Investigating the pathogenic role of PADI4 in oesophageal cancer

Investigating the cell membrane localization of PADI4 in breast cancer cells and inhibition of anti-PADI4 monoclonal antibody

BACKGROUND

Peptidyl arginine deiminase 4 (PADI4) is a post-translational modification enzymecan that converts arginine in protein into citrulline in the presence of calcium ions, which is called citrullination. PADI4 has been reported to be expressed in the cytoplasm and nucleus in a variety of malignant tumors. Based on the GeneCards database and our previous research, it is speculated that PADI4 may also be expressed on the cell membrane. This study aimed to confirm the membrane expression of PADI4 and the effect of anti-PADI4 antibodies on cell membrane PADI4. This may be another mechanism of action of anti-PADI4 monoclonal antibodies in the treatment of breast cancer.

METHODS

The subcellular localizations of PADI4 in MDA-MB-231 and MCF-7 breast cancer cells were determined by immunofluorescence, immunoelectron microscopy, and Western blot analysis. The tumor cells were treated with PADI4 antibody, and cell proliferation, migration, colony formation, apoptosis, glycolysis, and epithelial-mesenchymal transition (EMT) were measured as well as the expression of some essential tumor genes.

RESULTS

PADI4 was not only localized in the nucleus and cytoplasm of breast cancer cells but was also detected on the cell membrane. Following PADI4 antibody treatment, cell proliferation, migration, colony formation, EMT, and ATP production through glycolysis were decreased, and the mRNA expression of MYC proto-oncogene (MYC), FAT atypical cadherin 1 (FAT1), nuclear factor kappa B subunit 1 (NFκB), and tumor necrosis factor (TNF-α) in breast cancer cells was downregulated, while the mRNA expression of tumor protein p63 (TP63) was upregulated.

CONCLUSIONS

PADI4 is expressed on the cell membrane in breast cancer cells. Anti-PADI4 antibodies can affect the biological functions of cell membrane PADI4, including proliferation, migration, apoptosis, and glycolysis, thereby inhibiting tumor progression.

Role of the PADI family in inflammatory autoimmune diseases and cancers: A systematic review

The peptidyl arginine deiminase (PADI) family is a calcium ion-dependent group of isozymes with sequence similarity that catalyze the citrullination of proteins. Histones can serve as the target substrate of PADI family isozymes, and therefore, the PADI family is involved in NETosis and the secretion of inflammatory cytokines. Thus, the PADI family is associated with the development of inflammatory autoimmune diseases and cancer, reproductive development, and other related diseases. In this review, we systematically discuss the role of the PADI family in the pathogenesis of various diseases based on studies from the past decade to provide a reference for future research.

Pediatric Brain Tumors: Signatures from the Intact Proteome

The present investigation aimed to explore the intact proteome of tissues of pediatric brain tumors of different WHO grades and localizations, including medulloblastoma, pilocytic astrocytoma, and glioblastoma, in comparison with the available data on ependymoma, to contribute to the understanding of the molecular mechanisms underlying the onset and progression of these pathologies. Tissues have been homogenized in acidic water−acetonitrile solutions containing proteases inhibitors and analyzed by LC−high resolution MS for proteomic characterization and label-free relative quantitation. Tandem MS spectra have been analyzed by either manual inspection or software elaboration, followed by experimental/theoretical MS fragmentation data comparison by bioinformatic tools. Statistically significant differences in protein/peptide levels between the different tumor histotypes have been evaluated by ANOVA test and Tukey’s post-hoc test, considering a p-value > 0.05 as significant. Together with intact protein and peptide chains, in the range of molecular mass of 1.3−22.8 kDa, several naturally occurring fragments from major proteins, peptides, and proteoforms have been also identified, some exhibiting proper biological activities. Protein and peptide sequencing allowed for the identification of different post-translational modifications, with acetylations, oxidations, citrullinations, deamidations, and C-terminal truncations being the most frequently characterized. C-terminal truncations, lacking from two to four amino acid residues, particularly characterizing the β-thymosin peptides and ubiquitin, showed a different modulation in the diverse tumors studied. With respect to the other tumors, medulloblastoma, the most frequent malignant brain tumor of the pediatric age, was characterized by higher levels of thymosin β4 and β10 peptides, the latter and its des-IS form particularly marking this histotype. The distribution pattern of the C-terminal truncated forms was also different in glioblastoma, particularly underlying gender differences, according to the definition of male and female glioblastoma as biologically distinct diseases. Glioblastoma was also distinguished for the peculiar identification of the truncated form of the α-hemoglobin chain, lacking the C-terminal arginine, and exhibiting oxygen-binding and vasoconstrictive properties different from the intact form. The proteomic characterization of the undigested proteome, following the top-down approach, was challenging to originally investigate the post-translational events that differently characterize pediatric brain tumors. This study provides a contribution to elucidate the molecular profiles of the solid tumors most frequently affecting the pediatric age, and which are characterized by different grades of aggressiveness and localization.

PAD-2-mediated citrullination of nucleophosmin provides an effective target for tumor immunotherapy

BACKGROUND

The enzymatic conversion of arginine to citrulline is involved in gene and protein regulation and in alerting the immune system to stressed cells, including tumor cells. Nucleophosmin (NPM) is a nuclear protein that plays key roles in cellular metabolism including ribosome biogenesis, mRNA processing and chromatin remodeling and is regulated by citrullination. In this study, we explored if the same citrullinated arginines within NPM are involved in gene regulation and immune activation.

METHODS

HLA-DP4 and HLA-DR4 transgenic mice were immunized with 22 citrullinated NPM overlapping peptides and immune responses to the peptides were assessed by ex vivo ELISpot assays. Antitumor immunity of NPM targeted vaccination was assessed by challenging transgenic mice with B16F1 HHDII/iDP4, B16F1 HHDII/PAD2KOcDP4, B16F1 HHDII and Lewis lung carcinoma cells/cDP4 cells subcutaneously. Peripheral blood mononuclear cells isolated from healthy donors were stimulated with NPM266-285cit peptides with/without CD45RO+memory cell depletion to assess if the responses in human were naïve or memory.

RESULTS

In contrast to NPM regulation, which is mediated by peptidylarginine deiminase (PAD4) citrullination of arginine at position 197, only citrullinated NPM266-285 peptide induced a citrulline-specific CD4 T cell response in transgenic mice models expressing human HLA-DP4 or HLA-DR4. Vaccinations with the NPM266-285cit peptide stimulated antitumor responses that resulted in dramatic tumor therapy, greatly improved survival, and protected against rechallenge without further vaccination. The antitumor response was lost if MHCII expression on the tumor cells was knocked out demonstrating direct presentation of the NPM266-285cit epitope in tumors. This antitumor response was lost in B16 tumors lacking PAD2 enzyme indicating NPM266cit is citrullinated by PAD2 in this model. Assessment of the T cell repertoire in healthy individuals and patients with lung cancer also showed CD4 T cells that respond to NPM266-285cit. The proliferative CD4 responses displayed a Th1 profile as they were accompanied with increased IFNγ and granzyme B expression. Depletion of CD45RO+ memory cells prior to stimulation suggested that responses originated from a naïve population in healthy donors.

CONCLUSION

This study indicates PAD2 can citrullinate the nuclear antigen NPM at position 277 which can be targeted by CD4 T cells for antitumor therapy. This is distinct from PAD4 citrullination of arginine 197 within NPM which results in its transport from the nucleoli to the nucleoplasm.

PADI4 promotes epithelial-mesenchymal transition(EMT) in gastric cancer via the upregulation of interleukin 8

Background

Gastric cancer (GC) is one of the deadliest tumours due to its ability to metastasize. The Epithelial–to-mesenchymal transition plays a crucial role in promoting the GC metastasis, which increases the migration and metastasis of tumour cells. Peptidyl arginine deiminase IV (PADI4) is a susceptibility gene for gastric carcinoma. The aim of this study was to evaluate the functional roles of PADI4 in gastric cancer.

Methods

The expression of PADI4 was examined by qRT-PCR, western blot and immunohistochemistry. In addition, the functional roles of PADI4 were explored by over-expression PADI4 plasmids in gastric cancer cells.

Results

We found that the expression of PADI4 was up-regulated in GC. PADI4 overexpression in GC cells increased the proliferation, migration, metastasis, clone forming ability, and tumorigenic ability, but reduced the apoptosis ability. The Multi-Analyte ELISArray Kit results showed that interleukin 8 (IL-8) is upregulated in PADI4-overexpressing gastric cells. Using short interfering RNA (siRNA) to silence the expression of IL-8, we demonstrated that IL-8 silencing significantly inhibited the increased migratory capacity in PADI4-overexpressing GC cells.

Conclusions

Our data suggest that PADI4 accelerate metastasis by promoting IL-8 expression in gastric cancer cells, indicating that it is a new PADI4/IL-8 signalling pathway in metastatic GC.

Acupuncture Can Regulate the Distribution of Lymphocyte Subsets and the Levels of Inflammatory Cytokines in Patients With Mild to Moderate Vascular Dementia

Background: Vascular dementia (VD) is the second most common type of dementia after Alzheimer’s disease, but there is a lack of definitive treatment for VD. Acupuncture treatment is effective in improving the cognitive impairment and behavioral capacity of patients with VD. In recent years, more studies indicated that peripheral inflammation and abnormal peripheral immune function may aggravate neuroinflammation and cognitive dysfunction. However, there are few studies about the acupuncture and the abnormal peripheral immune function of VD. Also, few studies concern the regulating effect of acupuncture on peripheral immunity of patients with VD.

Objective: The aim of this study was to explore the effect of the “sanjiao” acupuncture method on peripheral immunity of patients with mild to moderate VD.

Methods: A total of 30 patients with VD were involved in the acupuncture group (AG), which was treated with the “sanjiao” acupuncture method once a day for six times a week and lasted for 12 weeks, and 30 healthy elderly people were assigned to the normal group (NG), which had no treatment. The distribution of lymphocyte subsets and the levels of some inflammatory cytokines in the peripheral blood of subjects were evaluated using the flow cytometry (FCM) and the enzyme-linked immunosorbent assay (ELISA).

Results: A total of 60 subjects were involved in this study, while 58 subjects completed the entire trial. Before treatment, the levels of CD3⁺ T, CD4⁺ T cells, CD4⁺/CD8⁺, Tregs, B cells, IFN-γ, and IL-10 in patients with VD were significantly decreased compared with the normal group (all P < 0.05 or P < 0.01). The level of TNF-α in peripheral blood of patients with VD was significantly increased (P < 0.01). After acupuncture treatment, the levels of CD3⁺ T, CD4⁺ T cells, and IFN-γ were significantly increased (all P < 0.05 or P < 0.01). The level of TNF-α was significantly decreased (P < 0.01). The proportion of Tregs was increased (P < 0.01), but it was still lower than that of the normal group (P < 0.05).

Conclusion: The acupuncture method can increase the proportion of CD3⁺, CD4⁺ T cells, and Tregs in peripheral blood of patients with VD. And, it reduces the levels of pro-inflammatory factor TNF-α, which achieves the anti-inflammatory effects and immunostimulation. It suggests that acupuncture can improve the peripheral immune dysfunction of patients with VD by regulating the distribution of lymphocyte subsets and the levels of inflammatory cytokines.

Clinical Trial Registration: [www.chictr.org.cn], identifier [ChiCTR-IOR-17012052].

Metabolic reprogramming and epigenetic modifications on the path to cancer

Metabolic rewiring and epigenetic remodeling, which are closely linked and reciprocally regulate each other, are among the well-known cancer hallmarks. Recent evidence suggests that many metabolites serve as substrates or cofactors of chromatin-modifying enzymes as a consequence of the translocation or spatial regionalization of enzymes or metabolites. Various metabolic alterations and epigenetic modifications also reportedly drive immune escape or impede immunosurveillance within certain contexts, playing important roles in tumor progression. In this review, we focus on how metabolic reprogramming of tumor cells and immune cells reshapes epigenetic alterations, in particular the acetylation and methylation of histone proteins and DNA. We also discuss other eminent metabolic modifications such as, succinylation, hydroxybutyrylation, and lactylation, and update the current advances in metabolism- and epigenetic modification-based therapeutic prospects in cancer.

The Role of Citrullination in Inflammatory Bowel Disease: A Neglected Player in Triggering Inflammation and Fibrosis?

Citrullination is a posttranslational modification of proteins mediated by a specific family of enzymes called peptidylarginine deiminases (PAD). Dysregulation of these enzymes is involved in the etiology of various diseases, from cancer to autoimmune disorders. In inflammatory bowel disease (IBD), data for a role of citrullination in the disease process are starting to accumulate at different experimental levels including gene expression analyses, RNA, and protein quantifications. Most data have been generated in ulcerative colitis, but data in Crohn disease are lacking so far. In addition, the citrullination of histones is the fundamental process promoting inflammation through the formation of neutrophil extracellular traps (NETs). Interestingly, NETs have also been shown to activate fibroblasts into myofibroblasts in fibrotic interstitial lung disease. Therefore, citrullination merits more thorough study in the bowel to determine its role in driving disease complications such as fibrosis. In this review we describe the process of citrullination and the different players in this pathway, the role of citrullination in autoimmunity with a special focus on IBD, the emerging role for citrullination and NETs in triggering fibrosis, and, finally, how this process could be therapeutically targeted.

Elucidating Citrullination by Mass Spectrometry and Its Role in Disease Pathogenesis

This review focuses on discussing key mechanisms in disease pathogenesis mediated by the protein post-translational modification citrullination. These processes are discussed in depth in the context of complex diseases such as rheumatoid arthritis, cancer, central nervous system disorders, and cardiovascular disease. Additionally, a critical evaluation of challenges in laboratory detection of citrullination sites is also outlined. In this context, the role of mass spectrometry is discussed with a focus on contemporary techniques that offer promising options to detect the exact site of protein citrullination. Novel methods described in the paper have the potential to detect and quantify the occurrence of post-translational modification sites for diagnosis and therapeutic purposes with a high degree of specificity and sensitivity. Furthermore, they offer a much faster performance than traditional techniques making them ideal for large-scale experimentation.

Post-translational modifications such as citrullination are excellent targets for cancer therapy

Under conditions of cellular stress, proteins can be post-translationally modified causing them to be recognized by the immune system. One such stress-induced post-translational modification (siPTM) is citrullination, the conversion of arginine residues to citrulline by peptidylarginine deiminase (PAD) enzymes. PAD enzymes are activated by millimolar concentrations of calcium which can occur during apoptosis, leading to precipitation of proteins, their subsequent uptake by B cells and stimulation of antibody responses. Detection of anti-citrullinated protein antibodies (ACPAs) is a diagnostic of rheumatoid arthritis (RA), where immune complexes stimulate inflammation around the joints. More recently, autophagy has been shown to play a role in the presentation of citrullinated peptides on MHC class II molecules to CD4⁺ helper T cells, suggesting that citrullination may be a way of alerting immune cells to cellular stress. Additionally, inflammation-induced IFNγ and concomitant MHC class II expression on target cells contributes to immune activation. Stressful conditions in the tumor microenvironment induce autophagy in cancer cells as a pro-survival mechanism. Cancer cells also over express PAD enzymes and in light of this the hypothesis that citrullinated peptides stimulate CD4⁺ T cell responses that would recognize these siPTM's produced during autophagy has been investigated. The induction of potent citrullinated peptide-specific CD4 responses has been shown in both humans and HLA transgenic mouse models. Responses in mouse models resulted in potent anti-tumour responses against tumours expressing either constitutive or IFNγ-inducible MHC class II. The anti-tumour effect relied upon direct recognition of tumours by specific CD4 T cells suggesting that citrullinated peptides are attractive targets for cancer vaccines.

Targeting epigenetic regulators for cancer therapy: mechanisms and advances in clinical trials

Epigenetic alternations concern heritable yet reversible changes in histone or DNA modifications that regulate gene activity beyond the underlying sequence. Epigenetic dysregulation is often linked to human disease, notably cancer. With the development of various drugs targeting epigenetic regulators, epigenetic-targeted therapy has been applied in the treatment of hematological malignancies and has exhibited viable therapeutic potential for solid tumors in preclinical and clinical trials. In this review, we summarize the aberrant functions of enzymes in DNA methylation, histone acetylation and histone methylation during tumor progression and highlight the development of inhibitors of or drugs targeted at epigenetic enzymes.

Citrullination in Cancer

Posttranslational modifications of proteins have been implicated in pathogenesis of numerous diseases. Arginine deimination (also known as citrullination) has a principal role in progression of rheumatoid arthritis through generation of autoantibodies and exacerbation of the inflammatory response. Recently, multiple research groups provided solid evidence of citrullination being in control of cancer progression; however, there is no comprehensive overview of these findings. This article summarizes and critically reviews the influence of citrullination on different aspects of tumor biology, including (i) regulation of apoptosis and differentiation, (ii) promoting EMT and metastasis, and (iii) potential use of citrullinated antigens for immunotherapy. In addition, (iv) the role of citrullination as a cancer biomarker and (v) implication of neutrophil extracellular traps in tumorigenesis are discussed. In summary, current findings testify to the significance of arginine deimination in tumor biology and thus more basic and translational studies are needed to further explore this topic.

PADI4 stimulates esophageal squamous cell carcinoma tumor growth and up-regulates CA9 expression

An increasing amount of evidence indicates that peptidylarginine deiminase isoform 4 (PADI4) plays an important role in tumorigenesis. However, the effects of PADI4 on tumor-bearing mice are unknown, and no studies have investigated this tumorigenic pathway in an animal model. In the present study, ECA109 cells originating from esophageal squamous cell carcinoma (ESCC) were transfected with PADI4-expressing lentivirus and were injected into BALB/c nude mice. Tumor size and weight were significantly increased in the mouse tumors established with PADI4-overexpressing ECA109 cells. PCR array analysis revealed increased CA9 expression in ECA109 cells transfected with a PADI4-expressing plasmid, while decreased CA9 expression levels were detected in cells transfected with anti-PADI4 siRNA. Furthermore, up-regulation of CA9 expression was detected in mouse tumors established with PADI4-overexpressing cells. Immunohistochemistry detected the increased expression and co-localization of PADI4 and CA9 in ESCC tissues compared with adjacent non-tumor tissues and normal tissue controls. These results were verified using Western blotting. Cell proliferation significantly increased or decreased in ECA109 and EC9706 (another ESCC-originating cell line) cells transfected with a PADI4-expressing plasmid or anti-PADI4 siRNA, respectively. The above findings suggest that increased PADI4 expression in ESCC stimulates tumor growth and up-regulates CA9 expression, which is known to promote metastatic properties in tumor cells.

ESCC ATLAS: A population wide compendium of biomarkers for Esophageal Squamous Cell Carcinoma

Esophageal cancer (EC) is the eighth most aggressive malignancy and its treatment remains a challenge due to the lack of biomarkers that can facilitate early detection. EC is identified in two major histological forms namely - Adenocarcinoma (EAC) and Squamous cell carcinoma (ESCC), each showing differences in the incidence among populations that are geographically separated. Hence the detection of potential drug target and biomarkers demands a population-centric understanding of the molecular and cellular mechanisms of EC. To provide an adequate impetus to the biomarker discovery for ESCC, which is the most prevalent esophageal cancer worldwide, here we have developed ESCC ATLAS, a manually curated database that integrates genetic, epigenetic, transcriptomic, and proteomic ESCC-related genes from the published literature. It consists of 3475 genes associated to molecular signatures such as, altered transcription (2600), altered translation (560), contain copy number variation/structural variations (233), SNPs (102), altered DNA methylation (82), Histone modifications (16) and miRNA based regulation (261). We provide a user-friendly web interface ( http://www.esccatlas.org , freely accessible for academic, non-profit users) that facilitates the exploration and the analysis of genes among different populations. We anticipate it to be a valuable resource for the population specific investigation and biomarker discovery for ESCC.

ESCC ATLAS: A population wide compendium of biomarkers for Esophageal Squamous Cell Carcinoma

Esophageal cancer (EC) is the eighth most aggressive malignancy and its treatment remains a challenge due to the lack of biomarkers that can facilitate early detection. EC is identified in two major histological forms namely - Adenocarcinoma (EAC) and Squamous cell carcinoma (ESCC), each showing differences in the incidence among populations that are geographically separated. Hence the detection of potential drug target and biomarkers demands a population-centric understanding of the molecular and cellular mechanisms of EC. To provide an adequate impetus to the biomarker discovery for ESCC, which is the most prevalent esophageal cancer worldwide, here we have developed ESCC ATLAS, a manually curated database that integrates genetic, epigenetic, transcriptomic, and proteomic ESCC-related genes from the published literature. It consists of 3475 genes associated to molecular signatures such as, altered transcription (2600), altered translation (560), contain copy number variation/structural variations (233), SNPs (102), altered DNA methylation (82), Histone modifications (16) and miRNA based regulation (261). We provide a user-friendly web interface ( http://www.esccatlas.org , freely accessible for academic, non-profit users) that facilitates the exploration and the analysis of genes among different populations. We anticipate it to be a valuable resource for the population specific investigation and biomarker discovery for ESCC.

PADI4 has genetic susceptibility to gastric carcinoma and upregulates CXCR2, KRT14 and TNF-α expression levels

PADI4 (peptidyl deiminase isoform 4) is overexpressed in many tumor tissues and converts arginine residues to citrulline residues. This study used an Illumina SNP microarray and a TaqMan assay to determine the possible association of the PADI4 gene with various tumor risks. Both genotyping methods demonstrated significant associations between the tag SNPs rs1635566 and rs882537 in the PADI4 locus with gastric carcinoma in two independent cohorts. Based on this genotyping result, we used the Cancer Pathway Finder, p53 Signaling, Signal Transduction and Tumor Metastasis PCR arrays to investigate the tumorigenic pathway of PADI4 in MNK-45 cells derived from gastric carcinoma. We detected significantly decreased expression levels of CXCR2, KRT14 and TNF-α in MNK-45 cells that were treated with anti-PADI4 siRNA. We also detected increased expression of these three genes in MNK-45 cells transfected with a pcDNA3.1 plasmid overexpressing PADI4. A highly similar result was also obtained for SGC 7901 cells, which also originate from gastric carcinoma. Our result indicates that the PADI4 gene has genetic susceptibility in gastric carcinoma. PADI4 contributes to gastric tumorigenesis by upregulating CXCR2, KRT14 and TNF-α expression, which are well known to activate angiogenesis, cell proliferation, cell migration and the immune microenvironment in tumors.

PADI4 rs2240337 G>A polymorphism is associated with susceptibility of esophageal squamous cell carcinoma in a Chinese population

Background

Esophageal cancer (EC) remains one of the major causes of cancer incidence and mortality worldwide. Genetic factors, such as single nucleotide polymorphisms (SNPs), may contribute to the carcinogenesis of EC.

Methods

We conducted a hospital based case-control study to evaluate the genetic susceptibility of SNPs on the development of EC. A total of 629 esophageal squamous cell carcinoma (ESCC) cases and 686 controls were enrolled for this study. Seven PADI4 SNPs were determined by ligation detection reaction method.

Results

Our findings suggested that the PADI4 rs2240337 GA/AA variants were significantly associated with decreased risk of ESCC. Haplotype PADI4 A_rs2477137C_rs1886302G_rs11203366G_rs16825533G_rs2240337A_rs1635564A_rs1635562 and C_rs2477137T_rs1886302G_rs11203366A_rs1635564G_rs2240337C_rs1635564T_rs1635562 polymorphism was correlated with decreased susceptibility to ESCC, while C_rs2477137T_rs1886302A_rs11203366A_rs1635564G_rs2240337A_rs1635564A_rs1635562 was correlated with increased susceptibility of ESCC. Stratification analyses demonstrated that smoking significantly increased ESCC risk in PADI4 rs11203366 AG/AA, rs1886302 CC/CT, rs1635562 AT, rs1635564 CA and rs2477137 AC genotype. Alcohol drinking increased ESCC risk in PADI4 rs11203366 AG, rs1635562 AT, rs1635564 CA, rs2477137 AC, rs1886302 CT genotype. In younger cohort (<63 years), rs11203366 AA genotype was associated with increased risk of ESCC. PADI4 rs1886302 CC variant was associated with ESCC susceptibility in female cohort.

Conclusions

Our study suggested that PADI4 rs2240337 G>A polymorphism may be correlated with individual susceptibility to ESCC. PADI4 rs11203366, rs1886302, rs1635562, rs1635564 and rs2477137 polymorphisms were implicated with altered susceptibility of ESCC based on sex, age, smoking status and alcohol consumption. However, larger studies among different ethnic populations and further experiments using genetically mutated cells or animals are warranted to verify our conclusion.

B-cell specific Moloney leukemia virus insert site 1 and peptidyl arginine deiminase IV positively regulate carcinogenesis and progression of esophageal squamous cell carcinoma

High expression of B-cell specific Moloney leukemia virus insert site 1 (Bmi-1) and peptidyl arginine deiminase IV (PADI4) is associated with esophageal carcinoma. However, few studies have investigated the association between the Bmi-1 and PADI4 genes. The aim of the present study was to evaluate the expression of Bmi-1 and PADI4 and identify the association between the Bmi-1 and PADI4 genes in esophageal squamous cell carcinoma (ESCC) tissues. Bmi-1 and PADI4 gene expression levels were measured using immunohistochemistry, western blotting and reverse transcription-quantitative polymerase chain reaction in ESCC tissues from 86 patients who had not received pre-operative chemoradiation. The results revealed that the Bmi-1 and PADI4 genes had increased expression in carcinoma tissues compared with pericarcinous tissue (P<0.05). Bmi-1 gene expression was revealed to be associated with differentiation degree, clinical stage and lymph node metastasis (P<0.05), but had no association with gender, age or depth of invasion (P>0.05). The expression of PADI4 was associated with clinical stage, depth of invasion and lymph node metastasis (P<0.05), but was not associated with gender, age or differentiation degree (P>0.05). In addition, there was a positive association between Bmi-1 and PADI4 gene expression in ESCC (P<0.05). These results indicated that Bmi-1 and PADI4 positively regulate carcinogenesis and progression of ESCC.

PADI4 Epigenetically Suppresses p21 Transcription and Inhibits Cell Apoptosis in Fibroblast-like Synoviocytes from Rheumatoid Arthritis Patients

Rheumatoid arthritis (RA) is characterized by synovial lining hyperplasia, which involves abnormal growth of fibroblast-like synoviocytes (FLSs). This study aimed to investigate the function and molecular mechanism of peptidylarginine deiminase type 4 (PADI4) in FLSs isolated from RA patients (RA-FLSs). FLSs were isolated from RA patients and transfected with small interfering RNAs (siRNAs) or PADI4 overexpression plasmid. FLSs were treated by Adriamycin (ADR) to induce apoptosis, and apoptotic cells were detected by flow cytometry. The expression of PADI4, p53 and p21 was detected by qRT-PCR and Western blot analysis. The recruitment of PADI4 and histone H3 arginine modifications to p21 promoter was measured by chromatin immunoprecipitation. The results showed that knockdown of PADI4 promoted the apoptosis of RA-FLSs and the expression of p53 and p21. Ectopic expression of PADI4 inhibited ADR-induced apoptosis of RA-FLSs, and down-regulated the expression of p53 and p21. In RA-FLSs, global H3 citrullination (CitH3) and H3 arginine 17 methylation levels were dynamically changed by PADI4 and ADR treatment. PADI4 and H3 could bind p21 promoter region to regulate p21 expression. In conclusion, PADI4 contributes to the pathogenesis of RA by protecting FLSs from apoptosis. PADI4 suppresses p21 transcription through altering histone H3 arginine modifications on p21 promoter region. Our study provides new insight into the anti-apoptotic role of PADI4 in RA development.

PAD4: pathophysiology, current therapeutics and future perspective in rheumatoid arthritis

INTRODUCTION

Peptidyl arginine deiminase 4 (PAD4) is an enzyme that plays an important role in gene expression, turning out genetic code into functional products in the body. It is involved in a key post translational modification, which involves the conversion of arginine to citrulline. It regulates various processes such as apoptosis, innate immunity and pluripotency, while its dysregulation has a great impact on the genesis of various diseases. Over the last few years PAD4 has emerged as a potential therapeutic target for the treatment of rheumatoid arthritis (RA). Areas covered: In this review, we discuss the basic structure and function of PAD4, along with the role of altered PAD4 activity in the onset of RA and other maladies. We also elucidate the role of PAD4 variants in etiology of RA among several ethnic groups and the current pre-clinical inhibitors to regulate PAD4. Expert opinion: Citrullination has a crucial role in RA and several other disorders. Since PAD4 is an initiator of the citrullination, it is an important therapeutic target for inflammatory diseases. Therefore, an in depth knowledge of the roles and activity of PAD4 is required to explore more effective ways to conquer PAD4 related ailments, especially RA.

The receptor for advanced glycation end products (RAGE) enhances autophagy and neutrophil extracellular traps in pancreatic cancer

Neutrophil extracellular traps (NETs) are formed when neutrophils expel their DNA, histones and intracellular proteins into the extracellular space or circulation. NET formation is dependent on autophagy and is mediated by citrullination of histones to allow for unwinding and subsequent expulsion of DNA. NETs play an important role in the pathogenesis of several sterile inflammatory diseases, including malignancy, therefore we investigated the role of NETs in the setting of pancreatic ductal adenocarcinoma (PDA). Neutrophils isolated from two distinct animal models of PDA had an increased propensity to form NETs following stimulation with platelet activating factor (PAF). Serum DNA, a marker of circulating NET formation, was elevated in tumor bearing animals as well as in patients with PDA. Citrullinated histone H3 expression, a marker of NET formation, was observed in pancreatic tumors obtained from murine models and patients with PDA. Inhibition of autophagy with chloroquine or genetic ablation of RAGE resulted in decreased propensity for NET formation, decreased serum DNA, and decreased citrullinated histone H3 expression in the pancreatic tumor microenvironment. We conclude that NETs are upregulated in pancreatic cancer through RAGE dependent/autophagy pathways.

Fluorescence-based monitoring of PAD4 activity via a pro-fluorescence substrate analog

Post-translational modifications may lead to altered protein functional states by increasing the covalent variations on the side chains of many protein substrates. The histone tails represent one of the most heavily modified stretches within all human proteins. Peptidyl-arginine deiminase 4 (PAD4) has been shown to convert arginine residues into the non-genetically encoded citrulline residue. Few assays described to date have been operationally facile with satisfactory sensitivity. Thus, the lack of adequate assays has likely contributed to the absence of potent non-covalent PAD4 inhibitors. Herein a novel fluorescence-based assay that allows for the monitoring of PAD4 activity is described. A pro-fluorescent substrate analog was designed to link PAD4 enzymatic activity to fluorescence liberation upon the addition of the protease trypsin. It was shown that the assay is compatible with high-throughput screening conditions and has a strong signal-to-noise ratio. Furthermore, the assay can also be performed with crude cell lysates containing over-expressed PAD4.

Peptidylarginine deiminase IV promotes the development of chemoresistance through inducing autophagy in hepatocellular carcinoma

BACKGROUND

Peptidylarginine deiminase IV (PADI4) is widely distributed in several tissues and the expression is correlated with many pathological processes. Chemotherapy remains a major treatment alternatively to surgery for a large number of patients at the advanced stage of hepatocellular carcinoma (HCC). However, the role of PADI4 in the chemoresistance of HCC has not been identified.

METHODS

MTT and PI/Annexin V assay were employed to examine the proliferation and apoptosis of HCC cell lines. The expression of MDR1 is detected by Realtime PCR. GFP tagged LC3 expression vector and electron microscopy are utilized to demonstrate the occurrence of autophagy.

RESULTS

We observed that the elevated PADI4 expression is associated with chemoresistance in HCC patients with TACE after surgery. In addition, we found that overexpression of PADI4 in HCC cell lines lead to the resistance to chemotherapeutic agents in vitro and in vivo. Interestingly, the HCC cells that overexpressed PADI4 were observed to undergo autophagy which was known as a protective mechanism for cells to resist the cell tosicity from chemotherapy. Autophagy inhibitor could effectively restore the sensitivity of HCC cells to chemotherapy in vitro and in vivo.

CONCLUSIONS

These results indicate that PADI4 may induce chemoresistance in HCC cells by leading autophagy.

Investigating citrullinated proteins in tumour cell lines

BACKGROUND

The conversion of arginine into citrulline, termed citrullination, has important consequences for the structure and function of proteins. Studies have found PADI4, an enzyme performing citrullination, to be highly expressed in a variety of malignant tumours and have shown that PADI4 participates in the process of tumorigenesis. However, as citrullinated proteins have not been systematically investigated in tumours, the present study aimed to identify novel citrullinated proteins in tumours by 2-D western blotting (2-D WB).

METHODS

Two identical two-dimensional electrophoresis (2-DE) gels were prepared using extracts from ECA, H292, HeLa, HEPG2, Lovo, MCF-7, PANC-1, SGC, and SKOV3 tumour cell lines. The expression profiles on a 2-DE gel were trans-blotted to PVDF membranes, and the blots were then probed with an anti-citrulline antibody. By comparing the 2-DE profile with the parallel 2-D WB profile at a global level, protein spots with immuno-signals were collected from the second 2-DE gel and identified using mass spectrometry. Immunoprecipitation was used to verify the expression and citrullination of the targeted proteins in tumour cell lines.

RESULTS

2-D WB and mass spectrometry identified citrullinated α-enolase (ENO1), heat shock protein 60 (HSP60), keratin 8 (KRT8), tubulin beta (TUBB), T cell receptor chain and vimentin in these cell lines. Immunoprecipitation analyses verified the expression and citrullination of ENO1, HSP60, KRT8, and TUBB in the total protein lysates of the tumour cell lines.

CONCLUSIONS

The citrullination of these proteins suggests a new mechanism in the tumorigenic process.

Folded Conformation, Cyclic Pentamer, Nano-Structure and PAD4 Binding Mode of YW3-56

The physical and chemical mechanisms of small molecules with pharmacological activity forming nano-structures are developing into a new field of nano-medicine. By using ROESY 2D NMR spectroscopy, trandem mass spectroscopy, transmission electron microscopy and computer-assisted molecular modeling, this paper demonstrated the contribution of the folded conformation, the intra- and intermolecular π-π stacking, the intra- and intermolecular hydrogen bonds, and the receptor binding free energy of 6-dimethylaminonaph-2-yl-{N-S-[1-benzylcarba-moyl-4-(2-chloroacetamidobutyl)]-carboxamide (YW3-56) to the rapid formation of nano-rings and the slow formation of nano-capsules. Thus we have developed a strategy that makes it possible to elucidate the physical and chemical mechanisms of bioactive small molecules forming nano-structures.

Anticancer peptidylarginine deiminase (PAD) inhibitors regulate the autophagy flux and the mammalian target of rapamycin complex 1 activity

Tumor suppressor genes are frequently silenced in cancer cells by enzymes catalyzing epigenetic histone modifications. The peptidylarginine deiminase family member PAD4 (also called PADI4) is markedly overexpressed in a majority of human cancers, suggesting that PAD4 is a putative target for cancer treatment. Here, we have generated novel PAD inhibitors with low micromolar IC(50) in PAD activity and cancer cell growth inhibition. The lead compound YW3-56 alters the expression of genes controlling the cell cycle and cell death, including SESN2 that encodes an upstream inhibitor of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. Guided by the gene expression profile analyses with YW3-56, we found that PAD4 functions as a corepressor of p53 to regulate SESN2 expression by histone citrullination in cancer cells. Consistent with the mTORC1 inhibition by SESN2, the phosphorylation of its substrates including p70S6 kinase (p70S6K) and 4E-BP1 was decreased. Furthermore, macroautophagy is perturbed after YW3-56 treatment in cancer cells. In a mouse xenograft model, YW3-56 demonstrates cancer growth inhibition activity with little if any detectable adverse effect to vital organs, whereas a combination of PAD4 and histone deacetylase inhibitors further decreases tumor growth. Taken together, our work found that PAD4 regulates the mTORC1 signaling pathway and that PAD inhibitors are potential anticancer reagents that activate tumor suppressor gene expression alone or in combination with histone deacetylase inhibitors.