Fragmentation pattern of mucins in normal and diseased gastric mucosae: a glycoprotein fractionates with gastric mucins purified from mucosal scrapings of cancer and peptic ulcer patients.
OBJECTIVE
Gastric cancer, a fatal malignancy, is prevalent in the Western Cape region of South Africa. The aim of this study was a biochemical characterisation of gastric mucins in this disease, compared with gastric ulceration and controls from transplant donors.


METHODS
Mucins were extracted in a denaturing medium (to prevent endogenous proteolysis) and purified by caesium chloride density gradient ultracentrifugation. Analysis of mucin was by gel filtration, SDS-PAGE and Western blotting methods.


RESULTS
All samples of mucin when analysed by gel filtration were found to contain polymeric glycoprotein together with varying amounts of lower-molecular-weight glycoprotein. SDS-PAGE and Western blot analysis showed that diseased stomachs had glycopeptides of a wider range in size and antigenicity with a greater number of smaller fragments immunoreactive to monoclonal antibodies 2-12M1 and 9-13M1. We identified by SDS-PAGE a glycoprotein which co-fractionates in a caesium chloride density gradient with mucins isolated from gastrectomy specimens resected for carcinoma and peptic ulceration and which was absent from mucins of the transplant donor control group. This neuraminidase-sensitive glycoprotein resisted dissociation from mucin during purification in a 3.5 M CsCl density gradient but was partially separable by Sepharose 2B gel chromatography and heat treatment (100 degrees C, 2.0 min) in SDS. Chemical analysis of the glycoprotein by HPLC favours it being an N-linked glycoprotein. Its non-ideal electrophoretic properties make its exact size estimation difficult and we ascribe to it a broad size range of Mr approximately 55-65 kD.


CONCLUSIONS
We conclude that mucins from diseased stomachs were more degraded than those from donors and that the diseased mucosa reproducibly secretes a Mr approximately 55-65 kD glycoprotein, the role of which needs to be established.
Mall
A S
AS
Department of Surgery and MRC Liver Research Centre, University of Cape Town Medical School, Cape Town, South Africa. amall@uctgsh1.uct.ac.za
McLeod
H A
HA
Hickman
R
R
Kahn
D
D
Dent
D M
DM
D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D000293:Adolescent; D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis; D015153:Blotting, Western; D002648:Child; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005752:Gastric Mucins / Q000378:metabolism*; D005753:Gastric Mucosa / Q000378:metabolism* / Q000473:pathology; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009005:Monosaccharides / Q000032:analysis; D013274:Stomach Neoplasms / Q000378:metabolism* / Q000473:pathology; D013276:Stomach Ulcer / Q000378:metabolism* / Q000473:pathology
D014408:Biomarkers, Tumor; D005752:Gastric Mucins; D006023:Glycoproteins; D009005:Monosaccharides