Jamieson Cara, Mills Kate M, Lui Christina, Semaan Crystal, Molloy Mark P, Sharma Manisha, Forwood Jade K, Henderson Beric R
Centre for Cancer Research, The Westmead Institute for Medical Research, The University of Sydney, Westmead, NSW 2145, Australia.
Centre for Cancer Research, The Westmead Institute for Medical Research, The University of Sydney, Westmead, NSW 2145, Australia; Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW 2109, Australia.
Exp Cell Res. 2016 Feb 15;341(2):196-206. doi: 10.1016/j.yexcr.2016.01.020. Epub 2016 Feb 1.
Beta-catenin plays a key role in transducing Wnt signals from the plasma membrane to the nucleus. Here we characterize an unusual subcellular distribution of beta-catenin in MCF-7 breast cancer cells, wherein beta-catenin localizes to the cytoplasm and membrane but atypically did not relocate to the nucleus after Wnt treatment. The inability of Wnt or the Wnt agonist LiCl to induce nuclear localization of beta-catenin was not due to defective nuclear transport, as the transport machinery was intact and ectopic GFP-beta-catenin displayed rapid nuclear entry in living cells. The mislocalization is explained by a shift in the retention of beta-catenin from nucleus to cytoplasm. The reduced nuclear retention is caused by unusually low expression of lymphoid enhancer factor/T-cell factor (LEF/TCF) transcription factors. The reconstitution of LEF-1 or TCF4 expression rescued nuclear localization of beta-catenin in Wnt treated cells. In the cytoplasm, beta-catenin accumulated in recycling endosomes, golgi and beta-COP-positive coatomer complexes. The peripheral association with endosomes diminished after Wnt treatment, potentially releasing β-catenin into the cytoplasm for nuclear entry. We propose that in MCF-7 and perhaps other breast cancer cells, beta-catenin may contribute to cytoplasmic functions such as ER-golgi transport, in addition to its transactivation role in the nucleus.
β-连环蛋白在将Wnt信号从质膜传导至细胞核的过程中发挥关键作用。在此，我们描述了MCF-7乳腺癌细胞中β-连环蛋白一种不同寻常的亚细胞分布情况，其中β-连环蛋白定位于细胞质和细胞膜，但在Wnt处理后未像通常那样重新定位于细胞核。Wnt或Wnt激动剂氯化锂无法诱导β-连环蛋白的核定位，这并非由于核转运缺陷，因为转运机制是完整的，异位表达的绿色荧光蛋白-β-连环蛋白在活细胞中能快速进入细胞核。这种定位错误是由β-连环蛋白从细胞核向细胞质的保留转移所解释的。核保留减少是由淋巴样增强因子/T细胞因子（LEF/TCF）转录因子异常低表达所致。LEF-1或TCF4表达的重建挽救了Wnt处理细胞中β-连环蛋白的核定位。在细胞质中，β-连环蛋白积聚在回收型内体、高尔基体和β-COP阳性衣被蛋白复合物中。Wnt处理后，与内体的外周关联减少，这可能会将β-连环蛋白释放到细胞质中以便进入细胞核。我们提出，在MCF-7细胞以及可能的其他乳腺癌细胞中，β-连环蛋白除了在细胞核中发挥反式激活作用外，可能还参与细胞质功能，如内质网-高尔基体运输。
