Induction of high-density-lipoprotein receptors in rat corpus luteum by human choriogonadotropin. Evidence of protein synthesis de novo.
The present studies investigated the specific binding of 125I-labelled high-density lipoprotein (125I-HDL) to plasma membranes. Golgi, rough endoplasmic reticulum and mitochondria/lysosomes, prepared from ovaries of rats injected with human choriogonadotropin (hCG) or 0.9% NaCl. Treatment in vivo with hCG resulted in 2-3-fold induction of 125I-HDL binding activity in all the subcellular organelles. The specific binding of HDL to various subcellular organelles was dependent on the amount of protein, lipoprotein concentration and incubation time. Equilibrium-binding studies revealed comparable Kd values (13-22 micrograms of HDL protein/ml) for HDL binding in all the subcellular organelles tested. Treatment with cycloheximide (2.0 mg/kg body wt.) before hCG administration abolished the induction of HDL receptors, suggesting the involvement of a protein-synthesis-dependent process in receptor induction. Analysis of equilibrium dissociation constants (Kd) for 125I-HDL binding in membranes from hCG-, cycloheximide-and saline-treated animals suggests that the increase in binding was due to an increase in the number of binding sites rather than a change in the affinity. Additionally, pretreatment with tunicamycin, an inhibitor of N-linked glycosylation, had no effect on hCG-mediated receptor induction, suggesting that glycosylation of the receptor may not be necessary for the interaction of HDL with its receptors.
Ghosh
D K
DK
Department of Obstetrics and Gynecology, University of Michigan Medical School, Ann Arbor 48109.
Menon
K M
KM
D000818:Animals; D002352:Carrier Proteins; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D003338:Corpus Luteum / Q000187:drug effects / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D008075:Lipoproteins, HDL / Q000378:metabolism*; D014176:Protein Biosynthesis; D016601:RNA-Binding Proteins; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000378:metabolism; D018110:Receptors, Lipoprotein; D013268:Stimulation, Chemical; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology
D002352:Carrier Proteins; D006063:Chorionic Gonadotropin; D008075:Lipoproteins, HDL; D016601:RNA-Binding Proteins; D011956:Receptors, Cell Surface; D018110:Receptors, Lipoprotein; C031616:high density lipoprotein receptors; D014415:Tunicamycin; C075197:high density lipoprotein binding protein; D003513:Cycloheximide