Department of Molecular Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, 33612, USA.
Proteomics and Metabolomics Core, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, 33612, USA.
Nat Commun. 2019 Apr 23;10(1):1870. doi: 10.1038/s41467-019-09844-0.
BRAF plays an indispensable role in activating the MEK/ERK pathway to drive tumorigenesis. Receptor tyrosine kinase and RAS-mediated BRAF activation have been extensively characterized, however, it remains undefined how BRAF function is fine-tuned by stimuli other than growth factors. Here, we report that in response to proinflammatory cytokines, BRAF is subjected to lysine 27-linked poly-ubiquitination in melanoma cells by the ITCH ubiquitin E3 ligase. Lysine 27-linked ubiquitination of BRAF recruits PP2A to antagonize the S365 phosphorylation and disrupts the inhibitory interaction with 14-3-3, leading to sustained BRAF activation and subsequent elevation of the MEK/ERK signaling. Physiologically, proinflammatory cytokines activate ITCH to maintain BRAF activity and to promote proliferation and invasion of melanoma cells, whereas the ubiquitination-deficient BRAF mutant displays compromised kinase activity and reduced tumorigenicity. Collectively, our study reveals a pivotal role for ITCH-mediated BRAF ubiquitination in coordinating the signals between cytokines and the MAPK pathway activation in melanoma cells.
BRAF 在激活 MEK/ERK 通路以驱动肿瘤发生中起着不可或缺的作用。受体酪氨酸激酶和 RAS 介导的 BRAF 激活已得到广泛研究，然而，除了生长因子之外，其他刺激因素如何精细调节 BRAF 功能仍未确定。在这里，我们报告在黑色素瘤细胞中，炎性细胞因子通过 ITCH 泛素 E3 连接酶使 BRAF 发生赖氨酸 27 位连接的多聚泛素化。BRAF 的赖氨酸 27 位泛素化招募 PP2A 来拮抗 S365 磷酸化，并破坏与 14-3-3 的抑制性相互作用，导致 BRAF 的持续激活和随后的 MEK/ERK 信号的升高。在生理上，炎性细胞因子激活 ITCH 以维持 BRAF 活性，并促进黑色素瘤细胞的增殖和侵袭，而泛素化缺陷的 BRAF 突变体显示出激酶活性降低和肿瘤发生能力降低。总之，我们的研究揭示了 ITCH 介导的 BRAF 泛素化在协调细胞因子与黑色素瘤细胞中 MAPK 通路激活之间信号中的关键作用。
