Identification of a crucial site for synoviolin expression

HRD1 in human malignant neoplasms: Molecular mechanisms and novel therapeutic strategy for cancer

In tumor cells, the endoplasmic reticulum (ER) plays an essential role in maintaining cellular proteostasis by stimulating unfolded protein response (UPR) underlying stress conditions. ER-associated degradation (ERAD) is a critical pathway of the UPR to protect cells from ER stress-induced apoptosis and the elimination of unfolded or misfolded proteins by the ubiquitin-proteasome system (UPS). 3-Hydroxy-3-methylglutaryl reductase degradation (HRD1) as an E3 ubiquitin ligase plays an essential role in the ubiquitination and dislocation of misfolded protein in ERAD. In addition, HRD1 can target other normal folded proteins. In various types of cancer, the expression of HRD1 is dysregulated, and it targets different molecules to develop cancer hallmarks or suppress the progression of the disease. Recent investigations have defined the role of HRD1 in drug resistance in types of cancer. This review focuses on the molecular mechanisms of HRD1 and its roles in cancer pathogenesis and discusses the worthiness of targeting HRD1 as a novel therapeutic strategy in cancer.

Enhanced expression of synoviolin in peripheral blood from obese/overweight donors

Obesity is currently a major medical and societal issue. Synoviolin (SYVN1) is an E3 ubiquitin ligase involved in endoplasmic reticulum (ER) stress. Overexpression of Syvn1 has been found in genetically obese mice (ob/ob and db/db), and treatment with a Syvn1 inhibitor suppresses weight gain in some mouse models (C57BL/6J and db/db). However, SYVN1 expression in humans has not yet been elucidated. In the present study, 35 human volunteers were analyzed, and the expression level of SYVN1 mRNA in peripheral blood mononuclear cells (PBMCs) was detected using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis. Expression of SYVN1 mRNA was significantly increased in PBMCs from volunteers with a BMI ≥25.0, compared with volunteers with a BMI <25.0. In addition, PCR array and RT-qPCR of ER stress-responsive genes revealed that the expression of activating transcription factor 6 (ATF6), which plays an important role in the transcriptional activation of SYVN1, was increased in PBMCs from volunteers with a BMI ≥25.0. These results suggest that the ATF6-SYVN1 axis might be an important pathway in the progression of obesity.

The NRF2‑PGC‑1β pathway activates kynurenine aminotransferase 4 via attenuation of an E3 ubiquitin ligase, synoviolin, in a cecal ligation/perforation‑induced septic mouse model

Sepsis‑associated encephalopathy (SAE) is a systemic inflammatory response syndrome of which the precise associated mechanisms remain unclear. Synoviolin (Syvn1) is an E3 ubiquitin ligase involved in conditions associated with chronic inflammation, including rheumatoid arthritis, obesity, fibrosis and liver cirrhosis. However, the role of Syvn1 in acute inflammation is not clear. The aim of the present study was to investigate the role of Syvn1 in a septic mouse model induced by cecal ligation/perforation (CLP). Metabolome analysis revealed that kynurenine (KYN), a key factor for the development of neuroinflammation, was increased in CLP‑induced septic mice. Notably, KYN was not detected in CLP‑induced septic Syvn1‑deficient mice. KYN is converted to kynurenic acid (KYNA) by kynurenine aminotransferases (KATs), which has a neuroprotective effect. The expression of KAT4 was significantly increased in Syvn1‑deficient mice compared to that in wild‑type mice. Promoter analysis demonstrated that Syvn1 knockdown induced the KAT4 promoter activity, as assessed by luciferase reporter activity, whereas Syvn1 overexpression repressed this activity in a dose‑dependent manner. Furthermore, the KAT4 promoter was significantly activated by the transcriptional factors, NF‑E2‑related factor 2 and peroxisome proliferator‑activated receptor coactivator 1β, which are targets of Syvn1‑induced degradation. In conclusion, the results of the current study demonstrates that the repression of Syvn1 expression induces the conversion of neurotoxic KYN to neuroprotective KYNA in a CLP‑induced mouse model of sepsis, and that Syvn1 is a potential novel target for the treatment of SAE.

HRD1 sensitizes breast cancer cells to Tamoxifen by promoting S100A8 degradation

Estrogen receptor alpha positive (ER+) of breast cancer could develop resistance to antiestrogens including Tamoxifen. Our previous study showed that the E3 ubiquitin ligase HRD1 played an important role in anti-breast cancer. However, its role in chemotherapy resistance hasn't been reported. In this study, we found that HRD1 expression was downregulated in Tamoxifen-resistant breast cancer cell line MCF7/Tam compared to the Tamoxifen sensitive cell line MCF7. Moreover, S100A8 is the direct target of HRD1 by proteome analysis. Our data showed that HRD1 decreased the protein level of S100A8 through ubiquitination while HRD1 was regulated by acetylation of histone. More importantly, HRD1 knockdown significantly increased the cell survival of MCF7 cells to the Tamoxifen treatment. HRD1 overexpression sensitized MCF7/Tam cells to the Tamoxifen treatment in vitro and in vivo. In conclusion, the decrease of HRD1 expression contributed to Tamoxifen resistance in breast cancer.

Icariin induces synoviolin expression through NFE2L1 to protect neurons from ER stress-induced apoptosis

By suppressing neuronal apoptosis, Icariin is a potential therapeutic drug for neuronal degenerative diseases. The molecular mechanisms of Icariin anti-apoptotic functions are still largely unclear. In this report, we found that Icariin induces the expression of Synoviolin, an endoplasmic reticulum (ER)-anchoring E3 ubiquitin ligase that functions as a suppressor of ER stress-induced apoptosis. The nuclear factor erythroid 2-related factor 1 (NFE2L1) is responsible for Icariin-mediated Synoviolin gene expression. Mutation of the NFE2L1-binding sites in a distal region of the Synoviolin promoter abolished Icariin-induced Synoviolin promoter activity, and knockdown of NFE2L1 expression prevented Icariin-stimulated Synoviolin expression. More importantly, Icariin protected ER stress-induced apoptosis of PC12 cells in a Synoviolin-dependent manner. Therefore, our study reveals Icariin-induced Synoviolin expression through NFE2L1 as a previously unappreciated molecular mechanism underlying the neuronal protective function of Icariin.

Synoviolin inhibitor LS-102 reduces endoplasmic reticulum stress-induced collagen secretion in an in vitro model of stress-related interstitial pneumonia

The deletion mutation of exon 4 in surfactant protein C (SP-C), a lung surfactant protein, has been identified in parent-child cases of familial interstitial pneumonia. It has been shown that this mutation induces endoplasmic reticulum (ER) stress. Synoviolin is an E3 ubiquitin ligase that is localized to the ER and is an important factor in the degradation of ER-related proteins. It has been demonstrated that synoviolin is involved in liver fibrosis. In the present study, we investigated the involvement of synoviolin in the pathogenesis of interstitial pneumonia caused by the exon 4 deletion in the SP-C gene. We transfected wild-type and exon 4-deleted SP-C genes into A549 human lung adenocarcinoma cells and measured the secretion of collagen, which is a representative extracellular matrix protein involved in fibrosis. Secreted collagen levels were increased in the culture medium in SP-C mutants compared to the wild-type cells. Furthermore, the transcription of mRNAs coding for factors associated with fibrosis was increased. Subsequently, to assess the involvement of synoviolin, we constructed plasmids with a luciferase gene under the control of the synoviolin promoter. The A549 cells were transfected with the construct along with the exon 4-deleted SP-C plasmid for use in the luciferase assay. We found a 1.6-fold increase in luciferase activity in the cells carrying exon 4 deleted SP-C, as well as an increase in intrinsic synoviolin expression at the mRNA and protein levels. Collagen secretion was decreased by the addition of LS-102, a synoviolin inhibitor, to the A549 culture medium following transfection with wild-type and exon 4-deleted SP-C. These results demonstrate that synoviolin is involved in the onset of interstitial pneumonia induced by exon 4-deleted SP-C, which suggests that synoviolin inhibitors may be used in the treatment of the disease.

Screening of differentially expressed genes associated with non-union skeletal fractures and analysis with a DNA microarray

The purpose of this study was to identify the feature genes that are associated with non-union skeletal fractures using samples of normal union and non-union skeletal fracture microarray data. The gene expression profile GSE494 was downloaded from the Gene Expression Omnibus database and included 12 samples based on three different platforms (GPL92, GPL93 and GPL8300). Each of the platforms had four sets of expression data, two from normal union skeletal fracture samples and two from non-union skeletal fracture samples. The differentially expressed genes within the three platforms of expression data were identified using packages in R language and the differentially expressed genes common to the three platforms were selected. The selected common differentially expressed genes were further analyzed using bioinformatic methods. The software HitPredict was used to search interactions of the common differentially expressed genes and then FuncAssociate was used to conduct a functional analysis of the genes in the interaction network. Further, the associated pathways were identified using the software WebGestalt. Under the three different platforms, GPL92, GPL93 and GPL8300, the numbers of differentially expressed genes identified were 531, 418 and 914, respectively. The common gene CLU and its interacting genes were most significantly associated with the regulation of sterol transport and the osteoclast differentiation pathway. Upregulation of the gene CLU was identified by comparing data for normal union and non-union skeletal fracture samples. According to the function of CLU and its interacting genes, it was concluded that they inhibit the normal healing process following a fracture, and result in non-union skeletal fractures through the regulation of sterol transport and the pathways of differentiation in osteoclasts.

Overexpression of synoviolin facilitates the formation of a functional synovial biomembrane

Digital flexor tendon repair poses a significant challenge for hand surgeons. Currently, extrasynovial tendon grafts are frequently used in clinical settings to bridge flexor tendon defects. However, the healing process is always accompanied by postoperative adhesion. This is mostly due to the fact that no synovial membrane covers the extrasynovial tendon surface, in contrast to the intrasynovial tendon. In this study, we present an efficient method of developing a functional synovial biomembrane on the surface of the extrasynovial tendon. Synoviocytes were isolated from the knee joint of a Japanese white rabbit. After being infected with lentivirus, the over-expression of synoviolin in these synoviocytes was confirmed by semi-quantitative RT-PCR and western blotting. Cellular proliferation and increased hyaluronic acid secretion were confirmed in the synoviolin over-expressing synoviocytes by MTT-based method, cell cycle assays and ELISA. Furthermore, the synoviolin over-expressing synoviocytes were co-cultured with extrasynovial tendons that were harvested from the hind leg of rabbits. After being co-cultured in vitro for 3 and 7 days, these infected synoviocytes were found to accelerate the formation of a biomembrane on the tendon surface compared to the control group. More importantly, Alcian blue staining confirmed the ability of this cultured biomembrane to produce specific matrices containing acidic carboxyl mucopolysaccharides (mainly hyaluronic acid). All these results demonstrate that the over-expression of synoviolin stimulates the proliferation and HA secretion of synoviocytes and facilitates the formation of a functional synovial biomembrane.

Synoviolin, protein folding and the maintenance of joint homeostasis

Rheumatoid arthritis is a disease associated with painful joints that affects approximately 1% of the population worldwide, and for which no specific cure is available. Among other functions, the endoplasmic reticulum (ER) has an important role in protein folding. When the level of unfolded proteins in the ER exceeds the folding capacity of this organelle, defective proteins are eliminated by ER-associated degradation (ERAD), an ATP-dependent ubiquitin-proteasome degradation process, to reduce the burden on the ER. Synoviolin is an E3 ubiquitin ligase that is involved in ERAD. This protein is a pathogenic factor for arthropathy; it is overexpressed in the synovial cells of patients with rheumatoid arthritis. This overexpression results in a 'hyper-ERAD' state, in which the cell deals with accumulated unfolded proteins excessively. Rheumatoid synovial cells produce large amounts of various proteins such as cytokines and proteases, which consequently might confer an autonomous proliferation property on the cells. At least 30% of all newly synthesized, ER-sorted proteins are unfolded. Although degradation of unfolded proteins consumes large amounts of ATP and would seem an unconventional process, it is essential for joint homeostasis.

A different pathway in the endoplasmic reticulum stress-induced expression of human HRD1 and SEL1 genes

Human HRD1 and SEL1 are components of endoplasmic reticulum-associated degradation (ERAD), which is a retrograde transport mechanism from the ER to the cytosol for removing unfolded proteins. The expression of HRD1 and SEL1 was induced by ER stress-inducing agents and overexpression of both ER stress-responsive transcription factors, ATF6 and XBP1. Inhibition of IRE1 and ATF6 revealed that ER stress-induced HRD1 and SEL1 expressions are mediated by IRE1-XBP1- and ATF6-dependent pathways, respectively. These results suggest that the ER stress-induced ERAD gene expressions are mediated by different pathways, which are attributed to the differences in the promoter regions.

Transcriptional responses in spleens from mice exposed to Yersinia pestis CO92

Yersinia pestis is one of the most threatening biological agents due to the associated high mortality and history of plague pandemics. Identifying molecular players in the host response to infection may enable the development of medical countermeasures against Y. pestis. In this study, microarrays were used to identify the host splenic response mechanisms to Y. pestis infection. Groups of Balb/c mice were injected intraperitoneally with 2-257CFU of Y. pestis strain CO92 or vehicle. One group was assessed for mortality rates and another group for transcriptional analysis. The time to death at the 8 and 257CFU challenge doses were 5.0+/-2.3 and 3.8+/-0.4 days, respectively. Gene profiling using Affymetrix Mouse Genome 430 2.0 Arrays revealed no probe sets were significantly altered for all five mice in the low-dose group when compared to the vehicle controls. However, 534 probe sets were significantly altered in the high dose versus vehicle controls; 384 probe sets were down-regulated and 150 probe sets were up-regulated. The predominant biological processes identified were immune function, cytoskeletal, apoptosis, cell cycle, and protein degradation. This study provides new information on the underlying transcriptional mechanisms in mice to Y. pestis infection.

The proinflammatory cytokines IL-1beta and TNF-alpha induce the expression of Synoviolin, an E3 ubiquitin ligase, in mouse synovial fibroblasts via the Erk1/2-ETS1 pathway

The overgrowth of synovial tissues is critical in the pathogenesis of rheumatoid arthritis (RA). The expression of Synoviolin (SYN), an E3 ubiquitin ligase, is upregulated in arthritic synovial fibroblasts and is involved in the overgrowth of synovial cells during RA. However, the molecular mechanisms involved in the elevated SYN expression are not known. Here, we found that SYN expression is elevated in the synovial fibroblasts from mice with collagen-induced arthritis (CIA). The proinflammatory cytokines interleukin (IL)-1beta and tumor necrosis factor-alpha (TNF-alpha) induce SYN expression in mouse synovial fibroblasts. Cultivation of mouse synovial fibroblasts with IL-1beta activates mitogen-activated protein kinases, including extra-cellular signal-regulated kinase (Erk), JNK (c-Jun N-terminal kinase), and p38, while only Erk-specific inhibitor blocks IL-1beta-induced SYN expression. Expression of transcription factor ETS1 further enhances IL-1beta-induced SYN expression. The dominant negative ETS1 mutant lacking the transcription activation domain inhibits SYN expression in a dose-dependent manner. The activation of both Erk1/2 and ETS1 is increased in the CIA synovial fibroblasts. Inhibition of Erk activation reduces ETS1 phosphorylation and SYN expression. Our data indicate that the proinflammatory cytokines IL-1beta and TNF-alpha induce the overgrowth of synovial cells by upregulating SYN expression via the Erk1/-ETS1 pathway. These molecules or pathways could therefore be potential targets for the treatment of RA.

Cytoplasmic destruction of p53 by the endoplasmic reticulum-resident ubiquitin ligase 'Synoviolin'

Synoviolin, also called HRD1, is an E3 ubiquitin ligase and is implicated in endoplasmic reticulum -associated degradation. In mammals, Synoviolin plays crucial roles in various physiological and pathological processes, including embryogenesis and the pathogenesis of arthropathy. However, little is known about the molecular mechanisms of Synoviolin in these actions. To clarify these issues, we analyzed the profile of protein expression in synoviolin-null cells. Here, we report that Synoviolin targets tumor suppressor gene p53 for ubiquitination. Synoviolin sequestrated and metabolized p53 in the cytoplasm and negatively regulated its cellular level and biological functions, including transcription, cell cycle regulation and apoptosis. Furthermore, these p53 regulatory functions of Synoviolin were irrelevant to other E3 ubiquitin ligases for p53, such as MDM2, Pirh2 and Cop1, which form autoregulatory feedback loops. Our results provide novel insights into p53 signaling mediated by Synoviolin.

Functional analysis of p53 binding under differential stresses

Hypoxia and DNA damage stabilize the p53 protein, but the subsequent effect that each stress has on transcriptional regulation of known p53 target genes is variable. We have used chromatin immunoprecipitation followed by CpG island (CGI) microarray hybridization to identify promoters bound by p53 under both DNA-damaging and non-DNA-damaging conditions in HCT116 cells. Using gene-specific PCR analysis, we have verified an association with CGIs of the highest enrichment (> 2.5-fold) (REV3L, XPMC2H, HNRPUL1, TOR1AIP1, glutathione peroxidase 1, and SCFD2), with CGIs of intermediate enrichment (> 2.2-fold) (COX7A2L, SYVN1, and JAG2), and with CGIs of low enrichment (> 2.0-fold) (MYC and PCNA). We found little difference in promoter binding when p53 is stabilized by these two distinctly different stresses. However, expression of these genes varies a great deal: while a few genes exhibit classical induction with adriamycin, the majority of the genes are unchanged or are mildly repressed by either hypoxia or adriamycin. Further analysis using p53 mutated in the core DNA binding domain revealed that the interaction of p53 with CGIs may be occurring through both sequence-dependent and -independent mechanisms. Taken together, these experiments describe the identification of novel p53 target genes and the subsequent discovery of distinctly different expression phenomena for p53 target genes under different stress scenarios.

Rheumatoid arthritis as a hyper-endoplasmic-reticulum-associated degradation disease

We introduce Synoviolin as a novel pathogenic factor in rheumatoid arthritis (RA). Experimental studies indicate that this endoplasmic reticulum (ER)-resident E3 ubiquitin ligase has important functions in the ER-associated degradation (ERAD) system, an essential system for ER homeostasis. Overexpression of Synoviolin in mice causes arthropathy with synovial hyperplasia, whereas heterozygous knockdown results in increased apoptosis of synovial cells and resistance to collagen-induced arthritis in mice. On the basis of these experimental data, we propose that excess elimination of unfolded proteins (that is, 'hyper-ERAD') by overexpression of Synoviolin triggers synovial cell overgrowth and hence a worsening of RA. Further analysis of the hyper-ERAD system may permit the complex pathomechanisms of RA to be uncovered.