E2 Ubiquitin-conjugating Enzyme, UBE2C Gene, Is Reciprocally Regulated by Wild-type and Gain-of-Function Mutant p53.

Spindle assembly checkpoint governs proper chromosomal segregation during mitosis to ensure genomic stability. At the cellular level, this event is tightly regulated by UBE2C, an E2 ubiquitin-conjugating enzyme that donates ubiquitin to the anaphase-promoting complex/cyclosome. This, in turn, facilitates anaphase-onset by ubiquitin-mediated degradation of mitotic substrates. UBE2C is an important marker of chromosomal instability and has been associated with malignant growth. However, the mechanism of its regulation is largely unexplored. In this study, we report that UBE2C is transcriptionally activated by the gain-of-function (GOF) mutant p53, although it is transcriptionally repressed by wild-type p53. We showed that wild-type p53-mediated inhibition of UBE2C is p21-E2F4-dependent and GOF mutant p53-mediated transactivation of UBE2C is NF-Y-dependent. We further explored that DNA damage-induced wild-type p53 leads to spindle assembly checkpoint arrest by repressing UBE2C, whereas mutant p53 causes premature anaphase exit by increasing UBE2C expression in the presence of 5-fluorouracil. Identification of UBE2C as a target of wild-type and GOF mutant p53 further highlights the contribution of p53 in regulation of spindle assembly checkpoint.

The anaphase promoting complex/cyclosome ubiquitylates histone H2B on the promoter during UbcH10 transactivation.

Among various post-translational modifications of histones, ubiquitylation plays a crucial role in transcription regulation. Histone mono-ubiquitylation by RING finger motif-containing ubiquitin ligases is documented in this respect. The RING finger ligases primarily regulate the cell cycle, where the anaphase-promoting complex/cyclosome (APC/C) takes charge as mitotic ubiquitin machinery. Reportedly, APC/C participates in transcriptional activation of the ubiquitin carrier protein UbcH10. However, the ubiquitylation activity of APC/C on the UBCH10 promoter remains elusive. This study shows that APC/C, with its adapter protein Cdc20, catalyses mono-ubiquitylation of Lysine-120 in histone 2B on the UBCH10 promoter. This study also identified a cell-cycle-specific pattern of this modification. Finally, APC/C-driven crosstalk of acetylation and ubiquitylation was found operational on UBCH10 trans-regulation. Together, these findings suggest a role for APC/C catalysed promoter ubiquitylation in managing transcription of cell cycle regulatory genes.

A comparative analysis of features and outcome of breast cancer in younger versus older women: A single center experience from Eastern Indian subcontinent.

Purpose: Globally, breast cancer is the leading malignancy in females. Indeed, Asian cohorts show prevalence of breast cancer among women with ages below 40 years. Moreover, these younger cases are globally characterized by poorer prognostic features as well as survival outcomes, than older sufferers with ages above 40 years. Despite this, comparative analyses between older and younger cohorts are sparse from India, where data from the country's eastern part falls shortest. This study attempted a comprehensive analysis of breast cancer between these two cohorts representing the Eastern Indian subcontinent. Methods: Documenting retrospective case-files registered between 2010 and 2015, 394 cases of younger (<40 years) and 1250 older (≥40 years) sufferers of primary breast cancer were noted. The relevant features and follow-up information were also retrieved. Kaplan-Meier analyses were performed to evaluate the survival outcome. Results: The data, in general, revealed a high percentage of younger sufferers from Eastern Indian regions. Moreover, this younger cohort showed poor survival. Among the younger cohort, cases with poor pathological features (triple negative, node-positive, grade III) were proportionately higher than the older cohort. Indeed, survival among these categories scored significantly low, compared to the older cohort. Conclusion: This Eastern Indian subcontinental data matched the analyses from other parts of India as well as Asian data and clearly showed the prevalence of younger sufferers of breast cancer with poor clinico-pathological features and survival outcomes. Impact: Analyzing age-based features and outcomes from Eastern India, this study provides data in supplementing Indian and Asian scenarios of breast cancer.

No association of the common Asian mitochondrial DNA haplogroups with lung cancer in East Indian population.

OBJECTIVES: Mitochondrial dysfunction has long been associated with the pathogenesis of lung cancer (LC). Mitochondrial DNA (mtDNA) haplogroups have been reported to modify the risk of LC in a few different populations; however, no study has been done among the Indians. Here, we explore the relationship between mtDNA haplogroups and LC in a representative eastern Indian sample set. METHODS: Different combinations of six mtDNA SNPs, which define the major Asian mtDNA haplogroups M and N, and their sub-haplogroups D, G, M7, R, and F were genotyped via polymerase chain reaction (PCR) - restriction fragment length polymorphism (RFLP) - sequencing approach in 94 smoker LC patients and 100 healthy smoker controls from an eastern Indian cohort. RESULTS: The distribution of 7 mtDNA haplogroups did not show any significant differences between patients and controls (p<0.05). We did not find sub-haplogroup M7 in our study population. CONCLUSIONS: Our study is the first to indicate that the major Asian mtDNA haplogroups have no significant (p<0.05) association with LC in East Indian population.

Reprogramming of glucose metabolism via PFKFB4 is critical in FGF16-driven invasion of breast cancer cells.

Fibroblast growth factors (FGFs) are expressed in both developing and adult tissues and play important roles in embryogenesis, tissue homeostasis, angiogenesis, and neoplastic transformation. Here, we report the elevated expression of FGF16 in human breast tumor and investigate its potential involvement in breast cancer progression. The onset of epithelial-mesenchymal transition (EMT), a prerequisite for cancer metastasis, was observed in human mammary epithelial cell-line MCF10A by FGF16. Further study unveiled that FGF16 alters mRNA expression of a set of extracellular matrix genes to promote cellular invasion. Cancer cells undergoing EMT often show metabolic alteration to sustain their continuous proliferation and energy-intensive migration. Similarly, FGF16 induced a significant metabolic shift toward aerobic glycolysis. At the molecular level, FGF16 enhanced GLUT3 expression to facilitate glucose transport into cells, which through aerobic glycolysis generates lactate. The bi-functional protein, 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 4 (PFKFB4) was found to be a mediator in FGF16-driven glycolysis and subsequent invasion. Furthermore, PFKFB4 was found to play a critical role in promoting lactate-induced cell invasion since silencing PFKFB4 decreased lactate level and rendered the cells less invasive. These findings support potential clinical intervention of any of the members of FGF16-GLUT3-PFKFB4 axis to control the invasion of breast cancer cells.

FBXW2 suppresses breast tumorigenesis by targeting AKT-Moesin-SKP2 axis.

Oncogene Moesin plays critical role in initiation, progression, and metastasis of multiple cancers. It exerts oncogenic activity due to its high-level expression as well as posttranslational modification in cancer. However, factors responsible for its high-level expression remain elusive. In this study, we identified positive as well as negative regulators of Moesin. Our study reveals that Moesin is a cellular target of F-box protein FBXW2. We showed that FBXW2 suppresses breast cancer progression through directing proteasomal degradation of Moesin. In contrast, AKT kinase plays an important role in oncogenic function of Moesin by protecting it from FBXW2-mediated proteasomal degradation. Mechanistically, AKT phosphorylates Moesin at Thr-558 and thereby prevents its degradation by FBXW2 via weakening the association between FBXW2 and Moesin. Further, accumulated Moesin prevents FBXW2-mediated degradation of oncogene SKP2, showing that Moesin functions as an upstream regulator of oncogene SKP2. In turn, SKP2 stabilizes Moesin by directing its non-degradable form of polyubiquitination and therefore AKT-Moesin-SKP2 oncogenic axis plays crucial role in breast cancer progression. Collectively, our study reveals that FBXW2 functions as a tumor suppressor in breast cancer by restricting AKT-Moesin-SKP2 axis. Thus, AKT-Moesin-SKP2 axis may be explored for the development of therapeutics for cancer treatment.

Identifying polymorphic cis-regulatory variants as risk markers for lung carcinogenesis and chemotherapy responses in tobacco smokers from eastern India.

Aberrant expression of xenobiotic metabolism and DNA repair genes is critical to lung cancer pathogenesis. This study aims to identify the cis-regulatory variants of the genes modulating lung cancer risk among tobacco smokers and altering their chemotherapy responses. From a list of 2984 SNVs, prioritization and functional annotation revealed 22 cis-eQTLs of 14 genes within the gene expression-correlated DNase I hypersensitive sites using lung tissue-specific ENCODE, GTEx, Roadmap Epigenomics, and TCGA datasets. The 22 cis-regulatory variants predictably alter the binding of 44 transcription factors (TFs) expressed in lung tissue. Interestingly, 6 reported lung cancer-associated variants were found in linkage disequilibrium (LD) with 5 prioritized cis-eQTLs from our study. A case-control study with 3 promoter cis-eQTLs (p < 0.01) on 101 lung cancer patients and 401 healthy controls from eastern India with confirmed smoking history revealed an association of rs3764821 (ALDH3B1) (OR = 2.53, 95% CI = 1.57-4.07, p = 0.00014) and rs3748523 (RAD52) (OR = 1.69, 95% CI = 1.17-2.47, p = 0.006) with lung cancer risk. The effect of different chemotherapy regimens on the overall survival of lung cancer patients to the associated variants showed that the risk alleles of both variants significantly decreased (p < 0.05) patient survival.

Spindle assembly checkpoint protein Cdc20 transcriptionally activates expression of ubiquitin carrier protein UbcH10.

The spindle assembly checkpoint (SAC) ensures accurate segregation of chromosomes by monitoring kinetochore attachment of spindles during mitosis. Proper progression of mitosis depends on orderly ubiquitination and subsequent degradation of various mitotic inhibitors. At the molecular level, upon removal of SAC, Cdc20 activates E3 ubiquitin ligase anaphase-promoting complex/cyclosome that, along with E2 ubiquitin-conjugating enzyme UbcH10, executes this function. Both Cdc20 and UbcH10 are overexpressed in many cancer types and are associated with defective SAC function leading to chromosomal instability. The precise mechanism of correlated overexpression of these two proteins remains elusive. We show that Cdc20 transcriptionally up-regulates UbcH10 expression. The WD40 domain of Cdc20 is required for this activity. Physical interaction between Cdc20 and anaphase-promoting complex/cyclosome-CBP/p300 complex and its subsequent recruitment to the UBCH10 promoter are involved in this transactivation process. This transcriptional regulatory function of Cdc20 was observed to be cell cycle-specific. We hypothesize that this co-regulated overexpression of both proteins contributes to chromosomal instability.

Is germline transmission of MAD2 gene deletion associated with human fetal loss?

The spindle assembly checkpoint (SAC) monitors proper attachment of spindles to the kinetochore during mitotic and meiotic cell divisions and thus prevents aneuploidy. Chromosomal aneuploidy has been found to be associated with pregnancy loss and birth defects. Mad2 is one of the critical molecules of SAC. Deregulated Mad2 expression has been found to be associated with defective SAC-mediated abnormal meiotic progression in cell studies using animal models. Whether mutation in MAD2L1 is associated with the loss of Mad2 expression in aborted human fetuses is unknown. In this study, a correlation between aneuploidy and MAD2 defect was examined in primary fibroblast cultures obtained from abortuses. We report three trisomic abortuses with undetectable Mad2 expression. Further, quantitative real-time PCR revealed copy number deletion of MAD2 gene in these fetuses. Analysis of parental DNA samples available from two families revealed copy number loss of the same gene, suggesting Mendelian inheritance of MAD2 deletion. This germline transmission of exonic deletion of MAD2 is possibly associated with its loss of expression resulting in abnormal SAC function, subsequent aneuploidy and pregnancy loss.

Deep sequencing reveals the spectrum of BCR-ABL1 mutations upon front-line therapy resistance in chronic myeloid leukemia: An Eastern-Indian cohort study.

The course of clinical management in chronic myeloid leukemia (CML) often faces a road-block in the form of front-line (imatinib) therapy resistance. Subsequently, several hotspot mutations were clinically validated in the kinase domain (KD) of BCR-ABL1, in deterring imatinib sensitivity and further, made targeted by next-generation tyrosine-kinase-inhibitor (TKI) drugs. Identifying KD mutations, occurring even at low frequencies, became pertinent here. Globally, cohorts from different origins were tested and the mutational spectra were mapped to categorize clinical management as well as related pathological features of CML. Moreover, targeted deep sequencing could reveal the mutational landscape more efficiently than the less sensitive Sanger sequencing method. However, no such efforts were reported from Eastern Indian cohorts of imatinib-resistant CML-sufferers. This study assessed a prospective study cohort of imatinib-resistant CML cases from Eastern India. Following dissecting the molecular and clinical parameters, the mutational spectrum was comparatively examined using conventional Sanger and next-generation deep sequencing method. This cohort showed a prevalence of e14a2-p210 variant of BCR-ABL1 and acquired resistance against imatinib, while the disease was mostly confined in its chronic phase. Together with a few common hotspot mutations identified in this cohort, deep sequencing revealed cases with a candidate mutation, otherwise undetermined by Sanger method. Also, cases with a second low frequency mutation were identified upon applying deep sequencing. Along with highlighting a few aspects of CML biology employing an Eastern-Indian cohort, this data could mark the immense importance of deep sequencing to contribute in the clinical management of CML upon front-line therapy resistance.

Molecular crosstalk between CUEDC2 and ERα influences the clinical outcome by regulating mitosis in breast cancer.

Development of endocrine resistance in hormone-receptor-positive (HR+ve) subtype and lack of definitive target in triple-negative subtype challenge breast cancer management. Contributing to such endocrine resistance is a protein called CUEDC2. It degrades hormone receptors, estrogen receptor-α (ERα) and progesterone receptor. Higher level of CUEDC2 in ERα+ve breast cancer corresponded to poorer disease prognosis. It additionally influences mitotic progression. However, the crosstalk of these two CUEDC2-driven functions in the outcome of breast cancer remained elusive. We showed that CUEDC2 degrades ERα during mitosis, utilising the mitotic-ubiquitination-machinery. We elucidated the importance of mitosis-specific phosphorylation of CUEDC2 in this process. Furthermore, upregulated CUEDC2 overrode mitotic arrest, increasing aneuploidy. Finally, recruiting a prospective cohort of breast cancer, we found significantly upregulated CUEDC2 in HR-ve cases. Moreover, individuals with higher CUEDC2 levels showed a poorer progression-free-survival. Together, our data confirmed that CUEDC2 up-regulation renders ERα+ve malignancies to behave essentially as HR-ve tumors with the prevalence of aneuploidy. This study finds CUEDC2 as a potential prognostic marker and a therapeutic target in the clinical management of breast cancer.

DNA damage induced p53 downregulates Cdc20 by direct binding to its promoter causing chromatin remodeling.

CDC20 is a critical molecule in the Spindle Assembly Checkpoint (SAC). It activates the Anaphase promoting complex and helps a dividing cell to proceed towards Anaphase. CDC20 is overexpressed in many tumor cells which cause chromosomal instability. There have been limited reports on the mechanism of SAC's response to genotoxic stress. We show that ectopically expressed p53 or DNA damage induced endogenous p53 can downregulate Cdc20 transcriptionally. We have identified a consensus p53-binding site on the Cdc20 promoter and have shown that it is being used by p53 to bind the promoter and bring about chromatin remodeling thereby repressing Cdc20. Additionally, p53 also downregulates Cdc20 promoter through CDE/CHR element, but in a p21 independent manner. This CDE/CHR element-mediated downregulation occurs only under p53 overexpressed condition but not in the context of DNA damage. The present results suggest that the two CCAAT elements in the Cdc20 promoter are not used by p53 to downregulate its activity, as reported earlier.

Steroid Hormone Receptors: Links With Cell Cycle Machinery and Breast Cancer Progression.

Progression of cells through cell cycle consists of a series of events orchestrated in a regulated fashion. Such processes are influenced by cell cycle regulated expression of various proteins where multiple families of transcription factors take integral parts. Among these, the steroid hormone receptors (SHRs) represent a connection between the external hormone milieu and genes that control cellular proliferation. Therefore, understanding the molecular connection between the transcriptional role of steroid hormone receptors and cell cycle deserves importance in dissecting cellular proliferation in normal as well as malignant conditions. Deregulation of cell cycle promotes malignancies of various origins, including breast cancer. Indeed, SHR members play crucial role in breast cancer progression as well as management. This review focuses on SHR-driven cell cycle regulation and moving forward, attempts to discuss the role of SHR-driven crosstalk between cell cycle anomalies and breast cancer.

Long-Term Outcome of Philadelphia Chromosome Positive Leukemia From Eastern Indian Subcontinent: An Experience in the Era of Tyrosine Kinase Inhibitor (TKI) Therapy.

INTRODUCTION: Philadelphia chromosome (Ph) marks a group of leukemia with almost all cases of chronic myeloid leukemia (CML), a subset of acute lymphoid leukemia (ALL) and rare cases of acute myeloid leukemia (AML). In the era of precision medicine, such cases are successfully managed with tyrosine kinase inhibitor (TKI) drugs. This study examined the features and long-term outcome of Ph+ve cases from a tertiary cancer care center from Eastern Indian subcontinent. MATERIALS AND METHODS: Reviewing retrospective case-records registered between 2005 and 2015, cases of CML and ALL were documented under Ph+ve category; while no instance of Ph+ve AML was found. RESULTS: In CML cohort, adult and juvenile incidences were 95.2% and 4.8% respectively; in ALL cohort, the same was found for 66.67% and 33.33% cases. Among the CML cases, 10-year overall survival (OS) and progression-free survival (PFS) were significantly affected upon the phase of disease at time of detection. Furthermore, both OS and PFS significantly dropped whenever non-TKI-based treatment was applied prior to TKI-commencement. Long-term (10-year) sensitivity to 1st generation TKI, imatinib, was noted 88.51% and 83.33% for adult and juvenile CML cohorts, respectively. For Ph+ ALL cohort, the OS was benefitted upon combinatorial TKI and chemotherapy. However, large fractions of affected individual from CML as well as ALL cohorts were found to discontinue follow-up. CONCLUSION: Together with differences in outcome on the basis of drug-use from onset, age (juvenile versus adult) and stage at diagnosis, our analyses bring forward the real-world scenario of Ph+ve leukemia managed with precision medicine.

MiRNA-146a/AKT/ß-Catenin Activation Regulates Cancer Stem Cell Phenotype in Oral Squamous Cell Carcinoma by Targeting CD24.

CD44highCD24low population has been previously reported as cancer stem cells (CSCs) in Oral Squamous Cell Carcinoma (OSCC). Increasing evidence suggests potential involvement of microRNA (miRNA) network in modulation of CSC properties. MiRNAs have thus emerged as crucial players in tumor development and maintenance. However, their role in maintenance of OSCC stem cells remains unclear. Here we report an elevated expression of miR-146a in the CD44highCD24low population within OSCC cells and primary HNSCC tumors. Moreover, over-expression of miR-146a results in enhanced stemness phenotype by augmenting the CD44highCD24low population. We demonstrate that miR-146a stabilizes ß-catenin with concomitant loss of E-cadherin and CD24. Interestingly, CD24 is identified as a novel functional target of miR-146a and ectopic expression of CD24 abrogates miR-146a driven potential CSC phenotype. Mechanistic analysis reveals that higher CD24 levels inhibit AKT phosphorylation leading to ß-catenin degradation. Using stably expressing miR-146a/CD24 OSCC cell lines, we also validate that the miR-146a/CD24/AKT loop significantly alters tumorigenic ability in vivo. Furthermore, we confirmed that ß-catenin trans-activates miR-146a, thereby forming a positive feedback loop contributing to stem cell maintenance. Collectively, our study demonstrates that miR-146a regulates CSCs in OSCC through CD24-AKT-ß-catenin axis.

A comprehensive meta-analysis and a case-control study give insights into genetic susceptibility of lung cancer and subgroups.

Reports of genetic association of polymorphisms with lung cancer in the Indian subcontinent are often conflicting. To summarise and replicate published evidence for association with lung cancer and its subgroups. We performed a meta-analysis of candidate associations on lung cancer, its histological subtypes and smoking status in the Indian subcontinent following PRISMA guidelines. Multiple testing corrections were done by the Benjamini-Hochberg method through assessment of significance at a false discovery rate of 10%. We genotyped and investigated rs1048943/CYP1A1 in a case-control sample from eastern India, followed by its global meta-analysis using a similar protocol. Meta-analysis of 18 variants of 11 genes reported in 39 studies (7630 cases and 8169 controls) showed significant association of rs1048943/CYP1A1 [2.07(1.49-2.87)] and rs4646903/CYP1A1 [1.48(1.93-1.95)] with overall lung cancer risk at 10% FDR, while nominal association (p < 0.05) was observed for del1/GSTT1, del2/GSTM1, rs1695/GSTP1 and rs17037102/ DKK2. Subtype analysis showed a significant association of del1/GSTT1 with adenocarcinoma, rs4646903/CYP1A1 with squamous carcinoma, and rs1048943/CYP1A1 with both. Association of rs4646903/CYP1A1 in smokers and effect modification by meta-regression analysis was observed. Genotyping of rs1048943/CYP1A1 that presented significant heterogeneity (p < 0.1) revealed an association with adenocarcinoma among eastern Indian smokers, while a global meta-analysis in 10458 cases and 10871 controls showed association with lung cancer and its subgroups. This study identified the susceptibility loci for lung cancer and its covariate-subgroups.

The extracellular role of DNA damage repair protein APE1 in regulation of IL-6 expression.

The human apurinic/apyrimidinic endonuclease 1 (APE1) is a pleiotropic nuclear protein with roles in DNA base excision repair pathway as well as in regulation of transcription. Recently, the presence of extracellular plasma APE1 was reported in endotoxemic rats. However, the biological significance and the extracellular function of APE1 remain unclear. In this study, we found that monocytes secrete APE1 upon inflammatory challenges. Challenging the monocytic cells with extracellular APE1 resulted in the increased expression and secretion of the pro-inflammatory cytokine IL-6. Additionally, the extracellular APE1 treatment activated the transcription factor NF-κB, followed by its increased occupancy at the IL-6 promoter, resulting in the induction of IL-6 expression. APE1-induced IL-6 further served to elicit autocrine and paracrine cellular responses. Moreover, the extracellular IL-6 promoted the secretion of APE1, thus indicating a functional feedforward loop in this pathway. Furthermore, we show that APE1 is secreted through extracellular vesicles formation via endosomal sorting complex required for transport (ESCRT)-dependent pathway. Together, our study demonstrates a novel role of extracellular APE1 in IL-6-dependent cellular responses.

Human Apurinic/Apyrimidinic Endonuclease (APE1) Is Acetylated at DNA Damage Sites in Chromatin, and Acetylation Modulates Its DNA Repair Activity.

Apurinic/apyrimidinic (AP) sites, the most frequently formed DNA lesions in the genome, inhibit transcription and block replication. The primary enzyme that repairs AP sites in mammalian cells is the AP endonuclease (APE1), which functions through the base excision repair (BER) pathway. Although the mechanism by which APE1 repairs AP sites in vitro has been extensively investigated, it is largely unknown how APE1 repairs AP sites in cells. Here, we show that APE1 is acetylated (AcAPE1) after binding to the AP sites in chromatin and that AcAPE1 is exclusively present on chromatin throughout the cell cycle. Positive charges of acetylable lysine residues in the N-terminal domain of APE1 are essential for chromatin association. Acetylation-mediated neutralization of the positive charges of the lysine residues in the N-terminal domain of APE1 induces a conformational change; this in turn enhances the AP endonuclease activity of APE1. In the absence of APE1 acetylation, cells accumulated AP sites in the genome and showed higher sensitivity to DNA-damaging agents. Thus, mammalian cells, unlike Saccharomyces cerevisiae or Escherichia coli cells, require acetylation of APE1 for the efficient repair of AP sites and base damage in the genome. Our study reveals that APE1 acetylation is an integral part of the BER pathway for maintaining genomic integrity.

Elevated level of acetylation of APE1 in tumor cells modulates DNA damage repair.

Apurinic/apyrimidinic (AP) sites are frequently generated in the genome by spontaneous depurination/depyrimidination or after removal of oxidized/modified bases by DNA glycosylases during the base excision repair (BER) pathway. Unrepaired AP sites are mutagenic and block DNA replication and transcription. The primary enzyme to repair AP sites in mammalian cells is AP endonuclease (APE1), which plays a key role in this repair pathway. Although overexpression of APE1 in diverse cancer types and its association with chemotherapeutic resistance are well documented, alteration of posttranslational modification of APE1 and modulation of its functions during tumorigenesis are largely unknown. Here, we show that both classical histone deacetylase HDAC1 and NAD+-dependent deacetylase SIRT1 regulate acetylation level of APE1 and acetylation of APE1 enhances its AP-endonuclease activity both in vitro and in cells. Modulation of APE1 acetylation level in cells alters AP site repair capacity of the cell extracts in vitro. Primary tumor tissues of diverse cancer types have higher level of acetylated APE1 (AcAPE1) compared to adjacent non-tumor tissue and exhibit enhanced AP site repair capacity. Importantly, in the absence of APE1 acetylation, cells accumulate AP sites in the genome and show increased sensitivity to DNA damaging agents. Together, our study demonstrates that elevation of acetylation level of APE1 in tumor could be a novel mechanism by which cells handle the elevated levels of DNA damages in response to genotoxic stress and maintain sustained proliferation.