Apurinic/apyrimidinic endonuclease 1 regulates angiogenesis in a transforming growth factor β-dependent manner in human osteosarcoma

Inhibition of miR-9 Combined With Cisplatin Targeting APE1 Against Angiogenesis in Osteosarcoma

Osteosarcoma (OS) is a highly malignant tumor, and chemotherapy resistance suggests poor prognosis in OS patients. In this study, the authors discovered that miR-9 has a pro-angiogenic role in OS. The anti-angiogenic effects of cisplatin were greatly increased when miR-9 was suppressed in OS. In addition, the authors demonstrated that miR-9 plays a pro-angiogenic role by targeting apoptosis-inducing factor 1 (APE1) in OS. Importantly, our in vivo experiments showed that inhibition of miR-9 combined with cisplatin could suppress xenograft tumor growth by targeting APE1 and decreasing angiogenesis in OS. In summary, our results suggest that miR-9 plays a role as a tumor promoter, and inhibiting miR-9 and APE1 is a new strategy for inhibiting OS angiogenesis and chemotherapy resistance.

Enteric neuroprotection-A matter of balancing redox potentials, limiting inflammation, and boosting resilience

The enteric nervous system (ENS) orchestrates intricate and autonomous functions throughout the gastrointestinal (GI) tract. Disruptions in ENS function are associated GI disorders. This mini review focuses on the past decade's research, utilizing rodent models, with an emphasis on protecting enteric neurons from loss. The review specifically looks at efforts to reduce oxidative stress, limit inflammation, and enhance neuronal resilience. Protective interventions including administration of antioxidants and compounds targeting cellular redox buffer systems, are evaluated for their effectiveness in preventing loss of enteric neurons in the ischemia-reperfusion model and streptozotocin-induced diabetes model. Interventions such as engrafting mesenchymal stem cells and targeting inflammatory signaling pathways in enteric neurons and glial cells are evaluated in inflammatory bowel disease models including the Winnie mouse, DSS-, and DNBS/TNBS-induced colitis models. The review also touches upon neuronal resilience, particularly in the context of Parkinson's disease models. Including estrogen's neuroprotective role, and the influence of metal ions on enteric neuronal protection. Understanding the dynamic interplay within the ENS and its role in disease pathogenesis holds promise for developing targeted therapies to effectively manage and treat various GI ailments.

The APE1/REF-1 and the hallmarks of cancer

APE1/REF-1 (apurinic/apyrimidinic endonuclease 1 / redox factor-1) is a protein with two domains, with endonuclease function and redox activity. Its main activity described is acting in DNA repair by base excision repair (BER) pathway, which restores DNA damage caused by oxidation, alkylation, and single-strand breaks. In contrast, the APE1 redox domain is responsible for regulating transcription factors, such as AP-1 (activating protein-1), NF-κB (Nuclear Factor kappa B), HIF-1α (Hypoxia-inducible factor 1-alpha), and STAT3 (Signal Transducers and Activators of Transcription 3). These factors are involved in physiological cellular processes, such as cell growth, inflammation, and angiogenesis, as well as in cancer. In human malignant tumors, APE1 overexpression is associated with lung, colon, ovaries, prostate, and breast cancer progression, more aggressive tumor phenotypes, and worse prognosis. In this review, we explore APE1 and its domain's role in cancer development processes, highlighting the role of APE1 in the hallmarks of cancer. We reviewed original articles and reviews from Pubmed related to APE1 and cancer and found that both domains of APE1/REF-1, but mainly its redox activity, are essential to cancer cells. This protein is often overexpressed in cancer, and its expression and activity are correlated to processes such as proliferation, invasion, inflammation, angiogenesis, and resistance to cell death. Therefore, APE1 participates in essential processes of cancer development. Then, the activity of APE1/REF-1 in these hallmarks suggests that targeting this protein could be a good therapeutic approach.

Microvessel Density (MVD) in Patients with Osteosarcoma: A Systematic Review and Meta-Analysis

A meta-analysis was designed and conducted to estimate the effect of tumoral microvessel density (MVD) on the survival of patients with osteosarcoma. There was no difference between high and low MVD regarding the overall (OS) and disease-free (DFS) survival. Low MVD tumors displayed a lower DFS at the third year of follow-up. Although primary metastases did not affect the mean MVD measurements, tumors with a good chemotherapy response had a higher MVD value. Although no significant differences between tumoral MVD, OS and DFS were found, good adjuvant therapy responders had a significant higher vascularization pattern.

Revisiting Two Decades of Research Focused on Targeting APE1 for Cancer Therapy: The Pros and Cons

APE1 is an essential endodeoxyribonuclease of the base excision repair pathway that maintains genome stability. It was identified as a pivotal factor favoring tumor progression and chemoresistance through the control of gene expression by a redox-based mechanism. APE1 is overexpressed and serum-secreted in different cancers, representing a prognostic and predictive factor and a promising non-invasive biomarker. Strategies directly targeting APE1 functions led to the identification of inhibitors showing potential therapeutic value, some of which are currently in clinical trials. Interestingly, evidence indicates novel roles of APE1 in RNA metabolism that are still not fully understood, including its activity in processing damaged RNA in chemoresistant phenotypes, regulating onco-miRNA maturation, and oxidized RNA decay. Recent data point out a control role for APE1 in the expression and sorting of onco-miRNAs within secreted extracellular vesicles. This review is focused on giving a portrait of the pros and cons of the last two decades of research aiming at the identification of inhibitors of the redox or DNA-repair functions of APE1 for the definition of novel targeted therapies for cancer. We will discuss the new perspectives in cancer therapy emerging from the unexpected finding of the APE1 role in miRNA processing for personalized therapy.

MicroRNAs and osteosarcoma: Potential targets for inhibiting metastasis and increasing chemosensitivity

Osteosarcoma (OS) is the third most common cancer in young adults after lymphoma and brain cancer. Metastasis, like other cellular events, is dependent on signaling pathways; a series of changes in some proteins and signaling pathways pave the way for OS cells to invade and migrate. Ezrin, TGF-β, Notch, RUNX2, matrix metalloproteinases (MMPs), Wnt/β-catenin, and phosphoinositide 3-kinase (PI3K)/AKT are among the most important of these proteins and signaling pathways. Despite the improvements in treating OS, the overall survival of patients suffering from the metastatic disease has not experienced any significant change after surgical treatments and chemotherapy and 5-years overall survival in patients with metastatic OS is about 20%. Studies have shown that overexpression or inhibition of some microRNAs (miRNAs) has significant effects in limiting the invasion and migration of OS cells. The results of these studies highlight the potential of the clinical application of some miRNA mimics and miRNA inhibitors (antagomiRs) to inhibit OS metastasis in the future. In addition, some studies have shown that miRNAs are associated with the most important drug resistance mechanisms in OS, and some miRNAs are highly effective targets to increase chemosensitivity. The results of these studies suggest that miRNA mimics and antagomiRs may be helpful to increase the efficacy of conventional chemotherapy drugs in the treatment of metastatic OS. In this article, we discussed the role of various signaling pathways and the involved miRNAs in the metastasis of OS, attempting to provide a comprehensive review of the literature on OS metastasis and chemosensitivity.

TGF‑β inhibitor RepSox suppresses osteosarcoma via the JNK/Smad3 signaling pathway

Osteosarcoma (OS) is the most common malignant bone tumor and the long-term survival rates remain unsatisfactory. Transforming growth factor-β (TGF-β) has been revealed to play a crucial role in OS progression, and RepSox is an effective TGF-β inhibitor. In the present study, the effect of RepSox on the proliferation of the OS cell lines (HOS and 143B) was detected. The results revealed that RepSox effectively inhibited the proliferation of OS cells by inducing S-phase arrest and apoptosis. Moreover, the inhibitory effect of RepSox on cell migration and invasion was confirmed by wound-healing and Transwell assays. Furthermore, western blotting revealed that the protein levels of molecules associated with the epithelial-mesenchymal transition (EMT) phenotype, including E-cadherin, N-cadherin, Vimentin, matrix metalloproteinase (MMP)-2 and MMP-9, were reduced by RepSox treatment. Concurrently, it was also revealed that the JNK and Smad3 signaling pathway was inhibited. Our in vivo findings using a xenograft model also revealed that RepSox markedly inhibited the growth of tumors. In general, our data demonstrated that RepSox suppressed OS proliferation, EMT and promoted apoptosis by inhibiting the JNK/Smad3 signaling pathway. Thus, RepSox may be a potential anti-OS drug.

APE1 facilitates PD-L1-mediated progression of laryngeal and hypopharyngeal squamous cell carcinoma

Laryngeal squamous cell carcinoma (LSCC) and hypopharyngeal squamous cell carcinoma (HSCC) seriously affect the life quality of patients. Nowadays, immunotherapy is widely used in the treatment of cancer. Tumor-infiltrating lymphocytes (TILs), programmed cell death 1 (PD-1) and its ligand programmed cell death ligand 1 (PD-L1) play key roles in the immunotherapy of cancer. Moreover, study has reported that the upregulation of PD-L1 and apurinic/apyrimidinic endonuclase 1 (APE1) are associated with tumorigenesis and poor prognosis of gastric cancer. In the present study, the number of CD3+ T lymphocytes and the expressions of PD-1 and PD-L1 in LSCC and HSCC were detected in clinical samples. In addition, the expressions of PD-L1 and APE1 and their correlation were explored. The results showed that PD-1+ T lymphocytes were wildly infiltrated and PD-L1 was overexpressed in LSCC and HSCC tissues. PD-1 had a positive correlation with cancer progression, and glottic and subglottic LSCC tissues might have a more active immune microenvironment. Moreover, the results showed that upregulated co-expression of PD-L1 and APE1 was a biomarker of LSCC, and APE1 could regulate the expression of PD-L1 through NF-κB signaling pathway. In conclusion, the combine detection of the expressions of PD-1, PD-L1 and APE1 will provide predictive value for the treatment of LSCC and HSCC via immune checkpoint inhibitors, which will help us to identify the patient population more likely to benefit from the immune checkpoint inhibitors based on the tumor immune microenvironment.

Bioinformatic Prediction of Signaling Pathways for Apurinic/Apyrimidinic Endodeoxyribonuclease 1 (APEX1) and Its Role in Cholangiocarcinoma Cells

Apurinic/apyrimidinic endodeoxyribonuclease 1 (APEX1) is involved in the DNA damage repair pathways and associates with the metastasis of several human cancers. However, the signaling pathway of APEX1 in cholangiocarcinoma (CCA) has never been reported. In this study, to predict the signaling pathways of APEX1 and related proteins and their functions, the effects of APEX1 gene silencing on APEX1 and related protein expression in CCA cell lines were investigated using mass spectrometry and bioinformatics tools. Bioinformatic analyses predicted that APEX1 might interact with cell division cycle 42 (CDC42) and son of sevenless homolog 1 (SOS1), which are involved in tumor metastasis. RNA and protein expression levels of APEX1 and its related proteins, retrieved from the Gene Expression Profiling Interactive Analysis (GEPIA) and the Human Protein Atlas databases, revealed that their expressions were higher in CCA than in the normal group. Moreover, higher levels of APEX1 expression and its related proteins were correlated with shorter survival time. In conclusion, the signaling pathway of APEX1 in metastasis might be mediated via CDC42 and SOS1. Furthermore, expression of APEX1 and related proteins is able to predict poor survival of CCA patients.

High nuclear expression of APE1 correlates with unfavorable prognosis and promotes tumor growth in hepatocellular carcinoma

APE1 is a multifunctional protein that plays important roles in cancer development. However, the association between APE1 expression and the clinicopathological parameters of HCC patients has not been fully characterized. In this study, bioinformatics analysis of APE1 was performed in several databases, including the TCGA, GeneCard, Human Protein Atlas and Ualcan databases. The relationship between APE1 mRNA expression and several attributes of liver cancer patients in TCGA was investigated. Then, the protein expression of APE1 was detected by IHC analysis in 95 HCC samples and the association between APE1 expression and the clinicopathological parameters of HCC patients was explored. GSEA-KEGG analysis was performed to predict the potential signaling pathways that associated with APE1 expression. Then the siRNA-mediated knockdown model of APE1 was constructed in HCC cell line to further detect the detailed function of APE1 in HCC development in vitro and in vivo. The results of the bioinformatics analysis showed that APE1 expression was primarily located in the cell nucleus. APE1 mRNA expression was substantially correlated with pathological grade and T status in TCGA database. Elevated APE1 expression was observed in HCC samples and was associated with unfavorable survival time in liver cancer patients. IHC data demonstrated that the nuclear expression of APE1 in HCC tissues was significantly higher than that in noncancerous tissues. The expression level of the APE1 protein in HCC was strongly associated with tumor diameter and overall survival. Survival analysis indicated that APE1 nuclear expression is an independent prognostic marker for the overall survival of HCC patients. GSEA-KEGG results confirmed that APE1 associated with the base excision repair signaling pathway. The data of phenotypic experiments indicated that APE1 remarkably promoted tumor growth both in HCC cells and xenografts. The findings firstly imply that nuclear expression of APE1 is a valuable prognostic marker for HCC. APE1 significantly facilitate HCC development and targeting APE1 may be a promising strategy for HCC treatment.

Mitochondrial APE1 promotes cisplatin resistance by downregulating ROS in osteosarcoma

Apurinic/apyrimidinic endonuclease 1 (APE1) is a primary nuclear-localized multifunctional protein in osteosarcoma. However, the cytoplasmic localization of APE1 was found to be functional and to increase with cisplatin resistance, yet the molecular mechanism is unknown. In the present study, we explored the cisplatin resistance mechanism in osteosarcoma from the new perspective of APE1 extranuclear biological activity. Using cisplatin-resistant and cisplatin-sensitive osteosarcoma cell lines, we found that mitochondrial APE1 (mtAPE1) was overexpressed in cisplatin-resistant cells but not in sensitive cells. Overexpression of mtAPE1 reduced cisplatin-induced apoptosis, while knockdown of APE1 reversed this phenomenon and caused oxidative DNA damage via overproduction of reactive oxygen species (ROS). We further demonstrated that high mtAPE1 expression could downregulate ROS production by decreasing the phosphorylation of Rac1 (p-Rac1), further promoting cisplatin resistance in osteosarcoma. Our findings suggest that mitochondrial APE1 promotes cisplatin resistance by decreasing ROS generation, which may provide new ideas for researching the molecular mechanism of osteosarcoma chemoresistance and strategies to overcome cisplatin resistance in osteosarcoma.

Cytoplasmic APE1 promotes resistance response in osteosarcoma patients with cisplatin treatment

Chemotherapy resistance has become a hold back and major clinical challenge in osteosarcoma cancer. The alteration and subcellular distribution of apurinic/apyrimidinic endonuclease 1 (APE1) has been reported to be involved in chemotherapy resistance in many cancers. Here, we report that the cytoplasmic distribution of APE1 plays a key role in the sensitivity of combination platinum chemotherapy in osteosarcoma. Interestingly, the prevalence of cisplatin-induced DNA damage and apoptosis in low cytoplasmic APE1 osteosarcoma cell lines was higher than in high expression of cytoplasmic APE1 cell lines. Overexpression of cytoplasmic APE1 protected the osteosarcoma cells from CDDP-induced apoptosis. In addition, clinical data also show that the level of cytoplasmic APE1 was negatively associated with sensitivity to combination chemotherapy of cisplatin in osteosarcoma patients. Our findings suggest that cytoplasmic APE1 plays a significant role in chemotherapy resistance. This role is a supplement to the extranuclear function of APE1, and cytoplasmic APE1 expression level could be a promising predictor of platinum treatment prognosis for osteosarcoma patients.

Multiplex fluorescent immunohistochemistry quantitatively analyses microvascular density (MVD) and the roles of TGF-β signalling in orchestrating angiogenesis in colorectal cancer

Background

Advances in multiplex fluorescent immunohistochemistry (mfIHC) techniques and digital pathology platforms allow the quantification of multiple proteins in the same tissue section and produce continuous data. Previously, we used mfIHC to establish the expressed profiles of proteins involved in TGF-β signalling in colorectal cancer (CRC).

Methods

We used mfIHC to show microvascular density (MVD) by staining CD31 in the tissues from CRC patients. We further investigated the relationship between MVD and TGF-β signalling.

Results

We found that the levels of MVD were significantly higher in cancer tissues than in paired normal tissues. Prognostic analysis revealed that the survival time for CRC patients with high levels of MVD was significantly shorter than that for those with low levels of MVD. Systematic analysis of the levels of MVD and TGF-β signalling proteins revealed that TGF-β signalling showed contradictory roles in sustained tumour angiogenesis. In CRC cells, the expression of VEGFA was increased by low concentrations of TGFB1 but decreased by high concentrations of TGFB1. Vessel-forming assays demonstrated that low-dose TGFB1 stimulated but high-dose TGFB1 inhibited HUVECs to form vessel tubes.

Conclusions

Our analysis based on mfIHC staining in CRC tissues supports the concept that TGF-β signalling either promotes or inhibits tumour angiogenesis.

The regulatory role of APE1 in epithelial-to-mesenchymal transition and in determining EGFR-TKI responsiveness in non-small-cell lung cancer

Background

Epithelial‐to‐mesenchymal transition (EMT) plays a pivotal role in resistance to EGFR tyrosine kinase inhibitors (TKIs) in non‐small‐cell lung cancer (NSCLC). Our previous study revealed that in osteosarcoma, human apurinic/apyrimidinic endonuclease 1 (APE1) regulates transforming growth factor‐β (TGF‐β), an important player in EMT. We therefore hypothesized a link between APE1 and EGFR‐TKI responsiveness in NSCLC.

Methods

The protein levels of APE1 were analyzed in tumors of NSCLC patients receiving EGFR‐TKI treatment. The correlation between APE1 expression and progression‐free survival (PFS), overall survival (OS), or response rate were analyzed. The impact of APE1 on the response to EGFR‐TKIs was measured by exogenous manipulation of APE1 in EGFR‐TKI‐sensitive and EGFR‐TKI‐resistant cells.

Results

We indicate that low expression of APE1 in tumors is associated with a significantly longer PFS (20.8 months vs 8.4 months, P = 0.008) and a preferential OS (39.0 months vs 17.0 months, P = 0.001), with no difference in initial response rate to EGFR‐TKIs. We observed that APE1 protein level was significantly increased in EGFR‐TKI‐resistant cells and was associated with downregulated E‐cadherin and upregulated vimentin. The EMT phenotype, as well as the levels of TGF‐β, was suppressed in APE1 knockdown HCC827/IR and PC‐9/ER cells, while the EMT phenotype was promoted in APE1‐overexpressed HCC827 and PC‐9 cells. Furthermore, a specific APE1 redox inhibitor (ie, E3330) effectively reversed the EMT phenotype and further sensitized the cells to EGFR‐TKIs.

Conclusion

This study revealed a significant role of APE1 in EGFR‐TKI resistance via novel regulatory effects on the EMT phenotype in NSCLC.

Solute carrier family 35 member F2 is indispensable for papillary thyroid carcinoma progression through activation of transforming growth factor-β type I receptor/apoptosis signal-regulating kinase 1/mitogen-activated protein kinase signaling axis

Solute carrier family members control essential physiological functions and are tightly linked to human diseases. Solute carrier family 35 member F2 (SLC35F2) is aberrantly activated in several malignancies. However, the biological function and molecular mechanism of SLC35F2 in papillary thyroid carcinoma (PTC) are yet to be fully explored. Here, we showed that SLC35F2 was prominently upregulated in PTC tissues at both protein and mRNA expression level compared with matched adjacent normal tissues. Besides, the high expression of SLC35F2 was significantly associated with lymph node metastasis in patients with PTC. CRISPR/Cas9-mediated knockout of SLC35F2 attenuated the tumorigenic properties of PTC, including cell proliferation, migration and invasion and induced G1 phase arrest. In contrast, ectopic expression of SLC35F2 brought about aggressive malignant phenotypes of PTC cells. Moreover, SLC35F2 expedited the proliferation and migration of PTC cells by targeting transforming growth factor-β type I receptor (TGFBR1) and phosphorylation of apoptosis signal-regulating kinase 1 (p-ASK-1), thereby activating the mitogen-activated protein kinase signaling pathway. The malignant behaviors induced by overexpression of SLC35F2 could be abrogated by silencing of TGFBR1 using a specific inhibitor. We conducted the first study on SLC35F2 in thyroid cancer with the aim of elucidating the functional significance and molecular mechanism of SLC35F2. Our findings suggest that SLC35F2 exerts its oncogenic effect on PTC progression through the mitogen-activated protein kinase pathway, with dependence on activation of TGFBR-1 and apoptosis signal-regulating kinase 1.

Ape1 protects against MPP+-induced neurotoxicity through ERK1/2 signaling in PC12 cells

Oxidative stress, induced by reactive oxygen species (ROS), is an apoptosis activator. Oxidative stress causes dopaminergic neuron loss and plays a pivotal role in the pathogenesis of Parkinson's disease (PD). A recent study showed that apurinic/apyrimidinic endonuclease 1 (Ape1) decreases cytotoxicity and promotes neuron survival under oxidative stress. Furthermore, it has been proven that Ape1 is involved in the pathogenesis of PD. However, little is known about the contribution of Ape1 toward the development of PD. Thus, the present study was designed to define a critical pathway by which Ape1 mediates neurotoxicity in a model of PD. The results show that Ape1 was upregulated in MPP-treated PC12 cells. Ape1 overexpression significantly increased cell viability and inhibited apoptosis compared with MPP treatment, whereas Ape1 knockdown showed the opposite effect. Ape1 overexpression markedly suppressed ROS levels, whereas Ape1 knockdown significantly elevated ROS levels. Furthermore, Ape1 overexpression markedly upregulated the p-ERK1/2 protein expression level and inhibited ERK1/2 signaling. The ERK1/2 inhibitor PD98059 significantly decreased cell viability and increased apoptosis and the ROS level compared with the Ape1 overexpression group. Taken together, these results suggest that Ape1 protects against neuron death by activating the ERK1/2 signaling pathway.

rs1760944 Polymorphism in the APE1 Region is Associated with Risk and Prognosis of Osteosarcoma in the Chinese Han Population

The effects of single nucleotide polymorphisms (SNPs) at APE1 have been investigated in several types of cancer. However, no reports of the association of APE1 polymorphisms with osteosarcoma (OS) have been published. The present study was designed to determine whether APE1 polymorphisms (rs1130409, rs1760944, rs1760941, rs2275008, rs17111750) are associated with OS. A 2-stage case-control study was performed in a total of 378 OS patients and 616 normal controls. Individuals carrying TG and GG genotypes had significantly lower risk of developing OS than those with the WT genotype TT at rs1760944 (OR = 0.65, 95%CI 0.49–0.86; OR = 0.50, 95%CI 0.34–0.74, respectively). OS patients with allele G at rs1760944 were less susceptible to low differentiation tumor and metastasis (OR = 0.73, 95%CI 0.54–0.98; OR = 0.63, 95%CI 0.43–0.92, respectively). Kaplan-Meier curves and log-rank results revealed that OS patients harboring genotype GG and G allele at rs1760944 had better survival (P < 0.001 for both). In addition, the APE1 protein was underexpressed in individuals who carried G allele at rs1760944. This study suggested that APE1 rs1760944 polymorphism is associated with decreased risk of developing OS and better survival of OS patients.

MicroRNA-765 Enhances the Anti-Angiogenic Effect of CDDP via APE1 in Osteosarcoma

Human osteosarcoma (HOS) is the most common malignancy in children and adolescents and has a heterogeneous presentation and high mortality. Previous studies have shown that microRNAs contribute to RNA silencing and post-transcriptional regulation of gene expression. Here, we showed that significantly increased expression of miR-765 with or without CDDP (Cisplatin) down-regulates APE1 expression and angiogenesis-related markers (VEGF, FGF2, TGFβ, and CD34). Further investigation showed that miR-765 modulates osteosarcoma cell migration and angiogenesis following treatment with cisplatin in vitro and in vivo. MiR-765 increases the anti-angiogenic effect of CDDP in human osteosarcoma. Elucidation of the mechanism of the miR-765-APE1 axis in tumor progression of HOS will be beneficial in identifying biomarkers and therapeutic target of osteosarcoma.

Dynamic Regulation of APE1/Ref-1 as a Therapeutic Target Protein

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is a multifunctional protein that plays a central role in the cellular response to DNA damage and redox regulation against oxidative stress. APE1/Ref-1 functions in the DNA base excision repair pathway, the redox regulation of several transcription factors, and the control of intracellular redox status through the inhibition of reactive oxygen species (ROS) production. APE1/Ref-1 is predominantly localized in the nucleus; however, its subcellular localization is dynamically regulated and it may be found in the mitochondria or elsewhere in the cytoplasm. Studies have identified a nuclear localization signal and a mitochondrial target sequence in APE1/Ref-1, as well as the involvement of the nuclear export system, as determinants of APE1/Ref-1 subcellular distribution. Recently, it was shown that APE1/Ref-1 is secreted in response to hyperacetylation at specific lysine residues. Additionally, post-translational modifications such as phosphorylation, S-nitrosation, and ubiquitination appear to play a role in fine-tuning the activities and subcellular localization of APE1/Ref-1. In this review, we will introduce the multifunctional role of APE1/Ref-1 and its potential usefulness as a therapeutic target in cancer and cardiovascular disease.