VEGF signaling in Mammary Tumorigenesis

本提案将检验α6β4整联蛋白（称为“β 4”）有助于 通过非细胞自主机制参与乳腺肿瘤的发生和转移。这一假设 来源于观察到β4在乳腺癌干细胞（CSC）中表达低或不表达， 它有助于乳腺癌的形成和转移。该提案的一个主要目标是 调和这些不一致的观察结果，并了解β4如何促进肿瘤形成和转移。 有趣的是，三阴性乳腺癌（TNBC）含有独特的细胞亚群，其特征在于： 与CSC（β4-/低/CD 24低/CD 44高）不同的β4整联蛋白（β 4高）的高表达，表现出基础的 上皮分化和缺乏干细胞特性。这些观察结果表明，β4的抑制是 这是CSC功能所必需的。事实上，我们出乎意料地观察到CSCs中的β4表达促进了它们的生长。 分化，抑制自我更新。第一个具体目标是研究 这一现象的基础，它将集中在令人兴奋的可能性，它涉及β4的能力， 调节粘着斑和细胞骨架张力，导致干细胞特性减弱。这一目标将 也测试了细胞骨架张力的改变在促进分化中起因果作用的可能性。 的CSC。 第二个具体目标将评估β 4 high亚群发挥非细胞自主性的假设。 CSCs的监管。换句话说，β 4 high亚群的关键功能是扩大CSC群体。 更具体地说，这一独特的亚群参与了CSC的旁分泌信号传导 由甲状旁腺相关蛋白（PTHrP）介导，这种信号传导有助于扩大 的CSC。这一假说是基于β4调节PTHrP表达和β 4高表达的观察结果。 在乳腺肿瘤中，肿瘤细胞亚群和肿瘤干细胞是接近的。此外，我们的初步数据表明，β 4高 子种群有助于维持自我更新和生存。这些观察结果解释了 β4整合素如何在不表达于CSC中的情况下促进肿瘤发生和转移。 最终的具体目标是在体内研究CSCs与β 4 high细胞之间的关系，并评估其在体内的作用。 相对于肿瘤起始和转移的贡献。第一组实验将检验 CSCs和β 4 high细胞是有效的肿瘤形成和转移所必需的， TNBC。第二个子目标通过以下方法更深入地探讨CSC与β 4 high细胞之间的关系： 评估CSC在体内分化的程度，并评估它们与β 4高细胞的相关性， 壁龛这些目标将通过使用报告构建体来标记这些不同的群体来促进。这 这种方法将使我们能够解决几个关键问题，包括CSC（GFP+）分化的频率， 在体内，β 4 high和CSC在“小生境”中的关联以及CSC和β 4 high细胞在“小生境”中的相对频率。 转移

This proposal will examine the unanticipated hypothesis that the α6β4 integrin (referred to as `β4') contributes to the initiation and metastasis of breast tumors by a non-cell autonomous mechanism. This hypothesis derives from the observations that the expression of β4 is low or absent in breast cancer stem cells (CSCs) but that it contributes to the formation and metastasis of breast cancers. A major goal of this proposal is to reconcile these discrepant observations and understand how β4 contributes to tumor formation and metastasis. Interestingly, triple-negative breast cancers (TNBCs) contain a distinct sub-population of cells characterized by high expression of the β4 integrin (β4high) that is distinct from CSCs (β4-/low/CD24low/CD44high), exhibits basal epithelial differentiation and lacks stem cell properties. These observations indicate that repression of β4 is necessary for CSC function. In fact, we observed unexpectedly that β4 expression in CSCs promotes their differentiation and inhibits their self-renewal. The first specific aim will investigate the mechanism that underlies this phenomenon and it will focus on the exciting possibility that it involves the ability of β4 to modulate focal adhesions and cytoskeletal tension resulting in diminished stem cell properties. This aim will also test the possibility that alterations in cytoskeletal tension have a causal role in promoting the differentiation of CSCs. The second specific aim will evaluate the hypothesis that the β4high sub-population exerts non-cell autonomous regulation of CSCs. In other terms, a key function of the β4high subpopulation is to expand the CSC population. More specifically, it is proposed that this distinct sub-population engages in paracrine signaling with CSCs mediated by parathyroid hormone-related protein (PTHrP) and that this signaling contributes to the expansion of CSCs. This hypothesis is based on the observations that β4 regulates PTHrP expression and that the β4high sub-population and CSCs are in proximity in breast tumors. Also, our preliminary data indicate that the β4high sub-population helps to maintain self-renewal and survival. These observations provide an explanation for how the β4 integrin contributes to tumor initiation and metastasis without being expressed in CSCs. The final specific aim will study the relationship between CSCs and β4high cells in vivo and evaluate their relative contribution to tumor initiation and metastasis. The first set of experiments will examine whether both CSCs and β4high cells are required for efficient tumor formation and metastasis using a transgenic model of TNBC. The second sub-aim probe more deeply into the relationship between CSCs and β4high cells by evaluating the extent to which CSCs differentiate in vivo and assessing their association with β4high cells in niches. These goals will be facilitated by the use of reporter constructs to tag these distinct populations. This approach will allow us to address several key issues including the frequency that CSCs (GFP+) differentiate in vivo, the association of β4high and CSCs in `niches' and the relative frequency of CSCs and β4high cells in metastases.