title: Modulation of MEK activity during G-CSF signaling alters proliferative versus differentiative balancing.
abstract: Previous studies of the granulocyte colony stimulating factor (G-CSF) receptor have demonstrated that discrete signals direct proliferative and maturation signaling. Receptor deletion/mutant studies have shown that although activation of the ras-mitogen activated protein (MAP) kinase pathway is necessary for G-CSF directed proliferation, it is not necessary for maturation induced by this cytokine. We have assessed the effects of selective inhibition or overexpression of MAP kinase kinase (MEK) in a cell line model of G-CSF-induced neutrophil progenitor growth. Using the human G-CSF responsive MPD cell line, we specifically inhibited MEK using PD 98059 and also transfected MPD cells with a constitutively active MEK construct. We then exposed the cells to G-CSF and assessed the effects of MEK inhibition and forced expression on proliferation and differentiation. Inhibition of MEK followed by G-CSF stimulation consistently resulted in an early 2.5-fold increase in morphologically differentiated neutrophils expressing CD11b and CD16 and containing lactoferrin over that produced by G-CSF alone. MEK inhibition alone had little effect on the differentiation stage of these cells, although proliferation was impaired. Forced expression of activated MEK resulted in a three- to five-fold decrease in differentiated, lactoferrin containing neutrophilic cells resultant from G-CSF induction, and a commensurate increase in cell proliferation. These observations suggest that modulation of MAPK activation may be a control point for altering the balance between proliferation and differentiation in response to G-CSF. Physiologically, this control is likely exerted by costimulatory cytokines.
authors.affiliation: Research Service, Department of Veterans Affairs, Dayton, Ohio, USA. michael.baumann@wright.edu
authors.forename: M A
authors.initials: MA
authors.lastname: Baumann
authors.forename: C C
authors.initials: CC
authors.lastname: Paul
authors.forename: S
authors.initials: S
authors.lastname: Lemley-Gillespie
authors.forename: M
authors.initials: M
authors.lastname: Oyster
authors.forename: J
authors.initials: J
authors.lastname: Gomez-Cambronero
mesh_terms: D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology* / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D007781:Lactoferrin / Q000187:drug effects / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology*; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014162:Transfection
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D016179:Granulocyte Colony-Stimulating Factor; D020929:Mitogen-Activated Protein Kinase Kinases; D007781:Lactoferrin; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one