The phosphatidylinositide 3'-kinase/Akt survival pathway is a target for the anticancer and radiosensitizing agent PKC412, an inhibitor of protein kinase C.
Activation of the phosphatidylinositol 3'-kinase (PI3K)/Akt survival pathway protects against apoptotic stress stimuli. Therefore, compounds that down-regulate this pathway are of clinical interest for single and combined anticancer treatment modalities. Here we demonstrate that the cytotoxic effect of the protein kinase C (PKC)-inhibitor N-benzoylated staurosporine (PKC412) is mediated via the PI3K/Akt pathway. Dose-dependent down-regulation of the proliferative activity, activation of the apoptotic machinery, and cell killing by PKC412 (0-1 microM) in Rat1a-fibroblasts and H-ras-oncogene-transformed fibroblasts correlated with a decrease of Akt phosphorylation and a reduced phosphorylation of the endogenous Akt-substrate GSK3-alpha. Expression of the dominant-active myristoylated form of Akt abrogated this cytotoxic effect of PKC412. Experiments with Apaf-1-deficient cells revealed that PKC412-induced cytotoxicity depends on an intact apoptosome but that the decrease of Akt phosphorylation is not attributable to apoptosis execution. Comparative experiments indicate that PKC412 and the parent-compound staurosporine down-regulate this survival pathway upstream or at the level of Akt but by a different mechanism than the PI3K-inhibitor LY294002. Furthermore, inhibition of this pathway by PKC412 is relevant for sensitization to ionizing radiation. These results demonstrate the specific role of this signaling pathway for the PKC412-mediated down-regulation of an apoptotic threshold and its cytotoxicity.
Tenzer
A
A
Department of Radiation Oncology, University Hospital Zurich, CH-8091 Zurich, Switzerland.
Zingg
D
D
Rocha
S
S
Hemmings
B
B
Fabbro
D
D
Glanzmann
C
C
Schubiger
P A
PA
Bodis
S
S
Pruschy
M
M
D000818:Animals; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D002867:Chromones / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D011905:Genes, ras / Q000502:physiology; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D019311:Staurosporine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019311:Staurosporine; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; C494920:Akt1 protein, rat; C059539:midostaurin