Modulation of MEK activity during G‐CSF signaling alters proliferative versus differentiative balancing

• Published in: American journal of hematology Vol. 68; no. 2; pp. 99 - 105
• Main Authors: Baumann, Michael A., Paul, Cassandra C., Lemley‐Gillespie, Susan, Oyster, Marlo, Gomez‐Cambronero, Julian
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01-10-2001; Wiley-Liss
• Subjects: Biological and medical sciences; Cell Differentiation - drug effects; Cell differentiation, maturation, development, hematopoiesis; Cell Division - drug effects; Cell Line; Cell physiology; Enzyme Activation - drug effects; Enzyme Activation - physiology; Enzyme Inhibitors - pharmacology; Flavonoids - pharmacology; Fundamental and applied biological sciences. Psychology; Granulocyte Colony-Stimulating Factor - pharmacology; Granulocyte Colony-Stimulating Factor - physiology; G‐CSF receptor; Humans; Immunohistochemistry; Lactoferrin - drug effects; Lactoferrin - metabolism; MAP kinase; Mitogen-Activated Protein Kinase Kinases - antagonists & inhibitors; Mitogen-Activated Protein Kinase Kinases - metabolism; Mitogen-Activated Protein Kinase Kinases - physiology; Molecular and cellular biology; neutrophils; Neutrophils - cytology; Neutrophils - drug effects; Neutrophils - enzymology; signal transduction; Signal Transduction - drug effects; Signal Transduction - physiology; stem cells; Transfection; Human; Cell proliferation; Enzyme; Transferases; Stem cell; Cytokine; Granulocyte; Hematopoietic cell; Cell differentiation; Biological activity; Signal transduction; Granulocyte colony stimulating factor; Regulation(control); Polypeptide; Hematopoiesis; Protein kinase; Myelopoiesis; Neutrophil; Growth factor; Granulopoiesis
• ISSN: 0361-8609; 1096-8652
• DOI: 10.1002/ajh.1160

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. Am. J. Hematol. 68:99–105, 2001. Published 2001 Wiley‐Liss, Inc.