Translational Oncology Research Unit, Department of Diagnostic Research and Technological Innovation, IRCCS - Regina Elena National Cancer Institute, Via Elio Chianesi, 53, 00144 Rome, Italy; Department of Science, University Roma TRE, Viale G. Marconi, 446 I, 00146 Rome, Italy.
Interdepartmental Centre for Comparative Medicine, Alternative Techniques and Aquaculture (CIMETA), University of Rome "Tor Vergata, Via Montpellier, 1, 00133 Rome, Italy.
Biomed Pharmacother. 2023 Nov;167:115480. doi: 10.1016/j.biopha.2023.115480. Epub 2023 Sep 15.
Colorectal cancer (CRC) patients with BRAF mutations develop resistance to BRAF inhibitors at a very early stage. Understanding the molecular mechanisms involved in BRAF inhibitor resistance is critical for the development of novel therapeutic opportunities for this subtype of CRC patients. CRC cells bearing BRAF mutations are mostly sensitive to the abrogation of Mitogen-Activated Protein Kinase Kinase 3 (MKK3), a specific activator of p38MAPKs signaling, suggesting that BRAF alterations might addict CRC cells to the MKK3/p38MAPK signaling. Interestingly, publicly available gene expression profiling data show significantly higher MKK3 transcript levels in CRC lines with acquired resistance to BRAF inhibitors. Herein, we investigated the roles of MKK3 in the response to BRAF targeting (dabrafenib) with COLO205 and HT29 BRAF CRC lines and derived dabrafenib-resistant (DABR) sublines. Dabrafenib treatments reduce MKK3 activation by inducing autophagy in parental but not DABR cells. The MKK3 knockdown induces cell death in DABR cells, whereas ectopic MKK3 expression reduces dabrafenib sensitivity in parental cells. Mechanistically, activated MKK3 interacts and co-localizes with c-Myc oncoprotein (MYC), sustaining MYC protein stability and thus preventing the dabrafenib induced effects in CRC DABR cells both in vitro and in vivo. Overall, we identify a novel molecular mechanism beyond the dabrafenib resistance, shedding light on an uncovered vulnerability for the development of novel therapeutic opportunities in BRAF CRC.
结直肠癌 (CRC) 患者的 BRAF 基因突变会使其在非常早期阶段对 BRAF 抑制剂产生耐药性。了解涉及 BRAF 抑制剂耐药性的分子机制对于开发这种 CRC 亚型的新治疗机会至关重要。携带 BRAF 突变的 CRC 细胞对丝裂原活化蛋白激酶激酶 3 (MKK3) 的抑制非常敏感，MKK3 是 p38MAPKs 信号的特异性激活剂，这表明 BRAF 改变可能使 CRC 细胞对 MKK3/p38MAPK 信号产生依赖性。有趣的是，公开的基因表达谱数据显示，对 BRAF 抑制剂获得性耐药的 CRC 细胞系中 MKK3 转录本水平明显更高。在此，我们研究了 MKK3 在 COLO205 和 HT29 BRAF CRC 细胞系及其衍生的对 dabrafenib 耐药 (DABR) 亚系对 BRAF 靶向治疗 (dabrafenib) 反应中的作用。Dabrafenib 通过诱导自噬来减少亲本细胞而非 DABR 细胞中的 MKK3 激活。MKK3 敲低会诱导 DABR 细胞死亡，而外源性 MKK3 表达会降低亲本细胞对 dabrafenib 的敏感性。从机制上讲，激活的 MKK3 与 c-Myc 癌蛋白 (MYC) 相互作用并共定位，维持 MYC 蛋白稳定性，从而防止 CRC DABR 细胞中的 dabrafenib 诱导作用，无论是在体外还是体内。总之，我们确定了一种新的分子机制，超越了 dabrafenib 耐药性，为开发 BRAF CRC 的新治疗机会提供了新的见解。
