表皮生长因子受体家族成员ErbB2/Her2在乳腺癌中的泛素化以及其降解调控机制研究

Epidermal Growth Factor Receptor (EGFR) family consists of four members, among which ErbB2/Her2 has been discovered to be over-expressed in a number of tumors and already considered as a key target oncoprotein in anti-cancer therapy.However,till now we still do not have very effective drug against ErbB2.HSP90 inhibitor gelanamycin (GA) and its derivatives has been found to be able to induce ErbB2 ubiquitylation and thus promote its degradation, which provides us with a novel strategy in ErbB2-targeted anti-cancer therapy.However, little detail about chemical-induced ErbB2 ubiquitylation and its subsequent degradation is known to us at the moment, which will apparently limit our ability to design correct ErbB2-targeted anti-cancer therapy.Therefore,further study is urgently required to help understand exactly how drug promotes ErbB2 ubiquitylation and degradation as well as how this process is regulated, which will eventually guide us to design appropriate method to cure ErbB2 overexpressing tumors.We have carried out screens of deubiquitylating enzymes and identified the proteasomal component POH1 as a regulator of steady state ubiquitylation of ErbB2. We have also extensive experiences in studying ubiquitylation in regulating cellular protein degradation pathways. Based on our earlier work,in this project, we aim to explore ErbB2 ubiquitylation upon different drug treatment and in different cancer cell lines, comparing its ubiquitylation sites and types as well as degradation pathways, in additon to try to identify deubiquitylases involved in GA-induced ErbB2 degradation.

表皮生长因子受体家族成员ErbB2/Her2在乳腺癌中多发现有过表达现象，是公认的靶向治疗的重要目标癌蛋白。但目前还缺乏有效治疗方法。化学药物可以促进ErbB2的泛素化以及降解，从而提供新的针对ErbB2的治疗思路。但对其泛素化及降解调控机制的有限了解阻碍设计合理有效的治疗方案。我们研究发现，去泛素化酶POH1调控ErbB2的常态泛素化(Plos ONE 2009 e5544); 还发现去泛素化酶USP8和USP15分别调控表皮生长因子受体ErbB1的内吞降解和信号传导(J Biol Chem 2007 282:30929和2012 287:43007)。在此基础上，本课题计划探索不同条件下ErbB2的泛素化信息以及其作用；在不同癌症细胞系内泛素化ErbB2的降解通路；并鉴定调控化学药物促ErbB2降解的去泛素化酶。从而为设计合理的ErbB2靶向治疗策略提供理论依据以及联合用药的新思路。

ErbB受体酪氨酸激酶家族成员ErbB2/HER2在乳腺癌、胃癌、卵巢癌等许多肿瘤中都发现有过度表达的现象，其激活下游信号传导通路促进肿瘤细胞生长，存活和侵袭。在乳腺癌中，ErbB2过度表达预示不良预后并被称为Her2/ErbB2阳性乳腺癌，约占总体乳腺癌的20-30%。针对ErbB2/HER2的靶向治疗策略比如曲妥珠单抗（赫赛汀）和拉帕替尼（泰立沙）已经应用于临床并取得了积极的疗效，但是最终耐药现象大多不可避免发生最后危及患者生命。在国家自然科学青年基金资助的本研究课题中，我们探索了通过不同ErbB2小分子抑制剂来治疗Her2/ErbB2阳性乳腺癌。我们比较了拉帕替尼（lapatinib）和来那替尼（neratinib）两种小分子抑制剂对ErbB2高表达乳腺癌的抑制作用，发现两种小分子抑制剂都能有效抑制ErbB2下游信号传导通路的激活，并且可以促进ErbB2转录水平的提高并且诱导细胞表面的ErbB2分子转运到细胞内部。其中，来那替尼对ErbB2的促进内吞作用远远强于拉帕替尼并促使ErbB2总体水平下降。后续研究发现，相比于拉帕替尼，来那替尼有效的抑制ErbB2与热应激蛋白HSP90的相互作用，从而促进ErbB2发生泛素化（ubiquitylation）。泛素化的ErbB2通过内吞（endocytosis）被有效的转运到早期内体上，然后通过晚期内体被最后运输到溶酶体（lysosome）内进行降解。所以，相比于拉帕替尼，来那替尼能够同等程度的抑制ErbB2下游主要的信号传导通路，包括RAS-MAPK和PI3K-AKT等通路。同时，来那替尼展示了促进ErbB2降解的优势作用。虽然在短期的处理上，拉帕替尼和来那替尼显示了相似的对ErbB2高表达乳腺癌的生长抑制作用和促进凋亡的效果，我们仍然在积极探索在长期用药的条件下来那替尼是否显示出明显的相对于拉帕替尼在ErbB2高表达乳腺癌治疗上的优势效果。本项研究揭示了抗ErbB2高表达乳腺癌靶向药物来那替尼的新型作用机制，从而指出了来那替尼对ErbB2高表达乳腺癌治疗的潜在优势作用。此项研究为新兴ErbB2靶向小分子药物来那替尼的临床应用提供了理论和实验依据，并展示了来那替尼在抵抗ErbB2耐药上的作用机制。本项研究主要成果已经发表学术论文（Cancer Letters）。