Defining the CD44-STAT3 axis in the pathogenesis of triple-negative breast cancer

描述(申请人提供)：三阴性乳腺癌(TNBCs)，不表达雌激素受体或孕激素受体或过度表达人表皮生长因子相关2(HER2)，是临床侵袭性肿瘤，转移率高，预后差。复发的TNBC被认为是由一群肿瘤启动细胞亚群介导的，这些细胞逃避化疗的细胞毒作用，并以细胞表面CD44的表达为特征。CD44+细胞在TNBC细胞系中的高发生率，其中许多细胞还具有转录因子STAT3的结构性激活，这表明CD44不仅是通常认为的启动肿瘤细胞的标志，而且直接参与调节STAT3的活性，并导致这些细胞的不适当生存。我们已经证明，在TNBC细胞中，CD44基因敲除会降低STAT3的转录活性，但不会降低STAT3的酪氨酸或丝氨酸磷酸化。CD44基因敲除也增加了TNBC细胞对常规化疗药物的敏感性，支持CD44在这些肿瘤的发病机制中的重要性。然而，CD44调节TNBC中STAT3活性的分子机制尚不清楚。本研究的目标是：(1)阐明CD44调节TNBC中STAT3转录活性的信号通路；(2)确定CD44在STAT3介导的TNBC基因调控中的功能；利用染色质免疫沉淀分析CD44在确定STAT3基因组结合部位中的作用，并利用质谱仪鉴定CD44在STAT3相关蛋白上的功能；(3)分析STAT3抑制对CD44+与CD44-TNBC亚群生物学的影响，使用BH3图谱检测细胞启动细胞凋亡。这一提议的完成将使人们对CD44-STAT3轴在TNBC发病机制中的作用有更深入的了解，TNBC的侵袭性对有效治疗构成严重障碍。阐明CD44表达在TNBC侵袭性表型中的作用将扩大我们对STAT3生物学的认识，并可能为CD44高表达的肿瘤提供新的治疗方法。此外，对CD44信号通路的了解的增加可能最终提供其他癌症表面标志物如何参与肿瘤发生的线索。

DESCRIPTION (provided by applicant): Triple-negative breast cancers (TNBCs), which do not express estrogen receptor or progesterone receptor or overexpress human epidermal growth factor-related 2 (HER2), are clinically aggressive tumors characterized by high rates of metastases and poor prognosis. Recurrent TNBC is thought to be mediated by a subpopulation of tumor-initiating cells that escape the cytotoxic effects of chemotherapy and are characterized by cell surface expression of CD44. The high incidence of CD44+ cells in TNBC cell lines, many of which also have constitutive activation of the transcription factor STAT3, suggests that CD44 is not merely a marker of tumor-initiating cells, as it is generally viewed, but rather directly involved in modulating STAT3 activity and contributing to the inappropriate survival of these cells. We have demonstrated that CD44 knockdown decreases STAT3 transcriptional activity but not STAT3 tyrosine or serine phosphorylation in TNBC cells. CD44 knockdown also increases TNBC cell sensitivity to conventional chemotherapeutic agents, supporting the importance of CD44 in the pathogenesis of these tumors. However, the molecular mechanism by which CD44 regulates STAT3 activity in TNBC is not yet understood. The goals of this research proposal are: (1) To elucidate the signaling pathway by which CD44 modulates STAT3 transcriptional activity in TNBC, (2) To determine the function of CD44 in STAT3-mediated gene regulation in TNBC, using chromatin immunoprecipitation to analyze the role of CD44 in defining STAT3 genomic binding sites and using mass spectrometry to identify the function of CD44 on STAT3-associated proteins, and (3) To dissect the effect of STAT3 inhibition on the biology of CD44+ versus CD44- TNBC subpopulations, using BH3 profiling to measure cell priming for apoptosis. The completion of this proposal will provide insights into the role of the CD44-STAT3 axis in the pathogenesis of TNBC whose aggressive nature presents serious obstacles to effective treatment. Elucidating how CD44 expression contributes to the aggressive phenotype of TNBC will expand our knowledge of STAT3 biology and may suggest novel therapeutic approaches for tumors with high CD44 expression. Furthermore, increased understanding of the CD44 signaling pathway may ultimately provide clues about how other cancer surface markers are involved in tumorigenesis.