Kuo Wu-Hsien, Chou Fen-Pi, Young Shun-Chieh, Chang Yun-Ching, Wang Chau-Jong
Division of Gastroenterology, Department of Internal Medicine, Armed Forces Taichung General Hospital, ROC, Taiwan.
Toxicol Appl Pharmacol. 2005 Oct 15;208(2):155-62. doi: 10.1016/j.taap.2005.02.013.
Geniposide, an iridoid glycoside isolated from the fruit of Gardenia jasminoides Ellis, has biological capabilities of detoxication, antioxidation, and anticarcinogenesis. We have recently found that geniposide possesses a potential for detoxication by inducing GST activity and the expression of GST M1 and GST M2 subunits. In this study, the signaling pathway of geniposide leading to the activation of GSH S-transferase (GST) was investigated. Primary cultured rat hepatocytes were treated with geniposide in the presence or absence of mitogen-activated protein kinase (MAPK) inhibitors and examined for GST activity, expression of GST M1 and M2 subunits, and protein levels of MAPK signaling proteins. Western blotting data demonstrated that geniposide induced increased protein levels of GST M1 and GST M2 (approximately 1.76- and 1.50-fold of control, respectively). The effect of geniposide on the increased protein levels of GST M1 and GST M2 was inhibited by the MEK-1 inhibitor PD98059, but not by other MAPK inhibitors. The GST M1 and GST M2 transcripts as determined by RT-PCR and GST activity were also inhibited concurrently by the MEK-1 inhibitor PD98059. The protein levels of up- and down-stream effectors of the MEK-1, including Ras, Raf, and Erk1/2, and the phosphorylation state of Erk1/2 were found to be induced by geniposide, indicating a two-phase influence of geniposide. The results suggest that geniposide induced GST activity and the expression of GST M1 and GST M2 acting through MEK-1 pathway by activating and increasing expression of Ras/Raf/MEK-1 signaling mediators.
栀子苷是从栀子果实中分离得到的一种环烯醚萜苷，具有解毒、抗氧化和抗癌等生物学功能。我们最近发现，栀子苷具有通过诱导谷胱甘肽S-转移酶（GST）活性以及GST M1和GST M2亚基表达来实现解毒的潜力。在本研究中，对栀子苷激活GSH S-转移酶（GST）的信号通路进行了研究。在有或无丝裂原活化蛋白激酶（MAPK）抑制剂存在的情况下，用栀子苷处理原代培养的大鼠肝细胞，并检测GST活性、GST M1和M2亚基的表达以及MAPK信号蛋白的蛋白水平。蛋白质印迹数据表明，栀子苷诱导GST M1和GST M2的蛋白水平升高（分别约为对照的1.76倍和1.50倍）。MEK-1抑制剂PD98059可抑制栀子苷对GST M1和GST M2蛋白水平升高的作用，但其他MAPK抑制剂则无此作用。MEK-1抑制剂PD98059同时也抑制了通过RT-PCR测定的GST M1和GST M2转录本以及GST活性。发现栀子苷可诱导MEK-1上下游效应分子（包括Ras、Raf和Erk1/2）的蛋白水平以及Erk1/2的磷酸化状态，表明栀子苷具有两阶段影响。结果表明，栀子苷通过激活并增加Ras/Raf/MEK-1信号介质的表达，通过MEK-1途径诱导GST活性以及GST M1和GST M2的表达。
