Synergistic activation of RSK correlates with c-fos induction in MO7e cells stimulated with GM-CSF plus Steel factor.
Steel factor (SLF) plus GM-CSF induces proliferative synergy in factor-dependent cell line MO7e and hematopoietic progenitor cells. We previously reported ERK1/2 involvement in this synergy, but its downstream signaling molecules are not defined. Here, we investigated activation of the 90-kDa ribosomal S6 kinase (RSK) proteins by measuring the phosphorylation status and in vitro kinase activity in MO7e cells. Both GM-CSF and SLF induced activation of RSK, and the combined stimulation with these two cytokines induced synergistic and persistent activation of RSK. RSK activity was reduced by PI3 kinase inhibitor LY294002 or MEK1 inhibitor PD98059, suggesting that the ERK as well as the PI3 kinase pathways are involved in regulation of RSK activity. Sensitivities of RSK activity to inhibitory drugs correlated well with those of c-fos gene induction. Taken together, synergistic activation of RSK may contribute, at least in part, to the synergistic induction of c-fos after combined stimulation with GM-CSF plus SLF.
Lee
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Department of Microbiology/Immunology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
Broxmeyer
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D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D016762:Genes, fos / Q000235:genetics*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D019089:Stem Cell Factor / Q000494:pharmacology*; D013997:Time Factors; D015533:Transcriptional Activation
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger; D019893:Ribosomal Protein S6 Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D019089:Stem Cell Factor; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C116919:mitogen and stress-activated protein kinase 1; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one