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.
Shelton
John G
JG
Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27858, USA.
Blalock
William L
WL
White
Edmond R
ER
Steelman
Linda S
LS
McCubrey
James A
JA
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