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.
Department of Cell Biology, Georgetown University Medical Center, Washington, DC 20007, USA.
M
M
Culty
H
H
Li
N
N
Boujrad
H
H
Amri
B
B
Vidic
J M
JM
Bernassau
J L
JL
Reversat
V
V
Papadopoulos
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