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Chronic lung allograft dysfunction is the major barrier to long-term survival in lung transplant recipients. Evidence supports type 1 alloimmunity as the predominant response in acute/chronic lung rejection, but the immunoregulatory mechanisms remain incompletely understood. We studied the combinatorial F-box E3 ligase system: F-box protein 3 (FBXO3; proinflammatory) and F-box and leucine-rich repeat protein 2 (FBXL2; anti-inflammatory and regulates TNFR-associated factor [TRAF] protein). Using the mouse orthotopic lung transplant model, we evaluated allografts from BALB/c → C57BL/6 (acute rejection; day 10) and found significant induction of FBXO3 and diminished FBXL2 protein along with elevated T-bet, IFN-γ, and TRAF proteins 1–5 compared with isografts. In the acute model, treatment with costimulation blockade (MR1/CTLA4-Ig) resulted in attenuated FBXO3, preserved FBXL2, and substantially reduced T-bet, IFN-γ, and TRAFs 1–5, consistent with a key role for type 1 alloimmunity. Immunohistochemistry revealed significant changes in the FBXO3/FBXL2 balance in airway epithelia and infiltrating mononuclear cells during rejection compared with isografts or costimulation blockade–treated allografts. In the chronic lung rejection model, DBA/2J/C57BL/6F1 > DBA/2J (day 28), we observed persistently elevated FBXO3/FBXL2 balance and T-bet/IFN-γ protein and similar findings from lung transplant recipient lungs with chronic lung allograft dysfunction versus controls. We hypothesized that FBXL2 regulated T-bet and found FBXL2 was sufficient to polyubiquitinate T-bet and coimmunoprecipitated with T-bet on pulldown experiments and vice versa in Jurkat cells. Transfection with FBXL2 diminished T-bet protein in a dose-dependent manner in mouse lung epithelial cells. In testing type 1 cytokines, TNF-α was found to negatively regulate FBXL2 protein and mRNA levels. Together, our findings show the combinatorial E3 ligase FBXO3/FBXL2 system plays a role in the regulation of T-bet through FBXL2, with negative cross-regulation of TNF-α on FBXL2 during lung allograft rejection.

SARS-CoV-2 (2019-nCoV) is the pathogenic coronavirus responsible for the global pandemic of COVID-19 disease. The Spike (S) protein of SARS-CoV-2 attaches to host lung epithelial cells through the cell surface receptor ACE2, a process dependent on host proteases including TMPRSS2. Here, we identify small molecules that reduce surface expression of TMPRSS2 using a library of 2,560 FDA-approved or current clinical trial compounds. We identify homoharringtonine and halofuginone as the most attractive agents, reducing endogenous TMPRSS2 expression at sub-micromolar concentrations. These effects appear to be mediated by a drug-induced alteration in TMPRSS2 protein stability. We further demonstrate that halofuginone modulates TMPRSS2 levels through proteasomal-mediated degradation that involves the E3 ubiquitin ligase component DDB1- and CUL4-associated factor 1 (DCAF1). Finally, cells exposed to homoharringtonine and halofuginone, at concentrations of drug known to be achievable in human plasma, demonstrate marked resistance to SARS-CoV-2 infection in both live and pseudoviral in vitro models. Given the safety and pharmacokinetic data already available for the compounds identified in our screen, these results should help expedite the rational design of human clinical trials designed to combat active COVID-19 infection.

Prostate cancer is the most common cancer in males and the fifth leading cause of cancer mortality worldwide. A variety of therapeutic approaches exist including steroid synthesis inhibitors and next-generation ligand binding domain (LBD) antagonists [e.g., enzalutamide (Enza)]. However, these approaches are only effective against tumors bearing the full-length androgen receptor (AR-FL). In the course of their disease, many patients acquire androgen receptor splice variant 7 (AR-V7), a mutant form of the receptor which lacks the LBD and is constitutively activated. To date, no effective therapy has been demonstrated for patients with metastatic prostate cancer bearing the AR-V7 signature. We have recently developed a high throughput platform that allows for the identification of ligands that can bind to wide variety of protein targets. Using this approach, we screened a diverse chemical library of 100,000 small molecules to identify compounds that bound to AR-V7. One such molecule, CL-AR-100, directly bound to AR-V7 and moreover, induced proteasomal-mediated targeted protein degradation of both AR-V7 and AR-FL. This compound did not affect the expression of other structurally related ligand-activated nuclear receptors. In prostate cancer cell lines expressing AR-FL, CL-AR-100 induced a gene expression profile similar to cells treated with Enza including a marked reduction in KLK3 (PSA) expression. Moreover, CL-AR-200 inhibited the growth of 22RV1 cells (IC50=0.3uM), a cell line that predominantly expresses AR-V7. In contrast, the compound did not affect the growth of a wide variety of non-tumorigenic cells, non-prostate tumor cell lines or PC3 cells, a prostate cell line that exhibits AR-independent cell growth. These results thereby identify a small molecule molecular degrader that can specifically induce the targeted protein degradation of the AR-V7 splice variant. Given the strong association of this isoform with treatment resistance, this approach would appear to provide an attractive strategy for patients with metastatic castration resistant prostate cancer. Citation Format: Yuan Liu, Bo Lin, Mads B. Larsen, Irene Alfaras, Jason R. Kennerdell, Daniel P. Camarco, Ferhan Tuncer, Toren Finkel, Bill B. Chen. Identification of a molecular degrader targeting the AR-V7 splice variant [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1620.

Adenosine deaminase acting on RNA (ADAR) are a family of enzymes that catalyzes the posttranscriptional conversion of adenosine to inosine in double-stranded RNA (dsRNA). Recent evidence suggests that genetic deletion of ADAR1 render tumors cells substantially more vulnerable to immunotherapy. In cells, ADAR1 is expressed as two different isoforms, the constitutively expressed ADAR1p110 and the inducible ADAR1p150. Evidence suggests that ADAR1p150 is the isoform that confers oncogenic and immune modulating effects in most tumors. Of note, many of the effects of ADAR1p150 appear to be independent of the protein’s RNA editing function suggesting that a small molecule which induces ADAR1p150 targeted protein degradation might be preferable to agents that simply block deaminase activity. We have recently developed a high throughput platform that allows for the identification of ligands that can bind to wide variety of protein targets. Using this approach, we screened a diverse chemical library of 100,000 small molecules to identify compounds that bind to the unique N-terminal region of ADAR1p150. One such molecule, CL-AD-100, directly bound to ADAR1p150 but not ADAR1p110. Moreover, sub-micromolar concentrations of CL-AD-100, induced proteasomal mediated degradation of ADAR1p150, without effecting ADAR1p110 expression. Cells treated with CL-AD-100 exhibited a signature consistent with what has been observed with ADAR1p150 genetic deletion, namely accumulation of dsRNA, an inflammatory gene expression profile and interferon-dependent cell death. These results therefore demonstrate the feasibility of generating a small molecule that induces the specific targeted protein degradation of ADAR1p150. Such a molecule should have wide applicability in ADAR1-addicted tumors, as well as more broadly, in immuno-oncology. Citation Format: Yuan Liu, Mads B. Larsen, Bo Lin, Jason R. Kennerdell, Irene Alfaras, Daniel P. Camarco, Ferhan Tuncer, Toren Finkel, Bill B. Chen. Identification of a small molecule that induces targeted protein degradation of ADAR1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1805.

Fulvestrant is an effective therapy to treat post-menopausal women with estrogen receptor (ER)-positive metastatic breast cancer. The compound works as a selective estrogen receptor degrader (SERD). Structurally similar to estrogen, fulvestrant binds to the ligand binding domain (LBD) of the ER, altering the stability of the protein, leading to its accelerated proteasomal degradation. While effective, fulvestrant must be given intramuscularly, which has limited its clinical adoption. Based on the success of fulvestrant, multiple attempts have been made to generate orally available SERDs. These attempts have focused on compounds that, like fulvestrant, bind within the LBD of the ER. Overall, these intensive efforts have generated limited success. We reasoned that it may be possible to identify potential SERDs that bind to the ER in regions outside the LBD. Such an approach would be useful for tumors bearing wildtype ER, and likely for those bearing a mutant form of the ER, since most mutations cluster in the LBD. We have recently developed a high throughput platform that allows for the identification of ligands that can bind to wide variety of protein targets. Using this approach, we screened a diverse chemical library of 100,000 small molecules to identify compounds that bind outside of the LBD, and in particular to the N-terminal region of the ER. This strategy identified CL-ER-100, a small molecule that directly bound to the N-terminal region of the ER and functioned as a SERD. While CL-ER-100 rapidly induced ER proteasomal-dependent degradation, it had no effect on the protein levels of other, structurally related nuclear receptors. Based on its structure and size (~ MW 300 Da), CL-ER-100 is expected to have excellent bioavailability. Consistent with its binding outside of the LBD, addition of tamoxifen had no effect on the ability of CL-ER-100 to induce ER protein degradation. In cells, CL-ER-100 was able to markedly inhibit the growth of breast cancer cell lines such as MCF7 and T47D (IC50 of ~ 100 nM) while not inhibiting the growth of a wide array of normal and non-breast cancer tumor cell lines. Taken together, these results identify a novel strategy to develop small molecule SERDs that induce ER protein degradation by binding to previously untargeted regions of the estrogen receptor. Citation Format: Yuan Liu, Jason R. Kennerdell, Bo Lin, Mads B. Larsen, Irene Alfaras, Daniel P. Camarco, Ferhan Tuncer, Toren Finkel, Bill B. Chen. Generation of a novel estrogen receptor degrader [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1619.

The adenosine monophosphate (AMP)-activated protein kinase (Ampk) is a central regulator of metabolic pathways, and increasing Ampk activity has been considered to be an attractive therapeutic target. Here, we have identified an orphan ubiquitin E3 ligase subunit protein, Fbxo48, that targets the active, phosphorylated Ampkα (pAmpkα) for polyubiquitylation and proteasomal degradation. We have generated a novel Fbxo48 inhibitory compound, BC1618, whose potency in stimulating Ampk-dependent signaling greatly exceeds 5-aminoimidazole-4-carboxamide-1-β-ribofuranoside (AICAR) or metformin. This compound increases the biological activity of Ampk not by stimulating the activation of Ampk, but rather by preventing activated pAmpkα from Fbxo48-mediated degradation. We demonstrate that, consistent with augmenting Ampk activity, BC1618 promotes mitochondrial fission, facilitates autophagy and improves hepatic insulin sensitivity in high-fat-diet-induced obese mice. Hence, we provide a unique bioactive compound that inhibits pAmpkα disposal. Together, these results define a new pathway regulating Ampk biological activity and demonstrate the potential utility of modulating this pathway for therapeutic benefit.

Systemic scleroderma (SSc) is an autoimmune disease that affects over 2.5 million people globally. SSc results in dysfunctional connective tissues with excessive profibrotic signaling, affecting skin, cardiovascular, and particularly lung tissue. Over three-quarters of individuals with SSc develop pulmonary fibrosis within 5 years, the main cause of SSc mortality. No approved medicines to manage lung SSc currently exist. Recent research suggests that profibrotic signaling by transforming growth factor β (TGF-β) is directly tied to SSc. Previous studies have also shown that ubiquitin E3 ligases potently control TGF-β signaling through targeted degradation of key regulatory proteins; however, the roles of these ligases in SSc-TGF-β signaling remain unclear. Here we utilized primary SSc patient lung cells for high-throughput screening of TGF-β signaling via high-content imaging of nuclear translocation of the profibrotic transcription factor SMAD family member 2/3 (SMAD2/3). We screened an RNAi library targeting ubiquitin E3 ligases and observed that knockdown of the E3 ligase Kelch-like protein 42 (KLHL42) impairs TGF-β-dependent profibrotic signaling. KLHL42 knockdown reduced fibrotic tissue production and decreased TGF-β-mediated SMAD activation. Using unbiased ubiquitin proteomics, we identified phosphatase 2 regulatory subunit B'ϵ (PPP2R5ϵ) as a KLHL42 substrate. Mechanistic experiments validated ubiquitin-mediated control of PPP2R5ϵ stability through KLHL42. PPP2R5ϵ knockdown exacerbated TGF-β-mediated profibrotic signaling, indicating a role of PPP2R5ϵ in SSc. Our findings indicate that the KLHL42-PPP2R5ϵ axis controls profibrotic signaling in SSc lung fibroblasts. We propose that future studies could investigate whether chemical inhibition of KLHL42 may ameliorate profibrotic signaling in SSc.

TLR8 (Toll-like receptor 8) is an intracellular pattern recognition receptor that senses RNA in endosomes to initiate innate immune signaling through NF-κB, and mechanisms regulating TLR8 protein abundance are not completely understood. Protein degradation is a cellular process controlling protein concentrations, accomplished largely through ubiquitin transfer directed by E3 ligase proteins to substrates. In the present study, we show that TLR8 has a short half-life in THP-1 monocytes (∼1 h) and that TLR8 is ubiquitinated and degraded in the proteasome. Treatment with the TLR8 agonist R848 causes rapid depletion of TLR8 concentrations at early time points, an effect blocked by proteasomal inhibition. We show a novel role for RNF216 (ring finger protein 216), an E3 ligase that targets TLR8 for ubiquitination and degradation. RNF216 overexpression reduces TLR8 concentrations, whereas RNF216 knockdown stabilizes TLR8. We describe a potential role for TLR8 activation by circulating RNA ligands in humans with acute respiratory distress syndrome (ARDS): Plasma and extracted RNA fractions from subjects with ARDS activated TLR8 in vitro. MicroRNA (miRNA) expression profiling revealed several circulating miRNAs from subjects with ARDS. miRNA mimics promoted TLR8 proteasomal degradation in THP-1 cells. These data show that TLR8 proteasomal disposal through RNF216 in response to RNA ligands regulates TLR8 cellular concentrations and may have implications for innate immune signaling. In addition, TLR8 activation by circulating RNA ligands may be a previously underrecognized stimulus contributing to excessive innate immune signaling characteristic of ARDS.

RATIONALE: Lymphopenia is common in severe coronavirus disease (COVID-19), yet the immune mechanisms are poorly understood. As inflammatory cytokines are increased in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, we hypothesized a role in contributing to reduced T-cell numbers. OBJECTIVES: We sought to characterize the functional SARS-CoV-2 T-cell responses in patients with severe versus recovered, mild COVID-19 to determine whether differences were detectable. METHODS: Using flow cytometry and single-cell RNA sequence analyses, we assessed SARS-CoV-2-specific responses in our cohort. MEASUREMENTS AND MAIN RESULTS: In 148 patients with severe COVID-19, we found lymphopenia was associated with worse survival. CD4(+) lymphopenia predominated, with lower CD4(+)/CD8(+) ratios in severe COVID-19 compared with patients with mild disease (P < 0.0001). In severe disease, immunodominant CD4(+) T-cell responses to Spike-1 (S1) produced increased in vitro TNF-alpha (tumor necrosis factor-alpha) but demonstrated impaired S1-specific proliferation and increased susceptibility to activation-induced cell death after antigen exposure. CD4(+) TNF-alpha(+) T-cell responses inversely correlated with absolute CD4(+) counts from patients with severe COVID-19 (n = 76; R = - 0.797; P < 0.0001). In vitro TNF-alpha blockade, including infliximab or anti-TNF receptor 1 antibodies, strikingly rescued S1-specific CD4 (+) T-cell proliferation and abrogated S1-specific activation-induced cell death in peripheral blood mononuclear cells from patients with severe COVID-19 (P < 0.001). Single-cell RNA sequencing demonstrated marked downregulation of type-1 cytokines and NFKB signaling in S1-stimulated CD4(+) cells with infliximab treatment. We also evaluated BAL and lung explant CD4(+) T cells recovered from patients with severe COVID-19 and observed that lung T cells produced higher TNF-alpha compared with peripheral blood mononuclear cells. CONCLUSIONS: Together, our findings show CD4(+) dysfunction in severe COVID-19 is TNF-alpha/TNF receptor 1-dependent through immune mechanisms that may contribute to lymphopenia. TNF-alpha blockade may be beneficial in severe COVID-19.

Classification of patients with acute respiratory distress syndrome into hyper- and hypoinflammatory subphenotypes using plasma biomarkers may facilitate more effective targeted therapy. We examined whether established subphenotypes are present not only in patients with acute respiratory distress syndrome but also in patients at risk for acute respiratory distress syndrome (ARFA) and then assessed the prognostic information of baseline subphenotyping on the evolution of host-response biomarkers and clinical outcomes.Prospective, observational cohort study.Medical ICU at a tertiary academic medical center.Mechanically ventilated patients with acute respiratory distress syndrome or ARFA.None.We performed longitudinal measurements of 10 plasma biomarkers of host injury and inflammation. We applied unsupervised latent class analysis methods utilizing baseline clinical and biomarker variables and demonstrated that two-class models (hyper- vs hypoinflammatory subphenotypes) offered improved fit compared with one-class models in both patients with acute respiratory distress syndrome and ARFA. Baseline assignment to the hyperinflammatory subphenotype (39/104 [38%] acute respiratory distress syndrome and 30/108 [28%] ARFA patients) was associated with higher severity of illness by Sequential Organ Failure Assessment scores and incidence of acute kidney injury in patients with acute respiratory distress syndrome, as well as higher 30-day mortality and longer duration of mechanical ventilation in ARFA patients (p0.0001). Hyperinflammatory patients exhibited persistent elevation of biomarkers of innate immunity for up to 2 weeks postintubation.Our results suggest that two distinct subphenotypes are present not only in patients with established acute respiratory distress syndrome but also in patients at risk for its development. Hyperinflammatory classification at baseline is associated with higher severity of illness, worse clinical outcomes, and trajectories of persistently elevated biomarkers of host injury and inflammation during acute critical illness compared with hypoinflammatory patients. Our findings provide strong rationale for examining treatment effect modifications by subphenotypes in randomized clinical trials to inform precision therapeutic approaches in critical care.

Mitochondria evolved from endosymbiotic bacteria to become essential organelles of eukaryotic cells. The unique lipid composition and structure of mitochondrial membranes are critical for the proper functioning of mitochondria. However, stress responses that help maintain the mitochondrial membrane integrity are not well understood. One reason for this lack of insight is the absence of efficient tools to specifically damage mitochondrial membranes. Here, through a compound screen, we found that two bis-biguanide compounds, chlorhexidine and alexidine, modified the activity of the inner mitochondrial membrane (IMM)-resident protease OMA1 by altering the integrity of the IMM. These compounds are well-known bactericides whose mechanism of action has centered on their damage-inducing activity on bacterial membranes. We found alexidine binds to the IMM likely through the electrostatic interaction driven by the membrane potential as well as an affinity for anionic phospholipids. Electron microscopic analysis revealed that alexidine severely perturbated the cristae structure. Notably, alexidine evoked a specific transcriptional/proteostasis signature that was not induced by other typical mitochondrial stressors, highlighting the unique property of alexidine as a novel mitochondrial membrane stressor. Our findings provide a chemical-biological tool that should enable the delineation of mitochondrial stress-signaling pathways required to maintain the mitochondrial membrane homeostasis.

Lymphopenia is common in severe COVID-19 disease, yet the mechanisms are poorly understood. In 148 patients with severe COVID-19, we found lymphopenia was associated with worse survival. CD4+ lymphopenia predominated, with lower CD4+/CD8+ ratios in severe COVID-19 compared to recovered, mild disease (p+ T cell responses to Spike-1(S1) produced increased in vitro TNF-α, but impaired proliferation and increased susceptibility to activation-induced cell death (AICD). CD4+TNF-α+ T cell responses inversely correlated with absolute CD4+ counts from severe COVID-19 patients (n=76; R=-0.744, P+ proliferation and abrogated S1-AICD in severe COVID-19 patients (P+ cells with infliximab treatment. Lung CD4+ T cells in severe COVID-19 were reduced and produced higher TNF-α versus PBMC. Together, our findings show COVID-19-associated CD4+ lymphopenia and dysfunction is autocrine TNF-α/TNFRI-dependent and therapies targeting TNF-α may be beneficial in severe COVID-19.One Sentence SummaryAutocrine TNF-α/TNFRI regulates CD4+ T cell lymphopenia and dysfunction in severe COVID-19 disease.

Hypothesis: Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease in developed countries yet there are no FDA-approved therapies for the disease. AMPK is a cellular energy sensor that coordinates metabolic pathways to balance energy demand with production. Growing evidence suggests loss of AMPK activity contributes to NAFLD. We recently identified an orphan F-box protein, FBXO48, which mediates the ubiquitination and proteasomal degradation of phosphorylated AMPKα (pAMPK). We hypothesized that increasing pAMPK levels via inhibition of FBXO48 would improve glucose homeostasis and slow NAFLD progression. Methods: Twelve-week old male wildtype (WT) mice were fed low-fat diet (LFD) or “fast food” diet (FFD) for 24 weeks and then given vehicle (VEH) or a small molecule FBXO48 inhibitor (SMI; 5 mg/kg/d) for 8 weeks. We measured changes in body weight/composition, performed glucose tolerance tests (GTT), and collected plasma and liver for analysis. Results: SMI had no significant effect on body weight or composition, although body weight and fat mass were 2.4 and 2.1 g less in SMI FFD compared with VEH FFD mice, suggesting a modest effect on weight loss. SMI significantly improved glucose homeostasis in FFD mice and restored plasma glucose levels during GTT to those observed in LFD mice. SMI had no effect on liver triglyceride levels in LFD mice and produced a 15% non-significant reduction in FFD mice. Gene expression of inflammation markers Cd68 and Ccl2 were significantly reduced in SMI FFD compared with VEH FFD mice, as were markers of fibrosis Col1a1 and Col3a1. Conclusions: Our data suggest that increasing pAMPK levels through inhibition of FBXO48 may be a viable treatment option for improving glucose homeostasis and reducing inflammation/fibrosis associated with NAFLD. Disclosure A. Murali: None. L. R. Edmunds: None. B. Xie: None. B. Chen: Board Member; Self; Generian, Employee; Self; Generian. Y. Liu: Employee; Self; Generian. M. J. Jurczak: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (DK007052R01, DK119627)

SARS‐CoV‐2 (2019‐nCoV) is the pathogenic coronavirus responsible for the global pandemic of COVID‐19 disease. The Spike (S) protein of SARS‐CoV‐2 attaches to host lung epithelial cells through the cell surface receptor ACE2, a process dependent on host proteases including TMPRSS2. Here, we identified small molecules that can reduce surface expression of TMPRSS2 using a 2,700 FDA‐approved or current clinical trial compounds. Among these, homoharringtonine and halofuginone appear the most potent agents, reducing endogenous TMPRSS2 expression at sub‐micromolar concentrations. These effects appear to be mediated by a drug‐induced alteration in TMPRSS2 protein stability. We further demonstrate that halofuginone modulates TMPRSS2 levels through proteasomal‐mediated degradation that involves the E3 ubiquitin ligase component DDB1‐ and CUL4‐associated factor 1 (DCAF1). Finally, cells exposed to homoharringtonine and halofuginone, at concentrations of drug known to be achievable in human plasma, demonstrated marked resistance to SARS‐CoV‐2 pseudoviral infection. Given the safety and pharmacokinetic data already available for the compounds identified in our screen, these results should help expedite the rational design of human clinical trials designed to combat COVID‐19 infection.

The endo-lysosomal pathway plays an important role in pathogen clearance and both bacteria and viruses have evolved complex mechanisms to evade this host system. Here, we describe a novel aspect of coronaviral infection, whereby the master transcriptional regulator of lysosome biogenesis – TFEB – is targeted for proteasomal-mediated degradation upon viral infection. Through mass spectrometry analysis and an unbiased siRNA screen, we identify that TFEB protein stability is coordinately regulated by the E3 ubiquitin ligase subunit DCAF7 and the PAK2 kinase. In particular, viral infection triggers marked PAK2 activation, which in turn, phosphorylates and primes TFEB for ubiquitin-mediated protein degradation. Deletion of either DCAF7 or PAK2 blocks viral-mediated TFEB degradation and protects against viral-induced cytopathic effects. We further derive a series of small molecules that interfere with the DCAF7-TFEB interaction. These agents inhibit viral-triggered TFEB degradation and demonstrate broad anti-viral activities including attenuating in vivo SARS-CoV-2 infection. Together, these results delineate a viral-triggered pathway that disables the endogenous cellular system that maintains lysosomal function and suggest that small molecule inhibitors of the E3 ubiquitin ligase DCAF7 represent a novel class of endo-lysosomal, host-directed, anti-viral therapies.

Mitochondria evolved from endosymbiotic bacteria to become essential organelles of eukaryotic cells. The defined lipid composition and structure of mitochondrial membranes are critical for the proper functioning of mitochondria. However, mitochondrial stress responses that help maintain the integrity of mitochondrial membranes against internal or external insults are not well understood. One reason for this lack of insight is the absence of efficient tools to specifically damage mitochondrial membranes. Here, through a compound screen originally aimed at identifying inhibitors of the inner mitochondrial membrane (IMM)-resident protease OMA1, we found that two bis-biguanide compounds, Chlorhexidine and Alexidine, modified OMA1 activity by altering the integrity of the IMM. Interestingly, these compounds are well-known bactericides whose mechanism of action has centered on their damage-inducing activity on bacterial membranes. We found Alexidine binds to the IMM likely through the electrostatic interaction driven by the membrane potential as well as an affinity for anionic phospholipids. Electron microscopic analysis revealed that Alexidine severely perturbated the IMM, especially the cristae structure. Along with this, we observed the altered localization of IMM-resident membrane-shaping proteins, including Mic60. Notably, Alexidine evoked a specific transcriptional/proteostasis signature that was not induced by other typical mitochondrial stressors, highlighting the unique property of Alexidine as a novel mitochondrial membrane stressor. Our findings provide a chemical-biological tool that can induce acute and selective perturbation of the IMM integrity, which should enable the delineation of mitochondrial stress-signaling pathways required to maintain the mitochondrial membrane homeostasis.

SARS-CoV-2 (2019-nCoV) is the pathogenic coronavirus responsible for the global pandemic of COVID-19 disease. The Spike (S) protein of SARS-CoV-2 attaches to host lung epithelial cells through the cell surface receptor ACE2, a process dependent on host proteases including TMPRSS2. Here, we identify small molecules that reduce surface expression of TMPRSS2 using a library of 2,560 FDA-approved or current clinical trial compounds. We identify homoharringtonine and halofuginone as the most attractive agents, reducing endogenous TMPRSS2 expression at sub-micromolar concentrations. These effects appear to be mediated by a drug-induced alteration in TMPRSS2 protein stability. We further demonstrate that halofuginone modulates TMPRSS2 levels through proteasomal-mediated degradation that involves the E3 ubiquitin ligase component DDB1- and CUL4-associated factor 1 (DCAF1). Finally, cells exposed to homoharringtonine and halofuginone, at concentrations of drug known to be achievable in human plasma, demonstrate marked resistance to SARS-CoV-2 infection in both live and pseudoviral in vitro models. Given the safety and pharmacokinetic data already available for the compounds identified in our screen, these results should help expedite the rational design of human clinical trials designed to combat active COVID-19 infection., The serine protease TMPRSS2 primes SARS-CoV-2 glycoprotein for cell entry. Here, the authors perform a screen to identify drugs that reduce TMPRSS2 expression and find that halofuginone modulates proteasome-mediated degradation of TMPRSS2 and reduces entry of SARS-CoV-2.

The Skp1-Cul1-F-box protein (SCF) E3 ligase complex is one of the largest ubiquitin E3 ligase families. FBXL19, a F-box protein in SCF(FBXL19) E3 ligase complex, regulates a variety of cellular responses including cell migration. We have shown that FBXL19 is not stable and its degradation is mediated by the ubiquitin-proteasome system, while the ubiquitin E3 ligase for FBXL19 ubiquitination and degradation has not been identified. In the study, we discovered that a new ubiquitin E3 ligase, SCF(FBXW17), ubiquitinates and induces FBXL19 degradation. Exogenous FBXW17 targets FBXL19 for its ubiquitination and degradation. Lysine 114 in FBXL19 is a potential ubiquitin acceptor site. Acetylation of FBXL19 attenuated SCF(FBXW17)-mediated FBXL19 degradation. SCF(FBXL19) E3 ligase reduced Rac1 levels and cell migration, while the effects were attenuated by exogenous FBXW17. Downregulation of FBXW17 attenuated lysophosphatidic acid (LPA)-induced lamellipodia formation and Rac1 accumulation at migration leading edge. Taken together with our previous studies, FBXL19 is degraded by the ubiquitin-proteasome system and its site-specific ubiquitination is mediated by SCF(FBXW17) E3 ligase, which promotes cell migration.

Mitochondrial quality control is mediated by the PTEN-induced kinase 1 (PINK1), a cytoprotective protein that is dysregulated in inflammatory lung injury and neurodegenerative diseases. Here, we show that a ubiquitin E3 ligase receptor component, FBXO7, targets PINK1 for its cellular disposal. FBXO7, by mediating PINK1 ubiquitylation and degradation, was sufficient to induce mitochondrial injury and inflammation in experimental pneumonia. A computational simulation-based screen led to the identification of a small molecule, BC1464, which abrogated FBXO7 and PINK1 association, leading to increased cellular PINK1 concentrations and activities, and limiting mitochondrial damage. BC1464 exerted antiinflammatory activity in human tissue explants and murine lung inflammation models. Furthermore, BC1464 conferred neuroprotection in primary cortical neurons, human neuroblastoma cells, and patient-derived cells in several culture models of Parkinson's disease. The data highlight a unique opportunity to use small molecule antagonists that disrupt PINK1 interaction with the ubiquitin apparatus to enhance mitochondrial quality, limit inflammatory injury, and maintain neuronal viability.

FBXL2 is an important ubiquitin E3 ligase component that modulates inflammatory signaling and cell cycle progression, but its molecular regulation is largely unknown. Here, we show that tumor necrosis factor alpha (TNF-α), a critical cytokine linked to the inflammatory response during skeletal muscle regeneration, suppressed Fbxl2 mRNA expression in C2C12 myoblasts and triggered significant alterations in cell cycle, metabolic, and protein translation processes. Gene silencing of Fbxl2 in skeletal myoblasts resulted in increased proliferative responses characterized by activation of mitogen-activated protein (MAP) kinases and nuclear factor kappa B and decreased myogenic differentiation, as reflected by reduced expression of myogenin and impaired myotube formation. TNF-α did not destabilize the Fbxl2 transcript (half-life [t(1/2)], ∼10 h) but inhibited SP1 transactivation of its core promoter, localized to bp −160 to +42 within the proximal 5′ flanking region of the Fbxl2 gene. Chromatin immunoprecipitation and gel shift studies indicated that SP1 interacted with the Fbxl2 promoter during cellular differentiation, an effect that was less pronounced during proliferation or after TNF-α exposure. TNF-α, via activation of JNK, mediated phosphorylation of SP1 that impaired its binding to the Fbxl2 promoter, resulting in reduced transcriptional activity. The results suggest that SP1 transcriptional activation of Fbxl2 is required for skeletal muscle differentiation, a process that is interrupted by a key proinflammatory myopathic cytokine. IMPORTANCE Skeletal muscle regeneration and repair involve the recruitment and proliferation of resident satellite cells that exit the cell cycle during the process of myogenic differentiation to form myofibers. We demonstrate that the ubiquitin E3 ligase subunit FBXL2 is essential for skeletal myogenesis through its important effects on cell cycle progression and cell proliferative signaling. Further, we characterize a new mechanism whereby sustained stimulation by a major proinflammatory cytokine, TNF-α, regulates skeletal myogenesis by inhibiting the interaction of SP1 with the Fbxl2 core promoter in proliferating myoblasts. Our findings contribute to the understanding of skeletal muscle regeneration through the identification of Fbxl2 as both a critical regulator of myogenic proliferative processes and a susceptible gene target during inflammatory stimulation by TNF-α in skeletal muscle. Modulation of Fbxl2 activity may have relevance to disorders of muscle wasting associated with sustained proinflammatory signaling.

NRF2 is a master regulator of cellular anti-oxidant and anti-inflammatory responses, and strategies to augment NRF2-dependent responses may beneficial in many diseases. Basal NRF2 protein level is constrained by constitutive KEAP1-mediated degradation, but in the presence of electrophiles, NRF2 ubiquitination is inhibited. Impeded NRF2 degradation increases NRF2 protein, resulting in up-regulation of anti-oxidant gene transcription, and decreased inflammation. KEAP1-independent mechanisms regulating NRF2 stability have also been reported. Here we employed an HTS approach and identified a small molecule, BC-1901S, that stabilized NRF2 and increased its activity. BC-1901S activated NRF2 by inhibiting NRF2 ubiquitination in a KEAP1-independent manner. It further increased NRF2-dependent anti-oxidant gene transcription, and exhibited anti-inflammatory effects in vitro and in vivo. Further, we identified a new NRF2-interacting partner, DDB1 and CUL4 Associated Factor 1 (DCAF1), an E3 ligase that targeted NRF2 for proteasomal degradation. Mechanistically, BC-1901S directly bound to DCAF1 and disrupted NRF2/DCAF1 interaction, thus activating NRF2. These findings provide new insights in NRF2 biology and NRF2 based anti-inflammatory therapy., Graphical abstract Image 1, Highlights • A small molecule BC-1901S was identified as NRF2 activator based on high-throughput screening. • BC-1901S activates NRF2 through KEAP1-independent pathway and exhibit anti-inflammatory and anti-oxidant properties. • BC-1901S potentially disrupts the interaction between NRF2 and its novel E3 ligase subunit DCAF1. • An unbiased high-throughput approach that directly measures the level of NRF2 protein in cells was used.

Interleukin-3 (IL-3) receptor α (IL-3Rα) is the α subunit of the ligand-specific IL-3R and initiates intracellular signaling in response to IL-3. IL-3 amplifies proinflammatory signaling and cytokine storm in murine sepsis models. Here we found that RNFT2 (RING finger transmembrane-domain containing protein 2, also TMEM118), a previously uncharacterized RING finger ubiquitin E3 ligase, negatively regulated IL-3-dependent cellular responses through IL-3Rα ubiquitination and degradation in the proteasome. In vitro, IL-3 stimulation promoted IL-3Rα proteasomal degradation dependent on RNFT2, and we identified IL-3Rα lysine 357 as a ubiquitin acceptor site. We determined that LPS priming reduces RNFT2 abundance, extends IL-3Rα half-life, and sensitizes cells to the effects of IL-3, acting synergistically to increase proinflammatory signaling. In vivo, IL-3 synergized with LPS to exacerbate lung inflammation in LPS and Pseudomonas aeruginosa-challenged mice; conversely, IL-3 neutralization reduced LPS-induced lung injury. Further, RNFT2 overexpression reduced lung inflammation and injury, whereas Rnft2 knockdown exacerbated inflammatory responses in LPS-induced murine lung injury. Last, we examined RNFT2 and IL-3Rα in human lung explants from patients with cystic fibrosis and also showed that IL-3 is elevated in mechanically ventilated critically ill humans at risk for acute respiratory distress syndrome. These results identify RNFT2 as a negative regulator of IL-3Rα and show a potential role for the RNFT2/IL-3Rα/IL-3 axis in regulating innate immune responses in the lung.

The IFN gamma receptor 1 (IFNGR1) binds IFN-γ and activates gene transcription pathways crucial for controlling bacterial and viral infections. Although decreases in IFNGR1 surface levels have been demonstrated to inhibit IFN-γ signaling, little is known regarding the molecular mechanisms controlling receptor stability. Here, we show in epithelial and monocytic cell lines that IFNGR1 displays K48 polyubiquitination, is proteasomally degraded, and harbors three ubiquitin acceptor sites at K277, K279, and K285. Inhibition of glycogen synthase kinase 3 beta (GSK3β) destabilized IFNGR1 while overexpression of GSK3β increased receptor stability. We identified critical serine and threonine residues juxtaposed to ubiquitin acceptor sites that impacted IFNGR1 stability. In CRISPR–Cas9 IFNGR1 generated knockout cell lines, cellular expression of IFNGR1 plasmids encoding ubiquitin acceptor site mutations demonstrated significantly impaired STAT1 phosphorylation and decreased STAT1-dependent gene induction. Thus, IFNGR1 undergoes rapid site-specific polyubiquitination, a process modulated by GSK3β. Ubiquitination appears to be necessary for efficient IFNGR1-dependent gamma gene induction and represents a relatively uncharacterized regulatory mechanism for this receptor.

The receptor for advanced glycation end products (RAGE) is a highly expressed cell membrane receptor serving to anchor lung epithelia to matrix components, and it also amplifies inflammatory signaling during acute lung injury. However, mechanisms that regulate its protein concentrations in cells remain largely unknown. Here we show that RAGE exhibits an extended life span in lung epithelia (t½ 6 h), is monoubiquitinated at K374, and is degraded in lysosomes. The RAGE ligand ODN2006, a synthetic oligodeoxynucleotide resembling pathogenic hypomethylated CpG DNA, promotes rapid lysosomal RAGE degradation through activation of protein kinase Cζ (PKCζ), which phosphorylates RAGE. PKCζ overexpression enhances RAGE degradation, while PKCζ knockdown stabilizes RAGE protein levels and prevents ODN2006-mediated degradation. We identify that RAGE is targeted by the ubiquitin E3 ligase subunit F-box protein O10 (FBXO10), which associates with RAGE to mediate its ubiquitination and degradation. FBXO10 depletion in cells stabilizes RAGE and is required for ODN2006-mediated degradation. These data suggest that modulation of regulators involved in ubiquitin-mediated disposal of RAGE might serve as unique molecular inputs directing RAGE cellular concentrations and downstream responses, which are critical in an array of inflammatory disorders, including acute lung injury.—Evankovich, J., Lear, T., Mckelvey, A., Dunn, S., Londino, J., Liu, Y., Chen, B. B., Mallampalli, R. K. Receptor for advanced glycation end products is targeted by FBXO10 for ubiquitination and degradation.

Background Ubiquitination is a common post-translational modification, tagging proteins for degradation. The ubiquitin proteasome system is activated in Crohn’s Disease (CD), and modulation of its components might be a novel strategy for therapeutic intervention to control inflammation. The conjugation of ubiquitin to a target protein is orchestrated by a series of enzymatic reactions, the last step being catalyzed by a selective ubiquitin E3 ligase. Among ubiquitin E3 ligases, Fbxl2 serves as a sentinel gatekeeper to limit inflammation by targeting and enhancing the degradation of tumor necrosis factor receptor associated factors (TRAF) proteins, which link cell surface signals (through NFkB signaling) to cytokine secretion. In addition, Fbxl2 controls the ubiquitination of the inflammasome, NOD-like receptor protein 3 (NLRP3), which mediates the release of interleukin (IL)1β and IL18 (Fig.1). Fbxl2 protein itself is ubiquitinated and degraded by another protein, called Fbxo3. Inhibition of Fbxo3 results in increased Fbxl2 levels and decreased TRAF and NLRP3. Individuals with a natural occurring polymorphism within Fbxo3V221Ihave decreased lipopolysaccharide(LPS)-induced cytokine (TNFα, IL1β & IL6) production, Fbxo3 and TRAF levels and increased Fbxl2, providing human genetic target validation for Fbxo3-Fbxl2 axis modulation in inflammatory conditions. BC1261 is a first-in-class, selective, orally available Fbxo3 inhibitor in clinical development for the treatment of CD. Methods and Results In vitro data demonstrated that BC1261 binds to Fbxo3, prevents Fbxo3/Fbxl2 association and produces a concentration-dependent inhibition of LPS-induced release of TNFα and IL1β from human peripheral blood mononuclear cells. In an acute DSS-mouse model, administration of BC-1261 via drinking water ad libitum (30 μg/ml) or by daily intraperitoneal (IP) injection (150 μg) for 5 days resulted in the attenuation of the shortening of colonic length, tissue damage (Fig2.A), and TNFα and IL6 tissue levels (Fig.2B). In a repeated DSS-mouse model, BC-1261 (10 mg/kg bid) given orally for 19 days was comparable to the positive control (anti-p40) in the DAI composite (Fig2.C), stool consistency (Fig2.D), and histopathology score in the proximal colon (Fig2.E). BC-1261 also lead to clinically relevant reductions on endoscopy score (Fig2.F). Conclusion BC1261, a Fbxo3 inhibitor, was efficacious in both acute and chronic preclinical models of colitis. Taken together, these results suggest the potential utility of selective Fbxo3-Fbxl2 modulation in the treatment of CD.

Dysregulated proinflammatory cytokine release has been implicated in the pathogenesis of several life-threatening acute lung illnesses such as pneumonia, sepsis, and acute respiratory distress syndrome. Suppressors of cytokine signaling proteins, particularly SOCS2, have recently been described as antiinflammatory mediators. However, the regulation of SOCS2 protein has not been described. Here we describe a mechanism of SOCS2 regulation by the action of the ubiquitin E3 ligase KIAA0317. KIAA0317-mediated degradation of SOCS2 exacerbated inflammation in vitro, and depletion of KIAA0317 in vivo ameliorated pulmonary inflammation. KIAA0317-knockout mice exhibited resistance to LPS-induced pulmonary inflammation, while KIAA03017 reexpression mitigated this effect. We uncovered a small molecule inhibitor of KIAA0317 protein (BC-1365) that prevented SOCS2 degradation and attenuated LPS- and P. aeruginosa-induced lung inflammation in vivo. These studies show KIAA0317 to be a critical mediator of pulmonary inflammation through its degradation of SOCS2 and a potential candidate target for therapeutic inhibition.

Nutrient sensing is a critical cellular process controlling metabolism and signaling. mTOR complex 1 (mTORC1) is the primary signaling hub for nutrient sensing and, when activated, stimulates anabolic processes while decreasing autophagic flux. mTORC1 receives nutrient status signals from intracellular amino acid sensors. One of these sensors, Sestrin-2, functions as an intracellular sensor of cytosolic leucine and inhibitor of mTORC1 activity. Genetic studies of Sestrin-2 have confirmed its critical role in regulating mTORC1 activity, especially in the case of leucine starvation. Sestrin-2 is known to be transcriptionally controlled by several mechanisms; however, the post-translational proteolytic regulation of Sestrin-2 remains unclear. Here, we explored how Sestrin-2 is regulated through the ubiquitin proteasome system. Using an unbiased screening approach of an siRNA library targeting ubiquitin E3 ligases, we identified a RING-type E3 ligase, ring finger protein 186 (RNF186), that critically mediates the Sestrin-2 ubiquitination and degradation. We observed that RNF186 and Sestrin-2 bind each other through distinct C-terminal motifs and that Lys-13 in Sestrin-2 is a putative ubiquitin acceptor site. RNF186 knockdown increased Sestrin-2 protein levels and decreased mTORC1 activation. These results reveal a new mechanism of E3 ligase control of mTORC1 activity through the RNF186-Sestrin-2 axis, suggesting that RNF186 inhibition may be a potential strategy to increase levels of the mTORC1 inhibitor Sestrin-2.

As an α-chemokine receptor specific for stromal-derived-factor-1 (SDF-1, also called CXCL12), C-X-C chemokine receptor type 4 (CXCR4) plays a vital role in chemotactically attracting lymphocytes during inflammation. CXCR4 also regulates HIV infection due to its role as one of the chemokine coreceptors for HIV entry into CD4+T cells. Chemokine receptors and their signaling pathways have been shown to be regulated by the process of ubiquitination, a posttranslational modification, guided by ubiquitin E3 ligases, which covalently links ubiquitin chains to lysine residues within target substrates. Here we describe a novel mechanism regulating CXCR4 protein levels and subsequent CXCR4/CXCL12 signaling pathway through the ubiquitination and degradation of the receptor in response to ligand stimulation. We identify that an uncharacterized really interesting new gene (RING) finger ubiquitin E3 ligase, RING finger protein 113A (RNF113A), directly ubiquitinates CXCR4 in cells, leading to CXCR4 degradation, and therefore disrupts the signaling cascade. We determined that the K331 residue within CXCR4 is essential for RNF113A-mediated ubiquitin conjugation. Overexpression of RNF113A significantly reduces CXCL12-induced kinase activation in HeLa cells, whereas RNF113A knockdown enhances CXCL12-induced downstream signaling. Further, RNF113A expression and silencing directly affect cell motility in a wound healing assay. These results suggest that RNF113A plays an important role in CXCR4 signaling through the ubiquitination and degradation of CXCR4. This mechanistic study might provide new understanding of HIV immunity and neutrophil activation and motility regulated by CXCR4.

Lear et al. report a novel molecular pathway in which Fibrosis Inducing E3 Ligase 1 (FIEL1) regulates TGFβ and fibrosis pathway through SUMO-E3 ligase PIAS4. They also develop a small molecule inhibitor toward FIEL1 that is highly effective in ameliorating fibrosis in mice., The E3 small ubiquitin-like modifier (SUMO) protein ligase protein inhibitor of activated STAT 4 (PIAS4) is a pivotal protein in regulating the TGFβ pathway. In this study, we discovered a new protein isoform encoded by KIAA0317, termed fibrosis-inducing E3 ligase 1 (FIEL1), which potently stimulates the TGFβ signaling pathway through the site-specific ubiquitination of PIAS4. FIEL1 targets PIAS4 using a double locking mechanism that is facilitated by the kinases PKCζ and GSK3β. Specifically, PKCζ phosphorylation of PIAS4 and GSK3β phosphorylation of FIEL1 are both essential for the degradation of PIAS4. FIEL1 protein is highly expressed in lung tissues from patients with idiopathic pulmonary fibrosis (IPF), whereas PIAS4 protein levels are significantly reduced. FIEL1 overexpression significantly increases fibrosis in a bleomycin murine model, whereas FIEL1 knockdown attenuates fibrotic conditions. Further, we developed a first-in-class small molecule inhibitor toward FIEL1 that is highly effective in ameliorating fibrosis in mice. This study provides a basis for IPF therapeutic intervention by modulating PIAS4 protein abundance.

The CARMA1/BCL10/MALT1 (CBM) signaling complex mediates antigen receptor-induced activation of NF-kB in lymphocytes to support normal adaptive immunity. As the effector protein of the complex, MALT1 exhibits two activities: protease and scaffolding activities. Gain-of-function mutations in the CARMA1 moiety or its upstream regulators trigger antigen-independent assembly of oligomeric CBM complexes, leading to constitutive activation of MALT1, unregulated NF-kB activity, and development of Activated B-Cell subtype of Diffuse Large B-Cell Lymphoma (ABC-DLBCL). Existing MALT1 inhibitors block only MALT1 protease activity, causing incomplete and unbalanced inhibition of MALT1, and have the potential for inducing autoimmune side effects. Since MALT1 is recruited to the CBM complex via its interaction with BCL10, we sought to identify inhibitors of BCL10-MALT1 interaction in order to target both the protease and scaffolding activities of MALT1 to treat ABC-DLBCL. Our previous work suggested that an antibody-epitope-like interface governs the interaction between BCL10 and MALT1, so that a therapeutic opportunity exists for developing a small molecule inhibitor of the interaction to terminate inappropriate CBM activity. Using co-immunoprecipitation studies, a mammalian two-hybrid system, and surface plasmon resonance (SPR), we confirmed that BCL10 residues 107-119 and the tandem Ig-like domains of MALT1 are critical for this interaction. We then performed a structure-guided in silico screen of 3 million compounds, based on a computational model of the BCL10-MALT1 interaction interface, to identify compounds with potential for disrupting the interaction. Compound 1 from the initial screening hits showed dose-responsive inhibition of BCL10-MALT1 interaction in both SPR and ELISA-based assays. Functionally, Compound 1 inhibits both MALT1 protease and scaffolding activities in Jurkat T cells, as demonstrated by its inhibition of CD3/CD28-induced RelB and N4BP1 cleavage, and inhibition of IKK phosphorylation, respectively. Compound 1 also blocks IL-2 transcription and IL-2 secretion by PMA/ionomycin-treated Jurkat T cells, as well as constitutive CBM-dependent secretion of IL-6 and IL-10 by ABC-DLBCL cells. Accordingly, Compound 1 selectively suppresses the growth of ABC-DLBCL cell lines, but does not affect the growth of MALT1-independent GCB-DLBCL cell lines. In conclusion, we have identified an early-stage small molecule compound that inhibits the BCL10-MALT1 interaction, MALT1 protease and scaffolding activities, downstream CBM-dependent signaling, and ABC-DLBCL cell growth. Structure-guided modification of this lead compound is underway to further develop a new class of protein-protein interaction inhibitors that could provide more efficacious blockade of MALT1, while offering protection from undesirable autoimmune side effects in the treatment of this aggressive form of lymphoma. Citation Format: Heejae Kang, Dong Hu, Marcelo Murai, Ahmed Mady, Bill Chen, Zaneta Nikolovska-Coleska, Linda M. McAllister-Lucas, Peter C. Lucas. Inhibition of BCL10-MALT1 interaction to treat diffuse large B-cell lymphoma [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 3404.

The pathogenetic heterogeneity of pulmonary fibrosis yields both challenges and opportunities for therapy. Its complexity implicates a variety of cellular processes, signaling pathways, and genetics as drivers of disease. TGF-β stimulation is one avenue, and is central to pro-fibrotic protein expression, leading to decreased pulmonary function. Here we report our recent findings, introducing the E3 ligase Fibrosis Inducing E3 Ligase 1 (FIEL1) as an important regulator of TGF-β signaling through the selective degradation of PIAS4. FIEL1 exacerbates bleomycin-induced murine pulmonary fibrosis, while its silencing attenuates the fibrotic phenotype. Further, we developed a small molecule inhibitor of FIEL1 (BC-1485) that inhibits the degradation of PIAS4, and ameliorates fibrosis in murine models. New understanding of this pathway illustrates the many targeting opportunities among the complexity of pulmonary fibrosis in the continuing search for therapy.

Inflammation is critical in the pathobiology of atherosclerosis. An essential player in the inflammatory process in atherosclerosis are macrophages that scavenge oxidatively modified low-density lipoproteins (OxLDL) deposited in the subendothelium of systemic arteries that secrete a myriad of pro-inflammatory mediators. Here, we identified that a subunit of the Skp-Cullin-F-box ubiquitin E3 ligase apparatus, termed FBXO3, modulates the inflammatory response in atherosclerosis. Specifically, individuals with a hypofunctioning genetic variant of FBXO3 develop less atherosclerosis. FBXO3 protein is present in cells of monocytic lineage within carotid plaques and its levels increase in those with symptomatic compared with asymptomatic atherosclerosis. Further, cellular depletion or small molecule inhibition of FBXO3 significantly reduced the inflammatory response to OxLDL by macrophages without altering OxLDL uptake. Thus, FBXO3 potentiates vascular inflammation and atherosclerosis that can be effectively mitigated by a small molecule inhibitor.