Role of p21 activated kinase in Leukemogenesis

描述（由申请人提供）：急性髓性白血病（AML）是一种侵袭性血液系统恶性肿瘤，其特点是预后不良。虽然近年来AML治疗的化疗方案有了渐进式的改进；大多数AML患者复发，其中相当一部分人死于这种疾病。虽然导致复发的确切机制尚不清楚，但缺乏消除白血病干细胞（LSCs）和获得耐药突变（如在FLT3受体患者中发现的那些）可能是一些重要的因素。在近30%的AML患者中观察到FLT3的内部串联重复（ITD），并导致预后不良。同样，KIT激活环突变（例如KITD816V）对格列卫具有耐药性，仅与约50%的核心结合因子(CBF)-AMLs和95%的全身性肥大细胞增多症（SM）患者（一种骨髓增殖性肿瘤（MPN））相关，并导致较差的总生存期。虽然针对上述适应症已经进行了几项使用FLT3和KIT抑制剂的临床试验，但没有一项显示出显著的长期临床疗效。因此，对于这些疾病的发病率和死亡率最高的老年人，迫切需要继续研究新的分子靶向和毒性较小的治疗方法。最近，由157名AML患者组成的四项独立临床研究表明，局灶黏附激酶（FAK）在高达50%的患者源性骨髓细胞中过表达，但在正常细胞中不表达。在这些患者中，FAK在Y397上被过度磷酸化，Y397是其激活的关键残基。与FAK-细胞相比，FAK+ AML细胞表现出更高的迁移能力和对柔红霉素的耐药性，FAK表达与高母细胞计数、早期死亡和较短存活率显著相关。除了FAK，最近一项针对112名AML患者的研究也表明，在新诊断的AML患者中，磷酸化(p) pStat5的表达与较差的总生存率相关。值得注意的是，在携带KITD816V突变的肥大细胞增多症患者中，pStat5的组成性激活达到100%。重要的是，在AML患者中观察到pStat5和FLT3ITD突变之间存在很强的相关性。这些临床结果表明，FLT3ITD/KITD814V、FAK和Stat5可能促进AML和mpn的发展；然而，这些信号分子在AML或mpn发生或进展中的关系尚不清楚。重要的是，尽管Stat5与几种涉及LSCs的血液恶性肿瘤有关；在AML或MPN的情况下，Stat5的激活是如何在细胞质或细胞核中精确调节的，以及参与其核输入的信号分子是什么，仍然是一个谜。我们将明确FAK及其下游效应物包括PAK1和Stat5在调控FLT3ITD/KITD814V诱导转化中的作用。我们假设FAK通过FLT3ITD/KITD814V的过度激活以及Stat5的下游磷酸化和核易位以PAK1依赖的方式导致FLT3ITD/KITD814V驱动的AML。

DESCRIPTION (provided by applicant): Acute myeloid leukemia (AML) is an aggressive hematologic malignancy characterized by poor prognosis. While incremental improvements in chemotherapy regimens have been described for AML treatment in recent years; majority of AML patients relapse and a significant number of them die of this disease. Although the precise mechanism(s) leading to relapse are poorly understood, lack of elimination of leukemia stem cells (LSCs) and the acquisition of drug resistance mutations such as those found in patients with FLT3 receptor may be some of the significant contributors. Internal tandem duplications (ITD) in FLT3 are observed in nearly 30% of all AML patients and confer poor prognosis. Likewise, KIT activation loop mutations (e.g. KITD816V), that are resistant to Gleevec, are exclusively associated with ~ 50% of core binding factor (CBF)-AMLs and 95% of systemic mastocytosis (SM) patients (a form of myeloproliferative neoplasm (MPN)) and confer poor overall survival. While several clinical trials have been conducted utilizing FLT3 and KIT inhibitors for above indications, none have shown significant long-term clinical efficacy. Thus, fo the elderly, who demonstrate the highest incidence of and mortality from these diseases, continued investigation for novel molecularly-targeted and less toxic therapies are desperately needed. Recently, four independent clinical studies comprising of 157 AML patients demonstrated overexpression of focal adhesion kinase (FAK) in up to 50% of patient derived BM cells but not in normal cells. In a significant number of these patients, FAK was hyper-phosphorylated on Y397, a critical residue for its activation. FAK+ AML cells displayed significantly higher migration and resistance to daunorubicin compared with FAK- cells and FAK expression significantly correlated with high blast cell counts, early death and shorter survival rate. In addition to FAK, a recent study utilizing 112 AML patients also showed that expression of phosphorylated (p) pStat5 in newly diagnosed AML patients is associated with poor overall survival. Remarkably, constitutive activation of pStat5 was seen in 100% of mastocytosis patients bearing the KITD816V mutation. Importantly, a strong correlation between the presence of pStat5 and FLT3ITD mutations was observed in AML patients. These clinical findings suggest that FLT3ITD/KITD814V, FAK and Stat5 are likely to contribute to the development of AML and MPNs; however, the relationship between these signaling molecules in the development or progression of AML or MPNs is poorly understood. Importantly, although Stat5 has been implicated in several hematologic malignancies involving LSCs; how precisely activation of Stat5 is regulated in the cytoplasm or in the nucleus and what are the signaling molecules involved in its nuclear import in the context of AML or MPN remains an enigma. We will define the role of FAK and its downstream effectors including PAK1 and Stat5 in regulating FLT3ITD/KITD814V induced transformation. We hypothesize that hyper-activation of FAK via FLT3ITD/KITD814V and downstream phosphorylation and nuclear translocation of Stat5 in a PAK1 dependent manner contributes to FLT3ITD/KITD814V driven AML.