Functional regulation of Zfp36l1 and Zfp36l2 in response to lipopolysaccharide in mouse RAW264.7 macrophages.

Background: The tristetraprolin (TTP) family of mRNA-binding proteins contains three major members, Ttp, Zfp36l1, and Zfp36l2. Ttp down-regulates the stability of AU-rich element-containing mRNAs and functions as an anti-inflammation regulator.

Methods: To examine whether other TTP family proteins also play roles in the inflammatory response, their expression profiles and the possible mRNA targets were determined in the knockdown cells.

Results: Ttp mRNA and protein were highly induced by lipopolysaccharide (LPS), whereas Zfp36l1 and Zfp36l2 mRNAs were down-regulated and their proteins were phosphorylated during early lipopolysaccharide stimulation. Biochemical and functional analyses exhibited that the decrease of Zfp36l2 mRNA was cross-regulated by Ttp. Knockdown of Zfp36l1 and Zfp36l2 increased the basal level of Mkp-1 mRNAs by prolonging its half-life. Increasing the expression of Mkp-1 inhibited the activation of p38 MAPK under lipopolysaccharide stimulation and down-regulated Tnfα, and Ttp mRNA. In addition, hyper-phosphorylation of Zfp36l1 might stabilize Mkp-1 expression by forming a complex with the adapter protein 14-3-3 and decreasing the interaction with deadenylase Caf1a.

Conclusions: Our findings imply that the expression and phosphorylation of Zfp36l1 and Zfp36l2 may modulate the basal level of Mkp-1 mRNA to control p38 MAPK activity during lipopolysaccharide stimulation, which would affect the inflammatory mediators production. Zfp36l1 and Zfp36l2 are important regulators of the innate immune response.