title: BRAFV600E cooperates with PI3K signaling, independent of AKT, to regulate melanoma cell proliferation.
abstract: Mutationally activated BRAF(V600E) cooperates with PTEN silencing in the conversion of normal melanocytes to metastatic melanoma cells, but the mechanism underlying this cooperation is poorly understood. Here, the consequences of pharmacologic blockade of BRAF(V600E) or phosphoinositide 3-kinase (PI3K) signaling were explored using pathway-targeted inhibitors and a panel of human BRAF-mutated melanoma-derived cell lines. Blockade of BRAF(V600E) → MEK1/2 → ERK1/2 or class I PI3K inhibited melanoma proliferation, whereas inhibition of AKT had only modest effects, even in cells with mutated or amplified AKT. Although single-agent inhibition of either BRAF(V600E) or PI3K signaling elicited antiproliferative effects, combinatorial inhibition was more potent. Analysis of signaling downstream of BRAF(V600E) or PI3K revealed that these pathways cooperated to regulate protein synthesis through AKT-independent, mTOR complex 1 (mTORC1)-dependent effects on p70(S6K), ribosomal protein S6, and 4E-BP1 phosphorylation. Moreover, inhibition of mTORC1/2 inhibited cell proliferation as profoundly as single-agent inhibition of either BRAF(V600E) or PI3K signaling. These data reveal a mechanism by which BRAF(V600E) and PI3K signaling cooperate to regulate melanoma proliferation through AKT-independent effects on protein translation. Furthermore, this study provides a potential foundation for pathway-targeted combination therapy designed to enhance the therapeutic benefit to patients with melanoma that contain combined alterations in BRAF and PI3K signaling.
  
  
  CONCLUSIONS
  PI3K, but not AKT, represent potential targets for melanoma therapy.
authors.affiliation: Diller Cancer Research Building, MC-0128, 1450 Third Street, Room HD-365, University of California, San Francisco, CA 94158. mcmahon@cc.ucsf.edu.
authors.forename: Jillian M
authors.initials: JM
authors.lastname: Silva
authors.forename: Christina
authors.initials: C
authors.lastname: Bulman
authors.forename: Martin
authors.initials: M
authors.lastname: McMahon
mesh_terms: D048708:Cell Growth Processes / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000235:genetics; D006801:Humans; D008545:Melanoma / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D038601:Ribosomal Protein S6 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology
chemical_list: D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D048493:Proto-Oncogene Proteins B-raf; D051057:Proto-Oncogene Proteins c-akt; D038601:Ribosomal Protein S6; C482119:BRAF protein, human