Using rat peritoneal neutrophils, the complete nucleotide sequence of rat macrophage inflammatory protein-2 (MIP-2) mRNA including 5'untranslated region (UTR) and 3'UTR was determined (GenBank Accession number, AB060092). It was found that the MIP-2 mRNA has a 70 bp 5'UTR, a 303 bp coding region and a 728 bp 3'UTR which contains adenylate/uridylate (AU)-rich areas defined as AU-rich elements (AREs). Site-directed mutagenesis studies using the tetracycline-sensitive transactivator protein-expressing rat basophilic leukemia cells (RBL-2H3-TO cells) revealed that MIP-2 mRNA mutants which lack the 3'UTR are more stable than MIP-2-wild-type (wt) mRNA. A MIP-2 mRNA mutant in which some mutations were introduced to the ARE was also stable. The stability of MIP-2 mRNA was low in untreated RBL-2H3-TO cells, but it increased in the antigen-stimulated immunoglobulin E (IgE)-sensitized cells. The antigen-induced MIP-2 mRNA stabilization was counteracted by the highly specific p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 and the MAPK/ERK kinase (MEK-1) inhibitor PD98059. These findings indicate that ARE is the cis-element which mediates the rapid decay of MIP-2 mRNA, and the antigen stimulation stabilizes MIP-2 mRNA and the p38 MAPK and p44/42 MAPK pathways are involved in the antigen-induced stabilization of MIP-2 mRNA.