Functions And Action Mechanisms Of PRDX3-UNG1 Interaction In Cellular Oxidative Stress

The mitochondrial DNA(mtDNA)is more susceptible to oxidative damage than the nuclear DNA due to its close proximity to the respiration chain.Thioredoxin dependent peroxide reductase(PRDX3)is a mitochondrial peroxide reductase that regulates cellular redox state.Isoform 1 of Uracil-DNA glycosylase(UNG1)is the major protein responsible for initiating base-excision repair in mitochondria DNA repair.Effects of oxidative stress on regulation and function of PRDX3-UNG1 have not been well characterized.Preliminary works showed that UNG1 mainly binded to PRDX3 under oxidative stress,and the binding of UNG1 and PRDX3 was confirmed by reciprocal IP.We further demonstrated that the uracil-containing double-stranded oligo DNA specifically binded to the complex of UNG1 and PRDX3 formed in the hydrogen peroxide-treated cells,suggesting that PRDX3 protects integrity of mtDNA from reactive oxygen species(ROS)through PRDX3-UNG1 interaction,On the other hand,our results showed that ROS induced degradation of UNG1 in both wild type and UNG1(+)cells,whereas the mRNA expression level of UNG1 was increased under oxidative stress.We also found that the ROS induced degradation of UNG1 was proteasome-independent and LonP1 was responsible for oxidative stress-induced UNG1 degradation.Taken together,these results demonstrated for the first time that ROS mediated degradation of UNG1 by Lonp1,and revealed a novel function of UNG1 in recruitment of PRDX3 to mtDNA,which enables protection of UNG1-bounded DNA from ROS damage and in turn enhances cells' resistance to oxidative stress.It has been reported that PRDX3 is overexpressed in liver cancer,but how PRDX3 is involved in hepatocellular carcinoma(HCC)tumorigenesis and progression has not been well characterized.In the present study,we established two stable cell lines by overexpressing or knocking down PRDX3 in HepG2 cells.We found that PRDX3 silencing decreased the growth rate of HepG2 cells and increased mtDNA oxidation.Quantitative proteomics identified 475 differentially expressed proteins between the PRDX3 knockdown and the control cells.These proteins were involved in antioxidant activity,angiogenesis,cell adhesion,cell growth,ATP synthesis,nucleic acid binding,redox and chaperones.PRDX3 knockdown led to down-regulation of ATP synthases andthe decreased cellular ATP level contributing to slow down of cell growth.Furthermore,silencing PRDX3 enhanced invasive properties of HepG2 cells via TIMP1(tissue inhibitors of metalloproteinase 1)down-regulation and the increased extracellular matrix(ECM)degradation.Taken together,our results indicate that PRDX3 promotes HCC growth and mediates cell migration and invasiveness and is a potential therapeutic target for HCC treatment.