The cell-specific elastase I enhancer comprises two domains.

Two separate domains within the 134-base-pair rat elastase I enhancer and a third domain at the enhancer-promoter boundary are required for selective expression in pancreatic acinar cells. The domains were detected by a series of 10-base-pair substitution mutations across the elastase I gene regulatory region from positions -200 to -61. The effect of each mutant on the pancreas-specific expression of a linked chloramphenicol acetyltransferase gene was assayed by transfection into pancreatic 266-6 acinar cells and control NIH/3T3 cells. The two enhancer domains are nonredundant, because mutations in either eliminated (greater than 100-fold reduction) expression in 266-6 cells. DNase I protection studies of the elastase I enhancer-promoter region with partially purified nuclear extracts from pancreatic tissue and 266-6 cells revealed nine discrete protected regions (footprints) on both DNA strands. One of three footprints that lie within the two functional domains of the enhancer contained a sequence, conserved among several pancreas-specific genes, which when mutated decreased linked chloramphenicol acetyltransferase expression up to 170-fold in 266-6 cells. This footprint may represent a binding site for one or more pancreas-specific regulatory proteins.     

Extinction of alpha-fetoprotein gene expression in somatic cell hybrids involves cis-acting DNA elements.

alpha-Fetoprotein (AFP), a liver-specific protein, is extinguished in somatic cell hybrids formed by the fusion of mouse hepatoma cells (BWTG3) with rat fibroblast cells (JF1). Our studies show that the extinction of mouse AFP expression in these somatic cell hybrids may involve at least two cis-acting regulatory domains, i.e., the enhancer elements and a tissue-specific promoter region, which are located in the 5'-flanking region of the AFP gene.     

Similarities and differences in the function of regulatory elements at the 5' end of the human apolipoprotein B gene in cultured hepatoma (HepG2) and colon carcinoma (CaCo-2) cells.

The arrangement of regulatory elements along the apolipoprotein B promoter region (positions -898 to +1) has been examined in transient transfection experiments performed in HepG2 and Hep3B (hepatic) and CaCo-2 (intestinal) cell lines, all of which express the apoB gene, and also in Chinese hamster ovary cells, which do not express the gene. The overall distribution of positive and negative regulatory segments was very similar in the two hepatoma cell lines (HepG2 and Hep3B) but different from that observed in the colon carcinoma cells (CaCo-2). Thus, whereas 260 base pairs of 5'-flanking sequence were sufficient for maximal expression of the promoter in HepG2 cells, only 139 nucleotides were required for maximal expression in CaCo-2 cells. Promoter activity in Chinese hamster ovary cells was exhibited by short constructs, with maximal activity for the -85 construct. DNase I footprinting of the apolipoprotein B promoter region using hepatic and intestinal extracts revealed multiple sites of interaction between the DNA and nuclear proteins. Gel retention experiments using the region from -262 to -88 (the region of greatest contrast between HepG2 and CaCo-2 cells) revealed interesting variations in the relative abundance of various nuclear proteins between the two cell types. A major functional difference between HepG2 and CaCo-2 cells was localized to the region between -111 and -88, which harbors the sequence TGTTTGCT, a motif present in the promoter region of several liver-specific genes. The molecular basis for the functional differences between these two cell types may be attributable to a difference in the relative abundance of three proteins that bind to sequences between -111 and -88.