Androgen hydroxylation catalysed by a cell line (SD1) that stably expresses rat hepatic cytochrome P-450 PB-4 (IIB1).
Androgen hydroxylation catalysed by Chinese hamster fibroblast SD1 cells, which stably express cytochrome P-450 form PB-4, the rat P450IIB1 gene product, was assessed and compared to that catalysed by purified cytochrome P-450 PB-4 isolated from rat liver. SD1 cell homogenates catalysed the NADPH-dependent hydroxylation of androstenedione and testosterone with a regioselectivity very similar to that purified by P-450 PB-4 (16 beta-hydroxylation/16 alpha-hydroxylation = 6.0-6.8 for androstenedione; 16 beta/16 alpha = 0.9 for testosterone). Homogenates prepared from the parental cell line V79, which does not express detectable levels of P-450 PB-4 or any other cytochrome P-450, exhibited no androgen 16 beta- or 16 alpha-hydroxylase activity. The hydroxylase activities catalysed by the SD1 cell homogenate were selectively and quantitatively inhibited (greater than 90%) by a monoclonal antibody to P-450 PB-4 at a level of antibody (40 pmol of antibody binding sites/mg of SD1 homogenate) that closely corresponds to the P-450 PB-4 content of the cells (48 pmol of PB-4/mg of SD1 homogenate). Fractionation of cell homogenates into cytosol and microsomes revealed that the P-450 PB-4-mediated activities are associated with the membrane fraction. Although the P-450 PB-4-specific content of the SD1 microsomes was 15% of that present in phenobarbital-induced rat liver microsomes, the P-450 PB-4-dependent androstenedione 16 beta-hydroxylase activity of the SD1 membrane fraction was only 2-3% of that present in the liver microsomes. This activity could be stimulated several-fold, however, by supplementation of SD1 microsomes with purified rat NADPH P-450 reductase. These studies establish that a single P-450 gene product (IIB1) can account for the hydroxylation of androgen substrates at multiple sites, and suggest that SD1 cells can be used to assess the catalytic specificity of P-450 PB-4 with other substrates as well.
Waxman
D J
DJ
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
Lapenson
D P
DP
Morrissey
J J
JJ
Park
S S
SS
Gelboin
H V
HV
Doehmer
J
J
Oesch
F
F
D000735:Androstenedione / Q000378:metabolism*; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D002384:Catalysis; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D005347:Fibroblasts / Q000378:metabolism; D006900:Hydroxylation; D008099:Liver / Q000201:enzymology*; D051381:Rats; D013252:Steroid 11-beta-Hydroxylase / Q000378:metabolism*; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013739:Testosterone / Q000378:metabolism*
D013739:Testosterone; D000735:Androstenedione; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D039181:Steroid 16-alpha-Hydroxylase; C022724:testosterone 7-alpha-hydroxylase, hamster; D013252:Steroid 11-beta-Hydroxylase