COP1 and GSK3β Cooperate to Promote c-Jun Degradation and Inhibit Breast Cancer Cell Tumorigenesis

• Published in: Neoplasia (New York, N.Y.) Vol. 15; no. 9; pp. 1075 - IN11
• Main Authors: Shao, Jing, Teng, Yong, Padia, Ravi, Hong, Sungguan, Noh, Hyangsoon, Xie, Xiayang, Mumm, Jeff S, Dong, Zheng, Ding, Han-Fei, Cowell, John, Kim, Jaejik, Han, Jiahuai, Huang, Shuang
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2013; Elsevier
• Subjects: Animals; Breast Neoplasms - metabolism; Cell Line, Tumor; Cell Movement; Cell Proliferation; Cell Transformation, Neoplastic - genetics; Cell Transformation, Neoplastic - metabolism; Female; Glycogen Synthase Kinase 3 - genetics; Glycogen Synthase Kinase 3 - metabolism; Glycogen Synthase Kinase 3 beta; Humans; JNK Mitogen-Activated Protein Kinases - metabolism; Neoplasm Invasiveness - genetics; Neoplasm Metastasis - genetics; Oncology; RNA Interference; RNA, Small Interfering; Ubiquitin-Protein Ligases - biosynthesis; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Ubiquitination; Zebrafish
• ISSN: 1476-5586; 1522-8002; 1476-5586
• DOI: 10.1593/neo.13966

Abstract High abundance of c-Jun is detected in invasive breast cancer cells and aggressive breast tumor malignancies. Here, we demonstrate that a major cause of high c-Jun abundance in invasive breast cancer cells is prolonged c-Jun protein stability owing to poor poly-ubiquitination of c-Jun. Among the known c-Jun-targeting E3 ligases, we identified constitutive photomorphogenesis protein 1 (COP1) as an E3 ligase responsible for c-Jun degradation in less invasive breast cancer cells because depletion of COP1 reduced c-Jun poly-ubiquitination leading to the stabilization of c-Jun protein. In a panel of breast cancer cell lines, we observed an inverse association between the levels of COP1 and c-Jun. However, overexpressing COP1 alone was unable to decrease c-Jun level in invasive breast cancer cells, indicating that efficient c-Jun protein degradation necessitates an additional event. Indeed, we found that glycogen synthase kinase 3 (GSK3) inhibitors elevated c-Jun abundance in less invasive breast cancer cells and that GSK3β nonphosphorylable c-Jun-T239A mutant displayed greater protein stability and poorer poly-ubiquitination compared to the wild-type c-Jun. The ability of simultaneously enforced expression of COP1 and constitutively active GSK3β to decrease c-Jun abundance in invasive breast cancer cells allowed us to conclude that c-Jun is negatively regulated through the coordinated action of COP1 and GSK3β. Importantly, co-expressing COP1 and active GSK3β blocked in vitro cell growth/migration and in vivo metastasis of invasive breast cancer cells. Gene expression profiling of breast tumor specimens further revealed that higher COP1 expression correlated with better recurrence-free survival. Our study supports the notion that COP1 is a suppressor of breast cancer progression.