Lipopolysaccharide and Raf-1 kinase regulate secretory interleukin-1 receptor antagonist gene expression by mutually antagonistic mechanisms.
Lipopolysaccharide (LPS) treatment of monocytic cells has been shown to activate the Raf-1/mitogen-activated protein kinase (MAPK) signaling pathway and to increase secretory interleukin-1 receptor antagonist (sIL-1Ra) gene expression. The significance of the activation of the Raf-1/MAPK signaling pathway to LPS regulation of sIL-1Ra gene expression, however, has not been determined. This study addresses the role of the Raf-1/MAPK signaling pathway in regulation of sIL-1Ra gene expression by LPS. Cotransfection of the murine macrophage cell line RAW 264.7 with a 294-bp sIL-1Ra promoter/luciferase construct (pRA-294-luc) and a constitutively active Raf-1 kinase expression vector (pRSV-Raf-BXB) resulted in induction of sIL-1Ra promoter activity, indicating that Raf-1, like LPS, can regulate sIL-1Ra promoter activity. An in vitro MAPK analysis indicated that both LPS treatment and pRSV-Raf-BXB transfection of RAW 264.7 cells increases p42 MAPK activity. An in vitro Raf-1 kinase assay, however, failed to detect LPS-induced Raf-1 kinase activity in RAW 264.7 cells, suggesting that in RAW 264.7 cells, Raf-1 kinase is not an activating component of the LPS signaling pathway regulating MAPK activity or sIL-1Ra promoter activity. This observation was supported by results from transfection studies which demonstrated that expression of a dominant-inhibitory Raf-1 mutant in RAW 264.7 cells does not inhibit LPS-induced MAPK activity or sIL-1Ra promoter activity, indicating that LPS-induced sIL-1Ra promoter activation occurs independent of the Raf-1/MAPK signaling pathway. In additional studies, cotransfection of RAW 264.7 cells with pRA-294-luc and increasing amounts of pRSV-Raf-BXB caused a dose-dependent inhibition of LPS-induced sIL-1Ra promoter activity, indicating that the role of the Raf-1 pathway in the regulation of sIL-1Ra promoter activity by LPS is as an antagonizer. Interestingly, LPS treatment of RAW 264.7 cells, cotransfected with pRA-294-luc and pRSV-Raf-BXB, also inhibited pRSV-Raf-BXB-induced sIL-1Ra promoter activity, suggesting that inductions of sIL-1Ra promoter activity by LPS and Raf-1 actually occur by mutually antagonistic mechanisms. In support of this conclusion, sIL-1Ra promoter mapping studies indicated that LPS and Raf-1 responses localized to different regions of the sIL-1Ra promoter. Further studies demonstrated that mutual antagonism between the LPS and Raf-1 kinase pathways is not promoter specific, as the same phenomenon is observed in assays using a c-fos enhancer/thymidine kinase promoter/luciferase construct (pc-fos-TK81-luc). Additionally, mutual antagonism with regard to sIL-1Ra promoter activity also was observed between the LPS and MEK kinase pathways, indicating that mutual antagonism can occur in more than one MAPK activation pathway.
Guthridge
C J
CJ
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262, USA.
Eidlen
D
D
Arend
W P
WP
Gutierrez-Hartmann
A
A
Smith
M F
MF
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D005786:Gene Expression Regulation / Q000187:drug effects*; D053590:Interleukin 1 Receptor Antagonist Protein; D008070:Lipopolysaccharides / Q000494:pharmacology*; D048728:MAP Kinase Kinase Kinase 1; D008264:Macrophages; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011993:Recombinant Fusion Proteins; D012795:Sialoglycoproteins / Q000235:genetics*; D015398:Signal Transduction / Q000502:physiology; D014162:Transfection
C507764:Il1rn protein, mouse; D053590:Interleukin 1 Receptor Antagonist Protein; D008070:Lipopolysaccharides; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D012795:Sialoglycoproteins; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048728:MAP Kinase Kinase Kinase 1; C482578:Map3k1 protein, mouse