UCH-L1调控雌激素受体的分子机制及对雌激素拮抗剂乳腺癌治疗的影响

The status of estrogen receptor (ER) in breast cancer is usually associated with prognosis and response to hormonal therapy. ER status varies among breast cancers, with one-third of the disease showing ER-negative. Absence of ER is known to be associated with poor differentiation of tumor cells, resistance to hormonal therapy, and poor clinical outcome; thus, a better understanding of the causes and mechanisms underlying the loss or reduction of ER in breast cancer may help identify novel strategy for treating breast cancer. We recently found that the expression of ubiquitin C-terminal hydrolase-L1 (UCH-L1), an enzyme that uniquely possesses both ubiquitin hydrolase and ligase activity, is conversely related with ERα status in breast cancer. UCH-L1 is overexpressed in ER(-) cell lines, but is barely detectable in ER(+) cell lines. Transfection of ER(+) cells with an UCH-L1 expression vector resulted in a remarkable reduction of ERα content. These results implicate a role of UCH-L1 in the down-regulation of ERα in breast cancer. This proposal is aimed at exploring the role of UCH-L1 in regulating ERα degradation and gene expression in human breast cancer cells and the therapeutic implication. We will test the hypothesis that overexpression of UCH-L1 contributes to the development of hormone-independent breast cancer by facilitating the degradation of ERα or/and by repressing the gene expression of the receptor, and that targeting this enzyme can sensitize hormone-resistant human breast cancers to the selective estrogen receptor modulators such as tamoxifen, the most commonly used anti-estrogen agent in the treatment of this disease. The proposed study may not only provide a basis for new approaches to up-regulating or maintaining ER level, but also present a new rationale for developing more effective and better therapies for breast cancer, and a new pharmacologic target for drug development.

雌激素受体（Estrogen receptor，ER）的状态是预测乳腺癌对内分泌治疗效果和预后的关键指标之一，但大约有三分之一的乳腺癌是呈ER阴性的。ER阴性乳腺癌细胞分化程度低，易转移且治疗及预后效果差。因此，阐明调控ER表达的分子机制可能为乳腺癌治疗提供新的策略和方法。申请人前期研究发现，乳腺癌细胞中泛素羧基末端水解酶UCH-L1与ERα表达呈负相关。ERα阴性和阳性细胞中UCH-L1蛋白分别显示出高表达和低表达，在ERα阳性细胞中过表达UCH-L1则导致ERα水平明显下调。本课题拟深入研究UCH-L1调控ERα表达的分子机制，阐明UCH-L1对ERα泛素化及蛋白降解的影响，探索UCH-L1对组蛋白泛素化及对ERα基因表达的调控作用；确定靶向UCH-L1对雌激素拮抗剂乳腺癌治疗效果的影响。本项目研究旨在揭示新的调控ERα表达的分子机制，为提高乳腺癌（包括ER阴性）的治愈率提供科学依据。

乳腺癌是女性最常见的恶性肿瘤之一，严重威胁女性生命健康。临床上，约有三分之二乳腺癌是雌激素受体（ER）阳性的，属于雌激素依赖性肿瘤，对抗雌激素药物如他莫昔芬治疗敏感。ER是乳腺癌重要的生物学标记物，是指导临床诊断、治疗和判定预后的重要指标，其在乳腺癌发生、发展和治疗中的作用已被广泛证实，是目前乳腺癌治疗的关键靶点之一。然而，约有三分之一乳腺癌由于缺乏ER，对内分泌抗激素治疗不敏感。 ER阴性乳腺癌细胞分化程度差、易转移、对抗激素治疗耐药、预后效果差，是目前乳腺癌临床治疗的一大难题。因此，研究调控ER表达的分子机制及信号通路，通过诱导乳腺癌细胞中ER的表达恢复，增强抗激素药物的敏感性，将为三阴性乳腺癌临床治疗提供新的策略和方法。我们研究发现，泛素羧基末端水解酶L1 (UCH-L1) 与ERα表达呈负相关。在ERα阳性乳腺癌细胞中过表达UCH-L1导致ERα mRNA和蛋白水平下调，而在ERα阴性乳腺癌细胞中沉默UCH-L1或使用UCH-L1小分子抑制剂则提高了ERα mRNA和蛋白水平。UCH-L1在转录水平调控ERα基因表达进而影响ERα蛋白水平，因此，我们进一步探讨UCH-L1调控ERα的分子机制。我们研究发现，UCH-L1能够与EGFR相互结合，UCH-L1通过去泛素化作用维持EGFR蛋白的稳定性从而介导UCH-L1对ERα的调控作用。最后，我们研究证明，通过靶向抑制UCH-L1能够显著增强ERα阴性乳腺癌细胞对他莫昔芬治疗的敏感性。这些研究结果揭示，去泛素化酶UCH-L1可能是提高内分泌治疗敏感性的一个潜在干预靶点。我们的研究不仅为提高ERα表达从而增强抗激素药物治疗三阴性乳腺癌的敏感性提供了理论依据，并且为临床上抗肿瘤药物的设计与开发提供了科学有效的药物靶点。