GATA-6 STIMULATES A CELL LINE-SPECIFIC ACTIVATION ELEMENT IN THE HUMAN LACTASE PROMOTER

Lactase-phlorizin hydrolase (LPH) synthesis is restricted to different iated small intestinal enterocytes and is highly regulated during deve lopment. Analysis of expression of LPH promoter segments fused with lu ciferase transfected in Caco-2 cells, a line that uniquely expresses L PH mRNA, mapped an 18-base pair (bp) segment 100 bp upstream of the tr anscription start site that is required for transactivation. Remarkabl y, the LPH upstream element (LUE) has no stimulatory activity in both human intestinal and nonintestinal lines in which LPH mRNA is absent. Electrophoretic analysis of sequence-specific DNA-nuclear protein comp lexes demonstrated the presence of a Caco-2 cell-specific protein(s) ( CCP), which is uniformly absent in LPH nonproducer cell lines. Mutatio nal analysis of the LUE demonstrated that bases contained within a GAT A consensus motif are critical for both CCP binding and transcription from the LPH promoter. Caco-2 cells express high levels of GATA-6 mRNA in a cell line-specific manner, suggesting that GATA-6 is a CCP that complexes with the LUE. When expressed by a plasmid, GATA-6 transactiv ated the LPH promoter. The stimulation was abrogated with mutations in the GATA consensus motif as well as mutations in a flanking downstrea m element. These studies are consistent with an important role of an i ntestinal GATA binding protein in cell type-specific transactivation o f the LPH promoter.