Abstract
Tristetraprolin (TTP), a substrate of p38 mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MK2), is an RNA-binding protein that binds to AU-rich elements (AREs) in the 3'-untranslated region (3'-UTR) of its target mRNAs and accelerates mRNA degradation. A previous study by our group showed that MK2 regulates tumor necrosis factor-α (TNF-α)-induced expression of intercellular adhesion molecule-1 (ICAM-1) and interleukin-8 (IL-8) in human lung microvascular endothelial cells; however, the downstream protein of MK2 remains unknown. Interestingly, both ICAM-1 and IL-8 have AREs in the 3'-UTR of their mRNAs. In the present study, we performed experiments to determine whether MK2 regulates TNF-α-induced expression of ICAM-1 and IL-8 via TTP in human pulmonary microvascular endothelial cells (HPMECs). The study revealed that MK2 silencing significantly reduced the half-lives of ICAM-1 and IL-8 mRNAs in TNF-α-stimulated HPMECs. TTP phosphorylation levels were decreased in MK2-silenced cells. TTP silencing led to mRNA stabilization of ICAM-1 and IL-8 and upregulation of protein production following TNF-α stimulation. These results, together with our previous study and others, suggest that MK2, in HPMECs, regulates TNF-α-induced expression of ICAM-1 and IL-8 via TTP at the mRNA decay level.