p38 MAPK but not ERK is required for eosinophil migration and degranulation (172.29)

Eosinophil-associated RNases (EARs); the human eosinophil-derived neurotoxin and eosinophilic cationic protein and their murine orthologs, are stored in eosinophil cytoplasmic granules and secreted upon inflammation as part of innate immune responses. In eosinophil-associated diseases, such as hyper eosinophilic syndrome, allergy and asthma, EARs play crucial roles in disease pathology and can be used as biomarkers for disease severity. However, secretion mechanisms of EARs are not fully understood, especially in mouse eosinophils, the major animal model for eosinophil-associated diseases. Our study aimed to understand the mechanisms of eosinophil EAR secretion following chemokine stimulation. Both ERK and p38 MAPK activation were found to increase in mouse eosinophils in response to CCL11. CCR3-mediated EAR secretion was blocked by p38 inhibitor (SB202190), confirming previous data in human eosinophils. However, a specific inhibitor for ERK, a MEK1-derived peptide, did not inhibit CCR3-mediated secretion or migration. These results are in contrast to previous studies in human eosinophils and our studies in mouse eosinophils, showing ERK is crucial for CCR3-mediated EARs secretion and migration using PD98059, a less specific inhibitor of the ERK-activating enzyme, MEK. Collectively, these data suggest a signaling pathway for CCR3-mediated EAR secretion that includes: PI3K and p38 but not ERK. These findings are pertinent to host defense and eosinophil-associated diseases.