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TuAg.1 Is the Liver Isoform of the Rat Colon Tumor-associated Antigen pE4 and a Member of the Immunoglobulin-like Supergene Family¹

Department of Medical Oncology, Rhode Island Hospital, Brown University School of Medicine, Providence, Rhode Island 02903

TuAg.1 is a tumor-associated membrane glycoprotein first identified in rat hepatocellular carcinoma by monoclonal antibodies (mAbs) 324.5 and 324.9. This oncofetal antigen is also expressed by hepatocytes in cell culture but not normal adult hepatocytes in vivo. Affinity chromatography and preparative continuous elution slab-gel electrophoresis were used to separate TuAg.1 from co-purified actin and immunoglobulin. TuAg.1 was recovered as a series of bands M_r 82,000–90,000, which were pooled and subjected to CNBr digestion for primary amino acid sequence analysis. Computer database analysis of TuAg.1 peptide sequence revealed homology to the rat colon carcinoma-associated antigen pE4, a member of the immunoglobulin gene superfamily. Oligonucleotide primers derived from sequences shared by TuAg.1 and pE4 were used in reverse transcription-PCR to amplify tumor-specific products corresponding to TuAg.1 cDNA. Northern blot analysis with one of these products confirmed the oncofetal expression of transcripts related to TuAg.1/pE4 and indicated an RNA species of different size expressed only in normal liver. Identity between TuAg.1 and pE4 was further confirmed by immunochemical analysis with mAb 324.5 and mAb E4. Both antibodies were reactive with the same protein on transplantable hepatocellular carcinoma AS30D but recognized different epitopes. The reactivity of human tumor cells with mAb 324.5 and 324.9 indicates the presence of a related TuAg.1 molecule expressed in human neoplasia as well.

¹ This investigation was supported by National Cancer Institute Grant CA 42715 (to D. C. H.) and American Cancer Society Grant CN-20 (to N. L. T.). L. C. F. was supported by National Cancer Institute National Research Service Award F31 CA09258. Y-P. L. was supported by an Amgen Oncology Fellowship Award.

² The first two authors contributed equally to this work.

³ To whom requests for reprints should be addressed, at Department of Medical Oncology, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903.

Received 4/ 1/96. Accepted 7/ 2/96.

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