The Differential Role of Extracellular Signal-Regulated Kinases and p38 Mitogen-Activated Protein Kinase in Eosinophil Functions

Abstract

The activation of eosinophils by cytokines is a major event in the pathogenesis of allergic diseases. We have investigated the activation of mitogen-activated protein (MAP) kinases and their functional relevance in eosinophil differentiation, survival, degranulation, and cytokine production. IL-5 induced phosphorylation and activation of extracellular signal-regulated kinases (ERK) and p38 MAP kinases in eosinophils. PD98059, a MAP/ERK kinase inhibitor, blocked phosphorylation of ERK1/2 in a dose-dependent manner. SB202190, a p38 inhibitor, blocked p38-dependent phosphorylation of activating transcription factor-2. To study the importance of the MAP kinases on eosinophil differentiation, we cultured mouse bone marrow cells with IL-3 and IL-5 in the presence of the inhibitors. SB202190 dramatically inhibited eosinophil differentiation by 71%. PD98059 was less potent and reduced eosinophil differentiation by 28%. Both inhibitors marginally inhibited eosinophil survival only at the highest doses. Prolonged incubation of eosinophils with IL-5 induced significant eosinophil-derived neurotoxin release. Both PD98059 and SB202190 nearly completely inhibited (87% and 100% inhibition, respectively) IL-5-stimulated eosinophil-derived neurotoxin release in a dose-dependent manner. Next, we examined the effect of the MAP kinase inhibitors on eosinophil production of the cytokine macrophage-inflammatory protein (MIP)-1α. PD98059 blocked C5a- but not ionomycin-induced MIP-1α production (59% inhibition at 50 μM concentration). In contrast, SB202190 nearly completely inhibited (99%) C5a-induced MIP-1α production. Further, it blocked ionomycin-stimulated production by 66%. Our results suggest that both p38 and ERK1/2 MAP kinases play an important role in eosinophil differentiation, cytokine production, and degranulation. The p38 MAP kinase plays a greater role than ERK1/2 in eosinophil differentiation and cytokine production.