Background: Polycystic ovarian syndrome (PCOS) symptoms include excessive body or facial hair, irregular periods, reduced fertility, and reoccurring pregnancy loss. Hyperandrogenism and chronic inflammation are hallmarks of PCOS, which is diagnosed by analyzing steroid hormones in the blood. Studies suggest that bioactive lipids are contributing to chronic inflammation. Methods: To research PCOS, animal models, such as letrozole-and dihydrotestosterone-treated rats, are used. They display similar ovarian and metabolic characteristics, although plasma lipid profiles have not been determined. Therefore, in order to validate the use of these models for PCOS, we have optimized a mass spectrometry-based targeted lipidomics workflow, which increases the sensitivity of measuring these lipids in rat plasma. Results: Our analysis shows that letrozole caused a significant elevation of 5 alpha-androstene-3,17-dione and testosterone. Dihydrotestoster one treatment resulted in increased dehydroepiandrosterone-sulphate and allopregnanolone but a reduction in testosterone, progesterone, pregnenolone, and D-sphingosine. In both models, 25-hydroxycholesterol and leukotriene C4 were significantly diminished, and 4-cholesten-3-one was significantly increased, and these particular metabolites are not known to be changed in human PCOS. Conclusion: These results suggest that the plasma lipids of these rodent models exert altered profiles of sterols, leukotrienes and steroid hormones akin to human PCOS but with notable differences.

Sphingosine-1-phosphate (S1P) is a signaling lysolipid critical to heart development, immunity, and hearing. Accordingly, mutations in the S1P transporter SPNS2 are associated with reduced white cell count and hearing defects. SPNS2 also exports the S1P-mimicking FTY720-P (Fingolimod) and thereby is central to the pharmacokinetics of this drug when treating multiple sclerosis. Here, we use a combination of cryo-electron microscopy, immunofluorescence, in vitro binding and in vivo S1P export assays, and molecular dynamics simulations to probe SPNS2's substrate binding and transport. These results reveal the transporter's binding mode to its native substrate S1P, the therapeutic FTY720-P, and the reported SPNS2-targeting inhibitor 33p. Further capturing an inward-facing apo state, our structures illuminate the protein's mechanism for exchange between inward-facing and outward-facing conformations. Finally, using these structural, localization, and S1P transport results, we identify how pathogenic mutations ablate the protein's export activity and thereby lead to hearing loss.

Interferon-induced ubiquitin (Ub)-like modifier ISG15 covalently modifies host and viral proteins to restrict viral infections. Its function is counteracted by the canonical deISGylase USP18 or Ub-specific protease 18. Notwithstanding indications for the existence of other ISG15 cross-reactive proteases, these remain to be identified. Here, we identify deubiquitinase USP16 as an ISG15 cross-reactive protease by means of ISG15 activity-based profiling. Recombinant USP16 cleaved pro-ISG15 and ISG15 isopeptide-linked model substrates in vitro, as well as ISGylated substrates from cell lysates. Moreover, interferon-induced stimulation of ISGylation was increased by depletion of USP16. The USP16-dependent ISG15 interactome indicated that the deISGylating function of USP16 may regulate metabolic pathways. Targeted enzymes include malate dehydrogenase, cytoplasmic superoxide dismutase 1, fructose-bisphosphate aldolase A, and cytoplasmic glutamic-oxaloacetic transaminase 1. USP16 may thus contribute to the regulation of a subset of metabolism-related proteins during type-I interferon responses.

ABSTRACT The ubiquitin-like modifier ISG15 can modulate host and viral proteins to restrict viral and microbial infections, and act as a cytokine. Its expression and conjugation are strongly up-regulated by type I interferons. Here we identify the deubiquitinating enzyme USP16 as an ISG15 cross-reactive protease. Ubiquitin-specific protease 16 (USP16) was found to react with an ISG15 activity-based probe in pull-down experiments using chronic myeloid leukaemia-derived human cells (HAP1). Supporting this finding, recombinant USP16 cleaved pro-ISG15 and ISG15 iso-peptide linked model substrates in vitro , as well as ISGylated substrates present in cell lysates. Moreover, the interferon-induced stimulation of ISGylation in human HAP1 cells was increased by knockdown or knockout of USP16. Depletion of USP16 did not affect interferon signaling, and interferon treatment did not affect USP16 expression or enzymatic activity either. A USP16-dependent ISG15 interactome was established by anti-ISG15 immunoprecipitation mass spectrometry (IP-MS), which indicated that the deISGylating function of USP16 may regulate metabolic pathways involving GOT1, ALDOA, SOD1 and MDH1, all of which were further confirmed to be deISGylated by USP16 in HEK293T cells. Together, our results indicate that USP16 may contribute to regulating the ISGylation status of a subset of proteins related to metabolism during type I interferon responses.

Bioactive lipids are involved in cellular signalling events with links to human disease. Many of these are involved in inflammation under normal and pathological conditions. Despite being attractive molecules from a pharmacological point of view, the detection and quantification of lipids has been a major challenge. Here, we have optimised a liquid chromatography–dynamic multiple reaction monitoring–targeted mass spectrometry (LC-dMRM-MS) approach to profile eicosanoids and fatty acids in biological samples. In particular, by applying this analytic workflow to study a cellular model of chronic myeloid leukaemia (CML), we found that the levels of intra- and extracellular 2-Arachidonoylglycerol (2-AG), intracellular Arachidonic Acid (AA), extracellular Prostaglandin F2α (PGF2α), extracellular 5-Hydroxyeicosatetraenoic acid (5-HETE), extracellular Palmitic acid (PA, C16:0) and extracellular Stearic acid (SA, C18:0), were altered in response to immunomodulation by type I interferon (IFN-I), a currently approved treatment for CML. Our observations indicate changes in eicosanoid and fatty acid metabolism, with potential relevance in the context of cancer inflammation and CML.

Lung squamous cell carcinoma (LSCC) is a considerable global health burden, with an incidence of over 600,000 cases per year. Treatment options are limited, and patient's 5-year survival rate is less than 5%. The ubiquitin-specific protease 28 (USP28) has been implicated in tumourigenesis through its stabilization of the oncoproteins c-MYC, c-JUN, and Δp63. Here, we show that genetic inactivation of Usp28-induced regression of established murine LSCC lung tumours. We developed a small molecule that inhibits USP28 activity in the low nanomole range. While displaying cross-reactivity against the closest homologue USP25, this inhibitor showed a high degree of selectivity over other deubiquitinases. USP28 inhibitor treatment resulted in a dramatic decrease in c-MYC, c-JUN, and Δp63 proteins levels and consequently induced substantial regression of autochthonous murine LSCC tumours and human LSCC xenografts, thereby phenocopying the effect observed by genetic deletion. Thus, USP28 may represent a promising therapeutic target for the treatment of squamous cell lung carcinoma.

The deubiquitylating enzyme USP18 is a major negative regulator of the interferon (IFN) signalling cascade. IFN pathways contribute to resistance to conventional chemotherapy, radiotherapy, and immunotherapy and are often deregulated in cancer. USP18 is the predominant human protease that cleaves interferon-stimulated gene ISG15, a ubiquitin-like protein tightly regulated in the context of innate immunity, from its modified substrate proteins in vivo . In this study, using advanced proteomic techniques, we have expanded the USP18-dependent ISGylome and proteome in a chronic myeloid leukaemia (CML)-derived cell line (HAP1) treated with type I IFN. Novel ISGylation targets were characterised that modulate the sensing of innate ligands, antigen presentation and secretion of cytokines. Consequently, CML USP18-deficient cells are more antigenic, driving increased activation of cytotoxic T lymphocytes (CTLs) and are more susceptible to irradiation. Our results suggest USP18 as a pharmacological target in cancer immunotherapy and radiotherapy.### Competing Interest StatementThe authors have declared no competing interest.

Abstract The innate immune response plays a critical role in modulating the efficacy of and mechanisms conferring resistance to immune checkpoint blockade (ICB) therapies in humans. A major negative regulator of the Interferon (IFN) stimulated gene (ISG) pathway, is the ubiquitin-specific protease 18 (USP18). USP18 is the predominant human deubiquitylating enzyme that processes Interferon Stimulated Gene 15 ISG15, a ubiquitin-like protein that covalently modifies protein substrates, a tightly regulated process in the context of innate immunity. In this study, using advanced mass spectrometry and chemical biology tools, we defined the USP18 Interactome and ISG15ylome in chronic myeloid leukemia (CML)-derived cells (HAP1) treated with Interferon alpha (IFNα). Novel ISG15ylation targets were characterized that reduce the sensing of innate ligands and secretion of cytokines. In addition, we show that USP18 deletion leads to enhanced ISG15ylation profiles. Furthermore, we demonstrate that CML USP18-/- cells are more antigenic, leading to increased activation of cytotoxic T lymphocytes (CTLs), and are more susceptible to irradiation. Our results reinforce the role of USP18 as a key “brake” for inflammatory signals in tumor cells. As USP18 expression is upregulated in lung, breast and colon cancers, USP18 pharmacological inhibition may reflect a target opportunity in cancer immunotherapy. Citation Format: Adan Pinto-Fernandez, Helene Greenwood, Mariolina Salio, Jianzhou Chen, Thomas Partridge, George Vere, Hannah C. Scott, Andreas Damianou, Persephone Borrow, Ruth Muschel, Vincenzo Cerundolo, Benedikt M. Kessler. USP18 modulates the ISGylome, immune signaling and sensitizes tumor cells to irradiation and CTL recognition [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-080.

The mitochondrial deubiquitylase USP30 negatively regulates the selective autophagy of damaged mitochondria. We present the characterisation of an N-cyano pyrrolidine compound, FT3967385, with high selectivity for USP30. We demonstrate that ubiquitylation of TOM20, a component of the outer mitochondrial membrane import machinery, represents a robust biomarker for both USP30 loss and inhibition. A proteomics analysis, on a SHSY5Y neuroblastoma cell line model, directly compares the effects of genetic loss of USP30 with chemical inhibition. We have thereby identified a subset of ubiquitylation events consequent to mitochondrial depolarisation that are USP30 sensitive. Within responsive elements of the ubiquitylome, several components of the outer mitochondrial membrane transport (TOM) complex are prominent. Thus, our data support a model whereby USP30 can regulate the availability of ubiquitin at the specific site of mitochondrial PINK1 accumulation following membrane depolarisation. USP30 deubiquitylation of TOM complex components dampens the trigger for the Parkin-dependent amplification of mitochondrial ubiquitylation leading to mitophagy. Accordingly, PINK1 generation of phospho-Ser65 ubiquitin proceeds more rapidly in cells either lacking USP30 or subject to USP30 inhibition.

The mitochondrial deubiquitylase USP30 negatively regulates the selective autophagy of damaged mitochondria. It has been proposed as an actionable target to alleviate the loss of function of the mitophagy pathway governed by the Parkinson’s Disease associated genes PINK1 and PRKN. We present the characterisation of a N-cyano pyrrolidine derived compound, FT3967385, with high selectivity for USP30. The compound is well tolerated with no loss of total mitochondrial mass. We demonstrate that ubiquitylation of TOM20, a component of the outer mitochondrial membrane import machinery that directly interacts with USP30, represents a robust biomarker for both USP30 loss and inhibition. We have conducted proteomics analyses on a SHSY5Y neuroblastoma cell line model to directly compare the effects of genetic loss of USP30 with selective inhibition in an unbiased fashion. We have thereby identified a subset of ubiquitylation events consequent to mitochondrial depolarisation that are USP30 sensitive. Within responsive elements of the ubiquitylome, several components of the outer mitochondrial membrane transport (TOM) complex are most prominent. Thus, our data support a model whereby USP30 can regulate the availability of ubiquitin at the specific site of mitochondrial PINK1 accumulation following membrane depolarisation. In this model, USP30 deubiquitylation of TOM complex components dampens the trigger for the Parkin-dependent amplification of mitochondrial ubiquitylation leading to mitophagy. Accordingly, PINK1 generation of phospho-Ser65 Ubiquitin proceeds more rapidly and to a greater extent in cells either lacking USP30 or subject to USP30 inhibition. ### Competing Interest Statement M.G. is receiving research funding from AstraZeneca, Pfizer and Merck MC,SU,HM and ODDI have received research funding from Celgene.

Background Interferon (IFN) signalling pathways, a key element of the innate immune response, contribute to resistance to conventional chemotherapy, radiotherapy, and immunotherapy, and are often deregulated in cancer. The deubiquitylating enzyme USP18 is a major negative regulator of the IFN signalling cascade and is the predominant human protease that cleaves ISG15, a ubiquitin-like protein tightly regulated in the context of innate immunity, from its modified substrate proteins in vivo. Methods In this study, using advanced proteomic techniques, we have significantly expanded the USP18-dependent ISGylome and proteome in a chronic myeloid leukaemia (CML)-derived cell line. USP18-dependent effects were explored further in CML and colorectal carcinoma cellular models. Results Novel ISGylation targets were characterised that modulate the sensing of innate ligands, antigen presentation and secretion of cytokines. Consequently, CML USP18-deficient cells are more antigenic, driving increased activation of cytotoxic T lymphocytes (CTLs) and are more susceptible to irradiation. Conclusions Our results provide strong evidence for USP18 in regulating antigenicity and radiosensitivity, highlighting its potential as a cancer target.

Enzymes that bind and process ubiquitin, a small 76-amino-acid protein, have been recognized as pharmacological targets in oncology, immunological disorders, and neurodegeneration. Mass spectrometry technology has now reached the capacity to cover the proteome with enough depth to interrogate entire biochemical pathways including those that contain DUBs and E3 ligase substrates. We have recently characterized the breast cancer cell (MCF7) deep proteome by detecting and quantifying ~10,000 proteins, and within this data set, we can detect endogenous expression of 65 deubiquitylating enzymes (DUBs), whereas matching transcriptomics detected 78 DUB mRNAs. Since enzyme activity provides another meaningful layer of information in addition to the expression levels, we have combined advanced mass spectrometry technology, pre-fractionation, and more potent/selective ubiquitin active-site probes with propargylic-based electrophiles to profile 74 DUBs including distinguishable isoforms for 5 DUBs in MCF7 crude extract material. Competition experiments with cysteine alkylating agents and pan-DUB inhibitors combined with probe labeling revealed the proportion of active cellular DUBs directly engaged with probes by label-free quantitative (LFQ) mass spectrometry. This demonstrated that USP13, 39, and 40 are non-reactive to probe, indicating restricted enzymatic activity under these cellular conditions. Our extended chemoproteomics workflow increases depth of covering the active DUBome, including isoform-specific resolution, and provides the framework for more comprehensive cell-based small-molecule DUB selectivity profiling.

USP28 deletion and small molecule inhibition destabilises c-MYC and elicits 1 regression of squamous cell lung carcinoma 2 3 E. Josue Ruiz , Adan Pinto-Fernandez, Andrew P. Turnbull, Linxiang Lan, 4 Thomas M. Charlton, Hannah Claire Scott , Andreas Damianou, George Vere, 5 Eva M. Riising, Clive Da Costa, Wojciech W. Krajewski, David Guerin, Jeffrey 6 Kearns, Stephanos Ioannidis, Marie Katz, Crystal McKinnon, Jonathan 7 C. O'Connell, Natalia Moncaut, Ian Rosewell, Emma Nye, Neil Jones, Claire 8 Heride, Malte Gersch, Min Wu, Christopher J. Dinsmore, Tim R. 9 Hammonds, Sunkyu Kim, David Komander, Sylvie Urbé, Michael J. Clague, 10 Benedikt M. Kessler and Axel Behrens 11 12