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

• 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
• 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
• 来源: https://reporter.nih.gov/project-details/8912922
• 关键词: Binding; Cell Line; Cell Nucleolus; Cells; Clustered Regularly Interspaced Short Palindromic Repeats; Complex; Consensus; Consensus Sequence; Coupled; Cyclin E; Environment; Event; Exclusion; Exhibits; Goals; Human; Individual; JUN gene; Knock-in Mouse; Ligase; Malignant Neoplasms; Mediating; Molecular; Mutate; Nuclear; Orthologous Gene; Pathway interactions; Peptide Hydrolases; Peptidylprolyl Isomerase; Phosphoserine; Phosphothreonine; Positioning Attribute; Process; Proline; Property; Protein Isoforms; Proteolysis; Regulation; Research; Specificity; Substrate Cycling; Technology; Testing; Ubiquitin; Ubiquitin-mediated Proteolysis Pathway; Variant; Yeasts; c-myc Genes; cis trans isomerization; design; genetic regulatory protein; human CCNE1 protein; mutant; prolyl-proline; public health relevance; research study; ubiquitin ligase

 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（由适用提供）：SCFFBW7是一种多亚基泛素连接酶，靶向数量重要的细胞调节蛋白用于泛素介导的蛋白水解。这些底物的靶向是通过特异性因子FBW7介导的，该因子FBW7识别出一种称为CPD的变性共识序列（对于CDC4磷酸根; Cdc4； Cdc4是FBW7的酵母直立性）。尽管单个CPD之间存在显着差异，但在要求在0位0和位置+1处的磷酸硫氨酸（磷serine频率较低）的共识是不变的。但是，对于大多数SCFFBW7的脊椎动物底物，位置+2的第二个脯氨酸，在SCFCDC4的酵母底物中未观察到序列基序。然而，SCFCDC4具有含有脯氨酸丙啉序列的无处不在的晚期哺乳动物底物。该观察结果表明，脯氨酸基序已经进化以执行额外的功能。我们已经显示了一种底物人类细胞周期蛋白E1，尽管第二个脯氨酸对于泛素化和蛋白水解并不重要，但本身确实对Cyclin e离职的某些方面产生了深远的影响。具体而言，第二个脯氨酸是将磷酸化的细胞周期蛋白E转移到该脯氨酸中所必需的 核仁由SCF配置为核特异性FBW7同工型FBW7进行泛素化。核仁易位需要核FBW7同工型，FBW7A和脯氨酰肽基顺式跨性异构酶PIN1，它们合作以对脯氨酸 - 丙啉键而不是磷酸胆红素 - 丙啉键进行非通道异构化，因为PIN1通常是PIN1的情况。拟议研究的一般目标是了解与FBW7A和PIN1结合的脯氨酸键键进行的机制，从而经历顺式传播异构化并促进细胞周期蛋白E核易位，并确定为什么泛素介导的细胞周期蛋白E的蛋白水解促进了细胞周期蛋白E的蛋白水解以融合了核转运。最后，我们将确定其他在其磷draphodgrons中等效位置的脯氨酸序列的SCFFBW7底物是否还表现出依赖性PIN1依赖性异构化和核仁易位与其降解相连。