The human peripheral benzodiazepine receptor gene: cloning and characterization of alternative splicing in normal tissues and in a patient with congenital lipoid adrenal hyperplasia.
The mitochondrial benzodiazepine receptor (mBzR) appears to be a key factor in the flow of cholesterol into mitochondria to permit the initiation of steroid hormone synthesis. The mBzR consists of three components; the 18-kDa component on the outer mitochondrial membrane appears to contain the benzodiazepine binding site, and is hence often termed the peripheral benzodiazepine receptor (PBR). Using a cloned human PBR cDNA as probe, we have cloned the human PBR gene. The 13-kb gene is divided into four exons, with exon 1 encoding only a short 5' untranslated segment. The 5' flanking DNA lacks TATA and CAAT boxes but contains a cluster of SP-1 binding sites, typical of "house-keeping" genes. The encoded PBR mRNA is alternately spliced into two forms: "authentic" PBR mRNA retains all four exons, while a short form termed PBR-S lacks exon 2. While PBR-S contains a 102-codon open reading frame with a typical initiator sequence, the reading frame differs from that of PBR, so that the encoded protein is unrelated to PBR. RT-PCR and RNase protection experiments confirm that both PBR and PBR-S are expressed in all tissues examined and that expression PBR-S is about 10 times the level of PBR. Expression of PBR cDNA in pCMV5 vectors transfected into COS-1 cells resulted in increased binding of [3H]PK11195, but expression of PBR-S did not. It has been speculated that patients with congenital lipoid adrenal hyperplasia, who cannot make any steroids, might have a genetic lesion in mBzR. RT-PCR analysis of testicular RNA from such a patient, sequencing of the cDNA, and blotting analysis of genomic DNA all indicate that the gene and mRNA for the PBR component of mBzR are normal in this disease.
Lin
D
D
Department of Pediatrics, University of California at San Francisco 94143-0978.
Chang
Y J
YJ
Strauss
J F
JF
Miller
W L
WL
D000312:Adrenal Hyperplasia, Congenital / Q000235:genetics*; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D002460:Cell Line; D003001:Cloning, Molecular; D005091:Exons; D005260:Female; D005333:Fetus; D015186:Hominidae / Q000235:genetics*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D007546:Isoquinolines / Q000378:metabolism; D007984:Leydig Cell Tumor / Q000235:genetics; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010920:Placenta / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism; D011963:Receptors, GABA-A / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012016:Reference Values; D016385:TATA Box; D013736:Testicular Neoplasms / Q000235:genetics*; D013737:Testis / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
D007546:Isoquinolines; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; C037850:PK 11195