Hemopoietic Growth Factors with the Exception of Interleukin-4 Activate the p38 Mitogen-activated Protein Kinase Pathway

Ian N Foltz,John C Lee,Peter R Young,John W Schrader

doi:10.1074/jbc.272.6.3296

Abstract

The mammalian mitogen-activated protein (MAP) kinase homologue p38 has been shown to be activated by pro-inflammatory cytokines as well as physical and chemical stresses. We now show that a variety of hemopoietic growth factors, including Steel locus factor, colony stimulating factor-1, granulocyte/macrophage-colony stimulating factor, and interleukin-3, activate p38 MAP kinase and the downstream kinase MAPKAP kinase-2. Furthermore, although these growth factors activate both p38 MAP kinase and Erk MAP kinases, we demonstrate using a specific inhibitor of p38 MAP kinase, SB 203580, that p38 MAP kinase activity was required for MAP kinase-activated protein kinase-2 activation. Conversely p38 MAP kinase was shown not to be required for in vivo activation of p90(rsk), known to be downstream of the Erk MAP kinases. Interleukin-4 was unique among the hemopoietic growth factors we examined in failing to induce activation of either p38 MAP kinase or MAP kinase-activated protein kinase-2. These findings demonstrate that the activation of p38 MAP kinase is involved not only in responses to stresses but also in signaling by growth factors that regulate the normal development and function of cells of the immune system.

Highlights

The p38 mitogen-activated protein (MAP)1 kinases (p38/ CSBP/RK) are mammalian homologues of the HOG-1 MAP kinase of Saccharomyces cerevisiae, necessary for their growth under hyperosmolar conditions (1–3). p38 MAP kinase is activated by physical and chemical stresses including UV irradiation, heat, and osmotic stress, as well as bacterial lipopolysaccharide, and the pro-inflammatory cytokines tumor necrosis factor-␣ and interleukin-1 (IL-1) (1, 2, 4, 5)
Similar results were obtained with two other hemopoietic growth factors, IL-3, which like GM-CSF acts through a hemopoietin receptor, and CSF-1, which like Steel locus factor (SLF) acts through a receptor with intrinsic tyrosine kinase activity
The anti-p38 MAP kinase antibody used for Western blotting, the anti-p90rsk antibody, and the truncated ATF-2 (1–96) were purchased from Santa Cruz Biotechnology (Santa Cruz, CA), the anti-phospho-p38 MAP kinasespecific antibody was from New England Biolabs (Beverly, MA), recombinant murine Hsp25 was from StressGen Biotechnologies (Victoria, BC, Canada), myelin basic protein (MBP) was from Sigma, and recombinant murine CSF-1 was from R & D Systems (Windsor, ON, Canada)

Summary

Introduction

The p38 mitogen-activated protein (MAP) kinases (p38/ CSBP/RK) are mammalian homologues of the HOG-1 MAP kinase of Saccharomyces cerevisiae, necessary for their growth under hyperosmolar conditions (1–3). p38 MAP kinase is activated by physical and chemical stresses including UV irradiation, heat, and osmotic stress, as well as bacterial lipopolysaccharide, and the pro-inflammatory cytokines tumor necrosis factor-␣ and interleukin-1 (IL-1) (1, 2, 4, 5). Our interest in p38 MAP kinase was prompted by our observation that a protein of Mr 38,000, which had a similar electrophoretic mobility and isoelectric point to p38 MAP kinase (3), was phosphorylated on tyrosine in primary mast cells stimulated with either of two hemopoietic growth factors, IL-3 or Steel locus factor (SLF) (21) These hemopoietic growth factors belong to a family of cytokines and hormones that are characterized by a four ␣-helix bundle three-dimensional structure (22). A minority of 4 ␣-helix bundle growth factors bind to conventional homodimeric protein-tyrosine kinase receptors, resembling the platelet-derived growth factor receptor (24) These include CSF-1, which stimulates the growth of cells of the macrophage lineage (24, 25), and SLF, which acts on pluripotent hemopoietic stem cells, the progenitors of a variety of hemopoietic lineages, mature mast cells, germ cells, and cells derived from the neural crest (25, 26). Our results demonstrate that p38 MAP kinase is activated by stress and by growth factors signaling through two distinct classes of receptors

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Conclusion