Abstract
Trefoil factor family 2 (TFF2) and the mucin MUC6 are co-secreted from human gastric and duodenal glands. TFF2 binds MUC6 as a lectin and is a constituent of the gastric mucus. Herein, we investigated human gastric extracts by FPLC and identified mainly high- but also low-molecular-mass forms of TFF2. From the high-molecular-mass forms, TFF2 can be completely released by boiling in SDS or by harsh denaturing extraction. The low-molecular-mass form representing monomeric TFF2 can be washed out in part from gastric mucosa specimens with buffer. Overlay assays with radioactively labeled TFF2 revealed binding to the mucin MUC6 and not MUC5AC. This binding is modulated by Ca2+ and can be blocked by the lectin GSA-II and the monoclonal antibody HIK1083. TFF2 binding was also inhibited by Me-β-Gal, but not the α anomer. Thus, both the α1,4GlcNAc as well as the juxtaperipheral β-galactoside residues of the characteristic GlcNAcα1→4Galβ1→R moiety of human MUC6 are essential for TFF2 binding. Furthermore, there are major differences in the TFF2 binding characteristics when human is compared with the porcine system. Taken together, TFF2 appears to fulfill an important role in stabilizing the inner insoluble gastric mucus barrier layer, particularly by its binding to the mucin MUC6.
Highlights
Trefoil factor family 2 (TFF2) belongs to the family of secretory trefoil factor family (TFF) peptides and mainly consists of two cysteine-rich TFF domains [1,2,3,4]
When human gastric extracts were subject to size exclusion chromatography (SEC) (Figure 1), TFF2 immunoreactivity appeared in two regions, i.e., in a periodic acid-Schiff (PAS)-positive high-molecular-mass peak and a low-molecular-mass peak (Figure 1A)
The high-molecular-mass peak contained the mucins MUC5AC and MUC6 as detected after agarose gel electrophoresis (AgGE, Figure 1B), and under these conditions, TFF2 was clearly associated with mucins (Figure 1B)
Summary
TFF2 (formerly: “spasmolytic polypeptide”) belongs to the family of secretory trefoil factor family (TFF) peptides and mainly consists of two cysteine-rich TFF domains (total length: 106 amino acid residues) [1,2,3,4]. The major expression sites in humans are the gastric mucous neck and antral gland cells and duodenal Brunner’s glands, where it is co-secreted with the mucin MUC6 [5,6,7]. TFF2 mRNA transcript expression in the gastric fundus is not parallel with peptide localization and rather marks a progenitor of mucous neck cells [8,9]. The unusual LacdiNAc moiety is carried by the gastric mucin MUC5AC and is recognized by the Helicobacter pylori adhesin LabA [13]. This is one reason why H. pylori mainly adhere to the MUC5AC layer. N-glycosylation varied diurnally with a maximum between 17:00 and 23:00 [14]
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