Kaushik Rachna, Yu Fengwei, Chia William, Yang Xiaohang, Bahri Sami
Institute of Molecular and Cell Biology, Singapore 117609.
Mol Biol Cell. 2003 Aug;14(8):3144-55. doi: 10.1091/mbc.e03-04-0212. Epub 2003 May 3.
Mammalian LGN/AGS3 proteins and their Drosophila Pins orthologue are cytoplasmic regulators of G-protein signaling. In Drosophila, Pins localizes to the lateral cortex of polarized epithelial cells and to the apical cortex of neuroblasts where it plays important roles in their asymmetric division. Using overexpression studies in different cell line systems, we demonstrate here that, like Drosophila Pins, LGN can exhibit enriched localization at the cell cortex, depending on the cell cycle and the culture system used. We find that in WISH, PC12, and NRK but not COS cells, LGN is largely directed to the cell cortex during mitosis. Overexpression of truncated protein domains further identified the Galpha-binding C-terminal portion of LGN as a sufficient domain for cortical localization in cell culture. In mitotic COS cells that normally do not exhibit cortical LGN localization, LGN is redirected to the cell cortex upon overexpression of Galpha subunits of heterotrimeric G-proteins. The results also show that the cortical localization of LGN is dependent on microfilaments and that interfering with LGN function in cultured cell lines causes early disruption to cell cycle progression.
哺乳动物的LGN/AGS3蛋白及其果蝇同源物Pins是G蛋白信号传导的细胞质调节剂。在果蝇中，Pins定位于极化上皮细胞的外侧皮质和神经母细胞的顶端皮质，在其不对称分裂中发挥重要作用。通过在不同细胞系系统中的过表达研究，我们在此证明，与果蝇Pins一样，LGN可以根据细胞周期和所使用的培养系统在细胞皮质处表现出富集定位。我们发现，在WISH、PC12和NRK细胞中，但在COS细胞中并非如此，LGN在有丝分裂期间主要定位于细胞皮质。截短蛋白结构域的过表达进一步确定LGN的Gα结合C末端部分是细胞培养中皮质定位的充分结构域。在正常情况下不表现出皮质LGN定位的有丝分裂COS细胞中，当异源三聚体G蛋白的Gα亚基过表达时，LGN会重新定位于细胞皮质。结果还表明，LGN的皮质定位依赖于微丝，并且干扰培养细胞系中的LGN功能会导致细胞周期进程的早期破坏。
