Proteomic biomarkers in seminal plasma as predictors of reproductive potential in azoospermic men.

Introduction: Azoospermia, characterized by an absence of sperm in the ejaculate, represents the most severe form of male infertility. While surgical sperm retrieval in obstructive azoospermia (OA) is successful in the majority of cases, patients with non-obstructive azoospermia (NOA) show retrieval rates of only about 50% and thus frequently have unnecessary surgery. Surgical intervention could be avoided if patients without preserved spermatogenesis are identified preoperatively. This prospective study aimed to discover biomarkers in seminal plasma that could be employed for a non-invasive differential diagnosis of OA/NOA in order to rationalize surgery recommendations and improve success rates. Methods: All patients signed written informed consent, underwent comprehensive andrological evaluation, received human genetics to exclude relevant pathologies, and patients with azoospermia underwent surgical sperm retrieval. Using label-free LC-MS/MS, we compared the proteomes of seminal plasma samples from fertile men (healthy controls (HC), n=8) and infertile men diagnosed with 1) OA (n=7), 2) NOA with successful sperm retrieval (mixed testicular atrophy (MTA), n=8), and 3) NOA without sperm retrieval (Sertoli cell-only phenotype (SCO), n=7). Relative abundance changes of two candidate markers of sperm retrieval, HSPA2 and LDHC, were confirmed by Western Blot. Results: We found the protein expression levels of 42 proteins to be significantly down-regulated (p ≤ 0.05) in seminal plasma from SCO NOA patients relative to HC whereas only one protein was down-regulated in seminal plasma from MTA patients. Analysis of tissue and cell expression suggested that the testis-specific proteins LDHC, PGK2, DPEP3, and germ-cell enriched heat-shock proteins HSPA2 and HSPA4L are promising biomarkers of spermatogenic function. Western blotting revealed a significantly lower abundance of LDHC and HSPA2 in the seminal plasma of men with NOA (SCO and MTA) compared to controls. Discussion: The results indicate that certain testis-specific proteins when measured in seminal plasma, could serve as indicators of the presence of sperm in the testis and predict the success of sperm retrieval. Used in conjunction with conventional clinical assessments, these proteomic biomarkers may assist in the non-invasive diagnosis of idiopathic male infertility.

Caspase-2 protects against ferroptotic cell death.

Caspase-2, one of the most evolutionarily conserved members of the caspase family, is an important regulator of the cellular response to oxidative stress. Given that ferroptosis is suppressed by antioxidant defense pathways, such as that involving selenoenzyme glutathione peroxidase 4 (GPX4), we hypothesized that caspase-2 may play a role in regulating ferroptosis. This study provides the first demonstration of an important and unprecedented function of caspase-2 in protecting cancer cells from undergoing ferroptotic cell death. Specifically, we show that depletion of caspase-2 leads to the downregulation of stress response genes including SESN2, HMOX1, SLC7A11, and sensitizes mutant-p53 cancer cells to cell death induced by various ferroptosis-inducing compounds. Importantly, the canonical catalytic activity of caspase-2 is not required for its role and suggests that caspase-2 regulates ferroptosis via non-proteolytic interaction with other proteins. Using an unbiased BioID proteomics screen, we identified novel caspase-2 interacting proteins (including heat shock proteins and co-chaperones) that regulate cellular responses to stress. Finally, we demonstrate that caspase-2 limits chaperone-mediated autophagic degradation of GPX4 to promote the survival of mutant-p53 cancer cells. In conclusion, we document a novel role for caspase-2 as a negative regulator of ferroptosis in cells with mutant p53. Our results provide evidence for a novel function of caspase-2 in cell death regulation and open potential new avenues to exploit ferroptosis in cancer therapy.

Identification of Serum Biomarkers to Monitor Therapeutic Response in Intestinal-Type Gastric Cancer.

There are a limited number of clinically useful serum biomarkers to predict tumor onset or treatment response in gastric cancer (GC). For this reason, we explored the serum proteome of the gp130Y757F murine model of intestinal-type gastric cancer (IGC). We identified 30 proteins with significantly elevated expression in early gp130Y757F IGC and 12 proteins that were significantly elevated in late gp130Y757F IGC compared to age- and gender-matched wild-type mice. Within these signatures, there was an overlap of 10 proteins commonly elevated in both early- and late-stage disease. These results highlight the potential to identify serum biomarkers of disease stage. Since IGC in the gp130Y757F model can be reversed following therapeutic inhibition of Interleukin (IL)-11, we explored whether the protein signatures we identified could be used to monitor tumor regression. We compared two different therapeutic modalities and found 5 proteins to be uniquely differentially expressed between control animals and animals halfway through treatment, with 10 differentially expressed at the end of treatment. Our findings highlight the potential to identify reliable biomarkers to track IGC tumor regression in response to treatment.

Capillary blood protein markers of posttraumatic headache in children after concussion.

OBJECTIVE: Posttraumatic headache (PTH) represents the most common acute and persistent symptom in children after concussion, yet there is no blood protein signature to stratify the risk of PTH after concussion to facilitate early intervention. This discovery study aimed to identify capillary blood protein markers, at emergency department (ED) presentation within 48 hours of concussion, to predict children at risk of persisting PTH at 2 weeks postinjury. METHODS: Capillary blood was collected using the Mitra Clamshell device from children aged 8-17 years who presented to the ED of the Royal Children's Hospital, Melbourne, Australia, within 48 hours of sustaining a concussion. Participants were followed up at 2 weeks postinjury to determine PTH status. PTH was defined per clinical guidelines as a new or worsened headache compared with preinjury. An untargeted proteomics analysis using data-independent acquisition (DIA) was performed. Principal component analysis and hierarchical clustering were used to reduce the dimensionality of the protein dataset. RESULTS: A total of 907 proteins were reproducibly identified from 82 children within 48 hours of concussion. The mean participant age was 12.78 years (SD 2.54 years, range 8-17 years); 70% of patients were male. Eighty percent met criteria for acute PTH in the ED, while one-third of participants with follow-up experienced PTH at 2 weeks postinjury (range 8-16 days). Hemoglobin subunit zeta (HBZ), cystatin B (CSTB), beta-ala-his dipeptidase (CNDP1), hemoglobin subunit gamma-1 (HBG1), and zyxin (ZYX) were weakly associated with PTH at 2 weeks postinjury based on up to a 7% increase in the PTH group despite nonsignificant Benjamini-Hochberg adjusted p values. CONCLUSIONS: This discovery study determined that no capillary blood protein markers, measured at ED presentation within 48 hours of concussion, can predict children at risk of persisting PTH at 2 weeks postinjury. While HBZ, CSTB, CNDP1, HBG1, and ZYX were weakly associated with PTH at 2 weeks postinjury, there was no specific blood protein signature predictor of PTH in children after concussion. There is an urgent need to discover new blood biomarkers associated with PTH to facilitate risk stratification and improve clinical management of pediatric concussion.

Mind bomb 2 limits inflammatory dermatitis in Sharpin mutant mice independently of cell death.

Skin inflammation is a complex process implicated in various dermatological disorders. The chronic proliferative dermatitis (cpd) phenotype driven by the cpd mutation (cpdm) in the Sharpin gene is characterized by dermal inflammation and epidermal abnormalities. Tumour necrosis factor (TNF) and caspase-8-driven cell death causes the pathogenesis of Sharpincpdm mice; however, the role of mind bomb 2 (MIB2), a pro-survival E3 ubiquitin ligase involved in TNF signaling, in skin inflammation remains unknown. Here, we demonstrate that MIB2 antagonizes inflammatory dermatitis in the context of the cpd mutation. Surprisingly, the role of MIB2 in limiting skin inflammation is independent of its known pro-survival function and E3 ligase activity. Instead, MIB2 enhances the production of wound-healing molecules, granulocyte colony-stimulating factor, and Eotaxin, within the skin. This discovery advances our comprehension of inflammatory cytokines and chemokines associated with cpdm pathogenesis and highlights the significance of MIB2 in inflammatory skin disease that is independent of its ability to regulate TNF-induced cell death.

Plasmepsin X activates the PCRCR complex of Plasmodium falciparum by processing PfRh5 for erythrocyte invasion.

Plasmodium falciparum causes the most severe form of malaria in humans. The protozoan parasite develops within erythrocytes to mature schizonts, that contain more than 16 merozoites, which egress and invade fresh erythrocytes. The aspartic protease plasmepsin X (PMX), processes proteins and proteases essential for merozoite egress from the schizont and invasion of the host erythrocyte, including the leading vaccine candidate PfRh5. PfRh5 is anchored to the merozoite surface through a 5-membered complex (PCRCR), consisting of Plasmodium thrombospondin-related apical merozoite protein, cysteine-rich small secreted protein, Rh5-interacting protein and cysteine-rich protective antigen. Here, we show that PCRCR is processed by PMX in micronemes to remove the N-terminal prodomain of PhRh5 and this activates the function of the complex unmasking a form that can bind basigin on the erythrocyte membrane and mediate merozoite invasion. The ability to activate PCRCR at a specific time in merozoite invasion most likely masks potential deleterious effects of its function until they are required. These results provide an important understanding of the essential role of PMX and the fine regulation of PCRCR function in P. falciparum biology.

S100 family proteins are linked to organoid morphology and EMT in pancreatic cancer.

Epithelial-mesenchymal transition (EMT) is a continuum that includes epithelial, partial EMT, and mesenchymal states, each of which is associated with cancer progression, invasive capabilities, and ultimately, metastasis. We used a lineage-traced sporadic model of pancreatic cancer to generate a murine organoid biobank from primary and secondary tumors, including sublines that underwent partial EMT and complete EMT. Using an unbiased proteomics approach, we found that organoid morphology predicts the EMT state, and the solid organoids are associated with a partial EMT signature. We also observed that exogenous TGFß1 induces solid organoid morphology that is associated with changes in the S100 family, complete EMT, and the formation of high-grade tumors. S100A4 may be a useful biomarker for predicting EMT state, disease progression, and outcome in patients with pancreatic cancer.

CIS controls the functional polarization of GM-CSF-derived macrophages.

The cytokine granulocyte-macrophage-colony stimulating factor (GM-CSF) possesses the capacity to differentiate monocytes into macrophages (MØs) with opposing functions, namely, proinflammatory M1-like MØs and immunosuppressive M2-like MØs. Despite the importance of these opposing biological outcomes, the intrinsic mechanism that regulates the functional polarization of MØs under GM-CSF signaling remains elusive. Here, we showed that GM-CSF-induced MØ polarization resulted in the expression of cytokine-inducible SH2-containing protein (CIS) and that CIS deficiency skewed the differentiation of monocytes toward immunosuppressive M2-like MØs. CIS deficiency resulted in hyperactivation of the JAK-STAT5 signaling pathway, consequently promoting downregulation of the transcription factor Interferon Regulatory Factor 8 (IRF8). Loss- and gain-of-function approaches highlighted IRF8 as a critical regulator of the M1-like polarization program. In vivo, CIS deficiency induced the differentiation of M2-like macrophages, which promoted strong Th2 immune responses characterized by the development of severe experimental asthma. Collectively, our results reveal a CIS-modulated mechanism that clarifies the opposing actions of GM-CSF in MØ differentiation and uncovers the role of GM-CSF in controlling allergic inflammation.

PCRCR complex is essential for invasion of human erythrocytes by Plasmodium falciparum.

The most severe form of malaria is caused by Plasmodium falciparum. These parasites invade human erythrocytes, and an essential step in this process involves the ligand PfRh5, which forms a complex with cysteine-rich protective antigen (CyRPA) and PfRh5-interacting protein (PfRipr) (RCR complex) and binds basigin on the host cell. We identified a heteromeric disulfide-linked complex consisting of P. falciparum Plasmodium thrombospondin-related apical merozoite protein (PfPTRAMP) and P. falciparum cysteine-rich small secreted protein (PfCSS) and have shown that it binds RCR to form a pentameric complex, PCRCR. Using P. falciparum lines with conditional knockouts, invasion inhibitory nanobodies to both PfPTRAMP and PfCSS, and lattice light-sheet microscopy, we show that they are essential for merozoite invasion. The PCRCR complex functions to anchor the contact between merozoite and erythrocyte membranes brought together by strong parasite deformations. We solved the structure of nanobody-PfCSS complexes to identify an inhibitory epitope. Our results define the function of the PCRCR complex and identify invasion neutralizing epitopes providing a roadmap for structure-guided development of these proteins for a blood stage malaria vaccine.

Simplifying MS1 and MS2 spectra to achieve lower mass error, more dynamic range, and higher peptide identification confidence on the Bruker timsTOF Pro.

For bottom-up proteomic analysis, the goal of analytical pipelines that process the raw output of mass spectrometers is to detect, characterise, identify, and quantify peptides. The initial steps of detecting and characterising features in raw data must overcome some considerable challenges. The data presents as a sparse array, sometimes containing billions of intensity readings over time. These points represent both signal and chemical or electrical noise. Depending on the biological sample's complexity, tens to hundreds of thousands of peptides may be present in this vast data landscape. For ion mobility-based LC-MS analysis, each peptide is comprised of a grouping of hundreds of single intensity readings in three dimensions: mass-over-charge (m/z), mobility, and retention time. There is no inherent information about any associations between individual points; whether they represent a peptide or noise must be inferred from their structure. Peptides each have multiple isotopes, different charge states, and a dynamic range of intensity of over six orders of magnitude. Due to the high complexity of most biological samples, peptides often overlap in time and mobility, making it very difficult to tease apart isotopic peaks, to apportion the intensity of each and the contribution of each isotope to the determination of the peptide's monoisotopic mass, which is critical for the peptide's identification. Here we describe four algorithms for the Bruker timsTOF Pro that each play an important role in finding peptide features and determining their characteristics. These algorithms focus on separate characteristics that determine how candidate features are detected in the raw data. The first two algorithms deal with the complexity of the raw data, rapidly clustering raw data into spectra that allows isotopic peaks to be resolved. The third algorithm compensates for saturation of the instrument's detector thereby recovering lost dynamic range, and lastly, the fourth algorithm increases confidence of peptide identifications by simplification of the fragment spectra. These algorithms are effective in processing raw data to detect features and extracting the attributes required for peptide identification, and make an important contribution to an analytical pipeline by detecting features that are higher quality and better segmented from other peptides in close proximity. The software has been developed in Python using Numpy and Pandas and made freely available with an open-source MIT license to facilitate experimentation and further improvement (DOI 10.5281/zenodo.6513126). Data are available via ProteomeXchange with identifier PXD030706.

TGFß and CIS Inhibition Overcomes NK-cell Suppression to Restore Antitumor Immunity.

Antibodies targeting "immune checkpoints" have revolutionized cancer therapy by reactivating tumor-resident cytotoxic lymphocytes, primarily CD8+ T cells. Interest in targeting analogous pathways in other cytotoxic lymphocytes is growing. Natural killer (NK) cells are key to cancer immunosurveillance by eradicating metastases and driving solid tumor inflammation. NK-cell antitumor function is dependent on the cytokine IL15. Ablation of the IL15 signaling inhibitor CIS (Cish) enhances NK-cell antitumor immunity by increasing NK-cell metabolism and persistence within the tumor microenvironment (TME). The TME has also been shown to impair NK-cell fitness via the production of immunosuppressive transforming growth factor ß (TGFß), a suppression which occurs even in the presence of high IL15 signaling. Here, we identified an unexpected interaction between CIS and the TGFß signaling pathway in NK cells. Independently, Cish- and Tgfbr2-deficient NK cells are both hyperresponsive to IL15 and hyporesponsive to TGFß, with dramatically enhanced antitumor immunity. Remarkably, when both these immunosuppressive genes are simultaneously deleted in NK cells, mice are largely resistant to tumor development, suggesting that combining suppression of these two pathways might represent a novel therapeutic strategy to enhance innate anticancer immunity.

The intracellular domains of the EphB6 and EphA10 receptor tyrosine pseudokinases function as dynamic signalling hubs.

EphB6 and EphA10 are two poorly characterised pseudokinase members of the Eph receptor family, which collectively serves as mediators of contact-dependent cell-cell communication to transmit extracellular cues into intracellular signals. As per their active counterparts, EphB6 and EphA10 deregulation is strongly linked to proliferative diseases. However, unlike active Eph receptors, whose catalytic activities are thought to initiate an intracellular signalling cascade, EphB6 and EphA10 are classified as catalytically dead, raising the question of how non-catalytic functions contribute to Eph receptor signalling homeostasis. In this study, we have characterised the biochemical properties and topology of the EphB6 and EphA10 intracellular regions comprising the juxtamembrane (JM) region, pseudokinase and SAM domains. Using small-angle X-ray scattering and cross-linking-mass spectrometry, we observed high flexibility within their intracellular regions in solution and a propensity for interaction between the component domains. We identified tyrosine residues in the JM region of EphB6 as EphB4 substrates, which can bind the SH2 domains of signalling effectors, including Abl, Src and Vav3, consistent with cellular roles in recruiting these proteins for downstream signalling. Furthermore, our finding that EphB6 and EphA10 can bind ATP and ATP-competitive small molecules raises the prospect that these pseudokinase domains could be pharmacologically targeted to counter oncogenic signalling.

The ubiquitylation of IL-1ß limits its cleavage by caspase-1 and targets it for proteasomal degradation.

Interleukin-1ß (IL-1ß) is activated by inflammasome-associated caspase-1 in rare autoinflammatory conditions and in a variety of other inflammatory diseases. Therefore, IL-1ß activity must be fine-tuned to enable anti-microbial responses whilst limiting collateral damage. Here, we show that precursor IL-1ß is rapidly turned over by the proteasome and this correlates with its decoration by K11-linked, K63-linked and K48-linked ubiquitin chains. The ubiquitylation of IL-1ß is not just a degradation signal triggered by inflammasome priming and activating stimuli, but also limits IL-1ß cleavage by caspase-1. IL-1ß K133 is modified by ubiquitin and forms a salt bridge with IL-1ß D129. Loss of IL-1ß K133 ubiquitylation, or disruption of the K133:D129 electrostatic interaction, stabilizes IL-1ß. Accordingly, Il1bK133R/K133R mice have increased levels of precursor IL-1ß upon inflammasome priming and increased production of bioactive IL-1ß, both in vitro and in response to LPS injection. These findings identify mechanisms that can limit IL-1ß activity and safeguard against damaging inflammation.

Sperm proteins and cancer-testis antigens are released by the seminiferous tubules in mice and men.

Sperm develop from puberty in the seminiferous tubules, inside the blood-testis barrier to prevent their recognition as "non-self" by the immune system, and it is widely assumed that human sperm-specific proteins cannot access the circulatory or immune systems. Sperm-specific proteins aberrantly expressed in cancer, known as cancer-testis antigens (CTAs), are often pursued as cancer biomarkers and therapeutic targets based on the assumption they are neoantigens absent from the circulation in healthy men. Here, we identify a wide range of germ cell-derived and sperm-specific proteins, including multiple CTAs, that are selectively deposited by the Sertoli cells of the adult mouse and human seminiferous tubules into testicular interstitial fluid (TIF) that is "outside" the blood-testis barrier. From TIF, the proteins can access the circulatory- and immune systems. Disruption of spermatogenesis decreases the abundance of these proteins in mouse TIF, and a sperm-specific CTA is significantly decreased in TIF from infertile men, suggesting that exposure of certain CTAs to the immune system could depend on fertility status. The results provide a rationale for the development of blood-based tests useful in the management of male infertility and indicate CTA candidates for cancer immunotherapy and biomarker development that could show sex-specific and male-fertility-related responses.

Physiological substrates and ontogeny-specific expression of the ubiquitin ligases MARCH1 and MARCH8.

MARCH1 and MARCH8 are ubiquitin ligases that control the expression and trafficking of critical immunoreceptors. Understanding of their function is hampered by three major knowledge gaps: (i) it is unclear which cell types utilize these ligases; (ii) their level of redundancy is unknown; and (iii) most of their putative substrates have been described in cell lines, often overexpressing MARCH1 or MARCH8, and it is unclear which substrates are regulated by either ligase in vivo. Here we address these questions by systematically analyzing the immune cell repertoire of MARCH1- or MARCH8-deficient mice, and applying unbiased proteomic profiling of the plasma membrane of primary cells to identify MARCH1 and MARCH8 substrates. Only CD86 and MHC II were unequivocally identified as immunoreceptors regulated by MARCH1 and MARCH8, but each ligase carried out its function in different tissues. MARCH1 regulated MHC II and CD86 in professional and "atypical" antigen presenting cells of hematopoietic origin, including neutrophils, eosinophils and monocytes. MARCH8 only operated in non-hematopoietic cells, such as thymic and alveolar epithelial cells. Our results establish the tissue-specific functions of MARCH1 and MARCH8 in regulation of immune receptor expression and reveal that the range of cells constitutively endowed with antigen-presentation capacity is wider than generally appreciated.

Cytotoxic T cells swarm by homotypic chemokine signalling.

Cytotoxic T lymphocytes (CTLs) are thought to arrive at target sites either via random search or following signals by other leukocytes. Here, we reveal independent emergent behaviour in CTL populations attacking tumour masses. Primary murine CTLs coordinate their migration in a process reminiscent of the swarming observed in neutrophils. CTLs engaging cognate targets accelerate the recruitment of distant T cells through long-range homotypic signalling, in part mediated via the diffusion of chemokines CCL3 and CCL4. Newly arriving CTLs augment the chemotactic signal, further accelerating mass recruitment in a positive feedback loop. Activated effector human T cells and chimeric antigen receptor (CAR) T cells similarly employ intra-population signalling to drive rapid convergence. Thus, CTLs recognising a cognate target can induce a localised mass response by amplifying the direct recruitment of additional T cells independently of other leukocytes.

Immune cells known as cytotoxic T lymphocytes, or CTLs for short, move around the body searching for infected or damaged cells that may cause harm. Once these specialised killer cells identify a target, they launch an attack, removing the harmful cell from the body. CTLs can also recognise and eliminate cancer cells, and can be infused into cancer patients as a form of treatment called adoptive cell transfer immunotherapy. Unfortunately, this kind of treatment does not yet work well on solid tumours because the immune cells often do not infiltrate them sufficiently. It is thought that CTLs arrive at their targets either by randomly searching or by following chemicals secreted by other immune cells. However, the methods used to map the movement of these killer cells have made it difficult to determine how populations of CTLs coordinate their behaviour independently of other cells in the immune system. To overcome this barrier, Galeano Niño, Pageon, Tay et al. employed a three-dimensional model known as a tumouroid embedded in a matrix of proteins, which mimics the tissue environment of a real tumour in the laboratory. These models were used to track the movement of CTLs extracted from mice and humans, as well as human T cells engineered to recognise cancer cells. The experiments showed that when a CTL identifies a tumour cell, it releases chemical signals known as chemokines, which attract other CTLs and recruit them to the target site. Further experiments and computer simulations revealed that as the number of CTLs arriving at the target site increases, this amplifies the chemokine signal being secreted, resulting in more and more CTLs being attracted to the tumour. Other human T cells that had been engineered to recognize cancer cells were also found to employ this method of mass recruitment, and collectively 'swarm' towards targeted tumours. These findings shed new light on how CTLs work together to attack a target. It is possible that exploiting the mechanism used by CTLs could help improve the efficiency of tumour-targeting immunotherapies. However, further studies are needed to determine whether these findings can be applied to solid tumours in cancer patients.

NK cell-derived GM-CSF potentiates inflammatory arthritis and is negatively regulated by CIS.

Despite increasing recognition of the importance of GM-CSF in autoimmune disease, it remains unclear how GM-CSF is regulated at sites of tissue inflammation. Using GM-CSF fate reporter mice, we show that synovial NK cells produce GM-CSF in autoantibody-mediated inflammatory arthritis. Synovial NK cells promote a neutrophilic inflammatory cell infiltrate, and persistent arthritis, via GM-CSF production, as deletion of NK cells, or specific ablation of GM-CSF production in NK cells, abrogated disease. Synovial NK cell production of GM-CSF is IL-18-dependent. Furthermore, we show that cytokine-inducible SH2-containing protein (CIS) is crucial in limiting GM-CSF signaling not only during inflammatory arthritis but also in experimental allergic encephalomyelitis (EAE), a murine model of multiple sclerosis. Thus, a cellular cascade of synovial macrophages, NK cells, and neutrophils mediates persistent joint inflammation via production of IL-18 and GM-CSF. Endogenous CIS provides a key brake on signaling through the GM-CSF receptor. These findings shed new light on GM-CSF biology in sterile tissue inflammation and identify several potential therapeutic targets.

Loss of Bcl-G, a Bcl-2 family member, augments the development of inflammation-associated colorectal cancer.

Gastrointestinal epithelial cells provide a selective barrier that segregates the host immune system from luminal microorganisms, thereby contributing directly to the regulation of homeostasis. We have shown that from early embryonic development Bcl-G, a Bcl-2 protein family member with unknown function, was highly expressed in gastrointestinal epithelial cells. While Bcl-G was dispensable for normal growth and development in mice, the loss of Bcl-G resulted in accelerated progression of colitis-associated cancer. A label-free quantitative proteomics approach revealed that Bcl-G may contribute to the stability of a mucin network, which when disrupted, is linked to colon tumorigenesis. Consistent with this, we observed a significant reduction in Bcl-G expression in human colorectal tumors. Our study identifies an unappreciated role for Bcl-G in colon cancer.