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

描述（由申请人提供）：三阴性乳腺癌（tnbc）不表达雌激素受体或孕激素受体，也不过度表达人表皮生长因子相关2 (HER2)，是一种临床侵袭性肿瘤，转移率高，预后差。复发性TNBC被认为是由肿瘤启动细胞亚群介导的，这些细胞逃避化疗的细胞毒性作用，其特征是细胞表面表达CD44。CD44+细胞在TNBC细胞系中的高发生率，其中许多也具有转录因子STAT3的组成激活，这表明CD44不仅仅是肿瘤启动细胞的标记物，正如它通常被认为的那样，而是直接参与调节STAT3活性并促进这些细胞的不适当存活。我们已经证明，CD44敲低会降低TNBC细胞中STAT3的转录活性，但不会降低STAT3酪氨酸或丝氨酸磷酸化。CD44敲低也增加了TNBC细胞对常规化疗药物的敏感性，支持CD44在这些肿瘤发病机制中的重要性。然而，CD44调控TNBC中STAT3活性的分子机制尚不清楚。本研究计划的目标是：(1)阐明CD44的信号通路调节STAT3在TNBC转录活动,(2)确定CD44在TNBC STAT3-mediated基因调控的功能,使用染色质免疫沉淀反应分析CD44在定义STAT3基因结合位点的作用和使用质谱识别CD44 STAT3-associated蛋白质的功能,和(3)解剖的影响抑制STAT3的生物学CD44 +和CD44 - TNBC亚种群,使用BH3谱分析来测量细胞凋亡的启动。这一建议的完成将有助于深入了解CD44-STAT3轴在TNBC发病机制中的作用，TNBC的侵袭性对有效治疗构成严重障碍。阐明CD44表达如何促进TNBC侵袭性表型将扩大我们对STAT3生物学的认识，并可能为高CD44表达肿瘤提供新的治疗方法。此外，对CD44信号通路的进一步了解可能最终为其他癌症表面标记物如何参与肿瘤发生提供线索。

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.