Pak1 and Hormone Response in Breast Cancer Progression

描述(申请人提供)：乳腺癌进展为更恶性行为的分子机制目前还不完全清楚，据信涉及雌激素受体和生长因子信号之间的串扰的解除调控，以及配体非依赖性的ER反式激活。例如，作为生长因子信号转导的主要靶点，p21激活的蛋白1调节细胞的运动性、侵袭性和存活率，所有这些都是肿瘤发生和正常乳腺发育所必需的。尽管有关生长因子和pak1生物学的信息有了显著的增长，但新的pak1靶点调控乳腺癌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PAC1的一个生理靶点，并且NRIF3和ESE1这两种新的与ER相互作用的具有相反功能的底物的磷酸化状态可能密切影响ER-PAC1通路的功能结果。这项建议代表了PI继续努力研究关键的生理性Ak1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。 我们的工作假说是“Ak1活性的解除调控刺激了ER途径，从而有助于增强激素反应、激素非依赖性和乳腺肿瘤细胞的肿瘤发生；ER的这些表型效应可能由NRIF3和Ese1的作用控制，这两个新的ER相互作用的Ak1底物分别以刺激或抑制的方式调节ER的反式激活。”本研究将通过明确PAC1的特定下游生理靶点如ER、NRIF3和ESE1的机制意义，阐明生长因子信号在激素非依赖性和乳腺癌进展中的作用，并确定ER-Ser305和Ser118激活在正常乳腺发育和肿瘤发生中的作用。 针对这些假说，我们的具体目标是确定：(1)Pak1-ER通路在乳腺发育和肿瘤发生中的功能意义；(2)Pak1调节NRIF3-Ser28在ER的作用及相关表型变化中的影响；(3)Ese1及其磷酸化在修饰ER功能和乳腺癌生物学中的作用；(4)Pak1、ER和Ese1在乳腺癌和浸润性乳腺癌患者多步骤发病过程中的表达特点和意义。我们建议的一个创新方面是使用新的体外、体内和转基因模型，以及具有后续数据的人类乳腺肿瘤，以获得关于NRIF3和Ese1在乳腺癌细胞中介导的Ak1-ER途径的机制和功能意义的新见解。这些研究将独一无二地确定ER及其上游的Pak1激酶以及下游的共同调节因子NRIF3和Ese1调节激素作用的机制。这项研究具有重要意义，因为从这项研究中获得的知识将加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.