Emodin induces apoptosis of cancer cells and inhibits retinoid X receptor transcriptional activity

大黄素(emodin)对多种肿瘤细胞有较强的抑制增殖和诱导凋亡的作用,但其作用机制尚不清楚。本研究通过配体-受体竞争结合实验以及报告基因检测了大黄素对维甲酸X受体(retinoid X receptor alpha,RXRα)的结合和转录活性的调控,并研究了大黄素对肺癌细胞H460和肝癌细胞SMMC-7721生长和凋亡的作用。结果发现,大黄素对两种癌细胞有很强的抑制增殖作用,加入RXRα的天然配体9-顺式视黄酸(9-cis-retinoid acid,9-cis-RA)共同处理可显著缓解这种抑制作用。大黄素能浓度依赖地引起两种癌细胞系的凋亡,使细胞核出现碎裂和染色质浓染。报告基因实验发现大黄素对RXRα同源和异源二聚体的转录激活有显著抑制作用。体外的配体竞争结合实验发现,大黄素不直接结合RXRα的配体结合区。蛋白质免疫印迹实验发现,大黄素不影响RXRα的蛋白表达。结果提示,大黄素具有诱导肺癌细胞H460和肝癌细胞SMMC-7721凋亡和抑制细胞生长的作用,大黄素抑制9-cis-RA对RXR转录激活作用以及9-cis-RA具有一定程度拮抗大黄素对肺癌细胞H460和肝癌细胞SMMC-7721的生长抑制作用,提示大黄素的抗癌作用可能与细胞内RXR的功能有关,并以RXR转录非依赖性的方式起作用。配体竞争结合实验结果提示大黄素可能间接作用于RXR。The mechanisms by which emodin induces apoptosis and inhibits proliferation of cancer cells remain unclear.In this study,we investigated whether the proapoptotic effect of emodin on human NIH-H460 lung cancer cells and SMMC-7721 liver cancer cells was related to regulating RXR expression and function.MTT assay and DAPI staining were used to detect the anti-proliferative and apoptotic effects of emodin with or without 9-cis-retinoid acid on H460 and SMMC-7721.The reporter assay was used to detect the effect of emodin on RXR homo-and hetero-dimer transactivation.Competitive ligand binding assay was carried out to detect whether emodin could directly bind to RXR.The result showed that emodin could strongly inhibit the proliferation and induce apoptosis of both cancer cell lines,which could be antagonized by 9cis-RA.The reporter assay showed that emodin could inhibit the transcriptional effect of the homo-and hetero-dimer transactivation of RXRα dose-dependently.However,in vitro binding assay did not show that emodin bind to RXRα-LBD directly.The findings suggest that exhibition of emodin its anti-cancer activity may be associated with involvement of RXRα signal transduction pathways.国家高技术研究发展计划(863计划)资助项目(2007AA09Z404);; 国家自然科学基金资助项目(30471939);; 福建省重点资助项目(2007I01021026);; 上海市科委重大科技攻关项目(OZ041915);; 上海市优秀学科带头人项目(06XD14021)