Inverse relationship between high intake of cruciferous vegetables and risks of many types of cancer has been observed in a number of case-controlled epidemiological studies as well as in many animal experiments. Hence, isothiocyanates (ITCs) have attracted considerable attention as important and effective chemopreventive agents. Although multiple mechanisms are involved, it appears that significant portion of the chemopreventive effects of isothiocyanates can be attributed to the enhancement of carcinogen detoxification, which is mostly mediated by Phase II drug detoxifying and antioxidant enzymes such as glutathione S-transferase (GST), UDP-glucuronosyl transferase (UDPGT), quinine-reductase (QR) and hemeoxygenase-1 (HO-1). Molecular mechanism studies have demonstrated that the induction of these enzymes is transcriptionally regulated by the antixodiant responsive element (ARE), which is located in the 5’-flanking region of these genes. Subsequent studies have identified two key cellular sensor proteins constituting the principal components for ARE activation, i.e. NF-E2 related factor 2 (Nrf2) as a positive transcriptional factor of the ARE and Kelch-like ECH-associated protein 1 (Keap1) as a cytosolic inhibitor of Nrf2. In an attempt to find other novel ITCs in the activation of the ARE, we have treated a number of structurally-different ITCs in HepG2 human hepatoma cells (HepG2C8 cells), which were stably transfected with the ARE-luciferase reporter. As a result, we have observed that most of isothiocyanates could significantly induce ARE-luciferase reporter activity in HepG2C8 cells in a dose-dependent manner. Notably, ARE activation by 3-morpholinopropyl isothiocyanate was particularly higher than other isothiocyanates and its activation was even superior to that of two well-known chemopreventive ITCs (PEITC and sulforaphane). In addition, we could see that 3-morpholinopropyl isothiocyanate strongly induced the endogenous hemoxygenase-1 (HO-1) expression under the same conditions. Real-time RT-PCR study has demonstrated that HO-1 induction by 3-morpholinopropyl isothiocyanate was transcriptionally increased in a time-dependent manner. Supporting this notion, treatment of 3-morpholinopropyl isothiocyanate significantly increased not only cellular Nrf2 expression, but inhibited cellular Keap1 expression. Moreover, we have observed that 3-morpholinopropyl isothiocyanate strongly induced phosphorylation of ERK1/2 and JNK, but not of p38 MAPK. Collectively, our data demonstrates that 3-morpholinopropyl isothiocyanate a novel isothiocyanate that induces phase II enzymes by transcriptionally activating ARE via ERK1/2- and JNK-dependent pathway.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]