EGF-dependent cell cycle progression is controlled by density-dependent regulation of Akt activation.
The normal human breast epithelial cell line, MCF10A, was used to investigate the mechanism by which high-density inhibits EGF-dependent cell cycle progression. EGF-dependent Akt activation was found to be transient in high-density cells and sustained in low-density cells. High-density cells also showed decreased EGF receptor (EGFR) autophosphorylation, decreased retinoblastoma protein phosphorylation, and increased p27 protein expression. Although EGFR activation was decreased in the high-density cells, the activation was sufficient to stimulate EGFR substrates comparable to low-density cells. EGF-dependent activation of the Erk1/2 pathway and the upstream activators of Akt (Gab1, erbB3, PI3 kinase, and PDK1) showed no density dependency. Antagonists of Akt activity provided further evidence that regulation of Akt activation is the critical signal transduction step controlling EGF-dependent cell cycle progression. Both adenovirus-mediated expression of dominant-negative Akt and inhibition of PI3 kinase-mediated Akt activation with LY294002 blocked cell cycle progression of low-density cells. In summary, we report the novel finding that high-density blocks EGF-dependent cell cycle progression by inhibiting EGF signaling at the level of EGF-dependent Akt activation rather than at the level of EGFR activation.
LeVea
C M
CM
Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.
Reeder
J E
JE
Mooney
R A
RA
D002450:Cell Communication / Q000235:genetics; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D025461:Feedback, Physiological / Q000235:genetics; D005260:Female; D006801:Humans; D042361:Mammary Glands, Human / Q000166:cytology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D016160:Retinoblastoma Protein / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000378:metabolism
D018797:Cell Cycle Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; C494918:AKT1 protein, human