The tyrosine kinase inhibitor genistein inhibits 3T3-L1 adipogenesis when present during the first 72h of differentiation. In this report, we investigated the underlying mechanisms involved in the anti-adipogenic effects of genistein. We found that genistein blocked the DNA binding and transcriptional activity of CCAAT/enhancer-binding protein β (C/EBPβ) during differentiation by promoting the expression of C/EBP homologous protein, a dominant-negative member of the C/EBP family. Loss of C/EBPβ activity was manifested as a loss of differentiation-induced C/EBPα and peroxisome-proliferator-activated receptor γ protein expression and a dramatic reduction in lipid accumulation. Further, we documented for the first time that C/EBPβ was tyrosine-phosphorylated in vivo during differentiation and in vitro by activated epidermal growth factor receptor. Genistein inhibited both of these events. Collectively, these results indicate that genistein blocks adipogenesis and C/EBPβ activity by increasing the level of C/EBP homologous protein and possibly by inhibiting the tyrosine phosphorylation of C/EBPβ.

Abbreviations used: ALLN, N-acetyl-Leu-Leu-norleucinal; C/EBP, CCAAT/enhancer-binding protein; CHOP, C/EBP homologous protein; DMEM, Dulbecco's modified Eagle's medium; DTT, dithiothreitol; EGF, epidermal growth factor; FBS, foetal bovine serum; GADD153, growth arrest and DNA damage-inducible gene 153; MIX, 1-methyl-3-isobutylxanthine; MDI, MIX, dexamethasone and insulin; NP40, Nonidet P40; PPAR, peroxisome-proliferator-activated receptor.

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