title: Ras-dependent and -independent pathways target the mitogen-activated protein kinase network in macrophages.
abstract: Mitogen-activated protein kinases (MAPKs) are activated upon a variety of extracellular stimuli in different cells. In macrophages, colony-stimulating factor 1 (CSF-1) stimulates proliferation, while bacterial lipopolysaccharide (LPS) inhibits cell growth and causes differentiation and activation. Both CSF-1 and LPS rapidly activate the MAPK network and induce the phosphorylation of two distinct ternary complex factors (TCFs), TCF/Elk and TCF/SAP. CSF-1, but not LPS, stimulated the formation of p21ras. GTP complexes. Expression of a dominant negative ras mutant reduced, but did not abolish, CSF-1-mediated stimulation of MEK and MAPK. In contrast, activation of the MEK kinase Raf-1 was Ras independent. Treatment with the phosphatidylcholine-specific phospholipase C inhibitor D609 suppressed LPS-mediated, but not CSF-1-mediated, activation of Raf-1, MEK, and MAPK. Similarly, down-regulation or inhibition of protein kinase C blocked MEK and MAPK induction by LPS but not that by CSF-1. Phorbol 12-myristate 13-acetate pretreatment led to the sustained activation of the Raf-1 kinase but not that of MEK and MAPK. Thus, activated Raf-1 alone does not support MEK/MAPK activation in macrophages. Phosphorylation of TCF/Elk but not that of TCF/SAP was blocked by all treatments that interfered with MAPK activation, implying that TCF/SAP was targeted by a MAPK-independent pathway. Therefore, CSF-1 and LPS target the MAPK network by two alternative pathways, both of which induce Raf-1 activation. The mitogenic pathway depends on Ras activity, while the differentiation signal relies on protein kinase C and phosphatidylcholine-specific phospholipase C activation.
authors.affiliation: Department of Immunobiology, Fraunhofer Institute for Toxicology and Molecular Biology, Hannover Medical School, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Büscher
authors.forename: R A
authors.initials: RA
authors.lastname: Hipskind
authors.forename: S
authors.initials: S
authors.lastname: Krautwald
authors.forename: T
authors.initials: T
authors.lastname: Reimann
authors.forename: M
authors.initials: M
authors.lastname: Baccarini
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001952:Bridged-Ring Compounds / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000378:metabolism; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D048728:MAP Kinase Kinase Kinase 1; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D008264:Macrophages / Q000201:enzymology*; D008301:Maleimides / Q000494:pharmacology; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D008969:Molecular Sequence Data; D009636:Norbornanes; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D015398:Signal Transduction; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology; D014157:Transcription Factors; D010738:Type C Phospholipases / Q000378:metabolism; D050807:ets-Domain Protein Elk-1
chemical_list: D001952:Bridged-Ring Compounds; D004268:DNA-Binding Proteins; D007211:Indoles; D008070:Lipopolysaccharides; D008301:Maleimides; D009636:Norbornanes; D010455:Peptides; D011518:Proto-Oncogene Proteins; D013859:Thiocarbamates; D013871:Thiones; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; C489525:p62TCF protein, mouse; C046498:tricyclodecane-9-yl-xanthogenate; D016173:Macrophage Colony-Stimulating Factor; D006160:Guanosine Triphosphate; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; C482578:Map3k1 protein, mouse; D010738:Type C Phospholipases; D016283:Proto-Oncogene Proteins p21(ras); C088060:bisindolylmaleimide