Abstract
The epithelial cell adhesion molecule (EpCAM) is a 40-kD type I transmembrane protein that is overexpressed in human epithelial cancers and is currently the target of molecular therapy based on its overexpression at the cell surface. Recently, we and others have shown a role for EpCAM in cell signaling and carcinogenesis, and EpCAM expression seems to promote breast cancer invasion. Interleukin-8 (IL-8/CXCL-8) is an inflammatory cytokine that has recently been shown to modulate breast cancer invasion and angiogenesis. In preliminary experiments, we identified a correlation between EpCAM and IL-8 expression in primary human breast cancers. Specific ablation of EpCAM in breast cancer cell lines results in decreased IL-8 expression, and IL-8 contributes to EpCAM-dependent breast cancer invasion. Specific ablation of EpCAM is also associated with decreased NF-κB transcription factor activity, decreased phosphorylation of the NF-κB family member RELA, and increased IκBα protein expression. EpCAM modulates IL-8 expression at baseline, and following IL-1β stimulation, which is known to be a potent inducer of NF-κB in breast cancer. In functional rescue experiments, specific ablation of RELA or forced expression of the NF-κB inhibitor protein IκBα prevented EpCAM-dependent rescue of IL-8 promoter activity. These studies show for the first time that EpCAM can modulate NF-κB transcription factor activity and IL-8 expression in breast cancer and confirm the role of EpCAM signaling in modulating breast cancer invasion. Further study is required to define the molecular mechanism(s) of EpCAM signaling in breast cancer and to direct the rational development of molecular therapies targeting EpCAM.