title: Tumor necrosis factor alpha rapidly activates the mitogen-activated protein kinase (MAPK) cascade in a MAPK kinase kinase-dependent, c-Raf-1-independent fashion in mouse macrophages.
abstract: Tumor necrosis factor alpha (TNF alpha) is bound by two cell surface receptors, CD120a (p55) and CD120b (p75), that belong to the TNF/nerve growth factor receptor family and whose signaling is initiated by receptor multimerization in the plane of the plasma membrane. The initial signaling events activated by receptor crosslinking are unknown, although activation of the mitogen-activated protein kinase (MAPK) cascade occurs shortly after ligand binding to CD120a. In this study, we investigated the upstream kinases that mediate the activation of the 42-kDa MAPK p42mapk/erk2 following crosslinking of CD120a in mouse macrophages. Exposure of mouse macrophages to TNF alpha stimulated a time-dependent increase in the activity of MAPK/ERK kinase (MEK) that temporally preceded peak activation of p42mapk/erk2. MEKs, dual-specificity threonine/tyrosine kinases, act as a convergence point for several signaling pathways including Ras/Raf, MEK kinase (MEKK), and Mos. Incubation of macrophages with TNF alpha was found to transiently stimulate a MEKK that peaked in activity within 30 sec of exposure and progressively declined toward basal levels by 5 min. By contrast, under these conditions, activation of either c-Raf-1 or Raf-B was not detected. These data suggest that the activation of the MAPK cascade in response to TNF alpha is mediated by the sequential activation of a MEKK and a MEK in a c-Raf-1- and Raf-B-independent fashion.
authors.affiliation: Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, CO 80206.
authors.forename: B W
authors.initials: BW
authors.lastname: Winston
authors.forename: C A
authors.initials: CA
authors.lastname: Lange-Carter
authors.forename: A M
authors.initials: AM
authors.lastname: Gardner
authors.forename: G L
authors.initials: GL
authors.lastname: Johnson
authors.forename: D W
authors.initials: DW
authors.lastname: Riches
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004789:Enzyme Activation; D048369:MAP Kinase Kinase 1; D048728:MAP Kinase Kinase Kinase 1; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008809:Mice, Inbred C3H; D020929:Mitogen-Activated Protein Kinase Kinases; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000502:physiology; D019908:Proto-Oncogene Proteins c-raf; D015398:Signal Transduction; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D011518:Proto-Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048728:MAP Kinase Kinase Kinase 1; C482578:Map3k1 protein, mouse; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases