河马通路是器官生长、干细胞更新和肿瘤发生的主要调控因子，其激活受到多种翻译后修饰的严格控制，包括泛素化修饰。虽然已经确定了数种E3泛素连接酶作为河马通路的调节因子，但对应的E2泛素连接酶（E2s）仍然未知。在此，我们利用果蝇进行筛选，鉴定参与调节Crumb（Crb）细胞内结构域过度表达引起翅膀过度生长的E2s，并确定Bruce作为关键的调控因子。Bruce的丧失下调河马通路靶基因表达，抑制河马信号失活引发的组织生长。出乎意料的是，我们的遗传数据表明Bruce在扩展（Ex）上游但与经典的河马（Hpo）-Warts（Wts）级联通路平行地调节了Hippo通路的下游效应物Yorkie（Yki）。在机理上，Bruce与E3连接酶POSH协同调节生长和与泛素化介导的Ex降解相关的机制。此外，我们证明了Bruce在河马介导的恶性肿瘤进程中的必要性。总之，我们的发现揭示了Bruce作为关键的E2酶，在果蝇中连通细胞表面信号以调节河马通路的激活。© 2023. 作者。

The Hippo pathway is a master regulator of organ growth, stem cell renewal, and tumorigenesis, its activation is tightly controlled by various post-translational modifications, including ubiquitination. While several E3 ubiquitin ligases have been identified as regulators of Hippo pathway, the corresponding E2 ubiquitin-conjugating enzymes (E2s) remain unknown. Here, we performed a screen in Drosophila to identify E2s involved in regulating wing overgrowth caused by the overexpression of Crumbs (Crb) intracellular domain and identified Bruce as a critical regulator. Loss of Bruce downregulates Hippo target gene expression and suppresses Hippo signaling inactivation induced tissue growth. Unexpectedly, our genetic data indicate that Bruce acts upstream of Expanded (Ex) but in parallel with the canonical Hippo (Hpo) -Warts (Wts) cascade to regulate Yorkie (Yki), the downstream effector of Hippo pathway. Mechanistically, Bruce synergizes with E3 ligase POSH to regulate growth and ubiquitination-mediated Ex degradation. Moreover, we demonstrate that Bruce is required for Hippo-mediated malignant tumor progression. Altogether, our findings unveil Bruce as a crucial E2 enzyme that bridges the signal from the cell surface to regulate Hippo pathway activation in Drosophila.© 2023. The Author(s).