Regulatory Role of Human AP-Endonuclease (APE1/Ref-1) in YB-1-Mediated Activation of the Multidrug Resistance Gene MDR1

Abstract

The mammalian AP-endonuclease APE1 is a ubiquitous and remarkably multifunctional protein. It plays a central role in the base excision repair (BER) pathway for repairing damaged bases and DNA single-strand breaks induced by reactive oxygen species and alkylating agents and also repairing AP sites that are generated spontaneously or after the excision of oxidized and alkylated bases by DNA glycosylases (12,40). APE1 was also shown to incise DNA 5Ј to oxidatively damaged bases including 5,6-dihydrothymidine and alpha-2Ј-deoxyadenosine in the nucleotide incision repair pathway (11,21). The deletion of the N-terminal 61 amino acid residues, which are dispensable for the AP-endonuclease activity, affected its incision activity as well (21, 28). Moreover, the ability of APE1 to incise DNA 5Ј to a bulky exocyclic adduct such as p-benozoquinone has also been reported (22). Besides its repair function, mammalian APE1 has two unique and apparently distinct transcriptional regulatory activities. It was independently identified as a reductive activator of c-Jun in vitro and named . Subsequently, several other transcription factors (including p53, NF-B, hypoxia-inducible factor 1-␣, PAX5, and PAX8) were also shown to be activated by APE1, presumably via the same redox process (13,31,55). A third and distinct function of APE1 as a trans-acting factor was discovered when APE1 was identified as being one of the regulatory proteins that binds to the negative Ca 2ϩ response elements (nCaRE-A and -B) in the Ca 2ϩ -dependent downregulation of the parathyroid hormone gene (48) and subsequently in the human renin gene (17). We later showed that human APE1 is acetylated at Lys6 and Lys7 by the histone acetyltransferase p300, both in vivo and in vitro, and that acetylation enhances APE1's binding to nCaRE-B, leading to the repression of the parathyroid hormone promoter (2). Our follow-up studies indicated that a small but significant fraction of APE1 in HeLa cells and mouse liver is present in the acetylated form (14,56). Recently, we have shown that the early growth response protein (Egr-1)-mediated activation of phosphoinositol phosphatase and tensin homologue (PTEN) is dependent on APE1 acetylation (14).Although APE1 heterozygous mice are viable and appear to be normal, APE1 nullizygous mice show early embryonic lethality (37,39,63). We recently showed that APE1 inactivation induced apoptosis in mouse embryo fibroblasts conditionally nullizygous for endogenous APE1, an effect that could be prevented by the ectopic expression of human APE1 (27). Using a complementation assay, we also showed that both the repair activity and acetylation-mediated transcriptional regulatory functions of APE1 are required to prevent the apoptosis of APE1-null mouse embryo fibroblasts. The unexpected essentiality of APE1's regulatory function suggests that APE1 is a coregulator of many critical genes.Resistance to many common anticancer drugs often occurs due to the enhanced expression of ATP-binding cassette (ABC) transporter proteins (6,20). Among the ...

Emerging Roles of the Nucleolus in Regulating the DNA Damage Response: The Noncanonical DNA Repair Enzyme APE1/Ref-1 as a Paradigmatical Example

“…Furthermore, the in vivo involvement of APE1 in RNA metabolic pathways was further corroborated by the observation of the APE1 association, through its N-terminal domain, with rRNA and the ribosome processing protein NPM1 within nucleoli (149). Furthermore, APE1 has been shown to interact with factors involved in the splicing process, such as the heterogeneous nuclear ribonucleoprotein L (81) [which is a key regulator of splicing that binds CA repeats with high affinity (65)], YB-1 (29,119), as well as with proteins involved in the ribosome assembly and RNA maturation within cytoplasm (149).…”

“…Actually, several noncanonical factors have been demonstrated to participate BER, even though their in vivo functions are yet to be fully unraveled. The list of non-BER proteins includes for instance: YB-1 [which has been shown to interact with the endonuclease VIII-like 2 (NEIL2) glycosylase (35), the endonuclease III-like glycosylase (NTH1) and APE1 (29)], NEIL2 [which was also found to interact with the RNA-binding protein hnRNP-U (6)], HMGB1 [which has been implicated in single-strand break (SSB) repair involving Polb (90)] and the tumor suppressor p53, which was also shown to play a role in DNA damage repair through direct binding to APE1 and Polb (168). The list of these non-BER proteins is still growing, supporting the notion that BER in vivo is far more complex than the simple model that we can reconstitute in vitro.…”

Targeting the Y/CCAAT box in cancer: YB-1 (YBX1) or NF-Y?

“…APE1 is also known as redox effector factor 1 (Ref1), as it affects the redox status of, among other proteins, many TFs. APE1/Ref1 and YB-1 directly interact, 110 they bind the MDR1 core promoter and removal of APE1 leads to decreased YB-1, Pol II and p300 promoter association in ChIP assays. 111 This led the authors to propose that the YB-1/CCAAT interaction mediates the recruitment of the APE1/p300/Pol II complex onto the promoter.…”

Human Apurinic/Apyrimidinic Endonuclease 1

“…Thus, APE1 may be required for oxidative DNA lesion processing or for a more general stress response. Moreover, Chattopadhyay et al (25) have reported that acetylated APE1, through an interaction with the transcription factor YB-1, can activate expression of the multi-drug resistance gene MDR1. Increased levels of the MDR1 P-glycoprotein membrane transporter are associated with enhanced drug efflux and resistance in cancer cells, and could explain the sensitizing effect of APE1 depletion to compounds such as cisplatin.…”