Abstract: 61

MELATONIN INHIBITS THE EXPRESSION OF STEROIDOGENIC ACUTE REGULATORY PROTEIN AND STEROIDOGENESIS IN MA-10 CELLS.

Ching-Shyi Wu¹ , Jih-Ing Chuang² , Sew-Fen Leu³ , Hsi-Yuan Yang⁴ , Bu-Miin Huang^{5 *}
Departments of Biology, National Cheng Kung University, Tainan, Taiwan, Republic of China. ¹
Departments of Physiology, College of Medicine, National Cheng Kung University, Tainan, Taiwan, Republic of China. ²
National Laboratory Animal Breeding and Research Center, National Science Council, Taipei, Taiwan, Republic of China. ³
Department of Zoology, National Taiwan University, Taipei, Taiwan, Republic of China. ⁴
Departments of Anatomy, College of Medicine, National Cheng Kung University, Tainan, Taiwan, Republic of China. ⁵

The effects of melatonin on steroidogenesis and StAR protein expression were investigated in MA-10 mouse Leydig tumor cells. MA-10 cells were treated with hCG/cAMP analogue alone or with hCG/cAMP analogue plus melatonin in different dosages (0.1 nM to 10 M). Steroid production and the expression of StAR protein were measured. Melatonin directly inhibited hCG- or dbcAMP-stimulated progesterone production in MA-10 cells within 3 hrs. The inhibitory effects of melatonin on hCG- or dbcAMP-stimulated steroid production in MA-10 cells were abolished by a comparative melatonin receptor antagonist, luzindole. 22R-OH cholesterol reversed melatonins inhibitory effects, which illustrated that melatonin did not suppress P450_scc enzyme activity. Moreover, StAR protein expression stimulated by hCG and dbcAMP was maximally reduced by 10 nM of melatonin treatment for 3 hr. The effects of prolonged exposure (12 hrs) to melatonin with dbcAMP stimulation in MA-10 cells were also examined. The expression of StAR protein and steroid production were reduced by melatonin concentrations from1 nM to 10 M. Melatonin at 1 nM dose had no effect in 3 hr treatment. Our results indicate that melatonin suppressed MA-10 mouse Leydig cell steroidogenesis through specific binding sites by blocking StAR protein expression without altering the activity of P450_scc enzyme.

    This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.