Genetic variation in a4GnT in relation to Helicobacter pylori serology and gastric cancer risk

Impaired Glycosylation of Gastric Mucins Drives Gastric Tumorigenesis and Serves as a Novel Therapeutic Target

BACKGROUND & AIMS

Gastric cancer is often accompanied by a loss of mucin 6 (MUC6), but its pathogenic role in gastric carcinogenesis remains unclear.

METHODS

Muc6 knockout (Muc6-/-) mice and Muc6-dsRED mice were newly generated. Tff1Cre, Golph3-/-, R26-Golgi-mCherry, Hes1flox/flox, Cosmcflox/flox, and A4gnt-/- mice were also used. Histology, DNA and RNA, proteins, and sugar chains were analyzed by whole-exon DNA sequence, RNA sequence, immunohistochemistry, lectin-binding assays, and liquid chromatography-mass spectrometry analysis. Gastric organoids and cell lines were used for in vitro assays and xenograft experiments.

RESULTS

Deletion of Muc6 in mice spontaneously causes pan-gastritis and invasive gastric cancers. Muc6-deficient tumor growth was dependent on mitogen-activated protein kinase activation, mediated by Golgi stress-induced up-regulation of Golgi phosphoprotein 3. Glycomic profiling revealed aberrant expression of mannose-rich N-linked glycans in gastric tumors, detected with banana lectin in association with lack of MUC6 expression. We identified a precursor of clusterin as a binding partner of mannose glycans. Mitogen-activated protein kinase activation, Golgi stress responses, and aberrant mannose expression are found in separate Cosmc- and A4gnt-deficient mouse models that lack normal O-glycosylation. Banana lectin-drug conjugates proved an effective treatment for mannose-rich murine and human gastric cancer.

CONCLUSIONS

We propose that Golgi stress responses and aberrant glycans are important drivers of and promising new therapeutic targets for gastric cancer.

Helicobacter pylori Immunoproteomic Profiles in Gastric Cancer

Chronic Helicobacter pylori infection is the major risk factor for gastric cancer (GC). However, only some infected individuals develop this neoplasia. Previous H. pylori serology studies have been limited by investigating small numbers of candidate antigens. Therefore, we evaluated humoral responses to a nearly complete H. pylori immunoproteome (1527 proteins) among 50 GC cases and 50 controls using Nucleic Acid Programmable Protein Array (NAPPA). Seropositivity was defined as median normalized intensity ≥2 on NAPPA, and 53 anti-H. pylori antibodies had >10% seroprevalence. Anti-GroEL exhibited the greatest seroprevalence (77% overall), which agreed well with ELISA using whole-cell lysates of H. pylori cells. After an initial screen by H. pylori-NAPPA, we discovered and verified that 12 antibodies by ELISA in controls had ≥15% of samples with an optical reading value exceeding the 95th percentile of the GC group. ELISA-verified antibodies were validated blindly in an independent set of 100 case-control pairs. As expected, anti-CagA seropositivity was positively associated with GC (odds ratio, OR = 5.5; p < 0.05). After validation, six anti-H. pylori antibodies showed lower seropositivity in GC, with ORs ranging from 0.44 to 0.12 (p < 0.05): anti-HP1118/Ggt, anti-HP0516/HsIU, anti-HP0243/NapA, anti-HP1293/RpoA, anti-HP0371/FabE, and anti-HP0875/KatA. Among all combinations, a model with anti-Ggt, anti-HslU, anti-NapA, and anti-CagA had an area under the curve of 0.73 for discriminating GC vs. controls. This study represents the first comprehensive assessment of anti-H. pylori humoral profiles in GC. Decreased responses to multiple proteins in GC may reflect mucosal damage and decreased bacterial burden. The higher prevalence of specific anti-H. pylori antibodies in controls may suggest immune protection against GC development.

Evolution of protein N-glycosylation process in Golgi apparatus which shapes diversity of protein N-glycan structures in plants, animals and fungi

Protein N-glycosylation (PNG) is crucial for protein folding and enzymatic activities, and has remarkable diversity among eukaryotic species. Little is known of how unique PNG mechanisms arose and evolved in eukaryotes. Here we demonstrate a picture of onset and evolution of PNG components in Golgi apparatus that shaped diversity of eukaryotic protein N-glycan structures, with an emphasis on roles that domain emergence and combination played on PNG evolution. 23 domains were identified from 24 known PNG genes, most of which could be classified into a single clan, indicating a single evolutionary source for the majority of the genes. From 153 species, 4491 sequences containing the domains were retrieved, based on which we analyzed distribution of domains among eukaryotic species. Two domains in GnTV are restricted to specific eukaryotic domains, while 10 domains distribute not only in species where certain unique PNG reactions occur and thus genes harboring these domains are supoosed to be present, but in other ehkaryotic lineages. Notably, two domains harbored by β-1,3 galactosyltransferase, an essential enzyme in forming plant-specific Le^a structure, were present in separated genes in fungi and animals, suggesting its emergence as a result of domain shuffling.

A germline chromothripsis event stably segregating in 11 individuals through three generations

PURPOSE

Parentally transmitted germ-line chromothripsis (G-CTH) has been identified in only a few cases. Most of these rearrangements were stably transmitted, in an unbalanced form, from a healthy mother to her child with congenital abnormalities probably caused by de novo copy-number changes of dosage sensitive genes. We describe a G-CTH transmitted through three generations in 11 healthy carriers.

METHODS

Conventional cytogenetic analysis, mate-pair sequencing, and polymerase chain reaction (PCR) were used to identify the chromosome rearrangement and characterize the breakpoints in all three generations.

RESULTS

We identified an apparently balanced translocation t(3;5), later shown to be a G-CTH, in all individuals of a three-generation family. The G-CTH stably segregated without occurrence of additional rearrangements; however, several spontaneous abortions were reported, possibly due to unbalanced transmission. Although seven protein-coding genes are interrupted, no clinical features can be definitively attributed to the affected genes. However, it can be speculated that truncation of one of these genes, encoding ataxia-telangiectasia and Rad3-related protein kinase (ATR), a key component of the DNA damage response, may be related to G-CTH formation.

CONCLUSION

G-CTH rearrangements are not always associated with abnormal phenotypes and may be misinterpreted as balanced two-way translocations, suggesting that G-CTH is an underdiagnosed phenomenon.Genet Med 18 5, 494-500.

Factors that mediate colonization of the human stomach by Helicobacter pylori

Helicobacter pylori (H. pylori) colonizes the stomach of humans and causes chronic infection. The majority of bacteria live in the mucus layer overlying the gastric epithelial cells and only a small proportion of bacteria are found interacting with the epithelial cells. The bacteria living in the gastric mucus may act as a reservoir of infection for the underlying cells which is essential for the development of disease. Colonization of gastric mucus is likely to be key to the establishment of chronic infection. How H. pylori manages to colonise and survive in the hostile environment of the human stomach and avoid removal by mucus flow and killing by gastric acid is the subject of this review. We also discuss how bacterial and host factors may together go some way to explaining the susceptibility to colonization and the outcome of infection in different individuals. H. pylori infection of the gastric mucosa has become a paradigm for chronic infection. Understanding of why H. pylori is such a successful pathogen may help us understand how other bacterial species colonise mucosal surfaces and cause disease.

Dual Roles of Gastric Gland Mucin-specific O-glycans in Prevention of Gastric Cancer

Gastric gland mucin is secreted from gland mucous cells, including pyloric gland cells and mucous neck cells located in the lower layer of the gastric mucosa. These mucins typically contain O-glycans carrying terminal α1,4-linked N-acetylglucosamine residues (αGlcNAc) attached to the scaffold protein MUC6, and biosynthesis of the O-glycans is catalyzed by the glycosyltransferase, α1,4-N-acetylglucosaminyltransferase (α4GnT). We previously used expression cloning to isolate cDNA encoding α4GnT, and then demonstrated that αGlcNAc functions as natural antibiotic against Helicobacter pylori, a microbe causing various gastric diseases including gastric cancer. More recently, it was shown that αGlcNAc serves as a tumor suppressor for differentiated-type adenocarcinoma. This review summarizes these findings and identifies dual roles for αGlcNAc in gastric cancer.