A HUMAN GENE ENCODING DIAZEPAM-BINDING INHIBITOR ACYL-COA-BINDING PROTEIN - TRANSCRIPTION AND HORMONAL-REGULATION IN THE ANDROGEN-SENSITIVEHUMAN PROSTATIC ADENOCARCINOMA CELL-LINE LNCAP

Diazepam-binding inhibitor (DBI)/acyl-CoA-binding protein (ACBP) is a highly conserved 10-kD polypeptide expressed in various organs and imp licated in the regulation of multiple biological processes such as GAB A(A)/benzodiazepine receptor modulation, acyl-CoA metabolism, steroido genesis, and insulin secretion, To extend our knowledge about the biol ogy of DBI/ACBP and to elucidate the molecular mechanisms responsible for regulating DBI/ACBP gene expression, we have studied the androgen- regulated expression of DBI/ACBP transcripts in the human prostatic ad enocarcinoma cell line LNCaP and have cloned and characterized a human gene encoding DBI/ACBP, Northern blotting, reverse transcription-assi sted polymerase chain reaction (RT-PCR), ribonuclease protection, and 5' RACE analysis (rapid amplification of cDNA ends) of DBI/ACBP transc ripts in LNCaP cells revealed androgen-regulated expression of multipl e transcripts originating from multiple transcription start sites and alternative processing, The most abundant type of transcripts (referre d to as type 1 transcripts) encodes genuine DBI/ACBP of 86 amino acids , while the minor type (type 2 transcripts) harbors an insertion of 86 bases and might encode an unrelated protein of 67 amino acids, Examin ation of a cloned DBI/ACBP gene revealed a structural organization of four exons present in all transcripts and one alternatively used exon present only in type 2 transcripts, The promoter region is located in a CPG island and lacks a canonical TATA box, Transient transfection of DBI/ACBP promoter fragments into LNCaP cells demonstrated that a regi on of 1.1 kb upstream of the translation start site is able to drive h igh-level expression of luciferase in LNCaP cells in an androgen-regul ated fashion, Taken together these data indicate that the isolated hum an gene encoding DBI/ACBP is functional, has a high degree of structur al similarity with the corresponding rat gene, exhibits hallmarks of a typical housekeeping gene, and harbors cis-acting elements that are a t least partially responsible for androgen-regulated transcription in LNCaP cells.