PITPβ Drives JAK2 V617F-Mediated Myeloproliferative Neoplasms by Promoting PtdIns(3,4)P _₂ -Dependent AKT...

JAK2 is a key regulator of cytokine-mediated proliferative signaling in hematopoietic stem and progenitor cells. Activating mutations, most commonly JAK2 V617F, trigger aberrant cytokine signaling driving the pathogenesis of myeloproliferative neoplasms (MPNs). Phosphatidylinositol transfer proteins (PITPs) facilitate phosphoinositide synthesis by delivering phosphatidylinositol to lipid kinases, though their roles in oncogenic signaling have remained poorly defined. Here we show that PITPβ is critical for the development of JAK2V617F-driven MPN in mice. Deleting Pitp β across the hematopoietic system, but not Pitp α, prolonged 25-week survival of Jak2V617F mice from 10% to 85%. Loss of Pitp β attenuated disease-associated splenomegaly and curtailed erythroid progenitors expansion both in vivo and in vitro . Mechanistically, PITPβ is necessary for AKT hyperactivation in hematopoietic progenitors, while STAT5 and ERK signaling remain unaffected. In alignment with this role, PITPβ promotes the production of PtdIns(3,4)P _₂ , a phosphoinositide that sustains aberrant AKT signaling in Jak2V617F progenitors. Pharmacologic inhibition of AKT with the FDA-approved inhibitor capivasertib in Jak2V617F-transplanted mice similarly reduced splenomegaly and erythroid proliferation, mimicking the effects of Pitp β loss. Collectively, these results identify a novel PITPβ-PtdIns(3,4)P _₂ signaling axis that selectively maintains pathological AKT activation in JAK2V617F-driven MPN, revealing a promising therapeutic vulnerability.