J. Biol. Chem., Vol. 261, Issue 18, 8270-8275, Jun, 1986
Induction of digitoxigenin monodigitoxoside UDP-glucuronosyltransferase activity by glucocorticoids and other inducers of cytochrome P-450p in primary monolayer cultures of adult rat hepatocytes and in human liver
EG Schuetz, GA Hazelton, J Hall, PB Watkins, CD Klaassen and PS Guzelian
We have recently proposed that glucocorticoids induce cytochrome P- 450p, a
liver microsomal hemoprotein originally isolated from rats treated with the
antiglucocorticoid pregnenolone 16 alpha-carbonitrile (PCN), through a
mechanism that involves a stereospecific recognition system clearly
distinguishable from the classic glucocorticoid receptor (Schuetz, E. G.,
Wrighton, S. A., Barwick, J. L., and Guzelian, P. S. (1984) J. Biol. Chem.
259, 1999-2012). We now report that digitoxigenin monodigitoxoside
UDP-glucuronosyltransferase (DIG UDP- glucuronosyltransferase), a liver
microsomal enzyme activity induced by PCN in rats, is also inducible, as is
P-450p, in primary monolayer cultures of adult rat hepatocytes. DIG
UDP-glucuronosyltransferase activity closely resembled reported
characteristics of induction of P- 450p in its time course of induction,
concentration-response relationships, exclusivity of induction by steroids
with glucocorticoid properties, unusual rank order of potency of
glucocorticoid agonists, unusually high ED50 for induction by
glucocorticoids, enhanced induction rather than inhibition by
anti-glucocorticoids in the presence of glucocorticoids, and finally,
induction by nonsteroidal inducers of P-450p. DIG
UDP-glucuronosyltransferase activity was also readily detected in human
liver microsomes and was elevated in two patients who had received inducers
of P-450p. We conclude that the liver enzymes controlled by the postulated
PCN recognition system include not only P-450p but also one or more UDP-
glucuronosyltransferases.