Independent Induction of Caspase-8 and cFLIP Expression during Colorectal Carcinogenesis in Sporadic and HNPCC Adenomas and Carcinomas

Background: TNF-Related Apoptosis Inducing Ligand (TRAIL) is a promising agent for the induction of apoptosis in neoplastic tissues. Important determinants of TRAIL sensitivity are two intracellular proteins of the TRAIL pathway, caspase-8 and its anti-apoptotic competitor cellular Flice-Like Inhibitory Protein (cFLIP). Methods: The aim of this study was to investigate basic expression of caspase-8 and cFLIP in normal colorectal epithelium (n = 20), colorectal adenomas (n = 66) and colorectal carcinomas (n = 44) using immunohistochemistry performed on both sporadic and Hereditary Non-Polyposis Colorectal Cancer (HNPCC or Lynch syndrome)-associated adenomas and carcinomas. Results: Expression of both caspase-8 and cFLIP was similar in cases with sporadic and hereditary origin. Expression of caspase-8 in colorectal adenomas and carcinomas was increased when compared to normal colon tissue (P = 0.02). Nuclear, paranuclear as well as cytoplasmic localizations of caspase-8 were detected. Immunohistochemistry revealed an upregulation of cFLIP in colorectal carcinomas in comparison to normal epithelium and colorectal adenomas (P < 0.001). A large variation in the caspase-8/cFLIP ratio was observed between the individual adenomas and carcinomas. Conclusion: Caspase-8 and cFLIP are upregulated during colorectal carcinogenesis. Upregulation of caspase-8 and/or downregulation of cFLIP may be interesting approaches to maximize TRAIL sensitivity in colorectal neoplasms.