4-Hydroxynonenal increases γ-glutamyl transpeptidase gene expression through mitogen-activated protein kinase pathways

Abstract

Abstractγ-Glutamyl transpeptidase (GGT) plays key roles in the metabolism of glutathione. Previous studies have shown that GGT expression was increased by oxidants, but the mechanism remains unclear. In the present study, the effects of 4-hydroxy-2-nonenal (HNE), an electrophilic end product of lipid peroxidation, on GGT expression were investigated in rat lung epithelial type II (L2) cells. We demonstrated that HNE increased GGT activity and mRNA content in both time-and dose-dependent manners. Actinomycin D, an RNA transcription inhibitor, blocked HNE-stimulated increase in GGT mRNA, suggesting transcriptional regulation of GGT mRNA by HNE. Of the seven GGT mRNA transcripts known to be produced from the single rat GGT gene, we found that types I, II, and V-2 were constitutively expressed in L2 cells, but only types I and V-2 were increased by HNE. PD98059 and SB203580, relatively specific inhibitors of the ERK and the p38MAPK kinase pathway, respectively, significantly attenuated HNE induction of both GGT activity and mRNA content. In contrast, studies with JNK inhibitor I, a cell-permeable peptide, indicated that JNK was not involved in the GGT induction by HNE. We also found that GGT induction by HNE could be completely blocked by a cocktail of PD98059 and SB203580, suggesting a combined effect of ERK and p38MAPK pathways in HNE-mediated GGT induction. In conclusion, our results demonstrate that HNE increased GGT expression in rat alveolar type II cells and that the induction of GGT by HNE was mediated through activation of the ERK and p38MAPK pathways.

γ-Glutamyl transpeptidase is induced by 4-hydroxynonenal via EpRE/Nrf2 signaling in rat epithelial type II cells

“…An example of this is the signaling pathways involved in the EpRE-mediated NQO-1 and GCL induction in HepG2 cells; protein kinase C (PKC) and ERK/p38MAPK were involved, respectively in their EpRE activation [66,69]. As to the signaling pathways responsible for GGT induction by HNE, recent studies from our laboratory suggest that ERK1/2 and P38MAPK mediate the induction of GGT mRNA V-2 through regulation of the activation of Nrf2 [31,87]. The present study, however, focused on the identification of the cis element regulating GGT V2 expression, verifying whether it was the element to which Nrf2 bound and the tissue distribution of GGT V2 expression.…”

“…Previously, we have demonstrated that GGT gene expression was increased by HNE in L2 cells, and GGT mRNA V-2 was the major type of GGT mRNA being induced [31]. To further examine the mechanism of GGT mRNA V-2 induction by HNE, we first determined its expression pattern in response to HNE.…”

“…Compared to V-1, V-2 does not have the 252 nucleotides (nt) corresponding to the second exon for the mRNA IV and V-1. Previously, we reported that mRNA V-2 was one of the major types of GGT and was induced by 4-hydroxynonenal in rat lung epithelial cells (L2 cells) [31]. The underlying mechanism of its induction by HNE, however, remains unclear.…”

The chemistry of cell signaling by reactive oxygen and nitrogen species and 4-hydroxynonenal

“…Numerous studies have shown that physiological concentrations of HNE can stimulate cellular proliferation (187)(188)(189), differentiation (190,191), and cytoprotective response (181,(192)(193)(194)(195)(196)(197), through affecting multiple signaling pathways. As low as 0.5 μM, HNE can induce transcription of glutamate cysteine ligase, the first enzyme of GSH synthesis, through activation of the Nrf2-EpRE signaling pathways (198).…”

“…Regarding p38MAPK, Kumagai et al reported that both p38MAPK and its upstream kinase MKK3/6, were phosphorylated (activated) upon exposure to 25 μM HNE (210). Other researchers also noticed that HNE could markedly increase p38MAPK phosphorylation (196,213). These suggest that HNE activate p38MAPK through targeting upstream signaling molecules, which again have not yet been identified.…”