STUB1 dampens IFNγ response in tumors by destabilizing the IFNγ receptor complex
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ABSTRACT:
PROVIDER: PRJNA644914 | ENA |
REPOSITORIES: ENA
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Project description:Despite its success, immune checkpoint blockade (ICB) cannot induce durable responses in most patients. This is partially attributed to reduced sensitivity to interferon gamma (IFNγ). Thus, elevating tumor IFNγ-receptor 1 (IFNγ-R1) expression to enhance IFNγ-mediated cytotoxicity is of clinical interest. Here, we demonstrate higher IFNγ-R1 expression to sensitize tumors to IFNγ-mediated killing. To unveil the largely undefined mechanisms of IFNγ-R1 expression, we performed a genome-wide CRISPR/Cas9 knockout screen for suppressors of IFNγ-R1 tumor cell surface abundance. We uncovered STUB1 as key mediator for proteasomally degrading IFNγ-R1/JAK1 complex. Conversely, STUB1 inactivation in tumor cells amplified IFNγ signaling and sensitized to cytotoxic T cells, but permitted IFNγ-induced PD-L1 expression. Rationally combining STUB1 inactivation with anti-PD-1 treatment effectively eliminated tumors in vivo. Clinically corroborating this is a STUB1 transcriptomic signature that associates with response to anti-PD-1 treatment in two patient cohorts. Thus, uncovering STUB1 as a pivotal regulator of IFNγ signaling and a synergistic target for anti-PD-1 treatment.
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Project description:The cytokine IFNγ differentially impacts on tumors upon immune checkpoint blockade (ICB). Despite our understanding of downstream signaling events, less is known about 36 regulation of its receptor (IFNγ-R1). With an unbiased genome-wide CRISPR/Cas9 screen for critical regulators of IFNγ-R1 cell surface abundance, we identified STUB1 as an E3 ubiquitin ligase for IFNγ-R1 in complex with its signal-relaying kinase JAK1. STUB1 mediates ubiquitination-dependent proteasomal degradation of IFNγ-R1/JAK1 complex through IFNγ-R1K285 and JAK1K249. Conversely, STUB1 inactivation amplifies IFNγ signaling, sensitizing tumor cells to cytotoxic T cells in vitro. This was corroborated by an anticorrelation between STUB1 expression and IFNγ response in ICB-treated patients. Consistent with the context-dependent effects of IFNγ in vivo, anti-PD-1 response was increased in heterogenous tumors comprising both wildtype and STUB1-deficient cells but not full STUB1 knockout tumors. These results uncover STUB1 as a critical regulator of IFNγ-R1, and highlight the context-dependency of STUB1-regulated IFNγ signaling for ICB outcome.
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Project description:Immune checkpoint blockade (ICB) leads to durable and complete tumour regression in some patients but in others gives temporary, partial or no response. Accordingly, significant efforts are underway to identify tumour-intrinsic mechanisms underlying ICB resistance. Results from a published CRISPR screen in a mouse model suggested that targeting STUB1, an E3 ligase involved in protein homeostasis, may overcome ICB resistance but the molecular basis of this effect remains unclear. Herein, we report an under-appreciated role of STUB1 to dampen the interferon gamma (IFNg) response. Genetic deletion of STUB1 increased IFNGR1 abundance on the cell surface and thus enhanced the downstream IFNg response as showed by multiple approaches including Western blotting, flow cytometry, qPCR, phospho-STAT1 assay, immunopeptidomics, proteomics, and gene expression profiling. Human prostate and breast cancer cells with STUB1 deletion were also susceptible to cytokine-induced growth inhibition. Furthermore, blockade of STUB1 protein function recapitulated the STUB1-null phenotypes. Despite these encouraging in vitro data and positive implications from clinical datasets, we did not observe in vivo benefits of inactivating Stub1 in mouse syngeneic tumour models - with or without combination with anti-PD-1 therapy. However, our findings elucidate STUB1 as a barrier to IFNg sensing, prompting further investigations to assess if broader inactivation of human STUB1 in both tumors and immune cells could overcome ICB resistance.
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Project description:RNA interference (RNAi) is a cell-intrinsic antiviral defense conserved in diverse organisms. However, the mechanism by which mammalian antiviral RNAi is regulated is largely unknown. Herein, we uncover that STUB1, an E3 ubiquitin ligase, interacts with and ubiquitinates AGO2, the core component of RNAi pathway, resulting in the degradation of AGO2 via ubiquitin-proteasome system. Additionally, STUB1 can induce the degradation of the other mammalian AGO proteins including AGO1, AGO3, and AGO4. Our further study reveals that STUB1 also interacts with and mediates the ubiquitination of Dicer, the endoribonuclease responsible for siRNA or miRNA biogenesis, via K48-linked poly-ubiquitin, which induces the degradation of Dicer and its specialized form, termed antiviral Dicer (aviDicer) that usually expresses in stem cells. Loss of STUB1 upregulated Dicer and AGO2, thereby enhancing antiviral RNAi to effectively inhibit viral RNA replication in mammalian cells. In vivo, the STUB1 deficiency markedly enhanced the production of virus-derived siRNAs and elicited a potent antiviral effect against Enterovirus-A71 (EV-A71) infection in newborn mouse. Our findings demonstrate STUB1 as a novel negative regulator of RNAi by mediating the ubiquitination and degradation of Dicer and AGO proteins, and provide novel insights into the regulatory mechanism of antiviral RNAi in mammals.
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