Nucleophosmin sustains WNT-driven cell proliferation and tumor initiation in vivo. Nucleophosmin sustains WNT-driven cell proliferation and tumor initiation in vivo

Nucleophosmin (NPM1) is a nucleolar protein frequently overexpressed in many solid tumours with little known about its functional role to support carcinogenesis. Here, we identify Npm1 as a commonly upregulated gene following Apc loss in highly proliferative tissues, and high expression correlates with increased proliferation in CRC patients. We show that NPM1 is dispensable for adult epithelial tissue homeostasis, however, it has a profound effect on WNT-driven intestinal and liver tumourigenesis, leading to reduced proliferation and extension of survival. Mechanistically, NPM1 depletion triggers integrated stress response (ISR) and p53 pathway activation. P53 deletion, or inhibition of the ISR effects, rescue proliferation following NPM1 loss. Overall, our results demonstrate that NPM1 supports WNT-driven cell proliferation and tumour initiation by attenuating p53 pathway activation or induction of ISR. Being dispensable for homeostasis, NPM1 presents as a promising target for cancer therapy in WNT-driven tumours with functional p53, including difficult to treat KRAS-mutant CRC and hepatic cancers. Overall design: To investigate the role of Nucleophosmin (Npm1) on colorectal cancer, we conditionally deleted it in an APC null/KRAS mutant cancer model. Epithelial extracts three days post-KO were harvested from mice. Ribo-seq and total cytoplasmic RNA sequencing were performed to address the effects on translation as well as transcript levels. The experiment was performed in four independent mice. Replicates are indicated by _1/_2/_3/_4. CRUK Scotland Institute Mouse IDs are indicated.

核仁磷酸蛋白（Nucleophosmin, NPM1）是一类定位于核仁的蛋白，在多种实体瘤中常呈高表达，但其支持肿瘤发生的功能性机制尚未明确。本研究鉴定发现，在高增殖组织中，Apc缺失后Npm1是常见的上调基因，且其高表达与结直肠癌（Colorectal Cancer, CRC）患者的肿瘤增殖水平升高相关。研究显示，NPM1对于成年上皮组织的稳态维持并非必需，但其对WNT信号驱动的肠道及肝脏肿瘤发生具有显著调控作用，可降低细胞增殖能力并延长小鼠生存周期。从机制层面而言，NPM1的敲除会触发整合应激反应（integrated stress response, ISR）与p53通路的激活；敲除p53或抑制整合应激反应的效应，可挽救NPM1缺失后的细胞增殖缺陷。综上，本研究结果证实，NPM1可通过减弱p53通路激活或抑制整合应激反应的诱导，支持WNT信号驱动的细胞增殖与肿瘤起始。鉴于NPM1对正常上皮组织稳态非必需，其可作为携带功能性p53的WNT驱动型肿瘤的潜在治疗靶点，包括难治性KRAS突变型结直肠癌及肝细胞癌。

总体实验设计：为探究核仁磷酸蛋白（Npm1）在结直肠癌中的功能作用，我们在APC缺失/KRAS突变的癌症小鼠模型中条件性敲除Npm1。在基因敲除（Knockout, KO）后第3天，从小鼠体内收集上皮组织提取物。通过核糖体测序（Ribo-seq）与总细胞质RNA测序，分别检测其对翻译过程及转录本水平的影响。本实验使用4只独立小鼠完成生物学重复，重复样本以_1/_2/_3/_4标注。实验小鼠的CRUK苏格兰研究所小鼠编号已予以标注。