Increased number of accessible sugar epitopes defined with monoclonal antibody AM-3 on colonic mucins is associated with malignant transformation of colonic mucosa.
Monoclonal antibody AM-3 detects a mucin sugar epitope (AM-3 epitope) the expression of which increases in the course of human colon carcinogenesis parallel to the gradual morphological alterations (so called adenoma-carcinoma sequence). In the present report the AM-3-positive mucin has been purified from human normal and carcinomatous colonic tissue. About 300-fold enrichment of the epitope per protein from both sources was achieved after ultracentrifugation, gel filtration on Sepharose CL-6B and isopyknic gradient centrifugation. Slot-blot and enzyme-linked immunosorbent assays of the purified preparation indicated not only different amounts of the mucins but also a consistent qualitative difference between the molecules from both sources. The qualitative difference could be obliterated by a partial removal of the AM-3 epitope from the tumor-derived mucin with neuraminidase. The visualization of the molecules by rotary shadowing indicated that the mucins from both sources have similar length distribution, 80% of the molecules being 100-600 nm long. The reaction with AM-3 antibody followed by rotary shadowing showed that in the purified preparations more than 95% of the tumor-derived molecules and 74% of the normal colon tissue-derived molecules carried the epitope. The tumor-derived mucins bound, on the average, 34 +/- 15 (SD) antibodies/1000 nm of the protein core while the mucin from normal colon tissue carried 12 +/- 11 antibodies/1000 nm of the protein core. These data indicate that the increased expression of AM-3 epitopes during malignant transformation of the human colon is due to accumulation of AM-3-positive mucin as well as a higher number of accessible AM-3 epitopes on this mucin.
Hanski
C
C
Department of Gastroenterology, Klinikum Steglitz, Freien Universität Berlin, Germany.
Sheehan
J
J
Kiehntopf
M
M
Stolze
B
B
Stein
H
H
Riecken
E O
EO
D000911:Antibodies, Monoclonal; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D003110:Colonic Neoplasms / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000096:biosynthesis; D015151:Immunoblotting; D007075:Immunoglobulin M / Q000096:biosynthesis; D007413:Intestinal Mucosa / Q000378:metabolism*; D008854:Microscopy, Electron; D009077:Mucins / Q000276:immunology*
D000911:Antibodies, Monoclonal; D000939:Epitopes; D007075:Immunoglobulin M; D009077:Mucins