Effects on proliferation and melanogenesis by inhibition of mutant BRAF and expression of wild-type INK4A in melanoma cells.
Activating BRAF mutations and loss of wild-type INK4A expression both occur at high frequencies in melanomas. Here, we present evidence that BRAF and INK4A have different effects on melanogenesis, a marker of melanocytic differentiation. Human melanoma cell line 624Mel harbors mutations in both BRAF and INK4A. The in vitro and in vivo growth of these cells was inhibited by either reduced expression of mutant BRAF using stable retroviral RNA interference (RNAi) or retrovirus-mediated stable expression of wild-type INK4A cDNA. Consistent with the observed growth inhibition, phosphorylation of S780 and S795 in pRB, both CDK4/6 targets, was suppressed in cells expressing either mutant BRAF RNAi or wild-type INK4A. Interestingly, melanoma cells expressing mutant BRAF RNAi had increased pigmentation, produced more mature melanosomes and melanin and expressed higher levels of tyrosinase and tyrosinase-related protein-1, whereas melanogenesis was not induced by wild-type INK4A. We found that the melanocyte lineage-specific master control protein microphthalmia-associated transcription factor was upregulated by inhibition of mutant BRAF, which may be the cause for the melanogenic effect of BRAF RNAi. The results suggest that, although both BRAF and INK4A lesions promote cell growth and tumor formation, mutant BRAF may also induce dedifferentiation in melanoma cells.
Rotolo
Sabrina
S
Department of Oncological Sciences, Mount Sinai School of Medicine, New York, NY 10029, USA.
Diotti
Raffaella
R
Gordon
Ronald E
RE
Qiao
Rui F
RF
Yao
Zhong
Z
Phelps
Robert G
RG
Dong
Jianli
J
D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D019070:Cell Lineage; D049109:Cell Proliferation; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000737:chemistry* / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D005822:Genetic Vectors; D006801:Humans; D015151:Immunoblotting; D019656:Loss of Heterozygosity; D008543:Melanins / Q000737:chemistry; D008544:Melanocytes / Q000166:cytology*; D008545:Melanoma / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D014442:Monophenol Monooxygenase / Q000378:metabolism; D009154:Mutation; D010088:Oxidoreductases / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D034622:RNA Interference; D012190:Retroviridae / Q000235:genetics; D012680:Sensitivity and Specificity; D015398:Signal Transduction; D015854:Up-Regulation
D019941:Cyclin-Dependent Kinase Inhibitor p16; D018076:DNA, Complementary; D008543:Melanins; D010088:Oxidoreductases; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf