Molecular mechanism of ID1 function in advanced breast cancer

描述(申请人提供)：2008年，超过20万名美国妇女将被诊断出患有乳腺癌，其中许多人将接受抗雌激素治疗。不幸的是，许多乳腺肿瘤最初对抗雌激素有反应，随着时间的推移会变得无反应，导致转移和死亡。乳腺癌进展的分子机制在很大程度上是未知的，这阻碍了晚期癌症靶向治疗的发展。我们最近的研究表明，ID1是一种分化抑制物，在促进乳腺癌细胞采用侵袭性、激素非依赖性表型方面发挥了作用，导致了抗雌激素耐药。最近的报道强调了我们的发现的重要性，即ID1在低分化的转移性肿瘤中高度表达。ID1的主要功能是抑制含有基本螺旋-环-螺旋(BHLH)结构域的一系列转录因子的DNA结合。为了确定在乳腺癌细胞中受ID1调控的潜在的bHLH转录因子，我们对已发表的人类乳腺肿瘤基因表达数据进行了全面的生物信息学分析。Meta分析表明，BHLHB2的表达与激素依赖性乳腺癌密切相关，BHLHB2与ESR1、FOXA1和GATA3共表达的基因显著重叠，ESR1、FOXA1和GATA3是决定乳腺癌激素依赖性表型的关键转录因子。此外，我们还发现BHLHB2识别的顺式调控序列E-box基序在ESR1直接靶基因中过度表达。我们假设BHLHB2是决定乳腺癌激素依赖表型的转录调控网络的组成部分，ID1通过抑制BHLHB2功能促进肿瘤细胞获得低分化表型。我们将通过对BHLHB2在乳腺癌细胞中的功能和调控进行系统和详细的研究，在以下三个具体目标中检验这一假说。具体地说，我们将：1)通过检测BHLHB2和ID1在人乳腺癌细胞中功能的获得或丧失的后果，研究BHLHB2在维持激素依赖的表型中的作用以及ID1对其的调节；2)通过高通量的全基因组基因表达分析和BHLHB2 DNA结合分析，识别和表征BHLHB2和ID1调控的基因；以及3)研究与福维斯特耐药相关的miRNAs的调控和功能，重点是FUVESTRANT耐药相关miRNA和激素依赖的乳腺癌细胞核心转录因子之间的交叉调节。

DESCRIPTION (provided by applicant): In 2008 more than 200,000 American women will be diagnosed with breast cancer and many will be treated with antiestrogens. Unfortunately, many breast tumors initially respond to antiestrogens will become unresponsive over time, leading to metastasis and mortality. The molecular mechanisms of breast cancer progression are largely unknown, which hinders the development of targeted therapies for advanced cancer. Our recent studies showed that ID1, an inhibitor of differentiation, played a role in promoting breast cancer cells to adopt an aggressive, hormone-independent phenotype, resulting in antiestrogen resistance. The significance of our finding is underscored by recent reports that ID1 is highly expressed in poorly differentiated, metastatic tumors. The primary function of ID1 is to inhibit DNA binding of a family of transcription factors that contain a basic helix-loop-helix (bHLH) domain. To identify the potential bHLH transcription factor that is regulated by ID1 in breast cancer cells, we performed a comprehensive bioinformatic analysis of published gene expression data of human breast tumors. Meta-analysis revealed that the expression of BHLHB2, a bHLH transcription factor and putative target of ID1, is strongly associated with hormone-dependent breast tumors, and BHLHB2-coexpressed genes significantly overlap with genes coexpressed with ESR1, FOXA1 and GATA3, the key transcription factors that specify the hormone-dependent phenotype of breast cancer. In addition, we found that E-box motif, the cis-regulatory sequence recognized by BHLHB2, was overrepresented in ESR1 direct target genes. We hypothesize that BHLHB2 is an integral component of a transcription regulatory network that dictates the hormone-dependent phenotype of breast cancer, and ID1 facilitates tumor cells to acquire a poorly differentiated phenotype by inhibiting BHLHB2 function. We will test this hypothesis in the following three specific aims by conducting a systematic and detailed study on the function and regulation of BHLHB2 in breast cancer cells. Specifically, we will: 1) investigate the role of BHLHB2 in maintaining hormone-dependent phenotype and its regulation by ID1 by examining the consequences of gain- or loss-of- function of BHLHB2 and ID1 in human breast cancer cells; 2) identify and characterize genes regulated by BHLHB2 and ID1 using high-throughput genome-wide analysis of gene expression and BHLHB2 DNA binding; and 3) investigate the regulation and function of fulvestrant resistance-related miRNAs, with emphasis on the cross-regulation between the fulvestrant resistant-relate miRNA and core transcription factors of hormone- dependent breast cancer cells.