Transcription factor Sp1 activates involucrin promoter activity in non-epithelial cell types

The gene for human involucrin (hINV) is selectively expressed in stratifyin g epithelial cells lining external body surfaces. Previously, we characteri zed the hINV promoter 5' distal regulatory region (DRR) located between nt -2473 and -2088 upstream of the transcription start site. This region is re quired for optimal hINV gene expression. The DRR contains weak and strong a ctivator elements. The strong activator comprises AP1- and Sp1-binding site s that combine to drive high-level promoter expression in human keratinocyt es. Here we show that the hINV promoter is expressed in a cell-specific man ner in vitro and that the DRR contains elements that are partly responsible for cell-type-specific expression of hINV. hINV promoter activity is barel y detectable in 3T3 fibroblasts or HEK-293 human embryonic kidney cells. Re porter plasmids containing the full-length promoter or the isolated DRR can , however, be activated in 3T3 and HEK-293 cells by co-transfection with a plasmid encoding the transcription factor Sp1. Consistently with the lower hINV promoter activity, immunoblotting studies indicate that Sp1 protein le vels are lower in 3T3 and HEK-293 cells than in human epidermal keratinocyt es. Increased Sp1 protein in transfected 3T3 cells and HEK-293 cells correl ates with increased promoter activity. In addition, Sp1 transfection activa tes the expression of the endogenous gene for hINV in HEK-293 cells, These studies suggest that Sp1 might have a role in cell-specific expression of h INV.