REGULATORY ELEMENTS AND DNA-BINDING PROTEINS MEDIATING TRANSCRIPTION FROM THE CHICKEN VERY-LOW-DENSITY APOLIPOPROTEIN-II GENE

The chicken Very-Low-Density Apolipoprotein ll (apoVLDL II) gene is specifically expressed in liver in response to estrogen. In this study, we performed a functional analysis of the 300-base pair region immediately 5' to the gene by gene transfer of chloramphenicol acetyl transferase (CAT) constructs into chicken embryonic hepatocytes (CEH). Two estrogen response elements (EREs) could be distinguished which together form a potent estrogen response unit. Stimulation of transient expression by co-transfection with a plasmid expressing rat C/EBP confirmed that a similar protein in chicken liver may be involved in apoVLDL ll transcription. In vitro DNasel footprinting and band-shift analysis with liver, oviduct and spleen nuclear extract revealed the tissue distribution of the proteins binding to the promoter region. A liver-specific protein bound to multiple sites of which some resembled the recognition sequence of the CCAAT/Enhancer binding protein, C/EBP. Of the other proteins binding to the apoVLDL 11 promoter, one was identified as the liver-specific LF-A1 by mobility shift analysis, using purified bovine LF-A1, and another as the general COUP-transcription factor, using an antiserum against the human COUP-TF.