乙酰化热休克蛋白hsp90在肿瘤转移中的作用

Heat shock protein (hsp) 90 is an ATP-dependent molecular chaperone whose association is required for the stability and function of client oncoproteins in the development of human cancer. Lysine (K) acetylation is a reversible modification mediated by opposing actions of acetyltransferases (HAT) and deacetylases (HDAC). Overall, hyperacetylation of hsp90 was shown to inhibit the ATP, cochaperone p23, and client protein binding to hsp90, directing the client proteins to proteasomal degradation. Although reversible acetylation attenuates ATP binding and chaperone function of hsp90 in vitro, almost nothing is known about the acetylation sites, functions, mechanisms of action on tumor metastasis, and regulation of acetylated hsp90 in vivo. In this proposal, the overall hypothesis is that acetylation at specific sites increase the chaperone function of hsp90 in tumor, which in turn stimulate tumor metastasis. The goal of this project is to obtain a greater mechanistic understanding of how acetylated hsp90 promotes tumor metastasis and how acetylation status of hsp90 might be intricately regulated in vivo. Particular emphasis will be devoted to determine the identity and functional significance of the specific lysine acetylation sites of hsp90 in vivo, as well as functional relevance of each acetylation site in tumorogenesis. Additionally, molecules that are regulated by acetylated hsp90 in breast cancer will be rigorously identified. Collectively, this study will not only provide a true role of lysine acetylation of hsp90 in tumorogenesis and the stoichiometry of binding between acetylated hsp90 and other chaperones as well as clients in vivo, but will contribute directly to our understanding of targeting acetylated hsp90 as an efficient strategy for reducing metastasis.

热休克蛋白（HSP）90是一个ATP依赖型的分子伴侣，对肿瘤发生发展中癌蛋白稳定性及功能方面扮演着十分重要的角色。总体而言，在体外细胞体系中乙酰化修饰抑制HSP90与ATP及伴侣底物结合，并削弱其分子伴侣功能。目前对体内体系中hsp90乙酰化位点及功能、乙酰化hsp90对肿瘤转移的作用及其本身的调控仍有待阐明。本项目提出，在肿瘤中特定位点乙酰化增强HSP90分子伴侣功能，促进肿瘤的转移。目的是为了从机理上弄清体内体系中，乙酰化HSP90如何促进肿瘤转移，体内HSP90的乙酰化状态又是如何调控的。我们将鉴定肿瘤内HSP90的乙酰化位点和功能上的重要性，及其与肿瘤生长转移的相关性，明确乳腺癌中调控乙酰化HSP90的重要分子。总的来说，这项研究将阐明肿瘤中乙酰化HSP90的作用，定量测定体内乙酰化HSP90与伴侣分子及伴侣底物之间的结合，还将有助于了解乙酰化HSP90为靶标抑制肿瘤转移的策略。

本项目的实施，颠覆了“乙酰化修饰抑制Hsp90分子伴侣功能”的传统观念，发现了可用于临床的乙酰化Hsp90抑制剂。我们发现，肿瘤里Hsp90乙酰化主要发生在K292位点，和K69乙酰化不同，该乙酰化极大地增强Hsp90和ATP的结合，增强Hsp90促进乳腺肿瘤转移的能力。K292乙酰化赋予Hsp90多方面的新功能，鉴定发现K292乙酰化Hsp90和许多蛋白分子形成复合物而发挥不同的作用：和乙酰化Hsp70一起增强Vps34依赖型自噬小体的形成，使肿瘤细胞产生防御性的自噬；还和信号传导密切相关的GAP（Rasal2）蛋白关联，共同调节肿瘤细胞EMT相关蛋白表达及蛋白激酶的活性；更重要的是，K292乙酰化增强Hsp90/CDC37伴侣机器的形成，由此增强肿瘤蛋白激酶的活性而促进乳腺肿瘤的发展。基于K292乙酰化Hsp90和CDC37形成伴侣机器的能力，我们以K292乙酰化Hsp90为靶标，筛选发现了Simvastatin是一个K292乙酰化Hsp90抑制剂，还发现了TL-2-8是一个AHA1抑制剂。.总的来说，这项研究阐明了肿瘤中K292乙酰化Hsp90的作用，有助于以乙酰化Hsp90为靶标的Hsp90抑制剂在临床上的应用。