Regulation of Snail in breast cancer progression and metastasis

描述（申请人提供）：基底样乳腺癌（BLBC）具有侵袭性的临床病史，易复发、远处转移，生存期较短，多见于年轻女性。BLBC本质上具有许多上皮-间充质转化（epithelial-mesenchymal transition， EMT）特征和癌症干细胞（cancer stem cell， CSC）样特征，这表明在BLBC中，激活EMT程序可产生具有CSC样特征的高级侵袭细胞。我们的长期目标是发现肿瘤细胞内的内在因素和来自肿瘤微环境的调节EMT的外在信号，并确定可能作为治疗这种致命疾病的药物靶点的分子。在过去的几年里，我们系统地研究了蜗牛在BLBC中的作用以及蜗牛抑制E-cadherin表达的分子机制。我们的研究清楚地表明，Snail是肿瘤细胞内负责EMT的关键内在因子之一；我们的研究还表明，炎症性肿瘤微环境为EMT提供了一个外在信号。然而，BLBC的外在肿瘤环境是如何开始和建立的，尽管它至关重要，仍然没有解决。最近，我们发现X-box结合蛋白（XBP1）在人乳腺肿瘤样本和小鼠乳腺癌组织的BLBC中表达显著降低。Snail抑制XBP1的表达并导致CCL2的显著上调，CCL2是肿瘤相关巨噬细胞（tam）和淋巴细胞的主要趋化因子。XBP1是最保守的“未折叠蛋白反应”（unfold -protein response， UPR）信号通路中的关键分子，细胞利用UPR来应对内质网（endoplasmic network， ER）中的环境和细胞应激。XBP1的缺失导致“未解决的内质网应激”，这是内源性细胞损伤的信号，触发白细胞浸润，并显著增强靶组织的炎症反应。我们假设，通过蜗牛介导的抑制，XBP1的缺失点燃了一个“内向外”的信号，用于募集tam和淋巴细胞，这些细胞通过提供额外的细胞因子和生长因子，建立炎症/伤口基质，进一步促进EMT，并在BLBC中培养csc样性状。本提案的目的是表征蜗牛对XBP1的抑制，并探索使用新开发的特异性蜗牛抑制剂来破坏这种恶性循环并恢复内质网稳态的治疗干预措施。在强有力的初步数据的指导下，我们将通过追求三个具体目标来验证这一假设：(1)确定蜗牛介导的BLBC中XBP1抑制的分子机制；(2)阐明为什么XBP1的缺失会增强BLBC中的炎症；(3)阐明XBP1在体内的功能作用。我们的研究具有创新性和重要意义，因为它不仅将开辟一个新的范式，显著影响我们对乳腺癌进展和转移过程中肿瘤细胞及其微环境的共同进化的看法，而且将为开发新的治疗策略奠定基础。

DESCRIPTION (provided by applicant): Basal-like breast cancer (BLBC) exhibits an aggressive clinical history, with development of recurrence, distant metastasis, shorter survival, and usually occurs in young women. BLBC intrinsically possesses many epithelial-mesenchymal transition (EMT) characteristics and cancer stem cell (CSC)-like features, suggesting that activation of EMT program generates high-grade invasive cells with CSC-like traits in BLBC. Our long-term goal is to discover the intrinsic factors within tumor cells and the extrinsic signals from tumor microenvironments that regulate EMT, and to identify molecules that may serve as druggable targets for treating this deadly disease. In the last several years, we have systematically studied the role of Snail and the molecular mechanism by which Snail represses E-cadherin expression in BLBC. Our study clearly indicates that Snail is one of the key intrinsic factors within tumor cells responsible for EMT; our study also implies that the inflammatory tumor microenvironment provides an extrinsic signal for EMT. However, how the extrinsic tumor milieu of BLBC is initiated and built up, despite its paramount importance, remains unaddressed. Recently, we found that expression of the X-box binding protein (XBP1) was significantly reduced in BLBC from human breast tumor samples and mouse breast cancer tissues. Snail suppressed XBP1 expression and resulted in a significant upregulation of CCL2, a major chemokine for tumor associated macrophages (TAMs) and lymphocytes. XBP1 is a key molecule in the most conserved "unfolded-protein response" (UPR) signaling pathway that cells use to cope with environmental and cellular stresses in endoplasmic reticulum (ER). Loss of XBP1 results in "unresolved ER stress", which signals endogenous cellular injury, triggering leukocyte infiltration, and a significant boost of inflammatory responses in target tissues. We hypothesize that the loss of XBP1 by Snail-mediated repression ignites an "inside out" signal for recruiting TAMs and lymphocytes, which establish an inflammatory/wound stroma to further boost EMT and cultivate CSC-like traits in BLBC by providing additional cytokines and growth factors. The objective of this proposal is to characterize the repression of XBP1 by Snail and explore therapeutic interventions that will disrupt this vicious cycle and thereby restore ER homeostasis using a newly developed specific Snail inhibitor. Guided by strong preliminary data, we will test this hypothesis by pursuing three specific aims: (1) to determine the molecular mechanisms responsible for Snail-mediated XBP1 repression in BLBC; (2) to delineate why loss of XBP1 enhances inflammation in BLBC; and (3) to elucidate the functional roles of XBP1 in vivo. Our proposal is innovative and significant, because it will not only open a new paradigm that significantly affects our views on the co- evolvement of tumor cells and their microenvironments in breast cancer progression and metastasis but will also lay groundwork for developing new therapeutic strategies against this disease.