Ability of the activated PI3K/Akt oncoproteins to synergize with MEK1 and induce cell cycle progression and abrogate the cytokine-dependence of hematopoietic cells.
Multiple signal transduction pathways, including the Raf/MEK/ERK and PI3K/Akt kinase cascades, play critical roles in transducing growth signals from activated cell surface receptors. Using conditionally and constitutively-active forms of MEK1 and either PI3K or Akt, we demonstrate synergy between these kinases in relieving cytokine-dependence of the FDC-P1 hematopoietic cell line. Cytokine-independent cells were obtained from DeltaMEK1:ER-infected cells at a frequency of 5 x 10(-5) indicating that low frequency of cells expressing beta-estradiol-regulated DeltaMEK1:ER became factor-independent, while activated PI3K or Akt by themselves did not relieve cytokine-dependence. In contrast, cytokine-independent cells were recovered approximately 25 to 250-fold more frequently from DeltaMEK1:ER infected cells also infected with either activated PI3K or Akt. MEK/PI3K and MEK/Akt-responsive cells could be maintained long-term as long as either beta-estradiol or the estrogen receptor antagonist 4-hydroxy-tamoxifen (4HT) were provided. The MEK/PI3K/Akt responsive cells were sensitive to both MEK and PI3K/Akt/p70S6K inhibitors. Synergy was observed when inhibitors which targeted both pathways were added together. These results indicate that there is synergy between the Raf/MEK/ERK and PI3K/Akt pathways in terms of abrogation of cytokine-dependence of hematopoietic cells. Likewise, suppression of multiple signal transduction pathways is a more effective means to inhibit cell cycle progression and induce apoptosis in leukemic cells.
Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27858, USA.
John G
JG
Shelton
William L
WL
Blalock
Edmond R
ER
White
Linda S
LS
Steelman
James A
JA
McCubrey
D000818:Animals; D017304:Annexin A5 / Q000494:pharmacology; D017209:Apoptosis; D002453:Cell Cycle; D002455:Cell Division; D002460:Cell Line; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D004396:Coloring Agents / Q000494:pharmacology; D016207:Cytokines / Q000096:biosynthesis / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D007377:Interleukin-3 / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors; D012190:Retroviridae / Q000235:genetics; D015398:Signal Transduction; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000378:metabolism
D017304:Annexin A5; D004396:Coloring Agents; D016207:Cytokines; D004247:DNA; D004791:Enzyme Inhibitors; D004958:Estradiol; D007377:Interleukin-3; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D011960:Receptors, Estrogen; D013629:Tamoxifen; C016601:afimoxifene; C482127:Map2k1 protein, mouse