STAUROSPORINE RESTORES SIGNALING AND INHIBITS INTERLEUKIN-8-INDUCED CHEMOTACTIC DESENSITIZATION

Interleukin 8 (IL-8) is a chemotactic cytokine (chemokine) that plays a key role in the accumulation and activation of neutrophils at inflam matory sites. In this report we demonstrate that homologous chemotacti c desensitization occurs upon pretreatment of neutrophils with IL-8 or N-formyl-methionyl-leucyl-phenylalanine (FMLP) and results in the inh ibition of neutrophil chemotaxis upon subsequent challenge with the sa me ligand. This homologous chemotactic desensitization could be preven ted by pretreating the neutrophils with the protein kinase inhibitor s taurosporine, indicating that protein kinases may play an essential ro le. The attenuation of homologous desensitization by staurosporine res tored chemotaxis but was not associated with a change in IL-8 receptor expression, affinity or the rate of ligand internalization, indicatin g that homologous desensitization does not alter ligand-receptor inter action. Using two-dimensional analysis we have shown that IL-8 induced a rapid serine/threonine phosphorylation of a number of neutrophil su bstrates the most prominent being phosphoprotein 39 (pp39), extracellu lar signal-related kinase-1, pp55 and pp66. Prior desensitization of n eutrophils with IL-8 blocked all subsequent phosphorylation upon recha llenge with IL-8. However, the desensitization was specific for IL-8 s ince normal phosphorylation of identical substrates was observed in re sponse to FMLP. When neutrophils were pretreated with staurosporine, p rior to desensitization, phosphorylation of pp39 was observed upon res timulation with IL-8. Further study revealed that pp55 and pp66 were n ot phosphorylated in the presence of staurosporine. Thus, homologous d esensitization of neutrophils in response to IL-8 does not result from changes in receptor expression, but rather from a staurosporine-sensi tive inactivation of subsequent signal transduction. This desensitizat ion is selective since the cells are able to respond to other ligands.