Mitogen-activated protein kinase-activated protein kinase 2 regulates tumor necrosis factor-induced interleukin-6 expression via human antigen R.

Background: Human antigen R (HuR) is a ubiquitously expressed member of the ELAV family, and has relatively high cytoplasmic abundance in lung tissue regenerating after injury. In this study, we investigated whether mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MK2) and HuR participate in the tumor necrosis factor (TNF)-induced expression of interleukin-6 (IL-6).

Methods: Human pulmonary microvascular endothelial cells were treated with TNF following short interfering RNA-mediated knockdown of MK2 or HuR. Cell supernatants were collected to detect the mRNA and protein expression of IL-6 at different time points. The expression and half-life of IL-6 mRNA were then determined in cells that had been treated with actinomycin D. Finally, after knockdown of MK2, the cytoplasmic expression of HuR protein was analyzed using Western blotting.

Results: MK2 or HuR knockdown decreased both the mRNA and protein expression of IL-6 in TNF-stimulated cells. In MK2 knockdown cells, the half-life of IL-6 mRNA was reduced to 36 minutes, compared with 67 minutes in the control group. In HuR knockdown cells, the half-life of IL-6 mRNA decreased from 62 minutes to 24 minutes. Further analysis revealed that knockdown of MK2 resulted in reduced HuR protein expression in the cytoplasm.

Conclusions: MK2 regulates the TNF-induced expression of IL-6 by influencing the cytoplasmic levels of HuR.