中文摘要：

目的研究褪黑素（melatonin，MT）对肝癌细胞系HepG2细胞的增殖抑制作用以及其对G蛋白-cAMP通路的影响。方法采用MTT法检测MT对HepG2细胞生长的影响，放免法检测细胞内cAMP水平，Western blot法检测抑制型G蛋白α1（Gαil）、抑制型G蛋白α2（Gαi2）、抑制型G蛋白α3（Gαi3）、刺激型G蛋白（Gαs）表达水平。结果MTT检测结果表明，MT在10^-8～10^-5mol·L^-1的浓度范围内，72h共培养后，可有效抑制HepG2细胞增殖，且呈一定的时间浓度依赖关系。为进一步研究MT细胞增殖抑制作用与G蛋白-cAMP信号通路的关系，检测浓度为10^-5mol·L^-1的MT作用HepG2细胞后0、15、30、45、60、90、120min后Gαil、Gαi2、Gαi3和Gαi和细胞内cAMP水平变化，结果发现MT作用HepG2细胞30min后可明显下调Gotil、Gαi2、Gαi3的表达水平，但对Gαs表达无明显影响，同时发现MT处理后cAMP水平有下降的趋势，但是没有统计学意义。结论MT呈时间浓度依赖性的抑制体外培养的HepG2细胞生长，其机制可能与影响G蛋白-cAMP信号通路有关。

英文摘要：

Aim The inhibitory effect of melatonin on hepatoma carcinoma cell line HepG2 proliferation was investigated and this suppression may be act through G protein-cAMP-dependent signal pathway. Method The proliferation of HepG2 cell in vitro was observed by MTT method. The expressions of Gαi1, Gαi2, Gαi3, Gas were detected by Western blot. The level of cAMP was determined by RIA method. Result Me- latonin at the concentration of 10^-8 -10 ^-5mol·L^-1 cultured with cells for 72 h could inhibit cell growth of HepG2 in a time- and concentration-dependent manner. To determine whether this inhibitory effect was related to G protein-cAMP-dependent signal pathway, the level of cAMP and expression of G-protein in HepG2 cell were detected at different time-points （0,15,30, 45,60,90 and 120 min） after treatment of melatonin （10 ^-5mol·L^-1 ）. Western blot results showed that treatment of melatonin for 30min significantly decreased the expression of Gαi1, Gαi2, Gαi3 and had no obvious effects on the expression of Gαs. Meanwhile, melatonin had a tendency to decrease the level of cAMP ,but there was no statistical difference. Conclusion Melatonin inhibited proliferation of HepG2 cell in a timeand concentration-dependent manner in vitro. This inhibitory effect might be possibly mediated through G-protein- cAMP signal pathway.