Oncogenic BRAFV600E induces expression of neuronal differentiation marker MAP2 in melanoma cells by promoter demethylation and down-regulation of transcription repressor HES1.
MAP2 is a neuron-specific microtubule-associated protein that binds and stabilizes dendritic microtubules. Previously, we showed that MAP2 expression is (a) activated in cutaneous primary melanoma and (b) inversely associated with melanoma tumor progression. We also showed that ectopic expression of MAP2 in metastatic melanoma cells inhibits cell growth by inducing mitotic spindle defects and apoptosis. However, molecular mechanisms of regulation of MAP2 gene expression in melanoma are not understood. Here, we show that in melanoma cells MAP2 expression is induced by the demethylating agent 5-aza-2'-cytidine, and MAP2 promoter is progressively methylated during melanoma progression, indicating that epigenetic mechanisms are involved in silencing of MAP2 in melanoma. In support of this, methylation of MAP2 promoter DNA in vitro inhibits its activity. Because MAP2 promoter activity levels in melanoma cell lines also correlated with activating mutation in BRAF, a gene that is highly expressed in neurons, we hypothesized that BRAF signaling is involved in MAP2 expression. We show that hyperactivation of BRAF-MEK signaling activates MAP2 expression in melanoma cells by two independent mechanisms, promoter demethylation or down-regulation of neuronal transcription repressor HES1. Our data suggest that BRAF oncogene levels can regulate melanoma neuronal differentiation and tumor progression.
Maddodi
Nityanand
N
Department of Dermatology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA.
Bhat
Kumar M R
KM
Devi
Sulochana
S
Zhang
Su-Chun
SC
Setaluri
Vijayasaradhi
V
D019943:Amino Acid Substitution / Q000187:drug effects / Q000235:genetics; D000818:Animals; D001374:Azacitidine / Q000494:pharmacology; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics*; D015415:Biomarkers / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000187:drug effects / Q000235:genetics*; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008545:Melanoma / Q000201:enzymology / Q000235:genetics*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology; D011401:Promoter Regions, Genetic; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D020218:Response Elements / Q000235:genetics; D000072056:Transcription Factor HES-1; D014158:Transcription, Genetic / Q000187:drug effects
D001374:Azacitidine; D051792:Basic Helix-Loop-Helix Proteins; D015415:Biomarkers; D018398:Homeodomain Proteins; D008869:Microtubule-Associated Proteins; D020929:Mitogen-Activated Protein Kinase Kinases; D050505:Mutant Proteins; D048493:Proto-Oncogene Proteins B-raf; D000072056:Transcription Factor HES-1; C489788:MAP2 protein, human; C078493:HES1 protein, human; C482119:BRAF protein, human