Regulation of Snail in breast cancer progression and metastasis

描述(申请人提供)：基底细胞样乳腺癌(BLBC)表现出侵袭性的临床病史，复发，远处转移，生存期较短，通常发生在年轻女性。BLBC本质上具有许多上皮-间充质转化(EMT)特性和肿瘤干细胞(CSC)样特性，提示EMT程序的激活可产生具有CSC样特性的高级别侵袭细胞。我们的长期目标是发现肿瘤细胞内的内在因素和肿瘤微环境中调节EMT的外部信号，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Snail的作用以及Snail抑制BLBC中E-钙粘蛋白表达的分子机制。我们的研究清楚地表明，Snail是肿瘤细胞内负责EMT的关键内在因素之一；我们的研究还表明，炎性肿瘤微环境为EMT提供了外部信号。然而，BLBC的外在肿瘤环境是如何启动和建立的，尽管它是至关重要的，仍然没有被解决。最近，我们发现X-box结合蛋白(XBP1)在人乳腺肿瘤标本和小鼠乳腺癌组织中的表达显著降低。Snail抑制XBP1的表达，并导致CCL2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”(UPR)信号通路中的一个关键分子，细胞用它来应对内质网(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，触发了白细胞的渗透，并显著促进了靶组织的炎症反应。我们推测，Snail介导的抑制作用导致XBP1的丢失，为招募TAM和淋巴细胞点燃了一个“由内而外”的信号，这建立了一个炎症/创伤基质，通过提供额外的细胞因子和生长因子，进一步促进EMT和培养BLBC的CSC样特征。该提案的目的是描述Snail对XBP1的抑制，并探索使用新开发的特异性Snail抑制剂来打破这一恶性循环从而恢复ER动态平衡的治疗干预措施。在强大的初步数据的指导下，我们将通过三个具体的目标来检验这一假说：(1)确定Snail介导的XBP1在BLBC中的抑制作用的分子机制；(2)描述XBP1缺失为什么会增强BLBC中的炎症；(3)阐明XBP1在体内的功能作用。我们的建议具有创新性和重大意义，因为它不仅将开启一种新的范式，显著影响我们对乳腺癌进展和转移中肿瘤细胞及其微环境的共同进化的看法，而且还将为开发针对这种疾病的新治疗策略奠定基础。

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.