The functions of immune cells in brain metastases are unclear because the brain has traditionally been considered “immune privileged.” However, we found that a subgroup of immunosuppressive neutrophils is recruited into the brain, enabling brain metastasis development. In brain metastatic cells, enhancer of zeste homolog 2 (EZH2) is highly expressed and phosphorylated at tyrosine-696 (pY696)–EZH2 by nuclear-localized Src tyrosine kinase. Phosphorylation of EZH2 at Y696 changes its binding preference from histone H3 to RNA polymerase II, which consequently switches EZH2’s function from a methyltransferase to a transcription factor that increases c-JUN expression. c-Jun up-regulates protumorigenic inflammatory cytokines, including granulocyte colony-stimulating factor (G-CSF), which recruits Arg1⁺- and PD-L1⁺ immunosuppressive neutrophils into the brain to drive metastasis outgrowth. G-CSF–blocking antibodies or immune checkpoint blockade therapies combined with Src inhibitors impeded brain metastasis in multiple mouse models. These findings indicate that pY696-EZH2 can function as a methyltransferase-independent transcription factor to facilitate the brain infiltration of immunosuppressive neutrophils, which could be clinically targeted for brain metastasis treatment.

脑转移中免疫细胞的功能尚不清楚，因为大脑传统上被认为是“免疫特权”。然而，我们发现一个免疫抑制性中性粒细胞亚群被招募到大脑中，从而促进脑转移的发展。在脑转移细胞中，zeste 同源物 2 (EZH2) 的增强子在酪氨酸 696 (pY696)-EZH2 处被核定位的 Src 酪氨酸激酶高度表达和磷酸化。EZH2 在 Y696 的磷酸化将其结合偏好从组蛋白 H3 改变为 RNA 聚合酶 II，从而将 EZH2 的功能从甲基转移酶转变为增加c-JUN表达的转录因子。c-Jun 上调促瘤性炎性细胞因子，包括募集 Arg1 ^{+的粒细胞集落刺激因子 (G-CSF)}- 和 PD-L1 ⁺免疫抑制性中性粒细胞进入大脑以驱动转移生长。G-CSF 阻断抗体或免疫检查点阻断疗法与 Src 抑制剂相结合可阻止多种小鼠模型的脑转移。这些发现表明，pY696-EZH2 可以作为甲基转移酶非依赖性转录因子，促进免疫抑制性中性粒细胞的脑浸润，临床上可以靶向治疗脑转移。