Identification of a Peptide Antagonist to the Peripheral-Type Benzodiazepine Receptor That Inhibits Hormone-Stimulated Leydig Cell Steroid Formation
- Division of Hormone Research, Departments of Cell Biology, Pharmacology & Neuroscience, Georgetown University Medical Center, Washington, District of Columbia
- V. Papadopoulos, Division of Hormone Research, Department of Cell Biology, Georgetown University Medical Center, 3900 Reservoir Road, Washington, D.C. 20007. E-mail:papadopv{at}georgetown.edu
Abstract
Peripheral-type benzodiazepine receptor (PBR) is an 18-kDa high-affinity cholesterol and drug ligand-binding protein involved in various cell functions, including cholesterol transport and steroid biosynthesis. To aid our investigation of the biological function of PBR, we have set out to identify functional antagonists. By screening phage display libraries, we have identified peptides that displace the high-affinity PBR benzodiazepine drug ligand, Ro5-4864 (4′-chlorodiazepam). Among these peptides, STPHSTP was the most potent (IC50 = 10 μM). All of the isolated peptides showed a conserved motif STXXXXP. The role of these peptides in Leydig cell steroidogenesis was examined using a transducible peptide composed of the TAT domain of human immunodeficiency virus and the peptides under investigation. Synthesized peptides efficiently transduced into MA-10 Leydig cells, and the peptide TAT-STPHSTP inhibited Ro5-4864- and human chorionic gonadotropin-stimulated steroid production in a dose-dependent manner (ED50 = 5 μM). TAT-STPHSTP behaved as a competitive PBR antagonist, which did not affect 22R-hydroxycholesterol-supported steroidogenesis. These results yield leads for the development of potent PBR antagonists and indicate that endogenous PBR agonist-receptor interaction is critical for hormone-induced steroidogenesis.
Footnotes
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↵1 Current address: Laboratory of Histology and Embryology, School of Medicine, University of Athens, Athens 11527, Greece.
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This work was supported by Grant HD-37032 from the National Institute of Child Health and Human Development, National Institutes of Health.
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DOI: 10.1124/jpet.102.039388
- Abbreviations:
- PBR
- peripheral-type benzodiazepine receptor
- PK 11195
- 1-(2-chlorophenyl)-N-methyl-N-(1-methyl-propyl)-3-isoquinoline carboxamide
- Ro5-4864
- 4′-chlorodiazepam
- DBI
- diazepam binding inhibitor
- PBS
- phosphate-buffered saline
- TBST
- Tris-buffered saline/Tween 20
- hCG
- human chorionic gonadotropin
- ANOVA
- analysis of variance
- HIV
- human immunodeficiency virus
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- Received May 21, 2002.
- Accepted July 2, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
