ABSTRACT
Activating mutations in BRAF are found in 50% of melanomas and although treatment with BRAF inhibitors (BRAFi) is effective, resistance often develops. We now show that recently discovered NRAS isoform 2 is up-regulated in the setting of BRAF inhibitor resistance in melanoma, in both cell lines and patient tumor tissues. When isoform 2 was overexpressed in BRAF mutant melanoma cell lines, melanoma cell proliferation and in vivo tumor growth were significantly increased in the presence of BRAFi treatment. shRNA-mediated knockdown of isoform 2 in BRAFi resistant cells restored sensitivity to BRAFi compared with controls. Signaling analysis indicated decreased mitogen-activated protein kinase (MAPK) pathway signaling and increased phosphoinositol-3-kinase (PI3K) pathway signaling in isoform 2 overexpressing cells compared with isoform 1 overexpressing cells. Immunoprecipitation of isoform 2 validated a binding affinity of this isoform to both PI3K and BRAF/RAF1. The addition of an AKT inhibitor to BRAFi treatment resulted in a partial restoration of BRAFi sensitivity in cells expressing high levels of isoform 2. NRAS isoform 2 may contribute to resistance to BRAFi by facilitating PI3K pathway activation.
Subject(s)
GTP Phosphohydrolases/genetics , Melanoma/drug therapy , Melanoma/genetics , Membrane Proteins/genetics , Proto-Oncogene Proteins B-raf/antagonists & inhibitors , Skin Neoplasms/drug therapy , Skin Neoplasms/genetics , Antineoplastic Agents/therapeutic use , Cell Line, Tumor , Cell Movement , Drug Resistance, Neoplasm/genetics , GTP Phosphohydrolases/antagonists & inhibitors , GTP Phosphohydrolases/metabolism , Gene Knockdown Techniques , Humans , Indoles/therapeutic use , MAP Kinase Signaling System/drug effects , MAP Kinase Signaling System/genetics , Melanoma/metabolism , Membrane Proteins/antagonists & inhibitors , Membrane Proteins/metabolism , Mutation , Phosphatidylinositol 3-Kinases/metabolism , Protein Isoforms/genetics , Proto-Oncogene Proteins B-raf/genetics , Proto-Oncogene Proteins c-akt/antagonists & inhibitors , Proto-Oncogene Proteins c-akt/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Neoplasm/genetics , RNA, Neoplasm/metabolism , Skin Neoplasms/metabolism , Sulfonamides/therapeutic use , Up-Regulation , VemurafenibABSTRACT
UNLABELLED: Chromosomal aberrations and multiple genome-wide association studies (GWAS) have established a major hematopoietic quantitative trait locus in chromosome 6q23.3. The locus comprises an active enhancer region, in which some of the associated SNPs alter transcription factor binding. We now identify miR-3662 as a new functional driver contributing to the associated phenotypes. The GWAS SNPs are strongly associated with higher miR-3662 expression. Genome editing of rs66650371, a three-base-pair deletion, suggests a functional link between the SNP genotype and the abundance of miR-3662. Increasing miR-3662's abundance increases colony formation in hematopoietic progenitor cells, particularly the erythroid lineage. In contrast, miR-3662 is not expressed in acute myeloid leukemia cells, and its overexpression has potent antileukemic effects in vitro and in vivo Mechanistically, miR-3662 directly targets NF-κB-mediated transcription. Thus, miR-3662 is a new player of the hematopoietic 6q23.3 locus. SIGNIFICANCE: The characterization of miR-3662 has identified a new actor in the prominent hematopoietic quantitative trait locus in chromosome 6q23.3. The mechanistic insights into miR-3662's function may reveal novel or only partially known pathways for normal and malignant hematopoietic cell proliferation. Cancer Discov; 6(9); 1036-51. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 932.
