title: Megakaryocytic differentiation induced by constitutive activation of mitogen-activated protein kinase kinase.
abstract: The K562 erythroleukemia cell line was used to study the molecular mechanisms regulating lineage commitment of hematopoietic stem cells. Phorbol esters, which initiate megakaryocyte differentiation in this cell line, caused a rapid increase in extracellular-signal-regulated kinase (ERK), which remained elevated for 2 h and returned to near-basal levels by 24 h. In the absence of extracellular stimuli, ERK could be activated by expression of constitutively active mutants of mitogen-activated protein (MAP) kinase kinase (MKK), resulting in cell adhesion and spreading, increased cell size, inhibition of cell growth, and induction of the platelet-specific integrin alphaIIb beta3, all hallmarks of megakaryocytic differentiation. In contrast, expression of wild-type MKK had little effect. In addition, constitutively active MKK suppressed the expression of an erythroid marker, alpha-globin, indicating the ability to suppress cellular responses necessary for alternative cell lineages. The MKK inhibitor PD98059 blocked MKK/ERK activation and cellular responses to phorbol ester, demonstrating that activation of MKK is necessary and sufficient to induce a differentiation program along the megakaryocyte lineage. Thus, the MAP kinase cascade, which promotes cell growth and proliferation in many cell types, instead inhibits cell proliferation and initiates lineage-specific differentiation in K562 cells, establishing a model system to investigate the mechanisms by which this signal transduction pathway specifies cell fate and developmental processes.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Whalen
authors.forename: S C
authors.initials: SC
authors.lastname: Galasinski
authors.forename: P S
authors.initials: PS
authors.lastname: Shapiro
authors.forename: T S
authors.initials: TS
authors.lastname: Nahreini
authors.forename: N G
authors.initials: NG
authors.lastname: Ahn
mesh_terms: D001483:Base Sequence; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D017931:DNA Primers / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D004920:Erythropoiesis / Q000502:physiology; D015870:Gene Expression; D005914:Globins / Q000235:genetics; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000201:enzymology / Q000473:pathology; D008533:Megakaryocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D020929:Mitogen-Activated Protein Kinase Kinases; D009154:Mutation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D017931:DNA Primers; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005914:Globins; D011494:Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D013755:Tetradecanoylphorbol Acetate