Structure and function of BCAR1 and BCAR3 association in breast cancer malignancy

描述（由申请人提供）：尽管有许多治疗选择，但乳腺癌是妇女癌症死亡的第二大原因。大多数乳腺癌是雌激素受体阳性，通常用抗雌激素治疗，而抗体和激酶抑制剂用于治疗过度表达HER2受体酪氨酸激酶的癌症。不幸的是，由于特定基因的过度表达，肿瘤通常具有内在的耐药性或对这些药物产生耐药性。其中一个基因是支架蛋白BCAR1（乳腺癌抗雌激素抵抗1或p130Cas），它是众所周知的信号通路的关键组成部分，调节细胞增殖、存活和整合素粘附受体下游的迁移/入侵。BCAR1也是HER2致癌信号通路的关键节点和对阿霉素耐药的介质，阿霉素常用于治疗抗雌激素或HER2靶向治疗无效的乳腺癌。因此，BCAR1在控制乳腺癌恶性肿瘤的信号网络中起着核心作用。抗雌激素耐药的另一个重要但不太清楚的因素是含有SH2结构域的蛋白BCAR3，它是一个三蛋白家族的成员，也包括SHEP1，我们在筛选Eph受体酪氨酸激酶结合分子时发现了它。BCAR1和BCAR3家族成员通过其c端区域的直接关联以协调一致的方式起作用，但其复合物的结构尚未被研究人员发现。为了深入了解这些关键而神秘的组装，我们已经解决了BCAR1- bcar3家族复合体的第一个晶体结构，BCAR1和SHEP1的晶体结构，揭示了一种新型的蛋白质相互作用。SHEP1 c端区域总体上类似于cdc25型鸟嘌呤核苷酸交换因子结构域。然而，关键区域被BCAR1结合改变，导致SHEP1的“封闭”构象不能结合Ras GTPases。我们现在试图揭示BCAR1与BCAR3（一种与SHEP1相关但在关键特征上存在明显差异的蛋白）联合介导的乳腺癌恶性和化疗耐药的机制基础。因此，我们提出了一种多学科的方法，整合了一系列有效的工具，从高分辨率结构和生化分析到培养和小鼠乳腺癌异种移植模型中工程癌细胞的功能研究。我们的目标将通过(1)揭示BCAR1-BCAR3信号关联的分子细节来精确定义复杂形成过程中发生的调控修饰；(2)阐明BCAR-BCAR3关联在乳腺癌生长、侵袭性和化疗耐药中的作用。我们的研究将导致对BCAR1-BCAR3信号节点以及相关蛋白复合物的新认识，并阐明乳腺癌细胞如何获得使其能够转移和应对化疗损伤的恶性特征。因此，这项工作将最终为开发克服癌症耐药性的治疗方案提供新的基础。

DESCRIPTION (provided by applicant): Breast cancer is the second leading cause of cancer deaths in women, despite a number of treatment options. Most breast cancers are estrogen receptor-positive and commonly treated with anti-estrogens, while antibodies and kinase inhibitors are used to treat cancers that overexpress the HER2 receptor tyrosine kinase. Unfortunately, tumors are often intrinsically resistant or develop resistance to these drugs due to overexpression of specific genes. One of these genes is the scaffolding protein BCAR1 (breast cancer anti- estrogen resistance 1 or p130Cas), which is a well-known key component of the signaling pathways that regulate cell proliferation, survival and migration/invasion downstream of integrin adhesion receptors. BCAR1 is also a critical node in HER2 oncogenic signaling pathways and mediator of resistance to adriamycin, a drug frequently used to treat breast cancers that do not respond to anti-estrogens or HER2-targeted therapies. Thus, BCAR1 is a central player in the signaling networks that control breast cancer malignancy. Another important but poorly characterized factor in anti-estrogen resistance is the SH2 domain-containing protein BCAR3, a member of a family of three proteins that also includes SHEP1, which we identified in a screen for Eph receptor tyrosine kinase-binding molecules. Members of the BCAR1 and BCAR3 families function in a concerted manner through direct association of their C-terminal regions, but the structure of their complexes has eluded investigators. To gain insight into these crucial yet enigmatic assemblies, we have solved the first crystal structure of a BCAR1-BCAR3 family complex, that of BCAR1 and SHEP1, revealing a novel type of protein interaction. The SHEP1 C-terminal region overall resembles a Cdc25-type guanine nucleotide exchange factor domain. However, crucial regions are altered by BCAR1 binding, resulting in a "closed" conformation of SHEP1 that cannot bind Ras GTPases. We now seek to unravel the mechanistic basis of breast cancer malignancy and resistance to chemotherapy mediated by BCAR1 association with BCAR3, a protein related to SHEP1 but with distinct differences in key features. Thus, we propose a multidisciplinary approach that integrates a spectrum of effective tools ranging from high resolution structural and biochemical analysis to functional studies in engineered cancer cells in culture and mouse breast cancer xenograft models. Our goals will be accomplished by (1) unraveling the molecular details of the BCAR1-BCAR3 signaling association to precisely define the regulatory modifications occurring upon complex formation; and (2) elucidating the role of the BCAR-BCAR3 association in breast cancer growth, invasiveness and resistance to chemotherapy. Our studies will lead to a new understanding of the BCAR1-BCAR3 signaling node as well as complexes of related proteins, and shed light on how breast cancer cells acquire the malignant characteristics that enable them to metastasize and cope with chemotherapeutic insults. Thus, this work will ultimately provide a new basis for developing treatment options to overcome cancer drug resistance.