Down-regulation of CEACAM1 in breast cancer.

Carcinoembryonic antigen-related adhesion molecule 1 (CEACAM1) is a type 1 transmembrane glycoprotein belonging to the CEA family, which has been found to exist as either soluble forms in body fluids or membrane-bound forms on the cell surface. Aberrant CEACAM1 expression is associated with tumor progression and has been found in a variety of human malignancies. Increasing interest has been devoted to the expression of CEACAM1 in breast cancer, but most of these findings are contradictory. The aim of this study was to investigate CEACAM1 expression in breast cancer in greater detail. Using immunohistochemical staining, we found that CEACAM1 expression was reduced or lost in breast cancer tissues compared with noncancerous breast tissues. In addition, soluble CEACAM1 levels in the culture medium of breast cancer cell lines were significantly lower than those in a nontumorigenic breast epithelial cell line. Immunofluorescence analysis consistently showed that breast cancer cell lines have relatively low expression of membrane-bound CEACAM1. Furthermore, CEACAM1 mRNA and protein expression levels were down-regulated in breast cancer cell lines as measured using real-time reverse transcriptase-polymerase chain reaction and western blot analysis, respectively. Taken together, our results demonstrate a systematic down-regulation of CEACAM1 in breast cancer and suggest that a strategy to restore CEACAM1 expression may be helpful for the treatment of breast cancer.