Poster Presentation 27th Lorne Cancer Conference 2015

IL3-Receptor Signaling is Dispensable for the Generation and Maintenance of the Jak2V617F-Induced Myeloproliferative Neoplasm (MPN) (#298)

Therese Vu 1 , Claudia Bruedigam 1 , Rebecca Austin 1 , Catherine Paine-Kuhn 1 , Hayley Ramshaw , Angel Lopez , Geoffrey R Hill 1 , Ann Mullally 2 , Steven Lane
  1. QIMR Berghofer Medical Research Institute, Herston, QLD, Australia
  2. Division of Hematology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA

Myeloproliferative neoplasms (MPN) are clonal diseases characterised by the overproduction of mature blood cells. This underlying disorder may predispose patients to developing secondary acute leukaemia. The most common driver mutation found in MPN patients is JAK2V617F, which leads to cytokine hypersensitivity and constitutive JAK2-STAT5 signaling through erythropoietin (EPO), thrombopoietin (TPO) or interleukin-3 (IL3) receptor scaffold. Physiological Jak2V617F expression in long-term haematopoietic stem cells (LTHSCs) is sufficient to generate MPN, and these LTHSCs contain the sole reservoir of Jak2V617F MPN-initiating cells. The EPO receptor is not expressed on LTHSCs, which suggests that hypersensitivity to IL3 and/or TPO signaling is responsible for driving LTHSC proliferation and survival.

To determine the respective contributions of IL3 and TPO signaling to Jak2V617F MPN, pStat5 was measured in LTHSC and progenitor populations from E2ACre+Jak2V617F+/- knockin mice (hereafter Jak2VF) after stimulation with IL3 or TPO. Committed myeloid progenitors showed robust pStat5 stimulation with IL3, but only low-level stimulation with TPO. In contrast, LTHSCs showed strong induction of pStat5 with TPO stimulation but less so with IL3 stimulation.

To further examine IL3-receptor signaling in Jak2V617F MPN, we crossed Jak2VF knockin mice with mice lacking IL3-receptors (hereafter Jak2VFIL3Rb-/-). IL3 was unable to stimulate pStat5 in Jak2VFIL3Rb-/- mice, but signaling was preserved in Jak2VF mice. Jak2VFIL3Rb-/- mice developed MPN with similar latency to Jak2VF controls and there were no differences in peripheral blood haematocrit or extramedullary erythropoiesis. Likewise, in bone marrow chimaeric mice, all recipients of Jak2VFIL3Rb-/- or Jak2VF cells developed MPN with similar diagnostic parameters.

These data show that while IL3-receptor signaling is dispensable for Jak2VF MPN and LTHSC function, it may regulate short-term myeloid progenitor cells. TPO signaling appears preferentially important for Jak2VF LTHSC pStat5 induction, whereas IL3 is more important for pStat5 induction in progenitor cells. These findings will help to inform strategies targeting Jak2V617F-initiating LTHSC populations.