Threonine phosphorylation sites in the beta 2 and beta 7 leukocyte integrin polypeptides.
The cytoplasmic domains of integrins play a key role in a variety of integrin-mediated events including adhesion, migration, and signaling. The molecular mechanisms that enhance integrin function are still incompletely understood. Because protein kinases are known to be involved in the signaling and the activation of integrins, the role of phosphorylation has been studied by several groups. The beta(2) leukocyte integrin subunit has previously been shown to become phosphorylated in leukocytes on cytoplasmic serine and functionally important threonine residues. We have now mapped the phosphorylated threonine residues in activated T cells. After phorbol ester stimulation, all three threonine residues (758-760) of the threonine triplet became phosphorylated but only two at a time. CD3 stimulation leads to a strong threonine phosphorylation of the beta(2) integrin, but differed from phorbol ester activation in that phosphorylation occurred only on threonine 758. The other leukocyte-specific integrin, beta(7), has also been shown to need the cytoplasmic domain and leukocyte-specific signal transduction elements for integrin activation. Cell activation with phorbol ester, and interestingly, through the TCR-CD3 complex, caused beta(7) integrin binding to VCAM-1. Additionally, cell activation led to increased phosphorylation of the beta(7) subunit, and phosphoamino acid analysis revealed that threonine residues became phosphorylated after cell activation. Sequence analysis by manual radiosequencing by Edman degradation established that threonine phosphorylation occurred in the same threonine triplet as in beta(2) phosphorylation.
Hilden
Tiina J
TJ
Department of Biosciences, Division of Biochemistry, and Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
Valmu
Leena
L
Kärkkäinen
Satu
S
Gahmberg
Carl G
CG
D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D018821:CD18 Antigens / Q000378:metabolism*; D019556:COS Cells; D002448:Cell Adhesion / Q000276:immunology; D002460:Cell Line; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000276:immunology / Q000378:metabolism; D006801:Humans; D039641:Integrin beta Chains / Q000378:metabolism*; D016023:Integrins / Q000378:metabolism / Q000502:physiology; D008213:Lymphocyte Activation / Q000187:drug effects; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019319:Okadaic Acid / Q000494:pharmacology; D010449:Peptide Mapping; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010748:Phosphopeptides / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017434:Protein Structure, Tertiary; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000378:metabolism / Q000502:physiology; D016176:T-Lymphocyte Subsets / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D013912:Threonine / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
D018821:CD18 Antigens; D039641:Integrin beta Chains; D016023:Integrins; D010748:Phosphopeptides; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D019010:Vascular Cell Adhesion Molecule-1; C071777:integrin alpha4beta7; C091368:integrin beta7; D019319:Okadaic Acid; D013912:Threonine; D015240:Phorbol 12,13-Dibutyrate; D000409:Alanine