Reduced expression of αGlcNAc in Barrett's oesophagus adjacent to Barrett's adenocarcinoma--a possible biomarker to predict the malignant potential of Barrett's oesophagus

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.

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.

Case of Barrett's adenocarcinoma with marked endoscopic morphological changes in Barrett's esophagus over a long follow-up period of 15 years

The natural history of Barrett's esophagus (BE) is unclear. We herein describe a case of Barrett's adenocarcinoma (BAC) in which we could closely observe marked morphological changes in BE over a long follow-up period of 15 years. A man in his seventies received routine esophagogastroduodenoscopy (EGD) and was diagnosed as having reflux esophagitis and short-segment BE. The BE gradually became elongated, and BAC was detected 9 years following the initial EGD examination with continued administration of a proton pump inhibitor. We witnessed that BE elongated sporadically over time and mucosal breaks of reflux esophagitis were detectable several years before elongation. The patient underwent endoscopic submucosal dissection for BAC and has been monitored by EGD every year thereafter. These remarkable morphological changes may be representative of the natural history of BE and aid in deciding long-term disease management.

Reduced gland mucin-specific O-glycan in gastric atrophy: A possible risk factor for differentiated-type adenocarcinoma of the stomach

BACKGROUND AND AIMS

O-glycans exhibiting terminal α1,4-linked N-acetylglucosamine (αGlcNAc) are attached to MUC6 in gastric gland mucins and serve as a tumor suppressor for gastric adenocarcinoma. Gastric atrophy is associated with risk for gastric cancer. However, the significance of αGlcNAc expression in pyloric glands of chronic atrophic gastritis remains unknown. Here, we asked whether reduced αGlcNAc expression in chronic atrophic gastritis is associated with risk for gastric cancer.

METHODS

We quantitatively analyzed expression of αGlcNAc relative to MUC6 in pyloric glands by immunohistochemistry in 67 patients with normal mucosa, 70 with chronic atrophic gastritis, 68 with intramucosal differentiated-type adenocarcinoma, and 11 with intramucosal undifferentiated-type adenocarcinoma. We also compared the Ki-67 labeling index in gastric epithelial cells between chronic atrophic gastritis and normal gastric mucosa with respect to αGlcNAc reduction.

RESULTS

In normal pyloric mucosa, αGlcNAc was co-expressed with MUC6. By contrast, in chronic atrophic gastritis, pyloric gland αGlcNAc expression was significantly reduced relative to MUC6. In intramucosal gastric cancer, αGlcNAc expression in pyloric glands found just beneath differentiated-type adenocarcinoma was also reduced relative to MUC6. However, pyloric glands present beneath undifferentiated-type adenocarcinoma exhibited no αGlcNAc decrease. The Ki-67 labeling index in chronic atrophic gastritis showing αGlcNAc reduction was significantly increased relative to that in normal gastric mucosa.

CONCLUSIONS

Because αGlcNAc prevents the gastric cancer development, reduced αGlcNAc expression in chronic atrophic gastritis is a possible risk factor for differentiated-type adenocarcinoma of the stomach.

Serum Glycoprotein Biomarker Discovery and Qualification Pipeline Reveals Novel Diagnostic Biomarker Candidates for Esophageal Adenocarcinoma

We report an integrated pipeline for efficient serum glycoprotein biomarker candidate discovery and qualification that may be used to facilitate cancer diagnosis and management. The discovery phase used semi-automated lectin magnetic bead array (LeMBA)-coupled tandem mass spectrometry with a dedicated data-housing and analysis pipeline; GlycoSelector (http://glycoselector.di.uq.edu.au). The qualification phase used lectin magnetic bead array-multiple reaction monitoring-mass spectrometry incorporating an interactive web-interface, Shiny mixOmics (http://mixomics-projects.di.uq.edu.au/Shiny), for univariate and multivariate statistical analysis. Relative quantitation was performed by referencing to a spiked-in glycoprotein, chicken ovalbumin. We applied this workflow to identify diagnostic biomarkers for esophageal adenocarcinoma (EAC), a life threatening malignancy with poor prognosis in the advanced setting. EAC develops from metaplastic condition Barrett's esophagus (BE). Currently diagnosis and monitoring of at-risk patients is through endoscopy and biopsy, which is expensive and requires hospital admission. Hence there is a clinical need for a noninvasive diagnostic biomarker of EAC. In total 89 patient samples from healthy controls, and patients with BE or EAC were screened in discovery and qualification stages. Of the 246 glycoforms measured in the qualification stage, 40 glycoforms (as measured by lectin affinity) qualified as candidate serum markers. The top candidate for distinguishing healthy from BE patients' group was Narcissus pseudonarcissus lectin (NPL)-reactive Apolipoprotein B-100 (p value = 0.0231; AUROC = 0.71); BE versus EAC, Aleuria aurantia lectin (AAL)-reactive complement component C9 (p value = 0.0001; AUROC = 0.85); healthy versus EAC, Erythroagglutinin Phaseolus vulgaris (EPHA)-reactive gelsolin (p value = 0.0014; AUROC = 0.80). A panel of 8 glycoforms showed an improved AUROC of 0.94 to discriminate EAC from BE. Two biomarker candidates were independently verified by lectin magnetic bead array-immunoblotting, confirming the validity of the relative quantitation approach. Thus, we have identified candidate biomarkers, which, following large-scale clinical evaluation, can be developed into diagnostic blood tests. A key feature of the pipeline is the potential for rapid translation of the candidate biomarkers to lectin-immunoassays.

Decreased expression of gastric gland mucin-specific glycan α1,4-linked N-acetylglucosamine on its scaffold mucin 6 is associated with malignant potential of pyloric gland adenoma of the stomach

AIMS

Pyloric gland adenoma (PGA) is a unique gastric neoplasm expressing mucin 6 (MUC6), and is often associated with high-grade dysplasia and/or adenocarcinoma. MUC6 secreted from the gastric gland mucous cells, such as pyloric gland cells, carries unique O-glycans with terminal α1,4-linked N-acetylglucosamine (αGlcNAc) residues on its molecule. As we recently demonstrated that αGlcNAc serves as a tumour suppressor for gastric adenocarcinoma, this study aimed to investigate the significance of αGlcNAc expression in PGA.

METHODS AND RESULTS

Eighteen patients with PGA were examined with immunohistochemistry for αGlcNAc and MUC6. αGlcNAc and MUC6 were coexpressed in 12 of 18 PGAs. However, reduced αGlcNAc expression relative to MUC6 expression was observed in six cases. When the MIB-1 labelling index (LI) of tumour cells was examined with respect to reduced αGlcNAc expression, the MIB-1 LI was significantly higher in PGAs showing decreased αGlcNAc expression relative to MUC6 expression than in PGAs with unchanged αGlcNAc expression (P = 0.023).

CONCLUSIONS

The present study indicates that coexpression of αGlcNAc and MUC6 in PGA suggests the presence of fully glycosylated MUC6 on tumour cells, consistent with pyloric gland differentiation. However, the decreased glycosylation of αGlcNAc on MUC6 is associated with high mitotic activity of tumour cells, indicative of malignant potential of PGA.

Simple sugars to complex disease--mucin-type O-glycans in cancer

Mucin-type O-glycans are a class of glycans initiated with N-acetylgalactosamine (GalNAc) α-linked primarily to Ser/Thr residues within glycoproteins and often extended or branched by sugars or saccharides. Most secretory and membrane-bound proteins receive this modification, which is important in regulating many biological processes. Alterations in mucin-type O-glycans have been described across tumor types and include expression of relatively small-sized, truncated O-glycans and altered terminal structures, both of which are associated with patient prognosis. New discoveries in the identity and expression of tumor-associated O-glycans are providing new avenues for tumor detection and treatment. This chapter describes mucin-type O-glycan biosynthesis, altered mucin-type O-glycans in primary tumors, including mechanisms for structural changes and contributions to the tumor phenotype, and clinical approaches to detect and target altered O-glycans for cancer treatment and management.

Molecular markers and imaging tools to identify malignant potential in Barrett's esophagus

Due to its rapidly rising incidence and high mortality, esophageal adenocarcinoma is a major public health concern, particularly in Western countries. The steps involved in the progression from its predisposing condition, gastroesophageal reflux disease, to its premalignant disorder, Barrett’s esophagus, and to cancer, are incompletely understood. Current screening and surveillance methods are limited by the lack of population-wide utility, incomplete sampling of standard biopsies, and subjectivity of evaluation. Advances in endoscopic ablation have raised the hope of effective therapy for eradication of high-risk Barrett’s lesions, but improvements are needed in determining when to apply this treatment and how to follow patients clinically. Researchers have evaluated numerous potential molecular biomarkers with the goal of detecting dysplasia, with varying degrees of success. The combination of biomarker panels with epidemiologic risk factors to yield clinical risk scoring systems is promising. New approaches to sample tissue may also be combined with these biomarkers for less invasive screening and surveillance. The development of novel endoscopic imaging tools in recent years has the potential to markedly improve detection of small foci of dysplasia in vivo. Current and future efforts will aim to determine the combination of markers and imaging modalities that will most effectively improve the rate of early detection of high-risk lesions in Barrett’s esophagus.

Recent advances in molecular imaging of premalignant gastrointestinal lesions and future application for early detection of barrett esophagus

Recent advances in optical molecular imaging allow identification of morphologic and biochemical changes in tissues associated with gastrointestinal (GI) premalignant lesions earlier and in real-time. This focused review series introduces high-resolution imaging modalities that are being evaluated preclinically and clinically for the detection of early GI cancers, especially Barrett esophagus and esophageal adenocarcinoma. Although narrow band imaging, autofluorescence imaging, and chromoendoscopy are currently applied for this purpose in the clinic, further adoptions of probe-based confocal laser endomicroscopy, high-resolution microendoscopy, optical coherence tomography, and metabolomic imaging, as well as imaging mass spectrometry, will lead to detection at the earliest and will guide predictions of the clinical course in the near future in a manner that is beyond current advancements in optical imaging. In this review article, the readers will be introduced to sufficient information regarding this matter with which to enjoy this new era of high technology and to confront science in the field of molecular medical imaging.