors.initials: J
authors.lastname: Li
mesh_terms: D000818:Animals; D018821:CD18 Antigens / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins; D002460:Cell Line; D003599:Cytoskeleton / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D004789:Enzyme Activation; D005456:Fluorescent Dyes / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008264:Macrophages / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D051379:Mice; D008840:Microfilament Proteins; D018715:Microscopy, Video; D008863:Microspheres; D015233:Models, Statistical; D009068:Movement; D009154:Mutation; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D013997:Time Factors
chemical_list: D018821:CD18 Antigens; D002148:Calmodulin-Binding Proteins; D005456:Fluorescent Dyes; D047908:Intracellular Signaling Peptides and Proteins; C512945:Marcksl1 protein, mouse; D008565:Membrane Proteins; D008840:Microfilament Proteins; D010703:Phorbol Esters; D011493:Protein Kinase C