Abstract
The effects of sodium butyrate, a known differentiation-inducing agent, on carcinoembryonic antigen (CEA) production by human colonic adenocarcinoma cells in culture were studied using seven different colorectal tumor cell lines. Sodium butyrate (2 mm) treatment resulted in a marked induction of CEA content in two cell lines, HRT18 and HCT48; a moderate induction of CEA content in LS174T and SKCO-1; and no increase of CEA content in SW480, SW620, and SW1116. Of those showing an induction of CEA production by butyrate, a dose-related increase up to 5 mm butyrate concentration could be demonstrated. This enhanced phenotypic expression of CEA in cells treated with butyrate could be blocked by the protein synthesis inhibitor cycloheximide and by actinomycin D, an inhibitor of RNA transcription. Neither the subcellular distribution of CEA nor the rate of release of CEA into culture medium by the cells was changed by the treatment. Cell surface CEA was labeled with galactose oxidase, followed by reaction with sodium borotritide, and was subsequently immunoprecipitated specifically with anti-CEA antiserum. Examination of labeled cell surface CEA from control and butyrate-treated HCT48 and LS174T cells by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a major glycoprotein with a molecular weight of 200,000, indicating that no new form of CEA was induced with sodium butyrate treatment. A similar result was observed when the cell membrane proteins, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, were transferred onto nitrocellulose paper and reacted with rabbit anti-CEA antiserum and 125I-Protein A. Lectin affinity chromatography of cellular CEA revealed a higher binding of CEA from butyrate-treated HCT48 cells to Ricinus communis agglutinin-Sepharose 4B than that from untreated cells, while the binding of CEA to wheat germ agglutinin-Sepharose 4B and concanavalin A agglutinin-Sepharose 4B was similar in butyrate-treated and untreated cells.
It is concluded that butyrate may enhance expression of the differentiated function of some human colorectal tumor cells, as indicated by an elevation of CEA production. This elevated CEA content in butyrate-treated cells appears to be caused by increased synthesis of the CEA molecule.
This work was supported by USPHS Grant CA-14905 from the National Cancer Institute through the National Large Bowel Cancer Project and by the Veterans Administration Medical Research Service.
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