The role of sterol carrier protein 2 in the regulation of Leydig cell steroidogenesis

The aim of the studies described in this thesis was to clarify the rele of SCP2 in the regulation of steroid production in rat Leydig cells. The ra te of steroid production in the adrenal, the ovary, the placenta and the testis is determined by the rate of conversion of cholesterol to pregnenolone. The complex of reactions and the localization of the enzymes involved in this so called cholesterol side chain cleavage are well known. The P- 450scc enzyme complex catalyzing the production of pregnenolone from cholesterol is located in the inner mitochondria! membrane of steroidogenic cells (Fig.l.l). Several substances that regulate steroidogenesis, regulate the rate of pregnenolone formation via an intracellular transducing mechanism after binding to the plasma membrane of the cell. Different "second messengers" are involved in the transduetion of the signal from the plasma membrane to other processesjmessengers in the cell which are involved in regulation of steroid production. It is also known that protein synthesis and the transfer of cholesterol to the inner mitochondria! membrane are important in regulation of steroidogenesis. It is not known, however, if, and in which way the induction of secend messenger systems in steroidogenic cells is linked with protein synthesis, cholesterol transfer and activatien of the cholesterol side chain cleavage reaction inside the mitochondria. In this respect, sterol carrier protein 2 (SCP2) is one of the possible proteins that could be involved in transduetion of the signal from the secend messengers to the cscc enzyme complex