Anaplastic Large Cell Lymphoma (ALCL) is a Non-Hodgkin lymphoma found in children and young adults with poor survival rates. ALCLs frequently carry a chromosomal translocation that results in expression of the oncoprotein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK). The key molecular downstream events required for NPM-ALK triggered lymphoma growth are still not entirely clear. Here we show that the AP-1 proteins cJun and JunB promote lymphoma development and tumor dissemination in a murine NPM-ALK lymphomagenesis model via transcriptional regulation of PDGFRB. Therapeutic inhibition of PDGFRB markedly prolonged survival of NPM-ALK transgenic mice and increased the efficacy of an ALK-specific inhibitor in transplanted NPM-ALK tumors. Remarkably, inhibition of PDGFRs in a late stage patient with refractory NPM-ALK-positive ALCL resulted in complete and sustained remission within 10 days of treatment. Our data identify PDGFRB as novel cJun/JunB target that could be utilized for a highly effective therapy to cure ALCL. 3ALCLs are T-cell lymphomas 1,2 that comprise 10-20% of all Non-Hodgkin's lymphoma cases in children and 3% in adults 3 . About half of ALCL cases are positive for NPM-ALK fusion proteins caused by t(2;5)(p23;q35) translocation 4 . ALK translocations or point mutations have also been described in DLBCLs (diffuse large B-cell lymphomas) and in several nonlymphoid neoplasms [5][6][7][8] . Inhibition of ALK fusion proteins by specific compounds such as crizotinib showed promising clinical responses in ALCL and NSCLC (non-small cell lung cancer) 9,10 . However, ALK mutations conferring resistance to crizotinib have also been reported 11 .Recent studies have linked NPM-ALK expression to induction of AP-1 transcription factors JunB and cJun 12,13 . To investigate their role in NPM-ALK-driven T-cell lymphomas, we conditionally deleted cJun and/or JunB in T-cells of transgenic mice carrying the human NPM-ALK fusion-tyrosine-kinase under the control of the murine CD4-promotor 14 (CD4-NPM-ALK) (Fig. 1a). Gene deletion was confirmed by DNA genotyping (data not shown), real-time PCR, Western blotting and immunohistochemistry (IHC) (Suppl. (Fig.1b), however, inactivation of both, cJun and JunB, in CD4-NPM-ALK-CD4 ΔΔJun mice resulted in significantly prolonged survival (Fig. 1b). CD4-NPM-ALK-CD4 ΔΔJun lymphomas showed markedly reduced proliferation and significantly increased apoptosis when compared to CD4-NPM-ALK lymphomas ( Fig. 1c; Suppl. Fig. S2a,b). Consistently, (Fig. 2d) suggesting a transcriptional regulation of PDGFRB by Jun proteins. Consistently, AP-1 consensus sequences were identified within the murine PDGFRB promoter and first intron that were conserved among other species (Suppl. Fig. S3b,c) 15,16 . Moreover, analysis of ENCODE transcription factor binding tracks revealed binding of cJun and JunB to the PDGFRB intronic AP-1 site in the human K562 leukemia cell line (Suppl. Fig. S3d) 15,17 . CD4-NPM-ALK-CD4EMSA analysis of nuclear extracts from NPM-ALK lymphomas demonstrated AP-1 DNA ...

Natural killer (NK) cells are important components of the innate immune defense against infections and cancers. Signal transducer and activator of transcription 1 (STAT1) is a transcription factor that is essential for NK cell maturation and NK cell-dependent tumor surveillance. Two alternatively spliced isoforms of STAT1 exist: a full-length STAT1α and a C-terminally truncated STAT1β isoform. Aberrant splicing is frequently observed in cancer cells and several anti-cancer drugs interfere with the cellular splicing machinery. To investigate whether NK cell-mediated tumor surveillance is affected by a switch in STAT1 splicing, we made use of knock-in mice expressing either only the STAT1α (Stat1 α/α) or the STAT1β (Stat1 β/β) isoform. NK cells from Stat1 α/α mice matured normally and controlled transplanted tumor cells as efficiently as NK cells from wild-type mice. In contrast, NK cells from Stat1 β/β mice showed impaired maturation and effector functions, albeit less severe than NK cells from mice that completely lack STAT1 (Stat1 −/−). Mechanistically, we show that NK cell maturation requires the presence of STAT1α in the niche rather than in NK cells themselves and that NK cell maturation depends on IFNγ signaling under homeostatic conditions. The impaired NK cell maturation in Stat1 β/β mice was paralleled by decreased IL-15 receptor alpha (IL-15Rα) surface levels on dendritic cells, macrophages and monocytes. Treatment of Stat1 β/β mice with exogenous IL-15/IL-15Rα complexes rescued NK cell maturation but not their effector functions. Collectively, our findings provide evidence that STAT1 isoforms are not functionally redundant in regulating NK cell activity and that the absence of STAT1α severely impairs, but does not abolish, NK cell-dependent tumor surveillance.

SUMMARY Cytomegalovirus (CMV) has a high prevalence worldwide, is often fatal for immunocompromised patients, and causes bone marrow suppression. Deficiency of signal transducer and activator of transcription 1 (STAT1) results in severely impaired antiviral immunity. We have used cell-type restricted deletion of Stat1 to determine the importance of myeloid cell activity for the defense against murine CMV (MCMV). We show that myeloid STAT1 limits MCMV burden and infection-associated pathology in the spleen but does not affect ultimate clearance of infection. Unexpectedly, we found an essential role of myeloid STAT1 in the induction of extramedullary hematopoiesis (EMH). The EMH-promoting function of STAT1 was not restricted to MCMV infection but was also observed during CpG oligodeoxynucleotide-induced sterile inflammation. Collectively, we provide genetic evidence that signaling through STAT1 in myeloid cells is required to restrict MCMV at early time points post-infection and to induce compensatory hematopoiesis in the spleen.

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