Beta 2 integrin engagement triggers actin polymerization and phosphatidylinositol trisphosphate formation in non-adherent human neutrophils.
Beta 2 integrins are involved in the adhesion of leukocytes to other cells and surfaces. Although adhesion is required for cell locomotion, little is known regarding the way beta 2 integrin-receptors affect the actin network in leukocytes. In the present study filamentous actin (F-actin) levels in non-adherent human neutrophils have been measured by phalloidin staining after antibody cross-linking of beta 2 integrins. Antibody engagement of beta 2 integrins resulted in a rapid and sustained (146 and 131% after 30 and 300 s, respectively) increase in the neutrophil F-actin content. This is in contrast to stimulation with N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLP), which causes a prompt and pronounced but rapidly declining rise in F-actin (214 and 127% after 15 and 300 s, respectively). Priming neutrophils with 1 nM PMA, a low concentration that did not influence the F-actin content per se, increased the magnitude of the beta 2 integrin-induced response but had no effect on the kinetics (199% after 30 s and 169% after 300 s). Removal of extracellular Ca2+ only marginally affected the beta 2 integrin-induced F-actin response for cells that were pretreated with PMA whereas the response for nonprimed cells was reduced by half. This suggests that even though extracellular Ca2+ has a modulatory effect it is not an absolute requirement for beta 2 integrin-induced actin polymerization. beta 2 integrin engagement did not affect the resting cellular level of cAMP arguing against a role of cAMP in beta 2 integrin-induced actin assembly.(ABSTRACT TRUNCATED AT 250 WORDS)
Löfgren
R
R
Department of Cell Biology, University of Linköping, Sweden.
Ng-Sikorski
J
J
Sjölander
A
A
Andersson
T
T
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D008841:Actin Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure; D000199:Actins / Q000378:metabolism*; D015703:Antigens, CD / Q000502:physiology*; D018821:CD18 Antigens; D002118:Calcium / Q000494:pharmacology; D002448:Cell Adhesion; D000242:Cyclic AMP / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D016023:Integrins / Q000378:metabolism*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000199:Actins; D015703:Antigens, CD; D018821:CD18 Antigens; D016023:Integrins; D018129:Phosphatidylinositol Phosphates; D010566:Virulence Factors, Bordetella; D009240:N-Formylmethionine Leucyl-Phenylalanine; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine