Differential hepatic GSTA2 expression of arylalkyl isothiocyanates in vivo and in vitro: The molecular mechanism of gene induction by phenethyl isothiocyanate

Abstract

Naturally occurring isothiocyanates (ITCs) have been investigated for their chemopreventive actions. However, limited studies have determined the potential for regulation of hepatic glutathione S-transferase A2 (GSTA2) by arylalkyl or alkyl ITCs. The present study was designed to investigate the effects of ITCs on GSTA2 expression and upstream signaling analyzed by Northern blotting, RT-PCR, immunoblotting, and promoter-luciferase assay. A single dose of ethyl isothiocyanate and phenethyl isothiocyanate (PEITC) enhanced GSTA2 mRNA levels in rats. The three consecutive injections of arylalkyl ITCs resulted in the gene induction. PEITC was the most potent and sustained inducer of GSTA2 in vivo. PEITC induced GSTA2 mRNA and protein expression in H4IIE cells. PEITC increased the levels of nuclear factor erythroid 2 related factor 2 and CCAAT/enhancer binding protein β (C/EBPβ). The cells transfected with a pGL-ΔARE or pGL-ΔC/EBP-deleted promoter construct failed to increase GSTA2 promoter activity by PEITC. These effects of PEITC were downstream of multiple cellular signaling, including phosphoinositide 3-kinase (PI3K), c-jun N-terminal kinase (JNK), and/or protein kinase A (PKA). These results demonstrated that PEITC is the most efficacious of the arylalkyl ITCs for the induction of GSTA2 in vivo and in vitro, and that transactivation of C/EBP and nuclear factor erythroid 2 related factor 2 downstream of multiple signaling pathways is involved in this induction.