간암세포주에서의 Indole-3-Carbinol에 의해 유도되는 세포주기 억제 기전

Abstract

The naturally occurring chemical indole-3-carbinol (I3C), found in vegetables of the Brassica genus, is a promising anticancer agent that was shown previously to induce a G1 cell cycle arrest of human breast cancer cell lines, independent of estrogen receptor signaling. The anticancer activity of I3C and the possible mechanisms of its action were explored in a human hepatocellular carcinoma cell line, HepG2. Treatment of HepG2 cells with I3C suppressed the growth of the cells. The growth suppression caused by I3C(IC50: 444μM) was found to be partially due to its ability to stop the cell cycle in HepG2 cells. Western blot analysis for the G1 phase arrest demonstrated that the expression-levels of cyclin-dependent kinase (Cdk4, Cdk6) and cyclin D were reduced strongly after treatment of HepG2 cells with I3C (400μM) for 24-72hrs. Furthermore, I3C selectively abolished the expression of Cdk6 in a dose- and time-dependent manner, and accordingly, inhibited the phosphorylation of retinoblastoma. Interestingly, after the HepG2 cells reached their maximal growth arrest, the level of the p21, a well-known Cdk inhibitor, increased significantly. Therefore, it could be considered that the G1 arrest of HepG2 cells treated with I3C was due to the indirect inhibition of Cdk4/6 activities by p21. Western blot analysis for G2/M phase arrest of demonstrated the levels of Cdc2 and cyclin B1 were reduced dramatically after the treatment of HepG2 cells with I3C (40μM) for 24-72hrs. Flow cytometry of propidium iodide-stained HepG2 cells revealed that I3C induces a G1 (53%, 72hr incubation) and G2 (25%, 24hr incubation) cell cycle arrest. Thus, our observations have uncovered a previously undefined antiproliferative pathway for I3C that implicates Cdk4/6 and Cdc2 as a target for cell cycle control in human HepG2 cells. However, the I3C-mediated cell cycle arrest and repression of Cdk4/6 production did not affect the apoptotic induction of HepG2 cell.