Mechanisms of pertussis toxin-induced myelomonocytic cell adhesion: role of Mac-1(CD11b/CD18) and urokinase receptor (CD87).
Stimulation of monoblastic U937 cells with transforming growth factor beta 1 and 1,25-(OH)2 vitamin D3 (TGF-beta 1/D3) upregulates urokinase receptor (uPAR) and confers urokinase-dependent adhesiveness to the cells for serum- or vitronectin-coated surfaces. Recent studies show that uPAR itself is a high-affinity adhesion receptor for vitronectin and that urokinase (uPA) is an activator of this adhesive function. In the course of exploring possible G-protein involvement in this adhesion it was observed that TGF-beta 1/D3-primed U937 cells became adhesive to vitronectin in an uPAR-dependent manner when exposed to pertussis toxin (PTX). The adherent response is concentration- and time-dependent, and was not due to the ADP-ribosyltransferase activity of the toxin because the purified B-subunit of PTX was equally effective. Although promoting adhesion to serum- or vitronectin-coated surfaces, PTX blocked spontaneous cell adhesion to fibrinogen, an endogenous ligand for the Mac-1 receptor (CD11b/CD18). Flow cytometry study showed that expression of the alpha-subunit of Mac-1 (CD11b) on primed cells was increased by nearly threefold. Monoclonal antibody to CD11b abolished the PTX-induced cell adhesion and the binding of the primed cells to PTX-coated plates. Activation of Mac-1 receptor by its endogenous ligand fibrinogen induced cell adherent response similar to PTX. PTX, but not uPA, triggered a rapid rise in [Ca2+]i in primed U937 cells, and PTX-induced adhesion was significantly attenuated by 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid/acetoxy-methyl ester (BAPTA/AM), a selective membrane-permeant [Ca2+]i chelator. PTX-induced cell adhesion was also prevented by antibodies to uPAR and by conditioned medium containing soluble uPAR. Together these data indicate that PTX B-subunit may bind to Mac-1 integrin, which leads to a rapid rise in [Ca2+]i and subsequent activation of uPAR for adherence to vitronectin, suggesting a functional link between Mac-1 and activation of uPAR important to cellular trafficking and host defence in response to Bordetella pertussis infection.
Wong
W S
WS
Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
Simon
D I
DI
Rosoff
P M
PM
Rao
N K
NK
Chapman
H A
HA
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D006801:Humans; D015479:Leukemia, Myelomonocytic, Acute / Q000473:pathology; D016177:Macrophage-1 Antigen / Q000276:immunology / Q000502:physiology*; D037342:Pertussis Toxin; D010960:Plasminogen Activators / Q000276:immunology / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000276:immunology / Q000502:physiology*; D055293:Receptors, Urokinase Plasminogen Activator; D016212:Transforming Growth Factor beta / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*; D019096:Vitronectin / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D016177:Macrophage-1 Antigen; C524898:PLAUR protein, human; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D016212:Transforming Growth Factor beta; D010566:Virulence Factors, Bordetella; D019096:Vitronectin; D037342:Pertussis Toxin; D010960:Plasminogen Activators; D002118:Calcium