The SCFFbw7 Substrate Cycle: phosphodegron processing and nucleolar translocation

SCFFbw7 底物循环：磷酸化降解子加工和核仁转位

基本信息

批准号：
8912922
负责人：
Steven I Reed
金额：
$ 39.14万
依托单位：
SCRIPPS RESEARCH INSTITUTE, THE
依托单位国家：
美国
项目类别：
财政年份：
2015
资助国家：
美国
起止时间：
2015-03-01 至 2019-02-28
项目状态：
已结题

项目摘要

DESCRIPTION (provided by applicant): SCFFbw7 is a multisubunit ubiquitin ligase that targets number important cellular regulatory proteins for ubiquitin mediated proteolysis. Targeting of these substrates is mediated via the specificity factor Fbw7, which recognizes a somewhat degenerate consensus sequence known as the CPD (for Cdc4 PhosphoDegron; Cdc4 is the yeast ortholog of Fbw7). Although there is significant variation between individual CPDs, the consensus is invariant in demanding a phosphothreonine (less frequently a phosphoserine) at position 0 and a proline at position +1. However, for most vertebrate substrates of SCFFbw7, there is a second proline at position +2, a sequence motif not observed in yeast substrates of SCFCdc4. Nevertheless, SCFCdc4 is competent to ubiquity late mammalian substrates containing the proline-proline sequence. This observation suggests that the proline-proline motif has evolved to carry out an additional function. We have shown for one substrate, human cyclin E1, that although the second proline is not important for ubiquitylation and proteolysis, per se, it does have a profound effect on certain aspects of cyclin E turnover. Specifically, this second proline is required for translocation of phosphorylated cyclin E into the nucleolus where ubiquitylation is carried out by SCF constituted with a nucleolus-specific Fbw7 isoform, Fbw7. Nucleolar translocation requires both the nuclear Fbw7 isoform, Fbw7a, and the prolyl peptidyl cis-trans isomerase Pin1, which collaborate to carry out a non-cannonical isomerization of the proline-proline bond rather than the phosphothreonine-proline bond, as is typically the case for Pin1. The general goal of the proposed research is to understand the mechanism whereby a proline-proline bond in conjunction with Fbw7a and Pin1 undergoes cis-trans isomerization and promotes cyclin E nucleolar translocation, and to determine why ubiquitin-mediated proteolysis of cyclin E has evolved to incorporate nucleolar translocation. Finally, we will determine whether other SCFFbw7 substrates that contain a proline-proline sequence at an equivalent position in their phosphodegrons also exhibit Pin1- dependent isomerization and nucleolar translocation coupled to their degradation.

描述（由申请人提供）：SCFFbw7 是一种多亚基泛素连接酶，针对泛素介导的蛋白水解作用，靶向许多重要的细胞调节蛋白。这些底物的靶向是通过特异性因子 Fbw7 介导的，Fbw7 识别称为 CPD 的某种程度简并的共有序列。 Cdc4 PhosphoDegron；Cdc4 是 Fbw7 的酵母直系同源物）。在各个 CPD 之间，在位置 0 处需要磷酸苏氨酸（磷酸丝氨酸的情况较少）和位置 +1 处需要脯氨酸方面，共识是不变的。然而，对于 SCFFbw7 的大多数脊椎动物底物，在位置 +2 处有第二个脯氨酸，这是一个序列。然而，SCFCdc4 能够普遍存在于含有脯氨酸-脯氨酸序列的晚期哺乳动物底物中。我们已经证明，脯氨酸-脯氨酸基序已进化出一种额外的功能，即人细胞周期蛋白 E1，尽管第二个脯氨酸对于泛素化和蛋白水解本身并不重要，但它确实对某些物质具有深远的影响。具体来说，第二个脯氨酸是磷酸化的细胞周期蛋白 E 易位至细胞周期蛋白 E 中所必需的。核仁中的泛素化是由核仁特异性 Fbw7 同工型 Fbw7 构成的 SCF 进行的。核仁易位需要核 Fbw7 同工型 Fbw7a 和脯氨酰肽基顺反异构酶 Pin1，它们协同进行非规范异构化。脯氨酸-脯氨酸键而不是磷酸苏氨酸-脯氨酸键，就像 Pin1 的典型情况一样。拟议研究的总体目标是了解脯氨酸-脯氨酸键与 Fbw7a 和 Pin1 结合发生顺反异构化并促进细胞周期蛋白 E 核仁易位的机制，以及以确定为什么泛素介导的细胞周期蛋白 E 的蛋白水解已经进化到核仁易位。最后，我们将确定是否有其他原因。 SCFFbw7 底物在其磷酸降解子的等效位置处含有脯氨酸-脯氨酸序列，也表现出与降解相关的 Pin1 依赖性异构化和核仁易位。