Evaluation of the 4S polycyclic aromatic hydrocarbon binding protein in Harlan Sprague-Dawley rats

The polycyclic aromatic hydrocarbon (PAH) induced expression of the rat cytochrome P450IA1 gene is regulated by 8S and 4S PAH binding proteins. This gene is closely associated with aryl hydrocarbon hydroxylase enzyme activity (AHH), which is known to bio-activate PAHs. A recent study reported that AHH activity was inducible by PAHs in Harlan Sprague-Dawley rats in the absence of detectable 4S PAH binding protein. Our study was undertaken to determine hepatic 4S PAH binding protein levels in male Harlan rats using sucrose gradient analysis of 100,000 x g supernatant solution incubated with [3H]BP and various competitive ligands. Our results indicate that the 4S PAH binding protein is present in Harlan Sprague-Dawley rats and exhibits specific and saturable binding to benzo(a)pyrene, but not to the dioxin congener 2,3,7,8-tetra-chlorodibenzo-p-furan. The detection of the 4S protein in Harlan rats is dependent on ligand and prrotein concentration. However, under standard assay conditions (10nM [3H]BP and 7.5 - 10.0 mg/ml protein), Harlan and standard Sprague-Dawley rats contained equivalent amounts of 4S PAH binding protein. Our data suggest that the role of the 4S protein in P450IA1 gene regulation in Harlan rats requires re-evaluation