Role of MacMARCKS in integrin-dependent macrophage spreading and tyrosine phosphorylation of paxillin.
The cellular function of the MARCKS family of protein kinase C substrates is unknown. In this report, we present evidence that indicates a role for MacMARCKS, a member of the MARCKS family, in the integrin-dependent signal transduction pathways in macrophages. Using a dominant negative mutant of MacMARCKS, we showed that MacMARCKS participates in several integrin-dependent macrophage functions, including the phorbol ester-stimulated macrophage spreading, a process involving multiple integrins. The dominant negative mutant also blocks macrophage spreading on immune complex-coated surfaces, a process again requiring beta2 integrin. More direct evidence of the role of MacMARCKS in the integrin-dependent pathway is the ablation of macrophage binding to complement iC3b-coated sheep erythrocytes by MacMARCKS mutant, suggesting an effect of this mutant on the avidity of complement receptor 3, a member of the beta2 integrin family. To further evaluate the possible mechanism of MacMARCKS function, the integrin-dependent tyrosine phosphorylation of paxillin was examined. Concomitant with the inhibition of macrophage spreading and rosette formation, MacMARCKS mutant also inhibits integrin-dependent tyrosine phosphorylation of paxillin. Furthermore, immunofluorescent microscopy data showed that MacMARCKS and paxillin colocalize in the membrane ruffles at the leading edge of the spreading cells, providing a potential site and opportunity for MacMARCKS to participate in the regulation of integrin-dependent tyrosine phosphorylation of paxillin. Together, these data strongly suggest that MacMARCKS plays a role in integrin-dependent signal transduction pathways in macrophages.
Li
J
J
Department of Microbiology and Immunology, University of Tennessee at Memphis, College of Medicine, Memphis, Tennessee 38163, USA.
Zhu
Z
Z
Bao
Z
Z
D000595:Amino Acid Sequence; D018821:CD18 Antigens / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology*; D008565:Membrane Proteins; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D051419:Paxillin; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism*
D018821:CD18 Antigens; D003598:Cytoskeletal Proteins; D008565:Membrane Proteins; D051419:Paxillin; D010750:Phosphoproteins; D011506:Proteins; D014443:Tyrosine