Biology subjects

Calleja, D. J.

Publications and source records attributed to Calleja, D. J..

3 recordsLinked to original sources

bioRxiv2025

Global analysis of cancer cell responses to USP9X inhibition

The ubiquitin specific protease (USP) enzyme USP9X is amongst the best studied human deubiquitinases (DUBs), with a myriad of described targets and cellular roles. In cancer, USP9X has been touted as both an oncogene and a tumour suppressor in different contexts, which has confounded the field and questioned its viability as a cancer target. We here describe WEHI-092, a novel piperazine-based USP9X specific small molecule inhibitor and map its binding site to a unique region in the USP9X fingers subdomain, distinct from known DUB inhibitor binding sites. Using proteomics and ubiquitinomics, we show that USP9X has a distinct set of substrates compared to USP7 indicating remarkable DUB target specificity, yet the substrate profile of USP9X varies significantly across cancer cell lines. Interestingly, we reveal a core set of 17 proteins commonly regulated by USP9X in most or all cell lines, which we consider as proximal biomarkers for USP9X inhibition. Consistent with our proteomic analyses, we show that WEHI-092 treatment arrests cells in metaphase without inducing cell death, which may account for growth suppression seen in long-term clonogenic assays in most cancer cell lines, and positions USP9X inhibitors as a new potential class of selective mitotic poisons.

cell biology↗

bioRxiv2024

Mutational Profiling of SARS-CoV-2 PLpro in human cells reveals requirements for function, structure, and drug escape

SARS-CoV-2, the causative agent of COVID-19, is responsible for the recent global pandemic and remains a major source of mortality. Papain-like protease (PLpro) is a target for SARS-CoV-2 inhibitor development, as it is not only essential for viral replication through cleavage of the viral poly-proteins pp1a and pp1ab, but also has de-ubiquitylation and de-ISGylation activities, which can affect innate immune responses. To understand the features of PLpro that dictate activity and anticipate how emerging PLpro variants will affect function, we employed Deep Mutational Scanning to evaluate the mutational effects on enzymatic activity and protein stability in mammalian cells. We confirm features of the active site and identify all mutations in neighboring residues that support or ablate activity. We characterize residues responsible for substrate binding and demonstrate that although the blocking loop is remarkably tolerant to nearly all mutations, its flexibility is important for enzymatic function. We additionally find a connected network of mutations affecting function but not structure that extends far from the active site. Using our DMS libraries we were able to identify drug-escape variants to a common PLpro inhibitor scaffold and predict that plasticity in both the S4 pocket and blocking loop sequence should be considered during the drug design process.

biochemistry↗

bioRxiv2020

Mechanism and inhibition of SARS-CoV-2 PLpro

Coronaviruses, including SARS-CoV-2, encode multifunctional proteases that are essential for viral replication and evasion of host innate immune mechanisms. The papain-like protease PLpro cleaves the viral polyprotein, and reverses inflammatory ubiquitin and anti-viral ubiquitin-like ISG15 protein modifications1,2. Drugs that target SARS-CoV-2 PLpro (hereafter, SARS2 PLpro) may hence be effective as treatments or prophylaxis for COVID-19, reducing viral load and reinstating innate immune responses3. We here characterise SARS2 PLpro in molecular and biochemical detail. SARS2 PLpro cleaves Lys48-linked polyubiquitin and ISG15 modifications with high activity. Structures of PLpro bound to ubiquitin and ISG15 reveal that the S1 ubiquitin binding site is responsible for high ISG15 activity, while the S2 binding site provides Lys48 chain specificity and cleavage efficiency. We further exploit two strategies to target PLpro. A repurposing approach, screening 3727 unique approved drugs and clinical compounds against SARS2 PLpro, identified no compounds that inhibited PLpro consistently or that could be validated in counterscreens. More promisingly, non-covalent small molecule SARS PLpro inhibitors were able to inhibit SARS2 PLpro with high potency and excellent antiviral activity in SARS-CoV-2 infection models.

biochemistry↗