Department of Cell Biology, Key Laboratory of Cell Biology, Ministry of Public Health, and Key Laboratory of Medical Cell Biology, Ministry of Education, China Medical University, Shenyang, China.
Department of Diagnostics, School of Medicine, Hangzhou Normal University, Hangzhou, Zhejiang, China.
Oncogene. 2016 Apr 14;35(15):1943-54. doi: 10.1038/onc.2015.259. Epub 2015 Jul 27.
The p21-activated kinase 5 (PAK5) is overexpressed in advanced cancer and the transcription factor E47 is a direct repressor of E-cadherin and inducer of epithelial-mesenchymal transition (EMT). However, the relationship between PAK5 and E47 has not been explored. In this study, we found that PAK5-mediated E47 phosphorylation promoted EMT in advanced colon cancer. PAK5 interacted with E47 and phosphorylated E47 on Ser39 under hepatocyte growth factor (HGF) stimulation, which decreased cell-cell cohesion, increased cell migration and invasion in vitro and promoted metastasis in a xenograft model. Furthermore, phosphorylation of E47 facilitated its accumulating in nucleus in an importin α-dependent manner, and enhanced E47 binding to E-cadherin promoter directly, leading to inhibition of E-cadherin transcription. In contrast, PAK5-knockdown resulted in blockage of HGF-induced E47 phosphorylation, attenuated association of E47 with importin α and decreased E47 binding to E-cadherin promoter. In addition, we demonstrated a close correlation between PAK5 and phospho-Ser39 E47 expression in colon cancer specimens. More importantly, high expression of phospho-E47 was associated with an aggressive phenotype of colon cancer and nuclear phospho-E47 staining was found in certain cases of colon cancer with metastasis. Collectively, E47 is a novel substrate of PAK5, and PAK5-mediated phosphorylation of E47 promotes EMT and metastasis of colon cancer, suggesting that phosphorylated E47 on Ser39 may be a potential therapeutic target in progressive colon cancer.
p21 激活激酶 5（PAK5）在晚期癌症中过表达，转录因子 E47 是 E-钙黏蛋白的直接抑制剂和上皮-间充质转化（EMT）的诱导剂。然而，PAK5 与 E47 之间的关系尚未得到探索。在这项研究中，我们发现 PAK5 介导的 E47 磷酸化促进了晚期结肠癌中的 EMT。PAK5 与 E47 相互作用，并在肝细胞生长因子（HGF）刺激下使 E47 的丝氨酸 39 位磷酸化，这降低了细胞间的黏附力，增加了体外细胞迁移和侵袭，并在异种移植模型中促进了转移。此外，E47 的磷酸化促进了其以依赖 importinα 的方式在核内积累，并增强了 E47 与 E-钙黏蛋白启动子的直接结合，导致 E-钙黏蛋白转录的抑制。相比之下，PAK5 敲低导致 HGF 诱导的 E47 磷酸化受阻，E47 与 importinα 的结合减少，E47 与 E-钙黏蛋白启动子的结合减少。此外，我们在结肠癌标本中证实了 PAK5 和磷酸化 Ser39 E47 表达之间的密切相关性。更重要的是，结肠癌中高表达磷酸化 E47 与侵袭性表型相关，并且在某些具有转移的结肠癌病例中发现了核内磷酸化 E47 染色。总之，E47 是 PAK5 的一种新型底物，PAK5 介导的 E47 磷酸化促进了结肠癌的 EMT 和转移，表明 Ser39 上的磷酸化 E47 可能是进展性结肠癌的潜在治疗靶点。
