Regulation of TRAIL receptor expression by β-catenin in colorectal tumours

Expression of the pro-apoptotic TRAIL receptors is regulated, at least in part, by beta-catenin. We show that beta-catenin co-localizes with DR4/5 in human and mouse colorectal tumours and that downregulation of beta-catenin in cell line models reduces TRAIL receptor expression and TRAIL sensitivity.Tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL) is being investigated as a targeted cancer therapeutic and the expression of its pro-apoptotic receptors, DR4 and DR5, increases during colorectal carcinogenesis. This study investigated the role of beta-catenin in the regulation of these receptors. In human colorectal adenoma and carcinoma cell lines, downregulation of beta-catenin resulted in lower total DR4 and DR5 protein levels. Similarly, cell membrane expression of DR4 and DR5 was reduced after downregulation of beta-catenin in colon carcinoma cells, whereas induction of beta-catenin in HeLa cells led to increased cell membrane expression of DR4 and DR5. Downregulation of beta-catenin decreased the recombinant human TRAIL sensitivity of human colon carcinoma cells. Activation of the transcription factor T-cell factor-4 (TCF-4) is an important function of beta-catenin. Dominant-negative TCF-4 overexpression, however, did not significantly affect TRAIL receptor expression or recombinant human TRAIL sensitivity. Human colorectal adenomas (N = 158) with aberrant (cytoplasmic and nuclear) beta-catenin expression had a higher percentage of immunohistochemical DR4 and DR5 staining per tumour (mean: 73 and 88%, respectively) than those with membranous beta-catenin staining only (mean: 50 and 70%, respectively, P < 0.01 for both). Furthermore, aberrant beta-catenin staining co-localized with DR4 and DR5 expression in 92% of adenomas. In 53 human colorectal carcinomas, aberrant beta-catenin expression was present in most cases and DR4/5 expression was largely homogenous. Similarly, in adenomas from APC(min) mice, cytoplasmic beta-catenin staining co-localized with staining for the murine TRAIL death receptor. In conclusion, the gradual increase in TRAIL receptor expression during colorectal carcinogenesis is at least partially mediated through increased beta-catenin expression, independently of TCF-4-signalling.