Expression of APO‐1 (CD95), a member of the NGF/TNF receptor superfamily, in normal and neoplastic colon epithelium

Abstract

APO-I is a 48-kDa cell-membrane protein identical to the Fas antigen now designated CD95. It is a member of the NGF/TNF receptor superfamily. Anti-APO-I monoclonal antibody induces apoptosis in a variety of cell types expressing this antigen. We immunohistochemically investigated APO-I expression in normal colon mucosa, 20 adenomas, 258 colon carcinomas and 10 liver metastases and carried out in vitro studies using a panel of colon-carcinoma cell lines. Immunohistochemically, APO-I was regularly expressed at the basolateral membrane of normal colon epithelia. In a minor fraction of colon adenomas and in 39.1% of colon carcinomas APO-I expression was diminished and in 48.1% of carcinomas, predominantly of the non-mucinous type, APO-I expression was completely abrogated. The normal level of APO-I in carcinomas was correlated with the mucinous type. Reduced/lost APO-I expression was more frequent in rectal carcinomas. Complete loss of APO-I was more frequent in tumors that had already metastasized. APO-I expression in liver metastases essentially corresponded to that of the primary tumors. Comparative analysis with data from previous studies revealed that the mode of APO-I expression is correlated with that of HLA-A,B,C./β₂m, HLA-DR, HLA-D-associated invariant chain and of the secretory component. Surface expression of APO-I was heterogeneous in colon-carcinoma cell lines; SW480 expressed considerable amounts of APO-I on all cells, while HT-29 constitutively did less so and only in a minority of cells. Surface density of APO-I and the fraction of positive cells in HT-29 was enhanced by interferon-gamma (IFN-γ) and, additively, by tumor necrosis factor-alpha (TNF-α), whereas in SW480 APO-I expression was not modulated by these cytokines. We conclude that neoplastic transformation of colon epithelium often leads to a loss of the physiologic, high level of surface APO-I by giving rise either to a stable lack of APO-I or to an IFN-γ/TNF-α-sensitive phenotype of inducible APO-I expression.