Phosphorylated form of MacMARCKS is essential to LFA-1-dependent cell-cell adhesion of U937 monocytic cells.
MacMARCKS (MRP, F52), a protein kinase C (PKC) substrate, is involved in the activation of beta2-integrin. To determine the role of the PKC-mediated phosphorylation of MacMARCKS in this process, human U937 monocytic cells were transfected with cDNAs encoding wild type or mutant MacMARCKS. We observed that the expression of the exogenous wild type MacMARCKS greatly enhanced LFA-1-mediated cell-cell adhesion in U937 cells treated with phorbol 12-myristate 13-acetate (PMA). This MacMARCKS-stimulated adhesion depended on the phosphorylation status of MacMARCKS: whereas phosphorylated MacMARCKS enhanced adhesion, unphosphorylated MacMARCKS inhibited it. However, phosphorylated MacMARCKS alone could not induce LFA-1-mediated cell-cell adhesion unless phorbol esters were added, suggesting that the phosphorylation of other proteins might also be involved. Okadaic acid, a phosphatase inhibitor, induced LFA-1-mediated cell-cell adhesion only in the cells expressing wild type or phosphorylated MacMARCKS and not in the cells expressing unphosphorylated MacMARCKS. Therefore, we conclude that the phosphorylated form of MacMARCKS is essential to LFA-1-mediated cell-cell adhesion.
Yue
L
L
Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, Chicago, Illinois, USA.
Bao
Z
Z
Li
J
J
D000818:Animals; D002148:Calmodulin-Binding Proteins; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D018076:DNA, Complementary; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008840:Microfilament Proteins; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D020298:U937 Cells
D002148:Calmodulin-Binding Proteins; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; D016169:Lymphocyte Function-Associated Antigen-1; C070177:MARCKSL1 protein, human; C512945:Marcksl1 protein, mouse; D008565:Membrane Proteins; D008840:Microfilament Proteins; D011994:Recombinant Proteins; D019319:Okadaic Acid; D013755:Tetradecanoylphorbol Acetate