Analysis of the mechanism regulating the stability of rat macrophage inflammatory protein‐2 mRNA in RBL‐2H3 cells

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Abstract
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.