title: Active N-Ras and B-Raf inhibit anoikis by downregulating Bim expression in melanocytic cells.
abstract: B-Raf and N-Ras proteins are often activated in melanoma, yet their roles in producing inherent survival signals are not fully understood. In this study, we investigated how N-RAS(Q61K) and B-RAF(V600E) contribute to melanoma's resistance to apoptosis induced by detachment from the extracellular matrix (anoikis). We found that expression of constitutively active N-RAS(Q61K) and B-RAF(V600E) downregulated the proapoptotic Bim protein in an immortalized melanocyte cell line. Bim is one of the main proapoptotic mediators of anoikis. Western blot analysis showed that detachment increased Bim expression in melanocytes, and Annexin V staining indicated that detachment induced cell death significantly in melanocytes. Blocking Bim expression by using RNAi vectors or by expressing N-RAS(Q61K) significantly inhibited anoikis in melanocytes. In summary, this report indicates that N-RAS(Q61K) and B-RAF(V600E) contribute to melanoma's resistance to apoptosis in part by downregulating Bim expression, suggesting that Bim is a possible treatment target for overriding melanoma's inherent defenses against cell death.
authors.affiliation: Department of Dermatology, School of Medicine, University of Colorado Denver, Aurora, Colorado 80010, USA.
authors.forename: Nathaniel B
authors.initials: NB
authors.lastname: Goldstein
authors.forename: Widya U
authors.initials: WU
authors.lastname: Johannes
authors.forename: Agnessa V
authors.initials: AV
authors.lastname: Gadeliya
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Green
authors.forename: Mayumi
authors.initials: M
authors.lastname: Fujita
authors.forename: David A
authors.initials: DA
authors.lastname: Norris
authors.forename: Yiqun G
authors.initials: YG
authors.lastname: Shellman
mesh_terms: D023102:Anoikis / Q000502:physiology; D051017:Apoptosis Regulatory Proteins / Q000235:genetics*; D000072224:Bcl-2-Like Protein 11; D002461:Cell Line, Transformed; D015536:Down-Regulation / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D011905:Genes, ras / Q000502:physiology*; D006801:Humans; D008544:Melanocytes / Q000166:cytology / Q000502:physiology*; D008545:Melanoma / Q000473:pathology / Q000503:physiopathology*; D008565:Membrane Proteins / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics; D034622:RNA Interference; D012878:Skin Neoplasms / Q000473:pathology / Q000503:physiopathology*; D014162:Transfection
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; C491754:AKT3 protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D051057:Proto-Oncogene Proteins c-akt