Mechanisms of Action of Transforming Growth Factor (beta) on the Expression of Follicle-Stimulating Hormone Receptor Messenger Ribonucleic Acid Levels in Rat Granulosa Cells

The present study was undertaken to identify the mechanisms underlying the effect of transforming growth factor (TGF) (beta) on FSH receptor (FSH-R) in rat granulosa cells. Compared to the control, the treatment of granulosa cells with TGF(beta) (10 ng/ml) increased FSH-R mRNA transcripts (5.5 and 2.4 kilobases) in a timedependent manner, with a maximum increase of approximately 2-fold at 48 h. We then investigated whether the effect of TGF(beta) on FSH-R mRNA levels was the result of increased transcription and/or altered mRNA stability. To determine whether the FSH-R 5ʹ-flanking region plays a role in directing FSH-R mRNA expression, the proximal area of the FSH-R 5ʹ-flanking regions were inserted into an expression vector, pGLBasic, which contains luciferase as the receptor gene, and the resulting plasmids were transiently transfected into rat granulosa cells. The FSH (30 ng/ml) significantly enhanced the activity of 1862 base pairs of the FSHR 5ʹ-flanking region, but treatment with TGF(beta) did not significantly influence the activity induced by FSH. On the other hand, the decay curves for FSH-R mRNA transcript in primary granulosa cells showed a significant increase in half-life after the addition of TGF(beta). Transforming growth factor (beta) stimulates the expression of follistatin mRNA accumulation in a dose- and time-dependent manner. Treatment with activin produced a substantial increase in FSH-R mRNA level. Concurrent treatment with follistatin neutralized this activin effect on FSH-R mRNA, as reported, although concurrent treatment with follistatin did not affect TGF(beta)-induced FSH-R mRNA. Therefore, the profile of the TGF(beta) effect on FSH-R mRNA granulosa cells may be caused by the increased stability of FSH-R mRNA and insensitivity to the follistatin.