Nucleoprotein complexes that regulate gene expression in adipocyte differentiation: direct participation of c-fos

Adipocyte differentiation is accompanied by the transcriptional activation of many new genes, including a putative lipid-binding protein termed adipocyte P2 (aP2). The aP2 gene contains a regulatory element (FSE2) 124 bases 5′ to its start of transcription. This element binds nuclear factors in sequence-specific and differentiation-dependent fashion as determined by altered mobility in gel retardation assays. Deletion analysis of promoter-linked transfection assays and competition of these constructions in cells with a synthetic FSE2 element suggest that trans-acting factors bind to this region and act as negative regulators of aP2 gene activity in preadipocytes. c-fos appears to participate directly in this nucleoprotein complex, as demonstrated by the ability of antibodies to c-fos to disrupt specific binding of factors to the FSE2 sequence but not to factor-binding sequences from several other genes. Antibodies to c-fos specifically immunoprecipitate protein complexes covalently bound to FSE2 DNA via UV cross-linking.