Regulation of Wnt/β-catenin signaling by CCAAT/enhancer binding protein β during adipogenesis

Activation of the Wnt/β-catenin signaling pathway inhibits adipogenesis, while disruption of Wnt signaling leads to spontaneous adipogenesis. CCAAT/enhancer binding protein β (C/EBPβ) is rapidly induced in early stages of adipogenesis and is responsible for transcriptional induction of two major adipogenic transcription factors, peroxisome proliferator-activated receptor γ (PPARγ) and C/EBPα. In this study, we examined whether C/EBPβ is involved in the suppression of Wnt/β-catenin signaling during adipogenesis. Knockdown of C/EBPβ expression not only inhibited adipogenesis but also maintained active Wnt/β-catenin signaling, after addition of adipogenic inducers. In contrast, overexpression of C/EBPβ substantially inhibited Wnt signaling. Interestingly, our data showed that C/EBPβ is involved in the expression of Wnt10b, a major Wnt ligand in preadipocytes, even though C/EBPβ is not an essential factor to regulate Wnt10b expression during adipogenesis, and that C/EBPβ inhibits Wnt10b promoter activity by directly binding to specific regions of the promoter. These results suggest a dual function of C/EBPβ: stimulating expression of adipogenic genes and inhibiting Wnt signaling.