Subcellular expression of c-IAP1 and c-IAP2 in colorectal cancers: Relationships with clinicopathological features and prognosis

The Inhibitor of Apoptosis Protein (IAP) family includes several critical cell death inhibitors, the expression of which could be involved in colorectal carcinogenesis. Among them, c-IAP1 and c-IAP2 expression has never been investigated in colorectal cancer. The present study was designed to determine whether expression of both IAPs was related to pathological parameters and survival in sporadic colon carcinomas. Analysis of five human colon cancer cell lines by both western blotting of cell fractions and immunocytochemistry showed that the two IAPs could be expressed both in the nucleus and in the cytoplasm. Immunohistochemical analysis of a series of 46 sporadic colorectal adenocarcinomas demonstrated that c-IAP1 expression was more frequent in the nucleus (85%), and that c-IAP2 was more often expressed in the cytoplasm (82%). A significant association was identified between a strong lymphoid infiltrate in the stroma and the nuclear expression of c-IAP2 (p = 0.02). No other relationship was observed between IAP expression and pathological features. After adjusting by age and stage, the relative risk of death was lower for cytoplasmic c-IAP1, cytoplasmic c-IAP2, and nuclear c-IAP2 expression. It was higher for nuclear c-IAP1 expression. These associations were not statistically significant, but this work underlines the importance of taking into account the subcellular location of the IAP family members in the evaluation of their prognostic significance.