Department of Biochemistry and Center for Cancer Research, Purdue University, West Lafayette, IN, USA.
Cell Cycle. 2012 Jan 15;11(2):384-94. doi: 10.4161/cc.11.2.18944.
The anaphase-promoting complex (APC) is tightly regulated during cell division, often by pseudosubstrate binding to its coactivators Cdh1 and Cdc20. Budding yeast Acm1 is a Cdh1 pseudosubstrate inhibitor whose biological function is unknown. We show here that cells lacking Acm1 have defects in nuclear positioning and spindle morphology during mitosis. However, Cdh1 substrates are not destabilized in the absence of Acm1 and expression of inactive Cdh1 mutants that retain substrate binding is sufficient for the acm1 phenotype. We conclude that Acm1 is not required to inhibit APC(Cdh1) activity but rather prevents untimely Cdh1-substrate interactions. We further provide evidence suggesting that the substrate primarily responsible for the acm1 phenotype is the bud neck-localized kinase, Hsl1. Our results imply that at least some coactivator-substrate interactions require regulation. Several unrelated APC pseudosubstrates have been identified in diverse eukaryotes and their ability to simultaneously inhibit enzymatic activity and substrate binding may partly explain why this regulatory mechanism has been selected repeatedly during evolution.
后期促进复合物（APC）在细胞分裂过程中受到严格的调控，通常通过与共激活因子 Cdh1 和 Cdc20 的假底物结合来实现。芽殖酵母 Acm1 是 Cdh1 的假底物抑制剂，但其生物学功能尚不清楚。我们在这里表明，缺乏 Acm1 的细胞在有丝分裂过程中存在核定位和纺锤体形态缺陷。然而，在缺乏 Acm1 的情况下，Cdh1 的底物并没有不稳定，并且表达保留底物结合的无活性 Cdh1 突变体足以表现出 acm1 表型。我们得出结论，Acm1 不需要抑制 APC(Cdh1)活性，而是防止 Cdh1-底物过早相互作用。我们进一步提供的证据表明，主要负责 acm1 表型的底物是位于芽颈的激酶 Hsl1。我们的结果表明，至少一些共激活因子-底物相互作用需要调节。在不同的真核生物中已经鉴定出几种不相关的 APC 假底物，它们同时抑制酶活性和底物结合的能力部分解释了为什么这种调节机制在进化过程中被反复选择。
