| Summary: | Abstract: Interferon-α (IFN-α) exhibits antiviral and antiproliferative effects on normal and neoplastic cells. Intracellular signaling of IFN-α is mediated by tyrosine kinase 2 (TYK2) and janus kinase 1 (JAK1), followed by signal transducers and activators of transcription (STATs). TYK2 is redundant for the antiviral effect of IFN-α; however, the requirements for antiproliferative effects are unknown. We assessed the role of TYK2 in the effects of IFN-α in myeloproliferative neoplasm (MPN) model mice. Jak2V617F transgenic mice develop MPNs resembling human primary myelofibrosis, and ropeginterferon-α-2b ameliorated their features. However, these IFN-α effects were absent in Jak2V617F;Tyk2−/− mice. In mixed wild-type (WT)/Jak2V617F chimeric mice, IFN-α treatment induces Jak2V617F hematopoietic stem cells (HSCs) to enter the cell cycle and skew their differentiation into the megakaryocyte lineage, decreasing the number of Jak2V617F HSCs. The effects of IFN-α on Jak2V617F HSCs were not observed in mixed WT/Jak2V617F;Tyk2−/− mice, indicating that TYK2 is essential for the effects of IFN-α on both Jak2V617F progenitors and HSCs. The mechanism of IFN-α in Jak2V617F HSCs and progenitors differed: genes regulating the cell cycle were enriched in IFN-α–stimulated Jak2V617F HSCs, but not in Jak2V617F progenitors; genes regulating antiproliferation were enriched in IFN-α–stimulated Jak2V617F progenitors but not in Jak2V617F HSCs. The major IFN-α signaling molecule activated by JAKs is STAT1, which is essential for the antiviral effect. Most effects of IFN-α on Jak2V617F cells were preserved in Jak2V617F;Stat1−/− mice but to a moderate degree compared with Jak2V617F mice. Our study reveals essential roles of TYK2 for the preferential suppressive effect of IFN-α on Jak2V617F progenitors and HSCs.
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