The RNA-binding protein HuR stabilizes cytosolic phospholipase A ₂α mRNA under Interleukin-1β treatment in non-small cell lung cancer A549 cells

The activation of cytosolic phospholipase A ₂α (cPLA ₂α) plays an important role in initiating the inflammatory response. The regulation of cPLA ₂α mRNA turnover has been proposed to control cPLA ₂α gene expression under cytokine and growth factor stimulation. However, the detailed mechanism is still unknown. In this report, we have demonstrated that the cPLA ₂α mRNA stability was increased under IL-1β treatment in A549 cells. By using EMSAs, HuR was identified as binding with the cPLA ₂α mRNA 3′-UTR, and the binding region was located at nucleotides 2716-2807, a fragment containing AUUUA flanked by U-rich sequences. IL-1β treatment enhanced the association of cPLA ₂α mRNA with cytosolic HuR. The reduction of HuR expression by RNA interference technology inhibited IL-1β-induced cPLA ₂α mRNA and protein expression. Furthermore, blocking the p38 MAPK signaling pathway with SB203580 abolished the effect of IL-1β-induced cPLA ₂α gene expression. Phosphorylation at residue Thr-118 of HuR is crucial in regulating the interaction between HuR and its target mRNAs. Mutation of HuR Thr-118 reduced the association between HuR and cPLA ₂α mRNA under IL-1β treatment. This inhibitory effect was also observed in binding with COX-2 mRNA. This result indicated that p38 MAPK-mediated Thr-118 phosphorylation may play a key role in regulating the interaction of HuR with its target mRNAs in inflammation.