Department of Medicine, Division of Infectious Diseases and Immunology
Adaptor Proteins, Signal Transducing; Animals; Antigens, Differentiation; Cells, Cultured; DNA-Binding Proteins; Escherichia coli K12; Gene Expression Profiling; Gene Expression Regulation; Genetic Markers; Humans; Inflammation; Interferon Regulatory Factor-3; Kidney; Lipopolysaccharides; Macrophage Activation; Macrophages; Mice; Mice, Inbred C57BL; Microarray Analysis; Myeloid Differentiation Factor 88; NF-kappa B; Proteins; Receptors, Immunologic; Signal Transduction; Toll-Like Receptor 4; Transcription Factors; Transfection
Immunology and Infectious Disease
Myeloid differentiation protein-88 (MyD88) is a signal adaptor protein required for cytokine production following engagement of Toll-like receptors (TLRs) by their cognate ligands. Activation of both TLR-3 and TLR-4, however, can engage signaling events independent of MyD88 expression. The relative importance of these MyD88-dependent and -independent signaling pathways in the macrophage response to lipopolysaccharide (LPS) is unknown. Here we define these events using microarray expression profiling of LPS-stimulated macrophages taken from MyD88-null and wild-type mice. Of the 1,055 genes found to be LPS responsive, only 21.5% were dependent on MyD88 expression, with MyD88-independent genes constituting 74.7% of the genetic response. This MyD88-independent gene expression was predominantly transcriptionally regulated, as it was unaffected by cycloheximide blockade of new protein synthesis. A previously undescribed group of LPS-regulated genes (3.8%), whose induction or repression was significantly greater in the absence of MyD88, was also identified by these studies. The regulation of these genes suggested that MyD88 could serve as a molecular brake, constraining gene activity in a subset of LPS-responsive genes. The findings generated with LPS stimulation were recapitulated by exposure of macrophages to live Escherichia coli. These expression-profiling studies redefine the current dogma of TLR-4 signaling and establish that MyD88, although essential for some of the best-characterized macrophage responses to LPS, is not required for the regulation of the majority of genes engaged by macrophage exposure to endotoxin or live bacteria.
DOI of Published Version
Physiol Genomics. 2004 Nov 17;19(3):319-30. Epub 2004 Sep 14. Link to article on publisher's site
Bjorkbacka, Harry; Fitzgerald, Katherine A.; Huet, Francois; Li, Xiaoman; Gregory, James A.; Lee, Melinda; Ordija, Christine M.; Dowley, Nicole E.; Golenbock, Douglas T.; and Freeman, Mason W., "The induction of macrophage gene expression by LPS predominantly utilizes Myd88-independent signaling cascades" (2004). Infectious Diseases and Immunology Publications and Presentations. 95.