Institute of Molecular Medicine, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany.
Faculty of Biology, University of Freiburg, Freiburg, Germany.
Sci Adv. 2023 Sep;9(35):eade7486. doi: 10.1126/sciadv.ade7486. Epub 2023 Sep 1.
In-frame exon 12 deletions are increasingly identified in various tumor types. The resultant BRAF oncoproteins usually lack five amino acids in the β3-αC helix linker and sometimes contain de novo insertions. The dimerization status of BRAF oncoproteins, their precise pathomechanism, and their direct druggability by RAF inhibitors (RAFi) has been under debate. Here, we functionally characterize BRAF and two novel mutants, BRAF and BRAF, and compare them with other BRAF oncoproteins. We show that BRAF oncoproteins not only form stable homodimers and large multiprotein complexes but also require dimerization. Nevertheless, details matter as aromatic amino acids at the deletion junction of some BRAF oncoproteins, e.g., BRAF, increase their stability and dimerization propensity while conferring resistance to monomer-favoring RAFi such as dabrafenib or HSP 90/CDC37 inhibition. In contrast, dimer-favoring inhibitors such as naporafenib inhibit all BRAF mutants in cell lines and patient-derived organoids, suggesting that tumors driven by such oncoproteins are vulnerable to these compounds.
在各种肿瘤类型中，越来越多的框内外显子 12 缺失被发现。由此产生的 BRAF 癌蛋白通常在β3-αC 螺旋接头处缺失五个氨基酸，有时还含有新插入的氨基酸。BRAF 癌蛋白的二聚化状态、其确切的发病机制以及 RAF 抑制剂（RAFi）对其的直接可用药性一直存在争议。在这里，我们对 BRAF 和两种新型突变体 BRAF 和 BRAF 进行了功能表征，并将其与其他 BRAF 癌蛋白进行了比较。我们表明，BRAF 癌蛋白不仅形成稳定的同源二聚体和大型多蛋白复合物，而且还需要二聚化。然而，细节很重要，因为一些 BRAF 癌蛋白（例如 BRAF）的缺失连接处的芳香族氨基酸会增加其稳定性和二聚化倾向，同时赋予其对单体有利的 RAFi（如 dabrafenib 或 HSP90/CDC37 抑制）的抗性。相比之下，二聚体有利的抑制剂，如 naporafenib，在细胞系和患者来源的类器官中抑制所有 BRAF 突变体，表明由这些癌蛋白驱动的肿瘤对这些化合物敏感。
