Newly identified tumor-associated role of human Sharpin

Mechanism of multifunctional adaptor protein SHARPIN regulating myocardial fibrosis and how SNP mutation affect the prognosis of myocardial infarction

Myocardial fibrosis (MF) is characterized by the excessive deposition of extracellular matrix within the heart, often following a cardiovascular insult. SHARPIN, a protein implicated in fibrosis, has emerged as a potential therapeutic target. This study aimed to elucidate the molecular mechanisms of SHARPIN in MF and to investigate the influence of its single nucleotide polymorphism (SNP), rs117299156, on myocardial infarction (MI) patients. A mouse model of Angiotensin II (AngII)-induced MF was established in SHARPIN heterozygous (SHARPIN+/-) and wild-type mice. Adult mouse cardiac fibroblasts (CFs) were isolated and subjected to adenovirus-encapsulated SHARPIN short hairpin RNA (shRNA) infection. Transcriptomic analysis was performed on CFs from SHARPIN+/- and wild-type (WT) mice, complemented by single-cell sequencing data from human cardiac tissues. Additionally, the association between the rs117299156 mutation and cardiovascular events in MI patients was assessed. Our findings indicate that SHARPIN is predominantly expressed in CFs and is upregulated in fibrotic myocardium. Partial knockdown of SHARPIN in murine hearts mitigated AngII-induced cardiac dysfunction and MF. Furthermore, reduced SHARPIN expression in CFs attenuated TGF-β1-induced collagen synthesis, cell proliferation, and myofibroblast transformation. Notably, MI patients carrying the rs117299156_C allele exhibited a reduced incidence of stroke events compared to those without the mutation.

Genetic Analysis Implicates Dysregulation of SHANK2 in Renal Cell Carcinoma Progression

SH3 and multiple ankyrin repeat domains (SHANK) is a family of scaffold proteins that were first identified to be involved in balancing synaptic transmission via regulation of intracellular signalling crosstalk and have been linked to various cancers. However, the role of the SHANK genes in renal cell carcinoma (RCC) remains to be elucidated. In this study, we aimed to evaluate whether genetic variants in SHANK family genes affect the risk of RCC and survival of patients. A genetic association study was conducted using logistic regression and Cox regression analyses, followed by the correction for a false discovery rate (FDR), in 630 patients with RCC and controls. A pooled analysis was further performed to summarise the clinical relevance of SHANK gene expression in RCC. After adjustment for known risk factors and the FDR, the SHANK2 rs10792565 T allele was found to be associated with an increased risk of RCC (adjusted odds ratio = 1.79, 95% confidence interval = 1.32-2.44, p = 1.96 × 10^-4, q = 0.030), whereas no significant association was found with RCC survival. A pooled analysis of 19 independent studies, comprising 1509 RCC and 414 adjacent normal tissues, showed that the expression of SHANK2 was significantly lower in RCC than in normal tissues (p < 0.001). Furthermore, low expression of SHANK2 was correlated with an advanced stage and poor prognosis for patients with clear cell and papillary RCC. This study suggests that SHANK2 rs10792565 is associated with an increased risk of RCC and that SHANK2 may play a role in RCC progression.

Overexpression of SHARPIN promotes tumor progression in ovarian cancer

SHARPIN (Shank-associated RH domain interacting protein) plays an important role in tumorigenesis. However, its role in ovarian cancer remains largely unknown. To investigate this issue, we systematically analyzed the amplification and expression of the SHARPIN in the TCGA database. From the database, we found that SHARPIN was amplified in ovarian cancer compared to normal ovarian tissue, and the mRNA level of SHARPIN was significantly elevated in ovarian cancer compared to non-tumorigenic ovarian tissue. In addition, we observed similar results from ovarian cancer cell lines and clinical samples from ovarian cancer patients, which indicated that increased SHARPIN expression is associated with tumorigenesis in ovarian cancer. SHARPIN knockdown inhibited the migration and invasion of ovarian cancer cells, also inhibited cell cycle and promoted apoptosis, thereby suppressing cell proliferation. RNA-seq results showed that SHARPIN significantly increased the expression of P53 and P21 and decreased the expression of Cyclin D1 and c-Myc, all of which are involved in the regulation of cell proliferation. Subsequent mechanistic exploration revealed that SHARPIN knockdown increased the expression of caspases 3 and 9, leading to apoptosis of ovarian cancer cells. We also found that high expression of SHARPIN was associated with poor prognosis of ovarian cancer patients. Collectively, we demonstrated a positive correlation between SHARPIN and ovarian cancer progression and provide a basis for combined targeted therapy strategies for future ovarian cancer treatment.

SHARPIN: Role in Finding NEMO and in Amyloid-Beta Clearance and Degradation (ABCD) Pathway in Alzheimer's Disease?

SHANK- associated RH domain-interacting protein (SHARPIN) is a multifunctional protein associated with numerous physiological functions and many diseases. The primary role of the protein as a LUBAC-dependent component in regulating the activation of the transcription factor NF-κB accounts to its role in inflammation and antiapoptosis. Hence, an alteration of SHARPIN expression or genetic mutations or polymorphisms leads to the alteration of the above-mentioned primary physiological functions contributing to inflammation-associated diseases and cancer, respectively. However, there are complications of targeting SHARPIN as a therapeutic approach, which arises from the wide-range of LUBAC-independent functions and yet unknown roles of SHARPIN including neuronal functions. The identification of SHARPIN as a postsynaptic protein and the emerging studies indicating its role in several neurodegenerative diseases including Alzheimer's disease suggests a strong role of SHARPIN in neuronal functioning. This review summarizes the functional roles of SHARPIN in normal physiology and disease pathogenesis and strongly suggests a need for concentrating more studies on identifying the unknown neuronal functions of SHARPIN and hence its role in neurodegenerative diseases.

Advances in the Structural and Physiological Functions of SHARPIN

SHARPIN was initially found as a SHANK-associated protein. SHARPIN can be used as an important component to form the linear ubiquitin chain assembly complex (LUBAC) with HOIL-1L, HOIP to produce a linear ubiquitin chain connected N-terminal Met1, playing a critical role in various cellular processes including NF-κB signaling, inflammation, embryogenesis and apoptosis. SHARPIN alone can also participate in many critical physiological activities and cause various disorders such as chronic dermatitis, tumor, and Alzheimer’s disease. Mice with spontaneous autosomal recessive mutations in the SHARPIN protein mainly exhibit chronic dermatitis and immunodeficiency with elevated IgM. Additionally, SHARPIN alone also plays a key role in various cellular events, such as B cells activation and platelet aggregation. Structural studies of the SHARPIN or LUBAC have been reported continuously, advancing our understanding of it at the molecular level. However, the full-length structure of the SHARPIN or LUBAC was lagging, and the molecular mechanism underlying these physiological processes is also unclear. Herein, we summarized the currently resolved structure of SHARPIN as well as the emerging physiological role of SHARPIN alone or in LUBAC. Further structural and functional study of SHARPIN will provide insight into the role and underlying mechanism of SHARPIN in disease, as well as its potential application in therapeutic.

SHARPIN regulates the development of clear cell renal cell carcinoma by promoting von Hippel-Lindau protein ubiquitination and degradation

SHANK-associated RH domain interacting protein (SHARPIN) plays an important role in carcinogenesis, as well as inflammation and immunity. Our study explored the effects and underlying mechanisms of SHARPIN in clear cell renal cell carcinoma (ccRCC). By analyzing The Cancer Genome Atlas database, we found that upregulated SHARPIN in patients with ccRCC led to a poor prognosis. Semiquantitative immunohistochemical analysis of clinical samples was carried out and the results suggested the positive association between SHARPIN and hypoxia-induced factor-2α (HIF-2α). Von Hippel-Lindau protein (pVHL) is a tumor suppressor that contributes to degrading HIF-2α. Mechanically, SHARPIN promoted the ubiquitination and proteasomal degradation of pVHL, resulting in the sustained activation of HIF-2α. The α and β domains of pVHL and ubiquitin-like domain of SHARPIN are required for the interaction. The knockdown of SHARPIN effectively inhibited acquired sorafenib resistance in ccRCC cell lines and tumor growth in xenograft models. In conclusion, our work reveals a novel posttranslational regulation of SHARPIN on pVHL, indicating that SHARPIN could be a potential target for ccRCC treatment.

Monocarboxylate transporter 9 (MCT9) is down-regulated in renal cell carcinoma

BACKGROUND

The renal cell carcinoma (RCC) incidences are continuously increasing, however, their proper characterization remains difficult. Mammalian kidneys require large amounts of energy, and monocarboxylate transporter (MCT) gene family is responsible for the transport of monocarboxylic compounds across plasma membranes.

OBJECTIVE

A total of 14 MCT members have been identified in humans, which show highly distinct substrate affinities and tissue distributions. To understand the yet-uncharacterized renal cancer-specific role of MCTs, we identified MCT members that are differentially regulated during the renal tumor progression.

METHODS

We examined the expression level of MCT members in renal cell tumors and their relationship with survival rate of patients using a public database. Quantitative RT-PCR and northern blotting were performed to validate the expression of MCTs. Anti-MCT9 antiserum was raised in rabbit and used to examine MCT9 expression in normal and tumor tissue arrays. Effect of MCT9 overexpression on cell proliferation was measured using renal cancer cell lines.

RESULTS

MCT9 was found to be abundantly and exclusively expressed in human kidney cells, and was highly downregulated in renal cancers. Kaplan-Meier plotter analysis revealed an increased survival rate of MCT9 high-expressing RCC patients. MCT9 proteins were detected in normal kidney tissue sections and their overexpression clearly attenuated renal cell proliferation.

CONCLUSIONS

MCT9 was identified as a novel highly downregulated gene in renal cell cancer, and its overexpression clearly attenuated RCC cell proliferation. Thus, functional analysis of MCT9 may help in deciphering a yet-undiscovered kidney-specific energy metabolism during renal tumor progression.

Keratinocyte-specific deletion of SHARPIN induces atopic dermatitis-like inflammation in mice

Spontaneous mutations in the SHANK-associated RH domain interacting protein (Sharpin) resulted in a severe autoinflammatory type of chronic proliferative dermatitis, inflammation in other organs, and lymphoid organ defects. To determine whether cell-type restricted loss of Sharpin causes similar lesions, a conditional null mutant was created. Ubiquitously expressing cre-recombinase recapitulated the phenotype seen in spontaneous mutant mice. Limiting expression to keratinocytes (using a Krt14-cre) induced a chronic eosinophilic dermatitis, but no inflammation in other organs or lymphoid organ defects. The dermatitis was associated with a markedly increased concentration of serum IgE and IL18. Crosses with S100a4-cre resulted in milder skin lesions and moderate to severe arthritis. This conditional null mutant will enable more detailed studies on the role of SHARPIN in regulating NFkB and inflammation, while the Krt14-Sharpin-/- provides a new model to study atopic dermatitis.

Shank-associated RH domain interactor signaling in tumorigenesis

Shank-associated RH domain interactor (SHARPIN) is a component of the linear ubiquitin chain activation complex, which is essential for p53 signaling and inflammation. Previous studies have demonstrated that SHARPIN functions in tumor cell survival, growth, invasion and tumorigenesis. These functions include the regulation of p53 proteins via poly-ubiquitination, interaction with a type II protein arginine methyltransferase 5 in melanoma cells, modulating ras-associated protein-1 through p38 and c-Jun N-terminal kinases/c-Jun signaling, and mediating phosphoinositide 3-kinase/AKT signaling via phosphatase and tensin homologue deleted on chromosome 10. Hence, SHARPIN not only participates in the inflammatory response but also serves a critical role in tumor cells. The present review summarizes the biological functions of the absence or presence of SHARPIN with regard to activating the canonical NF-κB signaling pathway and the effects on p53 and other signaling pathways for the modulation of tumorigenesis. Therefore, this review provides insight into the underlying role and mechanisms of SHARPIN in tumorigenesis, as well as its potential application in cancer therapy.

SHARPIN regulates cell proliferation of cutaneous basal cell carcinoma via inactivation of the transcriptional factors GLI2 and c‑JUN

SHANK‑associated RH domain‑interacting protein (SHARPIN) is a component of the linear ubiquitin chain assembly complex that can enhance the NF‑κB and JNK signaling pathways, acting as a tumor‑associated protein in a variety of cancer types. The present study investigated the role of SHARPIN in cutaneous basal cell carcinoma (BCC). Human BCC (n=26) and normal skin (n=5) tissues, and BCC (TE354.T) and normal skin (HaCaT) cell lines were used to evaluate SHARPIN expression level using immunohistochemistry and western blotting, respectively. A lentivirus carrying SHARPIN‑targeting or negative control short hairpin RNA was infected into TE354.T cells, and the infected stable cells were assayed to analyze tumor cell proliferation, cell cycle, apoptosis, migration and invasion by Cell Counting Kit‑8 and 5‑ethynyl‑2'‑deoxyuridine incorporation assays, flow cytometry and Transwell assays. Western blotting was performed to assess the protein expression levels of gene signaling in SHARPIN‑silenced BCC cells. SHARPIN protein expression levels were downregulated or absent in BCC cancer nests and precancerous lesions compared with normal skin samples. In addition, SHARPIN expression levels were lower in TE354.T cells compared with HaCaT cells. SHARPIN shRNA enhanced tumor cell proliferation and the S phase of the cell cycle, whereas BCC cell apoptotic rates, and migratory and invasive abilities were not significantly altered. The expression levels of cyclin D1, cyclin‑dependent kinase 4, phosphorylated‑c‑JUN and GLI family zinc finger 2 proteins were increased, whereas Patched 1 (PTCH1) and PTCH2 were decreased in the SHARPIN‑shRNA‑infected BCC cells. Therefore, the present results suggested that SHARPIN may act as a tumor suppressor during BCC development.

SHARPIN overexpression promotes TAK1 expression and activates JNKs and NF-κB pathway in Mycosis Fungoides

Mycosis Fungoides (MF) is the most common subtype of cutaneous T-cell lymphomas (CTCL). Shank-associated RH domain-interacting protein (SHARPIN) participates in the initiation and development of multiple tumors. However, the clinical significance of SHARPIN in MF hasn't been investigated. The c-Jun N-terminal kinases (JNKs) pathway is a member of mitogen-activated protein kinases (MAPKs). Its dysregulation is observed in various tumors including CTCL, whereas the roles of JNKs pathway in MF remain largely unknown, the relationship between SHARPIN and JNKs pathway remains elusive. Herein, we showed that upregulated expression of SHARPIN was related to poor prognosis of MF patients. In vitro experiments found increased SHARPIN expression and activation of JNKs pathway in MF cell line MyLa2059. SHARPIN induced transforming growth factor β activated kinase-1 (TAK1) transcription, which is an upstream kinase of JNKs, NF-κB and p38 pathway, leading to activation of JNKs and NF-κB pathway. SHARPIN also promoted p38 signalling independent of TAK1 expression, by which overexpression of SHARPIN induced cell proliferation, inhibited apoptosis, enhanced migration and invasion of MyLa2059. Our work provided direct evidences for effects of SHARPIN on JNKs and NF-κB pathway, and the contributing roles of JNKs, NF-κB and p38 pathway regulated by SHARPIN in the development of MF.

SHARPIN Promotes Melanoma Progression via Rap1 Signaling Pathway

SHARPIN, as a tumor-associated gene, is involved in the metastatic process of many kinds of tumors. Herein, we studied the function of Shank-associated RH domain interacting protein (SHARPIN) in melanoma metastasis and the relevant molecular mechanisms. We found that SHARPIN expression was increased in melanoma tissues and activated the process of proliferation, migration, and invasion in vitro and in vivo, resulting in a poor prognosis of the disease. Functional analysis demonstrated that SHARPIN promoted melanoma migration and invasion by regulating Ras-associated protein-1(Rap1) and its downstream pathways, including p38 and JNK/c-Jun. Rap1 activator (8-pCPT-2'-O-Me-cAMP) and inhibitor (ESI-09 and farnesylthiosalicylic acid-amide) treatments could partially rescue invasion and migration of tumor cells. Additionally, SHARPIN expression in cell lines and public datasets also indicated that molecules other than BRAF and N-RAS may contribute to SHARPIN activation. In conclusion, our broad-in-depth work suggests that SHARPIN promotes melanoma development via p38 and JNK/c-Jun pathways through upregulation of Rap1 expression.

68Ga-DOTA-E[c(RGDfK)]2 PET Imaging of SHARPIN-Regulated Integrin Activity in Mice

Shank-associated RH domain-interacting protein (SHARPIN) is a cytosolic protein that plays a key role in activation of nuclear factor κ-light-chain enhancer of activated B cells and regulation of inflammation. Furthermore, SHARPIN controls integrin-dependent cell adhesion and migration in several normal and malignant cell types, and loss of SHARPIN correlates with increased integrin activity in mice. Arginyl-glycyl-aspartic acid (RGD), a cell adhesion tripeptide motif, is an integrin recognition sequence that facilitates PET imaging of integrin upregulation during tumor angiogenesis. We hypothesized that increased integrin activity due to loss of SHARPIN protein would affect the uptake of α_vβ₃-selective cyclic, dimeric peptide ⁶⁸Ga-DOTA-E[c(RGDfK)]₂, where E[c(RGDfk)]₂ = glutamic acid-[cyclo(arginyl-glycyl-aspartic acid-D-phenylalanine-lysine)], both in several tissue types and in the tumor microenvironment. To test this hypothesis, we used RGD-based in vivo PET imaging to evaluate wild-type (wt) and SHARPIN-deficient mice (Sharpin ^cpdm , where cpdm = chronic proliferative dermatitis in mice) with and without melanoma tumor allografts. Methods: Sharpin ^cpdm mice with spontaneous null mutation in the Sharpin gene and their wt littermates with or without B16-F10-luc melanoma tumors were studied by in vivo imaging and ex vivo measurements with cyclic-RGD peptide ⁶⁸Ga-DOTA-E[c(RGDfK)]₂ After the last ⁶⁸Ga-DOTA-E[c(RGDfK)]₂ peptide PET/CT, tumors were cut into cryosections for autoradiography, histology, and immunohistochemistry. Results: The ex vivo uptake of ⁶⁸Ga-DOTA-E[c(RGDfK)]₂ in the mouse skin and tumor was significantly higher in Sharpin ^cpdm mice than in wt mice. B16-F10-luc tumors were detected 4 d after inoculation, without differences in volume or blood flow between the mouse strains. PET imaging with ⁶⁸Ga-DOTA-E[c(RGDfK)]₂ peptide at day 10 after inoculation revealed significantly higher uptake in the tumors transplanted into Sharpin ^cpdm mice than in wt mice. Furthermore, tumor vascularization was increased in the Sharpin ^cpdm mice. Conclusion: Sharpin ^cpdm mice demonstrated increased integrin activity and vascularization in B16-F10-luc melanoma tumors, as demonstrated by RGD-based in vivo PET imaging. These data indicate that SHARPIN, a protein previously associated with increased cancer growth and metastasis, may also have important regulatory roles in controlling the tumor microenvironment.

Aberrant expression and high-frequency mutations of SHARPIN in nonmelanoma skin cancer

Squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) have exhibited a marked increase in incidence in previous decades and are the most common malignancies in Caucasian populations. Src homology 3 and multiple ankyrin repeat domains protein-associated RH domain-interacting protein (SHARPIN) has been identified as a commonly overexpressed proto-oncogene in several types of visceral cancer. However, to the best of our knowledge, the functions of SHARPIN in nonmelanoma skin cancer (NMSC) have not been described. The present study aimed to investigate the expression of SHARPIN protein and SHARPIN mutations in NMSC. A total of 85 BCC, 77 SCC and 21 keratoacanthoma (KA) formalin-fixed paraffin-embedded (FFPE) samples were collected. SHARPIN expression was detected using immunohistochemistry. DNA was extracted from the FFPE samples, and the sequences of SHARPIN were analyzed using polymerase chain reaction. In addition, high and moderate expression levels of SHARPIN were observed in normal skin tissues and KA samples. However, the expression of SHARPIN was absent in cancer nests and was significantly low in precancerous NMSC lesions. The total mutation frequency of SHARPIN was 21.8% in BCC and 17.0% in SCC. These data indicate that SHARPIN may serve a tumor-suppressing role and be a promising diagnostic, prognostic and therapeutic biomarker in NMSC.

Proteoglycans Are Attractive Biomarkers and Therapeutic Targets in Hepatocellular Carcinoma

Proteoglycans, which consist of a protein core and glycosaminoglycan chains, are major components of the extracellular matrix and play physiological roles in maintaining tissue homeostasis. In the carcinogenic tissue microenvironment, proteoglycan expression changes dramatically. Altered proteoglycan expression on tumor and stromal cells affects cancer cell signaling pathways, which alters growth, migration, and angiogenesis and could facilitate tumorigenesis. This dysregulation of proteoglycans has been implicated in the pathogenesis of diseases such as hepatocellular carcinoma (HCC) and the underlying mechanism has been studied extensively. This review summarizes the current knowledge of the roles of proteoglycans in the genesis and progression of HCC. It focuses on well-investigated proteoglycans such as serglycin, syndecan-1, glypican 3, agrin, collagen XVIII/endostatin, versican, and decorin, with particular emphasis on the potential of these factors as biomarkers and therapeutic targets in HCC regarding the future perspective of precision medicine toward the "cure of HCC".

Shank-associated RH domain-interacting protein expression is upregulated in entodermal and mesodermal cancer or downregulated in ectodermal malignancy

Shank-associated RH domain-interacting protein (SHARPIN) is a type of linear ubiquitin chain-associated protein, which serves an important role in cell proliferation, apoptosis, organ development, immune and inflammatory reaction, initiation and development of malignant tumors. To evaluate SHARPIN expression in multiple malignant tumors derived from different germ layers, 14 types of cancer and their corresponding normal tissues were examined. Immunohistochemistry was performed to semi-quantify SHARPIN expression in multiple malignant tumors, and immunofluorescence was performed to evaluate the subcellular localization of SHARPIN in various malignant tumors. All the recruited cancer and paracancer samples originated from entoderm and mesoderm showed an upregulated expression of SHARPIN, whereas the cancer types that originated from ectoderm exhibited a downregulated or loss of SHARPIN expression. SHARPIN was primarily localized in the cytoplasm of cells and exhibited a faint signal in the nucleus, with the exception for lung cancer and esophagus cancer, in which malignant cells had aberrantly large nuclei and limited cytoplasm, which produced a signal in the nucleus but not in the cytoplasm. Conclusively, SHARPIN expression was upregulated in entodermal and mesodermal cancer types, but downregulated in ectodermal cancer types, indicating SHARPIN could act as either oncogene or anti-oncogene in malignant tumors derived from different germ layers.

Expression of the three components of linear ubiquitin assembly complex in breast cancer

Proteins belonging to the linear ubiquitin assembly complex (LUBAC) are believed to be important in tumorigenesis. LUBAC has been demonstrated to be composed of RBCK1, RNF31 and SHARPIN. The aim of this study was to explore all members of the LUBAC complex as novel biomarkers in breast cancer. We have already reported that RNF31 mRNA levels are higher in breast cancer samples compared to adjacent non-tumor tissue. In this study we extend these findings by demonstrating that the mRNA levels of RBCK1 and SHARPIN are also higher in tumors compared to adjacent non-tumor tissue in the same cross sectional study of samples (p < 0.001). In addition, up-regulated mRNA expression of all three members of the LUBAC complex displayed high predictive value in distinguishing tumor tissues from adjacent non-tumor tissue as determined by ROC curve analysis. Furthermore, we investigated whether there is an association between the mRNA and protein expression levels of RBCK1, RNF31 and SHARPIN and clinicopathological parameters including estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor (HER2) status and found that RNF31 protein is significantly higher in ERalpha-negative tumors than ERalpha-positive tumors (p = 0.034). Collectively, our findings indicate that up-regulated mRNA expression of RNF31, RBCK1 and SHARPIN could potentially be diagnostic biomarkers of breast cancer and RNF31 might be a drug target for ERalpha-negative breast cancers.

Hepatitis B virus X protein influences enrichment profiles of H3K9me3 on promoter regions in human hepatoma cell lines

We previously showed that hepatitis B virus (HBV) X protein (HBx) could promote the trimethylation of histone H3 lysine 9 (H3K9me3) to repress tumor suppressor genes in hepatocellular carcinoma (HCC). In this work, we analyze 23,148 human promoters using ChIP-chip to determine the effects of HBx on H3K9me3 enrichments in hepatoma cells with transfection of HBx-expressing plasmid. Immunohistochemistry for HBx and H3K9me3 was performed in 21 cases of HBV-associated HCC tissues. We identified that H3K9me3 immunoreactivity was significantly correlated with HBx staining in HCC tissues. ChIP-chip data indicated that HBx remarkably altered promoter enrichments of H3K9me3 in hepatoma cells. We identified 25 gene promoters, whose H3K9me3 enrichments are significantly altered in hepatoma cells transfected HBx-expressing plasmid, including 19 gaining H3K9m3, and six losing this mark. Most of these genes have not been previously reported in HCC, and BTBD17, MIR6089, ZNF205-AS1 and ZP1 have not previously been linked to cancer; only two genes (DAB2IP and ZNF185) have been reported in HCC. Genomic analyses suggested that genes with the differential H3K9me3 enrichments function in diverse cellular pathways and many are involved in cancer development and progression.

A role of SIPL1/SHARPIN in promoting resistance to hormone therapy in breast cancer

SIPL1 inhibits PTEN function and stimulates NF-κB signaling; both processes contribute to resistance to hormone therapy in estrogen receptor positive breast cancer (ER+ BC). However, whether SIPL1 promotes tamoxifen resistance in BC remains unclear. We report here that SIPL1 enhances tamoxifen resistance in ER+ BC. Overexpression of SIPL1 in MCF7 and TD47 cells conferred tamoxifen resistance. In MCF7 cell-derived tamoxifen resistant (TAM-R) cells, SIPL1 expression was upregulated and knockdown of SIPL1 in TAM-R cells re-sensitized the cells to tamoxifen. Furthermore, xenograft tumors produced by MCF7 SIPL1 cells but not by MCF7 empty vector cells resisted tamoxifen treatment. Collectively, we demonstrated a role of SIPL1 in promoting tamoxifen resistance in BC. Increases in AKT activation and NF-κB signaling were detected in both MCF7 SIPL1 and TAM-R cells; using specific inhibitors and unique SIPL1 mutants to inhibit either pathway significantly reduced tamoxifen resistance. A SIPL1 mutant defective in activating both pathways was incapable of conferring resistance to tamoxifen, showing that both pathways contributed to SIPL1-derived resistance to tamoxifen in ER+ BCs. Using the Curtis dataset of breast cancer (n=1980) within the cBioPortal database, we examined a correlation of SIPL1 expression with ER+ BC and resistance to hormone therapy. SIPL1 upregulation strongly associates with reductions in overall survival in BC patients, particularly in patients with hormone naïve ER+ BCs. Taken together, we provide data suggesting that SIPL1 contributes to promote resistance to tamoxifen in BC cells through both AKT and NF-κB actions.

Biophysical and biological evaluation of optimized stapled peptide inhibitors of the linear ubiquitin chain assembly complex (LUBAC)

Linear ubiquitylation, in which ubiquitin units are covalently linked through N- and C-terminal amino acids, is a unique cellular signaling mechanism. This process is controlled by a single E3 ubiquitin ligase, the linear ubiquitin chain assembly complex (LUBAC), which is composed of three proteins - HOIL-1L, HOIP and SHARPIN. LUBAC is involved in the activation of the canonical NF-κB pathway and has been linked to NF-κB dependent malignancies. In this work, we present HOIP-based stapled alpha-helical peptides designed to inhibit LUBAC through the disruption of the HOIL-1L-HOIP interaction and loss of the functional complex. We find our HOIP peptides to be active LUBAC ubiquitylation inhibitors in vitro, though through interaction with HOIP rather than HOIL. Active peptides were shown to have inhibitory effects on cell viability, reduced NF-κB activity and decreased production of NF-κB related gene products. This work further demonstrates the potential of LUBAC as a therapeutic target and of the use of stapled peptides as inhibitors of protein-protein interactions.

The Sharpin interactome reveals a role for Sharpin in lamellipodium formation via the Arp2/3 complex

Sharpin, a multifunctional adaptor protein, regulates several signalling pathways. For example, Sharpin enhances signal-induced NF-κB signalling as part of the linear ubiquitin assembly complex (LUBAC) and inhibits integrins, the T cell receptor, caspase 1 and PTEN. However, despite recent insights into Sharpin and LUBAC function, a systematic approach to identify the signalling pathways regulated by Sharpin has not been reported. Here, we present the first 'Sharpin interactome', which identifies a large number of novel potential Sharpin interactors in addition to several known ones. These data suggest that Sharpin and LUBAC might regulate a larger number of biological processes than previously identified, such as endosomal trafficking, RNA processing, metabolism and cytoskeleton regulation. Importantly, using the Sharpin interactome, we have identified a novel role for Sharpin in lamellipodium formation. We demonstrate that Sharpin interacts with Arp2/3, a protein complex that catalyses actin filament branching. We have identified the Arp2/3-binding site in Sharpin and demonstrate using a specific Arp2/3-binding deficient mutant that the Sharpin-Arp2/3 interaction promotes lamellipodium formation in a LUBAC-independent fashion.This article has an associated First Person interview with the first author of the paper.

Signatures derived from increase in SHARPIN gene copy number are associated with poor prognosis in patients with breast cancer

We report three signatures produced from SHARPIN gene copy number increase (GCN-Increase) and their effects on patients with breast cancer (BC). In the Metabric dataset (n = 2059, cBioPortal), SHARPIN GCN-Increase occurs preferentially or mutual exclusively with mutations in TP53, PIK3CA, and CDH1. These genomic alterations constitute a signature (SigMut) that significantly correlates with reductions in overall survival (OS) in BC patients (n = 1980; p = 1.081e − 6). Additionally, SHARPIN GCN-Increase is associated with 4220 differentially expressed genes (DEGs). These DEGs are enriched in activation of the pathways regulating cell cycle progression, RNA transport, ribosome biosynthesis, DNA replication, and in downregulation of the pathways related to extracellular matrix. These DEGs are thus likely to facilitate the proliferation and metastasis of BC cells. Additionally, through forward (FWD) and backward (BWD) stepwise variate selections among the top 160 downregulated and top 200 upregulated DEGs using the Cox regression model, a 6-gene (SigFWD) and a 50-gene (SigBWD) signature were derived. Both signatures robustly associate with decreases in OS in BC patients within the Curtis (n = 1980; p = 6.16e − 11 for SigFWD; p = 1.06e − 10, for SigBWD) and TCGA cohort (n = 817; p = 4.53e − 4 for SigFWD and p = 0.00525 for SigBWD). After adjusting for known clinical factors, SigMut (HR 1.21, p = 0.0297), SigBWD (HR 1.25, p = 0.0263), and likely SigFWD (HR 1.17, p = 0.062) remain independent risk factors of BC deaths. Furthermore, the proportion of patients positive for these signatures is significantly increased in ER −, Her2-enriched, basal-like, and claudin-low BCs compared to ER + and luminal BCs. Collectively, these SHARPIN GCN-Increase-derived signatures may have clinical applications in management of patients with BC.

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SHARPIN genomic increase correlates with poor prognosis in breast cancer patients

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SHARPIN genomic increase associates with enrichment of mutations in TP53 and others

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SHARPIN genomic increases occur along with many differentially expressed genes (DEGs)

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These DEGs enhance breast cancer cell proliferation and reduces extracellular matrix

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Enriched mutations and DEGs strongly associate with reductions in overall survival

SHARPIN stabilizes estrogen receptor α and promotes breast cancer cell proliferation

Estrogen receptor α is expressed in the majority of breast cancers and promotes estrogen-dependent cancer progression. In our study, we identified the novel E3 ubiquitin ligase SHARPIN function to facilitate ERα signaling. SHARPIN is highly expressed in human breast cancer and correlates with ERα protein level by immunohistochemistry. SHARPIN expression level correlates with poor prognosis in ERα positive breast cancer patients. SHARPIN depletion based RNA-sequence data shows that ERα signaling is a potential SHARPIN target. SHARPIN depletion significantly decreases ERα protein level, ERα target genes expression and estrogen response element activity in breast cancer cells, while SHARPIN overexpression could reverse these effects. SHARPIN depletion significantly decreases estrogen stimulated cell proliferation in breast cancer cells, which effect could be further rescued by ERα overexpression. Further mechanistic study reveals that SHARPIN mainly localizes in the cytosol and interacts with ERα both in the cytosol and the nuclear. SHARPIN regulates ERα signaling through protein stability, not through gene expression. SHARPIN stabilizes ERα protein via prohibiting ERα protein poly-ubiquitination. Further study shows that SHARPIN could facilitate the mono-ubiquitinaiton of ERα at K302/303 sites and facilitate ERE luciferase activity. Together, our findings propose a novel ERα modulation mechanism in supporting breast cancer cell growth, in which SHARPIN could be one suitable target for development of novel therapy for ERα positive breast cancer.

A novel SHARPIN-PRMT5-H3R2me1 axis is essential for lung cancer cell invasion

SHARPIN (Shank-associated RH domain interacting protein) is the main component of the linear ubiquitin chain activation complex (LUBAC). SHARPIN is involved in regulating inflammation and cancer progression. However, whether SHARPIN plays an important role in lung cancer metastasis and the potential underlying mechanism are still unknown. Here, for the first time, we reported that SHARPIN expression is closely related to lung cancer progression. Moreover, SHARPIN plays a central role in controlling lung cancer cell metastasis. Mechanistic studies further revealed that PRMT5 (Protein arginine methyltransferase 5), responsible for catalyzing arginine methylation on histones, is a novel cofactor of SHARPIN. This finding provides the basis for further study of the crosstalk between protein ubiquitination and histone methylation. We further found that SHARPIN-PRMT5 is essential for the monomethylation of histones of chromatins at key metastasis-related genes, defining a new mechanism regulating cancer invasion. A novel MLL complex (ASH2 and WDR5) was implied in the link between histone arginine2 monomethylation (H3R2me1) and histone lysine4 trimethylation (H3K4me3) for the activation of metastasis-related genes. These novel findings establish a new epigenetic paradigm in which SHARPIN-PRMT5 has distinct roles in orchestrating chromatin environments for cancer-related genes via integrating signaling between H3R2me1 and H3K4me3.

Elevation of SHARPIN Protein Levels in Prostate Adenocarcinomas Promotes Metastasis and Impairs Patient Survivals

BACKGROUND

SHARPIN, SHANK-associated RH domain interacting protein, associates with a linear ubiquitin chain assembly complex (LUBAC) to regulate inflammation and immunity. It has been reported that SHARPIN is highly expressed in several human tumors including ovarian cancer and liver cancer. We found that SHARPIN is also highly expressed in prostate cancer cell lines of DU145, LNCAP, and PC-3. Suppression of SHARPIN caused an inhibition of NF-κB signal and decreases in tumorigenesis of cultured cells in NOD/SCID mouse model. Overexpression of SHARPIN in prostate cancer cells promoted cell growth and reduced apoptosis through NF-kB/ERK/Akt pathway and apoptosis-associated proteins.

METHODS

We analyzed the expression of SHARPIN in prostate cancer tissues from 95 patients and its relationship with other clinical characteristics associated with PCA malignancies and patient survivals, and examined the impacts of SHARPIN suppression with siRNA on proliferation, angiogenesis, invasion, and expression levels of MMP-9 of prostate cancer cells and metastasis to lung by these cells in nude mice.

RESULTS

High levels of SHARPIN were associated with high malignancies of PCA and predicted shorter survivals of PCA patients. Suppression of SHARPIN impaired cell proliferation, angiogenesis, and invasion and reduced levels of MMP-9 in prostate cancer cells and reduced the size of metastatic lung tumors induced by these cells in mice.

CONCLUSIONS

SHARPIN enhances the metastasis of prostate cancer and impair patient survivals. Prostate 77:718-728, 2017. © 2017 Wiley Periodicals, Inc.

Sharpin promotes hepatocellular carcinoma progression via transactivation of Versican expression

Sharpin (Shank-associated RH domain-interacting protein, also known as SIPL1) is a multifunctional molecule that participates in various biological settings, including nuclear factor-κB signaling activation and tumor suppressor gene inhibition. Sharpin is upregulated in various types of cancers, including hepatocellular carcinoma (HCC), and is implicated in tumor progression. However, the exact roles of Sharpin in tumorigenesis and tumor progression remain largely unknown. Here we report novel mechanisms of HCC progression through Sharpin overexpression. In our study, Sharpin was upregulated in human HCC tissues. Increased Sharpin expression enhanced hepatoma cell invasion, whereas decrease in Sharpin expression by RNA interference inhibited invasion. Microarray analysis identified that Versican, a chondroitin sulfate proteoglycan that plays crucial roles in tumor progression and invasion, was also upregulated in Sharpin-expressing stable cells. Versican expression increased in the majority of HCC tissues and knocking down of Versican greatly attenuated hepatoma cell invasion. Sharpin expression resulted in a significant induction of Versican transcription synergistically with Wnt/β-catenin pathway activation. Furthermore, Sharpin-overexpressing cells had high tumorigenic properties in vivo. These results demonstrate that Sharpin promotes Versican expression synergistically with the Wnt/β-catenin pathway, potentially contributing to HCC development. A Sharpin/Versican axis could be an attractive therapeutic target for this currently untreatable cancer.

Overexpression of MAPK15 in gastric cancer is associated with copy number gain and contributes to the stability of c-Jun

This study was aimed at understanding the functional and clinicopathological significance of MAPK15 alteration in gastric cancer. Genome-wide copy number alterations (CNAs) were first investigated in 40 gastric cancers using Agilent aCGH-244K or aCGH-400K, and copy number gains of MAPK15 found in aCGH were validated in another set of 48 gastric cancer tissues. The expression of MAPK15 was analyzed using immunohistochemistry in concurrent lesions of normal, adenoma, and carcinoma from additional 45 gastric cancer patients. The effects of MAPK15 on cell cycle, c-Jun phosphorylation, and mRNA stability were analyzed in gastric cancer cells. Copy number gains of MAPK15 were found in 15 (17%) of 88 tumor tissues. The mRNA levels of MAPK15 were relatively high in the gastric cancer tissues and gastric cancer cells with higher copy number gains than those without. Knockdown of MAPK15 using siRNA in gastric cancer cells significantly suppressed cell proliferation and resulted in cell cycle arrest at G₁-S phase. Reduced c-Jun phosphorylation and c-Jun half-life were observed in MAPK15-knockdowned cells. In addition, transient transfection of MAPK15 into AGS gastric cancer cells with low copy number resulted in an increase of c-Jun phosphorylation and stability. The overexpression of MAPK15 occurred at a high frequency in carcinomas (37%) compared to concurrent normal tissues (2%) and adenomas (21%). In conclusion, the present study suggests that MAPK15 overexpression may contribute to the malignant transformation of gastric mucosa by prolonging the stability of c-Jun. And, patients with copy number gain of MAPK15 in normal or premalignant tissues of stomach may have a chance to progress to invasive cancer.

The multifaceted role of the E3 ubiquitin ligase HOIL-1: beyond linear ubiquitination

Ubiquitination controls and fine-tunes many signaling processes driving immunity, inflammation, and cancer. The E3 ubiquitin ligase HOIL-1 (heme-oxidized IRP2 ubiquitin ligase-1) is increasingly implicated in different signaling pathways and plays a vital role in immune regulation. HOIL-1 co operates with the E3 ubiquitin ligase HOIP (HOIL-1 interacting protein) to modify specific nuclear factor-κB (NF-κB) signaling proteins with linear M1-linked polyubiquitin chains. In addition, through its ability to also add K48-linked polyubiquitin chains to specific substrates, HOIL-1 has been linked with antiviral signaling, iron and xenobiotic metabolism, cell death, and cancer. HOIL-1 deficiency in humans leads to myopathy, amylopectinosis, auto-inflammation, and immunodeficiency associated with an increased frequency of bacterial infections. HOIL-1-deficient mice exhibit amylopectin-like deposits in the myocardium, pathogen-specific immunodeficiency, but minimal signs of hyper-inflammation. This review summarizes current knowledge on the mechanism of action of HOIL-1 and highlights recent advances regarding its role in health and disease.

Mutually Exclusive Roles of SHARPIN in Integrin Inactivation and NF-κB Signaling

SHANK-associated RH domain interactor (SHARPIN) inhibits integrins through interaction with the integrin α-subunit. In addition, SHARPIN enhances nuclear factor-kappaB (NF-κB) activity as a component of the linear ubiquitin chain assembly complex (LUBAC). However, it is currently unclear how regulation of these seemingly different roles is coordinated. Here, we show that SHARPIN binds integrin and LUBAC in a mutually exclusive manner. We map the integrin binding site on SHARPIN to the ubiquitin-like (UBL) domain, the same domain implicated in SHARPIN interaction with LUBAC component RNF31 (ring finger protein 31), and identify two SHARPIN residues (V267, L276) required for both integrin and RNF31 regulation. Accordingly, the integrin α-tail is capable of competing with RNF31 for SHARPIN binding in vitro. Importantly, the full SHARPIN RNF31-binding site contains residues (F263A/I272A) that are dispensable for SHARPIN-integrin interaction. Importantly, disrupting SHARPIN interaction with integrin or RNF31 abolishes SHARPIN-mediated regulation of integrin or NF-κB activity, respectively. Altogether these data suggest that the roles of SHARPIN in inhibiting integrin activity and supporting linear ubiquitination are (molecularly) distinct.

The pathogenesis of chronic eosinophilic esophagitis in SHARPIN-deficient mice

Increased numbers of eosinophils in the esophagus are common in several esophageal and systemic diseases, and a prominent feature of eosinophilic esophagitis. Mouse models can provide insight into the mechanisms of eosinophil infiltration and their pathogenic role. SHARPIN-deficient cpdm mice develop a chronic proliferative dermatitis and an esophagitis characterized by epithelial hyperplasia and the accumulation of eosinophils in the serosa, submucosa, lamina propria and epithelium of the esophagus. We conducted a detailed investigation of the pathogenesis of the esophagitis by light microscopy, immunohistochemistry, and gene expression as the mice aged from 4 to 10 weeks. The thickness of the esophageal epithelium and the number of eosinophils in the esophagus both increased with age. There were scattered apoptotic epithelial cells in mice at 6-10 weeks of age that reacted with antibodies to activated caspase 3 and caspase 9. The expression of CCL11 (eotaxin-1), IL4, IL13 and TSLP was increased in cpdm mice compared with wild type (WT) mice, and there was no change in the expression of CCL24 (eotaxin-2), IL5 and IL33. The expression of chitinase-like 3 and 4 (YM1 and YM2) proteins, markers of type 2 inflammation, was greatly increased in cpdm mice, and this was replicated in vitro by incubation of WT esophagus in the presence of IL4 and IL13. Immunohistochemistry showed that these proteins were localized in esophageal epithelial cells. The severity of the esophagitis was not affected by crossing SHARPIN-deficient mice with lymphocyte-deficient Rag1 null mice indicating that the inflammation is independent of B and T lymphocytes.

LUBAC Formation Is Impaired in the Livers of Mice with MCD-Dependent Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a disorder characterized by hepatic lipid accumulation followed by the inflammation-induced death of hepatocytes and fibrosis. In this process, oxidative stress contributes to the induction of several inflammatory cytokines including TNF-α andIL-1β in macrophages, while, in hepatocytes, NF-κB reportedly induces the expressions of cell survival genes for protection from apoptosis. Recently, it was reported that the new ubiquitin ligase complex termed linear ubiquitin chain assembly complex (LUBAC), composed of SHARPIN (SHANK-associated RH domain-interacting protein), HOIL-1L (longer isoform of heme-oxidized iron-regulatory protein 2 ubiquitin ligase-1), and HOIP (HOIL-1L interacting protein), forms linear ubiquitin on NF-κB essential modulator (NEMO) and thereby induces NF-κB pathway activation. In this study, we demonstrated the formation of LUBAC to be impaired in the livers of NASH rodent models produced by methionine and choline deficient (MCD) diet feeding, first by either gel filtration or Blue Native-PAGE, with subsequent confirmation by western blotting. The reduction of LUBAC is likely to be attributable to markedly reduced expression of SHARPIN, one of its components. Thus, impaired LUBAC formation, which would result in insufficient NF-κB activation, may be one of the molecular mechanisms underlying the enhanced apoptotic response of hepatocytes in MCD diet-induced NASH livers.

Elevation of SIPL1 (SHARPIN) Increases Breast Cancer Risk

SIPL1 (Sharpin) or Sharpin plays a role in tumorigenesis. However, its involvement in breast cancer tumorigenesis remains largely unknown. To investigate this issue, we have systemically analyzed SIPL1 gene amplification and expression data available from Oncomine datasets, which were derived from 17 studies and contained approximately 20,000 genes, 3438 breast cancer cases, and 228 normal individuals. We found a SIPL1 gene amplification in invasive ductal breast cancers compared to normal breast tissues and a significant elevation of SIPL1 mRNA in breast cancers in comparison to non-tumor breast tissues. These results collectively reveal that increases in SIPL1 expression occur during breast cancer tumorigenesis. To further investigate this association, we observed increases in the SIPL1 gene and mRNA in the breast cancer subtypes of estrogen receptor (ER)+, progesterone receptor (PR)+, HER2+, or triple negative. Additionally, a gain of the SIPL1 gene correlated with breast cancer grade and the levels of SIPL1 mRNA associated with both breast cancer stages and grades. Elevation of SIPL1 gene copy and mRNA is linked to a decrease in patient survival, especially for those with PR+, ER+, or HER2- breast cancers. These results are supported by our analysis of SIPL1 protein expression using a tissue microarray containing 224 breast cancer cases, in which higher levels of SIPL1 relate to ER+ and PR+ tumors and AKT activation. Furthermore, we were able to show that progesterone significantly reduced SIPL1 mRNA and protein expression in MCF7 cells. As progesterone enhances breast cancer tumorigenesis in a context dependent manner, inhibition of SIPL1 expression may contribute to progesterone's non-tumorigenic function which might be countered by SIPL1 upregulation. Taken together, we demonstrate a positive correlation of SIPL1 with BC tumorigenesis.

Expression profile of genes modulated by Aloe emodin in human U87 glioblastoma cells

Glioblastoma, the most aggressive and malignant form of glioma, appears to be resistant to various chemotherapeutic agents. Hence, approaches have been intensively investigated to targeti specific molecular pathways involved in glioblastoma development and progression. Aloe emodin is believed to modulate the expression of several genes in cancer cells. We aimed to understand the molecular mechanisms underlying the therapeutic effect of Aloe emodin on gene expression profiles in the human U87 glioblastoma cell line utilizing microarray technology. The gene expression analysis revealed that a total of 8,226 gene alterations out of 28,869 genes were detected after treatment with 58.6 μg/ml for 24 hours. Out of this total, 34 genes demonstrated statistically significant change (p<0.05) ranging from 1.07 to 1.87 fold. The results revealed that 22 genes were up-regulated and 12 genes were down-regulated in response to Aloe emodin treatment. These genes were then grouped into several clusters based on their biological functions, revealing induction of expression of genes involved in apoptosis (programmed cell death) and tissue remodelling in U87 cells (p<0.01). Several genes with significant changes of the expression level e.g. SHARPIN, BCAP31, FIS1, RAC1 and TGM2 from the apoptotic cluster were confirmed by quantitative real-time PCR (qRT-PCR). These results could serve as guidance for further studies in order to discover molecular targets for the cancer therapy based on Aloe emodin treatment.

Newly Identified Cancer-Associated Role of Human Neuronal Growth Regulator 1 (NEGR1)

Neuronal growth regulator 1 (NEGR1) has become a great interest based on the recent findings that its genetic alteration is implicated in human obesity and human dyslexia. By analyzing the gene expression profiles of tumor biopsies and normal tissues, we identified NEGR1 as a commonly down-regulated gene in many types of human cancer tissues. NEGR1 contains a C-terminal GPI anchor attachment site and is primarily localized to cell membrane rafts, especially in cell-to-cell contacting areas. The oncogenic phenotype was clearly attenuated when NEGR1 was overexpressed in the human ovarian cancer cell line SKOV-3. Furthermore, cell aggregation and neurite outgrowth was greatly increased by NEGR1 overexpression. On the contrary, cell migration and invasion was increased in NEGR1-depleted cells, suggesting that NEGR1 may contribute to tumor suppression. Taken together, we suggest that NEGR1 is a raft-associated extracellular protein that may participate in cell recognition and interaction, which is important in growth control and malignant transformation.

Activation of nuclear factor κB pathway and downstream targets survivin and livin by SHARPIN contributes to the progression and metastasis of prostate cancer

BACKGROUND

Nuclear factor κB (NFκB) signaling is strongly associated with tumor progression, and studies have shown that SHANK-associated RH domain interacting protein (SHARPIN) is crucial for NFκB pathway activation. However, the expression and functions of SHARPIN in prostate cancer (PCa) have not yet been defined.

METHODS

The expression of SHARPIN in PCa cell lines and tissues was evaluated with western blotting, quantitative real-time polymerase chain reaction, and immunohistochemistry. After SHARPIN was silenced in the PCa cell lines, western blots were used to confirm that SHARPIN physically associated with components of the NFκB pathway and the downstream targets (survivin and livin). The functions of SHARPIN in cell proliferation, migration, and invasion in vitro were measured with 5-(3-carboxymethoxyphenyl)-2-(4,5-dimenthylthiazoly)-3-(4-sulfophenyl)tetrazolium, inner salt (MTS), Transwell, and invasion assays, respectively. Flow cytometry was employed to evaluate cell apoptosis. Furthermore, tumorigenesis in vivo was examined with tumorigenicity assays.

RESULTS

SHARPIN expression was upregulated in PCa cell lines and tissues. The knockdown of SHARPIN or incubation with Bay 11-7082 (an NFκB inhibitor) led to dramatically decreased levels of phosphorylated IκBα and phosphorylated p65 in comparison with the control group. Downregulation of survivin and livin due to SHARPIN inhibition was attributable to transcriptional repression (P < .05). Decreases in cell viability, migration, invasion, and survival with a higher sensitivity to docetaxel in vitro and with repressed tumorigenesis in vivo were observed upon SHARPIN silencing, and this was consistent with the results from inhibition of the NFκB pathway and its downstream targets.

CONCLUSION

The current study demonstrates that overexpression of SHARPIN promotes activation of the NFκB pathway and downstream targets survivin and livin, which potentially contributes to PCa development.

Linear ubiquitination-mediated NF-κB regulation and its related disorders

Ubiquitination is a post-translational modification involved in the regulation of a broad variety of cellular functions, such as protein degradation and signal transduction, including nuclear factor-κB (NF-κB) signalling. NF-κB is crucial for inflammatory and immune responses, and aberrant NF-κB signalling is implicated in multiple disorders. We found that linear ubiquitin chain assembly complex (LUBAC), composed of HOIL-1L, HOIP and SHARPIN, generates a novel type of Met1 (M1)-linked linear polyubiquitin chain and specifically regulates the canonical NF-κB pathway. Moreover, specific deubiquitinases, such as CYLD, A20 (TNFAIP3) and OTULIN/gumby, inhibit LUBAC-induced NF-κB activation by different molecular mechanisms, and several M1-linked ubiquitin-specific binding domains have been structurally defined. LUBAC and these linear ubiquitination-regulating factors contribute to immune and inflammatory processes and apoptosis. Functional impairments of these factors are correlated with multiple disorders, including autoinflammation, immunodeficiencies, dermatitis, B-cell lymphomas and Parkinson's disease. This review summarizes the molecular basis and the pathophysiological implications of the linear ubiquitination-mediated NF-κB activation pathway regulation by LUBAC.

SHARPIN is a key regulator of immune and inflammatory responses

Mice with spontaneous mutations in the Sharpin gene develop chronic proliferative dermatitis that is characterized by eosinophilic inflammation of the skin and other organs with increased expression of type 2 cytokines and dysregulated development of lymphoid tissues. The mutant mice share phenotypic features with human hypereosinophilic syndromes. The biological function of SHARPIN and how its absence leads to such a complex inflammatory phenotype in mice are poorly understood. However, recent studies identified SHARPIN as a novel modulator of immune and inflammatory responses. The emerging mechanistic model suggests that SHARPIN functions as an important adaptor component of the linear ubiquitin chain assembly complex that modulates activation of NF-κB signalling pathway, thereby regulating cell survival and apoptosis, cytokine production and development of lymphoid tissues. In this review, we will summarize the current understanding of the ubiquitin-dependent regulatory mechanisms involved in NF-κB signalling, and incorporate the recently obtained molecular insights of SHARPIN into this pathway. Recent studies identified SHARPIN as an inhibitor of β1-integrin activation and signalling, and this may be another mechanism by which SHARPIN regulates inflammation. Furthermore, the disrupted lymphoid organogenesis in SHARPIN-deficient mice suggests that SHARPIN-mediated NF-κB regulation is important for de novo development of lymphoid tissues.

Structural analysis of SHARPIN, a subunit of a large multi-protein E3 ubiquitin ligase, reveals a novel dimerization function for the pleckstrin homology superfold

SHARPIN (SHANK-associated RH domain interacting protein) is part of a large multi-protein E3 ubiquitin ligase complex called LUBAC (linear ubiquitin chain assembly complex), which catalyzes the formation of linear ubiquitin chains and regulates immune and apoptopic signaling pathways. The C-terminal half of SHARPIN contains ubiquitin-like domain and Npl4-zinc finger domains that mediate the interaction with the LUBAC subunit HOIP and ubiquitin, respectively. In contrast, the N-terminal region does not show any homology with known protein interaction domains but has been suggested to be responsible for self-association of SHARPIN, presumably via a coiled-coil region. We have determined the crystal structure of the N-terminal portion of SHARPIN, which adopts the highly conserved pleckstrin homology superfold that is often used as a scaffold to create protein interaction modules. We show that in SHARPIN, this domain does not appear to be used as a ligand recognition domain because it lacks many of the surface properties that are present in other pleckstrin homology fold-based interaction modules. Instead, it acts as a dimerization module extending the functional applications of this superfold.

TNF and ubiquitin at the crossroads of gene activation, cell death, inflammation, and cancer

Tumor necrosis factor (TNF) is crucial for innate immunity, but deregulated TNF signaling also plays an eminent role in the pathogenesis of many chronic inflammatory diseases and cancer-related inflammation. The signals that mediate both the beneficial and the harmful effects of TNF are initiated when TNF binds to its receptors on the surface of target cells. TNF receptor 1 (TNFR1) is ubiquitously expressed, whereas TNFR2 is mainly expressed on lymphocytes and endothelial cells. This review focuses on the molecular and physiological consequences of the interaction of TNF with TNFR1. The different outcomes of TNF signaling originate at the apical signaling complex that forms when TNF binds to TNFR1, the TNFR1 signaling complex (TNF-RSC). By integrating recently gained insight on the functional importance of the presence of different types of ubiquitination in the TNF-RSC, including linear ubiquitin linkages generated by the linear ubiquitin chain assembly complex (LUBAC), with the equally recent elucidation of the mode in which ubiquitin-binding domains interact with specific di-ubiquitin linkages, this review develops a new concept for the way the concerted action of different ubiquitination events enables the TNF-RSC to generate its signaling output in a spatio-temporally controlled manner. Finally, it will be explained how these new findings and the emerging concept of differential ubiquitination governing the TNF-RSC may impact future research on the molecular mechanism of TNF signaling and the function of this cytokine in normal physiology, chronic inflammation, and cancer.

SHARPINing integrin inhibition

The activity state of integrins is crucial for cell adhesion, migration and differentiation, and is regulated predominantly by protein interactions of the integrin β cytoplasmic domain. SHARPIN is now shown to negatively regulate integrin activation by binding the α-integrin subunit and interfering with the association of the β cytodomain with activating proteins.

SHARPIN is an endogenous inhibitor of β1-integrin activation

Regulated activation of integrins is critical for cell adhesion, motility and tissue homeostasis. Talin and kindlins activate β1-integrins, but the counteracting inhibiting mechanisms are poorly defined. We identified SHARPIN as an important inactivator of β1-integrins in an RNAi screen. SHARPIN inhibited β1-integrin functions in human cancer cells and primary leukocytes. Fibroblasts, leukocytes and keratinocytes from SHARPIN-deficient mice exhibited increased β1-integrin activity, which was fully rescued by re-expression of SHARPIN. We found that SHARPIN directly binds to a conserved cytoplasmic region of integrin α-subunits and inhibits recruitment of talin and kindlin to the integrin. Therefore, SHARPIN inhibits the critical switching of β1-integrins from inactive to active conformations.

SHARPIN negatively associates with TRAF2-mediated NFκB activation

NFκB is an inducible transcriptional factor controlled by two principal signaling cascades and plays pivotal roles in diverse physiological processes including inflammation, apoptosis, oncogenesis, immunity, and development. Activation of NFκB signaling was detected in skin of SHAPRIN-deficient mice and can be diminished by an NFκB inhibitor. However, in vitro studies demonstrated that SHARPIN activates NFκB signaling by forming a linear ubiquitin chain assembly complex with RNF31 (HOIP) and RBCK1 (HOIL1). The inconsistency between in vivo and in vitro findings about SHARPIN's function on NFκB activation could be partially due to SHARPIN's potential interactions with downstream molecules of NFκB pathway. In this study, 17 anti-flag immunoprecipitated proteins, including TRAF2, were identified by mass spectrum analysis among Sharpin-Flag transfected mouse fibroblasts, B lymphocytes, and BALB/c LN stroma 12 cells suggesting their interaction with SHARPIN. Interaction between SHARPIN and TRAF2 confirmed previous yeast two hybridization reports that SHARPIN was one TRAF2's partners. Furthermore, luciferase-based NFκB reporter assays demonstrated that SHARPIN negatively associates with NFκB activation, which can be partly compensated by over-expression of TRAF2. These data suggested that other than activating NFκB signaling by forming ubiquitin ligase complex with RNF31 and RBCK1, SHARPIN may also negatively associate with NFκB activation via interactions with other NFκB members, such as TRAF2.

Linear ubiquitination in NF-κB signaling and inflammation: What we do understand and what we do not

Despite its small size, ubiquitin is one of the most versatile signaling molecules in the cell and affects distinct cellular processes. It forms the building block of a repertoire of posttranslational modifications of cellular proteins, ranging from the attachment of a single ubiquitin to ubiquitin chains of different linkage. Proteins that contain ubiquitin chain-specific ubiquitin-binding domains recognize different types of ubiquitination and determine the mode of signaling of modified proteins. Polyubiquitin chains were thought to be formed only by the conjugation of the ubiquitin C-terminal Gly to one of the seven internal Lys residues of another ubiquitin. However, the C-terminal Gly was recently shown to also link to the N-terminus of another ubiquitin to form head-to-tail polyubiquitin chains, which is referred to as linear ubiquitination. These linear linkages can be assembled and conjugated to another protein by an E3 ligase complex known as LUBAC, and are recognized by a particular ubiquitin-binding domain known as UBAN. Both have been implicated in the regulation of TNF-induced NF-κB signaling, which induces the expression of a wide range of proteins that mediate many biological processes including inflammation and cell survival. We discuss the molecular players and mechanisms that determine the specificity and outcome of linear ubiquitination in NF-κB signaling, as well as future directions and challenges ahead.