Activation and centromeric localization of CCAAT/enhancer-binding proteinsduring the mitotic clonal expansion of adipocyte differentiation

Hormonal induction of 3T3-L1 preadipocytes triggers a cascade of events tha t initiate differentiation into adipocytes. CCAAT/enhancer-binding proteins beta and delta (C/EBP beta/delta) are expressed early in the differentiati on program, but are not immediately active. After a long lag, C/EBP beta/de lta become competent to bind to the C/EBP regulatory element in the C/EBP a lpha gene promoter, C/EBP alpha being a transcriptional activator of numero us adipocyte genes. As C/EBP beta/delta acquire binding activity, they beco me localized to centromeres as preadipocytes synchronously enter S phase at the onset of mitotic clonal expansion. Localization to centromeres occurs through C/EBP consensus-binding sites in centromeric satellite DNA. C/EBP a lpha, which is antimitotic, becomes centromere-associated much later in the differentiation program as mitotic clonal expansion ceases and the cells b ecome terminally differentiated.