Role of JAK2V617F in the Pathogenesis of Myeloproliferative Neoplasms

 描述(申请人提供)：骨髓增生性肿瘤(MPN)包括真性红细胞增多症(PV)、原发性血小板增多症(ET)和原发性骨髓纤维化(PMF)，是一组以髓系细胞过度生成为特征的慢性血液系统恶性肿瘤。JAK2V617F突变在95%的PV和50-60%的ET和PMF中被发现，但JAK2V617F在这三种不同MPN中的作用尚不清楚。使用可诱导的JAK2V617F敲入小鼠，我们已经证明在造血室中杂合子JAK2V617F的表达足以引起PV样疾病，而纯合子JAK2V617F的表达加速了骨髓纤维化(MF)的进展。我们还表明，只有表达JAK2V617F的造血干细胞(HSCs)才具有自我更新和传播MPN疾病的能力。然而，JAK2V617F在造血干细胞中的实际作用仍不清楚，也存在争议。大多数研究都集中在骨髓(BM)的HSC功能上。脾HSCs在维持JAK2V617F诱导的MPN中的作用尚不清楚。我们发现，在JAK2V617F基因敲除小鼠中，骨髓中的HSC数量随着时间的推移而减少，而脾HSC池则持续增加。我们推测JAK2V617F的表达可能导致HSC功能异常，表达JAK2V617F的脾HSC可能在MPNS的长期维持中发挥重要作用。JAK2抑制剂治疗对MPN患者有一定的益处，但由于JAK2对正常造血至关重要，因此会导致明显的造血毒性。 发展。在骨髓间充质干细胞中识别JAK2V617F的靶点是MPN所必需的，但不是正常造血发育所必需的，这将有助于开发新的靶向和更安全的MPN治疗方法。在初步研究中，利用微阵列基因表达谱，我们在HSCs中鉴定了JAK2V617F的几个靶点。因此，目标1将确定JAK2V617F对骨髓和脾HSCs的作用，并确定MPN所需的HSCs中JAK2V617F的下游靶点。虽然JAK2V617F是MF中发现的最常见的突变，但JAK2V617F诱发MF的机制尚不清楚。我们发现Shp2在JAK2V617F阳性的MPN/白血病患者来源的细胞系和JAK2V617F敲入小鼠的骨髓中被结构性磷酸化。在初步研究中，我们发现Shp2基因的缺失抑制了JAK2V617F小鼠的PV并阻止了MF的发展。我们推测Shp2可能在JAK2V617F诱导的PV和MF的发病机制中起重要作用。因此，目标2将确定Shp2在JAK2V617F诱导的PV和MF中的作用。在MF患者中发现了失活的EZH2突变。此外，相当大比例的EZH2突变的MF患者携带JAK2V617F突变。我们推测EZH2缺乏可能导致JAK2V617F阳性MPN的表型多样性。在目标3中，我们将确定EZH2缺乏在JAK2V617F诱导的MPN中的作用。总之，这些研究将为MPNS的分子发病机制提供重要的新见解，并可能为MPNS的治疗确定新的治疗靶点。

 DESCRIPTION (provided by applicant): Myeloproliferative neoplasms (MPNs) including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) are a group of chronic hematologic malignancies characterized by the overproduction of myeloid lineage cells. The JAK2V617F mutation has been found in ~95% cases of PV and 50-60% cases of ET and PMF However, the contribution of JAK2V617F in these three different MPNs still remains unclear. Using an inducible JAK2V617F knock-in mouse, we have shown that expression of heterozygous JAK2V617F in hematopoietic compartments is sufficient to cause a PV-like disease whereas homozygous JAK2V617F expression accelerates the progression to myelofibrosis (MF). We also have shown that only JAK2V617F-expressing hematopoietic stem cells (HSCs) have the capacity to self-renew and propagate the MPN disease. However, the actual role of JAK2V617F in HSCs has remained unclear and controversial. Most studies are focused on the bone marrow (BM) HSC function. The contribution of spleen HSCs in the maintenance of JAK2V617F-evoked MPN remains unknown. We have found that the number of HSCs in the BM is reduced over time while spleen HSC pool is consistently increased in JAK2V617F knock-in mice. We hypothesize that JAK2V617F expression may cause aberrant HSC function, and JAK2V617F-expressing spleen HSCs may play an important role in the long-term maintenance of MPNs. JAK2 inhibitor therapy exhibits some benefits to the MPN patients but results in significant hematopoietic toxicities since JAK2 is critical for normal hematopoietic development. Identification of the targets of JAK2V617F in HSCs that are required for MPN but are not essential for normal hematopoietic development would facilitate the development of new targeted and safer therapies for MPNs. In preliminary studies, using microarray gene expression profiling, we have identified several targets of JAK2V617F in HSCs. Therefore, Aim 1 will determine the effects of JAK2V617F on BM and spleen HSCs, and identify the downstream targets of JAK2V617F in HSCs that are required for MPN. Although JAK2V617F is the most common mutation found in MF, the mechanisms of MF induced by JAK2V617F remains unknown. We have found that Shp2 is constitutively phosphorylated in JAK2V617F- positive MPN/leukemia patient derived cell lines and in the BM of JAK2V617F knock-in mice. In preliminary studies, we have found that deletion of Shp2 inhibits PV and prevents the development of MF in JAK2V617F mice. We hypothesize that Shp2 may play an important role in the pathogenesis of PV and MF induced by JAK2V617F. Therefore, Aim 2 will define the role of Shp2 in PV and MF induced by JAK2V617F. Inactivating EZH2 mutations have been found in patients with MF. Moreover, a significant proportion of EZH2 mutated MF patients harbor the JAK2V617F mutation. We hypothesize that EZH2 deficiency may contribute to the phenotypic diversity in JAK2V617F-positive MPNs. In Aim 3, we will determine the contribution of EZH2 deficiency in JAK2V617F-evoked MPN. Collectively, these studies will provide important new insights into the molecular pathogenesis of MPNs and may identify new therapeutic targets for treatment of MPNs.