MAPK and P13K signaling pathways in isothiocyanates-induced gene expression, G2/M arrest and apoptosis

Dietary isothiocyanates (ITCs) can inhibit many types of tumor formation in animal models and their consumption is inversely correlated with the risk of human cancers including lung, breast and colon. The aim of this study was to investigate the molecular mechanisms underlying the relationship between ITCs-induced phase II enzyme expression, cell cycle arrest and cell death; and to examine the role of mitogen-activated protein kinase (MAPK) and phosphoinositide kinase (PI3K) in these events. The exposure of human colon adenocarcinoma Caco-2 cells to allyl-ITC, benzyl-ITC, phenethyl-ITC, sulforaphane and erucin resulted in the inhibition of G2/M progression, mitochondrial potential dissipation and induction of apoptosis. We showed that ITCs modulated gene expression of phase II detoxifying enzymes such as glutathione transferase (GST), UDP-glucuronosyl transferase (UGT), and quinone reductase (NQO1) as well as cellular antioxidant enzyme thioredoxin reductase-1 (TR1) and multidrug-resistant associated protein-2. We confirmed that ITCs activated extracellular signal-regulated kinases (ERK1/2) and PKB/Akt kinase but not c-Jun-terminal kinase and p38 MAPK. The effectiveness of MEK/ERK inhibitor PD98059 and PI3K/Akt inhibitor LY294002 pretreatments suggest that ITC-induced G2/M accumulation and apoptosis are regulated by the activation of these two kinases. Moreover, the extent of Ser10 phosphorylation of histone H3 in G2/M cells by ITCs was significantly decreased using PD98059 and LY294002. In addition, ITCs induced up-regulation of MRP2, NQO-1, UGT1A1 and TR1 mRNA expression attenuated by PD98059 and LY294002 inhibitors in Caco-2 and HepG2 cells. This study indicates that individual ITCs may modulate signaling pathways (PI3K and MAPK) differently and this may contribute to the complexity of chemopreventive mechanisms of ITCs. Building of a knowledge database of molecular mechanisms, including crosstalk of signaling pathways in phase II enzyme expression, cell proliferation and apoptosis, may lead to a better understanding of the role of ITCs in cancer chemoprevention.