CDX2 homeoprotein is involved in the regulation of ST6GalNAc-I gene in intestinal metaplasia.

De novo expression of Sialyl-Tn (STn) antigen is one of the most common features of intestinal metaplasia (IM) and gastric carcinomas, and its biosynthesis has been mostly attributed to ST6GalNAc-I activity. However, the regulation of this glycosyltransferase expression is not elucidated. In IM lesions and in the intestine, CDX2 homeobox transcription factor is co-expressed with STn and ST6GalNAc-I. We therefore hypothesized that CDX2 might induce STn expression by positive regulation of ST6GalNAc-I. We showed that ST6GalNAc-I transcript levels and CDX2 have a coordinated expression upon Caco-2 in vitro differentiation, and overexpression of CDX2 in MKN45 gastric cells increases ST6GalNAc-I transcript levels. Nine putative CDX-binding sites in the ST6GalNAc-I-regulatory sequence were identified and analyzed by chromatin immunoprecipitation in Caco-2 cells and in IM. The results showed that CDX2 protein is recruited to all regions, being the most proximal sites preferentially occupied in vivo. Luciferase assays demonstrated that CDX2 is able to transactivate ST6GalNac-I-regulatory region. The induction was stronger for the regions mapped in the neighbourhood of ATG start codon and site-directed mutagenesis of these sites confirmed their importance. In conclusion, we show that CDX2 transcriptionally regulates ST6GalNAc-I gene expression, specifically in the preneoplastic IM lesion.