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Ching-Shyi Wu1 , Jih-Ing Chuang2 , Sew-Fen Leu3 , Hsi-Yuan Yang4 , Bu-Miin Huang5 *
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 P450scc 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 P450scc enzyme.
This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.