Natural killer (NK) cells are tightly regulated by the JAK-STAT signaling pathway and cannot survive in the absence of STAT5. We now report that STAT5-defi cient NK cells can be rescued by overexpression of BCL2. Our experiments defi ne STAT5 as a master regulator of NK-cell proliferation and lytic functions. Although NK cells are generally responsible for killing tumor cells, the rescued STAT5-defi cient NK cells promote tumor formation by producing enhanced levels of the angiogenic factor VEGFA. The importance of VEGFA produced by NK cells was verifi ed by experiments with a conditional knockout of VEGFA in NK cells. We show that STAT5 normally represses the transcription of VEGFA in NK cells, in both mice and humans. These fi ndings reveal that STAT5-directed therapies may have negative effects: In addition to impairing NK-cell-mediated tumor surveillance, they may even promote tumor growth by enhancing angiogenesis. SIGNIFICANCE:The importance of the immune system in effective cancer treatment is widely recognized. We show that the new signal interceptors targeting the JAK-STAT5 pathway may have dangerous side effects that must be taken into account in clinical trials: inhibiting JAK-STAT5 has the potential to promote tumor growth by enhancing NK-cell-mediated angiogenesis. Cancer Discov; 6(4); ©2016 AACR . Ni and Cerwenka, p. 347. See related commentary by INTRODUCTIONNatural killer (NK) cells are innate lymphocytes that develop from a common lymphoid progenitor in the bone marrow ( 1 ). They represent the fi rst line of defense against infected, stressed, and malignant cells. Recent evidence has assigned distinct features and functions to tissue-specifi c NK cells ( 2 ). NK cells have organ-specifi c properties, such as distinct profi les of receptor expression or cytokine production ( 3 ). Uterine NK cells secrete high levels of VEGFA and are involved in placental vascularization. The physiologic functions of other organ-specifi c NK-cell subsets are less well understood ( 4 ). STAT5 Is a Key Regulator in NK Cells and Acts as a Molecular Switch from Tumor Surveillance to Tumor PromotionDagmarAll aspects of NK-cell development are regulated by cytokines, their downstream signaling pathways, and transcriptional regulators. These include key cytokines such as IL2, IL12, IL15, IL18, and IL21 ( 5 ), most of which signal via the common γ chain ( 5 ) and activate the JAK-STAT pathway ( 6 ). JAK kinases (JAK1-3 and TYK2) bind to cytokine receptors and are activated by ligand/receptor binding. The activated kinase phosphorylates STAT transcription factors refs. 6,7 ).Consistent with its function as the major STAT protein downstream of IL7, IL2, and IL15, STAT5 is absolutely essential for conventional NK-cell development and survival; Stat5 Δ / Δ Ncr1-iCre Tg mice lack NK cells ( 8 ). It is also important for lymphoid cell development ( 9 ): STAT5 is constitutively active in a plethora of lymphoid malignancies ( 10 ). Recent studies have described somatic Stat5b mutations as active drivers of lymphoid mali...

Tyrosine kinase 2 (TYK2) is a member of the Janus kinase (JAK) family, which transduces cytokine and growth factor signalling. Analysis of TYK2 loss-of-function revealed its important role in immunity to infection, (auto-) immunity and (auto-) inflammation. TYK2-deficient patients unravelled high similarity between mice and men with respect to cellular signalling functions and basic immunology. Genome-wide association studies link TYK2 to several autoimmune and inflammatory diseases as well as carcinogenesis. Due to its cytokine signalling functions TYK2 was found to be essential in tumour surveillance. Lately TYK2 activating mutants and fusion proteins were detected in patients diagnosed with leukaemic diseases suggesting that TYK2 is a potent oncogene. Here we review the cell intrinsic and extrinsic functions of TYK2 in the characteristics preventing and enabling carcinogenesis. In addition we describe an unexpected function of kinase-inactive TYK2 in tumour rejection.

Cyclin-dependent kinase 8 (CDK8) is a member of the transcription-regulating CDK family. CDK8 activates or represses transcription by associating with the mediator complex or by regulating transcription factors. Oncogenic activity of CDK8 has been demonstrated in several cancer types. Targeting CDK8 represents a potential therapeutic strategy. Because knockdown of CDK8 in a natural killer (NK) cell line enhances cytotoxicity and NK cells provide the first line of immune defense against transformed cells, we asked whether inhibiting CDK8 would improve NK-cell antitumor responses. In this study, we investigated the role of CDK8 in NK-cell function using mice with conditional ablation of CDK8 in NKp46 cells (). Regardless of CDK8 expression, NK cells develop and mature normally in bone marrow and spleen. However, CDK8 deletion increased expression of the lytic molecule perforin, which correlated with enhanced NK-cell cytotoxicity This translates into improved NK cell-mediated tumor surveillance in three independent models: B16F10 melanoma, lymphoma, and a slowly developing oncogene-driven leukemia. Our results thereby define a suppressive effect of CDK8 on NK-cell activity. Therapies that target CDK8 in cancer patients may enhance NK-cell responses against tumor cells..

The Janus kinase—signal transducers and activators of transcription (JAK-STAT) signaling pathway is critical in tuning immune responses and its dysregulation is tightly associated with cancer and immune disorders. Disruption of interleukin (IL)-15/STAT5 signaling pathway due to the loss of IL-15 receptor chains, JAK3 or STAT5 leads to immune deficiencies with natural killer (NK) cell abnormalities. JAK1, together with JAK3 transmits signals downstream of IL-15, but the exact contribution of JAK1 to NK cell biology remains to be elucidated. To study the consequences of JAK1 deficiency in NK cells, we generated mice with conditional deletion of JAK1 in NKp46+ cells (Jak1fl/flNcr1Cre). We show here that deletion of NK cell-intrinsic JAK1 significantly reduced NK cell numbers in the bone marrow and impaired their development. In line, we observed almost a complete loss of NK cells in the spleen, blood, and liver, proving a crucial role of JAK1 in peripheral NK cells. In line, Jak1fl/+Ncr1Cre mice showed significantly impaired NK cell-mediated tumor surveillance. Our data suggest that JAK2 is not able to compensate for the loss of JAK1 in NK cells. Importantly, conditional deletion of JAK2 in NKp46+ cells had no effect on peripheral NK cells revealing that NK cell-intrinsic JAK2 is dispensable for NK cell survival. In summary, we identified that loss of JAK1 in NK cells drives innate immune deficiency, whereas JAK2 deficiency leaves NK cell numbers and maturation unaltered. We thus propose that in contrast to currently used JAK1/JAK2 inhibitors, the use of JAK2-specific inhibitors would be advantageous for the patients by leaving NK cells intact.

Abbreviations: CCL3, chemokine (C-C motif) ligand 3; CFSE, carboxyfluorescein diacetate succinimidyl ester; GzmB, granzyme B; IFN, interferon; IFNAR, interferon a and b receptor; IL, interleukin; IL-12Rb1, interleukin-12 receptor subunit b-1; iNK, immature natural killer; JAK, xJanus kinase; MACS, magnetic-activated cell sorting; MFI, mean fluorescence intensity; MHC, major histocompatibility complex; miR, microRNA; mNK, mature natural killer; NK, natural killer; NKP, natural killer precursor; Prf1, perforin; SEM, standard error of the mean; STAT, signal transducer and activator of transcription; T-ALL, T cell acute lymphoblastic leukemia; TYK2, tyrosine kinase 2; TYK2 K923E , kinase-inactive tyrosine kinase 2; WT, wild-typeTyrosine kinase 2 (TYK2) is a Janus kinase (JAK) that is crucially involved in inflammation, carcinogenesis and defense against infection. The cytotoxic activity of natural killer (NK) cells in TYK2-deficient (Tyk2 ¡/¡ ) mice is severely reduced, although the underlying mechanisms are largely unknown. Using Tyk2 ¡/¡ mice and mice expressing a kinase-inactive version of TYK2 (Tyk2 K923E ), we show that NK cell function is partly independent of the enzymatic activity of TYK2. Tyk2 ¡/¡ and Tyk2 K923E NK cells develop normally in the bone marrow, but the maturation of splenic Tyk2 ¡/¡ NK cells (and to a lesser extent of Tyk2 K923E NK cells) is impaired. In contrast, the production of interferon g (IFNg) in response to interleukin 12 (IL-12) or to stimulation through NK cell-activating receptors strictly depends on the presence of enzymatically active TYK2. The cytotoxic activity of Tyk2 K923E NK cells against a range of target cells in vitro is higher than that of Tyk2 ¡/¡ NK cells. Consistently, Tyk2 K923E mice control the growth of NK cell-targeted tumors significantly better than TYK2-deficient mice, showing the physiological relevance of the finding. Inhibitors of TYK2's kinase activity are being developed for the treatment of inflammatory diseases and cancers, but their effects on tumor immune surveillance have not been investigated. Our finding that TYK2 has kinase-independent functions in vivo suggests that such inhibitors will leave NK cell mediated tumor surveillance largely intact and that they will be suitable for use in cancer therapy.