Oncogenic BRAF(V600E) inhibits BIM expression to promote melanoma cell survival.
Somatic activating mutations of BRAF are the earliest and most common genetic abnormality detected in the genesis of human melanoma. However, the mechanism(s) by which activated BRAF promotes melanoma cell cycle progression and/or survival remain unclear. Here we demonstrate that expression of BIM, a pro-apoptotic member of the BCL-2 family, is inhibited by BRAF-->MEK-->ERK signaling in mouse and human melanocytes and in human melanoma cells. Trophic factor deprivation of melanocytes leads to elevated BIM expression. However, re-addition of trophic factors or activation of a conditional form of BRAF(V600E) leads to rapid inhibition of BIM expression. In both cases, inhibition of BIM expression was dependent on the activity of MEK1/2 and the proteasome. Consistent with these observations, pharmacological inhibition of BRAF(V600E) or MEK1/2 in human melanoma cells (using PLX4720 and CI-1040 respectively) led to a striking elevation of BIM expression. Re-activation of BRAF-->MEK-->ERK signaling led to phosphorylation of BIM-EL on serine 69 and its subsequent degradation. Interestingly, endogenous expression of BIM in melanoma cells was insufficient to induce apoptosis unless combined with serum deprivation. Under these circumstances, inhibition of BIM expression by RNA interference provided partial protection from apoptosis. These data suggest that regulation of BIM expression by BRAF-->MEK-->ERK signaling is one mechanism by which oncogenic BRAF(V600E) can influence the aberrant physiology of melanoma cells.
Cartlidge
Robert A
RA
Cancer Research Institute and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, Helen Diller Family Comprehensive Cancer Center, San Francisco, CA, USA.
Thomas
G R
GR
Cagnol
Sebastien
S
Jong
Kimberly A
KA
Molton
Sarah A
SA
Finch
Andrew J
AJ
McMahon
Martin
M
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D045744:Cell Line, Tumor; D002470:Cell Survival; D016895:Culture Media, Serum-Free; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D017354:Point Mutation; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D015398:Signal Transduction / Q000502:physiology; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology*
D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D016895:Culture Media, Serum-Free; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2