S6 kinase p90rsk in granulocyte-macrophage colony-stimulating factor-stimulated proliferative and mature hematopoietic cells.
The ribosomal S6 kinase p90(rsk) was studied in mature and proliferating hemopoietic cells in response to the human cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF). In neutrophils, GM-CSF induced time-dependent electrophoretic mobility shifts in immunoreactive p90(rsk). Although these shifts suggested changes in the phosphorylation status of the molecule, a kinase assay with whole cell lysates detected minimal (1.5-fold) increments in enzymatic activity. Only immunoprecipitation followed by immune complex kinase assay or in-gel kinase assay performed against the RSK substrate RRLSSLRA evidenced an increase in p90(rsk) activity (3.4-fold). p90(rsk) was also detected in the GM-CSF-dependent erythroleukemia cell line TF-1. Normally cultured, cytokine-supplemented cells did not respond to further GM-CSF stimulation. However, the activity of p90(rsk) in cytokine-starved cells increased dramatically in response to short term GM-CSF challenge. This effect was readily observable in total cell lysates (6.6-fold increase over controls) and was paralleled by changes in mitogen-activated protein kinase activity (a substrate of p90(rsk)). Thus, p90(rsk) is present in mature hemopoietic cells, but the extent of the enzymatic response to GM-CSF is significantly lower than that seen in proliferative cells.
Joseph
D E
DE
Department of Physiology, Wright State University School of Medicine, Dayton, Ohio 45435 USA.
Paul
C C
CC
Baumann
M A
MA
Gomez-Cambronero
J
J
D000595:Amino Acid Sequence; D001853:Bone Marrow / Q000201:enzymology*; D001854:Bone Marrow Cells; D002455:Cell Division; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D011489:Protein Denaturation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases; D014407:Tumor Cells, Cultured
D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases