Rewiring ERBB Signaling in Cancer Cells

描述（由申请人提供）：在几种实体瘤中，尤其是在乳腺癌中，ERBB 2的过表达导致更具侵袭性的生长，并增强了转移潜力和出现耐药性的可能性。这种反应的一个重要方面是ERBB 2和ERBB 3之间的相互作用。同时升高的ERBB 3磷酸化水平（以及在许多情况下的受体水平）导致增强的抗凋亡信号传导，因为几个PI 3 K结合位点存在于激酶缺陷型ERBB 3中。除非ERBB 2抑制是定量的（目前尚不可行），否则在激酶抑制剂治疗后，磷酸化ERBB 3的稳态水平通过稳定残留的活化ERBB 3迅速恢复至抑制前水平，而不考虑ERBB 2的持续和实质性抑制。这严重削弱了ERBB 2导向治疗，但也反映了ERBB 2-ERBB 3信号传导的内在方面。ERBB 2显然已经进化为避免稳定的自缔合，并且在非常短暂的相互作用中组成性激活。我们的初步数据表明，ERBB 2具有内置的控制机制，以进一步抑制这种瞬时复合物中的“意外激活”。ERBB 2过表达导致高水平的活化ERBB 2，但处于空间分离和低活化分数的状态。我们认为，这反映了癌细胞为确保活化受体的低空间密度所做的努力，因为空间密度和排除ERBB 3在稳定的ERBB 2二聚体中的组合将有利于细胞毒性信号传导结果。我们已经通过使用具有改变的内在控制和缔合行为的嵌合受体构建体以及在ERBB 3簇的破坏程度上不同的配体变体来研究了这一点。与ERBB 2相反，ERBB 3似乎需要在激活过程中簇的自缔合和有序解离。干扰该系统以似乎与细胞粘附特性的变化相关的方式导致细胞死亡，这可能是因为细胞朝向更促转移的路径进展，而没有足够的信号传导来“支撑”抗失巢凋亡如细胞凋亡的发作。避免ERBB 2聚集和维持ERBB 3聚集对于获得平衡的信号响应非常重要，并且是故意系统干扰的非常容易达到的目标。我们将评估不同细胞环境中细胞死亡的性质，采用现有的和新的方法直接评估受体聚集和激活受体的空间邻近性，以评估它们对信号传导结果的贡献，并确定从背景和细胞死亡促进激活中发出的信号传导的性质。我们的长期目标是利用这一理解，通过工程治疗（抗体或适体）强制ERBB 2的上下文外激活。本文提出的研究也可能揭示目前使用的治疗方法（如赫赛汀）的机制，尽管没有机制基础，但可能已经利用了这种反应的一部分。我们还希望更好地理解为什么以前的尝试，积极加强ERBB 2介导的细胞凋亡没有更成功。

DESCRIPTION (provided by applicant): In several solid tumors, but especially in breast cancers, overexpression of ERBB2 results in more aggressive growth, and enhanced metastatic potential and probability of emergence of drug resistance. An important aspect in this response is the interaction between ERBB2 and ERBB3. Simultaneously elevated levels of ERBB3 phosphorylation (and in many cases receptor levels) result in enhanced anti-apoptotic signaling since several PI3K binding sites reside in the kinase-deficient ERBB3. Unless ERBB2 inhibition is quantitative (which is currently not feasible), steady state levels of phospho-ERBB3 rapidly return to pre-inhibition levels after kinase inhibitor treatment through stabilization of the residual activated ERBB3, regardless of sustained and substantial inhibition of ERBB2. This seriously undercuts ERBB2 directed therapy, but it also reflects on intrinsic aspects of ERBB2-ERBB3 signaling. ERBB2 has apparently evolved to avoid stable self-association and is constitutively activated in very transient interactions. Our preliminary data suggest that ERBB2 has built-in control mechanisms to further suppress "accidental activation" in such transient complexes. ERBB2 overexpression results in high levels of activated ERBB2 but at a state of spatial separation and low fraction of activation. We propose that this reflects efforts by the cancer cell to ensure a low spatial density of activated receptors, because the combination of spatial density and exclusion of ERBB3 in stable ERBB2 dimers would favor a cytotoxic signaling outcome. We have investigated this by using chimeric receptor constructs with altered intrinsic control and association behavior as well as ligand variants that differ in their degree of disruption of ERBB3 clusters. In contrast to ERBB2, self-association and orderly dissociation of clusters during activation appears to be required for ERBB3. Perturbing this system causes cell death in a manner that appears to be related to changes in cell adhesion characteristics, possibly because the cells progress towards a more pro-metastatic path without sufficient signaling to "brace" against the onset of anoikis like apoptosis. The avoidance of ERBB2 clustering and maintenance of ERBB3 clusters are important in getting a balanced signaling response and are very accessible targets for deliberate system perturbation. We will evaluate the nature of cell death in different cellular contexts, adopt existing and novel methodology for direct assessment of receptor clustering and spatial proximity of activated receptors to evaluate their contribution to signaling outcomes, and determine the nature of signaling that emanates from out-of-context and cell-death promoting activation. It is our long range goal to capitalize on this understanding to enforce out-of-context activation of ERBB2 by engineered therapeutics (antibodies or aptamers). The studies proposed here are also likely to shed light on the mechanisms of currently used therapeutics (such as Herceptin) which may, albeit without mechanistic foundation, already utilize part of this response. We also expect to better understand why previous attempts to actively enforce ERBB2 mediated apoptosis have not been more successful.