The Wnt destruction complex scaffold proteins APC and AXIN1 directly target SREBP2, the master regulator of cholesterol biosynthesis, for FBXW7-mediated degradation through a β-catenin-independent, GSK3β/CK1α-independent mechanism that requires phosphorylation of a conserved phosphodegron, and cancer-associated APC truncations that retain partial β-catenin-degrading activity completely abolish SREBP2 regulation, thereby linking loss of APC tumor suppressor function to dysregulated cholesterol metabolism in colorectal cancer.

APC, the core scaffold of the Wnt destruction complex, targets the transcriptional co-activator β-catenin for proteolysis. There is no convincing evidence that APC directs degradation of other substrates. Using a reconstituted cytosolic extract-based system and complementary in vivo and cellular assays, we show that SREBP2, the master regulator of cholesterol biosynthesis, is a direct APC–AXIN1 substrate. APC-dependent SREBP2 degradation is conserved in Xenopus embryos, mouse colon, and human colorectal cancer cells and restricts SREBP2 target-gene expression, cholesterol synthesis, and tissue cholesterol levels. Mechanistically, APC and AXIN1 promote SREBP2 degradation via a conserved phosphodegron, which marks SREBP2 for ubiquitination by the E3 enzyme, FBXW7. Like β-catenin, SREBP2 is stabilized by extracellular Wnt ligands; unlike β-catenin, its regulation is independent of GSK3β and CK1α and requires the entire APC mutational cluster region (MCR), whereas β-catenin turnover can operate with only a partial MCR. These findings define a β-catenin-independent branch of Wnt signaling that couples APC to sterol metabolism, providing a mechanistic rationale to target the mevalonate/SREBP2 axis in APC-mutant colorectal cancer.