IGF-1 Signaling & ER crosstalk in mammary cancer in vivo

描述(申请人提供)：胰岛素样生长因子1(IGF-1)刺激增殖和抑制细胞凋亡，从而影响包括乳腺癌在内的各种上皮性肿瘤的发生和发展。细胞培养实验已经确定了两条主要的信号通路，它们介导了IGF-1在体外对细胞转化和增殖的影响。研究表明，这两条通路都参与了与雌激素受体(ER)的串扰，并通过磷酸化特定的丝氨酸残基来增强受体的活性。转基因模型也证明了IGF-1在乳腺发育和肿瘤发生中的重要性。然而，许多模型使用激素或妊娠诱导的启动子，这排除了对ER串扰或激素操纵的影响的分析。我们已经开始了一种新的BK5.IGF-1转基因模型的研究，在该模型中，K5启动子是结构性的而不是激素调节的，并将转基因表达引导到乳腺的肌上皮细胞。肌上皮或基底层与导管上皮相邻，由具有上皮性和肌性的特化细胞组成。因此，该模型可以评估激素在IGF-1促进的乳腺肿瘤发生中的作用，也可以重述导管上皮细胞对局部产生的生长因子的旁分泌暴露。对BK5-IGF-1模型的初步研究表明，旁分泌/旁分泌暴露于IGF-1可刺激导管增生，并使腺上皮更容易受到DMBA引发的致癌作用。信号分析表明，与野生型肿瘤相比，转基因肿瘤增加了PI3K-Akt通路的激活。初步研究还表明，乳腺癌在信息和蛋白质水平上都表达功能性ER。本研究的目的是验证一种假说，即IGF-1主要通过激活PI3K-Akt通路刺激体内乳腺肿瘤的形成，并需要下游的ER激活(串扰)。一个必然的假设，即IGF-1介导的ER激活有助于他莫昔芬耐药，也将在拟议的研究中提出。1)研究PI3K-Akt通路在体内乳腺肿瘤发生中的作用。2)评价IGF-1介导的ER信号激活(串扰)在乳腺肿瘤发生和体内他莫昔芬/抗雌激素耐药中的重要性。

DESCRIPTION (provided by applicant): Insulin like growth factor 1 (IGF-1) stimulates proliferation and inhibits apoptosis, thereby affecting the development and progression of a variety of epithelial tumors, including breast cancer. Cell culture experiments have identified two major signaling pathways that mediate the effects of IGF-1 on cellular transformation and proliferation in vitro. Studies show that both pathways are involved in crosstalk with the estrogen receptor (ER) and enhance receptor activity through phosphorylation of specific serine residues. Transgenic models also demonstrate the importance of IGF-1 in mammary development and tumorigenesis. However, many models utilize hormonally- or pregnancy-induced promoters that preclude analysis of ER crosstalk or the impact of hormonal manipulation. We have initiated studies with a new BK5.IGF-1 transgenic model in which the K5 promoter is constitutively and not hormonally regulated and directs transgene expression to the myoepithelial cells in the mammary gland. The myoepithelial or basal layer lies adjacent to the ductal epithelium and is composed of specialized cells with both epithelial and muscular characteristics. Thus, this model allows assessment of hormonal contributions to IGF-1-promoted mammary tumorigenesis and also recapitulates the paracrine exposure of ductal epithelial cells to locally produced growth factor. Preliminary studies with the BK5.IGF-1 model indicate that paracrine/juxtacrine exposure to IGF-1 stimulates ductal hyperplasia and renders the glandular epithelium significantly more susceptible to DMBA-initiated carcinogenesis. Signaling analyses show that transgenic tumors have increased activation of the PI3K-Akt pathway compared to wild type tumors. Preliminary studies also demonstrate that mammary adenocarcinomas express functional ER as detected at both the message and protein level. The goal of the proposed studies is to test the hypothesis that IGF-1 stimulates mammary tumorigenesis in vivo predominantly through activation of the PI3K-Akt pathway and requires downstream activation of ER (crosstalk). A corollary hypothesis, that IGF-1-mediated activation of ER contributes to tamoxifen resistance, will also be addressed in the proposed studies. The following specific aims will be performed: 1) Investigate the contribution of the PI3K-Akt pathway to mammary tumorigenesis in vivo. 2) Evaluate the importance of IGF-1 mediated activation of ER signaling (crosstalk) in mammary tumorigenesis and in the development of tamoxifen/antiestrogen resistance in vivo.