HISTAMINE ANTAGONIZES SEROTONIN AND GROWTH FACTOR-INDUCED MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVATION IN BOVINE TRACHEAL SMOOTH-MUSCLE CELLS

We examined the effects of the bronchoconstrictor agonists serotonin ( 5-hydroxytryptamine; 5-HT) and histamine on mitogen-activated protein (MAP) kinase activation in cultured bovine tracheal myocytes, Kinase r enaturation assays demonstrated activation of the 42-and 44-kDa MAP ki nases within 2 min of 5-HT exposure, MAP kinase activation was mimicke d by alpha-methyl-5-HT and reduced by pretreatment with either phorbol 12,13-dibutyrate or forskolin, suggesting activation of the 5-HT, rec eptor, protein kinase C, and Raf-1, respectively, Raf-1 activation was confirmed by measurement of Raf-1 activity, and the requirement of Ra f-1 for 5-HT-induced MAP binase activation was demonstrated by transie nt transfection of cells with a dominant-negative allele of Raf-1, His tamine pretreatment significantly inhibited 5-HT and insulin-derived g rowth factor-1-induced MAP kinase activation, Attenuation of MAP kinas e activation was reversed by cimetidine, mimicked by forskolin, and ac companied by cAMP accumulation and inhibition of Raf-1, suggesting act ivation of the H-2 receptor and cAMP-dependent protein kinase A. Howev er, histamine treatment inhibited Raf-1 but not MAP kinase activation following treatment with either platelet-derived growth factor or epid ermal growth factor, implying a Raf-1-independent MAP kinase activatio n pathway, In summary, our data suggest a model whereby 5-HT activates MAP kinase via a protein kinase C/Raf-1 pathway, and histamine attenu ates MAP kinase activation by serotonin via activation of cAMP-depende nt protein kinase A and inhibition of Raf-1.