The peroxisome proliferator (PP) response element upstream of the human acyl CoA oxidase gene is inactive among a sample human population: significance for species differences in response to PPs

Peroxisome proliferators (PP) cause peroxisome proliferation, associated wi th rodent hepatocyte growth perturbation and hepatocarcinogenesis. However, in humans this class of non-genotoxic carcinogens does not appear to have the same adverse effects, The peroxisome proliferator-activated receptor al pha (PPAR alpha) mediates the effects of PPs in rodents via peroxisome prol iferator response elements (PPREs) upstream of PP-responsive genes such as acyl coenzyme A oxidase (ACO), When the human ACO promoter was cloned previ ously, it was found to be active and to contain a consensus PPRE (-1918 AGG TCA C TGGTCA -1906), To confirm and extend those original findings, we isol ated a 2 kb genomic fragment of the ACO gene promoter from a human liver bi opsy and used it to create a P-galactosidase reporter gene plasmid, The hum an ACO promoter reporter plasmid was added to both Hepa1c1c7 and NIH 3T3 ce lls together with a plasmid expressing mPPAR alpha and assessed for its abi lity to drive PP-mediated gene transcription. The human ACO promoter fragme nt was inactive, unlike the equivalent rat ACO promoter fragment used as a positive control. The PPRE within our cloned fragment of the human ACO prom oter differed at three positions (5'-AGGTCA G CTGTCA-3') from the previousl y published active human ACO promoter. Next, we studied the frequency of th e inactive versus the active human PPRE within the human population. Using a PCR strategy, we isolated and analysed genomic DNA fragments from 22 unre lated human individuals and from the human hepatoma cell line HepG2, In eac h case, the PPRE contained the inactive sequence. These data show that the human ACO gene promoter found in a sample human population is inactive. Thi s may explain at the genomic level the lack of response of humans to some o f the adverse effects of the pr class of non-genotoxic hepatocarcinogens.