Cloning and expression of the mRNA of human galectin-4, an S-type lectin down-regulated in colorectal cancer.

We are interested in the characterization of genes whose expressions in the colon are modified during colorectal carcinogenesis. Our approach was to establish the phenotype of a colon tumor by partial sequencing of a large number of transcripts, then to select mRNAs of potential interest by differential screening with complex probes from normal or cancerous colon. In this paper, we report the cloning and sequencing of a mRNA strongly underexpressed in colorectal cancer. It corresponded to a protein comprising 323 amino acids, that appeared to be human galectin-4 on the basis of 76% and 79% amino acid identity to the rat and pig counterparts, respectively. Tissue distribution analysis showed that its expression was restricted to the small intestine, colon and rectum. Galectin-4 expression was compared in tumor and normal adjacent colon of 19 patients. In 18 patients, the mRNA concentration was 1.5-50-times lower in the tumor. No significant correlation was observed between decreased expression of galectin-4 and the degree of differentiation of the tumor or Duke's state. These results suggest that decreased galectin-4 mRNA expression may be an early event in colon carcinogenesis. Among five cell lines derived from colon carcinoma, only two (HT29 and LS174T) expressed galectin-4 mRNA.