A Novel Citrullinated Modification of Histone 3 and Its Regulatory Mechanisms Related to IPO-38 Antibody-Labeled Protein

Role of non-canonical post-translational modifications in gastrointestinal tumors

Post-translational modifications (PTMs) of proteins contribute to the occurrence and development of tumors. Previous studies have suggested that canonical PTMs such as ubiquitination, glycosylation, and phosphorylation are closely implicated in different aspects of gastrointestinal tumors. Recently, emerging evidence showed that non-canonical PTMs play an essential role in the carcinogenesis, metastasis and treatment of gastrointestinal tumors. Therefore, we summarized recent advances in sumoylation, neddylation, isoprenylation, succinylation and other non-canonical PTMs in gastrointestinal tumors, which comprehensively describe the mechanisms and functions of non-classical PTMs in gastrointestinal tumors. It is anticipated that targeting specific PTMs could benefit the treatment as well as improve the prognosis of gastrointestinal tumors.

Chemical Biology Approaches to Identify and Profile Interactors of Chromatin Modifications

In eukaryotes, DNA is packaged with histone proteins in a complex known as chromatin. Both the DNA and histone components of chromatin can be chemically modified in a wide variety of ways, resulting in a complex landscape often referred to as the "epigenetic code". These modifications are recognized by effector proteins that remodel chromatin and modulate transcription, translation, and repair of the underlying DNA. In this Review, we examine the development of methods for characterizing proteins that interact with these histone and DNA modifications. "Mark first" approaches utilize chemical, peptide, nucleosome, or oligonucleotide probes to discover interactors of a specific modification. "Reader first" approaches employ arrays of peptides, nucleosomes, or oligonucleotides to profile the binding preferences of interactors. These complementary strategies have greatly enhanced our understanding of how chromatin modifications effect changes in genomic regulation, bringing us ever closer to deciphering this complex language.

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.

Inducement of ER Stress by PAD Inhibitor BB-Cl-Amidine to Effectively Kill AML Cells

OBJECTIVE

Acute myeloid leukemia (AML) is a highly heterogeneous and recurrent hematological malignancy. Despite the emergence of novel chemotherapy drugs, AML patients' complete remission (CR) remains unsatisfactory. Consequently, it is imperative to discover new therapeutic targets or medications to treat AML. Such epigenetic changes like DNA methylation and histone modification play vital roles in AML. Peptidylarginine deminase (PAD) is a protein family of histone demethylases, among which the PAD2 and PAD4 expression have been demonstrated to be elevated in AML patients, thus suggesting a potential role of PADs in the development or maintenance of AML and the potential for the identification of novel therapeutic targets.

METHODS

AML cells were treated in vitro with the pan-PAD inhibitor BB-Cl-Amidine (BB-Cl-A). The AML cell lines were effectively induced into apoptosis by BB-Cl-A. However, the PAD4-specific inhibitor GSK484 did not.

RESULTS

PAD2 played a significant role in AML. Furthermore, we found that BB-Cl-A could activate the endoplasmic reticulum (ER) stress response, as evidenced by an increase in phosphorylated PERK (p-PERK) and eIF2α (p-eIF2α). As a result of the ER stress activation, the BB-Cl-A effectively induced apoptosis in the AML cells.

CONCLUSION

Our findings indicated that PAD2 plays a role in ER homeostasis maintenance and apoptosis prevention. Therefore, targeting PAD2 with BB-Cl-A could represent a novel therapeutic strategy for treating AML.

Detection of salivary citrullinated cytokeratin 13 in healthy individuals and patients with rheumatoid arthritis by proteomics analysis

The immune response to citrullinated peptides in the mucosa has been suggested to play an important role in the transition from pre-onset rheumatoid arthritis (RA) to clinically evident RA. Although there are reports indicating the presence of anti-citrullinated peptide antibodies in the saliva, few studies have reported citrullinated peptide detection in human saliva. This study aimed to identify citrullinated peptides in human saliva and discuss their clinical significance. Saliva samples were collected from 11 patients with RA and from 20 healthy individuals. Citrullinated peptides were detected using an anti-modified citrulline (AMC) antibody. Saliva from the healthy individuals was subjected to two-dimensional protein electrophoresis to isolate citrullinated peptides, which were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and mass spectrometry by peptide mass fingerprinting. The results were corroborated by immunoprecipitation (IP)-western blotting. The signal intensities of the bands precipitated with anti-cytokeratin 13 (CK13) and AMC antibodies were quantified. The signal intensity ratio of the band produced by the AMC antibody was divided by that of the band produced by the anti-CK13 antibody to calculate the citrullinated CK13 (Cit-CK13) ratio. A citrullinated peptide band corresponding to a molecular weight of approximately 50 kDa was detected in the saliva of healthy individuals, and identified as CK13 via mass spectrometry and IP-western blotting. No significant difference was observed between the salivary Cit-CK13 ratios of patients with RA and healthy participants (p = 0.605). This is the first study to show that Cit-CK13 is present in human saliva, and that there is no significant difference between the Cit-CK13 ratios of patients with RA and healthy individuals, suggesting that salivary Cit-CK13 content and RA development may not be associated. The physiological and pathological roles of Cit-CK13 in the oral cavity, and its responsiveness to mucosal immunity, remain unknown and will be the subject of further investigation.

Histone citrullination: a new target for tumors

As the main protein components of chromatin, histones play central roles in gene regulation as spools of winding DNA. Histones are subject to various modifications, including phosphorylation, acetylation, glycosylation, methylation, ubiquitination and citrullination, which affect gene transcription. Histone citrullination, a posttranscriptional modification catalyzed by peptidyl arginine deiminase (PAD) enzymes, is involved in human carcinogenesis. In this study, we highlighted the functions of histone citrullination in physiological regulation and tumors. Additionally, because histone citrullination involves forming neutrophil extracellular traps (NETs), the relationship between NETs and tumors was illustrated. Finally, the clinical application of histone citrullination and PAD inhibitors was discussed.

Genetic Profiles Affect the Biological Effects of Serine on Gastric Cancer Cells

A high serine content in body fluid was identified in a portion of patients with gastric cancer, but its biological significance was not clear. Here, we investigated the biological effect of serine on gastric cancer cells. Serine was added into the culture medium of MGC803 and HGC27 cancer cells, and its influence on multiple biological functions, such as cell growth, migration and invasion, and drug resistance was analyzed. We examined the global transcriptomic profiles in these cultured cells with high serine content. Both MGC803 and HGC27 cell lines were originated from male patients, however, their basal gene expression patterns were very different. The finding of cell differentiation-associated genes, ALPI, KRT18, TM4SF1, KRT81, A2M, MT1E, MUC16, BASP1, TUSC3, and PRSS21 in MGC803 cells suggested that this cell line was more poorly differentiated, compared to HGC27 cell line. When the serine concentration was increased to 150mg/ml in medium, the response of these two gastric cancer cell lines was different, particularly on cell growth, cell migration, and invasion and 5-FU resistance. In animal experiment, administration of high concentration of serine promoted cancer cell metastasis to local lymph node. Taken together, we characterized the basal gene expressing profiles of MGC803 and HGC27. The HGC27 cells were more differentiated than MGC803 cells. MGC803 cells were more sensitive to the change of serine content. Our results suggested that the responsiveness of cancer cells to microenvironmental change is associated with their genetic background.

PADI4 modulates the invasion and migration of osteosarcoma cells by down-regulation of epithelial-mesenchymal transition

Osteosarcoma (OS) is the most common type of primary bone malignancy with high recurrence and metastasis. Peptidylarginine deiminase 4 (PADI4), as an important protein post-translational modification enzyme, has been identified as a potential regulator in the invasion and migration in several types of tumors. The role of PADI4 in osteosarcoma metastasis remains unknown. In this study, we revealed significant positive correlation between PADI4 and pulmonary metastasis of osteosarcoma. Wound-healing and transwell assay indicated that PADI4 induced invasion and migration of osteosarcoma cell in vitro while PADI4 inhibitor has repressive effect. PADI4 mutation with no deimination activity exhibited no significant effect on invasion and migration of osteosarcoma cells. Moreover, we evaluated the effect of PADI4 on expression of the markers of epithelial-mesenchymal transition and results showed that PADI4 promoted EMT while PADI4 inhibitor suppressed EMT in osteosarcoma cells. We also detected the expression of PADI4 and E-Cadherin in the tissues of osteosarcoma patients with or without pulmonary metastasis. Results showed positive relationship between the expression of PADI4 and osteosarcoma metastasis. In contrast, the expression of E-Cadherin exhibited negative correlation with PADI4 and osteosarcoma metastasis. Our research offered a novel link between PADI4 and osteosarcoma metastasis and demonstrated PADI4 as a promising target for treatment of osteosarcoma metastasis.