Submitted on February 13, 2007
Accepted on November 19, 2007
MNK kinases regulate multiple TLR pathways and innate proinflammatory cytokines in macrophages
Robert M Rowlett1, Carol A Chrestensen2, Mark Nyce1, Mary G. Harp1, Jared W Pelo1, Fabio Cominelli1, Peter B Ernst1, Theresa T. Pizarro3, Thomas W. Sturgill2, and Mark T Worthington4*
1 Medicine, University of Virginia, Charlottesville, Virginia, United States
2 Pharmacology, University of Virginia, Charlottesville, Virginia, United States
3 Internal Medicine & Immunology, University of Virginia Health Science Center, Charlottesville, Virginia, United States
4 Division of Digestive Diseases, Johns Hopkins Bayview Medical Center, Baltimore, Maryland, United States
* To whom correspondence should be addressed. E-mail: mworthi3{at}jhmi.edu.
The MNK kinases are downstream of both the p38 and ERK MAP kinase pathways and act to increase gene expression. MNK inhibition using the compound CGP57380 has recently been reported to inhibit tumor necrosis factor (TNF) production in macrophage cell lines stimulated with E. coli lipopolysaccharide (LPS). However, the range of receptors that signal through the MNK kinases and the extent of the resultant cytokine response are not known. We found that TNF production was inhibited in RAW264.7 macrophage cells by CGP57380 in a dose-responsive manner with agonists for TLR2 (HKLM), TLR4 (Salmonella LPS), TLR 6/2 (FSL), TLR7 (inquimod) and TLR 9 (CpG DNA). CGP57380 also inhibited the peak of TNF mRNA production and increased the rate of TNF mRNA decay, effects not due to the destabilizing RNA binding protein tristetraprolin (TTP). Similar to its effects on TNF, CGP57380 caused dose-responsive inhibition of TTP production from stimulation with either LPS or CpG DNA. MNK inhibition also blocked IL-6, but permitted IL-10 production in response to LPS. Studies using bone-marrow derived macrophages (BMDM) isolated from a spontaneous mouse model of Crohn's disease-like ileitis (SAMP1/YitFc strain) revealed significant inhibition by CGP57380 of the proinflammatory cytokines TNF, IL-6, and MCP-1 at 4 and 24 hours after LPS stimulation. IL-10 production was higher in CGP53870-treated BMDM at 4 hours, but was similar to the controls by 24 hours. Taken together, these data demonstrate that MNK kinases signal through a variety of TLR agonists and mediate a potent innate, proinflammatory cytokine response.
