Molecular Function of the Nf2 Tumor Suppressor, Merlin

描述（由申请人提供）：当细胞逃避通常限制其增殖的规则时，癌症就会发展。细胞表面的生长因子受体在细胞和环境之间提供了一个关键的接口，是第一个内在的控制水平。生长因子通常是持续可用的，需要对受体本身进行精确的控制，以确保细胞分裂只在必要时进行，例如在发育、伤口愈合或正常组织周转期间。受体在质膜上的分布和聚集是精心设计的；这反过来又通过调节内吞作用来控制它们的信号输出和表面丰度。膜和底层皮质细胞骨架之间的界面在这一过程中起着积极和动态的作用。神经纤维瘤病2型（NF2）肿瘤抑制因子Merlin和密切相关的ERM蛋白（Ezrin， Radixin和Moesin）定位于膜-细胞骨架界面，并准备组织膜受体的分布和信号传导。在该提案的初始资助期间，我们发现Merlin协调细胞之间稳定粘附连接（AJs）的建立，抑制表皮生长因子受体（EGFR）的内化和信号传导，特别是在接触细胞中，这为细胞如何实现接触依赖的增殖抑制现象提供了分子解释。最近我们发现，通过控制EGFR的膜分布，Merlin调节EGFR的内吞途径，这反过来决定了EGFR的内吞作用是否被细胞接触阻断，这表明Merlin控制EGFR的两步机制。最后，我们最近的研究表明，Merlin也可能通过类似的机制控制ErbB3的膜分布。因此，Merlin有望成为生长因子受体ErbB家族（EGFR/ErbB1, ErbB2， ErbB3和ErbB4）的中心调节剂，几乎与所有形式的人类癌症有关。在本应用中，为了扩展这一成功的研究途径，我们提出了一种多方面的方法来扩展我们对Merlin在控制膜受体分布和信号传导方面的分子功能的理解。具体来说，我们计划描述Merlin如何控制EGFR膜分布和内吞作用的分子基础，以及Merlin如何稳定AJs并阻断细胞接触时的EGFR内吞作用。我们还计划确定Merlin是否通过类似的机制控制ErbB3的表面可用性。

DESCRIPTION (provided by applicant): Cancer develops when cells evade the rules that normally limit their proliferation. Growth factor receptors on the cell surface provide a critical interface between the cell and its environment and are the first intrinsic level of control. Growth factors are often continuously available, necessitating exquisite control of the receptors themselves to ensure that cell division proceeds only when warranted, for example during development, wound healing or normal tissue turnover. The distribution and aggregation of receptors across the plasma membrane is exquisitely choreographed; this, in turn, controls their signaling output and surface abundance via regulated endocytosis. The interface between the membrane and the underlying cortical cytoskeleton plays an active and dynamic role in this choreography. The neurofibromatosis type 2 (NF2) tumor suppressor, Merlin, and closely related ERM proteins (Ezrin, Radixin and Moesin), localize to the membrane-cytoskeleton interface and are poised to organize the distribution of, and signaling by, membrane receptors. During the initial funding of this proposal, we discovered that Merlin coordinates the establishment of stable adherens junctions (AJs) between cells with the inhibition of Epidermal Growth Factor Receptor (EGFR) internalization and signaling specifically in contacting cells, suggesting a molecular explanation for how cells achieve the phenomenon of contact-dependent inhibition of proliferation. More recently we have found that, by controlling the membrane distribution of EGFR, Merlin regulates the endocytic pathway taken by EGFR, which, in turn, dictates whether EGFR endocytosis is blocked by cell contact, suggesting a two-step mechanism whereby Merlin controls EGFR. Finally, our most recent studies suggest that Merlin may also control the membrane distribution of ErbB3 via a similar mechanism. Thus Merlin is poised to be a central regulator of the ErbB family of growth factor receptors (EGFR/ErbB1, ErbB2, ErbB3 and ErbB4) that have been implicated in nearly all forms of human cancer. In this application to extend this successful avenue of investigation we propose a multifaceted approach to extending our understanding of the molecular function of Merlin in controlling membrane receptor distribution and signaling. Specifically we plan to delineate the molecular basis of how Merlin controls EGFR membrane distribution and endocytosis and how Merlin stabilizes AJs and blocks EGFR endocytosis upon cell:cell contact. We also plan to determine whether Merlin controls the surface availability of ErbB3 via a similar mechanism. PUBLIC HEALTH RELEVANCE: We will carry out molecular, cellular and in vivo studies to examine the molecular function of the Nf2 tumor suppressor, Merlin. Specifically, we will test the hypothesis that Merlin controls the membrane distribution of and signaling from EGFR in a contact- dependent manner. We will also determine whether Merlin controls the ErbB family member ErbB3 via a similar mechanism. These studies will advance our understanding of the molecular cause of NF2 and of the biology of ErbB receptors that have been widely implicated in human cancer.