Mitochondria-rich normal, metaplastic, and neoplastic cells show overexpression of the epitope H recognized by the monoclonal antibody H

Roles of O-GlcNAcylation in Mitochondrial Homeostasis and Cardiovascular Diseases

Protein posttranslational modifications are important factors that mediate the fine regulation of signaling molecules. O-linked β-N-acetylglucosamine-modification (O-GlcNAcylation) is a monosaccharide modification on N-acetylglucosamine linked to the hydroxyl terminus of serine and threonine of proteins. O-GlcNAcylation is responsive to cellular stress as a reversible and posttranslational modification of nuclear, mitochondrial and cytoplasmic proteins. Mitochondrial proteins are the main targets of O-GlcNAcylation and O-GlcNAcylation is a key regulator of mitochondrial homeostasis by directly regulating the mitochondrial proteome or protein activity and function. Disruption of O-GlcNAcylation is closely related to mitochondrial dysfunction. More importantly, the O-GlcNAcylation of cardiac proteins has been proven to be protective or harmful to cardiac function. Mitochondrial homeostasis is crucial for cardiac contractile function and myocardial cell metabolism, and the imbalance of mitochondrial homeostasis plays a crucial role in the pathogenesis of cardiovascular diseases (CVDs). In this review, we will focus on the interactions between protein O-GlcNAcylation and mitochondrial homeostasis and provide insights on the role of mitochondrial protein O-GlcNAcylation in CVDs.

The O-Linked N-Acetylglucosamine Containing Epitope H (O-GlcNAcH) is Upregulated in the Trophoblastic and Downregulated in the Fibroblastic Cells in Missed Miscarriage Human Chorionic Villi With Simple Hydropic Degeneration

Epitope H contains an O-linked N-acetylglucosamine (O-GlcNAcH) residue in a specific conformation and/or environment recognized by the mouse monoclonal antibody H. O-GlcNAcH is present in several types of cells and in several polypeptides, including cytokeratin 8 and vimentin, on the latter in cells under stress. In the present work, we examined the expression of the O-GlcNAcH in 60 cases of endometrial curettings from missed miscarriage cases containing normal and simple hydropic degenerated chorionic villi in each case, using monoclonal antibody H and indirect immunoperoxidase and Western blot immunoblot. In all cases examined the expression of the O-GlcNAcH was cytoplasmic as follows: (1) syncytiotrophoblastic cells showed very low expression in chorionic villi (CV) with nonhydropic degeneration (NHD) and high expression in hydropic degenerated (HD) CV; (2) cytotrophoblastic cells showed low expression in CV with NHD and high expression in HD CV; (3) fibroblastic cells showed high expression in CV with NHD and very low expression in HD CV; (4) histiocytes showed very low expression in both types of CV; (5) endothelial cells showed high expression in both types of CV. An immunoblot of CV from one case of a legal abortion from a normal first-trimester pregnancy showed 5 polypeptides with 118.5, 106.3, 85, 53, and 36.7 kD bearing the epitope H and the 53 kD corresponded to cytokeratin 8. The expression of the O-GlcNAcH is upregulated in the trophoblastic cells and downregulated in the fibroblastic cells in the HD CV in comparison to the NHD CV.

O-GlcNAcylation is a key regulator of multiple cellular metabolic pathways

O-GlcNAcylation modifies proteins in serine or threonine residues in the nucleus, cytoplasm, and mitochondria. It regulates a variety of cellular biological processes and abnormal O-GlcNAcylation is associated with diabetes, cancer, cardiovascular disease, and neurodegenerative diseases. Recent evidence has suggested that O-GlcNAcylation acts as a nutrient sensor and signal integrator to regulate metabolic signaling, and that dysregulation of its metabolism may be an important indicator of pathogenesis in disease. Here, we review the literature focusing on O-GlcNAcylation regulation in major metabolic processes, such as glucose metabolism, mitochondrial oxidation, lipid metabolism, and amino acid metabolism. We discuss its role in physiological processes, such as cellular nutrient sensing and homeostasis maintenance. O-GlcNAcylation acts as a key regulator in multiple metabolic processes and pathways. Our review will provide a better understanding of how O-GlcNAcylation coordinates metabolism and integrates molecular networks.

O-GlcNAc stabilizes SMAD4 by inhibiting GSK-3β-mediated proteasomal degradation

O-linked β-N-acetylglucosamine (O-GlcNAc) is a post-translational modification which occurs on the hydroxyl group of serine or threonine residues of nucleocytoplasmic proteins. It has been reported that the presence of this single sugar motif regulates various biological events by altering the fate of target proteins, such as their function, localization, and degradation. This study identified SMAD4 as a novel O-GlcNAc-modified protein. SMAD4 is a component of the SMAD transcriptional complex, a major regulator of the signaling pathway for the transforming growth factor-β (TGF-β). TGF-β is a powerful promoter of cancer EMT and metastasis. This study showed that the amount of SMAD4 proteins changes according to cellular O-GlcNAc levels in human lung cancer cells. This observation was made based on the prolonged half-life of SMAD4 proteins. The mechanism behind this interaction was that O-GlcNAc impeded interactions between SMAD4 and GSK-3β which promote proteasomal degradation of SMAD4. In addition, O-GlcNAc modification on SMAD4 Thr63 was responsible for stabilization. As a result, defects in O-GlcNAcylation on SMAD4 Thr63 attenuated the reporter activity of luciferase, the TGF-β-responsive SMAD binding element (SBE). This study’s findings imply that cellular O-GlcNAc may regulate the TGF-β/SMAD signaling pathway by stabilizing SMAD4.

Expression of cell adhesion molecule 1 in gastric neck and base glandular cells: Possible involvement in peritoneal dissemination of signet ring cells

AIMS

To determine cellular distribution of cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member, in the human oxyntic gastric mucosa, and to explore possible involvement in the development and peritoneal dissemination of signet ring cell (SRC) gastric carcinoma, which often develops in the oxyntic mucosa.

MAIN METHODS

Immunohistochemistry and double immunofluorescence were conducted on surgical specimens of normal and SRC-bearing stomachs and peritoneal metastatic foci of SRCs. KATO-III (lacking CADM1) and HSC-43 (expressing CADM1) SRC cell lines were cocultured on a Met-5A mesothelial or TIG-1 fibroblastic cell monolayer.

KEY FINDINGS

In the oxyntic gland, some neck and nearly all base glandular cells were CADM1-positive, and mucin 5AC-positive cells were CADM1-negative, while some mucin 6-positive neck cells were CADM1-positive. Foveolar-epithelial, parietal, and endocrine cells were CADM1-negative. CADM1 was negative in all SRC carcinomas that were confined within the submucosa (n = 11) and all but one of those invading deeper (n = 15). In contrast, peritoneal metastatic foci of SRCs were CADM1-positive in five out of eleven cases (P < 0.01). In the cocultures, exogenous CADM1 made KATO-III cells adhere more and grow faster on a Met-5A monolayer, not on TIG-1 monolayers. HSC-43 cells adhered more and grew faster on Met-5A than on TIG-1 monolayers, which were partly counteracted by a function-neutralizing anti-CADM1 antibody.

SIGNIFICANCE

Nearly all chief cells and a part of mucous neck cells express CADM1. SRC gastric carcinoma appears to emerge as a CADM1-negative tumor, but CADM1 may help SRCs develop peritoneal dissemination through promoting their adhesion and growth in the serosal tissue.

O-GlcNAc in cancer: An Oncometabolism-fueled vicious cycle

Cancer cells exhibit unregulated growth, altered metabolism, enhanced metastatic potential and altered cell surface glycans. Fueled by oncometabolism and elevated uptake of glucose and glutamine, the hexosamine biosynthetic pathway (HBP) sustains glycosylation in the endomembrane system. In addition, the elevated pools of UDP-GlcNAc drives the O-GlcNAc modification of key targets in the cytoplasm, nucleus and mitochondrion. These targets include transcription factors, kinases, key cytoplasmic enzymes of intermediary metabolism, and electron transport chain complexes. O-GlcNAcylation can thereby alter epigenetics, transcription, signaling, proteostasis, and bioenergetics, key 'hallmarks of cancer'. In this review, we summarize accumulating evidence that many cancer hallmarks are linked to dysregulation of O-GlcNAc cycling on cancer-relevant targets. We argue that onconutrient and oncometabolite-fueled elevation increases HBP flux and triggers O-GlcNAcylation of key regulatory enzymes in glycolysis, Kreb's cycle, pentose-phosphate pathway, and the HBP itself. The resulting rerouting of glucose metabolites leads to elevated O-GlcNAcylation of oncogenes and tumor suppressors further escalating elevation in HBP flux creating a 'vicious cycle'. Downstream, elevated O-GlcNAcylation alters DNA repair and cellular stress pathways which influence oncogenesis. The elevated steady-state levels of O-GlcNAcylated targets found in many cancers may also provide these cells with a selective advantage for sustained growth, enhanced metastatic potential, and immune evasion in the tumor microenvironment.

Detection of O-Linked-N-Acetylglucosamine Modification and Its Associated Enzymes in Human Degenerated Intervertebral Discs

Study Design

Human herniated discs were obtained from discectomy specimens for the immunohistochemical detection of O-GlcNAc and O-GlcNAcase (OGA)/O-GlcNAc transferase (OGT).

Purpose

This study aimed to quantify the extent of O-GlcNAcylation and its associated enzymes (OGT/OGA) in human degenerated intervertebral discs.

Overview of Literature

The O-GlcNAcylation of nuclear, cytoplasmic, and mitochondrial proteins as well as the effects of such post-translational modifications are currently the focus of extensive research. O-GlcNAcylation is believed to contribute to the etiology of chronic illnesses by acting as a nutrient and stress sensor in the cellular environment. Mature intervertebral disc cells are chondrocyte-like cells, and O-GlcNAc has been shown to promote chondrocyte apoptosis in vitro. We believe that O-GlcNAcylation is a key regulator of disc degeneration.

Methods

Fifty-six specimens were fixed for 24 hours in a 10% solution of neutral-buffered formaldehyde, dehydrated, and embedded in paraffin. Tissue slices (4-µm-thick) were used for hematoxylin-eosin staining and immunohistochemistry.

Results

We found that O-GlcNAcylation of cytoplasmic proteins was less than that of nuclear proteins in both single cells and cell clusters. Cytoplasmic O-GlcNAcylation occurs subsequent to nuclear O-GlcNAcylation and is directly proportional to disc degeneration. OGT and O-GlcNAc expression levels were identical in all specimens examined.

Conclusions

O-GlcNAc and OGA/OGT expression is shown to correlate for the first time with intervertebral disc cell degeneration. Increasing disc degeneration is associated with increasing O-GlcNAcylation in both nuclear and cytoplasmic proteins in human disc cells.

Hypoxia upregulates the expression of the O-linked N-acetylglucosamine containing epitope H in human ependymal cells

Epitope H contains an O-linked N-acetylglucosamine (O-GlcNAc) residue in a specific conformation and/or environment recognized by mouse IgM monoclonal antibody H (mabH). Epitope H is present in several types of cells and in several polypeptides outside the CNS. Previous results have shown that in the adult human brains, epitope H is confined mostly to a minority of fibrous astrocytes, and it is greatly upregulated in the reactive astrocytes. Post-translational modification with O-GlcNAc occurs on many proteins involved in several cell processes, such as cell cycle progression, apoptosis, proteasome degradation pathways, and modulation of cellular function in response to nutrition and stress. Hypoxia is one of the major causes of cellular stress. Therefore, in this study, we used the mAbH and the indirect immunoperoxidase method to investigate the expression of epitope H in ependymal cells in brains of persons who died with signs of hypoxic encephalopathy. The results of the present study showed that practically all ependymal cells showed cytoplasmic staining for epitope H in supranuclear cytoplasm in the brain of two premature neonates and in ten infants who died with signs of hypoxic encephalopathy. However, the overwhelming majority of ependymal cells of the nine human embryos taken from legal abortions, ranging from 26 days until 13 weeks of gestational age, and of the ten infants' brains without any sign of hypoxic encephalopathy remained negative. Only occasionally did the ependymal cells show weak cytoplasmic staining in some foci. In addition, the reactive astrocytes in the hypoxic brains showed strong cytoplasmic staining, confirming previous results.

The hexosamine signaling pathway: O-GlcNAc cycling in feast or famine

The enzymes of O-GlcNAc cycling couple the nutrient-dependent synthesis of UDP-GlcNAc to O-GlcNAc modification of Ser/Thr residues of key nuclear and cytoplasmic targets. This series of reactions culminating in O-GlcNAcylation of targets has been termed the hexosamine signaling pathway (HSP). The evolutionarily ancient enzymes of O-GlcNAc cycling have co-evolved with other signaling effecter molecules; they are recruited to their targets by many of the same mechanisms used to organize canonic kinase-dependent signaling pathways. This co-recruitment of the enzymes of O-GlcNAc cycling drives a binary switch impacting pathways of anabolism and growth (nutrient uptake) and catabolic pathways (nutrient sparing and salvage). The hexosamine signaling pathway (HSP) has thus emerged as a versatile cellular regulator modulating numerous cellular signaling cascades influencing growth, metabolism, cellular stress, circadian rhythm, and host-pathogen interactions. In mammals, the nutrient-sensing HSP has been harnessed to regulate such cell-specific functions as neutrophil migration, and activation of B-cells and T-cells. This review summarizes the diverse approaches being used to examine O-GlcNAc cycling. It will emphasize the impact O-GlcNAcylation has upon signaling pathways that may be become deregulated in diseases of the immune system, diabetes mellitus, cancer, cardiovascular disease, and neurodegenerative diseases.

Expression of the O-linked N-acetylglucosamine containing epitope H in normal myometrium and uterine smooth muscle cell tumors

Epitope H contains an O-linked N-acetylglucosamine (O-GlcNAc) residue in a specific conformation and/or environment recognized by monoclonal antibody H (mAbH). We have previously shown that epitope H is present in more than one polypeptide and in various types of normal and pathological cells. In the present study, we focused on uterine smooth muscle cell tumors and their adjacent normal myometrium to gain further insight into the expression patterns of epitope H in human tissues. The indirect immunoperoxidase method was applied using the mAbH and the monoclonal anti-cytokeratin 8 antibody (AbCK8) in 50 cases of typical uterine leiomyomas and in five cases of uterine leiomyosarcomas, with four cases belonging to Group II A and one to Group III according to Bell et al. [6]. Western immunoblotting was applied using mAbH and AbCK8 in five cases of uterine leiomyomas and their adjacent myometrium. The main results were as follows: (1) epitope H showed intense immunohistochemical expression in 46% (23/50) and moderate expression in 54% (27/50) of uterine leiomyomas, (2) epitope H showed intense immunohistochemical expression in 40% (2/5) and moderate expression in 60% (3/5) of uterine leiomyosarcomas, (3) epitope H showed no difference in the immunohistochemical expression between leiomyomas and their adjacent myometrium and between leiomyosarcomas and their adjacent myometrium, (4) immunohistochemical expression of cytokeratin 8 was not detected in the normal and neoplastic smooth muscle cells, (5) Western immunoblotting showed that in the smooth muscle cells of the myometrium and leiomyomas, epitope H is localized in four polypeptides with molecular weights of 100, 61, 59, and 54 kDa, and (6) Western immunoblotting did not detect cytokeratin 8 in the normal and neoplastic smooth muscle cells. The present results indicate fluctuations of the epitope expression levels in uterine smooth muscle cell tumors and their adjacent myometrium. These fluctuations may be of interest for gaining insight into the pathogenesis of uterine smooth muscle cell tumors, since O-GlcNAc glycosylation is involved in cell cycle and apoptosis pathways and may modify proteins involved in oncogenesis (tumor suppressor proteins and oncoproteins) and proteins with important biological functions such as cytoskeletal proteins, transcription factors, and heat-shock proteins. Furthermore, the present results indicate that cytokeratin 8, without being present in the cells of the myometrium, leiomyomas and leiomyosarcomas, shares its epitope H, which contains its unique sugar O-N-acetylglucosamine residue, with four other unrelated polypeptides produced by the normal and neoplastic smooth muscle cells. This should be considered when using anti-cytokeratin 8 antibodies in immunohistochemistry against smooth muscle cell tumors to avoid false positive immunohistochemical results.

Nuclear localization of cytokeratin 8 and the O-linked N-acetylglucosamine-containing epitope H in epithelial cells of infiltrating ductal breast carcinomas: a combination of immunogold and EDTA regressive staining methods

In a previous study, the authors have shown cytokeratin 8 (CK8) and epitope H ultrastructural localization in breast cancer cell nuclei. Epitope H contains an O-linked N-acetylglucosamine (O-GlcNAc) residue in a specific conformation and/or environment recognized by monoclonal antibody H. In this study, double immunogold labeling of CK8 and epitope H combined with the EDTA regressive staining method was applied in biopsy material from infiltrating ductal breast carcinomas and fibroadenomas, to localize both antigens in correlation to RNPs distribution in the nuclear subcompartments of cancer cells. CK8 and epitope H were localized mostly over condensed chromatin, whereas staining was weaker over interchromatin granule clusters and perichromatin fibers. These results revealed, the distribution of CK8 in the nucleus as MAR-binding protein, contributing in the organization of the nuclear DNA in the neoplastic cell, as well as the distribution of O-GlcNAc glycosylated polypeptides bearing the epitope H. The latter finding indicates that these polypeptides might play a significant role in the neoplastic behavior of breast cancer cells because they colocalize in the same nuclear subcompartments with proteins modified by O-GlcNAc, such as hnRNPs G and A1, RNA polymerase II, its transcription factors, and the oncogene product of c-myc. These proteins are known to participate in coordinated transcription/RNA processing events, contributing in the neoplastic behavior of breast cancer cells.

Cell signaling, the essential role of O-GlcNAc!

An increasing body of evidence points to a central regulatory role for glucose in mediating cellular processes and expands the role of glucose well beyond its traditional role(s) in energy metabolism. Recently, it has been recognized that one downstream effector produced from glucose is UDP-GlcNAc. Levels of UDP-GlcNAc, and the subsequent addition of O-linked beta-N-acetylglucosamine (O-GlcNAc) to Ser/Thr residues, is involved in regulating nuclear and cytoplasmic proteins in a manner analogous to protein phosphorylation. O-GlcNAc protein modification is essential for life in mammalian cells, highlighting the importance of this simple post-translational modification in basic cellular regulation. Recent research has highlighted key roles for O-GlcNAc serving as a nutrient sensor in regulating insulin signaling, the cell cycle, and calcium handling, as well as the cellular stress response.