Retinoic acid induces Gpx2 gene expression in MCF-7 human breast cancer cells

We showed previously that the selenium-dependent glutathione peroxidase, GP X-GI, encoded by the Gpx2 gene, is highly expressed in the epithelium of th e gastrointestinal (GI) tract and sporadically in breast tissue, To investi gate whether Gpx2 gene expression is epithelium specific, we used in situ h ybridization to show that Gpx2 mRNA is highly expressed in the crypt epithe lium of human intestine. We also used Northern analysis to study human brea st cells and found Gpx2 mRNA in human mammary epithelial cell lines as well as freshly isolated normal breast epithelial cells, Because we identified three putative retinoic acid response elements (RARE) in the Gpx2 gene, we examined the regulation of the Gpx2 gene expression by all-trans retinoic a cid (RA) in RA-sensitive MCF-7 cells and RA-resistant HT29 cells. Without R A, MCF-7 cells had very low levels of Gpx2 mRNA and a low level of glutathi one peroxidase (GPX) activity (17 mU/mg protein), whereas HT29 cells had a high level of Gpx2 mRNA and GPX activity (200 mU/mg protein). RA treatment increased Gpx2 mRNA level 3- to 11-fold and resulted in a fourfold increase of GPX activity (80 mU/mg protein) in MCF-7 cells. Neither Gpx2 mRNA level nor GPX activity was increased in HT29 cells, These results show that the Gpx2 gene is expressed in both breast and intestinal epithelium cells, and suggest that its expression can be highly regulated by retinoic acid, a kno wn differentiation agent.