血小板生成素受体（TpoR）是骨髓增生性肿瘤（MPNs）中的中心角色。JAK2、钙调蛋白或TpoR本身的突变导致TpoR的持续激活、造血干细胞和前体细胞的无限增殖和分化。 JAK2 V617F突变负责大部分MPNs，所有驱动突变体均诱导病理性TpoR激活。尽管TpoR在病理过程中起着关键作用，但现有的治疗策略仍集中在无法区分突变MPN克隆与健康细胞之间的JAK2激酶抑制剂上。令人惊讶的是，尽管其在病理过程中起着核心作用，但对TpoR本身的靶向治疗研究仍未得到充分探索。在本研究中，我们对生理和病理条件下的人类TpoR激活进行了全面的表征，重点关注JAK2 V617F突变体。通过对TpoR的跨膜和细胞质域进行受控二聚化，我们发现人类TpoR（hTpoR）在Tpo诱导和JAK2 V617F介导的激活过程中采用不同的二聚构型。我们确定了hTpoR的特定氨基酸和二聚构型与JAK2 V617F结合后的激活有关，并在造血细胞系和原代骨髓细胞的全长受体环境中验证了我们的发现。值得注意的是，我们发现通过点突变调节hTpoR的构型可实现对JAK2 V617F驱动的激活的特异性抑制，而不影响Tpo诱导的信号传导。我们的研究结果表明，调节hTpoR构型是一种可行的JAK2 V617F阳性MPNs治疗策略，并通过确定与JAK2 V617F特异性激活相关的hTpoR精确残基为新药开发铺平了道路。版权所有 ©2023美国血液学学会。

The Thrombopoietin Receptor (TpoR) is a central player in Myeloproliferative Neoplasms (MPNs). Mutations in JAK2, calreticulin or in TpoR itself drive constitutive activation of TpoR and uncontrolled proliferation and differentiation of hematopoietic stem cells and progenitors. The JAK2 V617F mutation is responsible for the majority of MPNs and all driver mutants induce pathologic TpoR activation. Existing therapeutic strategies have focused on JAK2 kinase inhibitors that are unable to differentiate between the mutated MPN clone and healthy cells. Surprisingly, targeting of TpoR itself has remained poorly explored despite its central role in the pathology. Here, we performed a comprehensive characterization of human TpoR activation in physiological and pathological conditions focusing on the JAK2 V617F mutant. Using a system of controlled dimerization of transmembrane and cytosolic domains of TpoR, we discovered that the human TpoR (hTpoR) adopts different dimeric conformations upon Tpo-induced versus JAK2 V617F-mediated activation. We identified the amino acids and the specific dimeric conformation of hTpoR responsible for activation in complex with JAK2 V617F and confirmed our findings in the full-length receptor context in hematopoietic cell lines and primary bone marrow cells. Remarkably, we find that modulation of hTpoR conformations by point mutations allows specific inhibition of the JAK2 V617F-driven activation without affecting Tpo-induced signaling. Our results demonstrate that modulation of hTpoR conformation is a viable therapeutic strategy for JAK2 V617F positive MPNs and set the path for novel drug development by identifying precise residues of hTpoR involved in JAK2 V617F specific activation.Copyright © 2023 American Society of Hematology.