Du Quansheng, Taylor Laura, Compton Duane A, Macara Ian G
Center for Cell Signaling, Department of Microbiology, University of Virginia, Charlottesville, VA 22908, USA.
Curr Biol. 2002 Nov 19;12(22):1928-33. doi: 10.1016/s0960-9822(02)01298-8.
LGN is closely related to a Drosophila protein, Partner of inscuteable (Pins), which is required for polarity establishment and asymmetric cell divisions during embryonic development. In mammalian cells, LGN binds with high affinity to the C-terminal tail of NuMA, a large nuclear protein that is required for spindle organization, and accumulates at the spindle poles during mitosis. LGN also regulates spindle organization, possibly through inhibition of NuMA function, but the mechanism of this effect has not yet been understood. Using mammalian cells, frog egg extracts, and in vitro assays, we now show that a small domain within the C terminus of NuMA stabilizes microtubules (MTs), and that LGN blocks stabilization. The nuclear localization signal adjacent to this domain is not involved in stabilization. NuMA can interact directly with MTs, and the MT binding domain on NuMA overlaps by ten amino acid residues with the LGN binding domain. We therefore propose that a simple steric exclusion model can explain the inhibitory effect of LGN on NuMA-dependent mitotic spindle organization.
外侧膝状体核（LGN）与果蝇蛋白“无定向蛋白的伙伴”（Pins）密切相关，后者是胚胎发育过程中极性建立和不对称细胞分裂所必需的。在哺乳动物细胞中，LGN与核有丝分裂器蛋白（NuMA）的C末端尾巴以高亲和力结合，NuMA是一种大型核蛋白，对纺锤体组织至关重要，并且在有丝分裂期间聚集在纺锤体极。LGN也调节纺锤体组织，可能是通过抑制NuMA功能，但这种效应的机制尚未明确。利用哺乳动物细胞、蛙卵提取物和体外实验，我们现在表明NuMA C末端的一个小结构域可稳定微管（MTs），而LGN会阻止这种稳定作用。邻近该结构域的核定位信号不参与稳定作用。NuMA可直接与MTs相互作用，且NuMA上的MT结合结构域与LGN结合结构域有十个氨基酸残基的重叠。因此，我们提出一个简单的空间位阻模型可以解释LGN对NuMA依赖的有丝分裂纺锤体组织的抑制作用。
