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. mRNA profiles from LKS sorted from the BM of pIpC-treated JAK2-cKI, JP and WT control mice (3-4 biological replicates/group)