Function and regulation of CCAAT/enhancer binding protein beta in Leydig cell development and steroidogenesis

Pituitary luteinizing hormone (LH) is required for the development of multiple cell types in both the male and female reproductive systems. In particular, LH promotes differentiation of testicular Leydig cells and stimulates steroid production by Leydig cells in the testis, theca, granulosa and luteal cells in the ovary. We have been interested in identifying nuclear transcription factors that are targets of LH signaling pathways in Leydig cells and concentrated on CCAAT/enhancer binding protein beta (C/EBPp). Our initial studies showed that C/EBPp is expressed in a differentiation specific pattern whose expression is stimulated by LH/human chorionic gonadotropin (hCG) and cyclic AMP (cAMP) in Leydig cells. We hypothesized that C/EBPp plays an important role in LH regulated Leydig cell development and steroidogenic function. To assess the specific roles of C/EBPp in Leydig cell function we have analyzed the steroidogenic capacity of Leydig cells from C/EBPp-deficient mice generated by gene targeting. This study revealed that testosterone production in male C/EBPp deficient mice is severally compromised suggesting that C/EBPp is essential for complete functional differentiation of Leydig cells. In order to understand how LH effects on Leydig cell differentiation and/or function may be mediated through C/EBPp, we attempted to identify genetic control elements that control C/EBPp transcription in steroidogenic and non-steroidogenic cells. We identified an evolutionarily conserved, steroidogenic cell-specific, distal enhancer element located in the C/EBPp 5'-flanking region. Our studies suggest that the activity of the enhancer may be, at least in part, controlled by as yet uncharacterized nuclear factors specifically detected in nuclear extracts of steroidogenic cells. These studies set the stage for elucidation of the molecular mechanisms controlling C/EBPp expression in steroidogenic cells in general, and may aid in uncovering alternative LH-dependent signaling pathways critical for functional maturation of Leydig cells