Peter Söderkvist

Liver cells contain constitutive DNase I-hypersensitive sites at the xenobiotic response elements 1 and 2 (XRE1 and -2) of the rat cytochrome P-450IA1 gene and a constitutive, nuclear XRE-binding factor that is distinct from the dioxin receptor.

Dioxin stimulates transcription from the cytochrome P-450IA1 promoter by interaction with the intracellular dioxin receptor. Upon binding of ligand, the receptor is converted to a form which specifically interacts in vitro with two dioxin-responsive positive control elements located in close proximity to each other about 1 kb upstream of the rat cytochrome P-450IA1 gene transcription start point. In rat liver, the cytochrome P-450IA1 gene is marked at the chromatin level by two DNase I-hypersensitive sites that map to the location of the response elements and exist prior to induction of transcription by the dioxin receptor ligand beta-naphthoflavone. In addition, a DNase I-hypersensitive site is detected near the transcription initiation site and is altered in nuclease sensitivity by induction. The presence of the constitutive DNase I-hypersensitive sites at the dioxin response elements correlates with the presence of a constitutive, labile factor which specifically recognizes these elements in vitro. This factor appears to be distinct from the dioxin receptor, which is observed only in nuclear extract from treated cells. In conclusion, these data suggest that a certain protein-DNA architecture may be maintained at the response elements at different stages of gene expression.

Induction of cytochrome P-450 related metabolic activities in the rat ventral prostate.

Rats were treated with beta-naphthoflavone (BNF) or phenobarbital (PB), 80 mg/kg i.p. for 4 days and microsomes prepared from the ventral prostate were assayed for aryl hydrocarbon hydroxylase (AHH), 7-ethoxyresorufin-o-deethylase (7-EOD) and NADPH-cytochrome c reductase activities. The relative increase after BNF treatment was approx. 1000 times for AHH, and 800 times for 7-EOD, while the NADPH-cytochrome c reductase activity was not significantly altered. PB treatment caused no significant effects. Treatment with BNF led to an increased in vitro formation of all measured benzo(a)pyrene (B(a)P) metabolites, especially phenols. Carbon monoxide (CO) and alpha-naphthoflavone (alpha-NF) inhibited 7-EOD- and AHH-activities. The rat ventral prostate contains inducible cytochrome P-450-dependent enzymes, a circumstance of potential important in the etiology of prostatic carcinoma.

Group I phospholipase A2 mRNA expression in rat glandular stomach and pancreas : Ontogenic development and effects of cortisone acetate.

The postnatal development of group I phospholipase A2 (group I PLA2) in the glandular stomach and pancreas of neonatal rats was investigated. The amounts of group I PLA2 mRNA (and also the PLA2 enzymatic activity) in the glandular stomach mucosa increased with age in 3-60-day-old animals. This postnatal development of rat stomach group I PLA2 mRNA agreed with that of group I PLA2 mRNA of the rat pancreas, and thus seems to follow the general development of the gastrointestinal tract during the neonatal period. The latter was further supported by the finding that maturation of group I PLA2 in both the stomach and pancreas was induced precociously in rats treated with cortisone acetate. It is suggested that the stomach group I PLA2 is involved in mucosal eicosanoid production.

Structure and function of the dioxin receptor: A DNA-binding protein similar to steroid hormone receptors

Abstract In analogy to steroid hormone receptors, the rat hepatic dioxin receptor binds to bulk DNA and heparin in vitro . The affinity of the dioxin receptor for both DNA and heparin is dependent on the binding of ligand and is negatively affected by the presence of sodium molybdate in the homogenization buffer. Limited proteolysis of the dioxin receptor with trypsin which is known to eliminate the DNA-binding property of the glucocorticoid receptor also resulted in a loss of DNA-binding activity and a decreased strength in the interaction with heparin of the in vitro liganded dioxin receptor. However, limited proteolysis with trypsin did not result in any change in gross structural properties of the dioxin receptor. These data suggest that the DNA-binding activity of the dioxin receptor resides within a discrete and relatively small functional domain of the protein.