Cullin Research Articles

PRAMEL7 and CUL2 decrease NuRD stability to establish ground-state pluripotency

Pluripotency is established in E4.5 preimplantation epiblast. Embryonic stem cells (ESCs) represent the immortalization of pluripotency, however, their gene expression signature only partially resembles that of developmental ground-state. Induced PRAMEL7 expression, a protein highly expressed in the ICM but lowly expressed in ESCs, reprograms developmentally advanced ESC+serum into ground-state pluripotency by inducing a gene expression signature close to developmental ground-state. However, how PRAMEL7 reprograms gene expression remains elusive. Here we show that PRAMEL7 associates with Cullin2 (CUL2) and this interaction is required to establish ground-state gene expression. PRAMEL7 recruits CUL2 to chromatin and targets regulators of repressive chromatin, including the NuRD complex, for proteasomal degradation. PRAMEL7 antagonizes NuRD-mediated repression of genes implicated in pluripotency by decreasing NuRD stability and promoter association in a CUL2-dependent manner. Our data link proteasome degradation pathways to ground-state gene expression, offering insights to generate in vitro models to reproduce the in vivo ground-state pluripotency.

Cullin5 drives experimental asthma exacerbations by modulating alveolar macrophage antiviral immunity

Asthma exacerbations caused by respiratory viral infections are a serious global health problem. Impaired antiviral immunity is thought to contribute to the pathogenesis, but the underlying mechanisms remain understudied. Here using mouse models we find that Cullin5 (CUL5), a key component of Cullin-RING E3 ubiquitin ligase 5, is upregulated and associated with increased neutrophil count and influenza-induced exacerbations of house dust mite-induced asthma. By contrast, CUL5 deficiency mitigates neutrophilic lung inflammation and asthma exacerbations by augmenting IFN-β production. Mechanistically, following thymic stromal lymphopoietin stimulation, CUL5 interacts with O-GlcNAc transferase (OGT) and induces Lys48-linked polyubiquitination of OGT, blocking the effect of OGT on mitochondrial antiviral-signaling protein O-GlcNAcylation and RIG-I signaling activation. Our results thus suggest that, in mouse models, pre-existing allergic injury induces CUL5 expression, impairing antiviral immunity and promoting neutrophilic inflammation for asthma exacerbations. Targeting of the CUL5/IFN-β signaling axis may thereby serve as a possible therapy for treating asthma exacerbations.

CAND1 inhibits Cullin-2-RING ubiquitin ligases for enhanced substrate specificity.

Through targeting essential cellular regulators for ubiquitination and serving as a major platform for discovering proteolysis-targeting chimera (PROTAC) drugs, Cullin-2 (CUL2)-RING ubiquitin ligases (CRL2s) comprise an important family of CRLs. The founding members of CRLs, the CUL1-based CRL1s, are known to be activated by CAND1, which exchanges the variable substrate receptors associated with the common CUL1 core and promotes the dynamic assembly of CRL1s. Here we find that CAND1 inhibits CRL2-mediated protein degradation in human cells. This effect arises due to altered binding kinetics, involving CAND1 and CRL2VHL, as we illustrate that CAND1 dramatically increases the dissociation rate of CRL2s but barely accelerates the assembly of stable CRL2s. Using PROTACs that differently recruit neo-substrates to CRL2VHL, we demonstrate that the inhibitory effect of CAND1 helps distinguish target proteins with different affinities for CRL2s, presenting a mechanism for selective protein degradation with proper pacing in the changing cellular environment.

Targeted regulation of miR-154-5p/Cullin2 pathway by hsa_circ_TRIM22 in promoting human papillomavirus 16 positive cervical cancer progression.

Background. Tripartite motif-containing 22 (TRIM22) is characterized by a canonical RING domain with ubiquitin E3 ligase activity and is closely associated with tumorigenesis. As a product of TRIM22 transcription, whether hsa_circ_TRIM22 has a function of regulating tumorigenesis is unclear. Thus, we aimed to explore the role and mechanism of hsa_circ_TRIM22 in human papillomavirus (HPV) 16 positive cervical cancer (CC). Methods. We collected HPV16-positive cervical tissues including chronic cervicitis, high-grade squamous intraepithelial lesions (HSIL), low-grade squamous intraepithelial lesions (LSIL), and CC, and along with CC cell lines to detect the hsa_circ_TRIM22 level using real-time fluorescence quantitative polymerase chain reaction (RT-qPCR). Hsa_circ_TRIM22 was silenced using specific short hairpin ribonucleic acid (shRNA) in CC cell lines and functional assays were performed thereafter. Mechanistically, the targeting and regulatory relationship between hsa_circ_TRIM22 and miR-154-5p were confirmed using the luciferase report assay and rescue experiments. Results. We found hsa_circ_TRIM22 expression level was significantly higher in CC cells and tissues. Further, hsa_circ_TRIM22 knockdown inhibited migration, proliferation, invasiveness, enhanced apoptosis, and slowed the cell cycle. Mechanistically, hsa_circ_TRIM22 could bind miR-154-5p and prevent miR-154-5p from reducing the levels of Cullin2 (CUL2). Notably, the application of miR-154-5p inhibitor significantly rescued hsa_circ_TRIM22-mediated tumorigenesis. Conclusions. Our observations suggest hsa_circ_TRIM22 is upregulated in HPV16-positive CC and promotes CC progression by regulating the miR-154-5p/CUL2 axis, thereby serving as a promising candidate for diagnosis and treatments of CC.

Investigation of cullin-3 gene expression changes in people with colorectal cancer and polyps in China.

Colorectal cancer (CRC) is one of the most common fatal malignancies caused by environmental and genetic factors. Considering the increasing frequency of CRC worldwide, especially in China, the importance of research on CRC is more widely defined. A recent study focused on molecular pathways involved in colon cancer carcinogenesis to improve cancer diagnosis and treatment to identify new biomarkers. Colon cancer is the result of dysplasia in primary growths of the intestine, known as polyps. These early growths are unknown and different in terms of morphology, molecular mechanisms, and the ability to cause colon cancer. This study aims to investigate the expression level of the CUL3 gene in polyps and colorectal cancer. This cross-sectional study collected 300 colorectal tissue biopsy samples, including 40 tumor tissue samples, 73 precancerous lesions with their adjacent tissue, and 31 normal tissue samples. The expression of the CUL3 gene was investigated by the Real-time PCR method. There was no significant difference in CUL3 mRNA expression between polyp tissues and their adjacent samples (p = 0.41). Our results showed no statistically significant difference in CUL3 gene expression between tumor tissues and their adjacent thermal samples (p = 0.78) and between tumor and polyp groups (p = 0.53). CUL3 may play an essential role in regulating cancer and CRC progression by stimulating the proteasomal degradation of various tumor suppressors or oncogenes. Studies on the effective substrates of CUL3 in colorectal cancer are essential.

Abstract B140: Elucidating the novel mechanism of action of VVD-065, an allosteric molecular glue for the KEAP1-CUL3 E3-ligase complex that promotes NRF2 degradation in NRF2-activated cancers

Abstract Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that plays a crucial role in various NRF2-dependent cancers. The protein levels of NRF2 are tightly controlled by a specific E3 ligase complex composed of Kelch-like ECH Associated Protein 1 (KEAP1), Cullin 3 (CUL3), and RING-box protein 1 (RBX1). Under normal conditions, KEAP1 acts as an oxidative sensor and facilitates the ubiquitination and subsequent degradation of NRF2. However, during oxidative or electrophilic stress, KEAP1 can be inactivated through covalent modification of sensor cysteine residues, allowing NRF2 levels to increase and regulate NRF2-dependent genes. In this study, we have elucidated a novel mechanism-of-action for a first-in-class NRF2 inhibitor, VVD-065. Through biochemical and biophysical investigations, we have discovered that VVD-065 functions by covalently interacting with KEAP1 at a sensor cysteine residue, but surprisingly this interaction results in an enhanced affinity between KEAP1 and CUL3, and an increased capacity for Keap1 mediated NRF2 degradation. High-resolution co-crystal structures have revealed that binding of VVD-065 allosterically induces a conformational change that mimics the conformation of KEAP1 when in complex with CUL3. By targeting the KEAP1-CUL3 interaction and promoting the degradation of NRF2, VVD-065 offers a means to modulate NRF2 levels in NRF2-dependent cancers. The unprecedented mechanism of action exhibited by VVD-065 has been confirmed through in vitro and in vivo studies, paving the way for the development of a clinically relevant Keap1 activator. Citation Format: Aaron Snead, Steffen Bernard, Kenneth Hee, Eileen Tran, Sarah Jacinto, Nil Roy, Tine Wyseure, Jonathan Pollock, Gabe Simon, Todd Kinsella, David Weinstein, Matt Patricelli. Elucidating the novel mechanism of action of VVD-065, an allosteric molecular glue for the KEAP1-CUL3 E3-ligase complex that promotes NRF2 degradation in NRF2-activated cancers [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B140.

DTL is a Novel Downstream Gene of E2F1 that Promotes the Progression of Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC), one of the world's most prevalent malignancies, accounts for 90% of primary liver cancer cases. Recent studies have shown an increased expression of denticles E3 ubiquitin protein ligase homolog (DTL) in several different tumor types, but its function and regulatory mechanisms remain unclear. This study aimed to investigate the expressions of the Cullin4 (CUL4) complex in HCC and elucidate the roles of DTL in HCC cells. The relative expression of the CUL4 complex and its clinical significance were analyzed with The Cancer Genome Atlas (TCGA) data, and the level of DTL was confirmed by immunohistochemistry. The functions of DTL1 and upstream E2F1 were evaluated by a Western blot, MTT, transwell, and xenograft in HCC cell lines. The elevated mRNA expression of the CUL4 complex, including CUL4B, DDB1 (Damage Specific DNA Binding Protein 1), and DTL, was associated with the overall survival of HCC patients. We also found that the DTL protein was elevated in HCC tissues, and patients with highly expressed DTL and nucleus-located DTL had a poorer survival time. DTL knockdown significantly inhibited cancer proliferation, migration, and invasion. Further experiments showed that E2F1 was an upstream regulatory molecule of DTL, which was bound to the promoter of DTL, promoting the expression of DTL. The study results demonstrate that E2F1-DTL signaling promotes the growth, migration, and invasion of HCC cells, which provides new insights and a potential biological target for future HCC therapies.

BCLAF1-induced HIF-1α accumulation under normoxia enhances PD-L1 treatment resistances via BCLAF1-CUL3 complex

Bcl-2-associated transcription factor-1 (BCLAF1), an apoptosis-regulating protein of paramount significance, orchestrates the progression of various malignancies. This study reveals increased BCLAF1 expression in hepatocellular carcinoma (HCC) patients, in whom elevated BCLAF1 levels are linked to escalated tumor grades and diminished survival rates. Moreover, novel BCLAF1 expression is particularly increased in HCC patients who were not sensitive to the combined treatment of atezolizumab and bevacizumab, but not in patients who had tumors that responded to the combined regimen. Notably, overexpression of BCLAF1 increases HCC cell proliferation in vitro and in vivo, while the conditioned medium derived from cells overexpressing BCLAF1 strikingly enhances the tube-formation capacity of human umbilical vein endothelial cells. Furthermore, compelling evidence demonstrates that BCLAF1 attenuates the expression of prolyl hydroxylase domain protein 2 (PHD2) and governs the stability of hypoxia-inducible factor-1α (HIF-1α) under normoxic conditions without exerting any influence on transcription, as determined by Western blot and RT‒qPCR analyses. Subsequently, employing coimmunoprecipitation and immunofluorescence, we validated the reciprocal interaction between BCLAF1 and Cullin 3 (CUL3), through which BCLAF1 actively upregulates the ubiquitination and degradation of PHD2. The Western blot and RT‒qPCR results suggests that programmed death ligand-1 (PD-L1) is one of the downstream responders to HIF-1α in HCC. Thus, we reveal the pivotal role of BCLAF1 in promoting PD-L1 transcription and, through binding to CUL3, in promoting the accumulation of HIF-1α under normoxic conditions, thereby facilitating the ubiquitination and degradation of PHD2.

Autophagy gene-dependent intracellular immunity triggered by interferon-γ.

Interferon-γ (IFNγ) is a critical mediator of cell-intrinsic immunity to intracellular pathogens. Understanding the complex cellular mechanisms supporting robust interferon-γ-induced host defenses could aid in developing new therapeutics to treat infections. Here, we examined the impact of autophagy genes in the interferon-γ-induced host response. We demonstrate that genes within the autophagy pathway including Wipi2, Atg9, and Gate-16, as well as ubiquitin ligase complex genes Cul3 and Klhl9 are required for IFNγ-induced inhibition of murine norovirus (norovirus hereinafter) replication in mouse cells. WIPI2 and GATE-16 were also required for IFNγ-mediated restriction of parasite growth within the Toxoplasma gondii parasitophorous vacuole in human cells. Furthermore, we found that perturbation of UFMylation pathway components led to more robust IFNγ-induced inhibition of norovirus via regulation of endoplasmic reticulum (ER) stress. Enhancing or inhibiting these dynamic cellular components could serve as a strategy to control intracellular pathogens and maintain an effective immune response.

THU598 Pseudohypoaldosteronism Type 2: A New Variant Of A Rare Disease

Abstract Disclosure: T.L. Cater: None. L. Borges Espinosa: None. Introduction: Familial hyperkalemia and hypertension syndrome or pseudohypoaldosteronism type 2 (PH2) is a rare monogenic hypertension resulting from WNK1, WNK4, KLHL3, or CUL3 gene mutation. Subsequent interference at the Na-Cl co-symporter, epithelial Na, or ROMK channel results in metabolic acidosis, hyperkalemia, and hypertension responsive to thiazide treatment. This case demonstrates PH2 resulting from a KLHL3 gene variant not previously described. Mutations to KLHL3 decrease Na-Cl cotransporter expression in the distal convoluted tubule leading to increased sodium and chloride reabsorption, volume expansion, hypertension, and, therefore, less sodium available for potassium exchange in the collecting duct. Case Description: A 30-year-old female G1P0 with twin gestation was admitted at 33 weeks for preeclampsia with severe features. PMH was unremarkable. She underwent C-section and was discharged home with healthy twin daughters. BMP during admission showed hyperkalemia with peak potassium 5.2 mmol/L which improved to 4.6 mmol/L by discharge. Essential hypertension was diagnosed 3 months later (BP 130/90, 78 bpm, RR 16, BMI 30.0 kg/m2). Labetalol 50 mg BID was initiated. BMP obtained showed hyperkalemia as high as 6.4 mmol/L. Further workup showed undetectable renin with normal aldosterone, hyperchloremic metabolic acidosis with chloride 111 mmol/L and bicarbonate 20 mmol/L, and normal EKG. She was managed in the ED where her potassium improved to 5.1 mmol/L with persistent hyperchloremic metabolic acidosis. A diagnosis of pseudohyperkalemia was presumed initially. Labetalol was discontinued in favor of hydrochlorothiazide 12.5 mg daily. Lost to follow-up, she presented 10 years later to Endocrinology at age 41 for chronic hyperkalemia and hyperchloremic metabolic acidosis. Labs showed potassium 6.5 mmol/L, chloride 108 mmol/L, and bicarbonate 23 mmol/L. Exam showed BP 133/98, BMI 26.63 kg/m2. She recounted several ER visits over the past decade for hyperkalemia with highest reported potassium of 7.8. She had stopped her thiazide due to dizziness, palpitations, and fatigue. Family history was now notable for hyperkalemia in her father, two brothers, and fraternal niece but no genetic testing was available. We resumed hydrochlorothiazide 12.5 mg every other day; follow-up labs showed improved potassium 5.2 mmol/L. Genetic testing revealed heterozygosity in the KLHL3 gene for the c.1064T &gt G sequence, a variant that has not been reported in the literature or large population database. Conclusion: Hypertension in PH2, distinct in its presentation with hyperkalemia and metabolic acidosis, requires a detailed family history and hormonal evaluation to make the diagnosis. Genetic testing in our case patient revealed a variant at the KLHL3 gene not previously described, underscoring the utility of genetic testing in understanding this rare condition. Presentation: Thursday, June 15, 2023

Pulse-SILAC and Interactomics Reveal Distinct DDB1-CUL4–Associated Factors, Cellular Functions, and Protein Substrates

Cullin-RING finger ligases represent the largest family of ubiquitin ligases. They are responsible for the ubiquitination of ∼20% of cellular proteins degraded through the proteasome, by catalyzing the transfer of E2-loaded ubiquitin to a substrate. Seven cullins are described in vertebrates. Among them, cullin 4 (CUL4) associates with DNA damage–binding protein 1 (DDB1) to form the CUL4–DDB1 ubiquitin ligase complex, which is involved in protein ubiquitination and in the regulation of many cellular processes. Substrate recognition adaptors named DDB1/CUL4-associated factors (DCAFs) mediate the specificity of CUL4-DDB1 and have a short structural motif of approximately forty amino acids terminating in tryptophan (W)-aspartic acid (D) dipeptide, called the WD40 domain. Using different approaches (bioinformatics/structural analyses), independent studies suggested that at least sixty WD40–containing proteins could act as adaptors for the DDB1/CUL4 complex. To better define this association and classification, the interaction of each DCAFs with DDB1 was determined, and new partners and potential substrates were identified. Using BioID and affinity purification–mass spectrometry approaches, we demonstrated that seven WD40 proteins can be considered DCAFs with a high confidence level. Identifying protein interactions does not always lead to identifying protein substrates for E3-ubiquitin ligases, so we measured changes in protein stability or degradation by pulse-stable isotope labeling with amino acids in cell culture to identify changes in protein degradation, following the expression of each DCAF. In conclusion, these results provide new insights into the roles of DCAFs in regulating the activity of the DDB1–CUL4 complex, in protein targeting, and characterized the cellular processes involved.

Abstract 084: Smooth Muscle Cullin-3 Regulates The Renal Baroreceptor Mechanism Via Lamin AC

Cullin-3 (CUL3) is a critical component of the CUL3-Ring-Ligase (CRL) ubiquitin ligase complex. Patients carrying mutations in CUL3 exhibit early onset of hypertension (HTN). We demonstrated that conditional ablation of CUL3 in vascular smooth muscle cells (VSMCs) results in vascular dysfunction, arterial stiffness, and severe HTN in mice. We hypothesized that 1) conditional deletion of CUL3 in VSMCs (S-CUL3KO) results in severe HTN via the renin-angiotensin system (RAS)-dependent mechanism, and 2) S-CUL3KO mice exhibit an impaired baroreceptor mechanism regulating renin. Mice carrying a conditional allele of CUL3 were bred with mice expressing a tamoxifen-inducible CRE-recombinase driven by a smooth muscle promoter (ISM-CRE, control). S-CUL3KO mice exhibited elevated systolic blood pressure (SBP) 3 weeks after tamoxifen administration (S-CUL3KO: 164±1 vs. ISM-CRE: 124±4 mmHg, p<0.05). To test the first hypothesis captopril or candesartan (10 mg/kg/day and 100 mg/kg/day in drinking water, respectively) were administered to S-CUL3KO once severe HTN was already established. Captopril or candesartan treatment for 1 week reversed elevated SBP to 117±4 mmHg (p<0.05) and 127±2 mmHg (p<0.05), respectively, in S-CUL3KO. Despite the severity of HTN in S-CUL3KO, the level of renin mRNA in the kidney was surprisingly unaltered (p>0.05) when compared to the normotensive control mice. The protein expression of lamin AC, a crucial component of the nuclear mechanotransducer controlling renin expression, was significantly increased in S-CUL3KO kidneys (0.11±0.02 vs. 0.05±0.01 normalized RFU, p<0.05). This suggests lamin AC may be a target protein of CUL3-ubiquitin ligase complex. Supporting this concept, treatment of A10 smooth muscle cells with MLN4914, an inhibitor of the Cullin pathway, results in a 2-fold increase in lamin AC expression (0.007±0.001 vs. 0.0154±0.0004, normalized RFU, p<0.05). Furthermore, co-immunoprecipitation of CUL3 in HEK293 cells immunoprecipitated lamin AC. Our findings support the hypothesis that 1) CUL3 regulates RAS via the renal baroreceptor mechanism and 2) lamin AC is a potential target of the CRL3-mediated regulation. Understanding CUL3 target proteins might help the development of new strategies to mitigate HTN.

Abstract 119: Exploring The Role Of Rho-related BTB Domain Containing 1(RhoBTB1) And Phosphodiesterase 5(PDE5) To Identify Potential Proteomic Targets In Cardiovascular Function

The study of macromolecular (protein:protein) interactions has significantly enhanced our comprehension of human impairments, such as cardiovascular diseases (CVDs). We previously identified that RhoBTB1 acts as a key regulator of vascular tone by associating with Cullin-3 (CUL3) to control the activity of phosphodiesterase 5 (PDE5) through the ubiquitination-proteasomal pathway. PDE5 selectively hydrolyzes cGMP thus regulating NO-mediated vasodilation. We hypothesized that the PDE5 binding region on RhoBTB1 could be responsible for binding to other unknown partners in RhoBTB1-CUL3 pathway. We truncated RhoBTB1 into its component domains individually (GTPase, BTB1, BTB2, and CT) and in combination (B1B2C, PB1B2, and B2C) and studied their interaction with PDE5 by co-immunoprecipitation (co-IP) in HEK293 cells. These analyses revealed that the B1B2C domain of RhoBTB1 is the minimal region required to bind PDE5. Interestingly, the CT region is essential as the truncations lacking CT could not participate in PDE5 binding and its subsequent proteasomal degradation. The GTPase and Proline-rich (P) domains were dispensable for binding of RhoBTB1 to PDE5. We identified that Pro 353 and Ser 363 are key amino acid residues in the B1B2C region involved in CUL3 binding to RhoBTB1. Mutation of these amino acids resulted in hampered binding to CUL3. The mutants failed to degrade PDE5 despite their preserved binding to PDE5. We employed ascorbate peroxidase (APEX2) labeling using a B1B2C-APEX2 fusion construct as a bait to identify unknown RhoBTB1 binding partners. As a contemporaneous screen, we used B1B2-APEX2 since it does not bind to PDE5, and therefore is not expected to bind to those unknown partners. We “filtered” the captured proteome for its interaction with B1B2C better than B1B2 (without the CT). SET Domain Containing 2 (SETD2) was among several B1B2C binding partners identified and validated. SETD2 and RhoBTB1 directly interacted, and the level of SETD2 increased in response to RhoBTB1-inhibition with siRNA, inhibition of proteasomal machinery either by pharmacological means or CUL3 editing. This suggests that SETD2 is regulated by the RhoBTB1-CUL3 axis. Future studies may pave a way to determine if SETD2 is important for cardiovascular function.

Chinese patients with 3M syndrome: clinical manifestations and two novel pathogenic variants.

Background: 3M syndrome is a rare autosomal recessive disease, characterized by intrauterine and postnatal growth retardation, facial dysmorphism, large head circumference, and skeletal changes, has rarely been reported in the Chinese population. Methods: We describe the clinical manifestations and gene variants in four sporadic cases of 3M syndrome in Chinese individuals from different families. Results: All cases had significant growth retardation, relative macrocephaly, and typical facial features. Exome sequencing revealed that two patients with 3M syndrome had homozygous variants of the CUL7 gene: one novel pathogenic variant and one previously reported pathogenic variant; the other two patients were heterozygous for variants in OBSL1, one of which had not been reported previously. Clinical evaluation indicated that these Chinese patients with 3M syndrome shared similar recognizable features with those reported in patients of other ethnic backgrounds, but not all patients with 3M syndrome in this study had normal development milestones. Two patients underwent recombinant human growth hormone (rhGH) therapy and showed accelerated growth in the first 2years; however, the growth rate slowed in the third year in one case. There were no obvious adverse reactions during rhGH treatment. Conclusion: We report one novel CUL7 and one novel OBSL1 mutation in patients with 3M syndrome. Children with short stature, specific facial features, and physical symptoms should be referred for genetic testing to obtain precise diagnosis and appropriate treatment. The effects of rhGH treatment on adult height requires long-term observation and study in a large sample.

Structural basis of HIV-1 Vif-mediated E3 ligase targeting of host APOBEC3H

Human APOBEC3 (A3) cytidine deaminases are antiviral factors that are particularly potent against retroviruses. As a countermeasure, HIV-1 uses a viral infectivity factor (Vif) to target specific human A3s for proteasomal degradation. Vif recruits cellular transcription cofactor CBF-β and Cullin-5 (CUL5) RING E3 ubiquitin ligase to bind different A3s distinctively, but how this is accomplished remains unclear in the absence of the atomic structure of the complex. Here, we present the cryo-EM structures of HIV-1 Vif in complex with human A3H, CBF-β and components of CUL5 ubiquitin ligase (CUL5, ELOB, and ELOC). Vif nucleates the entire complex by directly binding four human proteins, A3H, CBF-β, CUL5, and ELOC. The structures reveal a large interface area between A3H and Vif, primarily mediated by an α-helical side of A3H and a five-stranded β-sheet of Vif. This A3H-Vif interface unveils the basis for sensitivity-modulating polymorphism of both proteins, including a previously reported gain-of-function mutation in Vif isolated from HIV/AIDS patients. Our structural and functional results provide insights into the remarkable interplay between HIV and humans and would inform development efforts for anti-HIV therapeutics.

LZTR1 deficiency exerts high metastatic potential by enhancing sensitivity to EMT induction and controlling KLHL12-mediated collagen secretion

Leucine zipper-like transcriptional regulator 1 (LZTR1), a substrate adaptor of Cullin 3 (CUL3)-based E3 ubiquitin ligase, regulates proteostasis of the RAS subfamily. Mutations in LZTR1 have been identified in patients with several types of cancer. However, the role of LZTR1 in tumor metastasis and the target molecules of LZTR1, excluding the RAS subfamily, are not clearly understood. Here, we show that LZTR1 deficiency increases tumor growth and metastasis. In lung adenocarcinoma cells, LZTR1 deficiency induced the accumulation of the RAS subfamily and enhanced cell proliferation, invasion, and xenograft tumor growth. Multi-omics analysis to clarify the pathways related to tumor progression showed that MAPK signaling, epithelial-mesenchymal transition (EMT), and extracellular matrix (ECM) remodeling-related gene ontology terms were enriched in LZTR1 knockout cells. Indeed, LZTR1 deficiency induced high expression of EMT markers under TGF-β1 treatment. Our search for novel substrates that interact with LZTR1 resulted in the discovery of a Kelch-like protein 12 (KLHL12), which is involved in collagen secretion. LZTR1 could inhibit KLHL12-mediated ubiquitination of SEC31A, a component of coat protein complex II (COPII), whereas LZTR1 deficiency promoted collagen secretion. LZTR1-RIT1 and LZTR1-KLHL12 worked independently regarding molecular interactions and did not directly interfere with each other. Further, we found that LZTR1 deficiency significantly increases lung metastasis and promotes ECM deposition around metastatic tumors. Since collagen-rich extracellular matrix act as pathways for migration and facilitate metastasis, increased expression of RAS and collagen deposition may exert synergistic or additive effects leading to tumor progression and metastasis. In conclusion, LZTR1 deficiency exerts high metastatic potential by enhancing sensitivity to EMT induction and promoting collagen secretion. The functional inhibition of KLHL12 by LZTR1 provides important evidence that LZTR1 may be a repressor of BTB-Kelch family members. These results provide clues to the mechanism of LZTR1-deficiency carcinogenesis.

Potential Role of Phytochromes A and B and Cryptochrome 1 in the Adaptation of Solanum lycopersicum to UV-B Radiation.

UV-B causes both damage to the photosynthetic apparatus (PA) and the activation of specific mechanisms that protect the PA from excess energy and trigger a cascade of regulatory interactions with different photoreceptors, including phytochromes (PHYs) and cryptochromes (CRYs). However, the role of photoreceptors in plants' responses to UV-B radiation remains undiscovered. This study explores some of these responses using tomato photoreceptor mutants (phya, phyb1, phyab2, cry1). The effects of UV-B exposure (12.3 µmol (photons) m-2 s-1) on photosynthetic rates and PSII photochemical activity, the contents of photosynthetic and UV-absorbing pigments and anthocyanins, and the nonenzymatic antioxidant capacity (TEAC) were studied. The expression of key light-signaling genes, including UV-B signaling and genes associated with the biosynthesis of chlorophylls, carotenoids, anthocyanins, and flavonoids, was also determined. Under UV-B, phyab2 and cry1 mutants demonstrated a reduction in the PSII effective quantum yield and photosynthetic rate, as well as a reduced value of TEAC. At the same time, UV-B irradiation led to a noticeable decrease in the expression of the ultraviolet-B receptor (UVR8), repressor of UV-B photomorphogenesis 2 (RUP2), cullin 4 (CUL4), anthocyanidin synthase (ANT), phenylalanine ammonia-lease (PAL), and phytochrome B2 (PHYB2) genes in phyab2 and RUP2, CUL4, ANT, PAL, and elongated hypocotyl 5 (HY5) genes in the cry1 mutant. The results indicate the mutual regulation of UVR8, PHYB2, and CRY1 photoreceptors, but not PHYB1 and PHYA, in the process of forming a response to UV-B irradiation in tomato.

Targeted kinase degradation via the KLHDC2 ubiquitin E3 ligase

Chemically induced protein degradation is a powerful strategy for perturbing cellular biochemistry. The predominant mechanism of action for protein degrader drugs involves an induced proximity between the cellular ubiquitin-conjugation machinery and a target. Unlike traditional small molecule enzyme inhibition, targeted protein degradation can clear an undesired protein from cells. We demonstrate here the use of peptide ligands for Kelch-like homology domain-containing protein 2 (KLHDC2), a substrate adapter protein and member of the cullin-2 (CUL2) ubiquitin ligase complex, for targeted protein degradation. Peptide-based bivalent compounds that can induce proximity between KLHDC2 and target proteins cause degradation of the targeted factors. The cellular activity of these compounds depends on KLHDC2 binding. This work demonstrates the utility of KLHDC2 for targeted protein degradation and exemplifies a strategy for the rational design of peptide-based ligands useful for this purpose.

Deficiency of Cullin 3, a Protein Encoded by a Schizophrenia and Autism Risk Gene, Impairs Behaviors by Enhancing the Excitability of Ventral Tegmental Area (VTA) DA Neurons.

The dopaminergic neuromodulator system is fundamental to brain functions. Abnormal dopamine (DA) pathway is implicated in psychiatric disorders, including schizophrenia (SZ) and autism spectrum disorder (ASD). Mutations in Cullin 3 (CUL3), a core component of the Cullin-RING ubiquitin E3 ligase complex, have been associated with SZ and ASD. However, little is known about the function and mechanism of CUL3 in the DA system. Here, we show that CUL3 is critical for the function of DA neurons and DA-relevant behaviors in male mice. CUL3-deficient mice exhibited hyperactive locomotion, deficits in working memory and sensorimotor gating, and increased sensitivity to psychostimulants. In addition, enhanced DA signaling and elevated excitability of the VTA DA neurons were observed in CUL3-deficient animals. Behavioral impairments were attenuated by dopamine D2 receptor antagonist haloperidol and chemogenetic inhibition of DA neurons. Furthermore, we identified HCN2, a hyperpolarization-activated and cyclic nucleotide-gated channel, as a potential target of CUL3 in DA neurons. Our study indicates that CUL3 controls DA neuronal activity by maintaining ion channel homeostasis and provides insight into the role of CUL3 in the pathogenesis of psychiatric disorders.SIGNIFICANCE STATEMENT This study provides evidence that Cullin 3 (CUL3), a core component of the Cullin-RING ubiquitin E3 ligase complex that has been associated with autism spectrum disorder and schizophrenia, controls the excitability of dopamine (DA) neurons in mice. Its DA-specific heterozygous deficiency increased spontaneous locomotion, impaired working memory and sensorimotor gating, and elevated response to psychostimulants. We showed that CUL3 deficiency increased the excitability of VTA DA neurons, and inhibiting D2 receptor or DA neuronal activity attenuated behavioral deficits of CUL3-deficient mice. We found HCN2, a hyperpolarization-activated channel, as a target of CUL3 in DA neurons. Our findings reveal CUL3's role in DA neurons and offer insights into the pathogenic mechanisms of autism spectrum disorder and schizophrenia.

CUL3 induces mitochondrial dysfunction via MRPL12 ubiquitination in renal tubular epithelial cells.

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease worldwide and the strongest predictor of mortality in patients with diabetes. Despite its significance, the pathological mechanism underlying the onset and progression of DKD remains incompletely understood. In this study, we have shown that mitochondrial ribosomal protein L12 (MRPL12) plays a significant role in DKD by modulating mitochondrial function. We demonstrated that MRPL12 was mainly ubiquitinated at K150 in renal tubular epithelial cells. We have found that Cullin3 (CUL3), an E3 ubiquitin ligase, directly interacts with MRPL12 and induces the K63-linked ubiquitination of MRPL12, resulting in mitochondrial biosynthesis dysfunction. Moreover, under high-glucose (HG) conditions in renal tubular epithelial cells, we observed up-regulation of CUL3 expression, significant increase in CUL3-mediated ubiquitination of MRPL12 and dysregulation of mitochondrial biosynthesis. Notably, CUL3 knockdown stabilised the MRPL12 protein and protected mitochondrial biosynthesis under HG conditions. Our findings provide novel insight into how CUL3 affects mitochondrial biosynthesis in renal tubular epithelial cells through MRPL12 ubiquitination and suggest a potential therapeutic strategy for DKD in the future.