Induction of autophagy and inhibition of melanoma growth in vitro and in vivo by hyperactivation of oncogenic BRAF.
Activating mutations in NRAS and BRAF are found frequently in cutaneous melanomas. Because concurrent mutations of both BRAF and RAS are extremely rare, it is thought that transformation by RAS and BRAF occurs through a common mechanism. Also, there is evidence for a relationship of synthetic lethality between NRAS and BRAF oncogenes that leads to selection against cells with a hyperactive mitogen-activated protein kinase (MAPK) pathway. However, it is not known whether the hyperactivation of the MAPK pathway by overexpression of either oncogene alone could also inhibit melanoma tumorigenesis. Here, we show that in melanoma cells with oncogenic BRAF (mBRAF), high levels of mBRAF induce hyperactivation of ERK and senescence-like phenotype and trigger autophagy by inhibiting the mammalian target of rapamycin complex signaling. Growth inhibition and cell death caused by high mBRAF levels are partially rescued by downregulation of BRAF protein or inhibition of autophagy, but not by inhibition of the MAPK or apoptotic pathways. In nude mice, growth of mBRAF-overexpressing tumors is inhibited. Quantitative immunohistochemical analysis of human melanomas and cell lines showed a significant positive correlation between the levels of BRAF protein and autophagy marker light chain 3. Our data suggest that high oncogenic BRAF levels trigger autophagy, which may have a role in melanoma tumor progression.
Maddodi
Nityanand
N
Department of Dermatology, UW School of Medicine and Public Health, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA.
Huang
Wei
W
Havighurst
Thomas
T
Kim
KyungMann
K
Longley
B Jack
BJ
Setaluri
Vijayasaradhi
V
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D008297:Male; D008545:Melanoma / Q000473:pathology* / Q000503:physiopathology; D051379:Mice; D010957:Plasmids / Q000235:genetics / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D012878:Skin Neoplasms / Q000473:pathology* / Q000503:physiopathology; D058570:TOR Serine-Threonine Kinases; D023041:Xenograft Model Antitumor Assays
D047908:Intracellular Signaling Peptides and Proteins; C546842:MTOR protein, human; C546843:mTOR protein, mouse; C482119:BRAF protein, human; D017346:Protein Serine-Threonine Kinases; D048493:Proto-Oncogene Proteins B-raf; D058570:TOR Serine-Threonine Kinases