Laboratory of Molecular and Experimental Pathology, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China.
Kunming College of Life Science, University of Chinese Academy of Sciences, Kunming, China.
Sci Rep. 2017 Jun 19;7(1):3769. doi: 10.1038/s41598-017-04005-z.
Symplekin is a multifunctional protein that localizes to both tight junctions and the nucleus in polarized epithelial cells, with confirmed roles in mRNA maturation, transcriptional modulation and tight-junction assembly. However, the mechanisms governing its subcellular distribution and related functions remain unclear. In this study, we found that symplekin primarily localizes to the nuclei of cultured dedifferentiated colorectal cancer cells, and nuclear symplekin showed higher phosphorylation and binding affinity with YBX3 than its membrane fraction. Moreover, the accumulation of nuclear symplekin promoted cell proliferation and dedifferentiation as well as β-catenin transactivation in vitro. Nuclear symplekin acts as a transcriptional co-activator for the expression of many cell cycle-related genes. Furthermore, extracellular signal-regulated kinase (ERK) phosphorylated symplekin at T1257 to facilitate its nuclear accumulation upon epidermal growth factor (EGF) stimulation. Meanwhile, reduction of total symplekin also induced certain epithelial-mesenchymal transition features in HT-29 cells. Taken together, our results confirm the coordinated roles of symplekin in cell junctions and gene transcription, which are related to its subcellular localization. The significance of nuclear symplekin in tumorigenesis is also highlighted, and ERK-dependent phosphorylation represents a mechanism for its subcellular sorting.
Symplekin 是一种多功能蛋白，可定位于极化上皮细胞的紧密连接和核内，其在 mRNA 成熟、转录调节和紧密连接组装中具有明确的作用。然而，其亚细胞分布和相关功能的调控机制尚不清楚。在本研究中，我们发现 symplekin 主要定位于培养的去分化结直肠癌细胞的核内，核内 symplekin 的磷酸化水平和与 YBX3 的结合亲和力均高于其膜部分。此外，核内 symplekin 的积累促进了细胞增殖和去分化以及β-catenin 的体外转录激活。核内 symplekin 作为许多细胞周期相关基因表达的转录共激活因子。此外，细胞外信号调节激酶（ERK）在表皮生长因子（EGF）刺激时将 symplekin 磷酸化至 T1257，从而促进其核内积累。同时，总 symplekin 的减少也会诱导 HT-29 细胞中发生某些上皮-间充质转化特征。总之，我们的结果证实了 symplekin 在细胞连接和基因转录中的协调作用，这与其亚细胞定位有关。核内 symplekin 在肿瘤发生中的意义也得到了强调，ERK 依赖性磷酸化代表了其亚细胞分选的一种机制。
