Mishra Mithilesh, Karagiannis Jim, Sevugan Mayalagu, Singh Pritpal, Balasubramanian Mohan K
Cell Division Laboratory, Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604.
Curr Biol. 2005 Aug 9;15(15):1376-83. doi: 10.1016/j.cub.2005.06.070.
Schizosaccharomyces pombe cells divide through the use of an actomyosin-based contractile ring. In response to perturbation of the actomyosin ring, S. pombe cells delay in a "cytokinesis-competent" state characterized by continuous repair and maintenance of the actomyosin ring and a G2 delay. This checkpoint mechanism requires the function of the Cdc14p-family phosphatase Clp1p/Flp1p and the septation initiation network (SIN). In response to cytokinetic defects, Clp1p, normally nucleolar in interphase, is retained in the cytoplasm until completion of cell division in a SIN-dependent manner. Here, we show that a phosphorylated form of Clp1p binds the 14-3-3 protein Rad24p and is retained in the cytoplasm in a Rad24p-dependent manner in response to cytokinesis defects. This physical interaction depends on the function of the SIN component, Sid2p. In the absence of Rad24p, cells are unable to maintain SIN signaling and lose viability upon mild cytokinetic stress. The requirement of Rad24p in this checkpoint is bypassed by ectopic activation of the SIN. Furthermore, SIN-dependent nuclear exclusion of Clp1p is dependent on Rad24p function. We conclude that Rad24p-mediated cytoplasmic retention of Clp1p/Flp1p is important for cell viability upon stress to the division apparatus.
粟酒裂殖酵母细胞通过基于肌动球蛋白的收缩环进行分裂。响应肌动球蛋白环的扰动，粟酒裂殖酵母细胞会在一种“具备胞质分裂能力”的状态下延迟，其特征为肌动球蛋白环的持续修复和维持以及G2期延迟。这种检查点机制需要Cdc14p家族磷酸酶Clp1p/Flp1p和隔膜起始网络（SIN）的功能。响应胞质分裂缺陷，通常在间期位于核仁的Clp1p会以SIN依赖的方式保留在细胞质中，直到细胞分裂完成。在这里，我们表明Clp1p的一种磷酸化形式结合14-3-3蛋白Rad24p，并在响应胞质分裂缺陷时以Rad24p依赖的方式保留在细胞质中。这种物理相互作用依赖于SIN组分Sid2p的功能。在没有Rad24p的情况下，细胞无法维持SIN信号传导，并且在轻度胞质分裂应激下丧失活力。通过SIN的异位激活可绕过该检查点对Rad24p的需求。此外，SIN依赖的Clp1p核排除依赖于Rad24p功能。我们得出结论，Rad24p介导的Clp1p/Flp1p细胞质保留对于细胞在分裂装置受到应激时的活力很重要。
