ABSTRACT
BACKGROUND AND AIMS: The Tage4 gene (tumour associated glycoprotein E4) is overexpressed in rat colon tumours and Min mouse intestinal adenomas. The rat Tage4 protein has approximately 40% identity with human CD155, a member of the immunoglobulin superfamily coding for a transmembrane protein capable of serving as an entry receptor for poliovirus, porcine pseudorabies virus, and bovine herpesvirus 1. Analysis of the rat Tage4 gene has revealed structural and functional similarities with the human CD155 gene. We therefore investigated expression of the CD155 gene in human colorectal carcinomas. METHODS: Overall CD155 expression was assessed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical analysis using tissue specimens from patients with colorectal adenomas and adenocarcinomas. We also used a qualitative RT-PCR assay to determine relative expression of different splicing variants in each sample. RESULTS: mRNA levels of CD155 were increased in six of six colorectal cancer tissues compared with the tumour free colon mucosa. Immunohistochemical analysis revealed an increased level of CD155 protein in 12 of 12 samples. The qualitative RT-PCR assay revealed that relative expression of the different CD155 variant transcripts was similar in the different normal and cancer samples tested, indicating that this overexpression is not associated with a particular mRNA variant generated by alternative splicing of the CD155 gene. CONCLUSION: We have shown for the first time that the CD155 gene is overexpressed in colorectal carcinoma and that this overexpression begins at an early stage in tumorigenesis and continues to late stages.
Subject(s)
Adenocarcinoma/genetics , Adenoma/genetics , Colorectal Neoplasms/genetics , Membrane Proteins , Receptors, Virus/genetics , Adenocarcinoma/metabolism , Adenoma/metabolism , Adult , Aged , Aged, 80 and over , Alternative Splicing/genetics , Antibodies, Monoclonal , Blotting, Western , Colorectal Neoplasms/metabolism , Electrophoresis, Agar Gel , Electrophoresis, Polyacrylamide Gel , Female , Flow Cytometry , Humans , Male , Middle Aged , Oligonucleotide Probes , Protein Isoforms/chemistry , RNA, Messenger/analysis , Receptors, Virus/metabolism , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
The Tage4 gene (Tumor-Associated Glycoprotein E4) is a member of the immunoglobulin superfamily overexpressed in rat colon tumors and Min mouse intestinal adenomas. The Tage4 cDNA presents approximately 60% identity with the human CD155, a member of the immunoglobulin superfamily coding for a transmembrane protein capable of serving as an entry receptor for poliovirus, porcine pseudorabies virus and bovine herpesvirus 1. We determined the structure of the Tage4 gene. This gene covers approximately 15 kb and is composed of eight exons and seven introns. We also isolated approximately 2 kb of the 5' flanking region of the Tage4 gene and demonstrated the existence of closely clustered transcription start sites. No splicing variant was identified by RT-PCR indicating that the Tage4 gene is transcribed as a unique mRNA. Finally, the protein encoded by the Tage4 gene was tested for ability to mediate entry of several viruses. These structural and functional features of the rat Tage4 gene were compared to those of the human CD155 gene. The results indicated that the Tage4 gene is probably orthologous to the gene for CD155.
