Cell-specific Expression of Mouse Albumin Promoter: Evidence for Cell-specific DNA Elements within the Proximal Promoter Region and cis-acting DNA Elements Upstream of −160

Abstract

Regulation of albumin gene expression is believed to be mediated by multiple nuclear factors that interact with cis-acting DNA sequences within the first 160 base pairs (bp) of the promoter. The minimal promoter sequence required to generate tissue-specific expression has not been clearly defined. We have constructed a series of transient expression vectors containing progressive deletions of the mouse albumin gene 5′-flanking sequence fused to the bacterial chloramphenicol acetyltransferase (CAT) gene and include the Moloney murine leukemia viral (Mo-MuLV) enhancer. Promoter activity was determined in mouse hepatoma and fibroblast cell lines by chloramphenicol acetyltransferase and S1 nuclease analyses. All constructions were compared with −623 Albcat-Mo-MuLV which contains all the sequence homology between the rat and mouse promoters. Low levels of expression were observed with −60 Albcat-Mo-MuLV (10%) in hepatoma but not fibroblast cells. Addition of promoter sequence to −208 bp progressively increased activity to 190% in the hepatoma cells, while −308 and −1612 Albcat-Mo-MuLV had activity similar to the −623 Albcat-Mo-MuLV level, and −3000 Albcat-Mo-MuLV showed a 2-fold reduction in transcriptional activity. The inclusion of promoter sequences upstream of −60 generated low levels of expression in the fibroblasts. We also show that factors from mouse liver nuclear extracts protect at least five regions of the albumin promoter upstream of −160. Our results indicate that tissue specificity is established within the proximal promoter region and that additional cis-acting elements that may have a functional role in the efficiency of albumin gene expression are located upstream of −160 bp.