Two ubiquitin-conjugating enzymes, UbcP1/Ubc4 and UbcP4/Ubc11, have distinct functions for ubiquitination of mitotic cyclin
Two ubiquitin-conjugating enzymes, UbcP1/Ubc4 and UbcP4/Ubc11, have distinct functions for ubiquitination of mitotic cyclin
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DOI：
10.1128/mcb.23.10.3497-3505.2003
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发表时间：
2003-05-01
影响因子：
5.3
通讯作者：
Yamao, F
中科院分区：
文献类型：
--
作者：
Seino, H;Kishi, T;Yamao, F
细胞周期事件由CDK激酶的顺序激活和失活来调节。有丝分裂的退出是通过有丝分裂的CDK激酶失活完成的，这主要是通过细胞周期蛋白的降解来实现的。泛素-蛋白酶体系统参与了这个过程，需要APC/C(后期促进复合体/环体)作为泛素连接酶。在非洲爪哇和文蛤卵母细胞中，与APC/C功能相关的泛素结合酶被鉴定为两种蛋白：UBC4和UBCx/E2-C。先前我们报道了分裂酵母泛素结合酶UbcP4/Ubc11，它是UBCx/E2-C的同源物，是有丝分裂转换所必需的。在这里，我们证明了另一种分裂酵母泛素结合酶UbcP1/Ubc4，它与Ubc4同源，也是有丝分裂转换所必需的，其方式与UbcP4/Ubc11相同。这两种泛素偶联酶都是细胞分裂所必需的，并直接需要有丝分裂周期蛋白CDc13的降解。它们在CDC13的泛素化中起非冗余作用，因为ubcP1/ubc4(+)的缺陷不能被UbcP4/Ubc11的高表达所抑制，而ubcP4/ubc11(+)的缺陷不能被UbcP1/Ubc4的高表达所抑制。体内泛素化状态分析表明，在ubcP1/ubc4突变细胞中，cdc13上的泛素化链较短，而在ubcP4/ubc11突变细胞中，泛素化的cdc13被完全还原。综上所述，这些结果表明，这两种泛素结合酶在有丝分裂周期蛋白CDc13的降解过程中发挥着不同的重要作用，其中UbcP4/Ubc11途径启动了CDc13的泛素化，UbcP1/Ubc4途径延长了CDc13上的泛素短链。
Cell cycle events are regulated by sequential activation and inactivation of Cdk kinases. Mitotic exit is accomplished by the inactivation of mitotic Cdk kinase, which is mainly achieved by degradation of cyclins. The ubiquitin-proteasome system is involved in this process, requiring APC/C (anaphase-promoting complex/cyclosome) as a ubiquitin ligase. In Xenopus and clam oocytes, the ubiquitin-conjugating enzymes that function with APC/C have been identified as two proteins, UBC4 and UBCx/E2-C. Previously we reported that the fission yeast ubiquitin-conjugating enzyme UbcP4/Ubc11, a homologue of UBCx/E2-C, is required for mitotic transition. Here we show that the other fission yeast ubiquitin-conjugating enzyme, UbcP1/Ubc4, which is homologous to UBC4, is also required for mitotic transition in the same manner as UbcP4/Ubc11. Both ubiquitin-conjugating enzymes are essential for cell division and directly required for the degradation of mitotic cyclin Cdc13. They function nonredundantly in the ubiquitination of CDC13 because a defect in ubcP1/ubc4(+) cannot be suppressed by high expression of UbcP4/Ubc11 and a defect in ubcP4/ubc11(+) cannot be suppressed by high expression of UbcP1/Ubc4. In vivo analysis of the ubiquitinated state of Cdc13 shows that the ubiquitin chains on Cdc13 were short in ubcP1/ubc4 mutant cells while ubiquitinated Cdc13 was totally reduced in ubcP4/ubc11 mutant cells. Taken together, these results indicate that the two ubiquitin-conjugating enzymes play distinct and essential roles in the degradation of mitotic cyclin Cdc13, with the UbcP4/Ubc11-pathway initiating ubiquitination of Cdc13 and the UbcP1/Ubc4-pathway elongating the short ubiquitin chains on Cdc13.