Identification of new sites of binding and activation of the murine α1(I) collagen promoter by CCAAT/enhancer binding protein β

The CCAAT/enhancer binding protein β (C/EBPβ) was previously shown to bind to the α1(I) collagen promoter at -365 to -335 (site 1) and to activate it. Acetaldehyde also activates the promoter, and this effect is mediated by an increase in stellate-cell C/EBPβ protein and C/EBPβ binding. The present study identified two additional distal sites (sites 2 and 3) of binding of C/EBPβ, in the nuclear extracts of stellate cells, at -399 to -370 and -623 to -592 in the α1(I) collagen promoter. The C/EBPβ protein activates the promoter at all three sites. Acetaldehyde increases C/EBPβ binding to all three sites. Activation by acetaldehyde is abrogated in the transfected promoter mutated at either site 1 or site 3 but is not affected by mutation at site 2. Binding of the 20-kDa C/EBPβ isoform (p20C/EBPβ), which is eliminated by mutation at the distal site 3 of C/EBP binding, is necessary for the activation by acetaldehyde of the α1(I) collagen promoter.