Cell-type dependency of two Foxa/HNF3 sites in the regulation of vitronectin promoter activity

The mouse vitronectin promoter has two consensus sequences of the Foxa/hepatocyte nuclear factor (HNF) 3-binding site (from -34 to -25, site A, and +15 to +26 base pairs (bp), site B). Site-directed mutagenesis of site B inhibited binding of nuclear proteins from mouse neuroblastoma Neuro2a and reduced the promoter activity to 4.6% in a 101-bp fragment (from -48 to +53 bp) in Neuro2a cells. The nuclear proteins of site B were identified as the Foxa1/HNF3alpha and Foxa2/HNF3beta proteins by supershift assay. Next, we examined site A. Mutation of site A in Neuro2a cells did not affect the promoter activity, and binding of nuclear proteins was not detected. Overexpression of Foxa1 or Foxa2 protein activated the mutated site B promoter, but failed to activate the sites A and B double-mutated promoter in Neuro2a cells, indicating that site A is a potential transcription regulatory site. Recombinant Foxa1 and Foxa2 proteins and nuclear extract from mouse liver bound not only to site B, but also to site A. In human hepatoma HepG2 cells, mutation of sites A and B decreased the promoter activity to 82% and 38%, respectively, in the wild promoter, and double mutation of sites A and B decreased the wild promoter activity to 5%, indicating that sites A and B contribute to the promoter activity in HepG2 cells. These results demonstrate that the two Foxa-binding sites regulate the vitronectin promoter activity in cell type-dependent manner.