JBC, Vol. 253, Issue 7, 2271-2278, Apr, 1978
Glycoproteins from human colonic adenocarcinoma. Isolation and characterization of cell surface carcinoembryonic antigen from a cultured tumor cell line
D. Tsao and Y. S. Kim
Alterations in cell surface glycoproteins have been implicated in
malignancy. We examined surface membrane proteins of a cultured cell line,
SKCO-1, which had been derived from a human colonic adenocarcinoma. Cell
surface labeling of SKCO-1 cells with galactose oxidase, followed by
reduction with sodium borotritide, revealed five major labeled
glycoproteins upon sodium dodecyl sulfate (SDS)-polyacrylamide gel
electrophoresis. At least three additional labeled glycoproteins could be
detected if galactose oxidase treatment was preceded by neuraminidase
treatment. Some, but not all, of the glycoproteins could be iodinated by
lactoperoxidase. The predominantly labeled glycoprotein (GPI) had a
molecular weight of 200,000 and co-migrated in SDS gel with
carcinoembryonic antigen (CEA). GPI was not removed from the cell surface
by EDTA, hypertonic saline, or sonication but was released from the
membrane by detergents. This glycoprotein was subsequently purified using
lectin-agarose columns and gel filtration. GPI was judged homogenous by
protein- and carbohydrate-stained SDS-polyacrylamide gels and had an amino
acid composition similar to that of CEA. The carbohydrate composition of
GPI was qualitatively similar to CEA but quantitatively distinct. GPI had a
greater proportion of sialic acid and galactosamine and less fucose and
glucosamine than CEA. Immunological studies, however, demonstrated identity
between GPI and CEA. A study of the turnover rate of GPI showed it to have
a half-life of 5 days.
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