DEC1 is positively associated with the malignant phenotype of invasive breast cancers and negatively correlated with the expression of claudin-1

Differentiated embryo-chondrocyte expressed gene 1 (DEC1) is a basic helix-loop-helix transcriptional regulator, reportedly involved in cell growth, differentiation, apoptosis and tumorigenesis. In breast cancer, DEC1 expression correlates with increased malignant potential and invasiveness. Nevertheless, the detailed mechanisms by which DEC1 modulates breast cancer progression are still unclear. Claudin-1, an important tight junction protein, functions as a tumor invasion suppressor. In the present study, the relationship between DEC1 and claudin-1 in 147 cases of invasive breast ductal carcinomas was examined by immunohistochemistry. Based on the data, DEC1 expression was elevated in invasive breast ductal carcinomas and DEC1 levels were positively correlated with tumor grade (P=0.023). Moreover, DEC1 expression was negatively correlated with the claudin-1 level (correlation coefficient =-0.245, P=0.003). We further identified that, in MCF-7 and MDA-MB-231 breast cancer cell lines, DEC1 knockdown led to the enhanced expression of claudin-1 at both the mRNA and protein levels, and reduced cell invasive capacity. Collectively, our data suggest that overexpression of DEC1 may promote the invasiveness of breast cancer through downregulation of claudin-1.