Destabilization of EpCAM dimer is associated with increased susceptibility towards cleavage by TACE

The cell-surface protein EpCAM is a carcinoma marker utilized in diagnostics and prognostics, and a promising therapeutic target. It is involved in nuclear signaling via regulated intramembrane proteolysis (RIP). Many aspects of this process are not fully understood, including the events at the molecular level leading to the exposure of cleavage sites, buried at the dimerization interface. To investigate the effect of dimer stability on cleavage susceptibility we prepared two mutants of human EpCAM ectodomain: a monomeric form, and a disulfide-stabilized dimeric form. We show that the disulfide-stabilized dimer is resistant to tumor necrosis factor-α-converting enzyme (TACE) cleavage, while the monomeric form is more susceptible than the predominantly dimeric wild type. This provides experimental evidence that the oligomeric state of EpCAM is a determinant in RIP and demonstrates the usefulness of the oligomeric state-specific mutants in investigations of EpCAM biological function.