Novel Mechanisms of Nuclear Phosphoinositide Signaling in Regulation of the YAP/TAZ Pathway in Triple-negative Breast Cancer

磷脂酰肌醇(PI)是一种脂类信使，控制着人体生理的许多方面。一个重要的 核内存在部分PI(占总PI的40%)，但核的性质和功能 PI在很大程度上是未知的。我们发现磷脂酰肌醇4，5-二磷酸(PI4，5P2)是一种 胞核中含有丰富的磷脂酰肌醇和磷脂酰肌醇-4-磷酸-5-磷脂酰肌醇-5-磷脂酰肌醇 激酶1α(PIPKI􀁄)是调节核内PI4、5P2信号转导的主要酶。核PI4，5P2可以 被核定位的PI3K(PI3K)肌醇磷酸多激酶(IPMK)进一步磷酸化 产生一种与肿瘤发生有关的PI物种，PI3，4，5P3。这表明piki􀁄 和IPMK是癌症治疗的潜在靶点。始终如一地，我们证明了耗尽或 PIPKI、􀁄和IPMK的药理抑制在三重阴性中通过细胞凋亡导致癌细胞死亡 乳腺癌(TNBC)细胞。此外，在TNBC细胞中，我们发现PIPKI􀁄和IPMK的耗竭 显著降低YAP/TAZ靶基因的表达 致癌作用。TNBC是乳腺癌中最具侵袭性的亚型，与贫穷的患者相关 由于缺乏目前化疗的替代方案而存活。因此，迫切需要 在TNBC中发现新的靶向疗法。YAP/TAZ-PI激酶(PIPKI、􀁄和IPMK)通路 是有吸引力的药物靶点，因为在乳腺癌中经常发现YAP/TAZ的异常激活 尤其是在TNBC中，PIPKI􀁄基因在TNBC中普遍扩增，核内PI3，4，5P3途径是 在TNBC中经常放松管制。对核Pis介导的YAP/TAZ途径的精确理解将 提供可用于开发针对TNBC的靶向疗法的知识。在这 建议，我们将1)阐明YAP/TAZ途径的分子机制 PIPIK、􀁄和IPMK通过广泛的生化和细胞生物学方法和2)调查贡献 在培养的肿瘤细胞和小鼠模型中研究􀁄和IPMK在肿瘤发生中的作用。

Phosphoinositides (PIs) are lipid messengers that control many aspects of human physiology. A significant fraction of PIs (>40% of total PIs) is found in the nucleus, however the nature and functions of the nuclear PIs are largely unknown. We discovered that phosphatidylinositol 4,5-bisphosphate (PI4,5P2) is an abundant PI species in the nucleus and the PI4,5P2-generating kinase phosphatidylinositol-4-phosphate-5- kinase type 1 alpha (PIPKI􀁄) is a major enzyme modulating nuclear PI4,5P2 signaling. Nuclear PI4,5P2 can be further phosphorylated by a nuclear-localizing PI3-kinase (PI3K) inositol phosphate multikinase (IPMK) to produce a PI species, PI3,4,5P3, that has been implicated in oncogenesis. This suggests that PIPKI􀁄 and IPMK are potential targets for cancer therapy. Consistently, we showed that depletion or pharmacological inhibition of PIPKI􀁄 and IPMK leads to cancer cell death by apoptosis in triple negative breast cancer (TNBC) cells. Moreover, in TNBC cells, we discovered that depletion of PIPKI􀁄 and IPMK significantly reduces the expression of YAP/TAZ target genes that have established contributions to oncogenesis. TNBC is the most aggressive subtype of breast cancer and associated with poor patient survival due to lack of alternatives to current chemotherapies. As a result, there is an urgent need for discovering novel targeted therapeutics in TNBC. The YAP/TAZ-PI kinases (PIPKI􀁄 and IPMK) pathways are attractive drug targets because aberrant activation of YAP/TAZ is frequently found in breast cancer particularly in TNBC, PIPKI􀁄 gene is commonly amplified in TNBC, and the nuclear PI3,4,5P3 pathway is frequently deregulated in TNBC. Precise understanding of nuclear PIs-mediated YAP/TAZ pathway will provide knowledge which can be utilized for developing targeted therapeutics against TNBC. In this proposal, we will 1) elucidate molecular mechanisms by which the YAP/TAZ pathway is controlled by PIPIK􀁄 and IPMK via extensive biochemical and cell biological approaches and 2) investigate contributions of PIPIK􀁄 and IPMK in TNBC pathogenesis in cultured TNBC cells and mouse models.