Objective: To examine the role of CD10, a characteristic marker of liver metastasis of colorectal cancers (CRCs).
Design: The effect of CD10 and Met-enkephalin (MENK) in CD10-positive and -negative human CRC cells was investigated under in vitro and in vivo conditions. Human CRC samples were examined.
Main outcome measure: CD10-positive and CD10-knockdown HT29 cells and CD10-negative and CD10-transfected Colo320 cells in nude mice were treated with MENK and/or the CD10 inhibitor (thiorphan). Intracellular signaling of MENK and ƒÔ-opioid receptor (DOR) was examined by immunoblotting.
Results: MENK inhibited the growth, invasion, and survival of CRC cells following thiorphan-induced CD10 inactivation. Thiorphan suppressed liver metastasis of CD10-positive CRC cells. Inoculation of mice with CRC cells induced MENK expression in the liver. Inhibition of hepatic MENK expression by cholesterol-conjugated antisense S-oligodeoxynucleotide increased liver metastasis of CRC cells even when the cells did not express CD10. DOR activation by MENK decreased the phosphorylation of epidermal growth factor receptor and extracellular signal-regulated kinase and increased p38-dependent apoptosis. Nitric oxide was found to induce DOR expression in CRC cells. Co-treatment with thiorphan and a nitric oxide donor had a marked antitumor effect on liver metastasis of HT29 cells. Of 68 CRC patients, 19 (28%) showed CD10 expression, which was dependent on the extent of liver metastasis. MENK concentration in metastasis-positive human liver was higher than that in the normal liver.
Conclusion: CD10 expression in CRC cells abrogates the antitumor effect of hepatic MENK by degrading it, which enhances liver metastasis of CD10-positive CRC cells.