Downregulation of the PI3K/Akt survival pathway in cells with deregulated expression of c-Myc.
Oncogenic transformation leads to an increased sensitivity to apoptosis, a characteristic that is selectively lost during tumor progression. The sensitization process affects the mitochondrial pathway of apoptosis through signaling events that are poorly defined. We previously showed that a deregulated expression of c-Myc in cells treated with toxic agents caused an enhanced activation of p38 that acts in a death-promoting pathway. Here, we show that deregulated expression of c-Myc causes a severe reduction in the basal activity of Akt, which was further accelerated by serum deprivation. Furthermore, c-Myc expression repressed the activation of Akt induced by the toxic agents doxorubicin, cisplatin and H(2)O(2), and also by the physiological agonists PDGF and insulin. We determined that the activation of Akt was inhibited as a result of the action of c-Myc upstream of phosphatidylinositol 3-kinase (PI3K) activation. c-Myc overexpression impaired the induced association of the p85 subunit of PI3K with phosphotyrosine containing proteins, causing a reduction in the activation of PI3K and recruitment of Akt to the membrane. Inhibiting Akt in addition to enhancing p38 further exacerbate the imbalance between the death and survival signals and results in an enhanced sensitivity to apoptosis.
Bellmann
Kerstin
K
Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, 9 rue McMahon, Québec, Canada, G1R 2J6. kerstin.bellmann@crhdq.ulaval.ca
Martel
Julie
J
Poirier
Dominic J P
DJ
Labrie
Mireille M
MM
Landry
Jacques
J
D000818:Animals; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D002945:Cisplatin / Q000494:pharmacology; D015536:Down-Regulation; D004317:Doxorubicin / Q000494:pharmacology; D005786:Gene Expression Regulation; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis / Q000235:genetics*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis / Q000235:genetics*; D051381:Rats; D013629:Tamoxifen / Q000031:analogs & derivatives / Q000494:pharmacology; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology
D002867:Chromones; D007328:Insulin; D009025:Morpholines; D010982:Platelet-Derived Growth Factor; D016271:Proto-Oncogene Proteins c-myc; D013629:Tamoxifen; C016601:afimoxifene; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D004317:Doxorubicin; D006861:Hydrogen Peroxide; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases; D002945:Cisplatin