title: BRAF silencing by short hairpin RNA or chemical blockade by PLX4032 leads to different responses in melanoma and thyroid carcinoma cells.
abstract: BRAF-activating mutations have been reported in several types of cancer, including melanoma ( approximately 70% of cases), thyroid (30-70%), ovarian (15-30%), and colorectal cancer (5-20%). Mutant BRAF has constitutive kinase activity and causes hyperactivation of the mitogen-activated protein kinase pathway. BRAF silencing induces regression of melanoma xenografts, indicating the essential role of BRAF for cell survival. We set up an inducible short hairpin RNA system to compare the role of oncogenic BRAF in thyroid carcinoma versus melanoma cells. Although BRAF knockdown led to apoptosis in the melanoma cell line A375, the anaplastic thyroid carcinoma cell ARO underwent growth arrest upon silencing, with little or no cell death. Reexpression of the thyroid differentiation marker, sodium iodide symporter, was induced after long-term silencing. The different outcome of BRAF down-regulation in the two cell lines was associated with an opposite regulation of p21(CIP1/WAF1) expression levels in response to the block of the BRAF mitogenic signal. These results were confirmed using a specific BRAF small-molecule inhibitor, PLX4032. Restoration of p21(CIP1/WAF1) expression rescued melanoma cells from death. Altogether, our data indicate that oncogenic BRAF inhibition can have a different effect on cell fate depending on the cellular type. Furthermore, we suggest that a BRAF-independent mechanism of cell survival exists in anaplastic thyroid cancer cells.
authors.affiliation: University of Milano-Bicocca, via Cadore 48, Monza, 20052 Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Sala
authors.forename: Luca
authors.initials: L
authors.lastname: Mologni
authors.forename: Silvia
authors.initials: S
authors.lastname: Truffa
authors.forename: Carlo
authors.initials: C
authors.lastname: Gaetano
authors.forename: Gideon E
authors.initials: GE
authors.lastname: Bollag
authors.forename: Carlo
authors.initials: C
authors.lastname: Gambacorti-Passerini
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D002277:Carcinoma / Q000188:drug therapy* / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D020128:Inhibitory Concentration 50; D008545:Melanoma / Q000188:drug therapy* / Q000378:metabolism*; D008954:Models, Biological; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics* / Q000378:metabolism*; D012313:RNA / Q000737:chemistry; D027981:Symporters / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D000099209:Sodium-Iodide Symporters
chemical_list: D000970:Antineoplastic Agents; D053148:Caspase 3; D050759:Cyclin-Dependent Kinase Inhibitor p21; D048493:Proto-Oncogene Proteins B-raf; D012313:RNA; D027981:Symporters; D000099209:Sodium-Iodide Symporters; C493956:CDKN1A protein, human; C482119:BRAF protein, human