EphA2 Receptor Tyrosine Kinase in Malignant Tumor Cell

描述（由申请人提供）：EphA 2受体是最近克隆的Eph家族受体酪氨酸激酶（RTK）的成员，其在多种恶性肿瘤中过表达。EphA 2受体表达水平与恶性程度一致相关。EphA 2在非转化乳腺上皮细胞系中的过表达导致裸鼠中的肿瘤形成。然而，EphA 2在恶性肿瘤中过表达的机制仍不清楚。我们的初步数据表明，EphA 2在非转化乳腺上皮细胞MCF 10A中的过表达破坏了它们在三维培养中形成腺泡样球体的能力。此外，E-钙粘蛋白表达在过表达EphA 2受体的MCF 10A细胞中错误定位。这些数据表明高水平的EphA 2可能通过细胞-细胞粘附的不稳定性促进恶性行为。相反，阻断恶性肿瘤细胞中的EphA 2受体活化抑制体内RhoA GT3活化、细胞迁移和肿瘤生长，表明EphA 2受体信号传导是肿瘤恶性所需的。基于这些数据，我们假设EphA 2过表达（1）通过修饰连接复合物破坏细胞-细胞粘附，（2）通过调节Vav 3介导的RhoA GT3活性促进细胞运动，和（3）增强体内肿瘤侵袭和转移。为了测试这些假设，我们特别提出：（1）鉴定EphA 2过表达破坏细胞-细胞粘附的机制;（2）研究EphA 2过表达细胞中增加的细胞运动性是否由RhoA GT3的Vav 3依赖性活化介导;和（3）确定EphA 2过表达是否是促进多阶段转基因肿瘤模型中的肿瘤形成和转移所必需和足够的。该项目的成功不仅为EphA 2诱导的细胞侵袭和转移提供了分子基础，而且为EphA 2缺陷或EphA 2过表达对肿瘤进展和转移的影响提供了体内临床前数据。

DESCRIPTION (provided by applicant): EphA2 receptor is a member of the recently cloned Eph family receptor tyrosine kinases (RTKs) that overexpressed in a variety of malignant tumors. The level of EphA2 receptor expression consistently correlates with the degree of malignancy. Overexpression of EphA2 in non-transformed breast epithelial line has led to tumor formation in nude mice. However, the mechanism by which EphA2 overexpression in tumor malignancy remains unclear. Our preliminary data show that overexpression of EphA2 in non-transformed breast epithelial cells MCF10A disrupts their ability to form acini-like spheroids in a three-dimentional culture. In addition, E-cadherin expression is mis-localized in MCF10A cells overexpressing EphA2 receptor. These data suggest high levels of EphA2 may promote malignant behavior through destabilization of cell-cell adhesion. Conversely, blocking EphA2 receptor activation in malignant tumor cells inhibits RhoA GTPase activation, cell migration, and tumor growth in vivo, indicating that EphA2 receptor signaling is required for tumor malignancy. Based on these data, we hypothesize that EphA2 overexpression (1) disrupts cell-cell adhesion through modifying junctional complexes, (2) promotes cell motility by modulation of Vav3-mediated RhoA GTPase activity, and (3) enhances tumor invasion and metastasis in vivo. To test these hypotheses, we specifically propose to:(1) identify mechanisms by which EphA2 overexpression disrupts cell-cell adhesion; (2) investigate whether increased cell motility in EphA2 overexpressing cells is mediated by Vav3- dependent activation of RhoA GTPase; and (3) determine if EphA2 overexpression is necessary and sufficient to promote tumor formation and metastasis in multi-stage transgenic tumor models. The success of this project will not only provide molecular basis of EphA2-induced cell invasion and metastasis, but also provide in vivo pre-clinical data on the effect of EphA2-deficiency or EphA2 overexpression on tumor progression and metastasis.