Despite recent advances in the development of BRAF kinase inhibitors (BRAFi) for BRAF-mutant melanomas, development of resistance remains a major clinical problem. In addition to genetic alterations associated with intrinsic resistance, several adaptive response mechanisms are known to be rapidly activated to allow cell survival in response to treatment, limiting efficacy. A better understanding of the mechanisms driving resistance is urgently needed to improve the success of BRAF-targeted therapies and to make therapeutic intervention more durable. In this study, we identify the mitogen-activated protein kinase (MAPK) p38 as a novel mediator of the adaptive response of melanoma cells to BRAF-targeted therapy. Our findings demonstrate that BRAFi leads to an early increase in p38 activation, which promotes phosphorylation of the transcription factor SOX2 at Ser251, enhancing SOX2 stability, nuclear localization, and transcriptional activity. Furthermore, functional studies show that SOX2 depletion increases sensitivity of melanoma cells to BRAFi, whereas overexpression of a phosphomimetic SOX2-S251E mutant is sufficient to drive resistance and desensitize melanoma cells to BRAFi in vitro and in a zebrafish xenograft model. We also found that SOX2 phosphorylation at Ser251 confers resistance to BRAFi by binding to the promoter and increasing transcriptional activation of the ATP-binding cassette drug efflux transporter ABCG2. In summary, we unveil a p38/SOX2-mediated mechanism of adaptive response to BRAFi, which provides prosurvival signals to melanoma cells against the cytotoxic effects of BRAFi prior to acquiring resistance.

尽管最近在 BRAF 突变黑色素瘤的 BRAF 激酶抑制剂 (BRAFi) 的开发方面取得了进展，但耐药性的发展仍然是一个主要的临床问题。除了与内在抗性相关的遗传改变外，已知几种适应性反应机制被迅速激活，以使细胞在治疗后存活，从而限制了疗效。迫切需要更好地了解驱动耐药的机制，以提高 BRAF 靶向治疗的成功率，并使治疗干预更持久。在这项研究中，我们将丝裂原活化蛋白激酶 (MAPK) p38 鉴定为黑色素瘤细胞对 BRAF 靶向治疗的适应性反应的新介质。我们的研究结果表明，BRAFi 导致 p38 激活的早期增加，它促进转录因子 SOX2 在 Ser251 的磷酸化，增强 SOX2 的稳定性、核定位和转录活性。此外，功能研究表明，SOX2 消耗增加了黑色素瘤细胞对 BRAFi 的敏感性，而拟磷 SOX2-S251E 突变体的过表达足以驱动黑色素瘤细胞对 BRAFi 的抗性和脱敏在体外和斑马鱼异种移植模型中。我们还发现，Ser251 的 SOX2 磷酸化通过与启动子结合并增加 ATP 结合盒药物外排转运蛋白ABCG2的转录激活来赋予对 BRAFi 的抗性。总之，我们揭示了一种 p38/SOX2 介导的对 BRAFi 的适应性反应机制，该机制在获得耐药性之前向黑色素瘤细胞提供了针对 BRAFi 的细胞毒性作用的促生存信号。