leukotriene-b4 and staurosporine-aglycone

A single class of high affinity leukotriene B4 (LTB4) receptors has been identified on the surface of guinea pig peritoneal exudate T lymphocytes. The Kd of these receptors is 1.6 nM, with a Bmax of 25.2 fmol/10(7) cells (1500 sites/cell). Receptor binding activity can be blocked by specific LTB4 receptor antagonists, but not by a specific LTD4 receptor antagonist, lipoxins A4 or B4 (LXA4, LXB4) or K252a, a protein kinase C inhibitor. Pretreatment of T lymphocytes with phorbol myristyl acetate or LXA4, reduced LTB4 receptor density in a concentration-dependent manner, although similar concentrations of LXB4 had no effect. LTB4 receptor down-modulation by LXA4 was reversed by K252a. 4 alpha-Phorbol 12,13-didecanoate, an inactive structural analogue of phorbol myristyl acetate, did not activate protein kinase C or decrease LTB4 receptor density. These results suggest that LTB4 receptor density on T cells may by ultimately down-regulated by a protein kinase C-dependent mechanism and are consistent with a physiological role of LXA4 in the modulation of inflammatory process.

Topics: Animals; Carbazoles; Female; Guinea Pigs; Hydroxyeicosatetraenoic Acids; Indole Alkaloids; Inflammation; Leukotriene B4; Lipoxins; Protein Kinase C; Receptors, Leukotriene B4; T-Lymphocytes; Tetradecanoylphorbol Acetate

This paper focuses on eosinophil activation and its selective inhibition. Superoxide anion (O2-) production by human eosinophils, an indicator of their activation, was induced by a variety of activators. Several compounds which are known to inhibit protein kinase C (staurosporine, K252a, sphingosine) inhibited O2- production induced by phorbol ester (PMA) but failed to inhibit O2- production induced by IgG coupled to Sepharose beads. Inhibition of O2- production by other agents (plasma-activated zymosan, fMLP, and leukotriene B4 (LTB4), was intermediate. By contrast, wortmannin, a compound which has been previously reported to inhibit O2- production in neutrophils via a protein kinase-independent pathway, potently inhibited O2- production in eosinophils which had been activated by IgG and by Platelet-Activating Factor but was virtually inactive against PMA-induced O2- production. Taken together, the results indicate that, as a minimum, there must be two pathways of induction of O2- production in eosinophils. Moreover, the intermediate levels of inhibition in cells which had been activated with serum-activated zymosan, FMLP, and LTB4 suggest that these agents may either be acting via both of these pathways or that yet other pathways may exist.

Topics: Alkaloids; Androstadienes; Carbazoles; Eosinophils; Humans; Immunoglobulin G; Indole Alkaloids; Leukotriene B4; N-Formylmethionine Leucyl-Phenylalanine; Platelet Activating Factor; Protein Kinase C; Sphingosine; Staurosporine; Superoxides; Tetradecanoylphorbol Acetate; Wortmannin; Zymosan