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.