Bi Yanli, Chen Xiaoyu, Wei Bajin, Wang Linchen, Gong Longyuan, Li Haomin, Xiong Xiufang, Zhao Yongchao
Department of Hepatobiliary and Pancreatic Surgery, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.
Zhejiang Provincial Key Laboratory of Pancreatic Disease, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.
Theranostics. 2021 Apr 19;11(13):6355-6369. doi: 10.7150/thno.51286. eCollection 2021.
Dysregulation of the PI3K/AKT/mTOR pathway occurs frequently in cancers, providing an attractive therapeutic target for anticancer treatments. DEPTOR plays essential roles in regulation of cell proliferation and survival by directly modulating mTOR activity. However, whether DEPTOR regulates the growth of ErbB2-positive breast cancer cells remains unknown. DEPTOR expression was determined by TCGA data analysis and immunohistochemistry of human breast tissue microarrays. The membrane localization of DEPTOR was demonstrated by immunofluorescence and subcellular fractionation. The interaction of DEPTOR with ErbB2 was determined by immunoprecipitation. Furthermore, the biological significance of this interaction was assessed by ATPlite cell growth, clonogenic survival, and flow cytometry-based apoptosis assays. DEPTOR promoted the proliferation and survival of ErbB2-positive breast cancer cells by directly interacting with and stabilizing ErbB2. Specifically, DEPTOR translocates to cell membrane and interacts with ErbB2 to disrupt ErbB2 polyubiquitination and degradation promoted by β-TrCP, an E3 ubiquitin ligase. DEPTOR knockdown destabilizes ErbB2 by shortening its protein half-life to inactivate ErbB2-PI3K-AKT-mTOR signaling, leading to the suppression of cell proliferation and survival by inducing apoptosis. Ectopic expression of a constitutively active ErbB2 mutant completely rescued the reduction in cell proliferation and survival by DEPTOR knockdown. Importantly, DEPTOR expression is increased in human breast cancer tissues and its overexpression correlates with poor patient survival. Moreover, DEPTOR is located on the cell membrane in ErbB2-positive breast cancer tissues, but not in tumor-adjacent normal tissues, indicating that DEPTOR may contribute to the oncogenic characteristics of ErbB2. Our study reveals a novel mechanism by which DEPTOR promotes breast cancer cell proliferation and survival by stabilizing ErbB2.
PI3K/AKT/mTOR信号通路失调在癌症中频繁发生，为抗癌治疗提供了一个有吸引力的治疗靶点。DEPTOR通过直接调节mTOR活性在细胞增殖和存活的调控中发挥重要作用。然而，DEPTOR是否调节ErbB2阳性乳腺癌细胞的生长仍不清楚。通过TCGA数据分析和人乳腺组织微阵列的免疫组织化学确定DEPTOR的表达。通过免疫荧光和亚细胞分级分离证明DEPTOR的膜定位。通过免疫沉淀确定DEPTOR与ErbB2的相互作用。此外，通过ATPlite细胞生长、克隆形成存活和基于流式细胞术的凋亡测定评估这种相互作用的生物学意义。DEPTOR通过直接与ErbB2相互作用并使其稳定来促进ErbB2阳性乳腺癌细胞的增殖和存活。具体而言，DEPTOR转位到细胞膜并与ErbB2相互作用，破坏由E3泛素连接酶β-TrCP促进的ErbB2多聚泛素化和降解。DEPTOR敲低通过缩短其蛋白质半衰期使ErbB2不稳定，从而使ErbB2-PI3K-AKT-mTOR信号失活，导致通过诱导凋亡抑制细胞增殖和存活。组成型活性ErbB2突变体的异位表达完全挽救了DEPTOR敲低导致的细胞增殖和存活减少。重要的是，DEPTOR在人乳腺癌组织中的表达增加，其过表达与患者不良生存相关。此外，DEPTOR在ErbB2阳性乳腺癌组织的细胞膜上定位，但在肿瘤邻近的正常组织中不定位，表明DEPTOR可能有助于ErbB2的致癌特性。我们的研究揭示了一种新机制，即DEPTOR通过稳定ErbB2促进乳腺癌细胞增殖和存活。
