PARENT SESSION

Cell and Tissue Signaling

(PP279) GPx-1 inhibits UVA induced AP2 expression in HaCaT cells.

Yu, Lei^*,1, Domann, Frederick¹, ¹ Free Radical & Radiation Biology, Iowa City, IA, USA

ABSTRACT- UVA irradiation is well known as a carcinogen. There are many signal pathways can be turned on by UVA irradiation. In HaCaT human keratinocyte, we found after exposed to low dose UVA irradiation (1 J/cm²), the expression of transcription factor AP2, which is important to skin development and cell differentiation, was upregulated. The mRNA half-life and promoter activity reporter assay suggested that this upregulation was due to increase of mRNA expression. Although singlet oxygen was found the major reactive oxygen species (ROS) generated by UVA, other ROS such as superoxide radical, hydrogen peroxide, hydroxyl radical and lipid peroxidation in cell membranes are also increased after UVA irradiation. We found the H2O2 concentration in the culture medium increased from 0.5 fmol per cell to 13 fmol per cell after the low dose UVA irradiation. We hypothesize that this accumulation of H2O2 caused the upregulation of AP2 expression. HaCaT cells were treated with 200 M H2O2 for 20 minutes and then continue cultured in the H2O2 free medium. Both protein and mRNA levels showed robust increase. The cells were also treated with 4-NHE, a byproduct of cell membrane lipids peroxidation. Neither the mRNA level nor the protein level showed increase. The effects of antioxidant enzymes on AP2 expression were also studied. Over expressing GPx-1 but not MnSOD and empty vector control could abolish the UVA induced AP2 expression in HaCaT cells. Our results suggest that the accumulation of H2O2 in cells after UVA irradiation is another cause of upregulation of AP2 expression.

Key words: UVA, AP2, ROS, GPx-1