Trophic hormones acutely stimulate steroid production by acting on the rate-determining step of steroidogenesis, the transport of the substrate, cholesterol, from intracellular stores to the inner mitochondrial membrane. There, cholesterol will be metabolized to pregnenolone. Using various approaches we demonstrated that the mitochondrial peripheral-type benzodiazepine receptor (PBR) mediates the transport of cholesterol from the outer to the inner mitochondrial membrane and the subsequent steroid biosynthesis. We further demonstrated that PBR functions as a channel specific for cholesterol. It is our hypothesis that the acute (sec to min) hormonal regulation of the PBR receptor complex, preferentially located on the mitochondrial membrane contact sites, is responsible for the hormonal induction of steroidogenesis and that the interaction of the PBR complex with the hormone-induced steroidogenic acute regulatory protein (StAR) is responsible for sustaining steroid production for longer periods of time (hours). In the first aim we will establish the temporal and spatial relationship of PBR and StAR proteins in response to hCG. In the second aim we will examine the structure of the PBR complex in the mitochondrial contact sites isolated from control and LH-treated Leydig cells. In search for the """"""""molecular switch"""""""" responsible for the effects of LH/hCG on PBR we identified two candidate PBR-associated proteins (PAPs). In the third aim, we will investigate the role of the PAPs in the hormone-induced changes in PBR, cholesterol transport, and steroidogenesis. Considering the finding that StAR exerts its effect outside the mitochondrion, it is possible that it may act directly on PBR or indirectly via a PAP. In the fourth aim we will examine the StAR-PBR interaction and the functional consequences of this interaction. Our goal is to understand the sequence of events responsible for the induction and maintenance of steroidogenesis by hormones. Our Leydig cell model systems are the MA-10 hormone- responsive cell line, purified rat Leydig cells, the R2C cell line expressing constitutive steroidogenesis, and R2C PBR negative (-) cells, generated by gene targeting.

Agency
National Institute of Health (NIH)
Institute
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Type
Research Project (R01)
Project #
5R01HD037031-05
Application #
6627384
Study Section
Reproductive Biology Study Section (REB)
Program Officer
Rankin, Tracy L
Project Start
1998-12-15
Project End
2004-07-14
Budget Start
2002-12-01
Budget End
2004-07-14
Support Year
5
Fiscal Year
2003
Total Cost
$270,284
Indirect Cost
Name
Georgetown University
Department
Biochemistry
Type
Schools of Dentistry
DUNS #
049515844
City
Washington
State
DC
Country
United States
Zip Code
20057
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Midzak, Andrew; Akula, Nagaraju; Lecanu, Laurent et al. (2011) Novel androstenetriol interacts with the mitochondrial translocator protein and controls steroidogenesis. J Biol Chem 286:9875-87
Fan, Jinjiang; Liu, Jun; Culty, Martine et al. (2010) Acyl-coenzyme A binding domain containing 3 (ACBD3; PAP7; GCP60): an emerging signaling molecule. Prog Lipid Res 49:218-34
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Rone, Malena B; Liu, Jun; Blonder, Josip et al. (2009) Targeting and insertion of the cholesterol-binding translocator protein into the outer mitochondrial membrane. Biochemistry 48:6909-20
Papadopoulos, Vassilios; Lecanu, Laurent (2009) Translocator protein (18 kDa) TSPO: an emerging therapeutic target in neurotrauma. Exp Neurol 219:53-7
Rone, Malena B; Fan, Jinjiang; Papadopoulos, Vassilios (2009) Cholesterol transport in steroid biosynthesis: role of protein-protein interactions and implications in disease states. Biochim Biophys Acta 1791:646-58
Ostuni, Mariano Anibal; PĂ©ranzi, Gabriel; Ducroc, Robert A et al. (2009) Distribution, pharmacological characterization and function of the 18 kDa translocator protein in rat small intestine. Biol Cell 101:573-86
Ostuni, Mariano A; Ducroc, Robert; Peranzi, Gabriel et al. (2007) Translocator protein (18 kDa) ligand PK 11195 induces transient mitochondrial Ca2+ release leading to transepithelial Cl- secretion in HT-29 human colon cancer cells. Biol Cell 99:639-47
Veenman, Leo; Papadopoulos, Vassilios; Gavish, Moshe (2007) Channel-like functions of the 18-kDa translocator protein (TSPO): regulation of apoptosis and steroidogenesis as part of the host-defense response. Curr Pharm Des 13:2385-405

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