Deletion of the deISGylating enzyme USP18 enhances tumour cell antigenicity and radiosensitivity.

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.

Oncogenic mutations of KRAS modulate its turnover by the CUL3/LZTR1 E3 ligase complex.

KRAS is a proto-oncogene encoding a small GTPase. Mutations contribute to ∼30% of human solid tumours, including lung adenocarcinoma, pancreatic, and colorectal carcinomas. Most KRAS activating mutations interfere with GTP hydrolysis, essential for its role as a molecular switch, leading to alterations in their molecular environment and oncogenic signalling. However, the precise signalling cascades these mutations affect are poorly understood. Here, APEX2 proximity labelling was used to profile the molecular environment of WT, G12D, G13D, and Q61H-activating KRAS mutants under starvation and stimulation conditions. Through quantitative proteomics, we demonstrate the presence of known KRAS interactors, including ARAF and LZTR1, which are differentially captured by WT and KRAS mutants. Notably, the KRAS mutations G12D, G13D, and Q61H abrogate their association with LZTR1, thereby affecting turnover. Elucidating the implications of LZTR1-mediated regulation of KRAS protein levels in cancer may offer insights into therapeutic strategies targeting KRAS-driven malignancies.

Pathogenicity and virulence of Aspergillus fumigatus.

Pulmonary infections caused by the mould pathogen Aspergillus fumigatus are a major cause of morbidity and mortality globally. Compromised lung defences arising from immunosuppression, chronic respiratory conditions or more recently, concomitant viral or bacterial pulmonary infections are recognised risks factors for the development of pulmonary aspergillosis. In this review, we will summarise our current knowledge of the mechanistic basis of pulmonary aspergillosis with a focus on emerging at-risk populations.

Targeting the Ubiquitylation and ISGylation Machinery for the Treatment of COVID-19.

Ubiquitylation and ISGylation are protein post-translational modifications (PTMs) and two of the main events involved in the activation of pattern recognition receptor (PRRs) signals allowing the host defense response to viruses. As with similar viruses, SARS-CoV-2, the virus causing COVID-19, hijacks these pathways by removing ubiquitin and/or ISG15 from proteins using a protease called PLpro, but also by interacting with enzymes involved in ubiquitin/ISG15 machinery. These enable viral replication and avoidance of the host immune system. In this review, we highlight potential points of therapeutic intervention in ubiquitin/ISG15 pathways involved in key host-pathogen interactions, such as PLpro, USP18, TRIM25, CYLD, A20, and others that could be targeted for the treatment of COVID-19, and which may prove effective in combatting current and future vaccine-resistant variants of the disease.

USP28 deletion and small-molecule inhibition destabilizes c-MYC and elicits regression of squamous cell lung carcinoma.

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.

Ubiquitomics: An Overview and Future.

Covalent attachment of ubiquitin, a small globular polypeptide, to protein substrates is a key post-translational modification that determines the fate, function, and turnover of most cellular proteins. Ubiquitin modification exists as mono- or polyubiquitin chains involving multiple ways how ubiquitin C-termini are connected to lysine, perhaps other amino acid side chains, and N-termini of proteins, often including branching of the ubiquitin chains. Understanding this enormous complexity in protein ubiquitination, the so-called 'ubiquitin code', in combination with the ∼1000 enzymes involved in controlling ubiquitin recognition, conjugation, and deconjugation, calls for novel developments in analytical techniques. Here, we review different headways in the field mainly driven by mass spectrometry and chemical biology, referred to as "ubiquitomics", aiming to understand this system's biological diversity.