LEF1 and B9L Shield β-Catenin from Inactivation by Axin, Desensitizing Colorectal Cancer Cells to Tankyrase Inhibitors

Hyperactive beta-catenin drives colorectal cancer, yet inhibiting its activity remains a formidable challenge. Interest is mounting in tankyrase inhibitors (TNKSi), which destabilize beta-catenin through stabilizing Axin. Here, we confirm that TNKSi inhibit Wnt-induced transcription, similarly to carnosate, which reduces the transcriptional activity of beta-catenin by blocking its binding to BCL9, and attenuates intestinal tumors in Apc(Min) mice. By contrast, beta-catenin's activity is unresponsive to TNKSi in colorectal cancer cells and in cells after prolonged Wnt stimulation. This TNKSi insensitivity is conferred by beta-catenin's association with LEF1 and BCL9-2/B9L, which accumulate during Wnt stimulation, thereby providing a feed-forward loop that converts transient into chronic beta-catenin signaling. This limits the therapeutic value of TNKSi in colorectal carcinomas, most of which express high LEF1 levels. Our study provides proof-of-concept that the successful inhibition of oncogenic beta-catenin in colorectal cancer requires the targeting of its interaction with LEF1 and/or BCL9/B9L, as exemplified by carnosate. (c) 2014 AACR.