Molecular crosstalk between p70S6k and MAPK cell signaling pathways

• Published in: Biochemical and biophysical research communications Vol. 293; no. 1; pp. 463 - 469
• Main Authors: Lehman, Jason A, Gomez-Cambronero, Julian
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 26.04.2002
• Subjects: Amino Acid Sequence; Cell Division - drug effects; Cell signaling; Chemotaxis; Chemotaxis, Leukocyte - drug effects; Chemotaxis, Leukocyte - physiology; Enzyme Inhibitors - pharmacology; Flavonoids - pharmacology; GM-CSF; Granulocyte Colony-Stimulating Factor - pharmacology; Granulocyte-Macrophage Colony-Stimulating Factor - pharmacology; Humans; MAP Kinase Signaling System - drug effects; MAP Kinase Signaling System - physiology; Neutrophils; Neutrophils - cytology; Neutrophils - drug effects; Neutrophils - physiology; p70S6K Ribosomal kinase; Phosphorylation; Receptor Cross-Talk - physiology; Recombinant Proteins; Ribosomal Protein S6 Kinases - metabolism; Ribosomes - physiology; Substrate Specificity; Tetradecanoylphorbol Acetate - pharmacology; p70S6K Ribosomal kinase; GM-CSF; Chemotaxis; Cell signaling; Neutrophils
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/S0006-291X(02)00238-3

We report here for the first time that the specific MAPK kinase (MEK) inhibitor, PD-98059, completely knocked out granulocyte-macrophage colony-stimulating factor (GM-CSF)-stimulated MAPK activity but also partially inactivated the ribosomal kinase p70S6K. Since a connection between the two major signaling pathways, Ras/MEK/MAPK and PI3-K/p70S6K was suspected, experiments were designed to prove a molecular crosstalk between those. First, p70S6K protein could be co-immunoprecipitated with anti-MAPK antibodies, MAPK protein was similarly present in anti-p70S6K immunoprecipitates, indicating close spatial proximity of both signaling molecules. Second, p70S6K enzymatic activity was found in anti-MAPK immunoprecipitates and MAPK in anti-p70S6K immunoprecipitates, being the latter activity higher in samples derived from GM-CSF-treated cells. Since an upstream activator of p70S6K, phosphatidylinositol (PI)3-kinase, has been associated to cell movement in phagocytic cells, we studied a possible participation of p70S6K in chemotaxis and whether MAPK had an input. Our data show that functional chemotaxis was inhibited by rapamycin, a specific p70S6K inhibitor, as well as by PD-98059. Thus, a connection between these two kinases extends from the molecular level to cell migration, a key functionality in non-proliferative, mature phagocytes such as neutrophils.