Anne-Claude Gingras

Cellular processes are controlled by interconnected networks of protein–protein interactions that can be dynamically regulated by post-translational modifications such as phosphorylation. Dysregulation of signaling pathways can drive cellular transformation and contribute to cancer treatment resistance. Mass spectrometry (MS)-based approaches have emerged as key technologies to study both protein function and their dynamic regulation at a network level. Modern proteomics allows investigators to study how signaling networks are rewired in response to genetic lesions, external cues, and targeted therapies, enabling the comparison of baseline (steady-state) networks to perturbed states. Here, we briefly describe key advancements in proteomics to study signaling dynamics, including affinity-purification combined with MS, proximity proteomics (e.g., BioID, APEX), and phosphoproteomics. We highlight how proteomics has led to the identification of comprehensive protein–protein interaction networks, to the delineation of protein subcellular localization maps and to discoveries regarding their dynamics and rewiring in disease. Finally, we comment on the future directions of proteomics to study signaling dynamics, enabled by next-generation MS instruments and AI-driven data analysis, and discuss how these developments are paving the way for clinical translation by bringing quantitative network biology into patient-relevant contexts.

Reprogramming somatic cells into induced pluripotent stem cells involves a dramatic reorganization of the cytoskeleton and junctions during the critical mesenchymal-to-epithelial transition stage. While protein abundance changes have been profiled, the spatiotemporal dynamics of protein-protein associations involving these structural components remain poorly resolved. Here, we present a time-resolved proximity proteomics resource that maps cytoskeletal and junctional remodeling across 27 baits during the early stages of reprogramming. We identified over 1100 high-confidence interactions, including many not previously reported, capturing the dynamic reorganization of cell architecture. By integrating proximity-dependent biotinylation with quantitative proteomics, we distinguished spatial relocalizations from abundance-driven effects. Dynamic redistributions of actin regulators and desmosomal proteins were observed, and a targeted short interfering RNA screen uncovered early acting structural proteins essential for colony formation. Our findings reveal adhesion and cytoskeletal maturation as structural bottlenecks in reprogramming and provide a broadly applicable framework for mapping subcellular remodeling during dynamic cell fate transitions.

After endocytosis, transmembrane cargo reaches sorting endosomes where it is partitioned into physically distinct recycling or degradative microdomains. While the J-domain protein RME-8/DNAJC13 is known to maintain these boundaries by actively removing degradative machinery from the recycling microdomain, other factors that contribute to this spatial organization remain poorly defined. Here, we identify the conserved tetraspan protein SCM-1/SCAMP as a key microdomain organizer, discovered through RME-8 proximity-dependent biotinylation screens in C. elegans and human cells. Leveraging the large endosomes of C. elegans coelomocytes, we show that SCM-1 is selectively enriched within the recycling microdomain. In scm-1 mutants, recycling and degradative microdomains still assemble but fail to remain spatially distinct, resulting in inappropriate microdomain overlap. This loss of boundary integrity occurs without increasing the recruitment of sorting machineries, indicating a mechanism distinct from the RME-8-mediated uncoating pathway. scm-1 mutants exhibit significant sorting defects, including misrouting of recycling cargo MIG-14/Wls and v-SNARE SNB-2/VAMP3 to late endosomes and lysosomes. We find that snb-2 mutants themselves missort MIG-14 to late endosomes and lysosomes, suggesting that SNB-2 sorting is key for recycling function. Our data suggest that both microdomains lose efficiency in scm-1 mutants, as cargo missorted into late endosomes and lysosomes is not depleted overall, and degradation of an independent ESCRT-dependent cargo is delayed. We conclude that SCM-1 ensures endosomal sorting fidelity by stabilizing microdomain boundary integrity, a process required for efficient recycling and degradation of transmembrane cargo.

In low input mass spectrometry-based proteomics, Data Independent Acquisition (DIA), is quickly becoming the method of choice for label free quantification. Whether using empirical or in silico spectral libraries, performance is dependent on the library; however, the optimal library construction strategy for low input proteomics remains an open question. To address this, we examine and develop library construction approaches that are compatible with both spectrum-centric and peptide-centric analysis workflows. These approaches leverage a closely related, high-quality sample to improve library quality. First, we validated our approach in bulk sample amounts where we observed that the effects of gas-phase fractionation based library construction is dependent on the software framework, with improvements more pronounced in OpenSWATH compared to DIA-NN. In OpenSWATH, our peptide-centric library reconstruction workflow consistently outperforms a transfer learning strategy, an emerging alternative approach. In DIA-NN, trends are dependent on library source highlighting OpenSWATH's stronger dependence on the search space. In low-input applications, such as single-cell-equivalent injection amounts (100 pg) of HeLa cell digest on a timsTOF SCP, our library construction approach provided more pronounced improvements across both software tools compared to bulk samples. Using a peptide-centric reconstruction approach with the OpenSWATH analysis framework, we detected over 15,000 peptide precursors (2480 protein groups), a 90% improvement over the original library. Furthermore, using a spectrum-centric construction approach, peptide precursor identification rates improved over 6-fold ( ~1000 to ~6000). Our strategy provides a practical solution for generating high-quality libraries in low-input applications.

Molecular glues promote protein-protein interactions by enhancing the surface complementarity between proteins. Those that recruit an E3 ubiquitin ligase to a target can elicit ubiquitination and subsequent destruction of the target protein-a mechanism that underpins the field of targeted protein degradation (TPD). Here we explored whether small-molecule binders to the CTLH E3 ligase subunit GID4 could act as molecular glues. We discovered that CLEO4-88 functions as a molecular glue (EC₅₀ = 12.5 nM) to promote the interaction of GID4 with the peroxisomal thiolase ACAA1 in vitro and in cellulo. An atomic structure of the ternary complex revealed an allosteric mechanism whereby CLEO4-88 binds solely to GID4 and induces a conformational change conducive to binding ACAA1. Biochemical analysis demonstrated that, while ACAA1 cannot be recruited by GID4 to a CTLH holoenzyme for ubiquitination, ternary complex formation inhibits ACAA1 thiolase activity, thus demonstrating potential utility beyond TPD.

Objectives: To determine the incidence and outcomes of SARS-CoV-2 infection and to evaluate seroconversion rates and quantify antibody responses to COVID-19 vaccines in two cohorts of persons living with HIV at a possible higher risk of poor outcomes (HCV coinfection and those over the age of 65 years). Methods: We included participants from two established cohorts of persons living with HIV, those who were older than 65 years of age, and those with hepatitis C (HCV) co-infection. Four hundred and seventy-one participants completed questionnaires on SARS-CoV-2 infection and COVID-19 vaccine doses and submitted peripheral blood specimens for measuring antibody levels to COVID-19 antigens, full-length spike trimer, its receptor binding domain (RBD), and nucleocapsid protein (N) at 6-month intervals up to three visits between February 2021 and December 2024. Logistic and ordinal logistic regression models evaluated predictors of seroconversion and antibody levels. Results: Overall, 51% of participants developed a SARS-CoV-2 infection, but it was mild, with only nine requiring hospital admission and no deaths. Overall, 99% of tested specimens had antibodies above threshold to either spike or RBD proteins. Specimens that did not and those with lower antibody levels had testing earlier in the pandemic, and were from participants with fewer vaccine doses, and did not have natural infection. Age, depression, comorbidity, HCV co-infection, current substance use, CD4 count, or HIV viral load were predictive of antibody level. Those with hybrid immunity had higher antibody responses. Conclusions: In cohorts of persons with HIV-HCV coinfection and those who are ageing, we observed high rates of seroconversion to COVID-19 antigens. Antibody levels were higher among those with more vaccine doses, hybrid immunity, and later in the pandemic waves. Although 51% developed a breakthrough infection, outcomes were mild with no deaths.

The CBL E3 ubiquitin ligase is a critical regulator of tyrosine kinase (TK) signalling. CBL activity is regulated by a feedback loop in which an active TK phosphorylates CBL, relieving its autoinhibited conformation, and allowing ubiquitination of substrates, including TKs, leading to their degradation. Binding of the Src Like Adapter Protein 2 (SLAP2) to CBL can also activate autoinhibited CBL and promote substrate ubiquitination. Using an engineered CBL mutant in the SLAP2 binding interface, termed RE CBL, that mimics activation by SLAP2 binding, we characterized the cellular functions of this CBL activation mechanism. Comparison of wildtype and RE CBL interactomes using MiniTurboID showed extensive and overlapping interaction networks, with a discrete subset of proteins, including the known substrate, epidermal growth factor receptor (EGFR), as well as endocytic factors such as EPS15, in higher abundance with RE CBL compared to wildtype. Consistent with these observations, RE CBL interacted more readily with EGFR, enhanced EGFR internalization, and attenuated downstream signalling compared to WT. In Cbl null hematopoietic cells, RE CBL expression reduced sensitivity to cytokines IL-3 and GM-CSF, and decreased activation of the Src-family kinase Lyn. Furthermore, we optimized and conducted a small molecule screen to identify a group of structurally related compounds that, like SLAP2 binding, promoted CBL activation in vitro . Together these findings provide proof of concept for targeting CBL activity to downregulate TK signalling.

Human DNA polymerase θ (Polθ) is essential for microhomology-mediated end-joining (MMEJ) and represents a therapeutic vulnerability in homologous recombination (HR)-deficient cancers. Although reversible inhibitors of Polθ have advanced into clinical development, covalent chemical probes remain unexplored. Analysis of a previously described structure of the reversible inhibitor compound 37 bound to Polθ identified Cys2411 as an accessible residue 7.4 Å adjacent to the inhibitor binding site. Guided by X-ray crystallographic studies, we designed compound 29 to reduce the separating distance between inhibitor and Cys2411 to 4.7 Å and then synthesized RP-4029 by incorporating a vinyl sulfone electrophile. Functional studies revealed efficient covalent linkage to Cys2411 (K _inact = 11.6 s^-1), while a high-resolution (2.0 Å) cocrystal structure validated the design strategy. These findings establish Cys2411 as a privileged site for covalent inhibitor development and provide a highly potent, selective chemical probe useful for investigating Polθ biology.

Organisms regulate cell size and shape to function efficiently. Aberrant cell morphogenesis is commonly associated with disease, yet gene-regulatory mechanisms remain unknown. CISTR-ACT was the first lncRNA involved in inter-chromosomal proximities and Mendelian disease, and it is associated with mean corpuscular volume (red blood cell size). Here, functional dissection of CISTR-ACT’s DNA- and RNA-encoded mechanisms by in vitro and in vivo perturbations reveals that CISTR-ACT regulates cell size across cell types and species. CISTR-ACT’s locus is embedded in a stable inter-chromosomal environment which contains cell size genes that are regulated by CISTR-ACT in trans. CISTR-ACT’s RNA also has function and directly interacts with transcription factor FOSL2 to guide its regulation of cell morphogenesis and cell-cell adhesion genes. In the absence of CISTR-ACT, the FOSL2-chromatin binding is perturbed. Our study exemplifies how a functionally conserved lncRNA regulates cell size with multiple modes of action and ultimately contributes to clinically relevant phenotypes.

FGFR1 genetic alterations are associated with brain malignancies, including FGFR1 mutations in familial and sporadic cases of low-grade glioneuronal tumors, suggesting intrinsic mechanisms of selective pressure toward FGFR1 multiple events arising in the context of a quiet genome. To decipher the molecular mechanisms triggered by multiple concurrent FGFR1 mutations, we have mapped the proximal interactome of wild-type, single- and double-mutant FGFR1 proteins through a BioID-MS approach. Our data reveal novel oncogenic functionality for the two hotspot mutations N546K and K656E, linked to evasion of lysosomal degradation. Further, we identified a modulatory tumor-suppressive role for the susceptibility variant R661P, which hampers the oncogenic potential of both hotspot N546K and K656E mutations by rescuing receptor degradation and reducing N546K affinity for the downstream effector PLCγ. Introducing the R661P missense variant was sufficient to abolish self-renewal capacity of oligodendroglioma cells and downregulate genes involved in neurodevelopment and neuro-glial cell fate decisions, both aspects overcome in the double mutants. This study sheds light on contextual oncogenic effects associated with FGFR1 alterations and their recurrence in low-mutation burden and therapy naive tumors.