Cholest-4-en-3-one attenuates TGF-β responsiveness by inducing TGF-β receptors degradation in Mv1Lu cells and colorectal adenocarcinoma cells

Purpose: The transforming growth factor-beta (TGF-beta) pathway is an important in the initiation and progression of cancer. Due to a strong association between an elevated colorectal cancer risk and increase fecal excretion of cholest-4-en-3-one, we aim to determine the effects of cholest-4-en-3-one on TGF-beta signaling in the mink lung epithelial cells (Mv1Lu) and colorectal cancer cells (HT29) in vitro. Methods: The inhibitory effects of cholest-4-en-3-one on TGF-beta-induced Smad signaling, cell growth inhibition, and the subcellular localization of TGF-beta receptors were investigated in epithelial cells using a Western blot analysis, luciferase reporter assays, DNA synthesis assay, confocal microscopy, and subcellular fractionation. Results: Cholest-4-en-3-one attenuated TGF-beta signaling in Mv1Lu cells and HT29 cells, as judged by a TGF-beta-specific reporter gene assay of plasminogen activator inhibitor-1 (PAI-1), Smad2/3 phosphorylation and nuclear translocation. We also discovered that cholest-4-en-3-one suppresses TGF-beta responsiveness by increasing lipid raft and/or caveolae accumulation of TGF-beta receptors and facilitating rapid degradation of TGF-beta and thus suppressing TGF-beta-induced signaling. Conclusions: Our results suggest that cholest-4-en-3-one inhibits TGF-beta signaling may be due, in part to the translocation of TGF-beta receptor from non-lipid raft to lipid raft microdomain in plasma membranes. Our findings also implicate that cholest-4-en-3-one may be further explored for its potential role in colorectal cancer correlate to TGF- beta deficiency.