Massimi Paola, Gardiol Daniela, Roberts Sally, Banks Lawrence
International Centre for Genetic Engineering and Biotechnology, Padriciano 99, I-34012 Trieste, Italy.
Exp Cell Res. 2003 Nov 1;290(2):265-74. doi: 10.1016/s0014-4827(03)00317-3.
Drosophila discs large (Dlg) has been shown to be an essential regulator of cell polarity and attachment, and is classified as a potential tumour suppressor in higher eukaryotes. Human Dlg is expressed in epithelial cells at sites of cell-cell contact and acts as a negative regulator of cell growth. Although hDlg has been shown to be phosphorylated during mitosis, little is known about its activity during this stage of the cell cycle. To investigate this further we have analysed in detail the pattern of hDlg expression during mitotic cell division. In early mitosis there is a marked increase in membrane-bound hDlg which is then retained throughout mitosis, while during cytokinesis, there is a specific concentration of hDlg at the midbody. Using mutants of Dlg we show that this is mediated by sequences in the carboxy terminal region of Dlg, but it does not require the SH3 or PDZ domains, and is independent of binding to protein 4.1. Finally, using a mutant of Dlg that consists of just this carboxy terminal region of the protein, we show that it can compete with endogenous hDlg for midbody accumulation, and this mutant also gives rise to altered cell growth. We conclude that localisation of Dlg to the midbody indicates a role for Dlg at this critical point in cytokinesis.
果蝇盘大蛋白（Dlg）已被证明是细胞极性和附着的重要调节因子，在高等真核生物中被归类为潜在的肿瘤抑制因子。人Dlg在细胞间接触部位的上皮细胞中表达，并作为细胞生长的负调节因子。尽管已证明hDlg在有丝分裂期间会发生磷酸化，但对其在细胞周期这一阶段的活性了解甚少。为了进一步研究这一点，我们详细分析了有丝分裂细胞分裂过程中hDlg的表达模式。在有丝分裂早期，膜结合的hDlg显著增加，然后在整个有丝分裂过程中持续存在，而在胞质分裂期间，hDlg在中体处有特定的聚集。使用Dlg突变体，我们表明这是由Dlg羧基末端区域的序列介导的，但它不需要SH3或PDZ结构域，并且与蛋白质4.1的结合无关。最后，使用仅由该蛋白质的羧基末端区域组成的Dlg突变体，我们表明它可以与内源性hDlg竞争中体积累，并且该突变体还会导致细胞生长改变。我们得出结论，Dlg定位于中体表明Dlg在胞质分裂的这一关键点上发挥作用。
