Sequential gene promoter interactions of C/EBPβ, C/EBPα, and PPARγ during adipogenesis

Treatment of 3T3-L1 preadipocytes with differentiation inducers triggers a cascade in which C/EBPβ is rapidly expressed, followed by C/EBPα and PPARγ. C/EBPα and PPARγ then activate the expression of adipocyte genes that produce the differentiated phenotype. Circumstantial evidence indicates that C/EBPβ activates transcription of the C/EBPα and PPARγ genes, both of which possess C/EBP regulatory elements in their proximal promoters. Although C/EBPβ is expressed immediately upon induction of differentiation, acquisition of DNA binding activity is delayed for ∼14h. Chromatin immunoprecipitation (ChIP) analysis conducted 24h after induction revealed that C/EBPβ binds to C/EBP regulatory elements in the proximal promoters of the C/EBPα and PPARγ genes. After an additional delay ChIP analysis showed that C/EBPα binds to its own promoter and to the promoters of the PPARγ and 422/aP2 genes. These findings support the view that once expressed, C/EBPα is responsible for maintaining the expression of PPARγ and C/EBPα, as well as adipocyte proteins (e.g., 422/aP2) in the terminally differentiated state. Together these findings provide compelling evidence that C/EBPβ, C/EBPα, and PPARγ participate in a cascade during adipogenesis.