In vitro studies on the role of the peripheral-type benzodiazepine receptor in steroidogenesis.
In vitro studies using isolated cells, mitochondria and submitochondrial fractions demonstrated that in steroid synthesizing cells, the peripheral-type benzodiazepine receptor (PBR) is an outer mitochondrial membrane protein, preferentially located in the outer/inner membrane contact sites, involved in the regulation of cholesterol transport from the outer to the inner mitochondrial membrane, the rate-determining step in steroid biosynthesis. Mitochondrial PBR ligand binding characteristics and topography are sensitive to hormone treatment suggesting a role of PBR in the regulation of hormone-mediated steroidogenesis. Targeted disruption of the PBR gene in Leydig cells in vitro resulted in the arrest of cholesterol transport into mitochondria and steroid formation; transfection of the mutant cells with a PBR cDNA rescued steroidogenesis demonstrating an obligatory role for PBR in cholesterol transport. Molecular modeling of PBR suggested that it might function as a channel for cholesterol. This hypothesis was tested in a bacterial system devoid of PBR and cholesterol. Cholesterol uptake and transport by these cells was induced upon PBR expression. Amino acid deletion followed by site-directed mutagenesis studies and expression of mutant PBRs demonstrated the presence in the cytoplasmic carboxy-terminus of the receptor of a cholesterol recognition/interaction amino acid consensus sequence. This amino acid sequence may help for recruiting the cholesterol coming from intracellular sites to the mitochondria.
Culty
M
M
Department of Cell Biology, Georgetown University Medical Center, Washington, DC 20007, USA.
Li
H
H
Boujrad
N
N
Amri
H
H
Vidic
B
B
Bernassau
J M
JM
Reversat
J L
JL
Papadopoulos
V
V
D000818:Animals; D006063:Chorionic Gonadotropin / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics; D007985:Leydig Cells / Q000378:metabolism; D008297:Male; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013256:Steroids / Q000096:biosynthesis*
D006063:Chorionic Gonadotropin; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D013256:Steroids