CD10 is a widely expressed endopeptidase that is present in human colorectal cancer (CRC), which shows a high frequency of liver metastasis. CD10 expression in CRC cells is associated with liver metastasis in rodent models, and CD10 expression enhances the phosphorylation of epidermal growth factor (EGF) receptor (EGFR) and extracellular signalregulated kinase (ERK) l/2. Met-enkephalin (MENK), a CD10 substrate, activates its specific receptor δ-opioid receptor (DOR), which is expressed in CRCs. DOR is a partial agonist of ERK1/2, which suppresses EGF-induced phosphorylation of EGFR and ERK1/2. CD10 retains EGF-induced EGFR activation by degrading MENK. Paradoxically, CRCs express MENK at a high frequency. Since MENK suppresses T lymphocytes, CD10-expressing CRCs can escape from T-cell immunity without exhibiting auto-inhibition. CD10 is strongly associated with the metastasis of CRCs to the liver via an immunosuppressive mechanism. Additionally, CD10 may be an excellent serum marker for liver metastasis in patients with CRC and could represent a potential molecular target for antimetastatic treatment in patients with CRC
