PIASXβ介导的SUMO修饰抑制转录和组蛋白乙酰化修饰的机理研究

Regulation of gene expression is essential for all living organisms. Since the seminal discovery of PIAS family proteins as inhibitors of STAT transcription factors and SUMO E3 ligases, numerous studies have identified PIAS proteins and their mediated SUMO modifications with transcriptional repression. However, mechanistically how SUMO modification leads to general transcriptional repression remains poorly defined. Our preliminary study revealed that, although many PIAS proteins can globally repress transcription in mammalian cells when co-expressed with SUMO1, only PIASXβ has the capacity to repress transcription as well as global histone acetylation. Our preliminary study also suggested that PIASXβ is likely to repress histone acetylation by SUMO-modification of class I histone deacetylases, which in turn enhances their HDAC activity and results in global histone deacetylation. In this grant we aim to investigate in detail: 1) the underlying mechanism by which PIASXβ but not other PIAS selectively catalyzes class I HDAC SUMO modification; 2) the mechanism by which SUMO modifications enhance HDAC activity; 3) identification and characterization of site(s) of SUMO modifications on different HDACs and their functional relevance. The proposed studies in this grant will provide novel insights into the mechanisms by which SUMO modifications regulate histone acetylation and transcription.

基因表达调控在生命过程中具有重要意义。自从PIAS 家族蛋白最早作为抑制STAT 信号通路的蛋白因子被发现以来，众多的研究表明，PIAS家族蛋白作为细胞中介导SUMO修饰的主要E3连接酶与转录的抑制密切相关，但其分子作用机制还有待进一步阐明。我们前期工作发现虽然大部分PIAS家族成员与SUMO过表达能抑制细胞整体转录活性，但只有PIASXβ能够显著的抑制转录和组蛋白整体乙酰化，其分子机制可能是通过SUMO修饰组蛋白去乙酰化酶HDAC促进其去乙酰化酶活性。在此基础上，本项目拟深入研究：1）PIASXβ特异性介导HDAC SUMO修饰的分子机制；2）SUMO修饰增强HDAC组蛋白去乙酰化酶活性的分子机制；3）鉴定PIASXβ介导的HDAC的SUMO修饰位点并探究这些位点发生SUMO修饰的生理、病理学作用。本项目的有效实施将有助于揭示和阐明SUMO修饰调控组蛋白修饰及促进转录抑制的分子机制。

SUMO 是一种重要的蛋白质翻译后修饰。PIAS家族蛋白是SUMO修饰的重要E3连接酶。虽然许多调控组蛋白乙酰化修饰的蛋白都能发生SUMO化修饰，但SUMO修饰对组蛋白乙酰化是调控作用及机制并不明确。在这个课题中我们通过过表达PIAS家族E3连接酶发现过表达PIASXbeta可以显著降低细胞整体乙酰化水平，而敲低PIASXbeta则显著上调组蛋白乙酰化。我们发现PIASXbeta对组蛋白乙酰化的调控依赖于其E3连接酶活性，并证明PIASXbeta主要催化了HDAC1/2的SUMO修饰，SUMO修饰促进HDAC1/2的稳定性和染色质结合，显著增强HDAC1/2的去乙酰化酶活性。我们的工作也提示SUMO可能通过其与组蛋白的直接结合来促进HDAC其其它蛋白在染色质调控中的作用。这一研究揭示了SUMO在调控组蛋白去乙酰化酶活性中的重要作用及分子机制。

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