title: The intracellular signal transduction mechanism of interleukin 5 in eosinophils: the involvement of lyn tyrosine kinase and the Ras-Raf-1-MEK-microtubule-associated protein kinase pathway.
abstract: Interleukin 5 (IL-5) regulates the growth and function of eosinophils. The objective of this study was to investigate the intracellular signal transduction mechanism of IL-5 in eosinophils. Purified eosinophils were stimulated with IL-5, and the involvement of various kinases was investigated by immunoblotting, immune complex kinase assay, and in situ denatured/renatured kinase assay. We found that IL-5 induced tyrosine phosphorylation and activation of a number of kinases. Two species of lyn kinases (53 and 56 kD) were present in eosinophils. Both forms were Tyr-phosphorylated and activated rapidly within 1 min. Further, lyn kinase was physically associated with the IL-5 beta receptor in eosinophils. Ras was studied by immunoprecipitation followed by thin-layer chromatography. Ras bound higher quantities of [alpha-32P]guanosine 5'triphosphate upon stimulation with IL-5. Raf-1 kinase showed increased Tyr phosphorylation on immunoblotting and increased activity in the immune complex kinase assay. Two species of MEK (MAP or Erk kinase) (41 and 45 kD) were identified in eosinophils, which underwent autophosphorylation upon stimulation. Microtubule-associated protein (MAP) kinase (p44) was Tyr-phosphorylated on immunoblotting and had increased activity in the immune-complex kinase assay. MAP kinases were also studied after metabolic radiolabeling of the cells with [32P]orthophosphates. IL-5 stimulated phosphorylation of MAP kinases in situ. Thus, we have delineated major components of an important signaling pathway in eosinophils. We believe that one of the signals generated by IL-5 receptor activation is propagated through the lyn-Ras-Raf-1-MEK-MAP kinase pathway.
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston 77555-0762, USA.
authors.forename: K
authors.initials: K
authors.lastname: Pazdrak
authors.forename: D
authors.initials: D
authors.lastname: Schreiber
authors.forename: P
authors.initials: P
authors.lastname: Forsythe
authors.forename: L
authors.initials: L
authors.lastname: Justement
authors.forename: R
authors.initials: R
authors.lastname: Alam
mesh_terms: D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology*; D004804:Eosinophils / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D015848:Interleukin-5 / Q000494:pharmacology*; D048728:MAP Kinase Kinase Kinase 1; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf; D015398:Signal Transduction / Q000187:drug effects*; D018631:ras Proteins / Q000502:physiology; D019061:src-Family Kinases
chemical_list: D015848:Interleukin-5; D011518:Proto-Oncogene Proteins; D011505:Protein-Tyrosine Kinases; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; D018631:ras Proteins