Neutrophil-Derived Peptidyl Arginine Deiminase Activity Contributes to Pulmonary Emphysema by Enhancing Elastin Degradation.

In chronic obstructive pulmonary disease (COPD), inflammation gives rise to protease-mediated degradation of the key extracellular matrix protein, elastin, which causes irreversible loss of pulmonary function. Intervention against proteolysis has met with limited success in COPD, due in part to our incomplete understanding of the mechanisms that underlie disease pathogenesis. Peptidyl arginine deiminase (PAD) enzymes are a known modifier of proteolytic susceptibility, but their involvement in COPD in the lungs of affected individuals is underexplored. In this study, we showed that enzyme isotypes PAD2 and PAD4 are present in primary granules of neutrophils and that cells from people with COPD release increased levels of PADs when compared with neutrophils of healthy control subjects. By examining bronchoalveolar lavage and lung tissue samples of patients with COPD or matched smoking and nonsmoking counterparts with normal lung function, we reveal that COPD presents with markedly increased airway concentrations of PADs. Ex vivo, we established citrullinated elastin in the peripheral airways of people with COPD, and in vitro, elastin citrullination significantly enhanced its proteolytic degradation by serine and matrix metalloproteinases, including neutrophil elastase and matrix metalloprotease-12, respectively. These results provide a mechanism by which neutrophil-released PADs affect lung function decline, indicating promise for the future development of PAD-based therapeutics for preserving lung function in patients with COPD.

Iguratimod inhibits protein citrullination and inflammation by downregulating NBCe2 in patients with rheumatoid arthritis.

BACKGROUND: Bicarbonate has recently been identified as a crucial factor affecting peptidylarginine deiminase (PAD) activity; however, the mechanism underlying its role in rheumatoid arthritis (RA) remains unclear. Iguratimod (IGU), a small-molecule disease-modifying anti-rheumatic drug, requires further investigation. This study aimed to explore the mechanism by which bicarbonate affects citrullination and inflammation in RA and identify new targets for IGU. METHODS: We enrolled 20 patients with RA in the study. Sodium bicarbonate cotransporter 2 (NBCe2) was detected in the peripheral blood neutrophils and peripheral blood mononuclear cells (PBMCs) of these patients. The effects of varying concentrations of IGU, methotrexate (MTX), dexamethasone (DXM), and S0859 (an NBCe2 inhibitor) on NBCe2, PAD2, PAD4, and citrullinated histone H3 (cit-H3) levels in, migration ability of, and cytokine production from neutrophils and PBMCs were examined. RESULTS: Our findings showed that in patients with RA, citrullinated protein production by peripheral blood neutrophils instead of PBMCs, which showed higher NBCe2 expression levels, increased with an increase in the bicarbonate concentration. In addition, tumor necrosis factor-alpha (TNF-α) promoted NBCe2 expression in neutrophils from patients with RA. Furthermore, we revealed that the inhibitory effects of IGU on neutrophil NBCe2 and cit-H3 levels, degrees of inhibition of neutrophil and PBMC migration, and suppression of interleukin 6, TNF-α, and metalloproteinase-9 secretion from neutrophil-like differentiated HL-60 cells did not substantially differ from those of MTX, DXM, and S0859 at specific doses. CONCLUSIONS: Bicarbonate promotes protein citrullination and inflammation in RA via NBCe2, and IGU can downregulate NBCe2.

Delayed puberty, gonadotropin abnormalities and subfertility in male Padi2/Padi4 double knockout mice.

BACKGROUND: Peptidylarginine deiminase enzymes (PADs) convert arginine residues to citrulline in a process called citrullination or deimination. Recently, two PADs, PAD2 and PAD4, have been linked to hormone signaling in vitro and the goal of this study was to test for links between PAD2/PAD4 and hormone signaling in vivo. METHODS: Preliminary analysis of Padi2 and Padi4 single knockout (SKO) mice did not find any overt reproductive defects and we predicted that this was likely due to genetic compensation. To test this hypothesis, we created a Padi2/Padi4 double knockout (DKO) mouse model and tested these mice along with wild-type FVB/NJ (WT) and both strains of SKO mice for a range of reproductive defects. RESULTS: Controlled breeding trials found that male DKO mice appeared to take longer to have their first litter than WT controls. This tendency was maintained when these mice were mated to either DKO or WT females. Additionally, unsexed 2-day old DKO pups and male DKO weanlings both weighed significantly less than their WT counterparts, took significantly longer than WT males to reach puberty, and had consistently lower serum testosterone levels. Furthermore, 90-day old adult DKO males had smaller testes than WT males with increased rates of germ cell apoptosis. CONCLUSIONS: The Padi2/Padi4 DKO mouse model provides a new tool for investigating PAD function and outcomes from our studies provide the first in vivo evidence linking PADs with hormone signaling.

Molecular Mechanism of Protein Arginine Deiminase 2: A Study Involving Multiple Microsecond Long Molecular Dynamics Simulations.

Peptidylarginine deiminase 2 (PAD2) is a Ca2+-dependent enzyme that catalyzes the conversion of protein arginine residues to citrulline. This kind of structural modification in histone molecules may affect gene regulation, leading to effects that may trigger several diseases, including breast cancer, which makes PAD2 an attractive target for anticancer drug development. To design new effective inhibitors to control activation of PAD2, improving our understanding of the molecular mechanisms of PAD2 using up-to-date computational techniques is essential. We have designed five different PAD2-substrate complex systems based on varying protonation states of the active site residues. To search the conformational space broadly, multiple independent molecular dynamics simulations of the complexes have been performed. In total, 50 replica simulations have been performed, each of 1 µs, yielding a total simulation time of 50 µs. Our findings identify that the protonation states of Cys647, Asp473, and His471 are critical for the binding and localization of the N-α-benzoyl-l-arginine ethyl ester substrate within the active site. A novel mechanism for enzyme activation is proposed according to near attack conformers. This represents an important step in understanding the mechanism of citrullination and developing PAD2-inhibiting drugs for the treatment of breast cancer.

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.

Proximity-Dependent Labeling of Cysteines.

Mapping protein-protein interactions is crucial for understanding various signaling pathways in living cells, and developing new techniques for this purpose has attracted significant interest. Classic methods (e.g., the yeast two-hybrid) have been supplanted by more sophisticated chemical approaches that label proximal proteins (e.g., BioID, APEX). Herein we describe a proximity-based approach that uniquely labels cysteines. Our approach exploits the nicotinamide N-methyltransferase (NNMT)-catalyzed methylation of an alkyne-substituted 4-chloropyridine (SS6). Upon methylation of the pyridinium nitrogen, this latent electrophile diffuses out of the active site and labels proximal proteins on short time scales (≤5 min). We validated this approach by identifying known (and novel) interacting partners of protein arginine deiminase 2 (PAD2) and pyruvate dehydrogenase kinase 1 (PDK1). To our knowledge, this technology uniquely exploits a suicide substrate to label proximal cysteines in live cells.

Epitope-Based Chicken-Derived Novel Anti-PAD2 Monoclonal Antibodies Inhibit Citrullination.

The aberrant upregulation of protein arginine deiminase 2- (PAD2-) catalyzed citrullination is reported in various autoimmune diseases (rheumatoid arthritis and multiple sclerosis) and several cancers. Currently, there are no anti-PAD2 monoclonal antibodies (mAbs) that can inhibit the citrullination reaction. Here, an epitope 341YLNRGDRWIQDEIEFGY357 was examined as an antigenic site of PAD2. Chickens were immunized with this epitope, and the generated mAbs were screened for its reactivity against the full-length PAD2. Enzyme-linked immunosorbent assay revealed that six mAbs, which were screened from the phage display library, crossreacted with mouse PAD2. Kinetic analysis revealed that mAbs are bound to PAD2 in the nanomolar range, which indicated a strong binding. Results of the in vitro citrullination inhibition assay revealed that the half-maximal effective concentration values of mAbs for the inhibition of histone or benzoyl-L-arginine ethyl ester citrullination were in the range of 6-75 nM which supports strong inhibition capabilities. Alanine scanning of epitope revealed that the peptide fragment 344RGDRWIQDEIEF355 was responsible for generating strong antibody responses that inhibit the PAD2-catalyzed citrullination reaction. These antibodies can aid in understanding the extracellular PAD2 function and treating diseases associated with aberrant citrullination.

Peptidylarginine Deiminase Inhibitor Application, Using Cl-Amidine, PAD2, PAD3 and PAD4 Isozyme-Specific Inhibitors in Pancreatic Cancer Cells, Reveals Roles for PAD2 and PAD3 in Cancer Invasion and Modulation of Extracellular Vesicle Signatures.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive malignancies with limited survival rate. Roles for peptidylarginine deiminases (PADs) have been studied in relation to a range of cancers with roles in epigenetic regulation (including histone modification and microRNA regulation), cancer invasion, and extracellular vesicle (EV) release. Hitherto though, knowledge on PADs in PDAC is limited. In the current study, two PDAC cell lines (Panc-1 and MiaPaCa-2) were treated with pan-PAD inhibitor Cl-amidine as well as PAD2, PAD3, and PAD4 isozyme-specific inhibitors. Effects were assessed on changes in EV signatures, including EV microRNA cargo (miR-21, miR-126, and miR-221), on changes in cellular protein expression relevant for pancreatic cancer progression and invasion (moesin), for mitochondrial housekeeping (prohibitin, PHB), and gene regulation (deiminated histone H3, citH3). The two pancreatic cancer cell lines were found to predominantly express PAD2 and PAD3, which were furthermore expressed at higher levels in Panc-1, compared with MiaPaCa-2 cells. PAD2 isozyme-specific inhibitor had the strongest effects on reducing Panc-1 cell invasion capability, which was accompanied by an increase in moesin expression, which in pancreatic cancer is found to be reduced and associated with pancreatic cancer aggressiveness. Some reduction, but not significant, was also found on PHB levels while effects on histone H3 deimination were variable. EV signatures were modulated in response to PAD inhibitor treatment, with the strongest effects observed for PAD2 inhibitor, followed by PAD3 inhibitor, showing significant reduction in pro-oncogenic EV microRNA cargo (miR-21, miR-221) and increase in anti-oncogenic microRNA cargo (miR-126). While PAD2 inhibitor, followed by PAD3 inhibitor, had most effects on reducing cancer cell invasion, elevating moesin expression, and modulating EV signatures, PAD4 inhibitor had negligible effects and pan-PAD inhibitor Cl-amidine was also less effective. Compared with MiaPaCa-2 cells, stronger modulatory effects for the PAD inhibitors were observed in Panc-1 cells, which importantly also showed strong response to PAD3 inhibitor, correlating with previous observations that Panc-1 cells display neuronal/stem-like properties. Our findings report novel PAD isozyme regulatory roles in PDAC, highlighting roles for PAD isozyme-specific treatment, depending on cancer type and cancer subtypes, including in PDAC.

The roles of PAD2- and PAD4-mediated protein citrullination catalysis in cancers.

Peptidylarginine deiminases (PADs) catalyze the conversion of arginine residues to citrulline residues on target proteins in the presence of calcium ions. This elaborate type of posttranslational modification is termed citrullination. PADs may regulate gene transcriptional activity via histone citrullination. There has been an increasing appreciation for the roles of PADs in a wide variety of biological processes. In this review article, we summarize recent evidence indicating that PADs and citrullinated proteins are involved in several physiological and pathological processes related to cancer. Of particular interest is that PAD2 and PAD4 exhibit characteristic expression levels, activities and specific biological effects in diverse types of cancer. We also list several PAD inhibitors, propose the possible mechanisms underlying the biological actions of PAD-mediated protein citrullination in experimental models and discuss the potential therapeutic value of PADs and their inhibitors for disease diagnosis and treatment.

Angiogenic responses in a 3D micro-engineered environment of primary endothelial cells and pericytes.

Angiogenesis plays a key role in the pathology of diseases such as cancer, diabetic retinopathy, and age-related macular degeneration. Understanding the driving forces of endothelial cell migration and organization, as well as the time frame of these processes, can elucidate mechanisms of action of important pathological pathways. Herein, we have developed an organ-specific microfluidic platform recapitulating the in vivo angiogenic microenvironment by co-culturing mouse primary brain endothelial cells with brain pericytes in a three-dimensional (3D) collagen scaffold. As a proof of concept, we show that this model can be used for studying the angiogenic process and further comparing the angiogenic properties between two different common inbred mouse strains, C57BL/6J and 129S1/SvlmJ. We further show that the newly discovered angiogenesis-regulating gene Padi2 promotes angiogenesis through Dll4/Notch1 signaling by an on-chip mechanistic study. Analysis of the interplay between primary endothelial cells and pericytes in a 3D microfluidic environment assists in the elucidation of the angiogenic response.

The Essential Role of Peptidylarginine Deiminases 2 for Cytokines Secretion, Apoptosis, and Cell Adhesion in Macrophage.

OBJECTIVE: The study aims to investigate the functional roles of peptidylarginine deiminase 2 (PADI2) in macrophages. METHODS: The clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein-9 nuclease (Cas9) system was used to knockout PADI2 in U937 cells. U937 cells were introduced to differentiate macrophages and were stimulated with lipopolysaccharides (LPS). The protein expression of PADI2, PADI4, and citrullinated proteins were analyzed by Western blotting. The mRNA and protein levels of interleukin 1 beta (IL-1ß), IL-6, and tumor necrosis factor-alpha (TNF-α) were analyzed using RT-PCR and ELISA, respectively. Cell apoptosis was analyzed using flow cytometry. Cell adhesion assay was performed using a commercially available fibrinogen-coated plate. RESULTS: PADI2 knockout could markedly suppress the PADI2 protein expression, but not the PADI4 protein expression. PADI2 knockout decreased the protein levels of citrullinated nuclear factor κB (NF-κB) p65, but not those of citrullinated histone 3, resulting in the decreased mRNA expression levels of IL-1ß and TNF-α in the U937 cells and IL-1ß and IL-6 in the differentiated macrophages and the macrophages stimulated with LPS. The cytokines levels of IL-1ß, IL-6, and TNF-α were all dramatically decreased in the PADI2 knockout group compared with in the controls. PADI2 knockout prevented macrophages apoptosis via the decreased caspase-3, caspase-2, and caspase-9 activation. PADI2 knockout also impaired macrophages adhesion capacity through the decreased protein levels of focal adhesion kinase (FAK), phospho-FAK, paxillin, phospho-paxillin, and p21-activated kinase 1. CONCLUSION: This study showed that PADI2 could promote IL-1ß, IL-6, and TNF-α production in macrophages, promote macrophage apoptosis through caspase-3, caspase-2, and caspase-9 activation and enhance cell adhesion via FAK, paxillin, and PAK1. Therefore, targeting PADI2 could be used as a novel strategy for controlling inflammation caused by macrophages.

Citrullination Alters the Antiviral and Immunomodulatory Activities of the Human Cathelicidin LL-37 During Rhinovirus Infection.

Human rhinoviruses (HRV) are the most common cause of viral respiratory tract infections. While normally mild and self-limiting in healthy adults, HRV infections are associated with bronchiolitis in infants, pneumonia in immunocompromised patients, and exacerbations of asthma and COPD. The human cathelicidin LL-37 is a host defense peptide (HDP) with broad immunomodulatory and antimicrobial activities that has direct antiviral effects against HRV. However, LL-37 is known to be susceptible to the enzymatic activity of peptidyl arginine deiminases (PAD), and exposure of the peptide to these enzymes results in the conversion of positively charged arginines to neutral citrullines (citrullination). Here, we demonstrate that citrullination of LL-37 reduced its direct antiviral activity against HRV. Furthermore, while the anti-rhinovirus activity of LL-37 results in dampened epithelial cell inflammatory responses, citrullination of the peptide, and a loss in antiviral activity, ameliorates this effect. This study also demonstrates that HRV infection upregulates PAD2 protein expression, and increases levels of protein citrullination, including histone H3, in human bronchial epithelial cells. Increased PADI gene expression and HDP citrullination during infection may represent a novel viral evasion mechanism, likely applicable to a wide range of pathogens, and should therefore be considered in the design of therapeutic peptide derivatives.

Peptidylarginine Deiminase Isozyme-Specific PAD2, PAD3 and PAD4 Inhibitors Differentially Modulate Extracellular Vesicle Signatures and Cell Invasion in Two Glioblastoma Multiforme Cell Lines.

Glioblastoma multiforme (GBM) is an aggressive adult brain tumour with poor prognosis. Roles for peptidylarginine deiminases (PADs) in GBM have recently been highlighted. Here, two GBM cell lines were treated with PAD2, PAD3 and PAD4 isozyme-specific inhibitors. Effects were assessed on extracellular vesicle (EV) signatures, including EV-microRNA cargo (miR21, miR126 and miR210), and on changes in cellular protein expression relevant for mitochondrial housekeeping (prohibitin (PHB)) and cancer progression (stromal interaction molecule 1 (STIM-1) and moesin), as well as assessing cell invasion. Overall, GBM cell-line specific differences for the three PAD isozyme-specific inhibitors were observed on modulation of EV-signatures, PHB, STIM-1 and moesin protein levels, as well as on cell invasion. The PAD3 inhibitor was most effective in modulating EVs to anti-oncogenic signatures (reduced miR21 and miR210, and elevated miR126), to reduce cell invasion and to modulate protein expression of pro-GBM proteins in LN229 cells, while the PAD2 and PAD4 inhibitors were more effective in LN18 cells. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways for deiminated proteins relating to cancer, metabolism and inflammation differed between the two GBM cell lines. Our findings highlight roles for the different PAD isozymes in the heterogeneity of GBM tumours and the potential for tailored PAD-isozyme specific treatment.

Peptidyl Arginine Deiminase 2 (PADI2)-Mediated Arginine Citrullination Modulates Transcription in Cancer.

Protein arginine deimination leading to the non-coded amino acid citrulline remains a key question in the field of post-translational modifications ever since its discovery by Rogers and Simmonds in 1958. Citrullination is catalyzed by a family of enzymes called peptidyl arginine deiminases (PADIs). Initially, increased citrullination was associated with autoimmune diseases, including rheumatoid arthritis and multiple sclerosis, as well as other neurological disorders and multiple types of cancer. During the last decade, research efforts have focused on how citrullination contributes to disease pathogenesis by modulating epigenetic events, pluripotency, immunity and transcriptional regulation. However, our knowledge regarding the functional implications of citrullination remains quite limited, so we still do not completely understand its role in physiological and pathological conditions. Here, we review the recently discovered functions of PADI2-mediated citrullination of the C-terminal domain of RNA polymerase II in transcriptional regulation in breast cancer cells and the proposed mechanisms to reshape the transcription regulatory network that promotes cancer progression.

Iguratimod dose dependently inhibits the expression of citrullinated proteins and peptidylarginine deiminases 2 and 4 in neutrophils from rheumatoid arthritis patients.

INTRODUCTION: Anti-citrullinated protein antibodies (ACPAs) play an important role in rheumatoid arthritis (RA). Citrullinated proteins (CPs), which are produced by post-translational modification via peptidylarginine deiminase (PAD), are the target antigen of ACPAs and promote the generation thereof. Herein, we investigated whether iguratimod (IGU) affects the generation of CPs via PAD. METHODS: Neutrophils and peripheral blood mononuclear cells (PBMCs) were isolated from three patients diagnosed with RA and treated with various concentrations of IGU, methotrexate (MTX), or dexamethasone (DXM) or without any drugs as a control for 8 h. The levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1ß, IL-6, and IL-8 in culture supernatants were tested by ELISA. CPs were measured by western blot, and the expression of PAD2 and PAD4 in cells was detected by qRT-PCR and western blot. RESULTS: PAD2 and PAD4 expressions in neutrophils but not in PBMCs were decreased by IGU at both the protein and mRNA levels (P < 0.05). CP expression in neutrophils but not in PBMCs was also inhibited by IGU. The inhibitory effect of IGU was dose-dependent. IGU, MTX, and DXM dose dependently decreased the secretion of TNF-α, IL-1ß, IL-6, and IL-8 in neutrophils and PBMCs (P < 0.05); the inhibitory effect of IGU was not significantly different from that of MTX and DXM. CONCLUSIONS: IGU inhibited the expression of CPs by downregulating PADs in neutrophils from RA patients, and the effect was comparable to that of MTX and DXM at appropriate concentrations. These findings may provide guidance for more appropriate treatment of RA.Key Points• Iguratimod inhibited citrullinated protein expression in neutrophils from rheumatoid arthritis patients similarly to methotrexate and dexamethasone at appropriate concentrations.• The inhibitory effect was mediated by downregulation of peptidylarginine deiminases, providing insight into the mechanism of iguratimod as a treatment for rheumatoid arthritis.• This study may guide rheumatoid arthritis treatment and facilitate identification of other therapeutic targets.

Peptidyl Arginine Deiminase, Type II (PADI2) Is Involved in Urothelial Bladder Cancer.

Peptidyl arginine deiminase, type II (PADI2) expression has been shown to potentiate multiple different carcinogenesis pathway including breast carcinoma and spontaneous skin neoplasia. The objective of this study was to examine the role of PADI2 in urothelial bladder cancer which has not been evaluated previously. Analysis of mutation and genome amplification of bladder cancer within The Cancer Genome Atlas (TCGA) showed that PADI2 is both mutated and amplified in a cohort of bladder cancer patients, with the largest number of mutations detected in urothelial bladder cancer. Even though PADI2 expression was not significantly correlated to survival in bladder cancer patients, it was significantly overexpressed at the mRNA and protein levels, as revealed by TCGA data and immunohistochemistry analysis, respectively. PADI2 showed wide expression pattern in bladder cancer tissues but was hardly detected in tumor adjacent normal tissue. RNAi mediated silencing of PADI2 in the bladder cancer cell line T24 did not result in a change of proliferation. Interestingly knockdown of PADI2 expression did not affect Snail1 protein, which is associated with metastatic progression, in these cells. However, PADI2 silencing remarkably attenuated both in vitro migration and invasion- in T24 cells indicating a Snail1-independent effect of PADI2 on invasive potential of urothelial bladder cancer. This was further corroborated by in vivo xenograft assays where PADI2 shRNA harboring T24 cells did not have detectable tumors by week 4 as compared to robust tumors in the control Luciferase shRNA harboring cells. PADI2 silencing did not affect proliferation rates and hence this would suggest that PADI2 knockdown is perhaps causing increased apoptosis as well as transition through the cell cycle, which needs to be confirmed in future studies. Our results reveal a yet undefined role of PADI2 as an oncogene in urothelial bladder cancer.

Inhibiting PAD2 enhances the anti-tumor effect of docetaxel in tamoxifen-resistant breast cancer cells.

BACKGROUND: Tamoxifen resistance presents a huge clinical challenge for breast cancer patients. An understanding of the mechanisms of tamoxifen resistance can guide development of efficient therapies to prevent drug resistance. METHODS: We first tested whether peptidylarginine deiminase 2 (PAD2) may be involved in tamoxifen-resistance in breast cancer cells. The effect of depleting or inhibiting PAD2 in tamoxifen-resistant MCF-7 (MCF7/TamR) cells was evaluated both in vitro and in vivo. We then investigated the potential of Cl-amidine, a PAD inhibitor, to be used in combination with tamoxifen or docetaxel, and further explored the mechanism of the synergistic and effective drug regimen of PADs inhibitor and docetaxel on tamoxifen-resistant breast cancer cells. RESULTS: We report that PAD2 is dramatically upregulated in tamoxifen-resistant breast cancer. Depletion of PAD2 in MCF7/TamR cells facilitated the sensitivity of MCF7/TamR cells to tamoxifen. Moreover, miRNA-125b-5p negatively regulated PAD2 expression in MCF7/TamR cells, therefore overexpression of miR-125b-5p also increased the cell sensitivity to tamoxifen. Furthermore, inhibiting PAD2 with Cl-amidine not only partially restored the sensitivity of MCF7/TamR cells to tamoxifen, but also more efficiently enhanced the efficacy of docetaxel on MCF7/TamR cells with lower doses of Cl-amidine and docetaxel both in vivo and in vivo. We then showed that combination treatment with Cl-amidine and docetaxel enhanced p53 nuclear accumulation, which synergistically induced cell cycle arrest and apoptosis. Meanwhile, p53 activation in the combination treatment also accelerated autophagy processes by synergistically decreasing the activation of Akt/mTOR signaling, thus enhancing the inhibition of proliferation. CONCLUSION: Our results suggest that PAD2 functions as an important new biomarker for tamoxifen-resistant breast cancers and that inhibiting PAD2 combined with docetaxel may offer a new approach to treatment of tamoxifen-resistant breast cancers.

Differential Expression of TOM34, AL1A1, PADI2 and KLRBA in NNK Induced Lung Cancer in Wistar Rats and their Implications.

BACKGROUND: Lung cancer is the most common cancer with a high mortality rate. The diagnosis only at advanced stages and lack of effective treatment are the main factors responsible for high mortality. Tobacco smoke is the major responsible factor for inflammation and tumor development in lungs. OBJECTIVE: The present study was carried out to identify differentially expressed proteins and elucidate their role in carcinogenesis. METHODS: The lung cancer was developed in Wistar rats by using NNK as carcinogen and cancer development was confirmed by histopathological examination. The 2D SDS PAGE was used to analyse total proteins and find out differentially expressed proteins in NNK treated lung tissue vis-a-vis control tissue. The findings of proteomic analysis were further validated by quantification of corresponding transcripts using Real Time PCR. Finally, Cytoscape was used to find out protein-protein interaction. RESULTS: The histopathological examinations showed neoplasia at 9th month after NNK treatment. The proteomic analysis revealed several differentially expressed proteins, four of which were selected for further studies. (TOM34, AL1A1, PADI2 and KLRBA) that were up regulated in NNK treated lung tissue. The real time analysis showed over expression of the genes coding for the selected proteins. Thus, the proteomic and transcriptomic data corroborate each other. Further, these proteins showed interaction with the members of NF-κB family and STAT3. CONCLUSION: We conclude that these proteins play a substantial role in the induction of lung cancer through NF-κB and STAT3 pathway. Therefore, these may have the potential to be used as therapeutic targets and for early detection of lung cancer.

Neutrophil extracellular traps, B cells, and type I interferons contribute to immune dysregulation in hidradenitis suppurativa.

Hidradenitis suppurativa (HS), also known as acne inversa, is an incapacitating skin disorder of unknown etiology manifested as abscess-like nodules and boils resulting in fistulas and tissue scarring as it progresses. Given that neutrophils are the predominant leukocyte infiltrate in HS lesions, the role of neutrophil extracellular traps (NETs) in the induction of local and systemic immune dysregulation in this disease was examined. Immunofluorescence microscopy was performed in HS lesions and detected the prominent presence of NETs. NET complexes correlated with disease severity, as measured by Hurley staging. Neutrophils from the peripheral blood of patients with HS peripheral also displayed enhanced spontaneous NET formation when compared to healthy control neutrophils. Sera from patients recognized antigens present in NETs and harbored increased antibodies reactive to citrullinated peptides. B cell dysregulation, as evidenced by elevated plasma cells and IgG, was observed in the circulation and skin from patients with HS. Peptidylarginine deiminases (PADs) 1 to 4, enzymes involved in citrullination, were differentially expressed in HS skin, when compared to controls, in association with enhanced tissue citrullination. NETs in HS skin coexisted with plasmacytoid dendritic cells, in association with a type I interferon (IFN) gene signature. Enhanced NET formation and immune responses to neutrophil and NET-related antigens may promote immune dysregulation and contribute to inflammation. This, along with evidence of up-regulation of the type I IFN pathway in HS skin, suggests that the innate immune system may play important pathogenic roles in this disease.

Calcium Regulates the Nuclear Localization of Protein Arginine Deiminase 2.

Protein arginine deiminases (PADs) are calcium-dependent enzymes that mediate the post-translational conversion of arginine into citrulline. Dysregulated PAD activity is associated with numerous autoimmune disorders and cancers. In breast cancer, PAD2 citrullinates histone H3R26 and activates the transcription of estrogen receptor target genes. However, PAD2 lacks a canonical nuclear localization sequence, and it is unclear how this enzyme is transported into the nucleus. Here, we show for the first time that PAD2 translocates into the nucleus in response to calcium signaling. Using BioID2, a proximity-dependent biotinylation method for identifying interacting proteins, we found that PAD2 preferentially associates with ANXA5 in the cytoplasm. Binding of calcium to PAD2 weakens this cytoplasmic interaction, which generates a pool of calcium-bound PAD2 that can interact with Ran. We hypothesize that this latter interaction promotes the translocation of PAD2 into the nucleus. These findings highlight a critical role for ANXA5 in regulating PAD2 and identify an unusual mechanism whereby proteins translocate between the cytosol and nucleus.