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Effect of Heterogeneity of Carcinoembryonic Antigen on Liver Cell Membrane Binding and Its Kinetics of Removal from Circulation

Mallory Gastrointestinal Research Laboratory [R. A. B., P. M., P. T., N. Z.], Mallory Institute of Pathology, Boston City Hospital 02118; The Department of Medicine, Harvard Medical School [R. A. B., P. T., R. W. J., N. Z.] 02115; The Department of Pathology, Boston University School of Medicine [N. Z.] 02118; and The Laboratory for Carbohydrate Research, Massachusetts General Hospital [R. W. J], Boston, Massachusetts 02114

Carcinoembryonic antigen (CEA) is a glycoprotein metabolized primarily by the liver. Subcellular fractions of rat liver were examined for CEA binding activity. Hepatocyte plasma membrane and microsome fractions bound CEA, and this binding shared the calcium requirement, neuraminidase sensitivity, and carbohydrate specificity of the hepatocyte asialoglycoprotein receptor. CEA had previously been shown to react with this galactose-specific receptor, in vivo, only following neuraminidase treatment.

Galactose receptor binding of CEA was measured in three different purified CEA preparations. The fraction of CEA capable of binding to excess levels of galactose receptor on membranes varied (46.5%, 40.2%, and 4.7% for CEA-1, -2, and -3, respectively). These CEAs were shown to be 2.3%, 7.9%, and 0.7% as effective, respectively, as asialo-₁-acid glycoprotein in inhibiting the binding of radiolabeled asialo-₁-acid glycoprotein to liver cell membranes.

Each of the three CEA preparations showed different clearance kinetics from the circulation of mice. Coinjection of asialo-₁-acid glycoprotein with the CEAs revealed differing inhibition of the clearances. These results show that differences in the carbohydrate components of purified CEA preparations affect their rate of removal from circulation and thus possibly the relationship between CEA production and observed plasma levels in patients. The possible origin of these CEA differences is discussed with their clinical implications.

¹ Present address: Laboratory of Tumor Virus Genetics, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115.

² To whom requests for reprints should be addressed, at Gastrointestinal Research Laboratory, Boston City Hospital, 784 Massachusetts Avenue, Boston, MA 02118.

³ Recipient of Grant CA-04486 from the National Cancer Institute.

Received 1/25/84. Revised 4/ 9/85. Accepted 4/10/85.

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