Reduced transcript stabilization restricts TNF-alpha expression in RAW264.7 macrophages infected with pathogenic mycobacteria: evidence for an involvement of lipomannan.
Despite the critical role that TNF-alpha plays in the containment of mycobacterial infection, the mechanisms involved in regulation of its expression by mycobacteria are poorly defined. We addressed this question by studying MAP, which causes a chronic enteritis in ruminants and is linked to human Crohn's disease. We found that in MAP infected macrophages, TNF-alpha gene expression was substantially lower than in macrophages infected with nonpathogenic MS or stimulated with LPS. TNF-alpha transcriptional one could not fully explain the differential TNF-alpha mRNA expression, suggesting that there must be a substantial contribution by post-transcriptional mechanisms.Accordingly, we found reduced TNF-alpha mRNA stability in MAP-infected macrophages. Further comparison of MAP- and MS-infected macrophages revealed that lower TNF-alpha mRNA stability combined with lower mRNA and protein expression in MAP-infected macrophages correlated with lower p38 MAPK phosphorylation. These findings were independent of viability of MAP and MS. We demonstrate that the major mycobacterial cell-wall lipoglycan LM of MAP and MS induced TNF-alpha mRNA transcription,but only the MS-LM induced p38 MAPK-dependent transcript stabilization. Overall, our data suggest that pathogenic mycobacteria cause weak p38 and TNF-alpha mRNA stabilization as a result of their structural cell-wall components such as LM and thereby, restrict TNF-alpha expression in macrophages.
Institut fur Mikrobiologie, Stiftung Tierarztliche Hochschule Hannover, Hannover, Germany.
Tina
T
Basler
Helmut
H
Holtmann
Jens
J
Abel
Torsten
T
Eckstein
Wolfgang
W
Baumer
Peter
P
Valentin-Weigand
Ralph
R
Goethe
D000818:Animals; D002460:Cell Line / Q000378:metabolism / Q000382:microbiology; D002473:Cell Wall / Q000737:chemistry; D004789:Enzyme Activation; D015964:Gene Expression Regulation, Bacterial; D008070:Lipopolysaccharides / Q000502:physiology*; D008264:Macrophages / Q000378:metabolism / Q000382:microbiology*; D051379:Mice; D016927:Mycobacterium avium subsp. paratuberculosis / Q000737:chemistry / Q000472:pathogenicity / Q000502:physiology*; D020102:Mycobacterium smegmatis / Q000737:chemistry / Q000472:pathogenicity; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism; D013045:Species Specificity; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000235:genetics*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D008070:Lipopolysaccharides; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; C064351:lipomannan; D048051:p38 Mitogen-Activated Protein Kinases