EFFECTS OF PERIPHERAL-TYPE BENZODIAZEPINE RECEPTOR ANTISENSE KNOCKOUTON MA-10 LEYDIG-CELL PROLIFERATION AND STEROIDOGENESIS

The peripheral-type benzodiazepine receptor (PBR) is not only widely e xpressed throughout the body, but it is also genetically conserved. fr om bacteria to humans, Many functions have been attributed to it, but its primary role remains a puzzle. In the current study, we stably tra nsfected cultures of MA-10 Leydig cells with either control or 18-kDa PBR antisense knockout plasmids, The antisense knockout vector was dri ven by the human enkephalin promoter, which contains two cAMP response elements, such that cAMP treatment of transfected cells could superin duce 18-kDa PBR antisense RNA transcription and, hence, down-regulate endogenous 18-kDa PBR mRNA levels. Control and knockout MA-10 cell lin es were then compared at the level of receptor binding, thymidine inco rporation, and steroid biosynthesis. Eighteen-kilodalton PBR knockout reduced the maximal binding capacity of tritium-labeled PBR ligands, a nd the affinity of receptors to the ligands remained unaltered. Additi onally, 24-h accumulation of progesterone was lower in the knockout ce lls, Exposure of the two cell types to 8-bromo-cAMP resulted in a robu st increase in steroid production. However, a complex pattern of stero id accumulation was observed, in which further progestin metabolism wa s indicated, The later decline in accumulated progesterone as well as the synthesis of androstenedione were different in the two cell types. At the level of cell proliferation, reduction of 18-kDa PBR mRNA show ed no effect, Thus, we conclude that the 18-kDa PBR may have a more im portant role in steroidogenesis than in proliferation in this Leydig c ell line.