Overexpression of the CD155 gene in human colorectal carcinoma

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.

Figure 1

Overview of the different CD155 transcripts and localisation of the oligonucleotides used for reverse transcription-polymerase chain reaction (RT-PCR) analysis. (A) Exon/intron organisation of the CD155 gene. Oligonucleotides CD1 and CD2, used to quantify expression of the CD155 gene, are located in a region corresponding to the extracellular domain of the protein which is conserved in all splice variants. Primers CD5 and CD15, used for qualitative analysis of CD155 expression, are located on each side of the different splice sites. Part of intron 6 is missing in variant β. The entire exon 6 is missing from variant γ. The predicted size of the different amplicons is indicated. (B) Agarose gel electrophoresis of CD155 transcripts amplified by RT-PCR from SW1116 colon cancer cells. Amplification was performed with oligonucleotides CD1 and CD2 (lane 1) or CD5 and CD15 (lane 2). No DNA was amplified when the reverse transcription was performed in the absence of reverse transcriptase.

Figure 2

Increased levels of CD155 in human colorectal carcinoma. Reverse transcription-polymerase chain reaction analysis of CD155 expression was performed on paired tumorous (lanes T) and non-tumorous (lanes N) colorectal tissues from four patients, as described in materials and methods.

Figure 3

CD155 is overexpressed in malignant epithelial cells in colorectal carcinoma. (A) Colon adenocarcinoma shows immunoreactivity with monoclonal antibody D171 (×200). (B) Adjacent section stained with an irrelevant monoclonal antibody (×200). (C) Normal colonic tissue showing barely detectable CD155 immunoreactivity (×200). (D) Normal section stained with an irrelevant monoclonal antibody (×200).