Minoshima Yukinori, Kawashima Toshiyuki, Hirose Koichi, Tonozuka Yukio, Kawajiri Aie, Bao Ying Chun, Deng Xingming, Tatsuka Masaaki, Narumiya Shuh, May W Stratford, Nosaka Tetsuya, Semba Kentaro, Inoue Takafumi, Satoh Takaya, Inagaki Masaki, Kitamura Toshio
Division of Hematopoietic Factors, The Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
Dev Cell. 2003 Apr;4(4):549-60. doi: 10.1016/s1534-5807(03)00089-3.
Cell division is finely controlled by various molecules including small G proteins and kinases/phosphatases. Among these, Aurora B, RhoA, and the GAP MgcRacGAP have been implicated in cytokinesis, but their underlying mechanisms of action have remained unclear. Here, we show that MgcRacGAP colocalizes with Aurora B and RhoA, but not Rac1/Cdc42, at the midbody. We also report that Aurora B phosphorylates MgcRacGAP on serine residues and that this modification induces latent GAP activity toward RhoA in vitro. Expression of a kinase-defective mutant of Aurora B disrupts cytokinesis and inhibits phosphorylation of MgcRacGAP at Ser387, but not its localization to the midbody. Overexpression of a phosphorylation-deficient MgcRacGAP-S387A mutant, but not phosphorylation-mimic MgcRacGAP-S387D mutant, arrests cytokinesis at a late stage and induces polyploidy. Together, these findings indicate that during cytokinesis, MgcRacGAP, previously known as a GAP for Rac/Cdc42, is functionally converted to a RhoGAP through phosphorylation by Aurora B.
细胞分裂受到包括小G蛋白以及激酶/磷酸酶在内的多种分子的精确调控。其中，极光激酶B（Aurora B）、RhoA以及GTP酶激活蛋白MgcRacGAP均与胞质分裂有关，但其潜在的作用机制仍不清楚。在此，我们发现MgcRacGAP与极光激酶B和RhoA在中体处共定位，但不与Rac1/Cdc42共定位。我们还报告称，极光激酶B在丝氨酸残基上使MgcRacGAP磷酸化，并且这种修饰在体外诱导了对RhoA的潜在GAP活性。极光激酶B的激酶缺陷型突变体的表达会破坏胞质分裂，并抑制MgcRacGAP在Ser387处的磷酸化，但不影响其在中体的定位。磷酸化缺陷型MgcRacGAP-S387A突变体（而非磷酸化模拟型MgcRacGAP-S387D突变体）的过表达会使胞质分裂停滞在后期并诱导多倍体形成。总之，这些发现表明，在胞质分裂过程中，先前已知作为Rac/Cdc42的GAP的MgcRacGAP通过极光激酶B的磷酸化在功能上转变为RhoGAP。
