Prostaglandin A₂-mediated stabilization of p21 mRNA through an ERK-dependent pathway requiring the RNA-binding protein HuR

Treatment with the stress agent prostaglandin A₂ (PGA ₂) induces expression of the cyclin-dependent kinase inhibitor p21. Here, we present evidence that p21 expression increases through PGA ₂-triggered stabilization of the p21 mRNA and further show that these events require the mitogen-activated protein (MAP) kinase ERK. Binding experiments using either endogenous p21 mRNA or in vitro-labeled p21 transcripts revealed a specific PGA₂-dependent association of the p21 mRNA with the RNA-binding protein HuR. Interestingly, although inhibition of the ERK pathway did not prevent the PGA₂-triggered increase in cytoplasmic HuR, it did impair the formation of endogenous and in vitro [HuR-p21 mRNA] complexes and further prevented the PGA₂-mediated stabilization of the p21 mRNA, suggesting that ERK-mediated events were required for binding HuR to the p21 mRNA and preventing its decay. RNA interference-based knockdown of HuR abundance further served to demonstrate the contribution of HuR-mediated p21 mRNA stabilization toward enhancing p21 expression after PGA₂ treatment. Collectively, our results indicate that PGA₂ stabilizes the p21 mRNA through an ERK-independent increase in cytoplasmic HuR levels and an ERK-dependent association of HuR with the p21 mRNA.