Mutation Research/DNA Repair
Accelerated publicationGoing APE over ref-1
Introduction
Apurinic/apyrimidinic endonuclease/redox effector factor (Ape1/Ref-1) is a protein with multifunctional roles in cells impacting on a wide variety of important cellular functions (Fig. 1). It acts on apurinic/apyrimidinic (AP) sites in DNA as a major member of the base excision repair (BER) pathway, is involved in oxidative DNA damage repair, and stimulates the DNA binding activity of AP-1 (Fos, Jun) proteins, as well as nuclear factor-κB (NF-κB), polyoma virus enhancer-binding protein 2 (PEBP2), early growth response-1 (Egr-1), Myb, members of the ATF/CREB family, HIF-1α (hypoxia inducible factor-1α), HLF (HIF-like factor), Pax-5, and Pax-8 [2], [25], [52], [53], [71], [149], [150], [156]. The DNA binding activity of these latter proteins is sensitive to reduction–oxidation (redox). Ape1/Ref-1, which is the major AP-1 redox activity in cells, represents a novel redox component of signal transduction processes that regulate eukaryotic gene expression. Recent developments also have implicated Ape1/Ref-1 as a major controlling factor for p53 activity through redox dependent and independent mechanisms [33], [60]. Ape1/Ref-1 has been shown to be closely linked to apoptosis [110] and altered levels or cellular location of Ape1/Ref-1 have been found in some cancers, including ovarian, cervical, prostate and germ cell tumors [66], [67], [88], [153]. Therefore, Ape1/Ref-1 appears to form a unique link between the DNA BER pathway, cancer, transcription factor regulation, oxidative signaling, and cell-cycle control.
Section snippets
AP site formation and base excision repair
AP sites are a common type of DNA lesion [28], [90]. In fact, the in vitro spontaneous depurination rate is estimated at ∼10,000 bases per cell per day [73], [91]. Nakamura and Swenberg recently expanded these findings in vivo using a slot blot assay, and estimate 2000–8000 sites form per cell per day depending on the tissue type [90]. The maximum number of AP sites is found in the brain, followed by heart and colon, whereas liver, lung, and kidney have the lowest rates in rats. Interestingly,
Ape1/Ref-1 genes, proteins, and structure
AP endonucleases are classified into two families according to their homology to E. coli endonucleases: exonuclease III (xth) and endonuclease IV (nfo). The first family of AP endonucleases derives from organisms across several phyla including, exonulcease III (E. coli), Exo A (Steptococcus pneumoniae), Rrp 1 (Drosophila melanogaster), Arp (Arabidopsis thaliana), Apn2 (S. cerevisiae), APEX (mouse), BAP1 (bovine), rAPE (rat), chAPE1 (hamster), and Ape1/Ref-1 (humans; previously referred to as
Ape1/Ref-1 tissue and cellular location
Since Ape1/Ref-1 is an important protein for cellular survivability, it was expected to be ubiquitously expressed in cells. Indeed, Ape1/Ref-1 expression is ubiquitous, however, it exhibits a complex and heterogeneous staining pattern that differs among tissue types and even differs between neighboring cells. At least five different patterns of Ape1/Ref-1 staining are observed; presumably, the expression complexity is congruent with its multifunctional roles. First, regional variation in the
Regulation of gene expression
Ape1/Ref-1 is regulated at both the transcriptional and post-translational level. In terms of transcriptional regulation, the effects of reactive oxygen species (ROS) on Ape1/Ref-1 induction have been the most intensely studied (Table 1). In both in vivo and in vitro studies, oxidative agents induce Ape1/Ref-1 [35], [39], [40], [107], [131], [133], [137], [156] (although see [23]). Induction is characterized by a transient increase in Ape1/Ref-1 protein and mRNA. The exception to this is a
Regulation of transcription factors
The importance of reduction–oxidation (redox) control of transcription factors was suggested when v-Jun, a transcription factor with transforming and oncogenic qualities, was shown to have a serine mutation at the normally conserved cysteine residue [93]. Moreover, when a cysteine to serine mutation was introduced in Fos, it resulted in an increase in DNA binding, a resistance to oxidizing agents and an increase in cellular transforming activity (i.e. colony formation) [1], [95]. Thus, the
Over-expression of Ape1/Ref-1 and antisense studies
Ape1/Ref-1 is a critical component of BER. Indeed, unrepaired abasic sites can result in a block to DNA replication, cytotoxicity, mutations, and genetic instability [74]. The functional importance of this protein is underscored by the findings that mice nullizygous for Ape1/Ref-1 gene are embryonic lethal [152]. Consequently, a number of studies have investigated the effects of manipulating cellular levels of Ape1/Ref-1 with the expectation that healthy normal cells could be afforded added
Concluding remarks
Ape1/Ref-1 is a multifunctional protein that is critical to the survival of animals and, presumably, humans [152]. It impacts on a wide variety of important cellular functions. As a major member of the BER pathway, Ape1/Ref-1 acts on AP sites in DNA, which, if left unrepaired, can result in a block to DNA replication, cytotoxicity, mutations, and genetic instability [74]. Ape1/Ref-1 has also been found to stimulate the transcriptional activity of numerous transcription factors that have
Acknowledgements
We would like to thank David M. Wilson III (Lawrence Livermore National Laboratory) and Martin L. Smith (Indiana University Medical School) for their reading and comments on this manuscript pre-submission. We also want to thank Dr. Daniel Barsky, Lawrence Livermore National Laboratory, for generating and giving us the Ape1/Ref-1 structure found in Fig. 5. The authors were supported in this endeavor by NIH/NCI Program Project Grant PO1-CA75426 and by NIH Grants CA76643, ES07815, NS38506, the
References (158)
- et al.
Redox regulation of the DNA binding activity in transcription factor PEBP2. The roles of two conserved cysteine residues
J. Biol. Chem.
(1997) - et al.
Structure, promoter analysis and chromosomal assignment of the human APEX gene
Biochim. Biophys. Acta
(1994) - et al.
Increase in Ref-1 mRNA and protein by thyrotropin in rat thyroid FRTL-5 cells
Biochem. Biophys. Res. Commun.
(1997) - et al.
The interaction between Ku antigen and REF1 protein mediates negative gene regulation by extracellular calcium
J. Biol. Chem.
(1996) - et al.
Redox factor-1 (Ref-1) mediates the activation of AP-1 in HeLa and NIH 3T3 cells in response to heat shock
J. Biol. Chem.
(1999) - et al.
The enzymology of apurinic/apyrimidinic endonucleases
Mutat. Res.
(1990) - et al.
The role of Mg2+ and specific amino acid residues in the catalytic reaction of the major human abasic endonuclease: new insights from EDTA-resistant incision of acyclic abasic site analogs and site-directed mutagenesis
J. Mol. Biol.
(1999) - et al.
Two pathways for base excision repair in mammalian cells
J. Biol. Chem.
(1996) - et al.
Transcriptional activation by the Myb proteins requires a specific local promoter structure
FEBS Lett.
(1999) - et al.
Expression of nuclear redox factor Ref-1 in the rat hippocampus following global ischemia induced by cardiac arrest
Brain Res. Mol. Brain Res.
(1997)