Department of Pathology, Brigham and Women's Hospital, Boston, MA.
Broad Institute of MIT and Harvard, Cambridge, MA.
Blood. 2021 Apr 22;137(16):2209-2220. doi: 10.1182/blood.2020006528.
Casitas B-lineage lymphoma (CBL) encodes an E3 ubiquitin ligase and signaling adaptor that regulates receptor and nonreceptor tyrosine kinases. Recurrent CBL mutations occur in myeloid neoplasms, including 10% to 20% of chronic myelomonocytic leukemia (CMML) cases, and selectively disrupt the protein's E3 ubiquitin ligase activity. CBL mutations have been associated with poor prognosis, but the oncogenic mechanisms and therapeutic implications of CBL mutations remain incompletely understood. We combined functional assays and global mass spectrometry to define the phosphoproteome, CBL interactome, and mechanism of signaling activation in a panel of cell lines expressing an allelic series of CBL mutations. Our analyses revealed that increased LYN activation and interaction with mutant CBL are key drivers of enhanced CBL phosphorylation, phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1) recruitment, and downstream phosphatidylinositol 3-kinase (PI3K)/AKT signaling in CBL-mutant cells. Signaling adaptor domains of CBL, including the tyrosine kinase-binding domain, proline-rich region, and C-terminal phosphotyrosine sites, were all required for the oncogenic function of CBL mutants. Genetic ablation or dasatinib-mediated inhibition of LYN reduced CBL phosphorylation, CBL-PIK3R1 interaction, and PI3K/AKT signaling. Furthermore, we demonstrated in vitro and in vivo antiproliferative efficacy of dasatinib in CBL-mutant cell lines and primary CMML. Overall, these mechanistic insights into the molecular function of CBL mutations provide rationale to explore the therapeutic potential of LYN inhibition in CBL-mutant myeloid malignancies.
卡斯蒂亚 B 细胞淋巴瘤 (CBL) 编码一种 E3 泛素连接酶和信号适配器，可调节受体和非受体酪氨酸激酶。在髓系肿瘤中经常出现 CBL 突变，包括 10%至 20%的慢性粒单核细胞白血病 (CMML) 病例，并且选择性地破坏该蛋白的 E3 泛素连接酶活性。CBL 突变与不良预后相关，但 CBL 突变的致癌机制和治疗意义仍不完全清楚。我们结合功能测定和全局质谱法，在表达一系列 CBL 突变等位基因的细胞系中定义了磷酸蛋白质组、CBL 相互作用组以及信号激活的机制。我们的分析表明，LYN 的激活增加和与突变 CBL 的相互作用是增强 CBL 磷酸化、磷酸肌醇 3-激酶调节亚基 1 (PIK3R1) 募集以及 CBL 突变细胞中下游磷脂酰肌醇 3-激酶 (PI3K)/AKT 信号的关键驱动因素。CBL 的信号适配器域，包括酪氨酸激酶结合域、富含脯氨酸的区域和 C 末端磷酸酪氨酸位点，对于 CBL 突变体的致癌功能都是必需的。CBL 或 dasatinib 介导的 LYN 基因缺失抑制减少了 CBL 磷酸化、CBL-PIK3R1 相互作用和 PI3K/AKT 信号。此外，我们在体外和体内证明了 dasatinib 在 CBL 突变细胞系和原发性 CMML 中的抗增殖作用。总的来说，这些对 CBL 突变分子功能的机制见解为探索 LYN 抑制在 CBL 突变性髓系恶性肿瘤中的治疗潜力提供了依据。
