Toll-like receptor 2 and 4 (TLR2 and TLR4) agonists differentially regulate secretory interleukin-1 receptor antagonist gene expression in macrophages.
Treatment of macrophages with lipopolysaccharide (LPS) from Gram-negative bacteria or peptidoglycan (PGN) from Gram-positive bacteria activates multiple intracellular signaling pathways and a large, diverse group of nuclear transcription factors. The signaling receptors for PGN and LPS are now known to be the Toll-like receptors 2 and 4 (TLR2 and -4, respectively). While a large body of literature indicates that the members of the TLR family activate nearly identical cytoplasmic signaling programs, several recent reports have suggested that the functional outcomes of signaling via TLR2 or TLR4 are not equivalent. In the current studies, we compared the responses of the secretory IL-1 receptor antagonist (sIL-1Ra) gene to both LPS and PGN. Both LPS and PGN induced IL-1Ra gene expression; however, the combination of both stimuli synergistically increased sIL-1Ra mRNA expression and promoter activity, suggesting that the signals induced by PGN and LPS are not equivalent. While both LPS and PGN utilized the PU.1-binding sites in the proximal sIL-1Ra promoter region to generate a full response, additional distinct promoter elements were utilized by LPS or PGN. Activation of p38 stress-activated protein kinase was required for LPS- or PGN-induced IL-1Ra gene expression, but the p38-responsive promoter elements localized to distinct regions of the sIL-1Ra gene. Additionally, while the LPS-induced, p38-dependent response was dependent upon PU.1 binding, the PGN-induced, p38 response was not. Collectively, these data indicated that while some of the intracellular signaling events by TLR2 and TLR4 agonists are similar, there are clearly distinct differences in the responses elicited by these two bacterial products.
Carl
Virginia S
VS
Digestive Health Center of Excellence and Department of Microbiology, University of Virginia Health System, Charlottesville, Virginia 22908, USA.
Brown-Steinke
Kathleen
K
Nicklin
Martin J H
MJ
Smith
Michael F
MF
D000818:Animals; D002460:Cell Line; D029721:Drosophila Proteins; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000819:agonists*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010457:Peptidoglycan / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000819:agonists*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012795:Sialoglycoproteins / Q000235:genetics*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases; D000099232:Proto-Oncogene Protein Spi-1
D029721:Drosophila Proteins; D053590:Interleukin 1 Receptor Antagonist Protein; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D020928:Mitogen-Activated Protein Kinases; D010457:Peptidoglycan; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D012795:Sialoglycoproteins; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D015534:Trans-Activators; D048051:p38 Mitogen-Activated Protein Kinases; D000099232:Proto-Oncogene Protein Spi-1; C507763:IL1RN protein, human; C507764:Il1rn protein, mouse; C495342:TLR2 protein, human; C495345:TLR4 protein, human