Epidermal growth factor inhibition of c-Myc-mediated apoptosis through Akt and Erk involves Bcl-xL upregulation in mammary epithelial cells.
In earlier studies, we and others have established that activation of EGFR can promote survival in association with upregulation of Bcl-x(L). However, the mechanism responsible for upregulation of Bcl-x(L) is unknown. For the current studies we have chosen pro-apoptotic, c-Myc-overexpressing murine mammary epithelial cells (MMECs) derived from MMTV-c-Myc transgenic mouse tumors. We now demonstrate that EGFR activation promotes survival through Akt and Erk1/2. Blockade of EGFR kinase activity and the PI3-K/Akt and MEK/Erk pathways with pharmacological inhibitors resulted in a significant induction of cellular apoptosis, paralleled by a downregulation of both Akt and Erk1/2 proteins. Consistent with a survival-promoting role of Akt, we observed that constitutively activated Akt (Myr-Akt) inhibited apoptosis of pro-apoptotic, c-Myc-overexpressing cells following the inhibition of EGFR tyrosine kinase activity. In addressing possible downstream effectors of EGFR through activated Akt, we detected significant upregulation of Bcl-x(L) protein, suggesting this pro-survival protein is a target of Akt in MMECs. By using pharmacological inhibitors of PI3-K/Akt and MEK/Erk together with dominant-negative Akt and Erk1 we observed the decrease in Bcl-x(L) protein. Our findings may be of importance for understanding the emerging role of Bcl-x(L) as a potential marker of poor prognosis in breast cancer.
Ramljak
Danica
D
Department of Oncology, Lombardi Cancer Center, Georgetown University, Washington, DC 20057, USA. ramljakd@georgetown.edu
Coticchia
Christine M
CM
Nishanian
Tagvor G
TG
Saji
Motoyasu
M
Ringel
Matthew D
MD
Conzen
Suzanne D
SD
Dickson
Robert B
RB
D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D002070:Butadienes / Q000494:pharmacology; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000187:drug effects / Q000494:pharmacology*; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000187:drug effects; D009025:Morpholines / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000502:physiology; D016271:Proto-Oncogene Proteins c-myc / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology; D015854:Up-Regulation; D051020:bcl-X Protein
C494812:Bcl2l1 protein, mouse; D002070:Butadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D009570:Nitriles; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D011799:Quinazolines; C113580:U 0126; D051020:bcl-X Protein; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D004815:Epidermal Growth Factor; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; C088860:4-((3-bromophenyl)amino)-6,7-dimethoxyquinazoline