State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiamen, Fujian, China ; Department of Biochemistry and Molecular Biology, Medical College of Georgia, Georgia Regents University, Augusta, GA.
Neoplasia. 2013 Sep;15(9):1075-85. doi: 10.1593/neo.13966.
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.
高丰度的 c-Jun 在侵袭性乳腺癌细胞和侵袭性乳腺癌肿瘤恶性肿瘤中被检测到。在这里，我们证明，侵袭性乳腺癌细胞中 c-Jun 丰度高的一个主要原因是 c-Jun 蛋白稳定性差，导致 c-Jun 多聚泛素化不良。在已知的 c-Jun 靶向 E3 连接酶中，我们鉴定出组成型光形态发生蛋白 1（COP1）是一种 E3 连接酶，负责在侵袭性较低的乳腺癌细胞中降解 c-Jun，因为 COP1 的耗竭降低了 c-Jun 的多聚泛素化，导致 c-Jun 蛋白的稳定。在一组乳腺癌细胞系中，我们观察到 COP1 和 c-Jun 的水平呈负相关。然而，单独过表达 COP1 并不能降低侵袭性乳腺癌细胞中的 c-Jun 水平，这表明有效的 c-Jun 蛋白降解需要额外的事件。事实上，我们发现糖原合酶激酶 3（GSK3）抑制剂可增加侵袭性较低的乳腺癌细胞中 c-Jun 的丰度，并且与野生型 c-Jun 相比，非磷酸化的 GSK3β c-Jun-T239A 突变体显示出更高的蛋白稳定性和更差的多聚泛素化。同时强制表达 COP1 和组成型激活的 GSK3β 降低侵袭性乳腺癌细胞中 c-Jun 丰度的能力使我们得出结论，c-Jun 通过 COP1 和 GSK3β 的协调作用受到负调控。重要的是，共表达 COP1 和活性 GSK3β 可阻断侵袭性乳腺癌细胞的体外细胞生长/迁移和体内转移。乳腺癌肿瘤标本的基因表达谱分析进一步表明，COP1 表达水平较高与无复发生存率的改善相关。我们的研究支持 COP1 是乳腺癌进展的抑制剂的观点。
