AJP - Cell Physiology, Vol 258, Issue 3 C480-C488, Copyright © 1990 by American Physiological Society
Corticosterone 6 beta-hydroxylase in A6 epithelia: a steroid-inducible cytochrome P-450
W. M. Grogan, V. M. Phillips, E. G. Schuetz, P. S. Guzelian and C. O. Watlington
Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298-0145.
We found microsomal corticosterone 6 beta-hydroxylase (6 beta-OHase) from
cultured A6 kidney epithelial cells to be a cytochrome P-450 enzyme with
both similarities to and differences from the rat liver steroid 6
beta-OHase P-450p. Enzyme activity was inhibited by CO,
alpha-naphthoflavone, metyrapone, and clotrimazole, well-known inhibitors
of P-450 enzymes, and increased by known inducers of P-450 enzymes,
including dilantin, phenobarbital sodium, and corticosteroids. Moreover,
some additional, relatively specific inducers of P-450p (troleandomycin and
pregnenolone-16 alpha-carbonitrile) also induced the A6 6 beta-OHase,
whereas inducers of other forms of P-450 (aroclor, spironolactone, and
isosafrole) appeared to repress the A6 enzyme. The time course of increase
in enzyme activity and increased cellular cytochrome P-450 content were
consistent with increased levels of enzyme protein. Induction of 6
beta-OHase by the substrate (corticosterone), the metabolite (6
beta-OH-corticosterone), dexamethasone, and aldosterone was biphasic as a
function of inducer concentration, with approximate 50% effective
concentration (EC50) values of 10(-8)-10(-9) M and 10(-5)-10(-6) M for the
respective components of induction. Cortisol also induced the enzyme at
10(-8)-10(-6) M; however, its metabolite 6 beta-OH-cortisol was ineffective
or decreased activity at higher concentrations.(ABSTRACT TRUNCATED AT 250
WORDS)
