Role of TGFBeta in Microtubule Dynamics

转化生长因子β家族的信号分子广泛存在于脊椎动物和无脊椎动物中，在许多重要的动态平衡、发育和生物学过程中起着关键作用。到目前为止，所有已知的由转化生长因子β激活的信号通路都能刺激转录反应。鉴于TGFbeta下游细胞反应的多样性，这种生长抑制多肽很可能是其他重要细胞功能所必需的。我们已经克隆并测序了一种新的成分，称为km23，它直接与转化生长因子β受体相互作用并被其磷酸化。根据它与数据库中相关序列的同源性，我们认为TGFbeta介导了一种新的信号通路，该通路对细胞内沿微管的运输至关重要。有趣的是，我们发现，在9个卵巢肿瘤序列中，有5个在km23的关键位置发生了突变。尽管MT动力学的改变已被证明在癌症的发展和特定化疗药物的作用机制中都起到了作用，但尚未注意到MT负端动力学的控制与天然生长调节剂如TGFbeta之间的联系。此外，似乎没有一种抗癌药物专门调节MT的负端功能。基于我们的初步数据和本文提出的研究，我们将描绘这一新途径中的步骤，并确定它是否以及如何影响其他已知的主要TGFbeta信号通路，MAPK和Smads。激光捕获显微切割正常组织细胞和卵巢癌、乳腺癌和结肠癌不同发展阶段的组织细胞将被分析，以确定km23突变发生的阶段。分子图谱研究将解决这样一种假设，即当TGFbeta受体或信号通路被修饰时，km23的表达和/或活性会发生变化。最终，我们将提供证据，证明km23是癌症药物发现的新分子靶点。

Members of the TGFbeta family of signaling molecules are found ubiquitously in vertebrates and invertebrates and have critical roles in many essential homeostatic, developmental, and biological processes. To date, all of the known signaling pathways activated by TGFbeta stimulate transcriptional responses. In light of the diversity of TGFbeta's downstream cellular responses, this growth inhibitory polypeptide is likely to be essential for other important cellular functions. We have cloned and sequenced a novel component, termed km23, that directly interacts with and is phosphorylated by the TGFbeta receptors. Based upon its homology to related sequences in the database, we propose that TGFbeta mediates a novel signaling pathway which is critical for intracellular transport along microtubules (MT's). Of interest, we found that a critical site in km23 is mutated in 5 out of 9 ovarian tumor sequences. Although alterations in MT dynamics have been shown to play a role in both cancer development and the mechanism of action of specific chemotherapeutic agents, no link has been noted between control of minus-end MT dynamics and a natural growth regulator such as TGFbeta. Moreover, none of the anti-cancer agents appear to specifically regulate minus-end MT functions. Based upon our preliminary data and the studies proposed herein, we will delineate the steps in this novel pathway, and determine if and how it impinges upon the other major known TGFbeta signaling pathways, the Mapks and the Smads. Laser capture microdissection of normal tissue cells and of tissue cells from various stages of progression of ovarian, breast, and colon cancer will be analyzed to determine the stage at which km23 mutations occur. Molecular profiling studies will address the hypothesis that km23 expression and/or activity is altered when TGFbeta receptors or signaling pathways are modified. Ultimately, we will provide evidence that km23 is a novel molecular target for cancer drug discovery.