Insulin-like growth factor-binding protein-2: the effect of human chorionic gonadotropin on its gene regulation and protein secretion and its biological effects in rat Leydig cells.

Human CG (hCG) and insulin-like growth factor-I (IGF-I) have synergistic effects on Leydig cell function. Leydig cells express high affinity IGF-I receptors. The number of IGF-I receptors and IGF-I receptor mRNA levels can be up-regulated by hCG. The most abundant mRNA species of the IGF binding proteins (IGFBPs) in rat Leydig cells is IGFBP-2. In the present study, we investigated the effect of hCG on IGFBP-2 transcription, mRNA accumulation, and protein production/secretion. Biological effects of IGFBP-2 on Leydig cells were also examined. Rat Leydig cells were purified from testes using centrifugal elutriation followed by Percoll gradient centrifugation. Cells were cultured for 24 h and then treated with or without hCG (10 ng/ml) for 6 h. The expression of IGFBP-2 mRNA was decreased by hCG in a dose-dependent manner, and at a concentration of 10 ng/ml the expression of IGFBP-2 mRNA was reduced by 50%. As early as 2 h after the addition of hCG, there was a significant decrease in IGFBP-2 mRNA accumulation. To evaluate the mechanism(s) responsible for decreased IGFBP-2 gene expression by hCG, the effect of hCG on the rate of transcription and stability of the mRNA was determined. Human CG (10 ng/ml) reduced the IGFBP-2 transcription rate by 32%/h in comparison with the control, while the half-life (t1/2) of mRNA remained unaltered (hCG-treated cells, 0.58 h; control cells, 0.51 h). IGFBP-2 with a molecular size of 33 kilodaltons was detected as a major band in the Western ligand blot.(ABSTRACT TRUNCATED AT 250 WORDS)