PARENT SESSION

(M772) THE EFFECT OF FIBROBLAST GROWTH FACTOR-9 ON STEROIDOGENESIS IN MA-10 LEYDIG TUMOR CELL LINE.

Tsai, Chih-Chien¹, Tsai, Shaw-Jenq², Song Ling, Poon¹, Huang, Bu-Miin¹, ¹ National Cheng Kung University, Tainan, Taiwan R.O.C.² National Cheng Kung University, Tainan, Taiwan R.O.C.

ABSTRACT- It is well known that steroidogenesis can be modulated by trophic hormones through protein kinase A (PKA) and protein kinase C (PKC) signal transduction cascades. It has also been demonstrated that growth factors can regulate the steroidogenesis through different signal cascades. Fibroblast growth factors-9 (FGF-9), a potent mitogen for mesenchymal cells, is necessary for fetal testicular development, and can be localized inside adult testis. FGF-9 binds tyrosine kinase receptor (fibroblast growth factor receptors, FGFRs) and autophosphorylates several tyrosine residues. Phosphorylated tyrosine kinase then activates various downstream signaling kinases, such as Src tyrosine kinase, Ras signaling cascade and phospholipase C (PLC) . The activated Ras protein can induce mitogen-activated protein kinase (MAPK), which will then activate extracellular signal-regulate kinase (ERK1/2) to regulate the cyclic AMP-induced steroid synthesis. PLC can activate PKC, and then regulate steroidogenesis. It is interesting whether FGF-9 will have any effect on Leydig cell steroidogenesis. Thus, the effect and the regulatory mechanism of FGF-9 on steroidogenesis in MA-10 mouse Leydig tumor cell line is under investigation in the present study. The results showed that FGF-9 could stimulate progesterone production with dose-dependent manner in MA-10 cells. The stimulatory effect of FGF-9 reached maximum in 24 hrs. H89, the PKA inhibitor, could significantly suppress the FGF-9-stimulated progesterone production, indicating that FGF-9 might act through the PKA signaling pathway to modulate steroidogenesis. Nevertheless, FGF-9 could not stimulate either the forskolin- or dbcAMP-induced progesterone production. However, Cycloheximide, the general protein synthesis inhibitor, inhibited the FGF-9 stimulated progesterone production, indicating that de novo protein synthesis is required for FGF-9-stimulated steroidogenesis. In Western blot analysis, FGF-9 did induce the expression of phospho-ERK. In summary, FGF-9 might act through the MEK1/2—ERK1/2 signaling pathway to modulate the PKA signaling pathway and thus stimulate the progesterone production in MA-10 Leydig tumor cells.

KEY WORDS: FGF-9, steroidogenesis, MA-10, MAPK