CCAAT ENHANCER-BINDING PROTEIN-ALPHA (C/EBP-ALPHA) UNDIFFERENTIATED PROTEIN - A DEVELOPMENTALLY-REGULATED NUCLEAR-PROTEIN THAT BINDS TO THE C/EBP-ALPHA GENE PROMOTER

During differentiation of 3T3-L1 preadipocytes into adipocytes, transcription of the C/EBPalpha (CCAAT/enhancer binding protein alpha) gene is activated. The promotor of the C/EBPalpha gene contains a bipartite cis element with binding sites for C/EBPalpha undifferentiated protein (CUP) and an Sp1-like GT box binding protein. Binding of CUP to this element is markedly enhanced by its interaction with the Spl-like protein. CUP, purified almost-equal-to 100,000-fold from HeLa cell nuclear extracts, appears to be composed of at least two types of subunit. Evidence is presented that a CUP-containing protein complex bridges between the CUP/Sp1-like GT box element and a downstream cis element, which contains a C/EBP binding site. During differentiation of 3T3-L1 preadipocytes into adipocytes, CUP activity or expression decreases as expression of C/EBPalpha increases. It is suggested that bridging by the CUP-containing protein complex may play a role in transcriptional regulation of the C/EBPalpha gene.