Smad6 inhibits non-canonical TGF-β1 signalling by recruiting the deubiquitinase A20 to TRAF6

Therapeutic targeting of TGF-β in lung cancer

Transforming growth factor-β (TGF-β) plays a complex role in lung cancer pathophysiology, initially acting as a tumor suppressor by inhibiting early-stage tumor growth. However, its role evolves in the advanced stages of the disease, where it contributes to tumor progression not by directly promoting cell proliferation but by enhancing epithelial-mesenchymal transition (EMT) and creating a conducive tumor microenvironment. While EMT is typically associated with enhanced migratory and invasive capabilities rather than proliferation per se, TGF-β's influence on this process facilitates the complex dynamics of tumor metastasis. Additionally, TGF-β impacts the tumor microenvironment by interacting with immune cells, a process influenced by genetic and epigenetic changes within tumor cells. This interaction highlights its role in immune evasion and chemoresistance, further complicating lung cancer therapy. This review provides a critical overview of recent findings on TGF-β's involvement in lung cancer, its contribution to chemoresistance, and its modulation of the immune response. Despite the considerable challenges encountered in clinical trials and the development of new treatments targeting the TGF-β pathway, this review highlights the necessity for continued, in-depth investigation into the roles of TGF-β. A deeper comprehension of these roles may lead to novel, targeted therapies for lung cancer. Despite the intricate behavior of TGF-β signaling in tumors and previous challenges, further research could yield innovative treatment strategies.

Targeting SMAD-Dependent Signaling: Considerations in Epithelial and Mesenchymal Solid Tumors

SMADs are the canonical intracellular effector proteins of the TGF-β (transforming growth factor-β). SMADs translocate from plasma membrane receptors to the nucleus regulated by many SMAD-interacting proteins through phosphorylation and other post-translational modifications that govern their nucleocytoplasmic shuttling and subsequent transcriptional activity. The signaling pathway of TGF-β/SMAD exhibits both tumor-suppressing and tumor-promoting phenotypes in epithelial-derived solid tumors. Collectively, the pleiotropic nature of TGF-β/SMAD signaling presents significant challenges for the development of effective cancer therapies. Here, we review preclinical studies that evaluate the efficacy of inhibitors targeting major SMAD-regulating and/or -interacting proteins, particularly enzymes that may play important roles in epithelial or mesenchymal compartments within solid tumors.

miR-20a-5p regulated SMAD6 to inhibit chondrogenesis of hDPSCs

OBJECTIVES

Chondrogenic differentiation of human dental pulp stem cells (hDPSCs) is highly promising for cartilage repair. The specific mechanism, however, still needs to be explicated.

MATERIALS AND METHODS

In this study, we isolated hDPSCs and transfected cells with lentiviruses containing an over-expression, knock-down, or negative control of miR-20a-5p. Three-D pellet cultures of hDPSCs were used for the chondrogenic induction. Following the pellet culture period, chondrogenesis was assessed by histological and immunohistochemical analysis and expression of chondrogenic-related genes. Dual-luciferase report assay was performed to determine potential targeted genes of miR-20a-5p, and the phosphorylation levels of P65 and IκBα were explored. Animal experiments were performed to determine the effect of miR-20a-5p on cartilage regeneration.

RESULTS

miR-20a-5p was showed to repress the expression of SMAD6 to inhibit the chondrogenic differentiation of hDPSCs. Accordingly, the knock-down of miR-20a-5p promoted cartilage regeneration in the osteochondral defects of rats. Mechanically, it is indicated that NF-κB signaling is the potential down-stream network of miR-20a-5p/Smad6 crosstalk during chondrogenic differentiation.

CONCLUSIONS

miR-20a-5p could target SMAD6 to activate NF-κB signaling pathway, and thus inhibit chondrogenesis of hDPSCs, which provided promising therapeutic target for cartilage defects clinically.

Tbx5 overexpression in embryoid bodies increases TAK1 expression but does not enhance the differentiation of sinoatrial node cardiomyocytes

Genetic studies place Tbx5 at the apex of the sinoatrial node (SAN) transcriptional program. To understand its role in SAN differentiation, clonal embryonic stem (ES) cell lines were made that conditionally overexpress Tbx5, Tbx3, Tbx18, Shox2, Islet-1, and MAP3k7/TAK1. Cardiac cells differentiated using embryoid bodies (EBs). EBs overexpressing Tbx5, Islet1, and TAK1 beat faster than cardiac cells differentiated from control ES cell lines, suggesting possible roles in SAN differentiation. Tbx5 overexpressing EBs showed increased expression of TAK1, but cardiomyocytes did not differentiate as SAN cells. EBs showed no change in the expression of the SAN transcription factors Shox2 and Islet1 and decreased expression of the SAN channel protein HCN4. EBs constitutively overexpressing TAK1 direct cardiac differentiation to the SAN fate but have reduced phosphorylation of its targets, p38 and Jnk. This opens the possibility that blocking the phosphorylation of TAK1 targets may have the same impact as forced overexpression. To test this, we treated EBs with 5z-7-Oxozeanol (OXO), an inhibitor of TAK1 phosphorylation. Like TAK1 overexpressing cardiac cells, cardiomyocytes differentiated in the presence of OXO beat faster and showed increased expression of SAN genes (Shox2, HCN4, and Islet1). This suggests that activation of the SAN transcriptional network can be accomplished by blocking the phosphorylation of TAK1.

Peli3 ablation ameliorates acetaminophen-induced liver injury through inhibition of GSK3β phosphorylation and mitochondrial translocation

The signaling pathways governing acetaminophen (APAP)-induced liver injury have been extensively studied. However, little is known about the ubiquitin-modifying enzymes needed for the regulation of APAP-induced liver injury. Here, we examined whether the Pellino3 protein, which has E3 ligase activity, is needed for APAP-induced liver injury and subsequently explored its molecular mechanism. Whole-body Peli3-/- knockout (KO) and adenovirus-mediated Peli3 knockdown (KD) mice showed reduced levels of centrilobular cell death, infiltration of immune cells, and biomarkers of liver injury, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST), upon APAP treatment compared to wild-type (WT) mice. Peli3 deficiency in primary hepatocytes decreased mitochondrial and lysosomal damage and reduced the mitochondrial reactive oxygen species (ROS) levels. In addition, the levels of phosphorylation at serine 9 in the cytoplasm and mitochondrial translocation of GSK3β were decreased in primary hepatocytes obtained from Peli3-/- KO mice, and these reductions were accompanied by decreases in JNK phosphorylation and mitochondrial translocation. Pellino3 bound more strongly to GSK3β compared with JNK1 and JNK2 and induced the lysine 63 (K63)-mediated polyubiquitination of GSK3β. In rescue experiments, the ectopic expression of wild-type Pellino3 in Peli3-/- KO hepatocytes restored the mitochondrial translocation of GSK3β, but this restoration was not obtained with expression of a catalytically inactive mutant of Pellino3. These findings are the first to suggest a mechanistic link between Pellino3 and APAP-induced liver injury through the modulation of GSK3β polyubiquitination.

A20 functions as a negative regulator of the lipopolysaccharide-induced inflammation in corneal epithelial cells

A20, also called TNFAIP3, is a crucial regulator of inflammation in various diseases but has not evidenced its function in the cornea. We aimed to evaluate the existence and the functions of A20 in human corneal epithelial (HCE-T) cells. After being treated with lipopolysaccharide (LPS) in different concentrations or at separate times, cells were collected to analyze A20 expressions. We then constructed the A20 knockdown system by siRNA and the A20 overexpressing system by lentivirus transduction. Systems were further exposed to medium with or without LPS for indicated times. Next, we evaluated the production of inflammatory cytokines (IL-6 and IL-8) by qRT-PCR and ELISA. Also, the translocation of P65 and the phosphorylation of P65, P38 and JNK were observed in two systems. In addition, we used the nuclear factor kappa-B (NF-κB) antagonist TPCA-1 for the pretreatment in cells and then detected the A20 expressions. We found a low basal expression of A20 in HCE-T cells, and the expressions could be dose-dependently induced by LPS, peaking at 4 h in protein level after stimulation. Both the A20 knockdown and A20 overexpressing systems were confirmed to be effective. After the LPS treatment, productions of IL-6 and IL-8 were enhanced in the A20 knockdown system and reduced in the A20 overexpressing system. A20 reduced the translocation of P65 into the nucleus and the phosphorylation of P65, P38 and JNK. Furthermore, TPCA-1 pretreatment reduced the expression of A20 in cells. We concluded that A20 is a potent regulator for corneal epithelium's reaction to inflammation, and it thus is expected to be a potential therapy target for ocular surface diseases.

Extracellular matrix stiffness-The central cue for skin fibrosis

Skin fibrosis is a physiopathological process featuring the excessive deposition of extracellular matrix (ECM), which is the main architecture that provides structural support and constitutes the microenvironment for various cellular behaviors. Recently, increasing interest has been drawn to the relationship between the mechanical properties of the ECM and the initiation and modulation of skin fibrosis, with the engagement of a complex network of signaling pathways, the activation of mechanosensitive proteins, and changes in immunoregulation and metabolism. Simultaneous with the progression of skin fibrosis, the stiffness of ECM increases, which in turn perturbs mechanical and humoral homeostasis to drive cell fate toward an outcome that maintains and enhances the fibrosis process, thus forming a pro-fibrotic "positive feedback loop". In this review, we highlighted the central role of the ECM and its dynamic changes at both the molecular and cellular levels in skin fibrosis. We paid special attention to signaling pathways regulated by mechanical cues in ECM remodeling. We also systematically summarized antifibrotic interventions targeting the ECM, hopefully enlightening new strategies for fibrotic diseases.

TRAF trimers form immune signalling networks via RING domain dimerization

For many inflammatory cytokines, the response elicited is dependent on the recruitment of the tumour necrosis factor receptor-associated factor (TRAF) family of adaptor proteins. All TRAF proteins have a trimeric C-terminal TRAF domain, while at the N-terminus most TRAFs have a RING domain that forms dimers. The symmetry mismatch of the N- and C-terminal halves of TRAF proteins means that when receptors cluster, it is presumed that RING dimers connect TRAF trimers to form a network. Here, using purified TRAF6 proteins, we provide direct evidence in support of this model, and we show that TRAF6 trimers bind Lys63-linked ubiquitin chains to promote their processive assembly. This study provides critical evidence in support of TRAF trimers as key players in signalling.

Ubiquitin modification in osteogenic differentiation and bone formation: From mechanisms to clinical significance

The ubiquitin-proteasome system is an important pathway for mediating posttranslational modification and protein homeostasis and exerts a wide range of functions in diverse biological processes, including stem cell differentiation, DNA repair, and cell cycle regulation. Many studies have shown that ubiquitination modification plays a critical role in regulating the osteogenic differentiation of stem cells and bone formation through various mechanisms. This review summarizes current progress on the effects and mechanisms of ubiquitin modification on transcription factors and signaling pathways involved in osteogenic differentiation. Moreover, the review highlights the latest advances in the clinical application of drugs in bone tissue engineering. A thorough understanding of ubiquitin modifications may provide promising therapeutic targets for stem cell-based bone tissue engineering.

Association of TGF-β Canonical Signaling-Related Core Genes With Aortic Aneurysms and Aortic Dissections

Transforming growth factor-beta (TGF-β) signaling is essential for the maintenance of the normal structure and function of the aorta. It includes SMAD-dependent canonical pathways and noncanonical signaling pathways. Accumulated genetic evidence has shown that TGF-β canonical signaling-related genes have key roles in aortic aneurysms (AAs) and aortic dissections and many gene mutations have been identified in patients, such as those for transforming growth factor-beta receptor one TGFBR1, TGFBR2, SMAD2, SMAD3, SMAD4, and SMAD6. Aortic specimens from patients with these mutations often show paradoxically enhanced TGF-β signaling. Some hypotheses have been proposed and new AA models in mice have been constructed to reveal new mechanisms, but the role of TGF-β signaling in AAs is controversial. In this review, we focus mainly on the role of canonical signaling-related core genes in diseases of the aorta, as well as recent advances in gene-mutation detection, animal models, and in vitro studies.

The m6A reader IGF2BP3 promotes acute myeloid leukemia progression by enhancing RCC2 stability

N6-methyladenosine (m6A) is the most abundant posttranscriptional modification of mRNA in eukaryotes. Recent evidence suggests that dysregulated m6A-associated proteins and m6A modifications play a pivotal role in the initiation and progression of diseases such as cancer. Here, we identified that IGF2BP3 is specifically overexpressed in acute myeloid leukemia (AML), a subtype of leukemia associated with poor prognosis and high genetic risk. IGF2BP3 is required for maintaining AML cell survival in an m6A-dependent manner, and knockdown of IGF2BP3 dramatically suppresses the apoptosis, reduces the proliferation, and impairs the leukemic capacity of AML cells in vitro and in vivo. Mechanistically, IGF2BP3 interacts with RCC2 mRNA and stabilizes the expression of m6A-modified RNA. Thus, we provided compelling evidence demonstrating that the m6A reader IGF2BP3 contributes to tumorigenesis and poor prognosis in AML and can serve as a target for the development of cancer therapeutics.

Inhibiting a protein that is overexpressed in the bone marrow of acute myeloid leukemia patients may prove valuable in treating the disease. Recent research has demonstrated the important role played by epigenetics in cancers – for example, disruption to a common mRNA modification known as m6A can result in cancer initiation and progression. Jianchuan Deng and co-workers at Chongqing Medical Universit0y, China, examined the role of an m6A-related protein called IGF2BP3 in mice models and samples from leukemia patients. IGF2BP3 was overexpressed in patients’ bone marrows, the levels of the protein correlating with extent of proliferation of leukemia cells and poor prognosis. IGF2BP3 stabilises the activity of a known cancer-related protein, promoting leukemia progression. Blocking IGF2BP3 expression reduced cell proliferation and impaired activity of leukemic cells, suggesting the protein may be a useful therapeutic target.

Structural mechanism for regulation of Rab7 by site-specific monoubiquitination

Site-specific ubiquitination can regulate the functions of Rab proteins in membrane trafficking. Previously we showed that site-specific monoubiquitination on Rab5 downregulates its function. Rab7 acts in the downstream of Rab5. Although site-specific ubiquitination of Rab7 can affect its function, it remains elusive how the ubiquitination is involved in modulation of the function of Rab7 at molecular level. Here, we report molecular basis for the regulation of Rab7 by site-specific monoubiquitination. Rab7 was predominantly monoubiquitinated at multiple sites in the membrane fraction of cultured cells. Two major ubiquitination sites (K191 and K194), identified by mutational analysis with single K mutants, were responsible for membrane localization of monoubiquitinated Rab7. Using small-angle X-ray scattering, we derived structural models of site-specifically monoubiquitinated Rab7 in solution. Structural analysis combined with molecular dynamics simulation corroborated that the ubiquitin moieties on K191 and K194 are key determinants for exclusion of Rab7 from the endosomal membrane. Ubiquitination on the two major sites apparently mitigated colocalization of Rab7 with ORF3a of SARS-CoV-2, potentially deterring the egression of SARS-CoV-2. Our results establish that the regulatory effects of a Rab protein through site-specific monoubiquitination are commonly observed among Rab GTPases while the ubiquitination sites differ in each Rab protein.

Regional Diversities in Fibrogenesis Weighed as a Key Determinant for Atrial Arrhythmogenesis

Atrial fibrosis plays a key role in atrial myopathy, resulting in the genesis of atrial fibrillation (AF). The abnormal distribution of fibrotic tissue, electrical coupling, paracrine interactions, and biomechanical–electrical interactions have all been suggested as causes of fibrosis-related arrhythmogenesis. Moreover, the regional difference in fibrogenesis, specifically the left atrium (LA) exhibiting a higher arrhythmogenesis and level of fibrosis than the right atrium (RA) in AF, is a key contributor to atrial arrhythmogenesis. LA fibroblasts have greater profibrotic cellular activities than RA fibroblasts, but knowledge about the regional diversity of atrial regional fibrogenesis remains limited. This article provides a comprehensive review of research findings on the association between fibrogenesis and arrhythmogenesis from laboratory to clinical evidence and updates the current understanding of the potential mechanism underlying the difference in fibrogenesis between the LA and RA.

FGF-2 induces a failure of cell cycle progression in cells harboring amplified K-Ras, revealing new insights into oncogene-induced senescence

Paradoxically, oncogenes that drive cell cycle progression may also trigger pathways leading to senescence, thereby inhibiting the growth of tumorigenic cells. Knowledge of how these pathways operate, and how tumor cells may evade these pathways, is important for understanding tumorigenesis. The Y1 cell line, which harbors an amplification of the proto-oncogene Ras, rapidly senesces in response to the mitogen fibroblast growth factor-2 (FGF-2). To gain a more complete picture of how FGF-2 promotes senescence, we employed a multi-omics approach to analyze histone modifications, mRNA and protein expression, and protein phosphorylation in Y1 cells treated with FGF-2. Compared to control cells treated with serum alone, FGF-2 caused a delayed accumulation of acetylation on histone H4 and higher levels of H3K27me3. Sequencing analysis revealed decreased expression of cell cycle-related genes with concomitant loss of H3K27ac. At the same time, FGF-2 promoted the expression of p21, various cytokines, and MAPK-related genes. Nuclear envelope proteins, particularly lamin B1, displayed increased phosphorylation in response to FGF-2. Proteome analysis suggested alterations in cellular metabolism, as evident by modulated expression of enzymes involved in purine biosynthesis, tRNA aminoacylation, and the TCA cycle. We propose that Y1 cells senesce due to an inability to progress through the cell cycle, which may stem from DNA damage or TGFb signaling. Altogether, the phenotype of Y1 cells is consistent with rapidly established oncogene-induced senescence, demonstrating the synergy between growth factors and oncogenes in driving senescence and bringing additional insight into this tumor suppressor mechanism.

Genome-wide CRISPR screens reveal cyclin C as synthetic survival target of BRCA2

Poly (ADP-ribose) polymerase inhibitor (PARPi)-based therapies initially reduce tumor burden but eventually lead to acquired resistance in cancer patients with BRCA1 or BRCA2 mutation. To understand the potential PARPi resistance mechanisms, we performed whole-genome CRISPR screens to discover genetic alterations that change the gene essentiality in cells with inducible depletion of BRCA2. We identified that several RNA Polymerase II transcription Mediator complex components, especially Cyclin C (CCNC) as synthetic survival targets upon BRCA2 loss. Total mRNA sequencing demonstrated that loss of CCNC could activate the transforming growth factor (TGF)-beta signaling pathway and extracellular matrix (ECM)-receptor interaction pathway, however the inhibition of these pathways could not reverse cell survival in BRCA2 depleted CCNC-knockout cells, indicating that the activation of these pathways is not required for the resistance. Moreover, we showed that the improved survival is not due to restoration of homologous recombination repair although decreased DNA damage signaling was observed. Interestingly, loss of CCNC could restore replication fork stability in BRCA2 deficient cells, which may contribute to PARPi resistance. Taken together, our data reveal CCNC as a critical genetic determinant upon BRCA2 loss of function, which may help the development of novel therapeutic strategies that overcome PARPi resistance.

TGF-β signaling: A recap of SMAD-independent and SMAD-dependent pathways

Transforming growth factor-β (TGF-β) is a proinflammatory cytokine known to control a diverse array of pathological and physiological conditions during normal development and tumorigenesis. TGF-β-mediated physiological effects are heterogeneous and vary among different types of cells and environmental conditions. TGF-β serves as an antiproliferative agent and inhibits tumor development during primary stages of tumor progression; however, during the later stages, it encourages tumor development and mediates metastatic progression and chemoresistance. The fundamental elements of TGF-β signaling have been divulged more than a decade ago; however, the process by which the signals are relayed from cell surface to nucleus is very complex with additional layers added in tumor cell niches. Although the intricate understanding of TGF-β-mediated signaling pathways and their regulation are still evolving, we tried to make an attempt to summarize the TGF-β-mediated SMAD-dependent andSMAD-independent pathways. This manuscript emphasizes the functions of TGF-β as a metastatic promoter and tumor suppressor during the later and initial phases of tumor progression respectively.

Schisantherin A ameliorates liver fibrosis through TGF-β1mediated activation of TAK1/MAPK and NF-κB pathways in vitro and in vivo

BACKGROUD

Schisandra chinensis, a traditional Chinese medicine for liver protection, can significantly improve liver fibrosis. However, it is still unclear which active components in Schisandra chinensis play an anti-fibrosis role.

PURPOSE

The purpose of present study was to observe the anti-fibrosis effect of schisantherin A (SCA) on liver fibrosis and explore its underlying mechanism.

METHODS

The liver fibrosis model of mice was constructed by the progressive intraperitoneal injection of thioacetamide (TAA), and SCA (1, 2, and 4 mg/kg) was administered by gavage for 5 weeks. The biochemical indicators and inflammatory cytokines were measured, changes in the pathology of the mice liver were observed by hematoxylin & eosin (H&E) and Masson stainings for studying the anti-fibrosis effect of SCA. A hepatic stellate cell (HSCs) activation model induced by transforming growth factor-β1 (TGF-β1) was established, and the effect of SCA on the HSCs proliferation was observed by MTT assay. The expressions of target proteins related to transforming growth factor-β-activated kinase 1 (TAK1)/mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) pathways were evaluated by western blotting, immunohistochemistry or immunofluorescence analysis, to explore the potential mechanism of SCA.

RESULTS

SCA could significantly ameliorate the pathological changes of liver tissue induced by TAA, and reduce the serum transaminase level, the hydroxyproline level and the expression of α-smooth muscle actin (α-SMA) and collagen 1A1 (COL1A1) proteins in the liver tissue. SCA could significantly lower the levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) in the serum and liver tissue, and down-regulate the expression of target proteins related to TAK1/MAPK and NF-κB pathways in the liver tissue. The in vitro studies demonstrated that SCA significantly inhibited the proliferation and activation of HCS-T6 cells induced by TGF-β1, decreased TNF-α and IL-6 levels, and inhibited the TAK1 activation induced by TGF-β1 and then the expression of MAPK and NF-κB signaling pathway-related proteins.

CONCLUSION

Together, SCA can ameliorate the liver fibrosis induced by TAA and the HSC-T6 cell activation induced by TGF-β1 in mice, and its mechanism may be to inhibit the HSCs activation and inflammatory response by inhibiting TGF-β1 mediated TAK1/MAPK and signal pathways.

Origins, potency, and heterogeneity of skeletal muscle fibro-adipogenic progenitors-time for new definitions

Striated muscle is a highly plastic and regenerative organ that regulates body movement, temperature, and metabolism-all the functions needed for an individual's health and well-being. The muscle connective tissue's main components are the extracellular matrix and its resident stromal cells, which continuously reshape it in embryonic development, homeostasis, and regeneration. Fibro-adipogenic progenitors are enigmatic and transformative muscle-resident interstitial cells with mesenchymal stem/stromal cell properties. They act as cellular sentinels and physiological hubs for adult muscle homeostasis and regeneration by shaping the microenvironment by secreting a complex cocktail of extracellular matrix components, diffusible cytokines, ligands, and immune-modulatory factors. Fibro-adipogenic progenitors are the lineage precursors of specialized cells, including activated fibroblasts, adipocytes, and osteogenic cells after injury. Here, we discuss current research gaps, potential druggable developments, and outstanding questions about fibro-adipogenic progenitor origins, potency, and heterogeneity. Finally, we took advantage of recent advances in single-cell technologies combined with lineage tracing to unify the diversity of stromal fibro-adipogenic progenitors. Thus, this compelling review provides new cellular and molecular insights in comprehending the origins, definitions, markers, fate, and plasticity of murine and human fibro-adipogenic progenitors in muscle development, homeostasis, regeneration, and repair.

An Overview of the Posttranslational Modifications and Related Molecular Mechanisms in Diabetic Nephropathy

Diabetic nephropathy (DN), a common diabetic microvascular complication, is characterized by its complex pathogenesis, higher risk of mortality, and the lack of effective diagnosis and treatment methods. Many studies focus on the diagnosis and treatment of diabetes mellitus (DM) and have reported that the pathophysiology of DN is very complex, involving many molecules and abnormal cellular activities. Given the respective pivotal roles of NF-κB, Nrf2, and TGF-β in inflammation, oxidative stress, and fibrosis during DN, we first review the effect of posttranslational modifications on these vital molecules in DN. Then, we describe the relationship between these molecules and related abnormal cellular activities in DN. Finally, we discuss some potential directions for DN treatment and diagnosis. The information reviewed here may be significant in the design of further studies to identify valuable therapeutic targets for DN.

Effect of DNA methylation on gene transcription is associated with the distribution of methylation sites across the genome in osteoarthritis

Genetics and epigenetics are important subjects in the field of osteoarthritis (OA) research. DNA methylation may affect gene transcription, but the specific mechanisms have remained to be fully elucidated. In the present study, the ChAMP methylation analysis package was used to identify differentially methylated genes (DMGs) from the dataset GSE63695 from the Gene Expression Omnibus (GEO) database. The distribution of differentially methylated sites (DMS) and the total array sites across the genome were analyzed by enrichment analysis. Subsequently, two mRNA expression profiling datasets, GSE114007 and GSE113825, were obtained from the GEO database and common differentially expressed genes (DEGs) were identified using the Limma package. Key genes were screened by analyzing the distribution of DMS across the genome consisting of DEGs and DMGs. A total of 1,662 and 1,986 DEGs were identified between OA and normal human cartilage from the GSE113825 and GSE114007 dataset, respectively. A further screening revealed 292 genes with common differences between the two datasets. A total of 574 DMS containing 394 DMGs were observed between OA and normal cartilage. Integrative analysis revealed a corresponding subset of 15 genes. Of these, 6 genes were verified by reverse transcription-quantitative PCR, confirming that the mRNA expression of 5 genes (MAP1B, FNDC1, ANLN, SCNN1A and STC2) in OA cartilage was consistent with the mRNA expression from the analysis of the datasets. Upon treatment with the DNA methylation inhibitor 5-aza-2'-deoxycytidine, the mRNA levels of FNDC1 and SCNN1A were decreased, and no significant alteration in the mRNA levels of MAP1B, ANLN, KCNN4 and STC2 was observed. The incidence of differential methylation varied in subregions of the genome and the effects on transcription were associated with the distribution of DEGs across the genome. The regulation of this appears more complex than initially postulated. Combining the data on epigenetic differences of OA with the genome or transcriptome data for analysis may improve the understanding of the pathophysiological processes of OA. FNDC1 and SCNN1A may potentially be valuable biomarkers for OA.

Inhibitory Smads suppress pancreatic stellate cell activation through negative feedback in chronic pancreatitis

Background

Activation of pancreatic stellate cells (PSCs) is a key cause of chronic pancreatitis (CP), while inhibition of transforming growth factor-β (TGF-β) signaling renders PSCs inactive. Inhibitory Smads (I-Smads) impede TGF-β intracellular signaling and may provide a way to alleviate CP. Thus, we aimed to investigate the molecular mechanism of I-Smads in CP animals and freshly-isolated PSCs.

Methods

Sixteen male C57BL/6 mice were randomly divided into two groups; a control group (treated with saline) and a CP group (treated with caerulein) for 6 weeks. Masson’s staining was performed to identify fibrosis, and immunohistochemistry (IHC) was performed to measure the levels of Smad6 between the two groups. An improved method derived from internal digestion was used to isolate PSCs from male Sprague Dawley rats. Quantitative real-time polymerase chain reaction (qRT-PCR) and immunofluorescence staining were used to measure the messenger ribonucleic acid (mRNA) and protein levels of alpha-smooth muscle actin (α-SMA). Plasmids of I-Smads or SB431542 were transfected into freshly-isolated PSCs, and relative mRNA levels of marker genes were quantified by qRT-PCR. The two-tailed Student’s t-test was performed to assess significance.

Results

The Smad6 protein level was significantly higher in the pancreas tissue of CP mice compared to the control group. A large number of PSCs were isolated from rat pancreas using an improved isolating method and were confirmed by quiescent and active PSC markers including cluster differentiation antigen 133 (CD133), perilipin 2 (Plin2), α-SMA, Desmin, and collagen 1 (Col1). The mRNA levels of both Smad6 and Smad7 were down-regulated during freshly-isolated PSC activation. Over-expression of both Smad6 and Smad7 in freshly-isolated PSC reduced the mRNA level of α-SMA, glial fibrillary acidic protein (GFAP), Desmin, Col1, Col3, and fibronectin 1 (Fn1) significantly. SB431542 reduced the mRNA level of α-SMA, Col1, Col3, and Fn1 significantly in freshly-isolated PSCs.

Conclusions

This study demonstrated that CP promoted the expression of I-Smads, which suppressed the activation of freshly-isolated PSCs via a negative feedback loop.

E3 Ubiquitin Ligases: Key Regulators of TGFβ Signaling in Cancer Progression

Transforming growth factor β (TGFβ) is a secreted growth and differentiation factor that influences vital cellular processes like proliferation, adhesion, motility, and apoptosis. Regulation of the TGFβ signaling pathway is of key importance to maintain tissue homeostasis. Perturbation of this signaling pathway has been implicated in a plethora of diseases, including cancer. The effect of TGFβ is dependent on cellular context, and TGFβ can perform both anti- and pro-oncogenic roles. TGFβ acts by binding to specific cell surface TGFβ type I and type II transmembrane receptors that are endowed with serine/threonine kinase activity. Upon ligand-induced receptor phosphorylation, SMAD proteins and other intracellular effectors become activated and mediate biological responses. The levels, localization, and function of TGFβ signaling mediators, regulators, and effectors are highly dynamic and regulated by a myriad of post-translational modifications. One such crucial modification is ubiquitination. The ubiquitin modification is also a mechanism by which crosstalk with other signaling pathways is achieved. Crucial effector components of the ubiquitination cascade include the very diverse family of E3 ubiquitin ligases. This review summarizes the diverse roles of E3 ligases that act on TGFβ receptor and intracellular signaling components. E3 ligases regulate TGFβ signaling both positively and negatively by regulating degradation of receptors and various signaling intermediates. We also highlight the function of E3 ligases in connection with TGFβ's dual role during tumorigenesis. We conclude with a perspective on the emerging possibility of defining E3 ligases as drug targets and how they may be used to selectively target TGFβ-induced pro-oncogenic responses.

The Ubiquitin System and A20: Implications in Health and Disease

Inflammation is triggered by stimulation of innate sensors that recognize pathogens, chemical and physical irritants, and damaged cells subsequently initiating a well-orchestrated adaptive immune response. Immune cell activation is a strictly regulated and self-resolving process supported by an array of negative feedback mechanisms to sustain tissue homeostasis. The disruption of these regulatory pathways forms the basis of chronic inflammatory diseases, including periodontitis. Ubiquitination, a covalent posttranslational modification of target proteins with ubiquitin, has a profound effect on the stability and activity of its substrates, thereby regulating the immune system at molecular and cellular levels. Through the cooperative actions of E3 ubiquitin ligases and deubiquitinases, ubiquitin modifications are implicated in several biological processes, including proteasomal degradation, transcriptional regulation, regulation of protein-protein interactions, endocytosis, autophagy, DNA repair, and cell cycle regulation. A20 (tumor necrosis factor α-induced protein 3 or TNFAIP3) is a ubiquitin-editing enzyme that mainly functions as an endogenous regulator of inflammation through termination of nuclear factor (NF)-κB activation as part of a negative feedback loop. A20 interacts with substrates that reside downstream of immune sensors, including Toll-like receptors, nucleotide-binding oligomerization domain-containing receptors, lymphocyte receptors, and cytokine receptors. Due to its pleiotropic functions as a ubiquitin binding protein, deubiquitinase and ubiquitin ligase, and its versatile role in various signaling pathways, aberrant A20 levels are associated with numerous conditions such as rheumatoid arthritis, diabetes, systemic lupus erythematosus, inflammatory bowel disease, psoriasis, Sjögren syndrome, coronary artery disease, multiple sclerosis, cystic fibrosis, asthma, cancer, neurological disorders, and aging-related sequelae. Similarly, A20 has recently been implicated as an essential regulator of inflammation in the oral cavity. This review presents information on the ubiquitin system and regulation of NF-κB by ubiquitination using A20 as a representative molecule and highlights how the dysregulation of this system can lead to several immune pathologies, including oral cavity-related disorders mainly focusing on periodontitis.

Molecular Characterization and Clinical Relevance of RNA Binding Proteins in Colorectal Cancer

Abnormal expression of RNA binding proteins (RBPs) has been reported across various cancers. However, the potential role of RBPs in colorectal cancer (CRC) remains unclear. In this study, we performed a systematic bioinformatics analysis of RBPs in CRC. We downloaded CRC data from The Cancer Genome Atlas (TCGA) database. Our analysis identified 242 differentially expressed RBPs between tumor and normal tissues, including 200 upregulated and 42 downregulated RBPs. Next, we found eight RBPs (RRS1, PABPC1L, TERT, SMAD6, UPF3B, RP9, NOL3, and PTRH1) related to the prognoses of CRC patients. Among these eight prognosis-related RBPs, four RBPs (NOL3, PTRH1, UPF3B, and SMAD6) were selected to construct a prognostic risk score model. Furthermore, our results indicated that the prognostic risk score model accurately predicted the prognosis of CRC patients [area under the receiver operating characteristic curve (AUC)for 3- and 5-year overall survival (OS) and was 0.645 and 0.672, respectively]. Furthermore, we developed a nomogram based on a prognostic risk score model. The nomogram was able to demonstrate the wonderful performance in predicting 3- and 5-year OS. Additionally, we validated the clinical value of four risk genes in the prognostic risk score model and identified that these risk genes were associated with tumorigenesis, lymph node metastasis, distant metastasis, clinical stage, and prognosis. Finally, we used the TIMER and Human Protein Atlas (HPA)database to validate the expression of four risk genes at the transcriptional and translational levels, respectively, and used a clinical cohort to validate the roles of NOL3 and UPF3B in predicting the prognosis of CRC patients. In summary, our study demonstrated that RBPs have an effect on CRC tumor progression and might be potential prognostic biomarkers for CRC patients.

TGFβ as a gatekeeper of BMP action in the developing growth plate

The ligands that comprise the Transforming Growth Factor β superfamily highly govern the development of the embryonic growth plate. Members of this superfamily activate canonical TGFβ and/or BMP (Bone Morphogenetic Protein) signaling pathways. How these pathways interact with one another is an area of active investigation. These two signaling pathways have been described to negatively regulate one another through crosstalk involving Smad proteins, the primary intracellular effectors of canonical signaling. More recently, a mechanism for regulation of the BMP pathway through TGFβ and BMP receptor interactions has been described. Here in this review, we demonstrate examples of how TGFβ is a gatekeeper of BMP action in the developing growth plate at both the receptor and transcriptional levels.

Study on the relationship between hepatic fibrosis and epithelial-mesenchymal transition in intrahepatic cells

Hepatic fibrosis is a pathophysiological process, which causes excessive extracellular matrix (ECM) deposition resulting from persistent liver damage. Myofibroblasts are the core cells that produce ECM. It is known that epithelial-mesenchymal transition (EMT) is not a simple transition of cells from the epithelial to mesenchymal state. Instead, it is a process, in which epithelial cells temporarily lose cell polarity, transform into interstitial cell-like morphology, and acquire migration ability. Hepatocytes, hepatic stellate cells, and bile duct cells are the types of intrahepatic cells found in the liver. They can be transformed into myofibroblasts via EMT and play important roles in the development of hepatic fibrosis through a maze of regulations involving various pathways. The aim of the present study is to explore the relationship between the relevant regulatory factors and the EMT signaling pathways in the various intrahepatic cells.

TGF-β Signaling

Transforming growth factor-β (TGF-β) represents an evolutionarily conserved family of secreted polypeptide factors that regulate many aspects of physiological embryogenesis and adult tissue homeostasis. The TGF-β family members are also involved in pathophysiological mechanisms that underlie many diseases. Although the family comprises many factors, which exhibit cell type-specific and developmental stage-dependent biological actions, they all signal via conserved signaling pathways. The signaling mechanisms of the TGF-β family are controlled at the extracellular level, where ligand secretion, deposition to the extracellular matrix and activation prior to signaling play important roles. At the plasma membrane level, TGF-βs associate with receptor kinases that mediate phosphorylation-dependent signaling to downstream mediators, mainly the SMAD proteins, and mediate oligomerization-dependent signaling to ubiquitin ligases and intracellular protein kinases. The interplay between SMADs and other signaling proteins mediate regulatory signals that control expression of target genes, RNA processing at multiple levels, mRNA translation and nuclear or cytoplasmic protein regulation. This article emphasizes signaling mechanisms and the importance of biochemical control in executing biological functions by the prototype member of the family, TGF-β.

MicroRNA-127 Promotes Anti-microbial Host Defense through Restricting A20-Mediated De-ubiquitination of STAT3

The increasing rising of multiple drug-resistant Staphylococcus aureus has become a major public health concern, underscoring a pressing need for developing therapies essentially based on the understanding of host defensive mechanism. In the present study, we showed that microRNA (miR)-127 played a key role in controlling bacterial infection and conferred a profound protection against staphylococcal pneumonia. The protective effect of miR-127 was largely dependent on its regulation of macrophage bactericidal activity and the generation of IL-22, IL-17, and anti-microbial peptides (AMPs), the pathway primarily driven by STAT3. Importantly, we revealed that the ubiquitin-editing enzyme A20, a genuine target of miR-127, specifically interacted with and repressed K63-ubiquitination of STAT3, thereby compromising its phosphorylation upon bacterial infection. Thus, our data not only identify miR-127 as a non-coding molecule with anti-bacterial activity but also delineate an unappreciated mechanism whereby A20 regulates STAT3-driven anti-microbial signaling via modulating its ubiquitination.

The TGF-β pathway plays a key role in aortic aneurysms

Aortic dissection and aortic aneurysms are currently among the most high-risk cardiovascular diseases due to their rapid onset and high mortality. Although aneurysm research has been extensive, the pathogenesis remains unknown. Studies have found that the TGF-β/Smad pathway and aneurysm formation appear linked. For example, the TGF-β signaling pathway was significantly activated in aneurysm development and aortic dissection. Aneurysms are not, however, mitigated following knockdown of TGF-β signaling pathway-related genes. Incidence and mortality rate of ruptured thoracic aneurysms increase with the down-regulation of the classical TGF-β signaling pathway. In this review, we summarize recent findings and evaluate the differential role of classical and non-classical TGF-β pathways on aortic aneurysm. It is postulated that the TGF-β signaling pathway is necessary to maintain vascular function, but over-activation will promote aneurysms whereas over-inhibition will lead to bypass pathway over-activation and promote aneurysm occurrence.

MiR-32-5p aggravates intestinal epithelial cell injury in pediatric enteritis induced by Helicobacter pylori

BACKGROUND

Pediatric enteritis is one of the infectious diseases in the digestive system that causes a variety of digestive problems, including diarrhea, vomiting, and bellyache in children. Clinically, Helicobacter pylori (H. pylori) infection is one of the common factors to cause pediatric enteritis. It has been demonstrated that aberrant expression of microRNAs (miRNAs) is found in gastrointestinal diseases caused by H. pylori, and we discovered a significant increase of miR-32-5p in H. pylori-related pediatric enteritis. However, the exact role of miR-32-5p in it is still unknown.

AIM

To investigate the role of aberrant miR-32-5p in pediatric enteritis induced by H. pylori.

METHODS

MiR-32-5p expression was detected by quantitative real time-polymerase chain reaction. The biological role of miR-32-5p in H. pylori-treated intestinal epithelial cells was evaluated by Cell Counting Kit-8 assay and flow cytometry. The potential target of miR-32-5p was predicted with TargetScanHuman and verified by luciferase assay. The downstream mechanism of miR-32-5p was explored by using molecular biology methods.

RESULTS

We found that miR-32-5p was overexpressed in serum of H. pylori-induced pediatric enteritis. Further investigation revealed that H. pylori infection promoted the death of intestinal epithelial cells, and increased miR-32-5p expression. Moreover, miR-32-5p mimic further facilitated apoptosis and inflammatory cytokine secretion of intestinal epithelial cells. Further exploration revealed that SMAD family member 6 (SMAD6) was the direct target of miR-32-5p, and SMAD6 overexpression partially rescued cell damage induced by H. pylori. The following experiments showed that miR-32-5p/SMAD6 participated in the apoptosis of intestinal epithelial cells induced by transforming growth factor-β-activated kinase 1 (TAK1)-p38 activation under H. pylori infection.

CONCLUSION

Our work uncovered the crucial role of aberrant expression of miR-32-5p in H. pylori–related pediatric enteritis, and suggested that the TAK1-p38 pathway is involved in it.

Targeting Degradation of the Transcription Factor C/EBPβ Reduces Lung Fibrosis by Restoring Activity of the Ubiquitin-Editing Enzyme A20 in Macrophages

Although recent progress provides mechanistic insights into the pathogenesis of pulmonary fibrosis (PF), rare anti-PF therapeutics show definitive promise for treating this disease. Repeated lung epithelial injury results in injury-repairing response and inflammation, which drive the development of PF. Here, we report that chronic lung injury inactivated the ubiquitin-editing enzyme A20, causing progressive accumulation of the transcription factor C/EBPβ in alveolar macrophages (AMs) from PF patients and mice, which upregulated a number of immunosuppressive and profibrotic factors promoting PF development. In response to chronic lung injury, elevated glycogen synthase kinase-3β (GSK-3β) interacted with and phosphorylated A20 to suppress C/EBPβ degradation. Ectopic expression of A20 or pharmacological restoration of A20 activity by disturbing the A20-GSK-3β interaction accelerated C/EBPβ degradation and showed potent therapeutic efficacy against experimental PF. Our study indicates that a regulatory mechanism of the GSK-3β-A20-C/EBPβ axis in AMs may be a potential target for treating PF and fibroproliferative lung diseases.

Specificity, versatility, and control of TGF-β family signaling

Encoded in mammalian cells by 33 genes, the transforming growth factor-β (TGF-β) family of secreted, homodimeric and heterodimeric proteins controls the differentiation of most, if not all, cell lineages and many aspects of cell and tissue physiology in multicellular eukaryotes. Deregulation of TGF-β family signaling leads to developmental anomalies and disease, whereas enhanced TGF-β signaling contributes to cancer and fibrosis. Here, we review the fundamentals of the signaling mechanisms that are initiated upon TGF-β ligand binding to its cell surface receptors and the dependence of the signaling responses on input from and cooperation with other signaling pathways. We discuss how cells exquisitely control the functional presentation and activation of heteromeric receptor complexes of transmembrane, dual-specificity kinases and, thus, define their context-dependent responsiveness to ligands. We also introduce the mechanisms through which proteins called Smads act as intracellular effectors of ligand-induced gene expression responses and show that the specificity and impressive versatility of Smad signaling depend on cross-talk from other pathways. Last, we discuss how non-Smad signaling mechanisms, initiated by distinct ligand-activated receptor complexes, complement Smad signaling and thus contribute to cellular responses.

TGF-β signaling pathway mediated by deubiquitinating enzymes

Ubiquitination is a reversible cellular process mediated by ubiquitin-conjugating enzymes, whereas deubiquitinating enzymes (DUBs) detach the covalently conjugated ubiquitin from target substrates to counter ubiquitination. DUBs play a crucial role in regulating various signal transduction pathways and biological processes including apoptosis, cell proliferation, DNA damage repair, metastasis, differentiation, etc. Since the transforming growth factor-β (TGF-β) signaling pathway participates in various cellular functions such as inflammation, metastasis and embryogenesis, aberrant regulation of TGF-β signaling induces abnormal cellular functions resulting in numerous diseases. This review focuses on DUBs regulating the TGF-β signaling pathway. We discuss the molecular mechanisms of DUBs involved in TGF-β signaling pathway, and biological and therapeutic implications for various diseases.

Expression, purification, and evaluation of in vivo anti-fibrotic activity for soluble truncated TGF-β receptor II as a cleavable His-SUMO fusion protein

Excessive production of transforming growth factor-β1 (TGF-β1) and its binding to transforming growth factor-β receptor type II (TGF-βRII) promotes fibrosis by activation of the TGF-β1-mediated signaling pathway. Thus, the truncated extracellular domain of TGF-βRII (tTβRII) is a promising anti-fibrotic candidate, as it lacks the signal transduction domain. In this work, the native N-terminal tTβRII was prepared as a His-SUMO fusion protein (termed His-SUMO-tTβRII) in Escherichia coli strain BL21 (DE3). His-SUMO-tTβRII was expressed as a soluble protein under optimal conditions (6 h of induction with 0.5 mM IPTG at 37 °C). His-SUMO-tTβRII was purified by Ni-NTA resin chromatography, and then cleaved with SUMO protease to release native tTβRII, which was re-purified using a Ni-NTA column. Approximately 12 mg of native tTβRII was obtained from a one liter fermentation culture with no less than 95% purity. In vivo studies demonstrated that tTβRII prevented CCl₄-induced liver fibrosis, as evidenced by the inhibition of fibrosis-related Col I and α-SMA protein expression in C57BL/6 mice. In addition, tTβRII downregulated phosphorylation of SMAD2/3, which partly repressed TGF-β1-mediated signaling. These data indicate that the His-SUMO expression system is an efficient approach for preparing native tTβRII that possesses anti-liver fibrotic activity, allowing for the large-scale production of tTβRII, which potentially could serve as an anti-fibrotic candidate for treatment of TGF-β1-related diseases.

BCL3 regulates RANKL-induced osteoclastogenesis by interacting with TRAF6 in bone marrow-derived macrophages

OBJECTIVE

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an essential component of the signaling complex that mediates osteoclastogenesis. As an adaptor protein of E3 ligase function, TRAF6 regulates NF-κB signaling via TAK1 and I-κB kinase (IKK) activation. Here, we investigated novel mechanisms by which TRAF6 signaling is regulated under receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis.

DESIGN

A yeast two-hybrid screen system identified cellular factors that interact with TRAF6. The interactions were confirmed by glutathione S-transferase pull-down and co-immunoprecipitation assays, followed by immuno-blotting. The role of TRAF6 in bone growth and remodeling was determined by osteoclast differentiation and bone-resorption pit assays. Regulatory mechanisms were examined by co-immunoprecipitation, immuno-blotting, real-time polymerase chain reaction, and luciferase reporter assays.

RESULTS

We show that B-cell chronic lymphatic leukemia protein 3 (BCL3) interacts with TRAF6 through its ankyrin-repeat domain and inhibits osteoclastogenesis in bone marrow derived macrophages (BMDMs). Further, TRAF6 interacts with CYLD to mediate BCL3 deubiquitination, which facilitates the cytoplasmic accumulation of BCL3 and represses BCL3 and p50 complex-mediated cyclin D1 transcription.

CONCLUSIONS

TRAF6 promotes RANKL-induced osteoclastogenesis by regulating novel non-canonical NF-κB signaling via BCL3 deubiquitination, indicating that BCL3 provides valuable insights into bone loss-associated diseases.

Deubiquitinating Enzymes and Bone Remodeling

Bone remodeling, which is essential for bone homeostasis, is controlled by multiple factors and mechanisms. In the past few years, studies have emphasized the role of the ubiquitin-dependent proteolysis system in regulating bone remodeling. Deubiquitinases, which are grouped into five families, remove ubiquitin from target proteins and are involved in several cell functions. Importantly, a number of deubiquitinases mediate bone remodeling through regulating differentiation and/or function of osteoblast and osteoclasts. In this review, we review the functions and mechanisms of deubiquitinases in mediating bone remodeling.

Nuclear Smad6 promotes gliomagenesis by negatively regulating PIAS3-mediated STAT3 inhibition

To date, the molecular mechanism underlying constitutive signal transducer and activator of transcription 3 (STAT3) activation in gliomas is largely unclear. In this study, we report that Smad6 is overexpressed in nuclei of glioma cells, which correlates with poor patient survival and regulates STAT3 activity via negatively regulating the Protein Inhibitors of Activated STAT3 (PIAS3). Mechanically, Smad6 interacts directly with PIAS3, and this interaction is mediated through the Mad homology 2 (MH2) domain of Smad6 and the Ring domain of PIAS3. Smad6 recruits Smurf1 to facilitate PIAS3 ubiquitination and degradation, which also depends on the MH2 domain and the PY motif of Smad6. Consequently, Smad6 reduces PIAS3-mediated STAT3 inhibition and promotes glioma cell growth and stem-like cell initiation. Moreover, the Smad6 MH2 transducible protein restores PIAS3 expression and subsequently reduces gliomagenesis. Collectively, we conclude that nuclear-Smad6 enhances glioma development by inducing PIAS3 degradation and subsequent STAT3 activity upregulation.

In glioma STAT3 signaling contributes to gliomagenesis. Here, the authors show that Smad6 expression correlates with poor survival and is overexpressed in glioma cells, and regulates STAT3 activity via negatively regulating PIAS3.

The deubiquitinating enzyme USP20 stabilizes ULK1 and promotes autophagy initiation

Autophagy begins with the formation of autophagosomes, a process that depends on the activity of the serine/threonine kinase ULK1 (hATG1). Although earlier studies indicated that ULK1 activity is regulated by dynamic polyubiquitination, the deubiquitinase involved in the regulation of ULK1 remained unknown. In this study, we demonstrate that ubiquitin-specific protease 20 (USP20) acts as a positive regulator of autophagy initiation through stabilizing ULK1. At basal state, USP20 binds to and stabilizes ULK1 by removing the ubiquitin moiety, thereby interfering with the lysosomal degradation of ULK1. The stabilization of basal ULK1 protein levels is required for the initiation of starvation-induced autophagy, since the depletion of USP20 by RNA interference inhibits LC3 puncta formation, a marker of autophagic flux. At later stages of autophagy, USP20 dissociates from ULK1, resulting in enhanced ULK1 degradation and apoptosis. Taken together, our findings provide the first evidence that USP20 plays a crucial role in autophagy initiation by maintaining the basal expression level of ULK1.

Smad6 Methylation Represses NFκB Activation and Periodontal Inflammation

The balance between pro- and anti-inflammatory signals maintains tissue homeostasis and defines the outcome of chronic inflammatory diseases such as periodontitis, a condition that afflicts the tooth-supporting tissues and exerts an impact on systemic health. The induction of tissue inflammation relies heavily on Toll-like receptor (TLR) signaling, which drives a proinflammatory pathway through recruiting myeloid differentiation primary response gene 88 (MyD88) and activating nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB). TLR-induced production of proinflammatory cytokines and chemokines is reined in by anti-inflammatory cytokines, including the transforming growth factor β (TGFβ) family of cytokines. Although Smad6 is a key mediator of TGFβ-induced anti-inflammatory signaling, the exact mechanism by which TGFβ regulates TLR proinflammatory signaling in the periodontal tissue has not been addressed to date. In this study, we demonstrate for the first time that the ability of TGFβ to inhibit TLR-NFκB signaling is mediated by protein arginine methyltransferase 1 (PRMT1)-induced Smad6 methylation. Upon methylation, Smad6 recruited MyD88 and promoted MyD88 degradation, thereby inhibiting NFκB activation. Most important, Smad6 is expressed and methylated in the gingival epithelium, and PRMT1-Smad6 signaling promotes tissue homeostasis by limiting inflammation. Consistent with this, disturbance of Smad6 methylation exacerbates inflammation and bone loss in experimental periodontitis. The dissected mechanism is therapeutically important, as it highlights the manipulation of PRMT1-Smad6 signaling as a novel promising strategy to modulate the host immune response in periodontitis.

Hepatic SMARCA4 predicts HCC recurrence and promotes tumour cell proliferation by regulating SMAD6 expression

Hepatocellular carcinoma (HCC) is the most common form of liver cancer and is typically diagnosed at advanced stages. Identification and characterisation of genes within amplified and deleted chromosomal loci can provide new insights into the pathogenesis of cancer and lead to new approaches for diagnosis and therapy. In our previous study, we found a recurrent region of copy number amplification at 19p13.2 in hepatocellular carcinoma (HCC). In the present study, we performed integrated copy number analysis and expression profiling at this locus and a putative cancer gene, SMARCA4/BRG1, was uncovered in this region. BRG1 is a part of the large ATP-dependent chromatin remodelling complex SWI/SNF. The function of BRG1 in various cancers is unclear, including its role in HCC tumorigenesis. Here, we found that BRG1 is upregulated in HCC and that its level significantly correlates with cancer progression in HCC patients. Importantly, we also found that nuclear expression of BRG1 predicts early recurrence for HCC patients. Furthermore, we demonstrated that BRG1 promotes HCC cell proliferation in vitro and in vivo. BRG1 was observed not only to facilitate S-phase entry but also to attenuate cell apoptosis. Finally, we discovered that one of the mechanisms by which BRG1 promotes cell proliferation is the upregulation of SMAD6. These findings highlight the important role of BRG1 in the regulation of HCC proliferation and provide valuable information for cancer prognosis and treatment.

miR‑186, a serum microRNA, induces endothelial cell apoptosis by targeting SMAD6 in Kawasaki disease

Kawasaki disease (KD) is an acute, self‑limited vasculitis that predominantly affects medium‑sized arteries, particularly the coronary arteries. Recent studies have indicated that microRNAs are involved in many diseases, including KD. However, the detailed mechanism remains unclear. The aim of the present study was to explore the role of miR‑186 in KD and potentially discover a new target for KD treatment. The results demonstrated that miR‑186 was upregulated in serum from patients with KD and KD serum could increase miR‑186 transcript levels in endothelial cells (HUVECs). Overexpression of miR‑186 mimic induced HUVEC apoptosis through mitogen‑activated protein kinase (MAPK) activation by targeting and inhibiting SMAD family member 6 (SMAD6). Furthermore, KD serum induced HUVEC apoptosis through miR‑186. In conclusion, the present results suggested that KD serum‑associated miR‑186 has an essential role in endothelial cell apoptosis by activating the MAPK pathway through targeting the SMAD6 gene.

TRAF molecules in inflammation and inflammatory diseases

Purpose of Review

This review presents an overview of the current knowledge of TRAF molecules in inflammation with an emphasis on available human evidence and direct in vivo evidence of mouse models that demonstrate the contribution of TRAF molecules in the pathogenesis of inflammatory diseases.

Recent Findings

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic proteins was initially identified as signaling adaptors that bind directly to the intracellular domains of receptors of the TNF-R superfamily. It is now appreciated that TRAF molecules are widely employed in signaling by a variety of adaptive and innate immune receptors as well as cytokine receptors. TRAF-dependent signaling pathways typically lead to the activation of nuclear factor-κBs (NF-κBs), mitogen-activated protein kinases (MAPKs), or interferon-regulatory factors (IRFs). Most of these signaling pathways have been linked to inflammation, and therefore TRAF molecules were expected to regulate inflammation and inflammatory responses since their discovery in 1990s. However, direct in vivo evidence of TRAFs in inflammation and especially in inflammatory diseases had been lacking for many years, partly due to the difficulty imposed by early lethality of TRAF2^-/-, TRAF3^-/-, and TRAF6^-/- mice. With the creation of conditional knockout and lineage-specific transgenic mice of different TRAF molecules, our understanding about TRAFs in inflammation and inflammatory responses has rapidly advanced during the past decade.

Summary

Increasing evidence indicates that TRAF molecules are versatile and indispensable regulators of inflammation and inflammatory responses and that aberrant expression or function of TRAFs contributes to the pathogenesis of inflammatory diseases.

Site-specific monoubiquitination downregulates Rab5 by disrupting effector binding and guanine nucleotide conversion

Rab GTPases, which are involved in intracellular trafficking pathways, have recently been reported to be ubiquitinated. However, the functions of ubiquitinated Rab proteins remain unexplored. Here we show that Rab5 is monoubiquitinated on K116, K140, and K165. Upon co-transfection with ubiquitin, Rab5 exhibited abnormalities in endosomal localization and EGF-induced EGF receptor degradation. Rab5 K140R and K165R mutants restored these abnormalities, whereas K116R did not. We derived structural models of individual monoubiquitinated Rab5 proteins (mUbRab5s) by solution scattering and observed different conformational flexibilities in a site-specific manner. Structural analysis combined with biochemical data revealed that interactions with downstream effectors were impeded in mUbRab5_K140, whereas GDP release and GTP loading activities were altered in mUbRab5_K165. By contrast, mUbRab5_K116 apparently had no effect. We propose a regulatory mechanism of Rab5 where monoubiquitination downregulates effector recruitment and GDP/GTP conversion in a site-specific manner.

Deubiquitinases A20 and CYLD modulate costimulatory signaling via CD137 (4-1BB)

TRAF2 dependent K63-polyubiquitinations have been recently shown to connect CD137 (4-1BB) stimulation to NF-κB activation. In a search of deubiquitinase enzymes (DUBs) that could regulate such a signaling route, A20 and CYLD were found to coimmunoprecipitate with CD137 and TRAF2 complexes. Indeed, overexpression of A20 or CYLD downregulated CD137-elicited ubiquitination of TRAF2 and TAK1 upon stimulation with agonist monoclonal antibodies. Moreover, overexpression of A20 or CYLD downregulated CD137-induced NF-κB activation in cultured cells and in gene-transferred hepatocytes in vivo, while silencing these deubiquitinases enhanced CD137 costimulation of primary human CD8 T cells. Therefore A20 and CYLD directly downregulate the signaling from a T and NK-cell costimulatory receptor under exploitation for cancer immunotherapy in clinical trials.

Role of bone morphogenetic proteins in sprouting angiogenesis: differential BMP receptor-dependent signaling pathways balance stalk vs. tip cell competence

Before the onset of sprouting angiogenesis, the endothelium is prepatterned for the positioning of tip and stalk cells. Both cell identities are not static, as endothelial cells (ECs) constantly compete for the tip cell position in a dynamic fashion. Here, we show that both bone morphogenetic protein 2 (BMP2) and BMP6 are proangiogenic in vitro and ex vivo and that the BMP type I receptors, activin receptor-like kinase 3 (ALK3) and ALK2, play crucial and distinct roles in this process. BMP2 activates the expression of tip cell-associated genes, such as delta-like ligand 4 (DLL4) and kinase insert domain receptor (KDR), and p38-heat shock protein 27 (HSP27)-dependent cell migration, thereby generating tip cell competence. Whereas BMP6 also triggers collective cell migration via the p38-HSP27 signaling axis, BMP6 induces in addition SMAD1/5 signaling, thereby promoting the expression of stalk cell-associated genes, such as hairy and enhancer of split 1 (HES1) and fms-like tyrosine kinase 1 (FLT1). Specifically, ALK3 is required for sprouting from HUVEC spheroids, whereas ALK2 represses sprout formation. We demonstrate that expression levels and respective complex formation of BMP type I receptors in ECs determine stalk vs. tip cell identity, thus contributing to endothelial plasticity during sprouting angiogenesis. As antiangiogenic monotherapies that target the VEGF or ALK1 pathways have not fulfilled efficacy objectives in clinical trials, the selective targeting of the ALK2/3 pathways may be an attractive new approach.-Benn, A., Hiepen, C., Osterland, M., Schütte, C., Zwijsen, A., Knaus, P. Role of bone morphogenetic proteins in sprouting angiogenesis: differential BMP receptor-dependent signaling pathways balance stalk vs. tip cell competence.