p53-independent NOXA induction overcomes apoptotic resistance of malignant melanomas.
Once melanoma metastasizes, no effective treatment modalities prolong survival in most patients. This notorious refractoriness to therapy challenges investigators to identify agents that overcome melanoma resistance to apoptosis. Whereas many survival pathways contribute to the death-defying phenotype in melanoma, a defect in apoptotic machinery previously highlighted inactivation of Apaf-1, an apoptosome component engaged after mitochondrial damage. During studies involving Notch signaling in melanoma, we observed a gamma-secretase tripeptide inhibitor (GSI; z-Leu-Leu-Nle-CHO), selected from a group of compounds originally used in Alzheimer's disease, induced apoptosis in nine of nine melanoma lines. GSI only induced G2-M growth arrest (but not killing) in five of five normal melanocyte cultures tested. Effective killing of melanoma cells by GSI involved new protein synthesis and a mitochondrial-based pathway mediated by up-regulation of BH3-only members (Bim and NOXA). p53 activation was not necessary for up-regulation of NOXA in melanoma cells. Blocking GSI-induced NOXA using an antisense (but not control) oligonucleotide significantly reduced the apoptotic response. GSI also killed melanoma cell lines with low Apaf-1 levels. We conclude that GSI is highly effective in killing melanoma cells while sparing normal melanocytes. Direct enhancement of BH3-only proteins executes an apoptotic program overcoming resistance of this lethal tumor. Identification of a p53-independent apoptotic pathway in melanoma cells, including cells with low Apaf-1, bypasses an impediment to current cytotoxic therapy and provides new targets for future therapeutic trials involving chemoresistant tumors.
Qin
Jian-Zhong
JZ
Department of Pathology, Loyola University of Chicago Medical Center, Chicago, IL, USA.
Stennett
Lawrence
L
Bacon
Patricia
P
Bodner
Barbara
B
Hendrix
Mary J C
MJ
Seftor
Richard E B
RE
Seftor
Elisabeth A
EA
Margaryan
Naira V
NV
Pollock
Pamela M
PM
Curtis
Amy
A
Trent
Jeffrey M
JM
Bennett
Frank
F
Miele
Lucio
L
Nickoloff
Brian J
BJ
D017304:Annexin A5 / Q000494:pharmacology; D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D002455:Cell Division; D045744:Cell Line, Tumor; D002470:Cell Survival; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D016195:G2 Phase; D006801:Humans; D015151:Immunoblotting; D008544:Melanocytes / Q000378:metabolism; D008545:Melanoma / Q000473:pathology*; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D009362:Neoplasm Metastasis; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010641:Phenotype; D011506:Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D051880:Receptors, Notch; D015398:Signal Transduction; D013347:Subcellular Fractions; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism / Q000502:physiology*; D015854:Up-Regulation
C506592:APAF1 protein, human; D017304:Annexin A5; D053477:Apoptotic Protease-Activating Factor 1; D008565:Membrane Proteins; D016376:Oligonucleotides, Antisense; C498702:PMAIP1 protein, human; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D051880:Receptors, Notch; D016159:Tumor Suppressor Protein p53; D003513:Cycloheximide