OGG1-DNA Interactions Facilitate NF-?B Binding To DNA Targets

Aerobic organisms face the invasion of ROS(Reactive Oxygen Species)deriving from metabolism or environmental factors all the time.Oxidative stress known as oxidative state that intracellular ROS level exceeds the ability of enzyme system to remove.Oxidative stress will oxidaze various cellular macromolecules,including proteins,lipids and nucleic acids.Especially in DNA,ROS cause predominantly 8-hydroxy guanine(8-oxoG)formation.8-hydroxytridine DNA glycosylase 1(OGG1)is the repair enzyme that specifically recognizes 8-oxoG and repair through base excision repair pathway(OGG1-BER).To study the consequences of 8-oxoG accumulation in DNA and role of OGG1 in pathophysiological processes,Ogg1 knock out(Ogg1-/-)mice were developed.Unexpectedly,the resulting high levels of genomic 8-oxoG did not affect embryonic development or life span,moreover,Ogg1-/-mice showed no marked response to inflammation,exhibiting lower expression of pro-inflammatory cytokines and deficiency in inflammatory cells infiltration.Because of decreased gene expression in lack of functional OGG1,we hypothesize that OGG1 binding to 8-oxoG within or proximal to consensus motif may modulate transacting factors binding and transcriptional response upon oxidative stress.Oxidative DNA base lesions,particularly existed in promoter regions,can alter DNA protein interactions and have the capacity to regulate promoter function.Such lesions themselves and DNA repair processes thought to interfere with transcriptional output.Understanding the association between DNA damage repair and transcriptional regulation provides insights into the molecular mechanisms involved.Our previous work has documented that association of transcription factor NF-?B with of proinflammatory genes promoter is OGG1 dependent.In the present study,cells were stressed by cytokine(TNF?)and siRNA mediated gene knockdown,chromatin immune-precipitation(ChIP),ChIP-coupled sequencing(ChIP-seq),reporter assay,RT-qPCR,Western-Blot and electrophoretic mobility shift assays(EMSA)were performed to reveal in depth the effect of 8-oxoG present in gene promoter region on transcription and the mechanism of OGG1 involved in transcriptional regulation.Through our study,we found that(1)in response to oxidative stress,OGG1 can quickly identify the oxidized damage substrate on promoter of chromatin,and then facilitate transcription factor binding to its conserved sequence,as well as effectively promotes the large number of transcription factors,which provides a good prerequisite for the timely expression of specific genes;(2)OGG1 can also affect the activity of NF-?B driven gene promoter under oxidative stress;(3)ROS not only attack DNA,producingoxidative damage to DNA bases,but also oxidative modifiy proteins.OGG1 cysteine is oxidadized and base excision activity is inhibited,so that the integrity of the genome is insured and transcription initiation is possible;(4)the presence of damaged bases and DNA repair enzymes can specifically regulate gene expression,in a given time and space,there is a synergistic role between DNA damage and transcriptional regulation;(5)through the above molecular mechanism,the outcome for OGG1 in NF-?B-initiated transcriptional regulation is promote gene expression.Our study revealed a new mechanism for DNA damage repair enzyme OGG1 activativates transcription,that is,OGG1 recognizes 8-oxoG,a product of oxidative damage in the promoter region,that promotes and accelerates NF-?B binding to DNA,thereby contributing to gene expression.The expression of chemokines and chemokines is highly dependent on ROS signal,and the promoters of these genes are with high GC content and contain multiple NF-?B binding sites.The expression of proinflammatory cytokines is required for innate immune response.Oxidative damage response is a very important innate immune defense mechanism.Our study shows that DNA damage in the traditional concept within a given time and space has an important transcriptional response function;in response to oxidative stress,the mechanism of OGG1 recognizing damage sites may define the specificity of NF-?B transcription regulation.