Effect of sulforaphane on metallothionein expression and induction of apoptosis in human hepatoma HepG2 cells

Chi Tai Yeh, Gow Chin Yen

Research output: Contribution to journalArticle

81 Citations (Scopus)

Abstract

The molecular mechanism of sulforaphane on the induction of metallothionein (MT) genes in HepG2 cells and the antiproliferative effects of sulforaphane were investigated in this study. Treatment of the cells with sulforaphane at non-toxicity concentration (0-20 μM) resulted in coordinate increases in the induction of MT-I and MT-II mRNA, followed by corresponding increases in MT protein expression. Western blot analysis revealed the increased level of the transcription factor, Nrf2 in a time-dependent manner from sulforaphane-treated cells. Furthermore, sulforaphane activated the extracellular signal-regulated protein kinase (ERK), p38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathways. SB203580, a specific inhibitor of p38 and PD98059, a specific inhibitor of ERK, abolished sulforaphane-induced MT protein expression, whereas SP600125, a specific inhibitor of JNK, had no significant effect. At relatively high concentration (30-100 μM), sulforaphane is a cell growth modulator, as it induced apoptotic cell death characterized by internucleosomal DNA fragmentation and caused a rapid induction of caspase 3 activity, according to the appearance of the caspase 3 fragments and stimulated proteolytic cleavage of poly (ADP-ribose) polymerase in a time-dependent manner. Moreover, sulforaphane-induced apoptotic cell death was accompanied by upregulation of Bax and downregulation of Bcl-2 and Bcl-XL protein. Sulforaphane-induced DNA fragmentation was blocked by the N-acetyl-L-cysteine and catalase, suggesting that the death signaling was triggered by oxidative stress. Taken together these results strongly suggest that at low concentrations of sulforaphane, activation of MAPKs, such as ERK and p38 pathway, lead to Nrf2-mediated MT gene expression. Whereas at a higher concentration, sulforaphane is an effective apoptosis inducer in HepG2 cells through regulation of Bcl-2 family molecular and activation of ICE/Ced-3 protease (caspase 3) cascade. The results from this study may provide more evidence for its chemopreventive function.

Original languageEnglish
Pages (from-to)2138-2148
Number of pages11
JournalCarcinogenesis
Volume26
Issue number12
DOIs
Publication statusPublished - Dec 2005
Externally publishedYes

ASJC Scopus subject areas

  • Cancer Research

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