PIAS3 Suppresses NF-κB-mediated Transcription by Interacting with the p65/RelA Subunit

PIASy of orange-spotted grouper (Epinephelus coioides) negatively regulates RLRs-mediated innate antiviral immunity

During viral infection, RIG-I-like receptors (RLRs) are cytoplasmic pattern recognition receptors that recognize and bind to viral RNA components, initiating the transcription of interferon-related genes, inflammatory cytokines and other factors, thereby triggering the cellular production of an antiviral innate immune response. The protein inhibitor of activated signal transducer and activator of transcription (STAT) (PIAS) protein family has become a hot research topic due to its extensive involvement in the regulation of cytokines, inflammatory factors and innate immune signaling pathways. In the present study, we investigated the role of fish PIASy in Singapore grouper iridovirus (SGIV) and red spotted grouper nervous necrosis virus (RGNNV) infections. The homologous sequence of orange-spotted grouper (Epinephelus coioides) PIASy gene (EcPIASy) was cloned and characterized, which encoded a 498-amino acid protein with 99.20 % homology to Plectropomus leopardus. EcPIASy is expressed mainly in gills, blood, and liver. Subcellular localization showed that EcPIASy was uniformly distributed in the nucleus. Overexpression of EcPIASy promoted SGIV and RGNNV replication, and inhibited the expression of interferon related genes and pro-inflammatory factors induced by viruses. In addition, EcPIASy interacts with RLR signaling pathway-related genes EcMDA5, EcIRF3 and EcIRF7, whereas the interaction between EcPIASy and EcIRF3 does not depend on any specific structural domain of EcPIASy. The results provide a better understanding of the relationship between PIASy and viral infection in fish.

Identification of SUMOylation-related signature genes associated with immune infiltration in ulcerative colitis through bioinformatics analysis and experimental validation

OBJECTIVE

Ulcerative colitis (UC) is a chronic inflammatory disorder challenging to diagnose clinically. We focused on identifying and validating SUMOylation-related signature genes in UC and their association with immune infiltration.

METHODS

Five eligible gene expression profiles were selected from the Gene Expression Omnibus (GEO) database and merged into a single dataset comprising 260 UC patients and 76 healthy controls (HC). Differentially expressed genes (DEGs) were identified, and these were intersected with SUMOylation-related genes to obtain differentially expressed SUMOylation-related genes (DESRGs). Next, we identify the signature genes and validate them through comprehensive analyses employing GO, KEGG, GSVA, Lasso-cox regression, ROC curves, and clustering analysis. The infiltrating immune cells were analyzed using the CIBERSORT algorithm and Pearson correlation analysis. Finally, in vitro and in vivo experiments validated the identified signature genes.

RESULTS

PALMD, THRB, MAGED1, PARP1, and SLC16A1 were identified. Next, an excellent predictive model for UC was established and distinct subgroups of patients associated with SUMOylation were identified. Moreover, the NF-κB signaling pathway likely plays a pivotal role in the regulation of SUMOylation in UC. Additionally, we validated that the alterations in PALMD, THRB, and MAGED1 expression in LPS-induced Caco-2 cells concurred with our bioinformatics findings, particularly demonstrating statistically significant differences in PALMD and THRB expression. Finally, in a DSS-induced mouse colitis model, we observed a significant upregulation of PALMD expression. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation.

CONCLUSION

This study comprehensively elucidates the biological roles of SUMOylation-related genes in UC, identifying PALMD, MAGED1, THRB, PARP1, and SLC16A1 as signature genes that represent promising biomarkers for UC diagnosis and prognosis.

SUMOylation at the crossroads of gut health: insights into physiology and pathology

SUMOylation, a post-translational modification involving the covalent attachment of small ubiquitin-like modifier (SUMO) proteins to target substrates, plays a pivotal role at the intersection of gut health and disease, influencing various aspects of intestinal physiology and pathology. This review provides a comprehensive examination of SUMOylation's diverse roles within the gut microenvironment. We examine its critical roles in maintaining epithelial barrier integrity, regulating immune responses, and mediating host-microbe interactions, thereby highlighting the complex molecular mechanisms that underpin gut homeostasis. Furthermore, we explore the impact of SUMOylation dysregulation in various intestinal disorders, including inflammatory bowel diseases and colorectal cancer, highlighting its implications as a potential diagnostic biomarker and therapeutic target. By integrating current research findings, this review offers valuable insights into the dynamic interplay between SUMOylation and gut health, paving the way for novel therapeutic strategies aimed at restoring intestinal equilibrium and combating associated pathologies.

Protein inhibitor of activated STAT3 (PIAS3) attenuates psoriasis and associated inflammation

Psoriasis is a common chronic inflammatory multisystem disease accompanied by hyperproliferation and inflammation of epidermal keratinocytes. Signal transducer and activator of transcription 3 (STAT3) is constitutively activated and plays an important role in epidermal keratinocytes of human psoriatic skin lesions. In this study, we investigated the effects of an endogenous STAT3 inhibitor, a protein inhibitor of activated STAT3 (PIAS3), on the proliferation and inflammation of psoriatic cells. The expression of PIAS3 in psoriatic tissues and healthy skin was analyzed using the Gene Expression Omnibus database and clinical samples. The human immortalized epidermal (HaCaT) cells were used to establish an in vitro psoriasis-like cell model. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-thethrazolium (MTS) assay was used to detect cell proliferation. Flow cytometry was used to determine apoptosis levels. Real-time PCR, western blotting, and enzyme-linked immunosorbent assay (ELISA) were used to detect the expression levels of related factors. Furthermore, a mouse model of imiquimod (IMQ)-induced psoriatic dermatitis was established to verify the in vitro experimental results. The results showed that the mRNA and protein expression levels of PIAS3 were lower in psoriatic lesions than in normal tissues. PIAS3 inhibited the proliferation and promoted apoptosis of M5-induced HaCaT cells. Simultaneously, the mRNA and protein expression levels of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-8 (IL-8), and keratin 17 (K17) were significantly decreased and that of p53 was increased, thereby inhibiting the inflammatory response and promoting apoptosis. PIAS3 inhibited the transcription activity of STAT3 and noncanonical nuclear factor-kappaB (NF-κB). Furthermore, PIAS3 attenuated IMQ-induced psoriasis-like inflammation in mice. Our findings suggest that PIAS3 plays an important role in psoriasis by regulating the STAT3/NF-κB signaling pathway and p53. The lack of PIAS3 may represent a novel mechanism underlying the pathogenesis of psoriasis.

SUMO and PIAS repress NF-κB activation in a basal chordate

Small ubiquitin-like modifier (SUMO) regulates various biological processes, including the MyD88/TICAMs-IRAKs-TRAF6-NF-κB pathway, one of the core immune pathways. However, its functions are inconsistent between invertebrates and vertebrates and have rarely been investigated in lower chordates, including amphioxus and fishes. Here, we investigated the SUMOylation gene system in the amphioxus, a living basal chordate. We found that amphioxus has a SUMOylation system that has a complete set of genes and preserves several ancestral traits. We proceeded to study their molecular functions using the mammal cell lines. Both amphioxus SUMO1 and SUMO2 were shown to be able to attach to NF-κB Rel and to inhibit NF-κB activation by 50-75% in a dose-dependent fashion. The inhibition by SUMO2 could be further enhanced by the addition of the SUMO E2 ligase UBC9. In comparison, while human SUMO2 inhibited RelA, human SUMO1 slightly activated RelA. We also showed that, similar to human PIAS1-4, amphioxus PIAS could serve as a SUMO E3 ligase and promote its self-SUMOylation. This suggests that amphioxus PIAS is functionally compatible in human cells. Moreover, we showed that amphioxus PIAS is not only able to inhibit NF-κB activation induced by MyD88, TICAM-like, TRAF6 and IRAK4 but also able to suppress NF-κB Rel completely in the presence of SUMO1/2 in a dose-insensitive manner. This suggests that PIAS could effectively block Rel by promoting Rel SUMOylation. In comparison, in humans, only PIAS3, but not PIAS1/2/4, has been reported to promote NF-κB SUMOylation. Taken together, the findings from amphioxus, together with those from mammals and other species, not only offer insights into the functional volatility of the animal SUMO system, but also shed light on its evolutionary transitions from amphioxus to fish, and ultimately to humans.

TRIM8: a double-edged sword in glioblastoma with the power to heal or hurt

Glioblastoma multiforme (GBM) is an aggressive primary brain tumor and one of the most lethal central nervous system tumors in adults. Despite significant breakthroughs in standard treatment, only about 5% of patients survive 5 years or longer. Therefore, much effort has been put into the search for identifying new glioma-associated genes. Tripartite motif-containing (TRIM) family proteins are essential regulators of carcinogenesis. TRIM8, a member of the TRIM superfamily, is abnormally expressed in high-grade gliomas and is associated with poor clinical prognosis in patients with glioma. Recent research has shown that TRIM8 is a molecule of duality (MoD) that can function as both an oncogene and a tumor suppressor gene, making it a "double-edged sword" in glioblastoma development. This characteristic is due to its role in selectively regulating three major cellular signaling pathways: the TP53/p53-mediated tumor suppression pathway, NFKB/NF-κB, and the JAK-STAT pathway essential for stem cell property support in glioma stem cells. In this review, TRIM8 is analyzed in detail in the context of GBM and its involvement in essential signaling and stem cell-related pathways. We also discuss the basic biological activities of TRIM8 in macroautophagy/autophagy, regulation of bipolar spindle formation and chromosomal stability, and regulation of chemoresistance, and as a trigger of inflammation.

The Role of SUMO E3 Ligases in Signaling Pathway of Cancer Cells

Small ubiquitin-like modifier (SUMO)ylation is a reversible post-translational modification that plays a crucial role in numerous aspects of cell physiology, including cell cycle regulation, DNA damage repair, and protein trafficking and turnover, which are of importance for cell homeostasis. Mechanistically, SUMOylation is a sequential multi-enzymatic process where SUMO E3 ligases recruit substrates and accelerate the transfer of SUMO onto targets, modulating their interactions, localization, activity, or stability. Accumulating evidence highlights the critical role of dysregulated SUMO E3 ligases in processes associated with the occurrence and development of cancers. In the present review, we summarize the SUMO E3 ligases, in particular, the novel ones recently identified, and discuss their regulatory roles in cancer pathogenesis.

PIAS Factors from Rainbow Trout Control NF-κB- and STAT-Dependent Gene Expression

Four ‘protein inhibitors of activated STAT’ (PIAS) control STAT-dependent and NF-κB-dependent immune signalling in humans. The genome of rainbow trout (Oncorhynchus mykiss) contains eight pias genes, which encode at least 14 different pias transcripts that are differentially expressed in a tissue- and cell-specific manner. Pias1a2 was the most strongly expressed variant among the analysed pias genes in most tissues, while pias4a2 was commonly low or absent. Since the knock-out of Pias factors in salmonid CHSE cells using CRISPR/Cas9 technology failed, three structurally different Pias protein variants were selected for overexpression studies in CHSE-214 cells. All three factors quenched the basal activity of an NF-κB promoter in a dose-dependent fashion, while the activity of an Mx promoter remained unaffected. Nevertheless, all three overexpressed Pias variants from trout strongly reduced the transcript level of the antiviral Stat-dependent mx gene in ifnγ-expressing CHSE-214 cells. Unlike mx, the overexpressed Pias factors modulated the transcript levels of NF-κB-dependent immune genes (mainly il6, il10, ifna3, and stat4) in ifnγ-expressing CHSE-214 cells in different ways. This dissimilar modulation of expression may result from the physical cooperation of the Pias proteins from trout with differential sets of interacting factors bound to distinct nuclear structures, as reflected by the differential nuclear localisation of trout Pias factors. In conclusion, this study provides evidence for the multiplication of pias genes and their sub-functionalisation during salmonid evolution.

Genetic profiles of subcutaneous panniculitis-like T-cell lymphoma and clinicopathological impact of HAVCR2 mutations

Recent studies identified germline mutations in HAVCR2 (encoding T-cell immunoglobulin mucin 3) as a genetic factor that predisposes to subcutaneous panniculitis-like T-cell lymphoma (SPTCL). However, the differences between HAVCR2-mutated (HAVCR2MUT) and HAVCR2 wild-type (HAVCR2WT) SPTCLs remain unclear. A nationwide cohort of 53 patients with SPTCL diagnosed at 8 Korean institutions was established. Whole-exome sequencing and RNA-sequencing were performed on 8 patients in the discovery set. In the validation set, targeted gene sequencing or direct sequencing of HAVCR2 was performed. Of 49 patients with available HAVCR2 status, 25 (51.0%) were HAVCR2Y82C. HAVCR2Y82C was associated with younger age (P = .001), development of hemophagocytic lymphohistiocytosis or hemophagocytic lymphohistiocytosis-like systemic illness (P < .001), and short relapse-free survival (RFS) (P = .023). Most mutated genes in SPTCLs were involved in immune responses, epigenetic modifications, and cell signaling. Mutations in UNC13D, PIAS3, and KMT2D were more frequent in HAVCR2WT SPTCLs. At the gene expression level, HAVCR2Y82C SPTCLs were enriched in genes involved in IL6-JAK-STAT3 signaling and in tumor necrosis factor-α signaling via NF-κB. CCR4 was significantly upregulated in HAVCR2WT SPTCLs both at the messenger RNA level and at the protein level. We established a risk stratification system for SPTCL by integrating clinical and histopathological features, including age and HAVCR2 mutation status. This risk stratification system was strongly associated with RFS (P = .031). In conclusion, the HAVCR2Y82C mutation was common in Korean patients with SPTCL and was associated with unique clinicopathological and genetic features. Combining clinicopathological parameters could aid in predicting prognosis for patients with SPTCL.

Inhibitory feedback control of NF-κB signalling in health and disease

Cells must adapt to changes in their environment to maintain cell, tissue and organismal integrity in the face of mechanical, chemical or microbiological stress. Nuclear factor-κB (NF-κB) is one of the most important transcription factors that controls inducible gene expression as cells attempt to restore homeostasis. It plays critical roles in the immune system, from acute inflammation to the development of secondary lymphoid organs, and also has roles in cell survival, proliferation and differentiation. Given its role in such critical processes, NF-κB signalling must be subject to strict spatiotemporal control to ensure measured and context-specific cellular responses. Indeed, deregulation of NF-κB signalling can result in debilitating and even lethal inflammation and also underpins some forms of cancer. In this review, we describe the homeostatic feedback mechanisms that limit and ‘re-set’ inducible activation of NF-κB. We first describe the key components of the signalling pathways leading to activation of NF-κB, including the prominent role of protein phosphorylation and protein ubiquitylation, before briefly introducing the key features of feedback control mechanisms. We then describe the array of negative feedback loops targeting different components of the NF-κB signalling cascade including controls at the receptor level, post-receptor signalosome complexes, direct regulation of the critical ‘inhibitor of κB kinases’ (IKKs) and inhibitory feedforward regulation of NF-κB-dependent transcriptional responses. We also review post-transcriptional feedback controls affecting RNA stability and translation. Finally, we describe the deregulation of these feedback controls in human disease and consider how feedback may be a challenge to the efficacy of inhibitors.

MUC3A promotes non-small cell lung cancer progression via activating the NFκB pathway and attenuates radiosensitivity

Mucin 3A (MUC3A) is highly expressed in non-small cell lung cancer (NSCLC), but its functions and effects on clinical outcomes are not well understood. Tissue microarray of 92 NSCLC samples indicated that high levels of MUC3A were associated with poor prognosis, advanced staging, and low differentiation. MUC3A knockdown significantly suppressed NSCLC cell proliferation and induced G1/S accumulation via downregulating cell cycle checkpoints. MUC3A knockdown also inhibited tumor growth in vivo and had synergistic effects with radiation. MUC3A knockdown increased radiation-induced DNA double strain breaks and γ-H2AX phosphorylation in NSCLC cells. MUC3A downregulation inhibited the BRCA-1/RAD51 pathway and nucleus translocation of P53 and XCRR6, suggesting that MUC3A promoted DNA damage repair and attenuated radiation sensitivity. MUC3A knockdown also resulted in less nucleus translocation of RELA and P53 in vivo. Immunoprecipitation revealed that MUC3A interacted with RELA and activated the NFκB pathway via promoting RELA phosphorylation and interfering the binding of RELA to IκB. Our studies indicated that MUC3A was a potential oncogene and associated with unfavorable clinical outcomes. NSCLC patients with a high MUC3A level, who should be more frequent follow-up and might benefit less from radiotherapy.

Emerging Roles of TRIM8 in Health and Disease

The superfamily of TRIM (TRIpartite Motif-containing) proteins is one of the largest groups of E3 ubiquitin ligases. Among them, interest in TRIM8 has greatly increased in recent years. In this review, we analyze the regulation of TRIM8 gene expression and how it is involved in many cell reactions in response to different stimuli such as genotoxic stress and attacks by viruses or bacteria, playing a central role in the immune response and orchestrating various fundamental biological processes such as cell survival, carcinogenesis, autophagy, apoptosis, differentiation and inflammation. Moreover, we show how TRIM8 functions are not limited to ubiquitination, and contrasting data highlight its role either as an oncogene or as a tumor suppressor gene, acting as a “double-edged weapon”. This is linked to its involvement in the selective regulation of three pivotal cellular signaling pathways: the p53 tumor suppressor, NF-κB and JAK-STAT pathways. Lastly, we describe how TRIM8 dysfunctions are linked to inflammatory processes, autoimmune disorders, rare developmental and cardiovascular diseases, ischemia, intellectual disability and cancer.

SUMOylation Connects Cell Stress Responses and Inflammatory Control: Lessons From the Gut as a Model Organ

Conjugation with the small ubiquitin-like modifier (SUMO) constitutes a key post-translational modification regulating the stability, activity, and subcellular localization of its target proteins. However, the vast numbers of identified SUMO substrates obscure a clear view on the function of SUMOylation in health and disease. This article presents a comprehensive review on the physiological relevance of SUMOylation by discussing how global SUMOylation levels—rather than specific protein SUMOylation—shapes the immune response. In particular, we highlight the growing body of work on SUMOylation in intestinal pathologies, because of the unique metabolic, infectious, and inflammatory challenges of this organ. Recent studies show that global SUMOylation can help restrain detrimental inflammation while maintaining immune defenses and tissue integrity. These results warrant further efforts to develop new therapeutic tools and strategies to control SUMOylation in infectious and inflammatory disorders.

Duck PIAS2 negatively regulates RIG-I mediated IFN-β production by interacting with IRF7

The protein inhibitor of activated STAT (PIAS) proteins are important signal transduction modulator family and regulate the innate immune signaling pathway induced by certain transcription factors, including NF-κB, IRF3, and JAK/STAT. The PIAS protein mechanism that regulates innate immune response in mammals has been well described in the literature; however, whether the PIAS gene exists in ducks as well as the role of PIAS in duck IFN-β expression is still unclear. Here, we cloned duck PIAS (duPIAS), finding PIAS2 could repress IFN-β production. DuPIAS2 contains SAP-PINIT-RLD-S/T characteristic domains, and its overexpression could inhibit virus-induced IFN-β promoter activation. Moreover, duPIAS2 interacts with duck interferon regulatory factor 7 (IRF7) and inhibits IFN-β promoter activation induced by duck IRF7. Additionally, its inhibitory function does not rely on its SUMO E3 ligase activity but rather its C-terminal portion. The above results demonstrate that duPIAS2 is a repressor of IFN-β production induced by duck IRF7.

TNF deficiency dysregulates inflammatory cytokine production, leading to lung pathology and death during respiratory poxvirus infection

Excessive tumor necrosis factor (TNF) is known to cause significant pathology. Paradoxically, deficiency in TNF (TNF^-/-) also caused substantial pathology during respiratory ectromelia virus (ECTV) infection, a surrogate model for smallpox. TNF^-/- mice succumbed to fulminant disease whereas wild-type mice, and those engineered to express only transmembrane TNF (mTNF), fully recovered. TNF deficiency did not affect viral load or leukocyte recruitment but caused severe lung pathology and excessive production of the cytokines interleukin (IL)-6, IL-10, transforming growth factor beta (TGF-β), and interferon gamma (IFN-γ). Short-term blockade of these cytokines significantly reduced lung pathology in TNF^-/- mice concomitant with induction of protein inhibitor of activated STAT3 (PIAS3) and/or suppressor of cytokine signaling 3 (SOCS3), factors that inhibit STAT3 activation. Consequently, inhibition of STAT3 activation with an inhibitor reduced lung pathology. Long-term neutralization of IL-6 or TGF-β protected TNF^-/- mice from an otherwise lethal infection. Thus, mTNF alone is necessary and sufficient to regulate lung inflammation but it has no direct antiviral activity against ECTV. The data indicate that targeting specific cytokines or cytokine-signaling pathways to reduce or ameliorate lung inflammation during respiratory viral infections is possible but that the timing and duration of the interventive measure are critical.

ROR2 suppresses metastasis of prostate cancer via regulation of miR-199a-5p-PIAS3-AKT2 signaling axis

Bones are the most common metastatic sites for prostate cancer (PCa). Receptor tyrosine kinase-like orphan receptor 2 (ROR2), a noncanonical Wnt receptor, plays crucial roles in skeletal morphogenesis, osteoblast differentiation, and bone formation. The role of ROR2 in PCa metastasis is unclear. We analyzed online datasets from Oncomine as well as using IHC staining on tissue array to determine the relationship between ROR2 expression level and disease outcome of PCa. To investigate how ROR2 regulates migration and invasion of PCa cells, we performed transwell assay and orthotopic xenograft model in nude mice. We then applied the Micro-Western Array (MWA), a high-throughput western blotting platform to analyze the downstream signaling pathways being regulated by ROR2. Compared with nonmalignant PZ-HPV-7 and RWPE-1 cells, PCa cell lines express lower level of ROR2 protein. Constitutive expression of ROR2 in PC-3, DU-145, or C4-2B PCa cells significantly suppressed the cell migration, invasion, and epithelial-mesenchymal transition (EMT) proteins. MWA, western blotting, and microRNA analysis showed that elevation of ROR2 suppressed the expression of miR-199a-5p, which in turn increased the expression of PIAS3. The upregulation of PIAS3 then decreased AKT2 and the phosphorylation of AKT, resulting in the inhibition of migration and invasion of PCa cells both in vitro and in orthotopic xenograft mice model. IHC staining of tissue array and Oncomine datasets analysis indicated that the gene and protein level of ROR2 is much lower in metastatic prostate tumors as compared with primary tumors or adjacent normal prostate tissues. Low level of ROR2 correlated to poor survival and high recurrent frequency in PCa patients. In conclusion, we discovered that ROR2 suppresses PCa metastasis via regulation of PIAS3-PI3K-AKT2 signaling axis.

Chordate PIAS proteins act as conserved repressors of the TRAF6 self-polyubiquitination

In mammals, PIAS proteins are important SUMO E3 ligases and act as versatile regulators of over sixty different proteins, including components from the NF-κB pathways. But the PIAS functions are not well-understood due to complicated molecular mechanisms and multiple gene paralogs with overlapping roles, which is especially true in lower vertebrates where dedicated studies are scarce. As a basal chordate with a single PIAS gene, amphioxus is a convenient model to study PIAS from the evolutionary perspective. TRAF6 is a critical adaptor of the NF-κB pathways but it is not known whether TRAF6 is regulated by PIAS. Here we discover that in mammalian cells, amphioxus PIAS inhibited NF-κB activation by co-localizing and binding with TRAF6. The interaction relied on the N-terminal SAP and PINIT domains of PIAS. TRAF6 is an E3 ubiquitin ligase, which initiates downstream NF-κB signaling by promoting its self-ubiquitination. Both amphioxus SUMO1 and Ubc9 (SUMO E2 ligase) could suppress TRAF6 self-ubiquitination and NF-κB activation, suggesting that the SUMOylation activity competed away the ubiquitination activity of TRAF6. However, we show that the wild-type PIAS and the mutant PIAS without SUMO E3 ligase activity both could inhibit TRAF6-mediated NF-κB activation by reducing TRAF6 self-ubiquitination. This implies that SUMO ligase activity is not the only mechanism for PIAS to negatively regulate TRAF6. Finally, we tested the interactions between human PIAS1-4 and TRAF6. It reveals that human PIAS1, 3 and 4, but not 2, were able to repress NF-κB activation by reducing TRAF6 self-ubiquitination. Taken together, our study discovers a conserved regulatory interaction between chordate PIAS and TRAF6. It therefore sheds light on the complicated role of PIAS in immune regulation, and may help to understand the PIAS functions in other lower chordate taxa, such as jawless and jawed fishes.

STAT3 and STAT5 Activation in Solid Cancers

The Signal Transducer and Activator of Transcription (STAT)3 and 5 proteins are activated by many cytokine receptors to regulate specific gene expression and mitochondrial functions. Their role in cancer is largely context-dependent as they can both act as oncogenes and tumor suppressors. We review here the role of STAT3/5 activation in solid cancers and summarize their association with survival in cancer patients. The molecular mechanisms that underpin the oncogenic activity of STAT3/5 signaling include the regulation of genes that control cell cycle and cell death. However, recent advances also highlight the critical role of STAT3/5 target genes mediating inflammation and stemness. In addition, STAT3 mitochondrial functions are required for transformation. On the other hand, several tumor suppressor pathways act on or are activated by STAT3/5 signaling, including tyrosine phosphatases, the sumo ligase Protein Inhibitor of Activated STAT3 (PIAS3), the E3 ubiquitin ligase TATA Element Modulatory Factor/Androgen Receptor-Coactivator of 160 kDa (TMF/ARA160), the miRNAs miR-124 and miR-1181, the Protein of alternative reading frame 19 (p19ARF)/p53 pathway and the Suppressor of Cytokine Signaling 1 and 3 (SOCS1/3) proteins. Cancer mutations and epigenetic alterations may alter the balance between pro-oncogenic and tumor suppressor activities associated with STAT3/5 signaling, explaining their context-dependent association with tumor progression both in human cancers and animal models.

Toll-like receptor mediated inflammation requires FASN-dependent MYD88 palmitoylation

Toll-like receptor (TLR)/myeloid differentiation primary response protein (MYD88) signaling aggravates sepsis by impairing neutrophil migration to infection sites. However, the role of intracellular fatty acids in TLR/MYD88 signaling is unclear. Here, inhibition of fatty acid synthase by C75 improved neutrophil chemotaxis and increased the survival of mice with sepsis in cecal ligation puncture and lipopolysaccharide-induced septic shock models. C75 specifically blocked TLR/MYD88 signaling in neutrophils. Treatment with GSK2194069 that targets a different domain of fatty acid synthase, did not block TLR signaling or MYD88 palmitoylation. De novo fatty acid synthesis and CD36-mediated exogenous fatty acid incorporation contributed to MYD88 palmitoylation. The binding of IRAK4 to the MYD88 intermediate domain and downstream signal activation required MYD88 palmitoylation at cysteine 113. MYD88 was palmitoylated by ZDHHC6, and ZDHHC6 knockdown decreased MYD88 palmitoylation and TLR/MYD88 activation upon lipopolysaccharide stimulus. Thus, intracellular saturated fatty acid-dependent palmitoylation of MYD88 by ZDHHC6 is a therapeutic target of sepsis.

NF-κB/Rel Transcription Factors in Pancreatic Cancer: Focusing on RelA, c-Rel, and RelB

Regulation of Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)/Rel transcription factors (TFs) is extremely cell-type-specific owing to their ability to act disparately in the context of cellular homeostasis driven by cellular fate and the microenvironment. This is also valid for tumor cells in which every single component shows heterogenic effects. Whereas many studies highlighted a per se oncogenic function for NF-κB/Rel TFs across cancers, recent advances in the field revealed their additional tumor-suppressive nature. Specifically, pancreatic ductal adenocarcinoma (PDAC), as one of the deadliest malignant diseases, shows aberrant canonical-noncanonical NF-κB signaling activity. Although decades of work suggest a prominent oncogenic activity of NF-κB signaling in PDAC, emerging evidence points to the opposite including anti-tumor effects. Considering the dual nature of NF-κB signaling and how it is closely linked to many other cancer related signaling pathways, it is essential to dissect the roles of individual Rel TFs in pancreatic carcinogenesis and tumor persistency and progression. Here, we discuss recent knowledge highlighting the role of Rel TFs RelA, RelB, and c-Rel in PDAC development and maintenance. Next to providing rationales for therapeutically harnessing Rel TF function in PDAC, we compile strategies currently in (pre-)clinical evaluation.

The Dynamics of Deformed Wing Virus Concentration and Host Defensive Gene Expression after Varroa Mite Parasitism in Honey Bees, Apis mellifera

The synergistic interactions between the ectoparasitic mite Varroa destructor and Deformed wing virus (DWV) lead to the reduction in lifespan of the European honey bee Apis mellifera and often have been implicated in colony losses worldwide. However, to date, the underlying processes and mechanisms that form the multipartite interaction between the bee, mite, and virus have not been fully explained. To gain a better understanding of honey bees’ defense response to Varroa mite infestation and DWV infection, the DWV titers and transcription profiles of genes originating from RNAi, immunity, wound response, and homeostatic signaling pathways were monitored over a period of eight days. With respect to DWV, we observed low viral titers at early timepoints that coincided with high levels of Toll pathway transcription factor Dorsal, and its downstream immune effector molecules Hymenoptaecin, Apidaecin, Abaecin, and Defensin 1. However, we observed a striking increase in viral titers beginning after two days that coincided with a decrease in Dorsal levels and its corresponding immune effector molecules, and the small ubiquitin-like modifier (SUMO) ligase repressor of Dorsal, PIAS3. We observed a similar expression pattern for genes expressing transcripts for the RNA interference (Dicer/Argonaute), wound/homeostatic (Janus Kinase), and tissue growth (Map kinase/Wnt) pathways. Our results demonstrate that on a whole, honey bees are able to mount an immediate, albeit, temporally limited, immune and homeostatic response to Varroa and DWV infections, after which downregulation of these pathways leaves the bee vulnerable to expansive viral replication. The critical insights into the defense response upon Varroa and DWV challenges generated in this study may serve as a solid base for future research on the development of effective and efficient disease management strategies in honey bees.

PIAS3-mediated feedback loops promote chronic colitis-associated malignant transformation

Rationale: Colitis-associated colorectal cancer (CAC) usually exhibits an accelerated disease progression, an increased resistance to therapeutic drugs and a higher mortality rate than sporadic colorectal cancer (CRC). PIAS3 is a member of the protein inhibitor of activated STAT (PIAS) family; however, little is known about the expression and biological functions of PIAS3 in CAC. The aim of our study was to investigate the biological mechanisms of PIAS3 in CAC. Methods: PIAS3 expression was examined in colon tissues of CAC/CRC patients and azoxymethane-dextran sulfate sodium (AOM-DSS)-induced mice. The role of PIAS3 was studied using a series of in vitro, in vivo and clinical approaches. Results: Downregulated PIAS3 expression, upregulated miR-18a expression and highly activated NF-κB and STAT3 were observed in colon tissues of CAC/CRC patients and AOM-DSS-induced mice. In vitro experiments revealed that PIAS3 significantly inhibited the activation of NF-κB and STAT3 and demonstrated that activated NF-κB and STAT3 transcriptionally regulated miR-18a level, and up-regulation of miR-18a expression led to defective PIAS3 expression. Moreover, PIAS3-mediated autoregulatory feedback loops (PIAS3/NF-κB/miR-18a and PIAS3/STAT3/miR-18a) were verified in vitro and were found to regulate cell proliferation. Additionally, modulation of the feedback loops via overexpression of PIAS3 or knockdown of miR-18a significantly inhibited cell proliferation in a mouse CRC xenograft model. Furthermore, upregulation of PIAS3 by intracolonic administration of PIAS3 lentivirus or anti-miR-18a lentivirus in AOM-DSS-induced mice led to dramatically reduced tumor sizes/numbers, whereas knockdown of PIAS3 in CAC mice significantly promoted tumor growth. Conclusion: Our data clearly show that PIAS3-mediated feedback loops control cell proliferation and function as robust driving forces for CAC progression. Targeting these highly activated feedback loops might offer promising therapeutic strategies for CAC.

Functional domains of SP110 that modulate its transcriptional regulatory function and cellular translocation

Background

SP110, an interferon-induced nuclear protein, belongs to the SP100/SP140 protein family. Very recently, we showed that SP110b, an SP110 isoform, controls host innate immunity to Mycobacterium tuberculosis infection by regulating nuclear factor-κB (NF-κB) activity. However, it remains unclear how the structure of SP110 relates to its cellular functions. In this study, we provide experimental data illustrating the protein domains that are responsible for its functions.

Methods

We examined the effects of SP110 isoforms and a series of deletion mutants of SP110 on transcriptional regulation by luciferase reporter assays. We also employed confocal microscopy to determine the cellular distributions of enhanced green fluorescent protein-tagged SP110 isoforms and SP110 mutants. In addition, we performed immunoprecipitation and Western blotting analyses to identify the regions of SP110 that are responsible for protein interactions.

Results

Using reporter assays, we first demonstrated that SP110 isoforms have different regulatory effects on NF-κB-mediated transcription, supporting the notion that SP110 isoforms may have distinct cellular functions. Analysis of deletion mutants of SP110 showed that the interaction of the N-terminal fragment (amino acids 1–276) of SP110 with p50, a subunit of NF-κB, in the cytoplasm plays a crucial role in the down-regulation of the p50-driven tumor necrosis factor-α (TNFα) promoter activity in the nucleus, while the middle and C-terminal regions of SP110 localize it to various cellular compartments. Surprisingly, a nucleolar localization signal (NoLS) that contains one monopartite nuclear localization signal (NLS) and one bipartite NLS was identified in the middle region of SP110. The identification of a cryptic NoLS in the SP110 suggests that although this protein forms nuclear speckles in the nucleoplasm, it may be directed into the nucleolus to carry out distinct functions under certain cellular conditions.

Conclusions

The findings from this study elucidating the multidomain structure of the SP110 not only identify functional domains of SP110 that are required for transcriptional regulation, cellular translocation, and protein interactions but also implicate that SP110 has additional functions through its unexpected activity in the nucleolus.

Electronic supplementary material

The online version of this article (10.1186/s12929-018-0434-4) contains supplementary material, which is available to authorized users.

The conserved ancient role of chordate PIAS as a multilevel repressor of the NF-κB pathway

In vertebrates, PIAS genes encode versatile cellular regulators, with functions extremely complex and redundant. Here we try to understand their functions from an evolutionary perspective. we evaluate the sequences, expression and molecular functions of amphioxus PIAS genes and compare them with their vertebrate counterparts. Phylogenetic analysis suggests a single PIAS gene in ancestral chordates, which has been duplicated into four families (PIAS1-4) in vertebrates by 2R-WGD but remained single in a basal chordate (amphioxus). Amphioxus PIAS encodes two variants with and without a Serine/Threonine-rich tail, which are retained in human PIAS1-3 but lost in PIAS4. We show that amphioxus PIAS binds C-terminus of NF-κB Rel and blocks the DNA binding activity. In humans, such function is retained in PIAS1, altered in PIAS4, and lost in PIAS2-3. Instead, PIAS3 has evolved new ability to inhibit Rel by binding RHD and promoting SUMOylation. We show that amphioxus PIAS also inhibits NF-κB by binding with upstream signalling adaptor TICAM-like and MyD88. Finally, we verify that human PIAS1, 3 and 4, but not 2, were capable of these newly-discovered functions. Our study offers insight into the sub- and neo-functionalization of PIAS genes and suggests a conserved ancient role for chordate PIAS in NF-κB signalling.

The Role of PIAS SUMO E3-Ligases in Cancer

SUMOylation modifies the interactome, localization, activity, and lifespan of its target proteins. This process regulates several cellular machineries, including transcription, DNA damage repair, cell-cycle progression, and apoptosis. Accordingly, SUMOylation is critical in maintaining cellular homeostasis, and its deregulation leads to the corruption of a plethora of cellular processes that contribute to disease states. Among the proteins involved in SUMOylation, the protein inhibitor of activated STAT (PIAS) E3-ligases were initially described as transcriptional coregulators. Recent findings also indicate that they have a role in regulating protein stability and signaling transduction pathways. PIAS proteins interact with up to 60 cellular partners affecting several cellular processes, most notably immune regulation and DNA repair, but also cellular proliferation and survival. Here, we summarize the current knowledge about their role in tumorigenesis and cancer-related processes. Cancer Res; 77(7); 1542-7. ©2017 AACR.

Altholactone Inhibits NF-κB and STAT3 Activation and Induces Reactive Oxygen Species-Mediated Apoptosis in Prostate Cancer DU145 Cells

Altholactone, a natural compound isolated from Goniothalamus spp., has demonstrated anti-inflammatory and anticancer activities, but its molecular mechanisms are still not fully defined. Nuclear factor kappa B (NF-κB) and signal transducer and activator of transcription 3 (STAT3) play pivotal roles in the cell survival of many human tumors. The objective of this study was to elucidate the mechanism of action of altholactone against prostate cancer DU145 cells and to evaluate whether its effects are mediated by inhibition of NF-κB and STAT3 activity. Altholactone inhibited proliferation of DU145 cells and induced cell cycle arrest in S phase and triggered apoptosis. Reporter assays revealed that altholactone repressed p65- and TNF-α-enhanced NF-κB transcriptional activity and also inhibited both constitutive and IL-6-induced transcriptional activity of STAT3. Consistent with this, altholactone down-regulated phosphorylation of STAT3 and moreover, decreased constitutively active mutant of STAT3 (STAT3C)-induced transcriptional activity. Altholactone treatment also results in down-regulation of STAT3 target genes such as survivin, and Bcl-2 followed by up regulation of pro-apoptotic Bax protein. However, pre-treatment with the antioxidant N-acetylcysteine (NAC) significantly inhibited the activation of Bax and prevented down-regulation of STAT3 target genes. Collectively, our findings suggest that altholactone induces DU145 cells death through inhibition of NF-κB and STAT3 activity.

Isoliquiritigenin attenuates MiR-21 expression via induction of PIAS3 in breast cancer cells

Activated STAT3 triggered miR-21 transcription via binding to its promoter. ISL induced PIAS3 expression, a specific inhibitor of activated STAT3, leading to inhibition of STAT3 signaling and subsequent miR-21 transcription in breast cancer cells.

Protein Inhibitor of Activated STAT3 Suppresses Oxidized LDL-induced Cell Responses during Atherosclerosis in Apolipoprotein E-deficient Mice

Atherosclerosis is a serious public health concern. Excessive inflammatory responses of vascular cells are considered a pivotal pathogenesis mechanism underlying atherosclerosis development. It is known that Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3) signalling plays an important role in atherosclerosis progression. Protein inhibitor of activated STAT3 (PIAS3) is the key negative regulator of JAK/STAT3 signalling. However, its effect on atherogenesis is unknown. Here, we observed that PIAS3 levels are reduced in atherosclerotic lesions and that PIAS3 expression decreases in conjunction with increases in interleukin-6 expression and atherosclerosis severity. Oxidized low-density lipoprotein (ox-LDL), an atherogenic stimulus, reduced PIAS3 expression, an effect that may be attributed to nitric oxide synthesis upregulation. In turn, PIAS3 overexpression effectively suppressed ox-LDL-induced inflammation, lipid accumulation and vascular smooth muscle cell proliferation. These results indicate that PIAS3 is a critical repressor of atherosclerosis progression. The findings of this study have contributed to our understanding on the pathogenesis of atherosclerosis and have provided us with a potential target through which we can inhibit atherosclerosis-related cellular responses.

Human amnion mesenchymal cells are pro-inflammatory when activated by the Toll-like receptor 2/6 ligand, macrophage-activating lipoprotein-2

INTRODUCTION

Infection accounts for over 40% of preterm premature rupture of the fetal membranes (PPROM), a major cause of preterm birth. Toll-like receptors (TLR) play key roles in pathogen surveillance but their expression and function in amnion mesenchymal cells (AMC) is unclear. The aims of this study were to determine the expression of all TLR isoforms and the effect of macrophage-activating lipoprotein-2 (MALP-2), derived from a common pathogen involved in PPROM, on human AMC.

METHODS

AMC were isolated from normal, term amnion from repeat cesarean section. Semi-quantitative RT-PCR, immunocytochemistry, immunohistochemistry and western blotting were used to detect TLR isoform expression. Immunocytochemistry of NF-κB p65, pro-inflammatory cytokine secretion (ELISA), MTT assay, LDH assay, immunoblotting of cytosolic cytochrome c and cleaved caspase-3, and expression of 84 microRNAs by Qiagen miRNA PCR array were used to determine the functional effect of MALP-2 on AMC.

RESULTS

TLR1-10 was detected in AMC, and protein expression of TLR2, 4, and 6 were confirmed. MALP-2 induced nuclear translocation of p65, reaching significance after 45 min (ANOVA, P < 0.05). MALP-2 did not cause apoptosis but did lead to significant secretion of IL-4, IL-6, and IL-8 (P < 0.05, 0.01, 0.001, respectively) and significant changes in miRNA-320a and miRNA-18a (P < 0.05).

DISCUSSION

These results suggest that AMC elicit a pro-inflammatory response following stimulation with the known TLR2/6 ligand MALP-2. This data supports the idea that AMC express the innate immune system receptors that could help with immune surveillance during infection and contribute to inflammatory responses that lead to PPROM.

Protein Inhibitor of Activated STAT3 (PIAS3) Is Down-Regulated in Eutopic Endometrium of Women with Endometriosis

Endometriosis is a major cause of chronic pelvic pain and infertility. Activation of STAT3 appears central to the inflammatory phenotype of eutopic endometrium in women with endometriosis. However, the molecular mechanism by which this occurs remains unknown. Our objective is to determine how STAT3 activity is regulated in endometriosis. Protein inhibitor of activated STAT3 (PIAS3) is a negative regulator of STAT3 activity. We examined the levels of PIAS3 in endometrium from women with and without endometriosis using Western blot analysis and immunohistochemistry. Levels of PIAS3 are significantly lower, in contrast with phosphorylation of STAT3, in women with endometriosis compared to women without endometriosis. Furthermore, induction of endometriosis in the baboon showed a significant reduction of PIAS3 expression during the progression of the disease. Interferon-γ (INFγ) reduces PIAS3 protein levels and increases phospho-STAT3 levels through CXCL10 in endometrial cells, Ishikawa, and 12Z cells. These results suggest that attenuation of PIAS3 causes aberrant activation of STAT3 in endometriosis, leading to inflammatory changes that may impair fertility or cause pain.

TRIF-dependent TLR signaling, its functions in host defense and inflammation, and its potential as a therapeutic target

Toll/IL-1R domain-containing adaptor-inducing IFN-β (TRIF)-dependent signaling is required for TLR-mediated production of type-I IFN and several other proinflammatory mediators. Various pathogens target the signaling molecules and transcriptional regulators acting in the TRIF pathway, thus demonstrating the importance of this pathway in host defense. Indeed, the TRIF pathway contributes to control of both viral and bacterial pathogens through promotion of inflammatory mediators and activation of antimicrobial responses. TRIF signaling also has both protective and pathologic roles in several chronic inflammatory disease conditions, as well as an essential function in wound-repair processes. Here, we review our current understanding of the regulatory mechanisms that control TRIF-dependent TLR signaling, the role of the TRIF pathway in different infectious and noninfectious pathologic states, and the potential for manipulating TRIF-dependent TLR signaling for therapeutic benefit.

PDLIM1 inhibits NF-κB-mediated inflammatory signaling by sequestering the p65 subunit of NF-κB in the cytoplasm

Understanding the regulatory mechanisms for the NF-κB transcription factor is key to control inflammation. IκBα maintains NF-κB in an inactive form in the cytoplasm of unstimulated cells, whereas nuclear NF-κB in activated cells is degraded by PDLIM2, a nuclear ubiquitin E3 ligase that belongs to a LIM protein family. How NF-κB activation is negatively controlled, however, is not completely understood. Here we show that PDLIM1, another member of LIM proteins, negatively regulates NF-κB-mediated signaling in the cytoplasm. PDLIM1 sequestered p65 subunit of NF-κB in the cytoplasm and suppressed its nuclear translocation in an IκBα-independent, but α-actinin-4-dependent manner. Consistently, PDLIM1 deficiency lead to increased levels of nuclear p65 protein, and thus enhanced proinflammatory cytokine production in response to innate stimuli. These studies reveal an essential role of PDLIM1 in suppressing NF-κB activation and suggest that LIM proteins comprise a new family of negative regulators of NF-κB signaling through different mechanisms.

Multifunctional roles of leader protein of foot-and-mouth disease viruses in suppressing host antiviral responses

Foot-and-mouth disease virus (FMDV) leader protein (L^pro) is a papain-like proteinase, which plays an important role in FMDV pathogenesis. L^pro exists as two forms, Lab and Lb, due to translation being initiated from two different start codons separated by 84 nucleotides. L^pro self-cleaves from the nascent viral polyprotein precursor as the first mature viral protein. In addition to its role as a viral proteinase, L^pro also has the ability to antagonize host antiviral effects. To promote FMDV replication, L^pro can suppress host antiviral responses by three different mechanisms: (1) cleavage of eukaryotic translation initiation factor 4 γ (eIF4G) to shut off host protein synthesis; (2) inhibition of host innate immune responses through restriction of interferon-α/β production; and (3) L^pro can also act as a deubiquitinase and catalyze deubiquitination of innate immune signaling molecules. In the light of recent functional and biochemical findings regarding L^pro, this review introduces the basic properties of L^pro and the mechanisms by which it antagonizes host antiviral responses.

Transcriptional activity of erythroid Kruppel-like factor (EKLF/KLF1) modulated by PIAS3 (protein inhibitor of activated STAT3)

Erythroid Kruppel-like factor (EKLF or KLF1) is a transcription factor crucial for red cell development that is directly involved in regulation of a large number of erythroid genes. EKLF serves mostly as an activator of expression of these genes; however, it can act also as a repressor. Here, we present evidence that EKLF interacts with proteins from the PIAS (protein inhibitor of activated STAT) family that convey repressive activity to EKLF in the absence of sumoylation. Our studies identify PIAS3 as a transcriptional corepressor of EKLF for at least a subset of its target genes during erythropoiesis (e.g. β-globin, α-hemoglobin stabilizing protein). We demonstrate an interaction between EKLF and PIAS proteins confirmed by in vivo coimmunoprecipitation assays with both exogenous and endogenous proteins. We identified an LXXLL signature motif located near the N terminus of PIAS proteins that, although not involved in the EKLF-PIAS3 interaction, is required for the transrepression activity. Knockdown of endogenous PIAS3 accelerates differentiation of both murine erythroleukemia cells, as well as fetal liver cells, whereas an increase in PIAS3 levels inhibits this increase. Using chromatin immunoprecipitation assays, we show that PIAS3 preferentially occupies the β-globin promoter in undifferentiated murine erythroleukemia cells. Together these results demonstrate that an interaction between EKLF and PIAS3 provides a novel mode of regulation of EKLF activity in the absence of sumolylation and furthermore shows an important involvement of PIAS proteins in erythropoiesis.

A novel microRNA regulates osteoclast differentiation via targeting protein inhibitor of activated STAT3 (PIAS3)

MicroRNAs (miRNAs) involve in the regulation of a wide range of physiological processes. Recent studies suggested that miRNAs might play a role in osteoclast differentiation. Here, we identify a new miRNA (miR-9718) in primary mouse osteoclasts that promotes osteoclast differentiation by repressing protein inhibitor of activated STAT3 (PIAS3) at the post-transcriptional level. MiR-9718 was found to be transcribed during osteoclastogenesis, which was induced by macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor-κB ligand (RANKL). Overexpression of miR-9718 in RAW 264.7 cells promoted M-CSF and RANKL-induced osteoclastogenesis, whereas inhibition of miR-9718 attenuated it. PIAS3 was predicted to be a target of miR-9718. Luciferase reporter gene validated the prediction. Transfection of pre-miR-9718 in RAW 264.7 cells induced by both M-CSF and RANKL inhibited expression of PIAS3 protein, while the mRNA levels of PIAS3 were not attenuated. In vivo, our study showed that silencing of miR-9718 using a specific antagomir inhibited bone resorption and increased bone mass in mice receiving ovariectomy (OVX) and in sham-operated control mice. Thus, our study showed that miR-9718 played an important role in osteoclast differentiation via targeting PIAS3 both in vitro and in vivo.

HIV-1 gp120 activates the STAT3/interleukin-6 axis in primary human monocyte-derived dendritic cells

Dendritic cells (DCs) are fundamental for the initiation of immune responses and are important players in AIDS immunopathogenesis. The modulation of DC functional activities represents a strategic mechanism for HIV-1 to evade immune surveillance. Impairment of DC function may result from bystander effects of HIV-1 envelope proteins independently of direct HIV-1 infection. In this study, we report that exposure of immature monocyte-derived DCs (MDDCs) to HIV-1 R5 gp120 resulted in the CCR5-dependent production of interleukin-6 (IL-6) via mitogen-activated protein kinase (MAPK)/NF-κB pathways. IL-6 in turn activated STAT3 by an autocrine loop. Concomitantly, gp120 promoted an early activation of STAT3 that further contributed to IL-6 induction. This activation paralleled a concomitant upregulation of the STAT3 inhibitor PIAS3. Notably, STAT3/IL-6 pathway activation was not affected by the CCR5-specific ligand CCL4. These results identify STAT3 as a key signaling intermediate activated by gp120 in MDDCs and highlight the existence of a virus-induced dysregulation of the IL-6/STAT3 axis. HIV-1 gp120 signaling through STAT3 may provide an explanation for the impairment of DC function observed upon HIV exposure.

IMPORTANCE

This study provides new evidence for the molecular mechanisms and signaling pathways triggered by HIV-1 gp120 in human DCs in the absence of productive infection, emphasizing a role of aberrant signaling in early virus-host interaction, contributing to viral pathogenesis. We identified STAT3 as a key component in the gp120-mediated signaling cascade involving MAPK and NF-κB components and ultimately leading to IL-6 secretion. STAT3 now is recognized as a key regulator of DC functions. Thus, the identification of this transcription factor as a signaling molecule mediating some of gp120's biological effects unveils a new mechanism by which HIV-1 may deregulate DC functions and contribute to AIDS pathogenesis.

Mitochondrial STAT3 plays a major role in IgE-antigen-mediated mast cell exocytosis

BACKGROUND

The involvement of mitochondrial oxidative phosphorylation (OXPHOS) in mast cell exocytosis was recently suggested by the finding that mitochondria translocate to exocytosis sites upon mast cell activation. In parallel, mitochondrial signal transducer and activator of transcription 3 (STAT3) was found to be involved in ATP production. However, the regulation of mitochondrial STAT3 function and its connection to mast cell exocytosis is unknown.

OBJECTIVE

We sought to explore the role played by mitochondrial STAT3 in mast cell exocytosis.

METHODS

Experiments were performed in vitro with human and mouse mast cells and rat basophilic leukemia (RBL) cells and in vivo in mice. OXPHOS activity was measured after immunologic activation. The expression of STAT3, extracellular signal-regulated kinase 1/2, and protein inhibitor of activated STAT3 in the mitochondria during mast cell activation was determined, as was the effect of STAT3 inhibition on OXPHOS activity and mast cell function.

RESULTS

Here we show that mitochondrial STAT3 is essential for immunologically mediated degranulation of human and mouse mast cells and RBL cells. Additionally, in IgE-antigen-activated RBL cells, mitochondrial STAT3 was phosphorylated on serine 727 in an extracellular signal-regulated kinase 1/2-dependent manner, which was followed by induction of OXPHOS activity. Furthermore, the endogenous inhibitor of STAT3, protein inhibitor of activated STAT3, was found to inhibit OXPHOS activity in the mitochondria, resulting in inhibition of mast cell degranulation. Moreover, mice injected with Stattic, a STAT3 inhibitor, had a significant decrease in histamine secretion.

CONCLUSION

These results provide the first evidence of a regulatory role for mitochondrial STAT3 in mast cell functions, and therefore mitochondrial STAT3 could serve as a new target for the manipulation of allergic diseases.

Neuronal activity-dependent STAT3 localization to nucleus is dependent on Tyr-705 and Ser-727 phosphorylation in rat hippocampal neurons

Signal transducer and activator of transcription 3 (STAT3) dramatically increases during the first post-natal week, and supports the survival of mature hippocampal neurons. Recently, we reported that chronic elevation of excitability leads to a loss of STAT3 signal, inducing vulnerability in neurons. The loss of STAT3 signal was due to impaired Erk1/2 activation. While overnight elevation of activity attenuated STAT3 signal, brief low-frequency stimuli, which induce long-term depression, have been shown to activate STAT3. Here we investigated how STAT3 responds to depolarization in mature neurons. A brief depolarization results in the transient activation of STAT3: it induces calcium influx through L-type voltage-gated calcium channels, which triggers activation of Src family kinases. Src family kinases are required for phosphorylation of STAT3 at Tyr-705 and Ser-727. PTyr-705 is Janus kinase (JAK)-dependent, while PSer-727 is dependent on Akt, the Ser/Thr kinase. Both PTyr-705 and PSer-727 are necessary for nuclear translocation of STAT3 in these neurons. Chronic elevation of spontaneous activity by an A-type potassium blocker, 4-aminopyridine (4-AP), also induced the transient phosphorylation of STAT3, which after 4 h fell to basal levels despite the presence of 4-AP. These results suggest that phasic and chronic neuronal activation induce distinct molecular pathways, resulting in opposing regulation of STAT3 signal.

PIAS3 may represent a potential biomarker for diagnosis and therapeutic of human colorectal cancer

Colorectal cancer (CRC) is a challenging problem both for the developed and underdeveloped countries. Despite numerous improvements in early diagnosis and treatment, the incidence and mortality is still keeping in a high level. Molecule targeted therapy has drawn much attention as next generation anticancer agents for diagnosis and therapeutic of CRC. Protein Inhibitor of Activated Signal Transducer and Activators of Transcription 3 (PIAS3) as a novel biomarker has been focused to have a role in the development of malignancy, which was expressed at a higher level in most common malignancies compared with corresponding normal tissues. Furthermore, evidences suggest that the expression of PIAS3 can affect the growth of cancer cells by inhibiting the JAK/STAT and PI3-K/Akt signaling pathways or regulating its SUMO (small-ubiquitin like modifiers) ligase activity in some malignancy. Therefore, we hypothesized that PIAS3 may be a potential biomarker target for early cancer detection and therapeutic of human CRC.

SUMO and Parkinson's disease

Parkinson's disease (PD) is one of the most common degenerative disorders of the central nervous system that produces motor and non-motor symptoms. The majority of cases are idiopathic and characterized by the presence of Lewy bodies containing fibrillar α-synuclein. Small ubiquitin-related modifier (SUMO) immunoreactivity was observed among others in cases with PD. Key disease-associated proteins are SUMO-modified, linking this posttranslational modification to neurodegeneration. SUMOylation and SUMO-mediated mechanisms have been intensively studied in recent years, revealing nuclear and extranuclear functions for SUMO in a variety of cellular processes, including the regulation of transcriptional activity, modulation of signal transduction pathways, and response to cellular stress. This points to a role for SUMO more than just an antagonist to ubiquitin and proteasomal degradation. The identification of risk and age-at-onset gene loci was a breakthrough in PD and promoted the understanding of molecular mechanisms in the pathology. PD has been increasingly linked with mitochondrial dysfunction and impaired mitochondrial quality control. Interestingly, SUMO is involved in many of these processes and up-regulated in response to cellular stress, further emphasizing the importance of SUMOylation in physiology and disease.

Phosphorylation of protein inhibitor of activated STAT1 (PIAS1) by MAPK-activated protein kinase-2 inhibits endothelial inflammation via increasing both PIAS1 transrepression and SUMO E3 ligase activity

OBJECTIVE

Protein inhibitor of activated signal transducer and activator of transcription-1 (PIAS1) is known to function as small ubiquitin-like modifier (SUMO) E3 ligase as well as transrepressor. The aim of the study is to elucidate the regulatory mechanisms for these 2 different functions, especially with respect to endothelial inflammation.

METHODS AND RESULTS

The mitogen-activated protein kinase (MAPK)-activated protein kinase-2 is a proinflammatory kinase and phosphorylates PIAS1 at the Ser522 residue. Activation of MAPK-activated protein kinase-2 enhances p53-SUMOylation, but a PIAS1 phosphorylation mutant, PIAS1-S522A, abolished this p53-SUMOylation, suggesting a critical role for PIAS1-S522 phosphorylation in its SUMO ligase activity. Because nuclear p53 can inhibit Kruppel-like factor 2 promoter activity, we investigated the roles for PIAS1 phosphorylation and p53-SUMOylation in the Kruppel-like factor 2 and endothelial NO synthase expression. Both MAPK-activated protein kinase-2 and PIAS1 overexpression increased Kruppel-like factor 2 promoter activity and endothelial NO synthase expression, which were inhibited by expressing a p53-SUMOylation defective mutant, p53-K386R, and PIAS1-S522A. PIAS1-S522A also abolished the anti-inflammatory effect of wild-type PIAS1 in vitro and also in vivo, which was examined by leukocyte rolling in microvessels of skin grafts transduced by adenovirus encoding PIAS1-WT or - S522A mutant.

CONCLUSIONS

Our study has identified a novel negative feedback regulatory pathway through which MAPK-activated protein kinase-2 limits endothelial inflammation via the PIAS1 S522 phosphorylation-mediated increase in PIAS1 transrepression and SUMO ligase activity.

Essential role of cooperative NF-κB and Stat3 recruitment to ICAM-1 intronic consensus elements in the regulation of radiation-induced invasion and migration in glioma

Although radiotherapy improves survival in patients, glioblastoma multiformes (GBMs) tend to relapse with augmented tumor migration and invasion even after ionizing radiation (IR). Aberrant nuclear factor-κB (NF-κB) and signal transducer and activator of transcription factor 3 (Stat3) activation and interaction have been suggested in several human tumors. However, possible NF-κB/Stat3 interaction and the role of Stat3 in maintenance of NF-κB nuclear retention in GBM still remain unknown. Stat3 and NF-κB (p65) physically interact with one another in the nucleus in glioma tumors. Most importantly, glutathione S-transferase pull-down assays identified that Stat3 binds to the p65 transactivation domain and is present in the NF-κB DNA-binding complex. Irradiation significantly elevated nuclear phospho-p65/phospho-Stat3 interaction in correlation with increased intercellular adhesion molecule-1 (ICAM-1) and soluble-ICAM-1 levels, migration and invasion in human glioma xenograft cell lines 4910 and 5310. Chromatin immunopreicipitation and promoter luciferase activity assays confirmed the critical role of adjacent NF-κB (+399) and Stat3 (+479) binding motifs in the proximal intron-1 in elevating IR-induced ICAM-1 expression. Specific inhibition of Stat3 or NF-κB with Stat3.siRNA or JSH-23 severely inhibited IR-induced p65 recruitment onto ICAM-1 intron-1 and suppressed migratory properties in both the cell lines. On the other hand, Stat3C- or IR-induced Stat3 promoter recruitment was significantly decreased in p65-knockdown cells, thereby suggesting the reciprocal regulation between p65 and Stat3. We also observed a significant increase in NF-κB enrichment on ICAM-1 intron-1 and ICAM-1 transactivation in Stat3C overexpressing cells. In in vivo orthotopic experiments, suppression of tumor growth in Stat3.si+IR-treated mice was associated with the inhibition of IR-induced p-p65/p-Stat3 nuclear colocalization and ICAM-1 levels. To our knowledge, this is the first study showing the crucial role of NF-κB/Stat3 nuclear association in IR-induced ICAM-1 regulation and implies that targeting NF-κB/Stat3 interaction may have future therapeutic significance in glioma treatment.

Nucleo-cytoplasmic trafficking of TRIM8, a novel oncogene, is involved in positive regulation of TNF induced NF-κB pathway

TNF induced nuclear factor kappa B (NF-κB) is one of the central signaling pathways that plays a critical role in carcinogenesis and inflammatory diseases. Post-translational modification through ubiquitin plays important role in the regulation of this pathway. In the current study, we investigated the role of TRIM8, member of RING family ubiquitin ligase in regulation of NF-κB pathway. We observed that TRIM8 positively regulates TNF induced NF-κB pathway. Different domains of TRIM8 showed discrete functions at the different steps in regulation of TNF induced NF-κB pathway. Ubiquitin ligase activity of TRIM8 is essential for regulation of NF-κB activation in both cytoplasm as well as nucleus. TRIM8 negates PIAS3 mediated negative repression of NF-κB at p65 by inducing translocation of PIAS3 from nucleus to cytoplasm as well as its turnover. TNF induces translocation of TRIM8 from nucleus to cytoplasm, which positively regulates NF-κB. The cytoplasmic translocation of TRIM8 is essential for TNF induced NF-κB but not for p65 mediated NF-κB regulation. TRIM8 also enhanced the clonogenic and migration ability of cells by modulating NF-κB. The further study will help to understand the role of TRIM8 in inflammation and cancer.

SUMOylation of hnRNP-K is required for p53-mediated cell-cycle arrest in response to DNA damage

Heterogeneous ribonucleoprotein-K (hnRNP-K) is normally ubiquitinated by HDM2 for proteasome-mediated degradation. Under DNA-damage conditions, hnRNP-K is transiently stabilized and serves as a transcriptional co-activator of p53 for cell-cycle arrest. However, how the stability and function of hnRNP-K is regulated remained unknown. Here, we demonstrated that UV-induced SUMOylation of hnRNP-K prevents its ubiquitination for stabilization. Using SUMOylation-defective mutant and purified SUMOylated hnRNP-K, SUMOylation was shown to reduce hnRNP-K's affinity to HDM2 with an increase in that to p53 for p21-mediated cell-cycle arrest. PIAS3 served as a small ubiquitin-related modifier (SUMO) E3 ligase for hnRNP-K in an ATR-dependent manner. During later periods after UV exposure, however, SENP2 removed SUMO from hnRNP-K for its destabilization and in turn for release from cell-cycle arrest. Consistent with the rise-and-fall of both SUMOylation and stability of hnRNP-K, its ability to interact with PIAS3 was inversely correlated to that with SENP2 during the time course after UV exposure. These findings indicate that SUMO modification plays a crucial role in the control of hnRNP-K's function as a p53 co-activator in response to DNA damage by UV.

NF-κB repression by PIAS3 mediated RelA SUMOylation

Negative regulation of the NF-κB transcription factor is essential for tissue homeostasis in response to stress and inflammation. NF-κB activity is regulated by a variety of biochemical mechanisms including phosphorylation, acetylation, and ubiquitination. In this study, we provide the first experimental evidence that NF-κB is regulated by SUMOylation, where the RelA subunit of NF-κB is SUMOylated by PIAS3, a member of the PIAS (protein inhibitor of activated STAT) protein family with E3 SUMO ligase activity. PIAS3-mediated NF-κB repression was compromised by either RelA mutant resistant to SUMOylation or PIAS3 mutant defective in SUMOylation. PIAS3-mediated SUMOylation of endogenous RelA was induced by NF-κB activation thus forming a negative regulatory loop. The SUMOylation of endogenous RelA was enhanced in IκBα null as compared with wild type fibroblasts. The RelA SUMOylation was induced by TNFα but not leptomycin B mediated RelA nuclear translocation. Furthermore, RelA mutants defective in DNA binding were not SUMOylated by PIAS3, suggesting that RelA DNA binding is a signal for PIAS3-mediated SUMOylation. These results support a novel negative feedback mechanism for NF-κB regulation by PIAS3-mediated RelA SUMOylation.

Identification of novel miR-21 target proteins in multiple myeloma cells by quantitative proteomics

Substantial evidence indicates that microRNA-21 (miR-21) is a key oncomiR in carcinogenesis and is significantly elevated in multiple myeloma (MM). In this study, we explored the role of miR-21 in human MM cells and searched for miR-21 targets. By knocking down the expression of endogenous miR-21 in U266 myeloma cells, we observed reduced growth, an arrested cell cycle, and increased apoptosis. To further understand its molecular mechanism in the pathogenesis of MM, we employed a SILAC (stable isotope labeling by amino acids in cell culture)-based quantitative proteomic strategy to systematically identify potential targets of miR-21. In total, we found that the expression of 178 proteins was up-regulated significantly by miR-21 inhibition, implying that they could be potential targets of miR-21. Among these, the protein inhibitor of activated STAT3 (PIAS3) was confirmed as a direct miR-21 target by Western blotting and reporter gene assays. We further demonstrated that miR-21 enhances the STAT3-dependent signal pathway by inhibiting the function of PIAS3 and that down-regulation of PIAS3 contributes to the oncogenic function of miR-21. This elucidation of the role of PIAS3 in the miR-21-STAT3 positive regulatory loop not only may shed light on the molecular basis of the biological effects of miR-21 observed in MM cells but also has direct implications for the development of novel anti-MM therapeutic strategies.

Towards a quantitative understanding of the MITF-PIAS3-STAT3 connection

Background

Expression of the two transcription factors microphthalmia-associated transcription factor (MITF) and signal transducer and activator of transcription 3 (STAT3) are tightly connected to cell proliferation and survival, and are important for melanocyte development. The co-regulation of MITF and STAT3 via their binding to a common inhibitor Protein Inhibitor of Activated STAT3 (PIAS3) is intriguing. A better quantitative understanding of this regulation is likely to be important for elucidation of the melanocyte biology.

Results

We present a mathematical model describing the MITF-PIAS3-STAT3 signalling network. A default parameter set was developed, partly informed by the literature and partly by constraining the model to mimic reported behavioural features of the system. In addition, a set of experiment-specific parameters was derived for each of 28 experiments reported in the literature. The model seems capable of accounting for most of these experiments in terms of observed temporal development of protein amounts and phosphorylation states. Further, the results also suggest that this system possesses some regulatory features yet to be elucidated.

Conclusions

We find that the experimentally observed crosstalk between MITF and STAT3 via PIAS3 in melanocytes is faithfully reproduced in our model, offering mechanistic explanations for this behaviour, as well as providing a scaffold for further studies of MITF signalling in melanoma.

The PINIT domain of PIAS3: structure-function analysis of its interaction with STAT3

The protein inhibitor of activated signal transducer and activator of transcription 3 (PIAS3) regulates the transcriptional activity of signal transducer and activator of transcription 3 (STAT3) which regulates transcription of genes involved in cell growth, proliferation and apoptosis. The conserved proline, isoleucine, asparagine, isoleucine, threonine (PINIT) domain of PIAS3 is thought to promote STAT3-PIAS3 interaction. The (His)(7) -PINIT domain (PIAS3(85-272) ) was heterologously expressed and purified to homogeneity by nickel affinity and size exclusion chromatography, and shown to be a folded monomer in solution. Using surface plasmon resonance spectroscopy (SPR) the PINIT domain (PIAS3(85-272) ) alone was shown to specifically bind to STAT3 in a concentration dependent manner. L97A, R99N and R99Q mutations of the PINIT domain were found to abrogate binding to STAT3, suggesting that these residues were part of a potential binding surface. An homology model for the PINIT domain was calculated to analyse the potential locations of L97 and R99 in the structure, and to evaluate the potential role of these residues in interactions with STAT3.