UBAP2, A New Molecule in Pancreatic Cancer Progression

胰腺导管腺癌（PDAC）是最具侵袭性的恶性肿瘤之一， 预后不佳不幸的是，80-85%的患者被诊断患有不可切除，不可治愈的晚期肿瘤。 分期疾病使中位生存期<6个月，总5年生存期<5%。公 已知小GTP酶如K-RAS的激活突变在PDAC中几乎是普遍的，并且对于PDAC的发生至关重要。 发病机制不幸的是，即使经过30年的深入研究，RAS仍然是不可治愈的。在 2013年，NCI开展了“RAS计划”，以进一步深入了解RAS基因及其蛋白质 产品，在细胞信号传导中的作用以及在健康和疾病中的功能，强调迫切需要确定 K-RAS激活的新分子调节剂，可以药物化并设计新的治疗策略， 改善PDAC患者的不良结局。在这种情况下，定义UBAP 2（泛素结合）的作用 相关蛋白2），一种生物学功能未知的蛋白质，作为调节激活的分子开关 小GTP酶如KRAS和巨胞饮作用在胰腺癌中的应用是高度创新的。 使用抗体-金纳米缀合物作为独特的诱饵，我们将UBAP 2鉴定为蛋白质之一 可能参与胰腺癌的巨胞饮作用。我们在初步数据中证明， UBAP 2表达与PDAC患者总体生存率的显著增加相关。我们也 证明UBAP 2在转基因KPC的胰腺癌细胞系和肿瘤组织中过表达 小鼠和PDAC患者。沉默UBAP 2在体外和体内损害巨胞饮作用，抑制增殖， 胰腺癌细胞在体外的迁移和侵袭以及体内的肿瘤生长。从机制上讲，UBAP 2 稳定包括Rac 1、Cdc 42和K-RAS在内的小GTP酶的活化形式， 降解此外，与WAVE 2和Arp 2/3相关，UBAP 2调节膜皱褶， 对于流体相吸收至关重要。基于这些实验证据，我们假设UBAP 2的功能是 作为调节小GTP酶如K-RAS、巨胞饮作用和 胰腺肿瘤发生因此，确定UBAP 2作为小GT受体的关键调节因子的作用， 激活和巨胞饮作用将为开发UBAP 2作为新的治疗药物提供独特的机会。 靶向针对大量人类癌症，其中巨胞饮作用和小GT3活化起关键作用 作用为了检验这一假设并实现总体目标，我们将使用以下具体目标： 具体目的1：胰腺癌中UBAP 2调节巨胞饮的分子特征。 具体目标2：UBAP 2对小GTP酶活化的调节。 具体目标3：研究UBAP 2在KRAS驱动的胰腺肿瘤发生中的作用。 本申请将确立UBAP 2作为巨胞饮作用的新调节剂，揭示UBAP 2在巨胞饮作用中的独特作用。 KRAS激活的机制，并确定UBAP 2在正常胰腺发育和胰腺癌中的作用。 肿瘤发生这些研究将为靶向巨胞饮和KRAS激活提供新的途径 即使经过了30年的深入调查，这一点至今仍难以找到。

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive malignancies with a notoriously dismal prognosis. Unfortunately, 80-85% patients are diagnosed with an unresectable, incurable advanced stage disease putting the median survival at <6 months and the overall 5-year survival at <5%. It is well known that activating mutations of small GTPases such as K-RAS is near universal in PDAC and critical for pathogenesis. Unfortunately even after 3 decades of intense investigation RAS still remains undruggable. In 2013, NCI undertook “The RAS Initiative” to gain further molecular insight into RAS genes, their protein products, role in cellular signaling and functions in health and disease, underscoring a critical need to identify new molecular regulators of K-RAS activation that can be druggable and devise novel therapeutic strategies to improve dismal outcome in PDAC patients. In this context, defining a role for UBAP2 (Ubiquitin Binding Associated Protein 2), a protein of unknown biological function, as a molecular switch that regulates activation of small GTPases such as KRAS and macropinocytosis in pancreatic cancer is highly innovative. Using antibody-gold nanoconjugates as unique bait, we identified UBAP2 as one of the proteins potentially involved in macropinocytosis in pancreatic cancer. We demonstrate in our preliminary data low UBAP2 expression is correlated with significant increase in overall survival of PDAC patients. We also demonstrate that UBAP2 is overexpressed in pancreatic cancer cell lines and tumor tissues of transgenic KPC mice and PDAC patients. Silencing UBAP2 impairs macropinocytosis in vitro and in vivo, inhibits proliferation, migration and invasion of pancreatic cancer cells in vitro and tumor growth in vivo. Mechanistically, UBAP2 stabilizes the activated forms of small GTPases including Rac1, Cdc42 and K-RAS and protects them from degradation. Furthermore, in association with WAVE2 and Arp2/3, UBAP2 modulates membrane ruffling, critical for fluid phase uptake. Based on these experimental evidences we hypothesize that UBAP2 functions as a molecular switch that regulates activation of small GTPases such as K-RAS, macropinocytosis and pancreatic tumorigenesis. Therefore, establishing role of UBAP2 as a critical regulator of small GTPase activation and macropinocytosis will provide unique opportunities to exploit UBAP2 as a novel therapeutic target against a plethora of human cancers where macropinocytosis and small GTPase activation play a critical role. To test this hypothesis and achieve overall objectives, we will use following specific aims: Specific Aim 1: Molecular characterization of UBAP2 regulated macropinocytosis in pancreatic cancer. Specific Aim 2: Regulation of small GTPases activation by UBAP2. Specific Aim 3: Investigating a role of UBAP2 in KRAS driven pancreatic tumorigenesis. Present application will establish UBAP2 as a new regulator of macropinocytosis, unravel a unique mechanism of KRAS activation and define a role of UBAP2 in normal pancreas development and pancreatic tumorigenesis. These investigations will provide new avenues to target macropinocytosis and KRAS activation that remains elusive so far even after last 30 years of intense investigation.