title: Adenosine inhibits actin dynamics in human neutrophils: evidence for the involvement of cAMP.
abstract: The mechanisms by which adenosine regulates the inflammatory reaction are poorly characterized. In this study, we investigated the effects of adenosine on neutrophil actin polymerization elicited by the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) or IgG-opsonized yeast particles. We used bodipy-phallacidin staining in combination with flow cytometry and found that adenosine markedly reduced actin polymerization triggered by IgG-yeast, whereas the effect on the fMLP-response was less pronounced. Similar or even more pronounced effects were obtained with the adenosine A2 receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA), suggesting an A2 receptor-mediated mechanism. The following observations indicate that the A2 receptor-induced effects involve the cAMP-protein kinase A (PKA) signaling pathway: (1) a combination of NECA and the cAMP-specific phosphodiesterase (PDE) inhibitor Ro 20-1724 raised the cAMP content in both unstimulated and stimulated neutrophils and also further inhibited the actin dynamics; (2) the PKA inhibitor H89 reversed the inhibitory effects of NECA on the actin dynamics; (3) Ro 20-1724, isoproterenol and dibutyryl cAMP (DBcAMP) reduced actin polymerization in almost the same way as NECA did. NECA together with Ro 20-1724 impaired the fMLP-induced shape changes and cortical accumulation of actin filaments. In contrast, H89 potentiated the fMLP-induced formation of a submembranous ring of actin filaments. Neutrophils phagocytosing yeast particles in the presence of NECA and Ro 20-1724 were predominantly round in shape, and their ability to extend actin-rich pseudopods around the prey was reduced. These effects were partly antagonized by H89. In correlation with the effects on actin polymerization, NECA more effectively diminished IgG-induced upregulation of the beta2 integrin CD11b/CD18 than such upregulation induced by fMLP. The inhibitory effects of A2-receptor activation on actin dynamics and beta2 integrin expression in neutrophils exposed to IgG-yeast were also associated with a cAMP-dependent reduction of the phagocytic capacity. In conclusion, we show that adenosine inhibits actin dynamics and shape changes in neutrophils via a cAMP-dependent pathway. This finding further characterizes the mechanisms by which adenosine functions as an important modulator of the inflammatory response.
authors.affiliation: Department of Health and Environment, Faculty of Health Sciences, Linköping University, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Zalavary
authors.forename: T
authors.initials: T
authors.lastname: Bengtsson
mesh_terms: D000199:Actins / Q000378:metabolism*; D000241:Adenosine / Q000378:metabolism* / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D018821:CD18 Antigens / Q000096:biosynthesis; D000242:Cyclic AMP / Q000378:metabolism*; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology; D016177:Macrophage-1 Antigen / Q000096:biosynthesis; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D010587:Phagocytosis; D018047:Receptors, Purinergic P1 / Q000378:metabolism; D015003:Yeasts
chemical_list: D000199:Actins; D018821:CD18 Antigens; D007074:Immunoglobulin G; D016177:Macrophage-1 Antigen; D018047:Receptors, Purinergic P1; D019830:Adenosine-5'-(N-ethylcarboxamide); D009240:N-Formylmethionine Leucyl-Phenylalanine; D000242:Cyclic AMP; D000241:Adenosine