Comprehensive Cancer Center, The Ohio State University, Columbus, OH 43210.
Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH 43210.
Proc Natl Acad Sci U S A. 2017 Sep 5;114(36):9629-9634. doi: 10.1073/pnas.1704371114. Epub 2017 Aug 21.
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.
BRAF 中的激活突变存在于 50%的黑色素瘤中，尽管使用 BRAF 抑制剂（BRAFi）治疗有效，但通常会产生耐药性。我们现在表明，在黑色素瘤中 BRAF 抑制剂耐药的情况下，最近发现的 NRAS 同种型 2 被上调，无论是在细胞系还是患者肿瘤组织中。当同种型 2 在 BRAF 突变型黑色素瘤细胞系中过表达时，在 BRAFi 治疗存在的情况下，黑色素瘤细胞增殖和体内肿瘤生长显著增加。与对照相比，shRNA 介导的同种型 2 在 BRAFi 耐药细胞中的敲低恢复了对 BRAFi 的敏感性。信号分析表明，与同种型 1 过表达细胞相比，同种型 2 过表达细胞中的丝裂原活化蛋白激酶（MAPK）途径信号降低，磷酸肌醇-3-激酶（PI3K）途径信号增加。同种型 2 的免疫沉淀验证了这种同种型与 PI3K 和 BRAF/RAF1 的结合亲和力。在表达高水平同种型 2 的细胞中，将 AKT 抑制剂添加到 BRAFi 治疗中导致 BRAFi 敏感性部分恢复。NRAS 同种型 2 可能通过促进 PI3K 途径激活导致对 BRAFi 的耐药性。
