RE: Regulation of mammary branching morphogenesis by Slit/Robo 1 signaling

描述（由申请人提供）：组织生物学的核心目标是了解细胞如何相互作用以产生组织和器官。虽然在定义介导细胞相互作用的信号通路方面取得了很大进展，但我们对这些信号系统在哺乳动物器官发生过程中如何整合的知识存在根本性的空白。弥合这一知识差距对于确定癌症的药物靶点非常重要，因为肿瘤的生长和进展以组织结构的解体和特化细胞群（如干细胞）的失调为标志。本申请的目的是了解细胞外因子SLIT如何通过调节干细胞所在的单层基底细胞的增殖来影响组织形态发生。在这里，乳腺分支形态发生被用作模型系统，并在强有力的初步数据的指导下，研究了以下模型，其中乳腺分支的关键抑制剂TGF-21通过上调SLIT/ROBO 1途径的信号传导来抑制基底细胞增殖和粘附。这反过来又通过增加2-连环蛋白在膜上的粘附功能来控制基底细胞生长和分支形态发生，而代价是其在细胞核中的增殖功能。将采用各种细胞生物学、成像和生物化学技术，以及强大的移植技术来操纵转基因乳腺组织。在三个目标中测试了三个假设：I）TGF-21上调Robo 1表达，特别是在基底细胞中，并且这通过抑制基底细胞生长来抑制分支; II）SLIT/ROBO 1信号传导通过改变2-连环蛋白的亚细胞定位并以其转录功能为代价促进其细胞粘附功能来对抗典型WNT的作用;和III），SLIT是干细胞的非更新因子，其功能是通过调节2-连环蛋白对抗经典WNT信号传导的自我更新信号。总之，这些实验将对乳腺和其他含有基底干细胞亚群的腺体器官（例如前列腺，唾液等）的癌症生物学产生积极影响，因为它们描绘了一种新的肿瘤抑制信号网络，似乎在干细胞中起作用。

DESCRIPTION (provided by applicant): A core objective of tissue biology is to understand how cells interact to generate tissues and organs. While great strides have been made in defining signaling pathways that mediate cellular interactions, there is a fundamental gap in our knowledge concerning how these signaling systems are integrated during mammalian organogenesis. Bridging this knowledge gap is important in identifying druggable targets for cancer, as tumor growth and progression is marked by disorganization of tissue structure, and deregulation of specialized cell populations, such as stem cells. The goal of this application is to understand how extracellular factors, SLITs, influence tissue morphogenesis by regulating the proliferation of a single layer of basal cells in which stem cells reside. Here, mammary branching morphogenesis is used as a model system and, guided by strong preliminary data, the following model is investigated in which a key inhibitor of mammary branching, TGF-21, restrains basal cell proliferation and adhesion by upregulating signaling through the SLIT/ROBO1 pathway. This, in turn, controls basal cell growth and branching morphogenesis by increasing the adhesive functions of 2-catenin at the membrane, at the expense of its proliferative functions in the nucleus. A variety of cell biological, imaging and biochemical techniques will be employed, as well as powerful transplant techniques to manipulate genetically modified mammary tissue. Three hypotheses are tested in three Aims: I) that TGF-21 upregulates Robo1 expression, specifically in basal cells, and that this inhibits branching by restraining basal cell growth; II) that SLIT/ROBO1 signaling opposes the actions of canonical WNTs by altering the subcellular localization of 2-catenin and promoting its cell adhesive functions at the expense of its transcriptional functions; and III), that SLITs are non-renewal factors for stem cells that function to counter the self-renewal signals of canonical WNT signaling by regulating 2-catenin. Together, these experiments will have a positive impact on cancer biology of breast and other glandular organs containing basal stem cell subpopulations (e.g. prostate, salivary etc), because they delineate a novel tumor suppressive signaling network that appears to function in stem cells.