Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei, Taiwan.
Cancer Res. 2018 Sep 1;78(17):4984-4996. doi: 10.1158/0008-5472.CAN-17-3858. Epub 2018 Jun 26.
CBLC (CBL proto-oncogene c) belongs to the CBL protein family, which has E3 ubiquitin ligase activity toward activated receptor tyrosine kinases. CBLC is frequently upregulated in non-small cell lung cancer (NSCLC), yet very little is known about the functions of CBLC in tumorigenesis. Here we show that is an epigenetically demethylated target and its expression can be upregulated in NSCLC after treatment with the DNA methylation inhibitor 5'-azacytidine. Depletion of CBLC significantly inhibited cell viability and clonogenicity and reduced tumor growth in a xenograft model. CBLC silencing further sensitized EGFR-mutated NSCLC cells to treatment with tyrosine kinase inhibitors. Conversely, ectopic expression of CBLC enhanced the activation of EGFR and downstream ERK1/2 signaling after ligand stimulation by competing with CBL for EGFR binding. Analysis of ubiquitin linkages on activated EGFR (aEGFR) revealed that CBLC ubiquitinated and positively regulated aEGFR stability through the conjugation of polyubiquitin by K6 and K11 linkages. This CBLC-mediated polyubiquitination promoted either preferential recycling of aEGFR back to the plasma membrane or trafficking to the cell nucleus. IHC analyses revealed a positive correlation between phospho-EGFR and CBLC in lung adenocarcinoma. In summary, we demonstrate a novel mechanism by which aEGFR escapes lysosomal degradation in a CBLC/ubiquitin-dependent manner to sustain its activation. Our work identifies CBLC as a potential diagnostic biomarker and also points to its utilization as a novel therapeutic target for NSCLC therapy. This work demonstrates the role of CBLC expression as a diagnostic biomarker and potential therapeutic target in lung adenocarcinoma. .
CBLC（CBL 原癌基因 c）属于 CBL 蛋白家族，对激活的受体酪氨酸激酶具有 E3 泛素连接酶活性。CBLC 在非小细胞肺癌（NSCLC）中经常上调，但对 CBLC 在肿瘤发生中的作用知之甚少。在这里，我们表明 是一个表观遗传去甲基化的靶标，其表达可以在 NSCLC 中被 DNA 甲基化抑制剂 5'-氮杂胞苷处理上调。CBLC 耗竭显著抑制细胞活力和集落形成，并在异种移植模型中减少肿瘤生长。CBLC 沉默进一步使 EGFR 突变型 NSCLC 细胞对酪氨酸激酶抑制剂的治疗敏感。相反，CBLC 的异位表达通过与 CBL 竞争 EGFR 结合，增强配体刺激后 EGFR 和下游 ERK1/2 信号的激活。对激活的 EGFR（aEGFR）上的泛素连接的分析表明，CBLC 通过 K6 和 K11 连接将多泛素缀合到 aEGFR 上，从而对 aEGFR 稳定性进行泛素化和正调控。这种 CBLC 介导的多泛素化促进 aEGFR 优先回收到质膜或转运到细胞核。免疫组化分析显示肺腺癌中磷酸化 EGFR 和 CBLC 之间存在正相关。总之，我们证明了一种新的机制，即 aEGFR 通过 CBLC/泛素依赖性方式逃避溶酶体降解，从而维持其激活。我们的工作确定 CBLC 是一个潜在的诊断生物标志物，并指出其可用于 NSCLC 治疗的新型治疗靶点。这项工作证明了 CBLC 表达作为肺腺癌诊断生物标志物和潜在治疗靶点的作用。
