Mi H. Kim

Interleukin-1β stimulates IL-8 expression through MAP kinase and ROS signaling in human gastric carcinoma cells

Recent studies have suggested that the expression of interleukin-8 (IL-8) directly correlates with the vascularity of human gastric carcinomas. In this study, the effect of IL-1β on IL-8 expression in human gastric cancer TMK-1 cells and the underlying signal transduction pathways were investigated. IL-1β induced the IL-8 expression in a time- and concentration-dependent manner. IL-1β induced the activation of extracellular signal-regulated kinases-1/2 and P38 mitogen-activated protein kinase (MAPK), but not the activation of c-jun amino-terminal kinse and Akt. Specific inhibitors of MEK-1 (PD980590) and P38 MAPK (SB203580) were found to suppress the IL-8 expression and the IL-8 promoter activity. Expression of vectors encoding a mutated-type MEK-1 and P38 MAPK resulted in decrease in the IL-8 promoter activity. IL-1β also induced the production of reactive oxygen species (ROS). N-acetyl cysteine (NAC) prevented the IL-1β-induced ROS production and IL-8 expression. In addition, exogenous H2O2 could induce the IL-8 expression. Deletional and site-directed mutagenesis studies on the IL-8 promoter revealed that activator protein-1 (AP-1) and nuclear factor (NF)-κB sites were required for the IL-1β-induced IL-8 transcription. Electrophoretic mobility shift assay confirmed that IL-1β increased the DNA-binding activity of AP-1 and NF-κB. Inhibitor (PD980590, SB203580) and ROS scavenger (NAC) studies revealed that the upstream signalings for the transcription factors AP-1 and NF-κB were MAPK and ROS, respectively. Conditioned media from the TMK-1 cells pretreated with IL-1β could remarkably stimulate the in vitro growth of HUVEC and this effect was partially abrogated by IL-8-neutralizing antibodies. The above results suggest that MAPK-AP-1 and ROS-NF-κB signaling pathways are involved in the IL-1β-induced IL-8 expression and that these paracrine signaling pathways induce endothelial cell proliferation.

Ascorbic acid suppresses the 2,3,7,8-tetrachloridibenxo-p-dioxin (TCDD)-induced CYP1A1 expression in human HepG2 cells.

The mechanisms involving the inhibitory effects of ascorbic acid (AA) on carcinogenesis have not fully defined, except for its free-radical scavenging activity against oxidative DNA damage. In this study, we examined the effects of AA on the expression of the aryl hydrocarbon receptor (AhR)-regulated gene cytochrome P4501A1 (CYP1A1), which catalyzes the activation of genotoxic metabolites that can lead to mutagenesis. Cultured human HepG2 cells were incubated with AA with or without the potent AhR agonist/CYP1A1 inducer 2,3,7,8-tetrachloridibenxo-p-dioxin (TCDD). AA was highly effective at suppressing CYP1A1 induction following coincubation of the cells with 1nM TCDD. The preventive effects of AA were seen at the level of mRNA and protein expression as well as CYP1A1-specific 7-ethoxyresorufin O-deethylase (EROD) activity. A transient transfection assay using a dioxin response element (DRE)-linked luciferase reporter and an electrophoretic mobility shift assay revealed that AA reduced the amount of AhR that could form a complex with the DRE sequence in the promoter region of the CYP1A1 gene. In addition, AA inhibited the TCDD-induced Ecto-ATPase activity, which is known to be requiring for AhR translocation to the nucleus. These results suggest that AA may exert at least part of its anticarcinogenesis effect by controlling the expression of CYP1A1 at the transcription level.