拥有BRAF突变的结直肠癌（CRC）患者在早期阶段就对BRAF抑制剂产生抗药性。了解BRAF抑制剂抗药性的分子机制对于开发该亚型CRC患者的新治疗机会至关重要。表达BRAF突变的CRC细胞大多对丝裂原活化蛋白激酶激酶3（MKK3）的消除敏感，MKK3是p38MAPK信号通路的特异性激活物，这表明BRAF变异可能使CRC细胞对MKK3/p38MAPK信号通路上瘾。有趣的是，公开的基因表达谱数据显示，抗BRAF抑制剂获得性耐药的CRC细胞系具有显著更高的MKK3转录水平。在这里，我们研究了MKK3在COLO205和HT29 BRAFV600E CRC细胞系及其衍生的抗达博芬尼（DABR）亚细胞系对BRAF靶向（达博芬尼）治疗的响应中的作用。达博芬尼治疗降低父细胞中MKK3的活化，通过诱导自噬作用，而不对DABR细胞产生同样效果。MKK3的沉默在DABR细胞中诱导细胞死亡，而异位MKK3表达则降低了父细胞对达博芬尼的敏感性。在机制上，活化的MKK3与c-干扰蛋白（MYC）结合并共定位，维持MYC蛋白的稳定性，从而在体外和体内阻止了达博芬尼对CRC DABR细胞的影响。总体而言，我们发现了达博芬尼抗药性之外的一种新分子机制，揭示了BRAFV600E CRC在开发新治疗机会时的未知易感性。版权所有©2023作者。由Elsevier Masson SAS出版。保留所有权利。

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 BRAFV600E 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 BRAFV600E CRC.Copyright © 2023 The Authors. Published by Elsevier Masson SAS.. All rights reserved.