Dynamic state of beta 2 integrin phosphorylation: regulation of neutrophil aggregation involves a phosphatase-dependent pathway.
The role of phosphorylation and dephosphorylation events in homotypic neutrophil aggregation mediated by CD11b/CD18 molecules was investigated using okadaic acid, an inhibitor of serine and threonine phosphatases. In the absence of exogenous stimuli the addition of okadaic acid to neutrophils resulted in a dose-dependent increase in phosphorylation of the CD18 beta chain that was further augmented by PMA but unaffected by FMLP. Phosphorylation induced by okadaic acid was reversed by staurosporine and minimally decreased by the less selective PKA/PKC inhibitors, H-7 and H-8. This suggests the existence of constitutive phosphatase and kinase activity emphasizing the dynamic state of phosphorylation and dephosphorylation of the beta 2 integrins. Unlike PMA, okadaic acid did not promote homotypic neutrophil aggregation. Furthermore, both the PMA-induced pathway of irreversible aggregation, blocked by staurosporine, as well as the FMLP-induced pathway of reversible aggregation, augmented by staurosporine, were inhibited by okadaic acid in a dose- and time-dependent manner. These results provide evidence that a phosphatase-dependent step is involved in each of these two distinct pathways that regulate neutrophil aggregation mediated by beta 2 integrin activation.
Merrill
J T
JT
Department of Pediatrics, Columbia University College of Physicians and Surgeons, New York, New York 10027.
Winchester
R J
RJ
Buyon
J P
JP
D000328:Adult; D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000378:metabolism; D018821:CD18 Antigens; D002449:Cell Aggregation / Q000187:drug effects / Q000502:physiology; D002470:Cell Survival; D004988:Ethers, Cyclic / Q000494:pharmacology; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009504:Neutrophils / Q000166:cytology* / Q000201:enzymology*; D019319:Okadaic Acid; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000097:blood / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D015703:Antigens, CD; D018821:CD18 Antigens; D004988:Ethers, Cyclic; D016023:Integrins; D046911:Macromolecular Substances; D019319:Okadaic Acid; D009240:N-Formylmethionine Leucyl-Phenylalanine; D007770:L-Lactate Dehydrogenase; D017346:Protein Serine-Threonine Kinases; D010744:Phosphoric Monoester Hydrolases; D013755:Tetradecanoylphorbol Acetate