Pak1 and Hormone Response in Breast Cancer Progression

描述（由申请人提供）：目前尚未完全了解乳腺癌进展为更恶性行为的分子机制，据信涉及雌激素受体和生长因子信号传导之间的串扰失调，以及配体非依赖性ER反式激活。例如，p21激活激酶（Pak 1）（生长因子信号传导的主要靶点）的激活调节细胞运动性、侵袭性和存活，所有这些都是肿瘤发展和正常乳腺发育所需的。尽管有关生长因子和Pak 1生物学的信息显著增长，但新的Pak 1靶点在乳腺癌中调节这些过程的机制仍然难以捉摸。我们的初步研究首次发现，ER是Pak 1的生理靶点，并且ER-Pak 1通路的功能结果可能受到NRIF 3和Ese 1的磷酸化状态的密切影响，这两种新的ER相互作用的Pak 1底物具有相反的功能。这一提议代表了PI的持续努力，以研究关键生理Pak 1底物调节ER反式激活并参与乳腺癌细胞致瘤表型发展的机制。 我们的工作假设是，“Pak 1活性的失调刺激ER途径，因此，有助于增强激素反应，乳腺癌细胞的非依赖性和肿瘤发生; ER的这些表型效应可能是通过调节NRIF 3和Ese 1的作用来控制的，这两种新型的ER相互作用Pak 1底物分别以刺激或抑制的方式调节ER反式激活。“这项提案将通过定义Pak 1的特定下游生理靶点（如ER，NRIF 3和Ese 1）的机制意义来阐明生长因子信号传导在乳腺癌非依赖性和乳腺癌进展中的作用，并确定ER-Ser 305和Ser 118激活在正常乳腺发育和肿瘤发生中的作用。 为了解决这些假设，我们的具体目标是确定：（1）Pak 1-ER通路在乳腺发育和肿瘤发生中的功能意义;（2）Pak 1调节NRIF 3-Ser 28在ER作用和相关表型变化中的影响;（3）Ese 1及其Pak 1磷酸化在改变ER功能和乳腺癌生物学中的作用;（4）Pak 1、ER、Ese 1在乳腺癌多阶段发病过程中的表达特点及意义。我们的建议的一个创新方面是使用新的体外，体内和转基因模型，以及人类乳腺肿瘤的随访数据，以获得新的见解Pak 1-ER通路的机制和功能意义的NRIF 3和Ese 1在乳腺癌细胞。这些研究将独特地定义ER及其上游Pak 1激酶和下游辅助调节因子NRIF 3和Ese 1调节激素作用的机制。这项研究意义重大，因为从这项研究中获得的知识将增强我们对乳腺癌进展中具有既定作用的关键调控途径的理解。

DESCRIPTION (provided by applicant): The molecular mechanisms underlying the progression of breast cancer to more malignant behavior are not completely understood at the present time and are believed to involve deregulation of cross-talk between estrogen receptor and growth factor signaling, and also ligand-independent ER transactivation. For example, activation of p21-activated kinase (Pak1), a major target of growth factor signaling, regulates cell motility, invasiveness and survival, all of which are required for both tumor development and also normal mammary gland development. Despite the remarkable growth of information about growth factors and Pak1 biology, the mechanism by which novel Pak1 targets regulate these processes in breast cancer remains elusive. Our preliminary studies have discovered for the first time that ER is a physiological target of Pak1 and that the functional outcome of ER-Pak1 pathway may be closely influenced by the phosphorylation status of NRIF3 and Ese1, two novel ER-interacting Pak1 substrates with opposing functions. This proposal represents a continuing effort of the PI to investigate the mechanism by which critical physiologic Pak1 substrates modulate ER transactivation and participates in the development of tumorigenic phenotypes in breast cancer cells. Our working hypothesis is that "deregulation of Pak1 activity stimulates the ER pathway, and consequently, contributes to an enhanced hormone response, hormone-independence, and tumorigenesis of breast tumor cells; these phenotypic effects of ER might be controlled by the modulation of actions of NRIF3 and Ese1, two novel ER-interacting Pak1 substrates that modulate the ER transactivation in a stimulatory or inhibitory manner, respectively." This proposal will clarify the role of growth factor signaling in hormone-independence and breast cancer progression by defining the mechanistic significance of specific downstream physiologic targets of Pak1 such as ER, NRIF3 and Ese1, and to establish the role of ER-Ser305 and Ser118 activation in the normal mammary gland development and tumorigenesis. To address these hypotheses, our Specific Aims are to determine: (1 )The functional significance of Pak1-ER pathway in the mammary gland development and tumorigenesis; (2) The influence of Pak1 regulation of NRIF3-Ser28 in the action of ER and associated phenotypic changes; (3) The role of Ese1 and its phosphorylation by Pak1 in modifying ER functions and breast cancer biology; (4)The expression characteristics and significance of Pak1, ER, and Ese1 during multi-step pathogenesis of breast carcinoma and in-patients with invasive breast cancer. An innovative aspect of our proposal is the use of novel in vitro, in vivo and transgenic models, as well as human breast tumors with follow-up data to gain new insights about the mechanistic and functional significance of Pak1-ER pathway by NRIF3 and Ese1 in breast cancer cells. These studies will uniquely define the mechanisms through which ER and its upstream Pak1 kinase and downstream coregulators NRIF3 and Ese1 modulate hormone action. This research is significant in that the knowledge gained from this research will enhance our understanding of the critical regulatory pathways with established roles in breast cancer progression.