title: BRAF-induced tumorigenesis is IKKα-dependent but NF-κB-independent.
abstract: KRAS mutations contribute to cell proliferation and survival in numerous cancers, including colorectal cancers (CRC). One pathway through which mutant KRAS acts is an inflammatory pathway that involves the kinase IKK and activates the transcription factor NF-κB. BRAF, a kinase that is downstream of KRAS, is mutated in a subset of CRC and is predictive of poor prognosis and therapeutic resistance. We found that, in contrast to mutant KRAS, mutant BRAF (BRAF(V600E)) did not trigger NF-κB activation but instead triggered the phosphorylation of a proteolytic fragment of IKKα (p45-IKKα) in CRC cells. BRAF(V600E) CRC cells had a high abundance of phosphorylated p45-IKKα, which was decreased by a RAF inhibitor. However, the abundance and DNA binding of NF-κB in these cells were unaffected by the RAF inhibitor, and expression of BRAF(V600E) in human embryonic kidney-293T cells did not activate an NF-κB reporter. Moreover, BRAF-induced transformation of NIH-3T3 cells and BRAF-dependent transcription required phosphorylation of p45-IKKα. The kinase TAK1, which was associated with the endosomal compartment, phosphorylated p45-IKKα. Inhibition of endosomal vacuolar adenosine triphosphatase (V-ATPase) with chloroquine or bafilomycin A1 blocked p45-IKKα phosphorylation and induced apoptosis in BRAF-mutant CRC cells independent of autophagy. Treating mice with V-ATPase inhibitors reduced the growth and metastasis of BRAF(V600E) xenograft tumors in the cecum of mice.
authors.affiliation: Institut Hospital del Mar d'Investigacions Mèdiques (IMIM), Parc de Recerca Biomèdica de Barcelona, Barcelona 08003, Spain.
authors.forename: Pol
authors.initials: P
authors.lastname: Margalef
authors.affiliation: Institut Hospital del Mar d'Investigacions Mèdiques (IMIM), Parc de Recerca Biomèdica de Barcelona, Barcelona 08003, Spain.
authors.forename: Carlota
authors.initials: C
authors.lastname: Colomer
authors.affiliation: Laboratori de Recerca Translacional, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), Institut Català d'Oncologia, Gran Via km 2.7, Hospitalet, Barcelona 08907, Spain.
authors.forename: Alberto
authors.initials: A
authors.lastname: Villanueva
authors.affiliation: Department of Oncology, IMIM, Universitat Pompeu Fabra, Barcelona 08003, Spain.
authors.forename: Clara
authors.initials: C
authors.lastname: Montagut
authors.affiliation: Department of Pathology, IMIM, Barcelona 08003, Spain.
authors.forename: Mar
authors.initials: M
authors.lastname: Iglesias
authors.affiliation: Department of Pathology, IMIM, Barcelona 08003, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Bellosillo
authors.affiliation: Department of Oncology, Hospital de Bellvitge, Hospitalet, Barcelona 08907, Spain.
authors.forename: Ramón
authors.initials: R
authors.lastname: Salazar
authors.affiliation: Laboratori de Recerca Translacional, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), Institut Català d'Oncologia, Gran Via km 2.7, Hospitalet, Barcelona 08907, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Martínez-Iniesta
authors.affiliation: Institut Hospital del Mar d'Investigacions Mèdiques (IMIM), Parc de Recerca Biomèdica de Barcelona, Barcelona 08003, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Bigas
authors.affiliation: Institut Hospital del Mar d'Investigacions Mèdiques (IMIM), Parc de Recerca Biomèdica de Barcelona, Barcelona 08003, Spain. lespinosa@imim.es.
authors.forename: Lluís
authors.initials: L
authors.lastname: Espinosa
mesh_terms: D000818:Animals; D017209:Apoptosis; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D002471:Cell Transformation, Neoplastic; D002738:Chloroquine / Q000737:chemistry; D004247:DNA / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D011992:Endosomes / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism*; D007249:Inflammation; D018942:Macrolides / Q000737:chemistry; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D052002:NF-kappa B p50 Subunit / Q000378:metabolism*; D041681:NIH 3T3 Cells; D009362:Neoplasm Metastasis; D009368:Neoplasm Transplantation; D010766:Phosphorylation; D011379:Prognosis; D048493:Proto-Oncogene Proteins B-raf / Q000378:metabolism*
chemical_list: D018942:Macrolides; D052002:NF-kappa B p50 Subunit; C489548:NFKB1 protein, human; C057620:bafilomycin A; C073701:Nfkb1 protein, mouse; D002738:Chloroquine; D004247:DNA; C482119:BRAF protein, human; C482120:Braf protein, mouse; D048493:Proto-Oncogene Proteins B-raf; C496559:CHUK protein, human; C496564:Chuk protein, mouse; D051550:I-kappa B Kinase