title: Mycobacterium paratuberculosis, Mycobacterium smegmatis, and lipopolysaccharide induce different transcriptional and post-transcriptional regulation of the IRG1 gene in murine macrophages.
abstract: Mycobacterium avium subspecies paratuberculosis (MAP) causes a chronic enteritis in ruminants. In addition, MAP is presently the most favored pathogen linked to Crohn's disease. In this study, we were interested in dissecting the molecular mechanisms of macrophage activation or deactivation after infection with MAP. By subtractive hybridization of cDNAs, we identified the immune-responsive gene 1 (IRG1), which was expressed substantially higher in lipopolysaccharide (LPS)-stimulated than in MAP-infected murine macrophage cell lines. A nuclear run-on transcription assay revealed that the IRG1 gene was activated transcriptionally in LPS-stimulated and MAP-infected macrophages with higher expression in LPS-stimulated cells. Analysis of post-transcriptional regulation demonstrated that IRG1 mRNA stability was increased in LPS-stimulated but not in MAP-infected macrophages. Furthermore, IRG1 gene expression of macrophages infected with the nonpathogenic Mycobacterium smegmatis differed from those of LPS-stimulated and MAP-infected macrophages. At 2 h postinfection, M. smegmatis-induced IRG1 gene expression was as low as in MAP-infected, and 8 h postinfection, it increased nearly to the level in LPS-stimulated macrophages. Transient transfection experiments revealed similar IRG1 promoter activities in MAP- and M. smegmatis-infected cells. Northern analysis demonstrated increased IRG1 mRNA stability in M. smegmatis-infected macrophages. IRG1 mRNA stabilization was p38 mitogen-activated protein kinase-independent. Inhibition of protein synthesis revealed that constitutively expressed factors seemed to be responsible for IRG1 mRNA destabilization. Thus, our data demonstrate that transcriptional and post-transcriptional mechanisms are responsible for a differential IRG1 gene expression in murine macrophages treated with LPS, MAP, and M. smegmatis.
authors.affiliation: Institut fuer Mikrobiologie, Zentrum fuer Infektionsmedizin, Stiftung Tieraerztliche Hochschule Hannover, Bischofsholer Damm 15, 30173 Hannover, Germany.
authors.forename: Tina
authors.initials: T
authors.lastname: Basler
authors.forename: Sabine
authors.initials: S
authors.lastname: Jeckstadt
authors.forename: Peter
authors.initials: P
authors.lastname: Valentin-Weigand
authors.forename: Ralph
authors.initials: R
authors.lastname: Goethe
mesh_terms: D000818:Animals; D002460:Cell Line; D003424:Crohn Disease / Q000235:genetics / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000378:metabolism / Q000382:microbiology / Q000503:physiopathology; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D006836:Hydro-Lyases / Q000235:genetics*; D018836:Inflammation Mediators / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism* / Q000382:microbiology*; D051379:Mice; D009161:Mycobacterium / Q000235:genetics* / Q000378:metabolism; D009164:Mycobacterium Infections / Q000235:genetics / Q000378:metabolism; D016927:Mycobacterium avium subsp. paratuberculosis / Q000235:genetics / Q000378:metabolism; D020102:Mycobacterium smegmatis / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D012323:RNA Processing, Post-Transcriptional / Q000235:genetics*; D020871:RNA Stability / Q000235:genetics; D050436:Regulatory Elements, Transcriptional / Q000235:genetics*; D013997:Time Factors; D015533:Transcriptional Activation / Q000235:genetics; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D048051:p38 Mitogen-Activated Protein Kinases; D006836:Hydro-Lyases; C487648:Acod1 protein, mouse