PAD4 controls tumor immunity via restraining the MHC class II machinery in macrophages

Tumor-associated macrophages (TAMs) shape tumor immunity and therapeutic efficacy. However, it is poorly understood whether and how post-translational modifications (PTMs) intrinsically affect the phenotype and function of TAMs. Here, we reveal that peptidylarginine deiminase 4 (PAD4) exhibits the highest expression among common PTM enzymes in TAMs and negatively correlates with the clinical response to immune checkpoint blockade. Genetic and pharmacological inhibition of PAD4 in macrophages prevents tumor progression in tumor-bearing mouse models, accompanied by an increase in macrophage major histocompatibility complex (MHC) class II expression and T cell effector function. Mechanistically, PAD4 citrullinates STAT1 at arginine 121, thereby promoting the interaction between STAT1 and protein inhibitor of activated STAT1 (PIAS1), and the loss of PAD4 abolishes this interaction, ablating the inhibitory role of PIAS1 in the expression of MHC class II machinery in macrophages and enhancing T cell activation. Thus, the PAD4-STAT1-PIAS1 axis is an immune restriction mechanism in macrophages and may serve as a cancer immunotherapy target.

Integrative analysis revealed a correlation of PIAS family genes expression with prognosis, immunomodulation and chemotherapy

BACKGROUND

Protein inhibitor of activated STATs (PIAS) has pleiotropic biological effects, such as protein post-translational modification, transcriptional coregulation and gene editing. It is reported that PIAS family genes are also correlated with immune cells infiltration in cancers that highlights their unnoticed biological role in tumor progression. However, the relationship of their expression with prognosis, immune cell infiltration, tumor microenvironment, and immunotherapy in pan-cancer has been rarely reported.

METHODS

The multi-omics data were used to investigate the expression level of PIAS family members in pan-cancer, and the prognostic value of their expression in different tumors was analyzed by univariate Cox regression and Kaplan-Meier. Correlation analysis was used to investigate the relationship of PIAS gene expression with tumor microenvironment, immune infiltrating subtypes, stemness score and drug sensitivity. In addition, we also used wound healing and transwell assays to verify the biological effects of PIAS family gene expression on invasion and metastasis of HCC cells.

RESULTS

We found that PIAS family genes expression is significantly heterogeneous in tumors by multi-genomic analysis, and associated with poor prognosis in patients with multiple types of cancer. Furthermore, we also found that genetic alterations of PIAS family genes were not only common in different types of human tumors, but were also significantly associated with disease-free survival (DFS) across pan-cancer. Single-cell analysis revealed that PIAS family genes were mainly distributed in monocytes/macrophages. Additionally, we also found that their expression was associated with tumor microenvironment (including stromal cells and immune cells) and stemness score (DNAss and RNAss). Drug sensitivity analysis showed that PIAS family genes were able to predict the response to chemotherapy and immunotherapy. PIAS family genes expression is closely related to tumor metastasis, especially PIAS3. High PIAS3 expression significantly promotes the migration and invasion of liver cancer cell lines (HCC-LM3 and MHCC97-H).

CONCLUSIONS

Taking together, these findings contribute to determine whether the PIAS family genes are a potential oncogenic target gene, which have important contribution for the development of cancer immunotherapy.

PIAS family in cancer: from basic mechanisms to clinical applications

Protein inhibitors of activated STATs (PIAS) are proteins for cytokine signaling that activate activator-mediated gene transcription. These proteins, as versatile cellular regulators, have been described as regulators of approximately 60 proteins. Dysregulation of PIAS is associated with inappropriate gene expression that promotes oncogenic signaling in multiple cancers. Multiple lines of evidence have revealed that PIAS family members show modulated expressions in cancer cells. Most frequently reported PIAS family members in cancer development are PIAS1 and PIAS3. SUMOylation as post-translational modifier regulates several cellular machineries. PIAS proteins as SUMO E3 ligase factor promotes SUMOylation of transcription factors tangled cancer cells for survival, proliferation, and differentiation. Attenuated PIAS-mediated SUMOylation mechanism is involved in tumorigenesis. This review article provides the PIAS/SUMO role in the modulation of transcriptional factor control, provides brief update on their antagonistic function in different cancer types with particular focus on PIAS proteins as a bonafide therapeutic target to inhibit STAT pathway in cancers, and summarizes natural activators that may have the ability to cure cancer.

Gene expression analysis of SOCS, STAT and PIAS genes in lung cancer patients

One of the most devastating diseases with the highest prevalence and mortality rate worldwide is lung cancer. Non-small cell lung cancer (NSCLC) is the subtype of lung cancer in 85% of cases. In this work, the expression levels of the STAT, SOCS and PIAS family genes involved in angiogenesis, proliferation and differentiation were examined. Using QRT-PCR technique, the expression level of STAT3 gene was assessed and tumor tissue samples had higher expression than normal tissue. In addition, the histological grade of adenocarcinoma was associated with the increase in STAT3 gene expression. The expression of the SOCS1 and SOCS2 genes in tumors was measured to be 0.58-fold and 0.36-fold lower than in healthy samples adjacent to the tumor, but this reduction in expression was not significant. In addition, when examining the relationship between the expression of SOCS1 and 2 and the clinical features of tumor samples, there was a significant decrease in the expression of the SOCS1 and 2 genes in the adenocarcinoma subtype. Compared to neighboring tumor samples, the expression of PIAS1 in the tumors was not different with controls. Our research revealed that tissue samples from adenocarcinoma had higher levels of STAT3 expression. Taken together, the mentioned genes can be suggested as possible targets for further studies in NSCLC.

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.

A protein inhibitor of activated STAT (CgPIAS) negatively regulates the expression of ISGs by inhibiting STAT activation in oyster Crassostrea gigas

The protein inhibitor of activated STAT (PIAS) family proteins act as the important negative regulators in janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway, which can be also involved in regulating the expression of interferon-stimulated genes (ISGs). In the present study, a PIAS homologue (designated as CgPIAS) was identified from oyster Crassostrea gigas. The open reading frame (ORF) of CgPIAS cDNA was of 1887 bp encoding a peptide of 628 amino acid residues. The CgPIAS protein contains a conserved scaffold attachment factor A/B/acinus/PIAS (SAP) domain, a Pro-Ile-Asn-Ile-Thr (PINIT) motif, a RING-finger-like zinc-binding domain (RLD) and two SUMO-interaction Motifs (SIMs). The deduced amino acid sequence of CgPIAS shared 74.58-81.36% similarity with other PIAS family members in the RLD domain. The mRNA transcripts of CgPIAS were detected in all the tested tissues with highest level in haemocytes (32.98-fold of mantles, p < 0.001). After poly (I:C) and recombinant Interferon-like protein (rCgIFNLP) stimulation, the mRNA expression of CgPIAS in haemocytes significantly up-regulated to the highest level at 48 h (7.38-fold, p < 0.001) and at 24 h (13.08-fold, p < 0.01), respectively. Moreover, the nuclear translocation of CgPIAS was observed in haemocytes after poly (I:C) stimulation. Biolayer Interferometry (BLI) assay revealed that the recombinant protein CgPIAS-RLD could interact with the recombinant protein CgSTAT in vitro with the K_D value of 3.88 × 10^-8 M. In the CgPIAS-RNAi oysters, the green signals of CgSTAT protein in nucleus of haemocytes increased compared with that in NC-RNAi group, and the mRNA expression of myxovirus resistance (CgMx1), oligoadenylate synthase-like proteins (CgOASL), CgViperin and IFN-induced protein 44-like (CgIFI44L-1) in haemocytes significantly increased at 12 h after poly (I:C) stimulation, which were 2.39-fold (p < 0.05), 2.18-fold (p < 0.001), 1.74-fold (p < 0.05), and 2.89-fold (p < 0.01) of that in control group, respectively. The above results indicated that CgPIAS negatively regulated the ISG expression by inhibiting STAT activation in oyster C. gigas.

Regulation of Serotonin 1A Receptor SUMOylation by SENP2 and PIASxα

Serotonin 1A receptors (5-HT1ARs) are implicated in the control of mood, cognition, and memory and in various neuropsychiatric disorders such as depression and anxiety. As such, understanding the regulation of 5-HT1ARs will inform the development of better treatment approaches. We previously demonstrated 5-HT1ARs are SUMOylated by SUMO1 in the rat brain. Agonist stimulation increased SUMOylation and was further enhanced when combined with 17β-estradiol-3-benzoate (EB), which are treatments that cause the transient and prolonged desensitization of 5-HT1AR signaling, respectively. In the current study, we identified the protein inhibitor of activated STAT (PIAS)xα as the enzyme that facilitates SUMOylation, and SENP2 as the protein that catalyzes the deSUMOylation of 5-HT1ARs. We demonstrated that PIASxα significantly increased in the membrane fraction of rats co-treated with EB and an agonist, compared to either the EB-treated or vehicle-treated groups. The acute treatment with an agonist alone shifted the location of SENP2 from the membrane to the cytoplasmic fraction, but it has little effect on PIASxα. Hence, two separate mechanisms regulate SUMOylation and the activity of 5-HT1ARs by an agonist and EB. The effects of EB on 5-HT1AR SUMOylation and signaling may be related to the higher incidence of mood disorders in women during times with large fluctuations in estrogens. Targeting the SUMOylation of 5-HT1ARs could have important clinical relevance for the therapy for several neuropsychiatric disorders in which 5-HT1ARs are implicated.

Expression Analysis of Protein Inhibitor of Activated STAT in Inflammatory Demyelinating Polyradiculoneuropathy

Protein inhibitors of activated STAT (PIAS) are involved in the regulation of the JAK/STAT signaling pathway and have interactions with NF-κB, p73 and p53. These proteins regulate immune responses; therefore dysregulation in their expression leads to several immune-mediated disorders. In the present study, we examined expression of PIAS1-4 in peripheral blood of patients with acute/chronic inflammatory demyelinating polyradiculoneuropathy (AIDP/CIDP) compared with healthy subjects. We demonstrated down-regulation of all PIAS genes in both AIDP and CIDP cases compared with controls. Similarly, comparisons in gender-based groups revealed down-regulation of these gene0s in patients of each gender compared with gender-matched controls. There was no significant difference in expression of PIAS genes between AIDP and CIDP cases. Based on the area under the receiver operating characteristic curves, PIAS1-4 genes could distinguish between inflammatory demyelinating polyradiculoneuropathy and healthy status with accuracy values of 0.87, 0.87, 0.79 and 0.80, respectively. In differentiation between AIDP cases and healthy controls, these values were 0.92, 0.92, 0.83 and 0.86, respectively. Finally, PIAS1-4 genes could discriminate CIDP from healthy status with accuracy values of 0.82, 0.83, 0.75 and 0.75, respectively. The current study underscores the role of PIAS genes in the pathogenesis of inflammatory demyelinating polyradiculoneuropathy and their potential usage as biomarkers.

Expression of PIAS Genes in Migraine Patients

Migraine is a complex disabling condition which is associated with dysregulation of several pathways particularly those being associated with immune responses. In order to assess contribution of protein inhibitor of activated STAT (PIAS) in the pathogenesis of migraine, we quantified expression levels of PIAS1-PIAS4 genes in the circulation of patients with migraine compared with controls. Expression of PIAS1 was substantially lower in total migraineurs compared with controls (ratio of mean expressions (RME) = 0.18, SE = 0.29, P value < 0.001) and in both male and female migraineurs compared with sex-matched controls. Expression of PIAS2 was lower in migraineurs without aura compared with controls (RME = 0.64, SE = 0.31, P value = 0.04) and in male subgroup of these patients compared with male controls (RME = 0.60, SE = 0.22, P value < 0.001). In migraineurs with aura, downregulation of PIAS2 was only observed among male subgroups (RME = 0.37, SE = 0.49, P value = 0.01). PIAS3 was downregulated in total male migraineurs (RME = 0.52, SE = 0.43, P value = 0.04) and in male migraineurs with aura (RME = 0.49, SE = 0.45, P value = 0.03) compared with male controls. Finally, PIAS4 was upregulated in total migraineurs (RME = 3.78, SE = 0. 34, P value < 0.001), female migraineurs (RME = 5.26, SE = 0.36, P value < 0.001), migraineurs with aura (RME = 4.24, SE = 0.42, P value < 0.001), female migraineurs with aura (RME = 6.13, SE = 0.47, P value < 0.001), migraineurs without aura (RME = 3.33, SE = 0.38, P value < 0.001), and female migraineurs without aura (RME = 4.47, SE = 0.41, P value < 0.001) compared with the corresponding controls. The present study suggests contribution of PIAS genes in the pathogenesis of migraine and warrants future studies to clarify the functional routes of their contribution.

Identification and Allelic Variants Associated With Cold Tolerance of PmPIAS in Pinctada fucata martensii

The protein inhibitor of activated STAT (PIAS) functions in diverse aspects, including immune response, cell apoptosis, cell differentiation, and proliferation. In the present study, the PIAS in the pearl oyster Pinctada fucata martensii was characterized. The sequence features of PmPIAS were similar to that of other PIAS sequences with PIAS typical domains, including SAP, Pro-Ile-Asn-Ile-Thr (PINIT), RLD domain, AD, and S/T-rich region. Homologous analysis showed that PmPIAS protein sequence showed the conserved primary structure compared with other species. Ribbon representation of PIAS protein sequences also showed a conserved structure among species, and the PINIT domain and RLD domain showed the conserved structure compared with the sequence of Homo sapiens. The expression pattern of PmPIAS in different tissues showed significant high expression in the gonad. PmPIAS also exhibited a significantly higher expression in the 1 and 2 days after cold tolerance stress (17°C) and showed its potential in the cold tolerance. The SNP analysis of the exon region of PmPIAS obtained 18 SNPs, and among them, 11 SNPs showed significance among different genotypes and alleles between cold tolerance selection line and base stock, which showed their potential in the breeding for cold tolerance traits.

PIAS1 modulates striatal transcription, DNA damage repair, and SUMOylation with relevance to Huntington's disease

DNA damage repair genes are modifiers of disease onset in Huntington's disease (HD), but how this process intersects with associated disease pathways remains unclear. Here we evaluated the mechanistic contributions of protein inhibitor of activated STAT-1 (PIAS1) in HD mice and HD patient-derived induced pluripotent stem cells (iPSCs) and find a link between PIAS1 and DNA damage repair pathways. We show that PIAS1 is a component of the transcription-coupled repair complex, that includes the DNA damage end processing enzyme polynucleotide kinase-phosphatase (PNKP), and that PIAS1 is a SUMO E3 ligase for PNKP. Pias1 knockdown (KD) in HD mice had a normalizing effect on HD transcriptional dysregulation associated with synaptic function and disease-associated transcriptional coexpression modules enriched for DNA damage repair mechanisms as did reduction of PIAS1 in HD iPSC-derived neurons. KD also restored mutant HTT-perturbed enzymatic activity of PNKP and modulated genomic integrity of several transcriptionally normalized genes. The findings here now link SUMO modifying machinery to DNA damage repair responses and transcriptional modulation in neurodegenerative disease.

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.

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.

SUMOylation down-regulates rDNA transcription by repressing expression of upstream-binding factor and proto-oncogene c-Myc

Ribosome biogenesis is critical for proliferating cells and requires the coordinated activities of three eukaryotic RNA polymerases. We recently showed that the small ubiquitin-like modifier (SUMO) system controls the global level of RNA polymerase II (Pol II)-controlled transcription in mammalian cells by regulating cyclin-dependent kinase 9 activity. Here, we present evidence that the SUMO system also plays a critical role in the control of Pol I transcription. Using an siRNA-based knockdown approach, we found that multiple SUMO E3 ligases of the PIAS (protein inhibitor of activated STAT) family are involved in SUMO-mediated repression of ribosomal DNA (rDNA) gene transcription. We demonstrate that endogenous SUMO represses rDNA transcription primarily by repressing upstream-binding factor and proto-oncogene c-Myc expression and that ectopic overexpression of SUMO-associated enzymes additionally represses rDNA transcription via c-Myc SUMOylation and its subsequent degradation. The results of our study reveal a critical role of SUMOylation in the control of rDNA transcription, uncover the underlying mechanisms involved, and indicate that the SUMO system coordinates Pol I- and Pol II-mediated transcription in mammalian cells.

Negative regulators of STAT3 signaling pathway in cancers

STAT3 is the most ubiquitous member of the STAT family and involved in many biological processes, such as cell proliferation, differentiation, and apoptosis. Mounting evidence has revealed that STAT3 is aberrantly activated in many malignant tumors and plays a critical role in cancer progression. STAT3 is usually regarded as an effective molecular target for cancer treatment, and abolishing the STAT3 activity may diminish tumor growth and metastasis. Recent studies have shown that negative regulators of STAT3 signaling such as PIAS, SOCS, and PTP, can effectively retard tumor progression. However, PIAS, SOCS, and PTP have also been reported to correlate with tumor malignancy, and their biological function in tumorigenesis and antitumor therapy are somewhat controversial. In this review, we summarize actual knowledge on the negative regulators of STAT3 in tumors, and focus on the potential role of PIAS, SOCS, and PTP in cancer treatment. Furthermore, we also outline the STAT3 inhibitors that have entered clinical trials. Targeting STAT3 seems to be a promising strategy in cancer therapy.

Expression analysis of protein inhibitor of activated STAT (PIAS) genes in IFNβ-treated multiple sclerosis patients

Objectives

Protein inhibitors of activated STAT (PIAS) are transcription co-regulator of the Janus kinase/signal transducer and activator of transcription signaling pathway as well as nuclear factor-κB family of transcription factors. Both of them are involved in cytokine release during inflammatory response.

Patients and methods

Considering the role of cytokine imbalance in the pathogenesis of multiple sclerosis (MS), we compared blood expressions of PIAS1-4 genes in 48 interferon β (IFNβ)-treated MS patients with those of healthy subjects by means of real time PCR.

Results

Although the expression levels of these genes were not significantly different between MS patients and healthy subjects, significant inverse correlations have been found between PIAS1 expression and age at disease onset. PIAS2 and PIAS3 expressions were inversely correlated with Expanded Disability Status Scale (EDSS) in patients. Moreover, PIAS3 expression was correlated with disease duration in patients and with age in controls. In addition, PIAS4 expression was inversely correlated with EDSS and age at disease onset while it was positively correlated with disease duration.

Conclusion

The present study provides evidences for altered expression of PIAS genes in IFNβ-treated MS patients compared with healthy subjects. However, future studies are needed for elaboration of their exact function in this disorder.

Post-Receptor Inhibitors of the GHR-JAK2-STAT Pathway in the Growth Hormone Signal Transduction

The growth hormone (GH) plays a key role in the regulation of metabolic processes in an organism. Determination of the correct structure and functioning of the growth hormone receptor (GHR) allowed for a more detailed research of its post-receptor regulators, which substantially influences its signal transduction. This review is focused on the description of the post-receptor inhibitors of the GHR-JAK2-STAT pathway, which is one of the most important pathways in the transduction of the somatotropic axis signal. The aim of this review is the short characterization of the main post-receptor inhibitors, such as: cytokine-inducible SH2-containing protein (CIS), Suppressors of Cytokine Signaling (SOCS) 1, 2 and 3, sirtuin 1 (SIRT1), protein inhibitors of activated STAT (PIAS) 1, 3 and PIAS4, protein tyrosine phosphatases (PTP) 1B and H1, Src homology 2 (SH2) domain containing protein tyrosine phosphatase (SHP) 1, 2 and signal regulatory protein (SIRP) α1. The equilibrium between these regulators activity and inhibition is of special concern because, as many studies showed, even slight imbalance may disrupt the GH activity causing serious diseases. The regulation of the described inhibitors expression and activity may be a point of interest for pharmaceutical industry.

Targeting Oncogenic Transcription Factors: Therapeutic Implications of Endogenous STAT Inhibitors

Misregulation of transcription factors, including signal transducer and activator of transcription (STAT) proteins, leads to inappropriate gene expression patterns that can promote tumor initiation and progression. Under physiologic conditions, STAT signaling is stimulus dependent and tightly regulated by endogenous inhibitors, namely, suppressor of cytokine signaling (SOCS) proteins, phosphatases, and protein inhibitor of activated STAT (PIAS) proteins. However, in tumorigenesis, STAT proteins become constitutively active and promote the expression of progrowth and prosurvival genes. Although STAT activation has been widely implicated in cancer, therapeutic STAT inhibitors are still largely absent from the clinic. This review dissects the mechanisms of action of two families of endogenous STAT inhibitors, the SOCS and PIAS families, to potentially inform the development of novel therapeutic inhibitors.

A SUMO-Dependent Protein Network Regulates Chromosome Congression during Oocyte Meiosis

During Caenorhabditis elegans oocyte meiosis, a multi-protein ring complex (RC) localized between homologous chromosomes, promotes chromosome congression through the action of the chromokinesin KLP-19. While some RC components are known, the mechanism of RC assembly has remained obscure. We show that SUMO E3 ligase GEI-17/PIAS is required for KLP-19 recruitment to the RC, and proteomic analysis identified KLP-19 as a SUMO substrate in vivo. In vitro analysis revealed that KLP-19 is efficiently sumoylated in a GEI-17-dependent manner, while GEI-17 undergoes extensive auto-sumoylation. GEI-17 and another RC component, the kinase BUB-1, contain functional SUMO interaction motifs (SIMs), allowing them to recruit SUMO modified proteins, including KLP-19, into the RC. Thus, dynamic SUMO modification and the presence of SIMs in RC components generate a SUMO-SIM network that facilitates assembly of the RC. Our results highlight the importance of SUMO-SIM networks in regulating the assembly of dynamic protein complexes.

Distinct functional modes of SUMOylation for retinoid X receptor alpha

The present study investigated human retinoid X receptor alpha (hRXRα) as a substrate for modification with small ubiquitin like modifier (SUMO) and how members of the protein inhibitor of activated STAT (PIAS) family may impact upon this process. In agreement with a previous study, we validate Ubc9 to facilitate SUMOylation of hRXRα at lysine 108 but note this modification to occur for all isoforms rather than specifically with SUMO1 and to preferentially occur with the unliganded form of hRXRα. SUMOylation of hRXRα is significantly enhanced through PIAS4-mediated activity with lysine 245 identified as a specific SUMO2 acceptor site modified in a PIAS4-dependent fashion. While individual mutations at lysine 108 or 245 modestly increase receptor activity, the combined loss of SUMOylation at both sites significantly potentiates the transcriptional responsiveness of hRXRα suggesting both sites may cooperate in a DNA element-dependent context. Our findings highlight combinatorial effects of SUMOylation may regulate RXRα-directed signalling in a gene-specific fashion.

Tuning NF-κB activity: a touch of COMMD proteins

NF-κB is an important regulator of immunity and inflammation, and its activation pathway has been studied extensively. The mechanisms that downregulate the activity of NF-κB have also received a lot of attention, particularly since its activity needs to be terminated to prevent chronic inflammation and subsequent tissue damage. The COMMD family has been identified as a new group of proteins involved in NF-κB termination. All ten COMMD members share the structurally conserved carboxy-terminal motif, the COMM domain, and are ubiquitously expressed. They seem to play distinct and non-redundant roles in various physiological processes, including NF-κB signaling. In this review, we describe the mechanisms and proteins involved in the termination of canonical NF-κB signaling, with a specific focus on the role of the COMMD family in the down-modulation of NF-κB.

A role for paralog-specific sumoylation in histone deacetylase 1 stability

Histone deacetylase 1 (HDAC1) is an essential epigenetic regulator belonging to a highly conserved family of deacetylases. Increased HDAC1 activity and expression often correlates with neoplastic transformation. Here we show how specific modification of HDAC1 by SUMO1, but not by SUMO2, facilitates HDAC1 degradation. Our findings reveal that SUMO1, but not SUMO2, conjugation to HDAC1 promotes HDAC1 ubiquitination and degradation. This is suggested by the observation that in non-tumorigenic mammary epithelial cells HDAC1 is preferentially conjugated to SUMO1 leading to HDAC1 proteolysis, whereas in breast cancer cells HDAC1 is more conjugated to SUMO2, promoting HDAC1 protein stability. SUMO E3 ligases play an important role in paralog-specific conjugation; in particular, the SUMO E3 ligase PIASy, which is overexpressed in breast cancer cells, selectively promotes the conjugation of HDAC1 to SUMO2. Therefore, cell environment affects paralog-specific sumoylation of HDAC1, whose conjugation to SUMO1 but not to SUMO2 facilitates its protein turnover. Our findings uncover a role for paralog-specific sumoylation of HDAC1 whose significance is emphasized by the use of HDAC inhibitors as anticancer drugs.

Sumoylation regulates nuclear localization and function of zinc finger transcription factor ZIC3

ZIC3, an X-linked zinc finger transcription factor, was the first identified gene involved in establishing normal left-right patterning in humans. Mutations in the Zic3 gene in patients cause heterotaxy, which includes congenital heart defects. However, very little is known about how the function of the ZIC3 protein is regulated. Sumoylation is a posttranslational modification process in which a group of small ubiquitin-like modifier (SUMO) proteins is covalently attached to targets via a series of enzymatic reactions. Here, we report for the first time that sumoylation targets human ZIC3 primarily on the consensus lysine residue K248, which is critical for the nuclear retention of ZIC3. Consequently, SUMO modification potentiates the repressive activity of ZIC3 on the promoter of its target gene cardiac α-actin, and the mutation of lysine 248 to arginine (K248R) abolishes its repressive function. We further revealed that ZIC3 variants with mutations found in human patients with congenital anomalies exhibit aberrant sumoylation activity, which at least partially accounts for their cytoplasmic diffusion. Improved sumoylation of human disease-associated ZIC3 variants reestablishes their nuclear occupancy in the presence of SUMO E3 ligase and SUMO-1. Thus, the altered sumoylation status of ZIC3 underpins the developmental abnormalities associated with these ZIC3 mutants. The SUMO targeting consensus sequence in ZIC3 is highly conserved in its paralogs and orthologs, pointing to sumoylation as a general mechanism underlying the functional control of ZIC proteins. This study provides a potential therapeutic strategy to regain the normal subcellular distribution and function of ZIC3 mutants by restoring SUMO conjugation.

PIAS3 promotes homology-directed repair and distal non-homologous end joining

A DNA double-strand break (DSB) is the most severe form of DNA damage and is mainly repaired through homologous recombination (HR), which has a high fidelity, or non-homologous end joining (NHEJ), which is prone to errors. Defects in the DNA damage response lead to genomic instability and ultimately the predisposition of organs to cancer. Protein inhibitor of activated STAT-1 (PIAS1), which is a potential small ubiquitin-related modifier (SUMO) ligase, has been reported to be involved in DSB repair. The present study identified that another member of the PIAS family, PIAS3, is also an enhancer for HR- and NHEJ-mediated DSB repair. Furthermore, the overexpression of PIAS3 was demonstrated to increase the resistance of HeLa cells to ionizing radiation (IR), indicating a significant role for PIAS3 in the DNA damage response (DDR) pathway.

Protein inhibitors of activated STAT (Pias1 and Piasy) differentially regulate pituitary homeobox 2 (PITX2) transcriptional activity

Protein inhibitors of activated STAT (Pias) proteins can act independent of sumoylation to modulate the activity of transcription factors and Pias proteins interacting with transcription factors can either activate or repress their activity. Pias proteins are expressed in many tissues and cells during development and we asked if Pias proteins regulated the pituitary homeobox 2 (PITX2) homeodomain protein, which modulates developmental gene expression. Piasy and Pias1 proteins are expressed during craniofacial/tooth development and directly interact and differentially regulate PITX2 transcriptional activity. Piasy and Pias1 are co-expressed in craniofacial tissues with PITX2. Yeast two-hybrid, co-immunoprecipitation and pulldown experiments demonstrate Piasy and Pias1 interactions with the PITX2 protein. Piasy interacts with the PITX2 C-terminal tail to attenuate its transcriptional activity. In contrast, Pias1 interacts with the PITX2 C-terminal tail to increase PITX2 transcriptional activity. The E3 ligase activity associated with the RING domain in Piasy is not required for the attenuation of PITX2 activity, however, the RING domain of Pias1 is required for enhanced PITX2 transcriptional activity. Bimolecular fluorescence complementation assays reveal PITX2 interactions with Piasy and Pias1 in the nucleus. Piasy represses the synergistic activation of PITX2 with interacting co-factors and Piasy represses Pias1 activation of PITX2 transcriptional activity. In contrast, Pias1 did not affect the synergistic interaction of PITX2 with transcriptional co-factors. Last, we demonstrate that Pias proteins form a complex with PITX2 and Lef-1, and PITX2 and β-catenin. Lef-1, β-catenin, and Pias interactions with PITX2 provide new molecular mechanisms for the regulation of PITX2 transcriptional activity and the activity of Pias proteins.