Understanding breast cancer progression as a defect in the mechanics of tissue self-organization

摘要 乳腺双层结构的进行性崩溃是所有乳腺癌的标志， 但发生在导管原位癌(DCIS)和浸润性导管癌之间的结构变化 (IDC)特别重要，因为它代表着患者风险的一个主要转折点。乳腺癌 起源于乳腺上皮的内腔层，在那里转化的腔上皮细胞(LEP) 增殖以填充DCIS的导管和小叶。令人惊讶的是，DCIS中的LEP已经获得了所有必要的 侵袭的遗传异常，但仍受完整的外肌上皮(MEP)的限制 层-一组形成动态屏障的细胞，阻止原位肿瘤进入基底区 细胞膜(BM，包围乳腺上皮的特殊细胞外基质(ECM))。因此，我们 提出转化的LEP易位通过MEP层，而不是基因突变，是一个关键的比率- 限制向IDC迈进的一步。在这里，我们的目标是确定必须发生的物理和分子变化 在LEP，以促进这一结构转型。我们通过乳腺上皮细胞的晶状体来应对这一挑战 自我组织。我们先前证明了正常人的LEP和MEP在体外可以自组织，并且 MEP从BM中排除LEP的能力由硬连线和谱系特定的界面决定 每个细胞-细胞和细胞-细胞外基质界面的紧张状态。我们用实验和数学模型展示了 与MEP-ECM界面相比，LEP-ECM界面在能量上非常不利，这 防止LEP将自己定位在BM旁边。我们假设存在一个速率限制和 DCIS向IDC发展过程中的高能结构中间体，其中LEP转移到MEP 层，紧挨着BM。我们提出了一个统计力学框架来理解微扰如何 肿瘤细胞的界面性质和动力学促进了这种中间体的形成。具体来说，我们 预测LEP-ECM界面能的变化是促进 转化的LEP的基底性易位。初步研究支持这一假设：我们发现一个频繁的 失控基因PIK3CA在LEP中激活时通过呈现LEP-ECM来破坏自组织 界面更具活力优势。在这份提案中，我们将确定这一点和其他物理因素 LEP的改变对于它们的基础易位是必要的，并识别其下游的分子变化 导致这些物理变化的PIK3CA。我们将在体外使用互补性来检验我们的假设 体内实验系统：使用从人乳房缩小整形组织和 转基因小鼠模型。我们的长期目标是揭示促进和抑制 从DCIS到IDC的发展。更好的物理和分子进展预测将使DCIS受益 本来会被过度治疗的患者，因为只有三分之一的DCIS病例进展到IDC。此外，阻止 LEP易位将代表一种防止乳腺癌进展的治疗策略。

ABSTRACT A progressive breakdown in the bilayered structure of the mammary gland is the hallmark of all breast cancers, but the structural change that occurs between ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) is of particular importance because it represents a major inflection point in risk for patients. Breast cancers originate in the inner luminal layer of the mammary epithelium, where transformed luminal epithelial cells (LEP) proliferate to fill the ducts and lobules in DCIS. Surprisingly, LEP in DCIS have acquired all the necessary genetic aberrations to invade, but remain constrained within the tissue by an intact outer myoepithelial (MEP) layer—a group of cells that forms a dynamic barrier blocking access of the in situ tumor to the basement membrane (BM, the specialized extracellular matrix (ECM) that surrounds the mammary epithelium). Thus, we propose that translocation of transformed LEP past the MEP layer, and not genetic mutations, is a key rate- limiting step in progression to IDC. Here, we aim to identify the physical and molecular changes that must occur in LEP to facilitate this structural transition. We approach this challenge through the lens of mammary epithelial self-organization. We previously demonstrated that normal human LEP and MEP can self-organize in vitro, and that the capacity of MEP to exclude LEP from the BM is determined by hard-wired and lineage-specific interfacial tensions at each cell-cell and cell-ECM interface. We showed using experiments and mathematical modeling that the LEP-ECM interface is highly unfavorable energetically compared to the MEP-ECM interface, which prevents LEP from positioning themselves next to the BM. We hypothesize the existence of a rate-limiting and high-energy structural intermediate during the progression of DCIS to IDC, where LEP translocate into the MEP layer, next to the BM. We propose a statistical mechanical framework for understanding how perturbations to the interfacial properties and dynamics of tumor cells facilitate the formation of this intermediate. Specifically, we predict that changes to the LEP-ECM interfacial energy are a critical physical change necessary to promote basal translocation of transformed LEP. Preliminary studies support this hypothesis: we found that a frequently dysregulated gene—PIK3CA—disrupts self-organization when activated in LEP by rendering the LEP-ECM interface more energetically favorable. In this proposal, we will determine whether this and other physical changes to LEP are necessary for their basal translocation, and identify the molecular changes downstream of PIK3CA that give rise to these physical changes. We will test our hypothesis using complementary in vitro and in vivo experimental systems: using organoids reconstituted from human reduction mammoplasty tissues and genetically engineered mouse models. Our long-term goal is to reveal the changes that promote and inhibit progression from DCIS to IDC. Better physical and molecular predictors of progression would benefit DCIS patients who would otherwise be over-treated, as only a third of DCIS cases progress to IDC. Further, blocking LEP translocation would represent a therapeutic strategy to prevent breast cancer progression.