SIGNALING MECHANISMS OF PERTUSSIS TOXIN-INDUCED MYELOMONOCYTIC CELL-ADHESION - ROLE OF TYROSINE PHOSPHORYLATION

Pertussis toxin (PTX) was thought to bind Mac-1 integrin receptor (CD1 1b/CD18) on TGF-beta 1/D-3-primed U937 cells and induced cellular adhe sion to serum-coated plate. The present study was to investigate the s ignal transduction pathway utilized by PTX to initiate myeloid cell ad hesion in serum, Immunoblotting study showed that PTX induced tyrosine phosphorylation of two cytoplasmic proteins of 150 kDa and 90 kDa in TGF-beta 1/D-3-primed U937 cells in a time-dependent manner, In additi on, PTX-induced myelomonocytic cell adhesion was abolished in the pres ence of genistein (100 mu M), a specific tyrosine kinase inhibitor. 2L PM19c (2 mu g/ml), a mouse monoclonal antibody against the CD11b subun it of Mac-1 integrin, or ethylenediamine tetraacetic acid (EDTA, 5 mM) prevented PTX-mediated U937 cell adhesion, On the other hand, nifedip ine (1 mu M), a calcium channel blocker, significantly reduced PTX-ind uced U937 cell adhesion. Taken together, it is suggested that binding of PTX to Mac-1 integrin receptor on primed U937 cells triggers protei n tyrosine phosphorylation and, to a lesser extent, Ca+2 influx, which eventually lead to monocytic cell adhesion in serum. (C) Academic Pre ss.