Decreased alpha-1,4-linked N-acetylglucosamine glycosylation in biliary tract cancer progression from biliary intraepithelial neoplasia to invasive adenocarcinoma

Glycoproteomics of Gastrointestinal Cancers and Its Use in Clinical Diagnostics

Cancer is a leading cause of death worldwide, resulting in substantial economic costs. Because cancer is a complex, heterogeneous group of diseases affecting a variety of cells, its detection may sometimes be difficult. Herein we review a large group of the gastrointestinal cancers (oral, esophageal, stomach, pancreatic, liver, and bowel cancers) and the possibility of using glycans conjugated to protein backbones for less-invasive diagnoses than the commonly used endoscopic approaches. The reality of bacterial N-glycosylation and the effect of epithelial mucosa on gut microbiota are discussed. Current advantages, barriers, and advantages in the prospective use of selected glycomic approaches in clinical practice are also detailed.

Cell lineage-specific immunohistochemical markers in biliary intraepithelial neoplasia: Implications for subclassification and grading

Biliary intraepithelial neoplasia (BilIN), a precursor to cholangiocarcinoma, is categorized into low- and high-grade based on histological characteristics. Although gastric, intestinal, and biliary phenotypes of BilIN have been identified, detailed analyses of their immunophenotypic profiles using cell lineage-specific markers remain limited. This study aimed to define the immunohistochemical profiles of BilIN lesions, subclassify them based on their immunophenotypes, and correlate these profiles with histological grades. We examined 77 BilIN lesions from extrahepatic bile ducts, including 30 low- and 47 high-grade lesions, using immunohistochemical staining for gastric (claudin-18, MUC5AC), intestinal (cadherin-17, glycoprotein A33), and biliary (carbohydrate sulfotransferase 4) markers, along with progression markers (S100P, IMP3). Expression levels were semiquantitatively scored and correlated with histopathological features. BilIN lesions were classified into four immunophenotypes: gastric (G-type), intestinal (I-type), gastrointestinal (GI-type), and biliary (B-type). Low-grade lesions comprised G- (33.3 %), GI- (40 %), I- (13.3 %), and B-types (13.3 %), while high-grade lesions included G- (40.4 %), GI- (29.8 %), I- (21.3 %), and B-types (8.5 %). In low-grade BilIN, G-type lesions corresponded to gastric mucous cells, I-type to intestinal epithelial cells, and B-type to bile duct epithelial cells, while most GI-type lesions exhibited mixed G- and I-type components. High-grade BilIN differentiation based solely on histological characteristics was challenging to delineate due to overlapping features among I-, GI-, and B-type cells. S100P and IMP3 expression levels were significantly elevated in high-grade lesions, particularly within the I+B-type BilIN group, with no notable differences in G- or GI-type BilIN. Immunophenotypic profiling with lineage-specific markers effectively subclassified BilIN, enhancing the understanding of its histogenesis and progression.

Decreased expression of TFF2 and decreased αGlcNAc glycosylation are malignant biomarkers of pyloric gland adenoma of the duodenum

Pyloric gland adenoma (PGA) is a duodenal neoplasm expressing MUC6 and is often associated with high-grade dysplasia and adenocarcinoma. MUC6 secreted from the pyloric gland cells carries unique O-glycans exhibiting terminal α1,4-linked N-acetylglucosamine residues (αGlcNAc). The small peptide trefoil factor 2 (TFF2) is also secreted from pyloric gland cells and binds to αGlcNAc. We recently demonstrated that αGlcNAc serves as a tumor suppressor for gastric neoplasm including PGA, but the significance of TFF2 expression remains unknown. We examined 20 lesions representing low- and high-grade PGA in 22 cases by immunohistochemistry for αGlcNAc, TFF2, MUC6, MUC5AC, MUC2 and p53. αGlcNAc, TFF2 and MUC6 were co-expressed on the cell surface and a dot-like pattern in the cytosol in low-grade PGA lesions. High-grade PGA also expressed MUC6, but reduced αGlcNAc and TFF2 expression. The ratios of αGlcNAc or TFF2 to MUC6 score in high-grade PGA were significantly lower than low-grade PGA (P < 0.001). Co-expression of αGlcNAc-glycosylated MUC6 and TFF2 in PGA suggests the existence of αGlcNAc/TFF2 form complex in PGA cells, a finding consistent with our observations in non-neoplastic Brunner's gland cells. The decreased αGlcNAc and TFF2 expression are associated with high grade atypical cells, indicative of the malignant potential of PGA.

Heterogeneous murine peribiliary glands orchestrate compartmentalized epithelial renewal

The extrahepatic branches of the biliary tree have glands that connect to the surface epithelium through narrow pits. The duct epithelia undergo homeostatic renewal, yet the identity and multiplicity of cells that maintain this tissue is unknown. Using marker-free and targeted clonal fate mapping in mice, we provide evidence that the extrahepatic bile duct is compartmentalized. Pit cholangiocytes of extramural glands renewed the surface epithelium, whereas basally oriented cholangiocytes maintained the gland itself. In contrast, basally positioned cholangiocytes replenished the surface epithelium in mural glands. Single-cell sequencing identified genes enriched in the base and surface epithelial populations, with trajectory analysis showing graded gene expression between these compartments. Epithelia were plastic, changing cellular identity upon fasting and refeeding. Gain of canonical Wnt signaling caused basal cell expansion, gastric chief cell marker expression, and a decrease in surface epithelial markers. Our results identify the cellular hierarchy governing extrahepatic biliary epithelial renewal.

Stepwise progression of invasive mucinous adenocarcinoma based on radiological and biological characteristics

INTRODUCTION

Invasive mucinous lung adenocarcinoma (IMA) has unique radiological findings and pathological characteristics. IMA is classified into solitary and pneumonic types; however, it is unclear whether these are biologically identical.

METHODS

A single-center retrospective analysis was performed for 70 IMA patients (solitary type [n = 38] and pneumonic type [n = 32]) who underwent pulmonary resection between January 2010 and December 2018. We compared clinical and biological characteristics between the two types.

RESULTS

The frequencies of genetic alternations such as EGFR, KRAS, BRAF, GNAS, ERBB2, TP53, NRG1, and MET were not different. Immunohistochemically, expression of MUC1 was significantly more common in the pneumonic type (5.0% versus 20.0%, p = 0.01) and diffuse MUC6 positive in the solitary type (39.0% versus 13.0%, p = 0.02). We further classified solitary types into those with or without ground-glass opacity (GGO) and pneumonic types into those with or without crazy-paving appearance (CPA), and evaluated their surgical outcomes. Five-year overall survival and relapse free survival rates were 95.8%/86.6%, 64.3%/70.7%, 74.6%/68.9%, and 50.0%/28.6% in patients with solitary type with GGO, solitary type without GGO, pneumonic type without CPA, and pneumonic type with CPA, respectively.

CONCLUSIONS

There were no differences in genetic alternations; however, mucin expression pattern was different. Surgical outcomes were different according to the presence of GGO in the solitary type and the presence of CPA in the pneumonic type. These findings suggested a stepwise progression from solitary to pneumonic IMA.

Understanding the Clinical Significance of MUC5AC in Biliary Tract Cancers

Biliary tract cancers (BTC) arise from biliary epithelium and include cholangiocarcinomas or CCA (including intrahepatic (ICC) and extrahepatic (ECC)) and gallbladder cancers (GBC). They often have poor outcomes owing to limited treatment options, advanced presentations, frequent recurrence, and poor response to available systemic therapy. Mucin 5AC (MUC5AC) is rarely expressed in normal biliary epithelium, but can be upregulated in tissues of benign biliary disease, premalignant conditions (e.g., biliary intraepithelial neoplasia), and BTCs. This mucin's numerous glycoforms can be divided into less-glycosylated immature and heavily-glycosylated mature forms. Reported MUC5AC tissue expression in BTC varies widely, with some associations based on cancer location (e.g., perihilar vs. peripheral ICC). Study methods were variable regarding cancer subtypes, expression positivity thresholds, and MUC5AC glycoforms. MUC5AC can be detected in serum of BTC patients at high concentrations. The hesitancy in developing MUC5AC into a clinically useful biomarker in BTC management is due to variable evidence on the diagnostic and prognostic value. Concrete conclusions on tissue MUC5AC are difficult, but serum detection might be relevant for diagnosis and is associated with poor prognosis. Future studies are needed to further the understanding of the potential clinical value of MUC5AC in BTC, especially regarding predictive and therapeutic value.

Abnormal B cell glycosylation in autoimmunity: A new potential treatment strategy

Systemic lupus erythematosus (SLE) and primary Sjögren’s syndrome (pSS) are two autoimmune diseases characterised by the production of pathogenic autoreactive antibodies. Their aetiology is poorly understood. Nevertheless, they have been shown to involve several factors, such as infections and epigenetic mechanisms. They also likely involve a physiological process known as glycosylation. Both SLE T cell markers and pSS-associated autoantibodies exhibit abnormal glycosylation. Such dysregulation suggests that defective glycosylation may also occur in B cells, thereby modifying their behaviour and reactivity. This study aimed to investigate B cell subset glycosylation in SLE, pSS and healthy donors and to extend the glycan profile to serum proteins and immunoglobulins. We used optimised lectin-based tests to demonstrate specific glycosylation profiles on B cell subsets that were specifically altered in both diseases. Compared to the healthy donor B cells, the SLE B cells exhibited hypofucosylation, whereas only the pSS B cells exhibited hyposialylation. Additionally, the SLE B lymphocytes had more galactose linked to N-acetylglucosamine or N-acetylgalactosamine (Gal-GlcNAc/Gal-GalNAc) residues on their cell surface markers. Interestingly, some similar alterations were observed in serum proteins, including immunoglobulins. These findings indicate that any perturbation of the natural glycosylation process in B cells could result in the development of pathogenic autoantibodies. The B cell glycoprofile can be established as a preferred biomarker for characterising pathologies and adapted therapeutics can be used for patients if there is a correlation between the extent of these alterations and the severity of the autoimmune diseases.

α1,4-linked N-acetylglucosamine suppresses gastric cancer development by inhibiting MUC1-mediated signaling

Gastric cancer is the second leading cause of cancer deaths worldwide, and more understanding of its molecular basis is urgently needed. Gastric gland mucin secreted from pyloric gland cells, mucous neck cells, and cardiac gland cells of the gastric mucosa harbors unique O‐glycans carrying terminal α1,4‐linked N‐acetylglucosamine (αGlcNAc) residues. We previously reported that αGlcNAc loss correlated positively with poor outcomes for patients with differentiated‐type gastric cancer. However, the molecular mechanisms underlying these outcomes remained poorly understood. Here, we examined the effects of upregulated αGlcNAc expression on malignant phenotypes of the differentiated‐type gastric cancer cell lines, AGS and MKN7. Upregulation of αGlcNAc following ectopic expression of its biosynthetic enzyme attenuated cell proliferation, motility, and invasiveness of AGS and MKN7 cells in vitro. Moreover, AGS cell tumorigenicity was significantly suppressed by αGlcNAc overexpression in a xenograft model. To define the molecular mechanisms underlying these phenotypes, we investigated αGlcNAc binding proteins in AGS cells and identified Mucin‐1 (MUC1) and podocalyxin. Both proteins were colocalized with αGlcNAc on human gastric cancer cells. We also found that αGlcNAc was bound to MUC1 in murine normal gastric mucosa. When we assessed the effects of αGlcNAc binding to MUC1, we found that αGlcNAc blocked galectin‐3 binding to MUC1, phosphorylation of the MUC1 C‐terminus, and recruitment of Src and β‐catenin to that C‐terminus. These results suggest that αGlcNAc regulates cancer cell phenotypes by dampening MUC1 signal transduction.

MUC6 expression is a preferable prognostic marker for invasive mucinous adenocarcinoma of the lung

Gastric gland mucin consists of core protein MUC6 with residues heavily glycosylated by unique O-glycans carrying α1,4-linked N-acetylglucosamine (αGlcNAc). αGlcNAc-glycosylated MUC6 protein is seen in normal gastric and duodenal glands. Decreased αGlcNAc glycosylation on MUC6-positive tumor cells is often observed in premalignant lesions of the stomach, pancreas, and bile duct, and decreased MUC6 expression is seen in invasive cancer of these organs. Lung cancer (LC) is the most common cause of cancer death worldwide. Recently, the adenocarcinoma subtype has become the most common histological subtype of LC, and one of its invasive forms is invasive mucinous adenocarcinoma (IMA). Currently, prognostic markers of LC IMA are unknown. Here, we analyzed MUC5AC, MUC6, and αGlcNAc expression in 54 IMA LC cases. MUC5AC was positively expressed in 50 (93%), MUC6 in 38 (70%), and αGlcNAc in 19 (35%). Each expression level was scored from 0 to 3. The αGlcNAc expression score was significantly decreased relative to MUC6 (P < 0.001). Interestingly, disease-free survival was significantly higher in MUC6-positive than MUC6-negative cases based on the log-rank test (P = 0.021). For in vitro analysis, we ectopically expressed MUC6 in A549 cells, derived from LC and harboring a KRAS mutation. MUC6-expressing A549 cells showed significantly lower proliferation, motility, and invasiveness than control cells. Finally, F-actin staining in MUC6-expressing cells revealed a decrease or loss of filopodia associated with decreased levels of FSCN transcripts, which encodes an actin-bundling protein fascin1 necessary for cell migration. We conclude that MUC6 expression is a preferable prognostic biomarker in IMA LC.

Glycosylation of MUC6 by α1,4-linked N-acetylglucosamine enhances suppression of pancreatic cancer malignancy

Biomarkers for early diagnosis of pancreatic cancer are greatly needed, as the high fatality of this cancer is in part due to delayed detection. α1,4‐linked N‐acetylglucosamine (αGlcNAc), a unique O‐glycan specific to gastric gland mucus, is biosynthesized by α1,4‐N‐acetylglucosaminyltransferase (α4GnT) and primarily bound at the terminal glycosylated residue to scaffold protein MUC6. We previously reported that αGlcNAc expression decreases at early stages of neoplastic pancreatic lesions, followed by decreased MUC6 expression, although functional effects of these outcomes were unknown. Here, we ectopically expressed α4GnT, the αGlcNAc biosynthetic enzyme, together with MUC6 in the human pancreatic cancer cell lines MIA PaCa‐2 and PANC‐1, neither of which expresses α4GnT and MUC6. We observed significantly suppressed proliferation in both lines following coexpression of α4GnT and MUC6. Moreover, cellular motility decreased following MUC6 ectopic expression, an effect enhanced by cotransduction with α4GnT. MUC6 expression also attenuated invasiveness of both lines relative to controls, and this effect was also enhanced by additional α4GnT expression. We found αGlcNAc‐bound MUC6 formed a complex with trefoil factor 2. Furthermore, analysis of survival curves of patients with pancreatic ductal adenocarcinoma using a gene expression database showed that samples marked by higher A4GNT or MUC6 mRNA levels were associated with relatively favorable prognosis. These results strongly suggest that αGlcNAc and MUC6 function as tumor suppressors in pancreatic cancer and that decreased expression of both may serve as a biomarker of tumor progression to pancreatic cancer.

Decreased Gastric Gland Mucin-specific O-glycans Are Involved in the Progression of Ovarian Primary Mucinous Tumours

Ovarian primary mucinous tumours (OPMTs) show an adenoma–borderline–carcinoma sequence with gastrointestinal metaplasia. Gastric gland mucin-specific O-glycans are unique with an α1,4-linked N-acetylglucosamine (αGlcNAc) residue attached to mucin 6 (MUC6). Although αGlcNAc is expected to be expressed in OPMTs, the relationship between αGlcNAc expression and OPMT progression remains unknown. Here, we analysed 104 areas of benign mucinous tumours (benign), 55 areas of borderline mucinous tumours (borderline), and 18 areas of malignant mucinous tumours (malignant) to investigate the expression patterns of αGlcNAc, mucin 2 (MUC2), mucin 5AC (MUC5AC), and MUC6 during the progression of OPMT from benign to malignant. MUC5AC expression was observed in all areas. The frequencies of MUC6- and αGlcNAc-positive areas were decreased with tumour progression. In particular, the decrease in αGlcNAc-positive areas was remarkable. Furthermore, αGlcNAc expression was lower than MUC6 expression at all grades (benign, p < 0.0001; borderline, p = 0.0014; malignant, p = 0.0039). Conversely, there was no difference in the expression frequency or level of MUC2 among the three grades. These results suggest that decreased expression of αGlcNAc relative to MUC6 occurs early in tumour development and marks the initiation of OPMT progression.

The Abnormal Glycopatterns of Salivary Glycoproteins in Esophageal Squamous Cell Carcinoma Patients

Glycosylation is one of the most crucial posttranslational modifications of proteins, containing a remarkable amount of biological information. The alteration of glycosylation is closely associated with certain diseases. Exploring glyco-code in the development of diseases is a hot topic in recent years. Esophageal squamous cell carcinoma (ESCC) is the primary pathological histology in developing countries and a severe threat to human health. Although the glycan profiles in the blood samples of ESCC patients were analyzed using glycomic and glycoproteomic methods, the difference of salivary glycopatterns between healthy subjects and ESCC patients is not explicit yet. In the present study, ESCC patients (n = 16) and healthy volunteers (HVs, n = 25) were enrolled. The glycomic strategy combining lectin microarray and lectin blotting was employed to investigate and confirm the altered salivary glycopatterns. Datura stramonium (DSA) was selected to isolate the GlcNAc or Galβ1-4GlcNA-containing glycoproteins due to the distinct difference between ESCC patients and HVs. The N-glycans from DSA-enriched glycoproteins were released by PNGase F and further identified by MALDI-TOF/TOF-MS to obtain the precise structural information of the altered glycans. As a result, the glycopatterns recognized by 13 lectins (e.g., ECA, RCA120, and DSA) showed significant alterations in ESCC patients' saliva. The ESCC patients showed higher levels of GalNAc and Gal, sialic acid, and GlcNAc expression profiles and lower levels of mannose and fucose expression profiles. The MALDI-TOF/TOF-MS results indicated that the proportion of the GlcNAc or Galβ1-4GlcNAc-containing N-glycans was increased in ESCC patients (79.04%) compared with HV (63.20%), which was consistent with the results of lectin microarrays. Our findings provide comprehensive information to understand the complex physiological changes in ESCC patients. And the altered salivary glycopatterns such as GlcNAc or Galβ1-4GlcNAc-containing N-glycans recognized by DSA might serve as potential biomarkers for the diagnosis of ESCC patients.

Decreased alpha-1,4-linked N-acetylglucosamine glycosylation in biliary tract cancer progression from biliary intraepithelial neoplasia to invasive adenocarcinoma

Biliary tract cancer (BTC) is typically lethal due to the difficulty of early stage diagnosis. Thus, novel biomarkers of BTC precursors are necessary. Biliary intraepithelial neoplasia (BilIN) is a major precursor of BTC and is classified as low or high grade based on cell atypia. In normal gastric mucosa, gastric gland mucin‐specific O‐glycans are unique in having α1,4‐linked N‐acetylglucosamine (αGlcNAc) attached to MUC6. Previously, we reported that αGlcNAc functions as a tumor suppressor of differentiated‐type gastric adenocarcinoma and that decreased αGlcNAc glycosylation on MUC6 in gastric, pancreatic, and uterine cervical neoplasms occurs in cancer as well as in their precursor lesions. However, αGlcNAc and MUC6 expression patterns in biliary tract neoplasms have remained unclear. Here, we analyzed MUC5AC, MUC6, and αGlcNAc expression status in 51 BTC cases and compared the expression of each with progression from low‐grade BilIN to invasive adenocarcinoma (IAC). The frequency of αGlcNAc‐positive and MUC6‐positive lesions decreased with tumor progression. When we compared each marker’s expression level with tumor progression, we found that the MUC6 expression score in IAC was significantly lower than in low‐grade or high‐grade BilIN (P < 0.001 or P < 0.01, respectively). However, the αGlcNAc expression score was low irrespective of histological grade, and also lower than that of MUC6 across all histological grades (P < 0.001 for low‐grade and high‐grade BilIN, and P < 0.01 for IAC). These results suggest that decreased expression of αGlcNAc relative to MUC6 marks the initiation of BTC progression.