Pbx1 expression is required for myeloproliferative neoplasm onset and maintenance

Pre B cell leukemia homeobox 1 (Pbx1) regulates the balance between self-renewal and differentiation of hematopoietic stem cells, and maintains proto-oncogenic transcriptional pathways implicated in several tumors. Its aberrant expression was found in a subset of myeloproliferative neoplasms (MPN) patients bearing the JAK2V617F mutation. To investigate if Pbx1 contributes to MPN, and to explore its potential as therapeutic target, we generated a new mouse strain, that we called JP, by crossing a known JAK2V617F inducible knock-in MPN model with a Pbx1 conditional-ko. In JP mice we can simultaneously activate the human JAK2 mutation and delete Pbx1. Typical MPN features, such as thrombocytemia and granulocytosis, did not develop in the absence of Pbx1. Erythrocytosis, initially displayed by JP mice, gradually resolved over time. Moreover, splenic myeloid metaplasia and in vitro cytokine independent growth were rescued by Pbx1 inactivation. Through RNA-Sequencing we analyzed molecular pathways downstream of Pbx1 and involved in MPN maintenance in stem and progenitor cells. The aberrant transcriptome in the MPN model compared to wild-type was rescued by the absence of Pbx1. Our results demonstrate that inhibition of the Pbx1-driven transcriptional program is beneficial in MPN. Modulation of Pbx1 activity by direct targeting or by targeting its downstream mediators might thus represent a novel therapeutic approach. Overall design: mRNA profiles from LKS sorted from the BM of pIpC-treated JAK2-cKI, JP and WT control mice (3-4 biological replicates/group)

前B细胞白血病同源框1（Pbx1）可调控造血干细胞的自我更新与分化平衡，并维持与多种肿瘤相关的致癌转录通路。研究人员在携带JAK2V617F突变的骨髓增殖性肿瘤（myeloproliferative neoplasms，MPN）患者亚群中，检测到Pbx1的异常表达。为探究Pbx1是否参与MPN的发生发展，并探索其作为治疗靶点的潜力，本研究将已报道的JAK2V617F诱导性敲入MPN模型与Pbx1条件性敲除模型进行杂交，构建了命名为JP的新型小鼠品系。在JP小鼠体内，可同时激活人源JAK2突变并敲除Pbx1。当Pbx1缺失时，MPN的典型特征如血小板增多症与粒细胞增多症均未出现。JP小鼠初期表现出的红细胞增多症随时间推移逐渐缓解。此外，脾脏髓样化生与体外细胞因子非依赖性生长的异常表型，可因Pbx1失活而得到挽救。本研究通过RNA测序（RNA-Sequencing）分析了Pbx1下游、且参与造血干祖细胞中MPN维持的分子通路。相较于野生型（Wild-type，WT）小鼠，MPN模型中出现的异常转录组可因Pbx1缺失而得到纠正。本研究结果证实，抑制Pbx1介导的转录程序对MPN治疗具有益处。通过直接靶向Pbx1或其下游介质来调控Pbx1活性，或可成为一种全新的MPN治疗策略。总体实验设计：对经聚肌苷酸-聚胞苷酸（polyinosinic-polycytidylic acid，pIpC）处理的JAK2条件敲入（JAK2-cKI）、JP及野生型对照小鼠的骨髓（Bone marrow，BM）中分离的LKS分选细胞进行mRNA表达谱分析，每组设置3-4个生物学重复。