An oxidative DNA “damage” and repair mechanism localized in the VEGF promoter is important for hypoxia-induced VEGF mRNA expression

Abstract

In hypoxia, mitochondria-generated reactive oxygen species not only stimulate accumulation of the transcriptional regulator of hypoxic gene expression, hypoxia inducible factor-1 (Hif-1), but also cause oxidative base modifications in hypoxic response elements (HREs) of hypoxia-inducible genes. When the hypoxia-induced base modifications are suppressed, Hif-1 fails to associate with the HRE of the VEGF promoter, and VEGF mRNA accumulation is blunted. The mechanism linking base modifications to transcription is unknown. Here we determined whether recruitment of base excision DNA repair (BER) enzymes in response to hypoxia-induced promoter modifications was required for transcription complex assembly and VEGF mRNA expression. Using chromatin immunoprecipitation analyses in pulmonary artery endothelial cells, we found that hypoxia-mediated formation of the base oxidation product 8-oxoguanine (8-oxoG) in VEGF HREs was temporally associated with binding of Hif-1α and the BER enzymes 8-oxoguanine glycosylase 1 (Ogg1) and redox effector factor-1 (Ref-1)/apurinic/apyrimidinic endonuclease 1 (Ape1) and introduction of DNA strand breaks. Hif-1α colocalized with HRE sequences harboring Ref-1/Ape1, but not Ogg1. Inhibition of BER by small interfering RNA-mediated reduction in Ogg1 augmented hypoxia-induced 8-oxoG accumulation and attenuated Hif-1α and Ref-1/Ape1 binding to VEGF HRE sequences and blunted VEGF mRNA expression. Chromatin immunoprecipitation-sequence analysis of 8-oxoG distribution in hypoxic pulmonary artery endothelial cells showed that most of the oxidized base was localized to promoters with virtually no overlap between normoxic and hypoxic data sets. Transcription of genes whose promoters lost 8-oxoG during hypoxia was reduced, while those gaining 8-oxoG was elevated. Collectively, these findings suggest that the BER pathway links hypoxia-induced introduction of oxidative DNA modifications in promoters of hypoxia-inducible genes to transcriptional activation.

Unveiling the non-repair face of the Base Excision Repair pathway in RNA processing: A missing link between DNA repair and gene expression?

“…Hif1α, STAT1, NF-κB and MYC) in conjunction with OGG1 protein and, in turn, regulates the expression of important genes involved in cancer development, such as VEGF [40], SIRT-1 [41] and inflammatory genes such as TNF-α and CXCL2 [42]. Interestingly, this last role of OGG1 on inflammatory genes may explain the reduced inflammatory response in Ogg1 −/− mice [43].…”

G-quadruplex–forming promoter sequences enable transcriptional activation in response to oxidative stress

“…Most oxidative DNA damage is efficiently processed by DNA repair pathways, primarily base excision repair (BER), the molecular details of which are generally well understood (2). However, an emerging area of research posits that certain oxidative DNA lesions and their associated repair complexes are intermediates in a signaling transduction cascade that uses ROS as secondary messengers to ultimately effect transcriptional regulation (3)(4)(5)(6)(7). In PNAS, Fleming et al (8) reinforce these notions by describing a compelling mechanism by which 8-oxoguanine (OG), a canonical oxidative DNA damage product, when occurring in guanine-rich, G-quadruplex-forming promoter sequences, directly up-regulates transcription of the downstream gene.…”

“…In the hypoxia field, it has been increasingly appreciated that the expression of hypoxia-inducible genes [e.g., vascular endothelial growth factor (VEGF)] depends, in part, on a controlled oxidative DNA damage and repair cycle (3,6). More intriguingly, even in normoxic conditions, the expression of estrogen-or androgenresponsive genes also requires DNA oxidation and repair (10,11).…”

DNA damage and base excision repair : an important role during zebrafish embryogenesis

“…This provides a precedent that controlled DNA damage and repair can regulate active transcription. Other studies have also shown that site specific DNA damage can activate gene transcription (Ba et al 2014;Fleming, Ding, and Burrows 2017;Pan et al 2016;Pastukh et al 2015), though the mechanism through which damage occurs to specific points in the genome remains relatively unexplored.…”

“…The resultant DNA lesion recruits OGG1 and topoisomerase IIb (TOPIIb) causing the conformational change to DNA required for gene activation (Perillo et al 2008). Likewise, oxidative damage to the vascular endothelial growth factor (VEGF) promoter enhances binding of hypoxiainducible factor 1a (HIF1a) with the subsequent assembly of BER components activating gene expression Ruchko 2009, 2010;Pastukh et al 2015). A similar process occurs in the promoters of tumor necrosis factor a (TNF-a) (Pan et al 2016) and sirtuin 1 (SIRT1) (Antoniali et al 2014).…”