Expression of type I interferons (IFN) can be induced by DNA damaging agents but the mechanisms and significance of this regulation are not completely understood. We found that the transcription factor IRF3, activated in an ATM-IKKα/β dependent manner, stimulates cell-autonomous IFNβ expression in response to double-stranded DNA breaks. Cells and tissues with accumulating DNA damage produce endogenous IFNβ and stimulate IFN signaling in vitro and in vivo. In turn, IFN acts to amplify DNA damage responses, activate the p53 pathway, promote senescence and inhibit stem cells function in response to telomere shortening. Inactivation of the IFN pathway abrogates the development of diverse progeric phenotypes and extends the life span of Terc knockout mice. These data identify DNA damage response-induced IFN signaling as a critical mechanism that links accumulating DNA damage with senescence and premature aging.

Refractoriness of solid tumors including colorectal cancers (CRC) to immunotherapies is attributed to the immunosuppressive tumor microenvironment that protects malignant cells from cytotoxic T lymphocytes (CTL). We found that downregulation of the type I interferon receptor chain IFNAR1 occurs in human CRC and mouse models of CRC. Downregulation of IFNAR1 in tumor stroma stimulated CRC development and growth, played a key role in formation of the immune privileged niche and predicted poor prognosis in human CRC patients. Genetic stabilization of IFNAR1 improved CTL survival and increased the efficacy of the chimeric antigen receptor T cell transfer and PD-1 inhibition. Likewise, pharmacologic stabilization of IFNAR1 suppressed tumor growth providing the rationale for upregulating IFNAR1 to improve anti-cancer therapies.

SUMMARY Lysine63-linked ubiquitin (K63-Ub) chains represent a particular ubiquitin topology that mediates proteasome-independent signaling events. The deubiquitinating enzyme (DUB) BRCC36 segregates into distinct nuclear and cytoplasmic complexes that are specific for K63-Ub hydrolysis. RAP80 targets the five-member nuclear BRCC36 complex to K63-Ub chains at DNA double-strand breaks. The alternative four-member BRCC36 containing complex (BRISC) lacks a known targeting moiety. Here we identify Serine Hydroxymethyltransferase (SHMT) as a heretofore-unappreciated component that fulfills this function. SHMT directs BRISC activity at K63-Ub chains conjugated to the type 1 interferon (IFN) receptor chain 1 (IFNAR1). BRISC-SHMT2 complexes localize to and deubiquitinate actively engaged IFNAR1, thus limiting its K63-Ub mediated internalization and lysosomal degradation. BRISC deficient cells and mice exhibit attenuated responses to IFN and are protected from IFN-associated immunopathology. These studies reveal a novel mechanism of DUB regulation, and suggest a therapeutic use of BRISC inhibitors for treating pathophysiologic processes driven by elevated IFN responses.

Graphical AbstractHighlights d Tumor-derived extracellular vesicles (TEV) downregulate IFNAR1 and CH25H d CH25H acts to restrict TEV uptake and limit the education of healthy cells d Downregulation of CH25H in normal cells promotes melanoma metastasis d Disruption of TEV uptake and education by reserpine elicits anti-metastatic effects SUMMARY Tumor-derived extracellular vesicles (TEV) ''educate'' healthy cells to promote metastases. We found that melanoma TEV downregulated type I interferon (IFN) receptor and expression of IFN-inducible cholesterol 25-hydroxylase (CH25H). CH25H produces 25-hydroxycholesterol, which inhibited TEV uptake. Low CH25H levels in leukocytes from melanoma patients correlated with poor prognosis. Mice incapable of downregulating the IFN receptor and Ch25h were resistant to TEV uptake, TEV-induced pre-metastatic niche, and melanoma lung metastases; however, ablation of Ch25h reversed these phenotypes. An anti-hypertensive drug, reserpine, suppressed TEV uptake and disrupted TEV-induced formation of the pre-metastatic niche and melanoma lung metastases. These results suggest the importance of CH25H in defense against education of normal cells by TEV and argue for the use of reserpine in adjuvant melanoma therapy.

Oncogene activation induces DNA damage responses and cell senescence. We report a key role of type I interferons (IFN) in oncogene-induced senescence. IFN signaling-deficient melanocytes expressing activated Braf do not exhibit senescence and develop aggressive melanomas. Restoration of IFN signaling in IFN-deficient melanoma cells induces senescence and suppresses melanoma progression. Additional data from human melanoma patients and mouse transplanted tumor models suggest the importance of non-cell-autonomous IFN signaling. Inactivation of IFN pathway is mediated by the IFN receptor IFNAR1 downregulation that invariably occurs during melanoma development. Mice harboring an IFNAR1 mutant, which is partially resistant to downregulation, delay melanoma development, suppress metastatic disease, and better respond to BRAF or PD1 inhibitors. These results suggest that IFN signaling is an important tumor suppressive pathway that inhibits melanoma development and progression and argue for targeting IFNAR1 downregulation to prevent metastatic disease and improve the efficacy of molecularly-targeted and immune-targeted melanoma therapies.

Type 1 interferons (IFN) protect the host against viruses by engaging a cognate receptor (consisting of IFNAR1/IFNAR2 chains) and inducing downstream signaling and gene expression. However, inflammatory stimuli can trigger IFNAR1 ubiquitination and downregulation thereby attenuating IFN effects in vitro. The significance of this paradoxical regulation is unknown. Presented here results demonstrate that inability to stimulate IFNAR1 ubiquitination in the Ifnar1SA knock-in mice renders them highly susceptible to numerous inflammatory syndromes including acute and chronic pancreatitis, and autoimmune and toxic hepatitis. Ifnar1SA mice (or their bone marrow-receiving wild type animals) display persistent immune infiltration of inflamed tissues, extensive damage and gravely inadequate tissue regeneration. Pharmacologic stimulation of IFNAR1 ubiquitination is protective against from toxic hepatitis and fulminant generalized inflammation in wild type but not Ifnar1SA mice. These results suggest that endogenous mechanisms that trigger IFNAR1 ubiquitination for limiting the inflammation-induced tissue damage can be purposely mimicked for therapeutic benefits.Subject Categories Immunology; Digestive System

The great preclinical promise of the pancreatic endoplasmic reticulum kinase (PERK) inhibitors in neurodegenerative disorders and cancers is marred by pancreatic injury and diabetic syndrome observed in PERK knockout mice and humans lacking PERK function and suffering from Wolcott-Rallison syndrome. PERK mediates many of the unfolded protein response (UPR)-induced events, including degradation of the type 1 interferon (IFN) receptor IFNAR1 in vitro. Here we report that whole-body or pancreas-specific Perk ablation in mice leads to an increase in IFNAR1 protein levels and signaling in pancreatic tissues. Concurrent IFNAR1 deletion attenuated the loss of PERKdeficient exocrine and endocrine pancreatic tissues and prevented the development of diabetes. Experiments using pancreas-specific Perk knockouts, bone marrow transplantation, and cultured pancreatic islets demonstrated that stabilization of IFNAR1 and the ensuing increased IFN signaling in pancreatic tissues represents a major driver of injury triggered by Perk loss. Neutralization of IFNAR1 prevented pancreatic toxicity of PERK inhibitor, indicating that blocking the IFN pathway can mitigate human genetic disorders associated with PERK deficiency and help the clinical use of PERK inhibitors.T umor microenvironment-associated deficit in oxygen and nutrients activate numerous pathways that aid cancer and tumor stroma cells by increasing their ability to survive, withstand anticancer therapies, and ultimately select for more aggressive and viable clones capable of metastasizing (1). Activation of the unfolded protein response (UPR) plays a central role in these processes (2). Three branches of this response include stimulation of activating transcription factor-6 and activation of two kinases, inositol requiring enzyme 1α/β and the eukaryotic translation initiation factor 2-alpha kinase 3 [also termed double-stranded RNA-activated protein kinase-like endoplasmic reticulum kinase, or pancreatic endoplasmic reticulum kinase (PERK)]. The latter kinase contributes to phosphorylation of the eukaryotic translation initiation factor 2-alpha and controls the rate of global translation and noncanonical induction of specific proteins that help cope with stress (reviewed in ref. 2).Among three main UPR pathways, signaling through PERK has received the most attention for its central role in cancer (3-6). Genetic studies have demonstrated that PERK is essential in supporting tumor growth and progression via diverse mechanisms, including stimulation of angiogenesis (7-12), potential effects on antitumor immunity (13,14), and direct increase in cancer cell viability by altering its metabolic status (15), promoting survival autophagy (16-18), and induction of prosurvival microRNAs (19). Accordingly, development of novel, potent, and selective PERK inhibitors as a means to treat cancers has been proposed (20, 21). Several PERK inhibitors have shown promising results in various preclinical tumor models (22-24). Furthermore, some of these inhibitors can protect against the prion-...

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