The BTB-zinc finger transcription factor Abrupt acts as an epithelial oncogene in Drosophila through maintaining a progenitor-like cell state. Drosophila melanogaster

The capacity of tumor cells to maintain continual overgrowth potential has been linked to the commandeering of normal self-renewal pathways. Using an epithelial cancer model in Drosophila we carried out an overexpression screen for oncogenes capable of cooperating with the loss of the epithelial apico-basal cell polarity regulator, scribbled, and identified the cell fate regulator, Abrupt, a BTB-zinc finger protein. Abrupt overexpression alone is insufficient to transform cells, but in cooperation with scrib loss of function, Abrupt promotes the formation of massive tumors in the eye/antennal disc. The steroid hormone receptor coactivator, Taiman (SRC3/AIB1), is known to associate with Abrupt, and Taiman overexpression also drives tumor formation in cooperation with the loss of Scribbled. Expression arrays and ChIP-Seq indicates that Abrupt overexpression represses a large number of genes, including steroid hormone-response genes and multiple cell fate regulators, thereby maintaining cells within an epithelial progenitor-like state. The progenitor-like state is characterised by the failure to express the conserved Eyes absent/Dachshund regulatory complex in the eye disc, and in the antennal disc by the failure to express cell fate regulators that define the temporal elaboration of the appendage along the proximo-distal axis downstream of Distalless. Loss of scribbled promotes cooperation with Abrupt through impaired Hippo signaling, which is required and sufficient for cooperative overgrowth with Abrupt, and JNK signaling, which is required for tumor cell migration/invasion but not overgrowth. These results thus identify a novel cooperating oncogene, mammalian family members of which are also known oncogenes, and demonstrate that epithelial tumors in Drosophila can be characterised by the maintenance of a progenitor-like state. Overall design: ChIP-Seq of Abrupt, ChIP-Seq of Abrupt (scrib-), Input, Input (scrib-)

肿瘤细胞维持持续增殖潜能的能力，与劫持正常自我更新通路密切相关。本研究以果蝇（Drosophila）上皮癌症模型为对象，针对可与上皮顶基极性调节因子scribbled（简称scrib）功能缺失协同发挥作用的癌基因开展过表达筛选，最终鉴定出细胞命运调节因子Abrupt——一种BTB锌指蛋白（BTB-zinc finger protein）。仅过表达Abrupt不足以诱导细胞转化，但当与scrib功能缺失协同作用时，Abrupt可促进果蝇眼/触角盘中形成大规模肿瘤。已知类固醇激素受体辅激活因子Taiman（SRC3/AIB1）可与Abrupt结合，且Taiman过表达同样可协同scrib功能缺失诱导肿瘤形成。基因表达芯片与染色质免疫共沉淀测序（ChIP-Seq）分析显示，Abrupt过表达可抑制大量基因的表达，其中包括类固醇激素应答基因与多种细胞命运调节因子，从而使细胞维持在上皮祖细胞样状态。该祖细胞样状态的特征为：在眼盘中无法表达保守的眼缺失/ Dachshund（Eya/Dac）调控复合物；在触角盘中则无法表达细胞命运调节因子，这些因子负责定义附肢沿Distalless（Dll，远端缺失基因）下游近远轴的时序特化。scrib功能缺失可通过削弱Hippo信号通路与JNK信号通路协同促进Abrupt的作用：其中Hippo信号通路削弱是与Abrupt协同诱导细胞过度增殖所必需且充分的条件，而JNK信号通路则仅参与肿瘤细胞的迁移/侵袭过程，对细胞过度增殖无影响。本研究鉴定出一种新型协同癌基因，其哺乳动物同源家族成员同样为已知癌基因；同时证实果蝇上皮肿瘤可通过维持祖细胞样状态进行特征性描述。实验整体设计：Abrupt染色质免疫共沉淀测序（ChIP-Seq）、Abrupt（scrib功能缺失组）染色质免疫共沉淀测序（ChIP-Seq）、Input对照、Input（scrib功能缺失组）对照。