Glycosylation-dependent mechanisms regulating ovarian tumor cell survival

描述(申请人提供)：表面糖链的改变是肿瘤细胞的一个众所周知的特征；然而，特定的糖链和相关的糖基转移酶调节肿瘤细胞行为的分子机制仍然不清楚。我们团队的工作已经确定，ST6Gal-I唾液酸基转移酶赋予卵巢癌细胞(OC)避免由Galectins、死亡受体激活剂和化疗药物等多种刺激诱导的凋亡的能力。在这项研究中，我们首次显示ST6Gal-I蛋白在绝大多数人卵巢肿瘤中上调，包括致命的乳头状浆液性腺癌亚型。ST6Gal-I的上调相应地导致包括整合素、Fas和TNFR1在内的选定受体的高唾液酸化。在范式转换机制研究中，我们发现ST6Gal-I介导的Fas和TNFR1的唾液酸化阻止了受体内部化，导致这些受体的信号向生存而不是凋亡转变。此外，ST6Gal-I的活性对凋亡的Galectin-3和化疗药物顺铂具有抵抗力。这一建议的中心假设是，ST6Gal-I的过度表达是导致OC致死性的两个关键因素：肿瘤细胞对铂类化疗的抵抗力(Aim 1)和腹膜肿瘤微环境中OC细胞对免疫刺激的保护(Aim 2)，后者富含Gal-3以及Fas和TNFR1的配体。初步研究表明，ST6Gal-I可促进OC细胞在患者腹水中的存活；这一发现对于OC细胞的腹膜转移具有重要意义。目的1：ST6Gal-I介导的受体唾液酸化在化疗耐药中的作用。我们将确定ST6Gal-I在顺铂耐药中的作用的分子机制，并确定受体唾液酸化是否控制完整的肿瘤微环境中的化疗耐药。从表达不同ST6Gal-I的OC细胞建立的小鼠原位肿瘤将评估顺铂的治疗效果，体内RNAi将用于实施ST6Gal-I的治疗性敲除，以恢复顺铂的敏感性。ST6Gal-I将在化疗敏感和耐药的人类肿瘤中进行量化，以评估其预后潜力。目的：探讨ST6Gal-I在腹膜微环境中对肿瘤细胞存活的影响，重点阐述腹水中依赖ST6Gal-I的OC细胞存活的机制，重点是Gal-3/β1整合素、FasL/Fas和肿瘤坏死因子α/TNFR1的相互作用。将检验ST6Gal-I介导的OC细胞免受细胞毒免疫细胞的保护，并筛查人卵巢肿瘤ST6Gal-I与免疫细胞渗透之间的关联。ST6Gal-I+/-ST6Gal-I原位肿瘤的生长将在免疫活性小鼠中进行监测。这些研究将产生影响，表明ST6Gal-I是控制肿瘤/微环境相互作用的主调节分子，调节推动肿瘤复发的OC细胞消除与持续之间的平衡。创新之处在于阐明：(1)新的糖基化依赖肿瘤机制，以及(2)OC发病机制中新的分子参与者和患者化疗耐药的生物标志物。

DESCRIPTION (provided by applicant): An altered profile of surface glycans is a well-known feature of tumor cells; however the molecular mechanisms by which specific glycans and associated glycosyltransferases regulate tumor cell behavior remain elusive. Work from our group has determined that the ST6Gal-I sialyltransferase endows ovarian cancer (OC) cells with the ability to avoid apoptosis induced by multiple stimuli including galectins, death receptor activators and chemotherapeutic drugs. In this proposal we show for the first time that ST6Gal-I protein is upregulated in the great majority of human ovarian tumors, including the lethal papillary serous adenocarcinoma subtype. Upregulation of ST6Gal-I correspondingly causes hypersialylation of selected receptors including the ¿1 integrin, Fas and TNFR1. In paradigm-shifting mechanistic studies, we find that ST6Gal-I-mediated sialylation of Fas and TNFR1 prevents receptor internalization, causing a shift in the signaling of these receptors toward survival rather than apoptosis. Additionally, ST6Gal-I activity confers resistance to apoptotic galectin-3 and the chemotherapeutic, cisplatin. The central hypothesis of this proposal is that ST6Gal-I overexpression underlies two crucial factors contributing to OC lethality: tumor cell resistance to platinum-based chemotherapy (Aim 1), and OC cell protection against immune stimuli within the peritoneal tumor microenvironment (Aim 2), which is rich in gal-3 as well as ligands for Fas and TNFR1. Preliminary studies show that ST6Gal-I promotes OC cell survival within patient peritoneal ascites fluid; this finding is significant in that OC cells metastasize va peritoneal transit. AIM 1: ST6Gal-I-mediated receptor sialylation in chemoresistance. We will define molecular mechanisms responsible for ST6Gal-I's role in cisplatin resistance, and determine whether receptor sialylation controls chemoresistance within the intact tumor microenvironment. Efficacy of cisplatin treatment will be evaluated for orthotopic tumors established in mice from OC cells with differential ST6Gal-I expression, and in vivo delivery of RNAi will be used to implement therapeutic knockdown of ST6Gal-I to restore cisplatin sensitivity. ST6Gal-I will be quantified in chemosensitive vs. chemoresistant human tumors to assess its prognostic potential. AIM 2: Contribution of ST6Gal-I to tumor cell survival within the peritoneal microenvironment Mechanisms underlying ST6Gal-I-dependent OC cell survival within ascites will be elucidated, with a focus on gal-3/ ¿1 integrin, FasL/Fas, and TNF?/TNFR1 interactions. ST6Gal-I-mediated protection of OC cells from cytotoxic immune cells will be examined, and human ovarian tumors screened for an association between ST6Gal-I and immune cell infiltration. The growth of orthotopic tumors +/- ST6Gal-I will be monitored in immunocompetent mice. The studies will have impact by showing that ST6Gal-I is a master regulatory molecule controlling tumor/ microenvironmental interactions that regulate the balance between elimination vs. persistence of OC cells that drive tumor recurrence. Innovation lies in the elucidation of: (1) novel glycosylation-dependent tumor mechanisms, and (2) a new molecular player in OC pathogenesis and biomarker for patient chemoresistance.