Anny Armas Cayarga

Background: IL-15 is a promising cytokine for cancer immunotherapy. IL-15 promotes differentiation and homeostasis of innate and adaptive immune cells, and their cytolytic effector functions. The IL-15 receptor is composed of IL-15Rα, IL-15Rβ and the common γ_c chains. IL-15 is also trans-presented as IL-15Rα:IL-15 complex to IL-15Rβ:γ_c on neighboring cells. IL-15Rα is dispensable for early immune response to infections and in autoimmune diabetes. The role of IL-15Rα in antitumor immune responses remains unclear. Methods: In WT, Il15^−/− and Il15ra^−/− mice, we studied the growth of syngeneic tumor cell lines and tumor immune surveillance against endogenous fibrosarcoma induced by methylcholanthrene (MCA). Immune gene signature and total proteome analysis were performed on MCA-induced tumors. Results: Lack of IL-15 or IL-15Rα did not enhance the growth of implanted tumor cell lines, despite reduced immune cell infiltration. MCA-induced tumor incidence was reduced in mice lacking IL-15Rα but not IL-15, although both are required for efficient tumor immunoediting. Il15^−/− and Il15ra^−/− tumors showed reduced Ifng expression but displayed differential modulation of Ifng-responsive genes. Proteome profiles of Il15^−/− tumors, but not tumor-derived cell lines, showed significant reduction in antigen presentation pathways. B16-F10 melanoma cells expressing NLRC5, the IFNγ-induced transcriptional activator of tumor antigen presentation, still required IL-15 but not IL-15Rα for efficient tumor control. Conclusions: Our findings show that IL-15 plays a negligible role in immunosurveillance against spontaneous tumor development, whereas IL-15Rα restrains immunosurveillance. Neither IL-15 nor IL-15Rα have a significant impact on implanted tumor models, although IL-15 facilitates efficient control of highly immunogenic tumors for which IL-15Rα is dispensable.

SOCS1 is a tumor suppressor in hepatocellular carcinoma (HCC). Recently, we showed that a loss of SOCS1 in hepatocytes promotes NRF2 activation. Here, we investigated how SOCS1 expression in HCC cells affected oxidative stress response and modulated the cellular proteome. Murine Hepa1-6 cells expressing SOCS1 (Hepa-SOCS1) or control vector (Hepa-Vector) were treated with cisplatin or tert-butyl hydroperoxide (t-BHP). The induction of NRF2 and its target genes, oxidative stress, lipid peroxidation, cell survival and cellular proteome profiles were evaluated. NRF2 induction was significantly reduced in Hepa-SOCS1 cells. The gene and protein expression of NRF2 targets were differentially induced in Hepa-Vector cells but markedly suppressed in Hepa-SOCS1 cells. Hepa-SOCS1 cells displayed an increased induction of reactive oxygen species but reduced lipid peroxidation. Nonetheless, Hepa-SOCS1 cells treated with cisplatin or t-BHP showed reduced survival. GCLC, poorly induced in Hepa-SOCS1 cells, showed a strong positive correlation with NFE2L2 and an inverse correlation with SOCS1 in the TCGA-LIHC transcriptomic data. A proteomic analysis of Hepa-Vector and Hepa-SOCS1 cells revealed that SOCS1 differentially modulated many proteins involved in diverse molecular pathways, including mitochondrial ROS generation and ROS detoxification, through peroxiredoxin and thioredoxin systems. Our findings indicate that maintaining sensitivity to oxidative stress is an important tumor suppression mechanism of SOCS1 in HCC.