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.
Keywords:
BRAF; NRAS; melanoma; resistance; vemurafenib.
Publication types
-
Research Support, N.I.H., Extramural
MeSH terms
-
Antineoplastic Agents / therapeutic use
-
Cell Line, Tumor
-
Cell Movement
-
Drug Resistance, Neoplasm / genetics
-
GTP Phosphohydrolases / antagonists & inhibitors
-
GTP Phosphohydrolases / genetics*
-
GTP Phosphohydrolases / metabolism
-
Gene Knockdown Techniques
-
Humans
-
Indoles / therapeutic use
-
MAP Kinase Signaling System / drug effects
-
MAP Kinase Signaling System / genetics
-
Melanoma / drug therapy*
-
Melanoma / genetics*
-
Melanoma / metabolism
-
Membrane Proteins / antagonists & inhibitors
-
Membrane Proteins / genetics*
-
Membrane Proteins / metabolism
-
Mutation
-
Phosphatidylinositol 3-Kinases / metabolism
-
Protein Isoforms / genetics
-
Proto-Oncogene Proteins B-raf / antagonists & inhibitors*
-
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 / drug therapy*
-
Skin Neoplasms / genetics*
-
Skin Neoplasms / metabolism
-
Sulfonamides / therapeutic use
-
Up-Regulation
-
Vemurafenib
Substances
-
Antineoplastic Agents
-
Indoles
-
Membrane Proteins
-
Protein Isoforms
-
RNA, Messenger
-
RNA, Neoplasm
-
Sulfonamides
-
Vemurafenib
-
Phosphatidylinositol 3-Kinases
-
AKT1 protein, human
-
BRAF protein, human
-
Proto-Oncogene Proteins B-raf
-
Proto-Oncogene Proteins c-akt
-
GTP Phosphohydrolases
-
NRAS protein, human