Reporter gene analysis of four DNaseI hypersensitive sites in the plasminogen/apolipoprotein(a) intergenic region.

We have previously described four DNaseI hypersensitive sites (DH 1 to DH4) in the 40-kb intergenic region between the plasminogen gene and the apo(a) gene. Here, we wanted to analyse whether any of these sites, located 4, 21, 28 and 34 kb upstream of the apo(a) transcriptional start site, would act as an enhancer on a minimal apo(a) promoter. Starting from a cloned, highly expressed apo(a) allele, we obtained four fragments comprising the DHI to DH4 sites, respectively. These fragments were cloned in both orientations into a luciferase reporter gene plasmid comprising a minimal apo(a) promoter (-100 to +141 with respect to the transcriptional start site). Our results from transfection studies with the resulting series of reporter gene plasmids into liver (HepG2) and non-liver (HeLa) cells suggest that the four DH sites from the selected apo(a) allele do not provide a strong, liver-specific enhancer activity.