http://repub.eur.nl/res/aut/7002/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/8936/ 1998-01-01T00:00:00Z Hepatic lipase (HL) and scavenger receptor type B class I (SR-BI) have both been implicated in high density lipoprotein (HDL)-cholesteryl ester uptake in cholesterol-utilizing tissues. Inactivation of HL by gene-directed targeting in mice results in up-regulation of SR-BI expression in adrenal gland (Wang, N., Weng, W., Breslow, J. L., and Tall, A. R. (1996) J. Biol. Chem. 271, 21001-21004). The net effect on HDL-cholesteryl ester uptake is not known. We determined the impact of acute in vivo inhibition of rat adrenal HL activity by antibodies on SR-BI expression and on human and rat HDL-[3H]cholesteryl ether (CEth) uptake in the adrenal gland. Rat HDL was isolated from rats in which HL activity had been inhibited for 1 h. The rats were studied under basal conditions (not ACTH-treated) and after previous treatment with ACTH for 6 days (ACTH-treated). Intravenous injection of anti-HL resulted in 70% lowering of adrenal HL activity in both conditions which were maintained for at least 8 h. In not ACTH-treated rats, inhibition of adrenal HL increased adrenal SR-BI mRNA (5.2-fold) and mass (1. 6-fold) within 4 h. HL inhibition resulted in 41% and 14% more adrenal accumulation of human HDL-[3H]CEth during 4 and 24 h, respectively. The adrenal uptake of rat HDL-[3H]CEth increased by 68%, 4 h after the antibody injection. ACTH treatment increased total adrenal HL activity from 3.7 +/- 0.5 milliunits to 34.0 +/- 17. 2 milliunits, as well as adrenal SR-BI mRNA from 2.9 +/- 0.7 arbitrary units (A.U.) to 86.8 +/- 41.1 A.U. and SR-BI mass from 7.7 +/- 1.8 A.U. to 63.16 +/- 46.7 A.U. The human HDL-[3H]CEth uptake by adrenals was also significantly increased from 0.58 +/- 0.11% of injected dose to 7.24 +/- 1.58% of injected dose. Inhibition of adrenal HL activity did not result in further induction of SR-BI expression and did not affect human HDL-[3H]CEth uptake. These findings indicate that SR-BI expression may be influenced by changes in HL activity. HL activity is not needed for the SR-BI-mediated HDL-cholesteryl ester uptake by rat adrenal glands. http://repub.eur.nl/res/pub/8623/ 1996-01-01T00:00:00Z Lipoprotein lipase (LPL) is functionally active only as a dimer. It is also generally assumed that the highly homologous hepatic lipase functions as a dimer, but no clear evidence has been presented. A hepatic lipase-like activity, also indicated as L-type lipase, is present in adrenal and ovary tissues. This enzyme is thought to originate from the liver and to be identical to hepatic lipase. We determined the functional molecular mass of hepatic lipase in rat liver, adrenal gland and ovary by radiation inactivation, a method for determining the functional size of a protein without the need of prior purification. Samples were exposed to ionizing radiation at -135 degrees C. Hepatic lipase activity in liver homogenate showed a single exponential decay. The functional molecular mass was calculated to be 63 +/- 10 kDa. Hepatic lipase activity in adrenal homogenate was found to have a functional molecular mass of 117 +/- 16 kDa. The functional molecular masses of the lipases partially purified from rat liver perfusate, adrenal homogenate or ovarian homogenate showed the same pattern, a target mass for the liver enzyme of 56 +/- 6 kDa and a target mass of 117 +/- 14 kDa for the enzyme from adrenal gland or ovary. In Western blot analysis the mass of the structural units of hepatic lipase in liver was 57 kDa and in adrenal and ovary tissue 51 kDa. We conclude that the functional unit of hepatic lipase in the liver is a monomer. The enzyme in adrenal gland and ovary is different from the liver and the functional unit may be a dimer.