Abstract
Increased maspin expression in the colon is related to colon cancer risk and patient survival. Maspin is induced by the hydrophobic bile acid, deoxycholate (DOC), which is an endogenous carcinogen and inducer of oxidative stress and DNA damage in the colon. Persistent exposure of colon epithelial cells, in vitro, to high physiologic levels of DOC results in increased constitutive levels of maspin protein expression associated with the development of apoptosis resistance. When an apoptosis-resistant colon epithelial cell line (HCT-116RC) developed in the authors' laboratory was treated with a maspin-specific siRNA probe, there was a statistically significant increase in apoptosis compared to treatment with an siRNA control probe. These results indicate, for the first time, that maspin is an anti-apoptotic protein in the colon. Immunohistochemical evaluation of maspin expression in human colonic epithelial cells during sporadic colon carcinogenesis (131 human tissues evaluated) indicated a statistically significant increase in maspin protein expression beginning at the polyp stage of carcinogenesis. There was no statistically significant difference in maspin expression between hyperplastic/adenomatous polyps and colonic adenocarcinomas. The absence of "field defects" in the non-neoplastic colonic mucosa of patients with colonic neoplasia indicates that maspin may drive the growth of tumors, in part, through its anti-apoptotic function.