Targeted disruption of p185/Cul7 gene results in abnormal vascular morphogenesis

Glucose controls lipolysis through Golgi PtdIns4P-mediated regulation of ATGL

Metabolic crosstalk of the major nutrients glucose, amino acids and fatty acids (FAs) ensures systemic metabolic homeostasis. The coordination between the supply of glucose and FAs to meet various physiological demands is especially important as improper nutrient levels lead to metabolic disorders, such as diabetes and metabolic dysfunction-associated steatohepatitis (MASH). In response to the oscillations in blood glucose levels, lipolysis is thought to be mainly regulated hormonally to control FA liberation from lipid droplets by insulin, catecholamine and glucagon. However, whether general cell-intrinsic mechanisms exist to directly modulate lipolysis via glucose sensing remains largely unknown. Here we report the identification of such an intrinsic mechanism, which involves Golgi PtdIns4P-mediated regulation of adipose triglyceride lipase (ATGL)-driven lipolysis via intracellular glucose sensing. Mechanistically, depletion of intracellular glucose results in lower Golgi PtdIns4P levels, and thus reduced assembly of the E3 ligase complex CUL7FBXW8 in the Golgi apparatus. Decreased levels of the E3 ligase complex lead to reduced polyubiquitylation of ATGL in the Golgi and enhancement of ATGL-driven lipolysis. This cell-intrinsic mechanism regulates both the pool of intracellular FAs and their extracellular release to meet physiological demands during fasting and glucose deprivation. Moreover, genetic and pharmacological manipulation of the Golgi PtdIns4P-CUL7FBXW8-ATGL axis in mouse models of simple hepatic steatosis and MASH, as well as during ex vivo perfusion of a human steatotic liver graft leads to the amelioration of steatosis, suggesting that this pathway might be a promising target for metabolic dysfunction-associated steatotic liver disease and possibly MASH.

Longitudinal skeletal growth and growth plate morphological characteristics of chondro-tissue specific CUL7 knockout mice

BACKGROUND

3 M syndrome is first reported in 1975，which characterized by severe pre- and postnatal growth retardation, skeletal malformation and facial dysmorphism. These three genes (CUL7, OBSL1 and CCDC8) have been identified to be respond for 3 M syndrome, of which CUL7 is accounting for approximately 70%. To date, the molecular mechanism underlying the pathogenesis of 3 M syndrome remains poorly understood. Previous studies showed that no Cul7-/- mice could survive after birth, because of growth retardation at late gestational stage and respiratory distress after birth. The establishment of the animal model of cartilage specific Cul7 knockout mice (Cul7fl/fl;Col2a1-CreERT2 mice) has confirmed that Cul7fl/fl;Col2a1-CreERT2 mice can be selective in a time- and tissue-dependent manner, which can provide an experimental basis for further research on severe genetic diseases related to growth plates.

OBJECTIVE

To establish a model of Cul7fl/fl;Col2a1-CreERT2 mice based on Cre/LoxP system, and to further observe its phenotype and morphological changes in growth plate.

METHODS

The Cul7fl/fl;Col2a1-CreERT2 mice were taken as the experimental group, while the genotype of Cul7fl/+;Col2a1-CreERT2 mice were used as the control group. The gross morphological features and X-ray films of limbs in the two groups were observed every week for 3-6 consecutive weeks, and the length of the mice from nose to the tail, the length of femur and tibia were recorded. In the meantime, The histological morphology of tibial growth plates was compared between the two groups.

RESULTS

A preliminary model of Cul7fl/fl;Col2a1-CreERT2 mice was established. The Cul7fl/fl;Col2a1-CreERT2 mice had abnormally short and deformed limbs (P<0.05), increased thickness of growth plate, the disorderly arranged chondrocyte columns, decreased number of cells in the proliferation zone, changes in the shape from flat to round, obviously expanded extracellular matrix, and disordered arrangement, thickening and loosening of bone trabecula at the proximal metaphysis of the femur.

CONCLUSIONS

The knockout of Cul7 gene may affect both the proliferation of chondrocytes and the endochondral osteogenesis, confirming that Cul7 is essential for the normal development of bone in the body.

Emerging Roles of Cullin-RING Ubiquitin Ligases in Cardiac Development

Heart development is a spatiotemporally regulated process that extends from the embryonic phase to postnatal stages. Disruption of this highly orchestrated process can lead to congenital heart disease or predispose the heart to cardiomyopathy or heart failure. Consequently, gaining an in-depth understanding of the molecular mechanisms governing cardiac development holds considerable promise for the development of innovative therapies for various cardiac ailments. While significant progress in uncovering novel transcriptional and epigenetic regulators of heart development has been made, the exploration of post-translational mechanisms that influence this process has lagged. Culling-RING E3 ubiquitin ligases (CRLs), the largest family of ubiquitin ligases, control the ubiquitination and degradation of ~20% of intracellular proteins. Emerging evidence has uncovered the critical roles of CRLs in the regulation of a wide range of cellular, physiological, and pathological processes. In this review, we summarize current findings on the versatile regulation of cardiac morphogenesis and maturation by CRLs and present future perspectives to advance our comprehensive understanding of how CRLs govern cardiac developmental processes.

Prenatal diagnosis and preimplantation genetics testing of 3M syndrome in a Chinese family with novel biallelic variants of CUL7

BACKGROUND

3M syndrome is a rare autosomal recessive developmental disorder characterized by pre and postnatal growth deficiency, dysmorphic facial features, and normal intelligence. 3M syndrome should be suspected in a proband with a combination of characteristic or recognizable dysmorphic features. The diagnosis of 3M syndrome could be confirmed by identifying biallelic variants in CUL7, OBSL1, or CCDC8.

METHODS

Whole-exome sequencing (WES) was performed to identify genetic causes. Reverse-transcription polymerase chain reaction (RT-PCR) was performed to detect aberrant splicing events. Haplotypes were constructed using multiplex PCR and sequencing. Variants of the parental haplotype and target likely pathogenic variants were detected by PCR and Sanger sequencing from the embryos. Copy number variant (CNV) detection was performed by next-generation sequencing.

RESULTS

We present the case of a nonconsanguineous Chinese couple with one abnormal pregnancy, where the fetus showed 3M phenotypes of shortened long bones. WES identified two novel heterozygous mutations in CUL7: NM_014780.5:c.354del (p.Gln119ArgfsTer52) and NM_014780.5:c.1373-15G>A. RT-PCR from RNA of the mother's peripheral blood leucocytes showed that c.1373-15G>A caused the insertion of a 13-bp extra intron sequence and encoded the mutant p.Leu459ProfsTer25. Both variants were classified as likely pathogenic according to ACMG/AMP guidelines and Clinical Genome Resource specifications. During genetic counseling, the options of prenatal diagnosis through chorionic villus sampling or amniocentesis, adoption, sperm donation, and electing not to reproduce, as well as preimplantation genetic testing for monogenic disorders (PGT-M), were discussed. The couple hopes to conceive a child of their own and refused to accept the 25% risk during the next pregnancy and opted for PGT-M. They finally successfully delivered a healthy baby through PGT-M.

CONCLUSION

This study expanded the mutation spectrum of CUL7, detected the aberrant splicing event of CUL7 via RT-PCR, constructed the haplotype for PGT-M, and demonstrated the successful delivery of a healthy baby using PGT-M.

Expression of the NUP153 and YWHAB genes from their canonical promoters and alternative promoters of the LINE-1 retrotransposon in the placenta of the first trimester of pregnancy

The placenta has a unique hypomethylated genome. Due to this feature of the placenta, there is a potential possibility of using regulatory elements derived from retroviruses and retrotransposons, which are suppressed by DNA methylation in the adult body. In addition, there is an abnormal increase in the level of methylation of the LINE-1 retrotransposon in the chorionic trophoblast in spontaneous abortions with both normal karyotype and aneuploidy on different chromosomes, which may be associated with impaired gene transcription using LINE-1 regulatory elements. To date, 988 genes that can be expressed from alternative LINE-1 promoters have been identified. Using the STRING tool, genes (NUP153 and YWHAB) were selected, the products of which have significant functional relationships with proteins highly expressed in the placenta and involved in trophoblast differentiation. This study aimed to analyze the expression of the NUP153 and YWHAB genes, highly active in the placenta, from canonical and alternative LINE-1 promoters in the germinal part of the placenta of spontaneous and induced abortions. Gene expression analysis was performed using real-time PCR in chorionic villi and extraembryonic mesoderm of induced abortions (n = 10), adult lymphocytes (n = 10), spontaneous abortions with normal karyotype (n = 10), and with the most frequent aneuploidies in the first trimester of pregnancy (trisomy 16 (n = 8) and monosomy X (n = 6)). The LINE-1 methylation index was assessed in the chorionic villi of spontaneous abortions using targeted bisulfite massive parallel sequencing. The level of expression of both genes from canonical promoters was higher in blood lymphocytes than in placental tissues (p < 0.05). However, the expression level of the NUP153 gene from the alternative LINE-1 promoter was 17 times higher in chorionic villi and 23 times higher in extraembryonic mesoderm than in lymphocytes (p < 0.05). The expression level of NUP153 and YWHAB from canonical promoters was higher in the group of spontaneous abortions with monosomy X compared to all other groups (p <0.05). The LINE-1 methylation index negatively correlated with the level of gene expression from both canonical (NUP153 - R = -0.59, YWHAB - R = -0.52, p < 0.05) and alternative LINE-1 promoters (NUP153 - R = -0.46, YWHAB - R = -0.66, p < 0.05). Thus, the observed increase in the LINE-1 methylation index in the placenta of spontaneous abortions is associated with the level of expression of the NUP153 and YWHAB genes not only from alternative but also from canonical promoters, which can subsequently lead to negative consequences for normal embryogenesis.

Structure of CRL7FBXW8 reveals coupling with CUL1-RBX1/ROC1 for multi-cullin-RING E3-catalyzed ubiquitin ligation

Most cullin-RING ubiquitin ligases (CRLs) form homologous assemblies between a neddylated cullin-RING catalytic module and a variable substrate-binding receptor (for example, an F-box protein). However, the vertebrate-specific CRL7^FBXW8 is of interest because it eludes existing models, yet its constituent cullin CUL7 and F-box protein FBXW8 are essential for development, and CUL7 mutations cause 3M syndrome. In this study, cryo-EM and biochemical analyses reveal the CRL7^FBXW8 assembly. CUL7’s exclusivity for FBXW8 among all F-box proteins is explained by its unique F-box-independent binding mode. In CRL7^FBXW8, the RBX1 (also known as ROC1) RING domain is constrained in an orientation incompatible with binding E2~NEDD8 or E2~ubiquitin intermediates. Accordingly, purified recombinant CRL7^FBXW8 lacks auto-neddylation and ubiquitination activities. Instead, our data indicate that CRL7 serves as a substrate receptor linked via SKP1–FBXW8 to a neddylated CUL1–RBX1 catalytic module mediating ubiquitination. The structure reveals a distinctive CRL–CRL partnership, and provides a framework for understanding CUL7 assemblies safeguarding human health.

The cryo-EM structure of CRL7^FBXW8 shows that CUL7–RBX1 binds FBXW8–SKP1 in an F-box-independent manner. Bridged by FBXW8–SKP1, CRL7^FBXW8 forms a multi-cullin E3 ligase complex with neddylated CUL1–RBX1, which ubiquitinates a substrate recruited to CUL7.

Whole-Genome Sequencing Association Analyses of Stroke and Its Subtypes in Ancestrally Diverse Populations From Trans-Omics for Precision Medicine Project

BACKGROUND AND PURPOSE

Stroke is the leading cause of death and long-term disability worldwide. Previous genome-wide association studies identified 51 loci associated with stroke (mostly ischemic) and its subtypes among predominantly European populations. Using whole-genome sequencing in ancestrally diverse populations from the Trans-Omics for Precision Medicine (TOPMed) Program, we aimed to identify novel variants, especially low-frequency or ancestry-specific variants, associated with all stroke, ischemic stroke and its subtypes (large artery, cardioembolic, and small vessel), and hemorrhagic stroke and its subtypes (intracerebral and subarachnoid).

METHODS

Whole-genome sequencing data were available for 6833 stroke cases and 27 116 controls, including 22 315 European, 7877 Black, 2616 Hispanic/Latino, 850 Asian, 54 Native American, and 237 other ancestry participants. In TOPMed, we performed single variant association analysis examining 40 million common variants and aggregated association analysis focusing on rare variants. We also combined TOPMed European populations with over 28 000 additional European participants from the UK BioBank genome-wide array data through meta-analysis.

RESULTS

In the single variant association analysis in TOPMed, we identified one novel locus 13q33 for large artery at whole-genome-wide significance (P<5.00×10-9) and 4 novel loci at genome-wide significance (P<5.00×10-8), all of which need confirmation in independent studies. Lead variants in all 5 loci are low-frequency but are more common in non-European populations. An aggregation of synonymous rare variants within the gene C6orf26 demonstrated suggestive evidence of association for hemorrhagic stroke (P<3.11×10-6). By meta-analyzing European ancestry samples in TOPMed and UK BioBank, we replicated several previously reported stroke loci including PITX2, HDAC9, ZFHX3, and LRCH1.

CONCLUSIONS

We represent the first association analysis for stroke and its subtypes using whole-genome sequencing data from ancestrally diverse populations. While our findings suggest the potential benefits of combining whole-genome sequencing data with populations of diverse genetic backgrounds to identify possible low-frequency or ancestry-specific variants, they also highlight the need to increase genome coverage and sample sizes.

Cullin neddylation inhibitor attenuates hyperglycemia by enhancing hepatic insulin signaling through insulin receptor substrate stabilization

Hepatic insulin resistance is a hallmark feature of nonalcoholic fatty liver disease and type-2 diabetes and significantly contributes to systemic insulin resistance. Abnormal activation of nutrient and stress-sensing kinases leads to serine/threonine phosphorylation of insulin receptor substrate (IRS) and subsequent IRS proteasome degradation, which is a key underlying cause of hepatic insulin resistance. Recently, members of the cullin-RING E3 ligases (CRLs) have emerged as mediators of IRS protein turnover, but the pathophysiological roles and therapeutic implications of this cellular signaling regulation is largely unknown. CRLs are activated upon cullin neddylation, a process of covalent conjugation of a ubiquitin-like protein called Nedd8 to a cullin scaffold. Here, we report that pharmacological inhibition of cullin neddylation by MLN4924 (Pevonedistat) rapidly decreases hepatic glucose production and attenuates hyperglycemia in mice. Mechanistically, neddylation inhibition delays CRL-mediated IRS protein turnover to prolong insulin action in hepatocytes. In vitro knockdown of either cullin 1 or cullin 3, but not other cullin members, attenuates insulin-induced IRS protein degradation and enhances cellular insulin signaling activation. In contrast, in vivo knockdown of liver cullin 3, but not cullin 1, stabilizes hepatic IRS and decreases blood glucose, which recapitulates the effect of MLN4924 treatment. In summary, these findings suggest that pharmacological inhibition of cullin neddylation represents a therapeutic approach for improving hepatic insulin signaling and lowering blood glucose.

Genomic imprinting in human placentation

Background

Genomic imprinting (GI) is a mammalian-specific epigenetic phenomenon that has been implicated in the evolution of the placenta in mammals.

Methods

Embryo transfer procedures and trophoblast stem (TS) cells were used to re-examine mouse placenta-specific GI genes. For the analysis of human GI genes, cytotrophoblast cells isolated from human placental tissues were used. Using human TS cells, the biological roles of human GI genes were examined.

Main findings

(1) Many previously identified mouse GI genes were likely to be falsely identified due to contaminating maternal cells. (2) Human placenta-specific GI genes were comprehensively determined, highlighting incomplete erasure of germline DNA methylation in the human placenta. (3) Human TS cells retained normal GI patterns. (4) Complete hydatidiform mole-derived TS cells were characterized by aberrant GI and enhanced trophoblastic proliferation. The maternally expressed imprinted gene p57KIP2 may be responsible for the enhanced proliferation. (5) The primate-specific microRNA cluster on chromosome 19, which is a placenta-specific GI gene, is essential for self-renewal and differentiation of human TS cells.

Conclusion

Genomic imprinting plays diverse and important roles in human placentation. Experimental analyses using TS cells suggest that the GI maintenance is necessary for normal placental development in humans.

Co-operative binding of SKP1, Cullin1 and Cullin7 to FBXW8 results in Cullin1-SKP1-FBXW8-Cullin7 functional complex formation that monitors cellular function of β-TrCP1

F-box protein FBXW8 is known to interact with scaffolding protein Cullin1 and Cullin7 to form SCF (SKP1, Cullin and F-box protein) complex. However, detail understanding about the importance of both Cullins for SCF-FBXW8 complex formation as well as its ubiquitin ligase activity remains elusive. Here, we show that, through in vitro and in vivo studies, Cullin1 and Cullin7 increase each other's binding to FBXW8 synergistically. Interestingly, absence of either Cullin results in abrogation of binding of other Cullin to FBXW8. Binding of SKP1 to FBXW8 also increases in the presence of both the Cullins. Thus, SKP1, Cullin1 and Cullin7 are essential to form Cullin1-SKP1-FBXW8-Cullin7 functional ubiquitin ligase complex. Further, using computational, mutational and biochemical analysis, we found that Cullin1 binds to N-terminus of FBXW8 through SKP1 while Cullin7 associates with C-terminus of FBXW8 to form Cullin1-SKP1-FBXW8-Cullin7 functional complex in a cooperative manner. Results showed that Cullin1-SKP1-FBXW8-Cullin7 complex plays a key role in maintaining the basal level expression of β-TrCP1. Moreover, Cullin1-SKP1-FBXW8-Cullin7 complex promotes cell migration by activating β-catenin via directing proteasomal degradation of β-TrCP1. Overall, our study reveals the intriguing molecular mechanism of assembly of SKP1, Cullin1, Cullin7 and FBXW8 to form Cullin1-SKP1-FBXW8-Cullin7 functional complex that control the function of β-TrCP1.

Forward genetic screens identified mutants with defects in trap morphogenesis in the nematode-trapping fungus Arthrobotrys oligospora

Nematode-trapping fungi (NTF) are carnivorous fungi that prey on nematodes under nutrient-poor conditions via specialized hyphae that function as traps. The molecular mechanisms involved in the interactions between NTF and their nematode prey are largely unknown. In this study, we conducted forward genetic screens to identify potential genes and pathways that are involved in trap morphogenesis and predation in the NTF Arthrobotrys oligospora. Using Ethyl methanesulfonate and UV as the mutagens, we generated 5552 randomly mutagenized A. oligospora strains and identified 15 mutants with strong defects in trap morphogenesis. Whole-genome sequencing and bioinformatic analyses revealed mutations in genes with roles in signaling, transcription or membrane transport that may contribute to the defects of trap morphogenesis in these mutants. We further conducted functional analyses on a candidate gene, YBP-1, and demonstrate that mutation of that gene was causative of the phenotypes observed in one of the mutants. The methods established in this study might provide helpful insights for establishing forward genetic screening methods for other non-model fungal species.

Genetic Basis and Therapies for Vascular Anomalies

Vascular and lymphatic malformations represent a challenge for clinicians. The identification of inherited and somatic mutations in important signaling pathways, including the PI3K (phosphoinositide 3-kinase)/AKT (protein kinase B)/mTOR (mammalian target of rapamycin), RAS (rat sarcoma)/RAF (rapidly accelerated fibrosarcoma)/MEK (mitogen-activated protein kinase kinase)/ERK (extracellular signal-regulated kinases), HGF (hepatocyte growth factor)/c-Met (hepatocyte growth factor receptor), and VEGF (vascular endothelial growth factor) A/VEGFR (vascular endothelial growth factor receptor) 2 cascades has led to the evaluation of tailored strategies with preexisting cancer drugs that interfere with these signaling pathways. The era of theranostics has started for the treatment of vascular anomalies. Registration: URL: https://www.clinicaltrialsregister.eu; Unique identifier: 2015-001703-32.

FBXW8 regulates G1 and S phases of cell cycle progression by restricting β-TrCP1 function

Sequential alteration in the expression levels of cell cycle regulatory proteins is crucial for faithful cell cycle progression to maintain the cellular homeostasis. F-box protein β-TrCP1 is known to control the expression levels of several important cell cycle regulatory proteins. However, how the function of β-TrCP1 is regulated in spatiotemporal manner during cell cycle progression remains elusive. Here, we show that expression levels of β-TrCP1 oscillate during cell cycle progression with a minimum level at the G1 and S phases of cell cycle. Using biochemical, flow cytometry, and immunofluorescence techniques, we found that oscillation of β-TrCP1 expression is controlled by another F-box protein FBXW8. FBXW8 directs the proteasomal degradation of β-TrCP1 in MAPK pathway-dependent manner. Interestingly, we found that the attenuation of β-TrCP1 by FBXW8 is important for Cdc25A-mediated cell cycle transition from G1 phase to S phase as well as DNA damage-free progression of S phase. Overall, our study reveals the intriguing molecular mechanism and significance of maintenance of β-TrCP1 levels during cell cycle progression by FBXW8-mediated proteasomal degradation.

A proteomics approach for the identification of cullin-9 (CUL9) related signaling pathways in induced pluripotent stem cell models

CUL9 is a non-canonical and poorly characterized member of the largest family of E3 ubiquitin ligases known as the Cullin RING ligases (CRLs). Most CRLs play a critical role in developmental processes, however, the role of CUL9 in neuronal development remains elusive. We determined that deletion or depletion of CUL9 protein causes aberrant formation of neural rosettes, an in vitro model of early neuralization. In this study, we applied mass spectrometric approaches in human pluripotent stem cells (hPSCs) and neural progenitor cells (hNPCs) to identify CUL9 related signaling pathways that may contribute to this phenotype. Through LC-MS/MS analysis of immunoprecipitated endogenous CUL9, we identified several subunits of the APC/C, a major cell cycle regulator, as potential CUL9 interacting proteins. Knockdown of the APC/C adapter protein FZR1 resulted in a significant increase in CUL9 protein levels, however, CUL9 does not appear to affect protein abundance of APC/C subunits and adapters or alter cell cycle progression. Quantitative proteomic analysis of CUL9 KO hPSCs and hNPCs identified protein networks related to metabolic, ubiquitin degradation, and transcriptional regulation pathways that are disrupted by CUL9 deletion in both hPSCs. No significant changes in oxygen consumption rates or ATP production were detected in either cell type. The results of our study build on current evidence that CUL9 may have unique functions in different cell types and that compensatory mechanisms may contribute to the difficulty of identifying CUL9 substrates.

The Role of E3s in Regulating Pluripotency of Embryonic Stem Cells and Induced Pluripotent Stem Cells

Pluripotent embryonic stem cells (ESCs) are derived from early embryos and can differentiate into any type of cells in living organisms. Induced pluripotent stem cells (iPSCs) resemble ESCs, both of which serve as excellent sources to study early embryonic development and realize cell replacement therapies for age-related degenerative diseases and other cell dysfunction-related illnesses. To achieve these valuable applications, comprehensively understanding of the mechanisms underlying pluripotency maintenance and acquisition is critical. Ubiquitination modifies proteins with Ubiquitin (Ub) at the post-translational level to monitor protein stability and activity. It is extensively involved in pluripotency-specific regulatory networks in ESCs and iPSCs. Ubiquitination is achieved by sequential actions of the Ub-activating enzyme E1, Ub-conjugating enzyme E2, and Ub ligase E3. Compared with E1s and E2s, E3s are most abundant, responsible for substrate selectivity and functional diversity. In this review, we focus on E3 ligases to discuss recent progresses in understanding how they regulate pluripotency and somatic cell reprogramming through ubiquitinating core ESC regulators.

Genetic ablation of Cullin-RING E3 ubiquitin ligase 7 restrains pressure overload-induced myocardial fibrosis

Fibrosis is a pathognomonic feature of structural heart disease and counteracted by distinct cardioprotective mechanisms, e.g. activation of the phosphoinositide 3-kinase (PI3K) / AKT pro-survival pathway. The Cullin-RING E3 ubiquitin ligase 7 (CRL7) was identified as negative regulator of PI3K/AKT signalling in skeletal muscle, but its role in the heart remains to be elucidated. Here, we sought to determine whether CRL7 modulates to cardiac fibrosis following pressure overload and dissect its underlying mechanisms. For inactivation of CRL7, the Cullin 7 (Cul7) gene was deleted in cardiac myocytes (CM) by injection of adeno-associated virus subtype 9 (AAV9) vectors encoding codon improved Cre-recombinase (AAV9-CMV-iCre) in Cul7^flox/flox mice. In addition, Myosin Heavy Chain 6 (Myh6; alpha-MHC)-MerCreMer transgenic mice with tamoxifen-induced CM-specific expression of iCre were used as alternate model. After transverse aortic constriction (TAC), causing chronic pressure overload and fibrosis, AAV9-CMV-iCre induced Cul7-/- mice displayed a ~50% reduction of interstitial cardiac fibrosis when compared to Cul7+/+ animals (6.7% vs. 3.4%, p<0.01). Similar results were obtained with Cul7^flox/floxMyh6-Mer-Cre-Mer^Tg(1/0) mice which displayed a ~30% reduction of cardiac fibrosis after TAC when compared to Cul7^+/+Myh6-Mer-Cre-Mer^Tg(1/0) controls after TAC surgery (12.4% vs. 8.7%, p<0.05). No hemodynamic alterations were observed. AKT^Ser473 phosphorylation was increased 3-fold (p<0.01) in Cul7-/- vs. control mice, together with a ~78% (p<0.001) reduction of TUNEL-positive apoptotic cells three weeks after TAC. In addition, CM-specific expression of a dominant-negative CUL7^1152stop mutant resulted in a 16.3-fold decrease (p<0.001) of in situ end-labelling (ISEL) positive apoptotic cells. Collectively, our data demonstrate that CM-specific ablation of Cul7 restrains myocardial fibrosis and apoptosis upon pressure overload, and introduce CRL7 as a potential target for anti-fibrotic therapeutic strategies of the heart.

The functional analysis of Cullin 7 E3 ubiquitin ligases in cancer

Cullin (CUL) proteins have critical roles in development and cancer, however few studies on CUL7 have been reported due to its characteristic molecular structure. CUL7 forms a complex with the ROC1 ring finger protein, and only two F-box proteins Fbxw8 and Fbxw11 have been shown to bind to CUL7. Interestingly, CUL7 can interact with its substrates by forming a novel complex that is independent of these two F-box proteins. The biological implications of CUL-ring ligase 7 (CRL7) suggest that the CRL7 may not only perform a proteolytic function but may also play a non-proteolytic role. Among the existing studied CRL7-based E3 ligases, CUL7 exerts both tumor promotion and suppression in a context-dependent manner. Currently, the mechanism of CUL7 in cancer remains unclear, and no studies have addressed potential therapies targeting CUL7. Consistent with the roles of the various CRL7 adaptors exhibit, targeting CRL7 might be an effective strategy for cancer prevention and treatment. We systematically describe the recent major advances in understanding the role of the CUL7 E3 ligase in cancer and further summarize its potential use in clinical therapy.

The Role of Cullin-RING Ligases in Striated Muscle Development, Function, and Disease

The well-orchestrated turnover of proteins in cross-striated muscles is one of the fundamental processes required for muscle cell function and survival. Dysfunction of the intricate protein degradation machinery is often associated with development of cardiac and skeletal muscle myopathies. Most muscle proteins are degraded by the ubiquitin-proteasome system (UPS). The UPS involves a number of enzymes, including E3-ligases, which tightly control which protein substrates are marked for degradation by the proteasome. Recent data reveal that E3-ligases of the cullin family play more diverse and crucial roles in cross striated muscles than previously anticipated. This review highlights some of the findings on the multifaceted functions of cullin-RING E3-ligases, their substrate adapters, muscle protein substrates, and regulatory proteins, such as the Cop9 signalosome, for the development of cross striated muscles, and their roles in the etiology of myopathies.

Rare Germline GLMN Variants Identified from Blue Rubber Bleb Nevus Syndrome Might Impact mTOR Signaling

BACKGROUND AND OBJECTIVE

Blue rubber bleb nevus syndrome (BRBN) or Bean syndrome is a rare Venous Malformation (VM)-associated disorder, which mostly affects the skin and gastrointestinal tract in early childhood. Somatic mutations in TEK have been identified from BRBN patients; however, the etiology of TEK mutation-negative patients of BRBN need further investigation.

METHODS

Two unrelated sporadic BRBNs and one sporadic VM were firstly screened for any rare nonsilent mutation in TEK by Sanger sequencing and subsequently applied to whole-exome sequencing to identify underlying disease causative variants. Overexpression assay and immunoblotting were used to evaluate the functional effect of the candidate disease causative variants.

RESULTS

In the VM case, we identified the known causative somatic mutation in the TEK gene c.2740C>T (p.Leu914Phe). In the BRBN patients, we identified two rare germline variants in GLMN gene c.761C>G (p.Pro254Arg) and c.1630G>T(p.Glu544*). The GLMN-P254R-expressing and GLMN-E544X-expressing HUVECs exhibited increased phosphorylation of mTOR-Ser-2448 in comparison with GLMN-WTexpressing HUVECs in vitro.

CONCLUSION

Our results demonstrated that rare germline variants in GLMN might contribute to the pathogenesis of BRBN. Moreover, abnormal mTOR signaling might be the pathogenesis mechanism underlying the dysfunction of GLMN protein.

Unique features and emerging in vitro models of human placental development

Background

The placenta is an essential organ for the normal development of mammalian fetuses. Most of our knowledge on the molecular mechanisms of placental development has come from the analyses of mice, especially histopathological examination of knockout mice. Choriocarcinoma and immortalized cell lines have also been used for basic research on the human placenta. However, these cells are quite different from normal trophoblast cells.

Methods

In this review, we first provide an overview of mouse and human placental development with particular focus on the differences in the anatomy, transcription factor networks, and epigenetic characteristics between these species. Next, we discuss pregnancy complications associated with abnormal placentation. Finally, we introduce emerging in vitro models to study the human placenta, including human trophoblast stem (TS) cells, trophoblast and endometrium organoids, and artificial embryos.

Main findings

The placental structure and development differ greatly between humans and mice. The recent establishment of human TS cells and trophoblast and endometrial organoids enhances our understanding of the mechanisms underlying human placental development.

Conclusion

These in vitro models will greatly advance our understanding of human placental development and potentially contribute to the elucidation of the causes of infertility and other pregnancy complications.

The ubiquitin ligase Cullin-1 associates with chromatin and regulates transcription of specific c-MYC target genes

Transcription is regulated through a dynamic interplay of DNA-associated proteins, and the composition of gene-regulatory complexes is subject to continuous adjustments. Protein alterations include post-translational modifications and elimination of individual polypeptides. Spatially and temporally controlled protein removal is, therefore, essential for gene regulation and accounts for the short half-life of many transcription factors. The ubiquitin-proteasome system is responsible for site- and target-specific ubiquitination and protein degradation. Specificity of ubiquitination is conferred by ubiquitin ligases. Cullin-RING complexes, the largest family of ligases, require multi-unit assembly around one of seven cullin proteins. To investigate the direct role of cullins in ubiquitination of DNA-bound proteins and in gene regulation, we analyzed their subcellular locations and DNA-affinities. We found CUL4A and CUL7 to be largely excluded from the nucleus, whereas CUL4B was primarily nuclear. CUL1,2,3, and 5 showed mixed cytosolic and nuclear expression. When analyzing chromatin affinity of individual cullins, we discovered that CUL1 preferentially associated with active promoter sequences and co-localized with 23% of all DNA-associated protein degradation sites. CUL1 co-distributed with c-MYC and specifically repressed nuclear-encoded mitochondrial and splicing-associated genes. These studies underscore the relevance of spatial control in chromatin-associated protein ubiquitination and define a novel role for CUL1 in gene repression.

A novel mutation within intron 17 of the CUL7 gene results in appearance of premature termination codon

A couple with five adverse pregnancy history required prenatal diagnosis. The fetus of this study was their fifth pregnancy. The fetus was found NT thickening at 12 weeks and 4 days gestation and the average long bone of limbs retardation 4SD at 27 weeks and 4 days gestation. Karyotype was normal. The next-generation sequencing (NGS) and Sanger sequencing were conducted of this fetus. The compound heterozygous mutations c.3722_3749dup[p.V1252fs*23] and c.3355 + 5 G > A at CUL7 gene were detected. The mutation c.3355 + 5 G > A was a novel mutation within intron 17 of the CUL7 gene. Minigene array was used to verify whether the novel mutation c.3355 + 5 G > A really affected the splicing of CUL7gene. The results showed that the mutation could result in the appearance of premature termination codon. The fetus could be diagnosed as 3 M syndrome. We suggested that close attention needed to be paid to fetuses with intrauterine growth restriction only by ultrasonic and avoid misdiagnosis and missed diagnosis of 3 M syndrome. In addition, our study enriched gene mutations of 3 M syndrome.

Identification of two CUL7 variants in two Chinese families with 3-M syndrome by whole-exome sequencing

Background

3‐M syndrome is a rare autosomal recessive disorder characterized by primordial growth retardation, large head circumference, characteristic facial features, and mild skeletal changes, which is associated with the exclusive variants in three genes, namely CUL7, OBSL1, and CCDC8. Only a few 3‐M syndrome patients have been reported in Chinese population.

Methods

Children with unexplained severe short stature, facial dysmorphism, and normal intelligence in two Chinese families and their relatives were enrolled. Trio‐whole‐exome sequencing (trio‐WES) and pathogenicity prediction analysis were conducted on the recruited patients. A conservative analysis of the mutant amino acid sequences and function prediction analysis of the wild‐type (WT) and mutant CUL7 protein were performed.

Results

We identified a homozygous missense variant (NM_014780.4: c.4898C > T, p.Thr1633Met) in CUL7 gene in a 6‐month‐old female infant from a non‐consanguineous family, and a homozygous frameshift variant (NM_014780.4: c.3722_3749 dup GGCTGGCACAGCTGCAGCAATGCCTGCA, p. Val1252Glyfs*23) in CUL7 gene in two affected siblings from a consanguinity family. These two variants may affect the properties and structure of CUL7 protein.

Conclusion

These two rare variants were observed in Chinese population for the first time and have not been reported in the literature. Our findings expand the variant spectrum of 3‐M syndrome in Chinese population and provide valuable insights into the early clinical manifestations and pathogenesis of 3‐M syndrome for pediatricians and endocrinologists.

Knockout Mouse Models Provide Insight into the Biological Functions of CRL1 Components

The CRL1 complex, also known as the SCF complex, is a ubiquitin ligase that in mammals consists of an adaptor protein (SKP1), a scaffold protein (CUL1), a RING finger protein (RBX1, also known as ROC1), and one of about 70 F-box proteins. Given that the F-box proteins determine the substrate specificity of the CRL1 complex, the variety of these proteins allows the generation of a large number of ubiquitin ligases that promote the degradation or regulate the function of many substrate proteins and thereby control numerous key cellular processes. The physiological and pathological functions of these many CRL1 ubiquitin ligases have been studied by the generation and characterization of knockout mouse models that lack specific CRL1 components. In this chapter, we provide a comprehensive overview of these mouse models and discuss the role of each CRL1 component in mouse physiology and pathology.

Cullin-RING E3 Ubiquitin Ligase 7 in Growth Control and Cancer

CRL7^Fbxw8 is an E3 ubiquitin ligase complex, containing cullin7 (CUL7) as a scaffold, the F-box protein Fbxw8 as a substrate receptor, the Skp1 adaptor, and the ROC1/Rbx1 RING finger protein for working with E2 enzyme to facilitate ubiquitin transfer. This chapter provides an update on studies linking CRL7^Fbxw8 to hereditary human growth retardation disease, as at least 64 cul7 germ line mutations were found in patients with autosomal recessive 3-M syndrome. CRL7^Fbxw8 interacts with two additional 3-M associated proteins OBSL1 and CCDC8, leading to subcellular localization of the E3 complex to regions including plasma membrane, centrosome, and Golgi. At least ten mammalian cellular proteins were identified or implicated as CRL7^Fbxw8 substrates. Discussion focuses on the possible impact of CRL7^Fbxw8-mediated proteolytic or non-proteolytic pathways in growth control and cancer.

Structural Biology of CRL Ubiquitin Ligases

Cullin-RING ubiquitin ligases (CRLs) represent the largest superfamily of multi-subunit E3s conserved in all eukaryotes. Soon after the discovery of these important ubiquitin ligase machineries, structural studies have made tremendous contributions to our understanding of their functions. Identification of the key components of CRLs by early studies raised immediate questions as to how these multi-subunit complexes assemble to promote the polyubiquitination of substrates. Specifically, how do the CRL subunits interact with each other to form a versatile E3 platform? How do they recognize specific substrates? How are the CRL-substrate interactions regulated in response to upstream signals? How are the CRL E3s themselves activated and deactivated, and how are substrate receptor subunits of CRLs exchanged in the cell? Even though we might not yet have complete answers to these questions, extensive structural analyses of CRL complexes in the past two decades have begun to unveil the themes and variations of CRL biology. In this chapter we will discuss both classic and emerging structures that help elucidate the overall architecture of CRLs, their substrate recognition modes, and regulatory mechanism of CRLs by NEDD8 modification.

Association of mRNA expression levels of Cullin family members with prognosis in breast cancer: An online database analysis

Cullin proteins couple with RING-finger proteins, adaptor proteins and substrate recognition receptors to form E3 ubiquitin ligases for recognizing numerous substrates and participating in a variety of cellular processes, especially in genome stability and tumorigenesis. However, the prognostic values of Cullins in breast cancer remain elusive.A "Kaplan-Meier plotter" (KM plotter) online survival analysis tool was used to evaluate the association of individual Cullin members' mRNA expression with overall survival (OS) in breast cancer patients.Our results revealed that elevated mRNA expression of CUL4A and PARC were significantly associated with poor OS for breast cancer patients. While high mRNA expression of CUL2, CUL4B, and CUL5 were correlated with better survival for breast cancers.The associated results suggested that some Cullin members could serve as new predictive prognostic indicators for breast cancer.

Impaired plasma membrane localization of ubiquitin ligase complex underlies 3-M syndrome development

3-M primordial dwarfism is an inherited disease characterized by severe pre- and postnatal growth retardation and by mutually exclusive mutations in three genes, CUL7, OBSL1, and CCDC8. The mechanism underlying 3-M dwarfism is not clear. We showed here that CCDC8, derived from a retrotransposon Gag protein in placental mammals, exclusively localized on the plasma membrane and was phosphorylated by CK2 and GSK3. Phosphorylation of CCDC8 resulted in its binding first with OBSL1, and then CUL7, leading to the membrane assembly of the 3-M E3 ubiquitin ligase complex. We identified LL5β, a plasma membrane protein that regulates cell migration, as a substrate of 3-M ligase. Wnt inhibition of CCDC8 phosphorylation or patient-derived mutations in 3-M genes disrupted membrane localization of the 3-M complex and accumulated LL5β. Deletion of Ccdc8 in mice impaired trophoblast migration and placental development, resulting in intrauterine growth restriction and perinatal lethality. These results identified a mechanism regulating cell migration and placental development that underlies the development of 3-M dwarfism.

CUL7 E3 Ubiquitin Ligase Mediates the Degradation of Activation-Induced Cytidine Deaminase and Regulates the Ig Class Switch Recombination in B Lymphocytes

Activation-induced cytidine deaminase (AID) initiates class switch recombination and somatic hypermutation in Ig genes. The activity and protein levels of AID are tightly controlled by various mechanisms. In this study, we found that CUL7 E3 ubiquitin ligases specifically mediated AID ubiquitination. CUL7 overexpression or knockdown influenced the decay of AID, affecting AID protein levels and subsequently IgA class switching in CH12F3 cells, a mouse B lymphocyte cell line. Further analysis indicated that CUL7 mediated AID ubiquitination by forming a complex with FBXW11. In a CUL7 ^fl/fl CD19 ^cre+ mouse model, we demonstrated that CUL7 knockout significantly enhanced AID protein levels in B cells in the germinal center and increased both the IgG1 and IgA class switching. Collectively, our results reveal a subtle regulation mechanism for tightly controlling AID protein levels. The manipulation of this pathway may be useful for regulating AID abundance and efficiency of Ig class switching and is therefore a potential target for developing immunologic adjuvants for vaccines of various pathogens such as HIV-1 and influenza viruses.

Murine obscurin and Obsl1 have functionally redundant roles in sarcolemmal integrity, sarcoplasmic reticulum organization, and muscle metabolism

Biological roles of obscurin and its close homolog Obsl1 (obscurin-like 1) have been enigmatic. While obscurin is highly expressed in striated muscles, Obsl1 is found ubiquitously. Accordingly, obscurin mutations have been linked to myopathies, whereas mutations in Obsl1 result in 3M-growth syndrome. To further study unique and redundant functions of these closely related proteins, we generated and characterized Obsl1 knockouts. Global Obsl1 knockouts are embryonically lethal. In contrast, skeletal muscle-specific Obsl1 knockouts show a benign phenotype similar to obscurin knockouts. Only deletion of both proteins and removal of their functional redundancy revealed their roles for sarcolemmal stability and sarcoplasmic reticulum organization. To gain unbiased insights into changes to the muscle proteome, we analyzed tibialis anterior and soleus muscles by mass spectrometry, uncovering additional changes to the muscle metabolism. Our analyses suggest that all obscurin protein family members play functions for muscle membrane systems.

CUL7 promotes cancer cell survival through promoting Caspase-8 ubiquitination

The Cullin 7 (CUL7) gene encodes a member of the cullin family of E3 ubiquitin ligases. Accumulated evidence suggests that CUL7 is oncogenic. However, the mechanism by which CUL7 improves cancer cell survival has not been fully elucidated. Here, we reported that CUL7 confers anti-apoptotic functions by interacting with Caspase-8. CUL7 prevents Caspase-8 activation by promoting Caspase-8 modification with non-degradative polyubiquitin chains at K215. CUL7 knockdown sensitized cancer cells to TRAIL-induced apoptosis in vitro and in nude mice. These results suggest that CUL7 limits extrinsic apoptotic signaling by promoting Caspase-8 ubiquitination.

Comparative Analysis of cul5 and rbx2 Expression in the Developing and Adult Murine Brain and Their Essentiality During Mouse Embryogenesis

BACKGROUND

The E3 Cullin 5-RING ubiquitin ligase (CRL5) is a multiprotein complex that has recently been highlighted as a major regulator of central nervous system development. Cullin 5 (Cul5) and the RING finger protein Rbx2 are two CRL5 core components required for CRL5 function in the brain, but their full expression patterns and developmental functions have not been described in detail.

RESULTS

Using a gene-trap mouse model for Cul5 and a knock-in-knockout mouse model for Rbx2, we show that lack of Cul5, but not Rbx2, disrupts blastocyst formation. However, Rbx2 is required for embryo survival at later embryonic stages. We also show that cul5 is expressed in the embryo proper as early as E7.5 and its expression is mostly restricted to the central nervous system and limbs at later time points. Finally, we show that rbx2 and cul5 are co-expressed in most areas of the brain during development and in the adult.

CONCLUSIONS

Our results show that Cul5, but not Rbx2, is required during early embryogenesis and suggests that Cul5 has Rbx2-independent functions in early development. In the brain, Cul5 and Rbx2 are expressed in a similar fashion, allowing the nucleation of an active CRL5 complex. Developmental Dynamics 247:1227-1236, 2018. © 2018 Wiley Periodicals, Inc.

CUL5 is required for thalidomide-dependent inhibition of cellular proliferation

Angiogenesis is essential for cancer metastasis, thus the discovery and characterization of molecules that inhibit this process is important. Thalidomide is a teratogenic drug which is known to inhibit angiogenesis and effectively inhibit cancer metastasis, yet the specific cellular targets for its effect are not well known. We discovered that CUL5 (previously identified as VACM-1), a scaffold protein in E3 ligase complexes, is involved in thalidomide-dependent inhibition of endothelial cell growth. Our results show that in human endothelial cells (HUVEC), thalidomide-dependent decrease in cell growth was associated with decreased nuclear localization of CUL5. In HUVEC transfected with anti-VACM-1 siRNA, thalidomide failed to decrease cell growth. Previously it was established that the antiproliferative effect of CUL5 is inhibited in rat endothelial cells (RAMEC) transfected with mutated CUL5 which is constitutively modified by NEDD8, a ubiquitin-like protein. In this study, the antiproliferative response to thalidomide was compromised in RAMEC expressing mutated CUL5. These results suggest that CUL5 protein is involved in the thalidomide-dependent regulation of cellular proliferation in vitro. Consequently, CUL5 may be an important part of the mechanism for thalidomide-dependent inhibition of cellular proliferation, as well as a novel biomarker for predicting a response to thalidomide for the treatment of disorders such as multiple myeloma and HIV infection.

Neddylation mediates ventricular chamber maturation through repression of Hippo signaling

During development, ventricular chamber maturation is a crucial step in the formation of a functionally competent postnatal heart. Defects in this process can lead to left ventricular noncompaction cardiomyopathy and heart failure. However, molecular mechanisms underlying ventricular chamber development remain incompletely understood. Neddylation is a posttranslational modification that attaches ubiquitin-like protein NEDD8 to protein targets via NEDD8-specific E1-E2-E3 enzymes. Here, we report that neddylation is temporally regulated in the heart and plays a key role in cardiac development. Cardiomyocyte-specific knockout of NAE1, a subunit of the E1 neddylation activating enzyme, significantly decreased neddylated proteins in the heart. Mice lacking NAE1 developed myocardial hypoplasia, ventricular noncompaction, and heart failure at late gestation, which led to perinatal lethality. NAE1 deletion resulted in dysregulation of cell cycle-regulatory genes and blockade of cardiomyocyte proliferation in vivo and in vitro, which was accompanied by the accumulation of the Hippo kinases Mst1 and LATS1/2 and the inactivation of the YAP pathway. Furthermore, reactivation of YAP signaling in NAE1-inactivated cardiomyocytes restored cell proliferation, and YAP-deficient hearts displayed a noncompaction phenotype, supporting an important role of Hippo-YAP signaling in NAE1-depleted hearts. Mechanistically, we found that neddylation regulates Mst1 and LATS2 degradation and that Cullin 7, a NEDD8 substrate, acts as the ubiquitin ligase of Mst1 to enable YAP signaling and cardiomyocyte proliferation. Together, these findings demonstrate a role for neddylation in heart development and, more specifically, in the maturation of ventricular chambers and also identify the NEDD8 substrate Cullin 7 as a regulator of Hippo-YAP signaling.

Deletion of the Syncytin A receptor Ly6e impairs syncytiotrophoblast fusion and placental morphogenesis causing embryonic lethality in mice

Fetal growth and survival is dependent on the elaboration and propinquity of the fetal and maternal circulations within the placenta. Central to this is the formation of the interhaemal membrane, a multi-cellular lamina facilitating exchange of oxygen, nutrients and metabolic waste products between the mother and fetus. In rodents, this cellular barrier contains two transporting layers of syncytiotrophoblast, which are multinucleated cells that form by cell-cell fusion. Previously, we reported the expression of the GPI-linked cell surface protein LY6E by the syncytial layer closest to the maternal sinusoids of the mouse placenta (syncytiotrophoblast layer I). LY6E has since been shown to be a putative receptor for the fusogenic protein responsible for fusion of syncytiotrophoblast layer I, Syncytin A. In this report, we demonstrate that LY6E is essential for the normal fusion of syncytiotrophoblast layer I, and for the proper morphogenesis of both fetal and maternal vasculatures within the placenta. Furthermore, specific inactivation of Ly6e in the epiblast, but not in placenta, is compatible with embryonic development, indicating the embryonic lethality reported for Ly6e^−/− embryos is most likely placental in origin.

Cleidocranial Dysplasia with 6p21.1-p12.3 Microdeletion: A Case Report and Literature Review

OBJECTIVE

The aim of this article is to publish a literature review and report on a new case of cleidocranial dysplasia syndrome with 6p21.1-p12.3 microdeletion.

DESIGN

A PubMed search using "cleidocranial dysplasia syndrome (CCD)" or "6p microdeletion" was performed. Articles with information relevant to our case were obtained for review. A new case of cleidocranial dysplasia syndrome is presented to describe and discuss clinical manifestations, pathogenesis, clinical progression of cleidocranial dysplasia syndrome, and management.

RESULTS

There were 22 articles with reports of cleidocranial dysplasia syndrome or 6p microdeletion. Cleidocranial dysplasia syndrome, a rare genetic disorder, documented to have an autosomal dominant inheritance pattern and caused by caused by mutations of the transcription factor RUNX2. RUNX2 has been mapped to chromosome 6p21. The anomalies in cleidocranial dysplasia syndrome can involve not only the clavicle and skull but the entire skeleton because the membranous as well as endochondral bone formation may be affected. Upon follow-up, our patient was found to have global developmental delay.

CONCLUSIONS

We report a near-term neonate with characteristic features of cleidocranial dysplasia and a 6p21.1-p12.3 microdeletion. Cleidocranial dysplasia syndrome is a rare autosomal dominant skeletal dysplasia. The mutation of the RUNX2 gene results in cleidocranial dysplasia syndrome.

CUL2 overexpression driven by CUL2/E2F1/miR-424 regulatory loop promotes HPV16 E7 induced cervical carcinogenesis

It has been shown that HPV16 E7, but not other genotypes, can bind to scaffold protein CUL2 during inducing cervical carcinogenesis, but the expression level, associated regulating mechanism, and potential carcinogenicity of CUL2 itself is still unknown as yet. Here, we demonstrated that CUL2 was specifically overexpressed in HPV16 positive cervical cancer cells and tissues, and CUL2 expression was significantly increased along with the cervical lesion progression and positively correlated with HPV16 E7. CUL2 knockdown slowed the growth of xenograft tumors in mouse models. Importantly, CUL2 specifically bound to HPV16 E7, but not HPV18 E7. Moreover, CUL2 acted as a direct target of miR-424, and reversely suppressed miR-424; E2F transcription factor 1 (E2F1) suppressed miR-424 expression; CUL2 bound to E2F1 and promoted E2F1 expression. Our results indicate the existence of a regulatory loop among CUL2, E2F1, and miR-424 in HPV16 positive cervical cancer cells. Our results suggest that E7 recruited CUL2, driven by CUL2/E2F1/miR-424 regulatory loop, is overexpressed and accelerates HPV16-induced cervical carcinogenesis. Our findings may serve as one of the explanations for a clinical phenomenon that HPV16 possesses the strongest cervical carcinogenicity among high-risk HPV genotypes.

Functional analysis of Cullin 3 E3 ligases in tumorigenesis

Cullin 3-RING ligases (CRL3) play pivotal roles in the regulation of various physiological and pathological processes, including neoplastic events. The substrate adaptors of CRL3 typically contain a BTB domain that mediates the interaction between Cullin 3 and target substrates to promote their ubiquitination and subsequent degradation. The biological implications of CRL3 adaptor proteins have been well described where they have been found to play a role as either an oncogene, tumor suppressor, or can mediate either of these effects in a context-dependent manner. Among the extensively studied CRL3-based E3 ligases, the role of the adaptor protein SPOP (speckle type BTB/POZ protein) in tumorigenesis appears to be tissue or cellular context dependent. Specifically, SPOP acts as a tumor suppressor via destabilizing downstream oncoproteins in many malignancies, especially in prostate cancer. However, SPOP has largely an oncogenic role in kidney cancer. Keap1, another well-characterized CRL3 adaptor protein, likely serves as a tumor suppressor within diverse malignancies, mainly due to its specific turnover of its downstream oncogenic substrate, NRF2 (nuclear factor erythroid 2-related factor 2). In accordance with the physiological role the various CRL3 adaptors exhibit, several pharmacological agents have been developed to disrupt its E3 ligase activity, therefore blocking its potential oncogenic activity to mitigate tumorigenesis.

Allele-Specific Methylome and Transcriptome Analysis Reveals Widespread Imprinting in the Human Placenta

DNA methylation is globally reprogrammed after fertilization, and as a result, the parental genomes have similar DNA-methylation profiles after implantation except at the germline differentially methylated regions (gDMRs). We and others have previously shown that human blastocysts might contain thousands of transient maternally methylated gDMRs (transient mDMRs), whose maternal methylation is lost in embryonic tissues after implantation. In this study, we performed genome-wide allelic DNA methylation analyses of purified trophoblast cells from human placentas and, surprisingly, found that more than one-quarter of the transient-in-embryo mDMRs maintained their maternally biased DNA methylation. RNA-sequencing-based allelic expression analyses revealed that some of the placenta-specific mDMRs were associated with expression of imprinted genes (e.g., TIGAR, SLC4A7, PROSER2-AS1, and KLHDC10), and three imprinted gene clusters were identified. This approach also identified some X-linked gDMRs. Comparisons of the data with those from other mammals revealed that genomic imprinting in the placenta is highly variable. These findings highlight the incomplete erasure of germline DNA methylation in the human placenta; understanding this erasure is important for understanding normal placental development and the pathogenesis of developmental disorders with imprinting effects.

Cell-fate determination by ubiquitin-dependent regulation of translation

Metazoan development depends on accurate execution of differentiation programs that allow pluripotent stem cells to adopt specific fates ¹. Differentiation requires changes to chromatin architecture and transcriptional networks, yet whether other regulatory events support cell fate determination is less well understood. Here, we have identified the vertebrate-specific ubiquitin ligase CUL3^KBTBD8 as an essential regulator of neural crest specification. CUL3^KBTBD8 monoubiquitylates NOLC1 and its paralog TCOF1, whose mutation underlies the neurocristopathy Treacher Collins Syndrome ^2,3. Ubiquitylation drives formation of a TCOF1-NOLC1 platform that connects RNA polymerase I with ribosome modification enzymes and remodels the translational program of differentiating cells in favor of neural crest specification. We conclude that ubiquitin-dependent regulation of translation is an important feature of cell fate determination.

Targeting Cullin-RING E3 ubiquitin ligases for drug discovery: structure, assembly and small-molecule modulation

In the last decade, the ubiquitin–proteasome system has emerged as a valid target for the development of novel therapeutics. E3 ubiquitin ligases are particularly attractive targets because they confer substrate specificity on the ubiquitin system. CRLs [Cullin–RING (really interesting new gene) E3 ubiquitin ligases] draw particular attention, being the largest family of E3s. The CRLs assemble into functional multisubunit complexes using a repertoire of substrate receptors, adaptors, Cullin scaffolds and RING-box proteins. Drug discovery targeting CRLs is growing in importance due to mounting evidence pointing to significant roles of these enzymes in diverse biological processes and human diseases, including cancer, where CRLs and their substrates often function as tumour suppressors or oncogenes. In the present review, we provide an account of the assembly and structure of CRL complexes, and outline the current state of the field in terms of available knowledge of small-molecule inhibitors and modulators of CRL activity. A comprehensive overview of the reported crystal structures of CRL subunits, components and full-size complexes, alone or with bound small molecules and substrate peptides, is included. This information is providing increasing opportunities to aid the rational structure-based design of chemical probes and potential small-molecule therapeutics targeting CRLs.

Ankyrin repeats of ANKRA2 recognize a PxLPxL motif on the 3M syndrome protein CCDC8

Peptide motifs are often used for protein-protein interactions. We have recently demonstrated that ankyrin repeats of ANKRA2 and the paralogous bare lymphocyte syndrome transcription factor RFXANK recognize PxLPxL/I motifs shared by megalin, three histone deacetylases, and RFX5. We show here that that CCDC8 is a major partner of ANKRA2 but not RFXANK in cells. The CCDC8 gene is mutated in 3M syndrome, a short-stature disorder with additional facial and skeletal abnormalities. Two other genes mutated in this syndrome encode CUL7 and OBSL1. While CUL7 is a ubiquitin ligase and OBSL1 associates with the cytoskeleton, little is known about CCDC8. Binding and structural analyses reveal that the ankyrin repeats of ANKRA2 recognize a PxLPxL motif at the C-terminal region of CCDC8. The N-terminal part interacts with OBSL1 to form a CUL7 ligase complex. These results link ANKRA2 unexpectedly to 3M syndrome and suggest novel regulatory mechanisms for histone deacetylases and RFX7.

Shigella IpaH7.8 E3 ubiquitin ligase targets glomulin and activates inflammasomes to demolish macrophages

When nucleotide-binding oligomerization domain-like receptors (NLRs) sense cytosolic-invading bacteria, they induce the formation of inflammasomes and initiate an innate immune response. In quiescent cells, inflammasome activity is tightly regulated to prevent excess inflammation and cell death. Many bacterial pathogens provoke inflammasome activity and induce inflammatory responses, including cell death, by delivering type III secreted effectors, the rod component flagellin, and toxins. Recent studies indicated that Shigella deploy multiple mechanisms to stimulate NLR inflammasomes through type III secretion during infection. Here, we show that Shigella induces rapid macrophage cell death by delivering the invasion plasmid antigen H7.8 (IpaH7.8) enzyme 3 (E3) ubiquitin ligase effector via the type III secretion system, thereby activating the NLR family pyrin domain-containing 3 (NLRP3) and NLR family CARD domain-containing 4 (NLRC4) inflammasomes and caspase-1 and leading to macrophage cell death in an IpaH7.8 E3 ligase-dependent manner. Mice infected with Shigella possessing IpaH7.8, but not with Shigella possessing an IpaH7.8 E3 ligase-null mutant, exhibited enhanced bacterial multiplication. We defined glomulin/flagellar-associated protein 68 (GLMN) as an IpaH7.8 target involved in IpaH7.8 E3 ligase-dependent inflammasome activation. This protein originally was identified through its association with glomuvenous malformations and more recently was described as a member of a Cullin ring ligase inhibitor. Modifying GLMN levels through overexpression or knockdown led to reduced or augmented inflammasome activation, respectively. Macrophages stimulated with lipopolysaccharide/ATP induced GLMN puncta that localized with the active form of caspase-1. Macrophages from GLMN(+/-) mice were more responsive to inflammasome activation than those from GLMN(+/+) mice. Together, these results highlight a unique bacterial adaptation that hijacks inflammasome activation via interactions between IpaH7.8 and GLMN.

MicroRNA-218 inhibits the proliferation of human choriocarcinoma JEG-3 cell line by targeting Fbxw8

MicroRNAs (miRNAs) are endogenous 19-25 nucleotide noncoding single-stranded RNAs that regulate gene expression by blocking the translation or decreasing the stability of mRNAs. In this study, we showed that miR-218 expression levels were decreased while Fbxw8 expression levels were increased in human choriocarcinoma cell lines, and identified Fbxw8 as a novel direct target of miR-218. Overexpression of miR-218 inhibited cell growth arrest at G2/M phase, suppressed the protein levels of cyclin A and up-regulated the expression levels of p27 through decreasing the levels of Fbxw8. On the other hand, forced expression of Fbxw8 partly rescued the effect of miR-218 in the cells, attenuated cell proliferation decrease the percentage of cells at G2/M phase, induced cyclin A protein expression and suppressed the protein level of p27 through up-regulating the levels of Fbxw8. Taken together, these findings will shed light the role to mechanism of miR-218 in regulating JEG-3 cells proliferation via miR-218/Fbxw8 axis, and miR-218 may serve as a novel potential therapeutic target in human choriocarcinoma in the future.

Age-dependent transcriptome and proteome following transection of neonatal spinal cord of Monodelphis domestica (South American grey short-tailed opossum)

This study describes a combined transcriptome and proteome analysis of Monodelphis domestica response to spinal cord injury at two different postnatal ages. Previously we showed that complete transection at postnatal day 7 (P7) is followed by profuse axon growth across the lesion with near-normal locomotion and swimming when adult. In contrast, at P28 there is no axon growth across the lesion, the animals exhibit weight-bearing locomotion, but cannot use hind limbs when swimming. Here we examined changes in gene and protein expression in the segment of spinal cord rostral to the lesion at 24 h after transection at P7 and at P28. Following injury at P7 only forty genes changed (all increased expression); most were immune/inflammatory genes. Following injury at P28 many more genes changed their expression and the magnitude of change for some genes was strikingly greater. Again many were associated with the immune/inflammation response. In functional groups known to be inhibitory to regeneration in adult cords the expression changes were generally muted, in some cases opposite to that required to account for neurite inhibition. For example myelin basic protein expression was reduced following injury at P28 both at the gene and protein levels. Only four genes from families with extracellular matrix functions thought to influence neurite outgrowth in adult injured cords showed substantial changes in expression following injury at P28: Olfactomedin 4 (Olfm4, 480 fold compared to controls), matrix metallopeptidase (Mmp1, 104 fold), papilin (Papln, 152 fold) and integrin α4 (Itga4, 57 fold). These data provide a resource for investigation of a priori hypotheses in future studies of mechanisms of spinal cord regeneration in immature animals compared to lack of regeneration at more mature stages.

Population genomics reveal recent speciation and rapid evolutionary adaptation in polar bears

Polar bears are uniquely adapted to life in the High Arctic and have undergone drastic physiological changes in response to Arctic climates and a hyper-lipid diet of primarily marine mammal prey. We analyzed 89 complete genomes of polar bear and brown bear using population genomic modeling and show that the species diverged only 479-343 thousand years BP. We find that genes on the polar bear lineage have been under stronger positive selection than in brown bears; nine of the top 16 genes under strong positive selection are associated with cardiomyopathy and vascular disease, implying important reorganization of the cardiovascular system. One of the genes showing the strongest evidence of selection, APOB, encodes the primary lipoprotein component of low-density lipoprotein (LDL); functional mutations in APOB may explain how polar bears are able to cope with life-long elevated LDL levels that are associated with high risk of heart disease in humans.

CUL9 mediates the functions of the 3M complex and ubiquitylates survivin to maintain genome integrity

The Cullin 9 (CUL9) gene encodes a putative E3 ligase that localizes in the cytoplasm. Cul9 null mice develop spontaneous tumors in multiple organs; however, both the cellular and the molecular mechanisms of CUL9 in tumor suppression are currently unknown. We show here that deletion of Cul9 leads to abnormal nuclear morphology, increased DNA damage, and aneuploidy. CUL9 knockdown rescues the microtubule and mitosis defects in cells depleted for CUL7 or OBSL1, two genes that are mutated in a mutually exclusive manner in 3M growth retardation syndrome and function in microtubule dynamics. CUL9 promotes the ubiquitylation and degradation of survivin and is inhibited by CUL7. Depletion of CUL7 decreases survivin level, and overexpression of survivin rescues the defects caused by CUL7 depletion. We propose a 3M-CUL9-survivin pathway in maintaining microtubule and genome integrity, normal development, and tumor suppression.

The 3M complex maintains microtubule and genome integrity

CUL7, OBSL1, and CCDC8 genes are mutated in a mutually exclusive manner in 3M and other growth retardation syndromes. The mechanism underlying the function of the three 3M genes in development is not known. We found that OBSL1 and CCDC8 form a complex with CUL7 and regulate the level and centrosomal localization of CUL7, respectively. CUL7 depletion results in altered microtubule dynamics, prometaphase arrest, tetraploidy, and mitotic cell death. These defects are recaptured in CUL7 mutated 3M cells and can be rescued by wild-type, but not by 3M patient-derived CUL7 mutants. Depletion of either OBSL1 or CCDC8 results in defects and sensitizes cells to microtubule damage similarly to loss of CUL7 function. Microtubule damage reduces the level of CCDC8 that is required for the centrosomal localization of CUL7. We propose that CUL7, OBSL1, and CCDC8 proteins form a 3M complex that functions in maintaining microtubule and genome integrity and normal development.