Impact of reduced levels of APE1 transcripts on the survival of patients with urothelial carcinoma of the bladder

Inhibition of human APE1 and MTH1 DNA repair proteins by dextran-coated γ-Fe2O3 ultrasmall superparamagnetic iron oxide nanoparticles

Aim: To quantitatively evaluate the inhibition of human DNA repair proteins APE1 and MTH1 by dextran-coated γ-Fe₂O₃ ultrasmall superparamagnetic iron oxide nanoparticles (dUSPIONs). Materials & methods: Liquid chromatography-tandem mass spectrometry with isotope-dilution was used to measure the expression levels of APE1 and MTH1 in MCL-5 cells exposed to increasing doses of dUSPIONs. The expression levels of APE1 and MTH1 were measured in cytoplasmic and nuclear fractions of cell extracts. Results: APE1 and MTH1 expression was significantly inhibited in both cell fractions at the highest dUSPION dose. The expression of MTH1 was linearly inhibited across the full dUSPION dose range in both fractions. Conclusion: These findings warrant further studies to characterize the capacity of dUSPIONs to inhibit other DNA repair proteins in vitro and in vivo.

The frequency and clinical significance of DNA polymerase beta (POLβ) expression in breast ductal carcinoma in situ (DCIS)

Background

The prediction of clinical behaviour of breast ductal carcinoma in situ (DCIS) and its progression to invasive disease remains a challenge. Alterations of DNA damage repair mechanisms are associated with invasive breast cancer (BC). This study aims to assess the role of base excision repair (BER) DNA Polymerase Beta (POLβ) in DCIS.

Methods

A cohort of DCIS comprising pure DCIS (n = 776) and DCIS coexisting with invasive BC (n = 239) were prepared as tissue microarrays. POLβ protein expression was assessed using immunohistochemistry and correlated with clinicopathological parameters and patient outcome. Preclinically, we investigated the impact of POLβ depletion on stem cell markers in representative DCIS cell line models.

Results

Reduced POLβ expression was associated with aggressive DCIS features including high nuclear grade, comedo necrosis, larger tumour size, hormonal receptor negativity, HER2 overexpression and high Ki67 index. Combined low nuclear/low cytoplasmic POLβ expression showed the strongest association with the features’ characteristics of aggressive behaviour. There was a gradual reduction in the POLβ expression from normal breast tissue, to DCIS, with the lowest expression observed in the invasive BC. Low POLβ expression was an independent predictor of recurrence in DCIS patients treated with breast conserving surgery (BCS). POLβ knockdown was associated with a significant increase in cell stemness markers including SOX2, NANOG and OCT4 levels in MCF10-DCIS cell lines.

Conclusion

Loss of POLβ in DCIS is associated with aggressive behaviour and it can predict recurrence. POLβ expression in DCIS provides an additional feature for patients’ risk stratification for personalised therapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10549-021-06357-7.

APE1 and SSRP1 is overexpressed in muscle invasive bladder cancer and associated with poor survival

Background

Human apurinic/apyrimidinic (AP) endonuclease 1 (APE1) plays a critical role in DNA base excision repair (BER) pathway and has been reported to be overexpressed in multiple cancers. Previously, we have shown that histone chaperone FACT complex (Facilitates Chromatin Transcription, a heterodimer of SSRP1 and SPT16 proteins) facilitates the chromatin access and DNA repair function of APE1, and their expression levels are correlated with promoting drug resistance in cancer. FACT inhibitor has been introduced in phase I and II clinical trials for chemosensitization of advanced solid cancers. However, the expression profile and prognostic significance of APE1 and FACT complex in bladder cancer remains largely unknown.

Methods

Retrospectively, 69 bladder cancer samples were retrieved and submitted for immunohistochemical staining of APE1 and SSRP1. Expression profile including cytoplasmic and nuclear staining of APE1 and expression level of SSRP1 was examined and semi-quantified to render a H-score. The prognostic significance of APE1 and SSRP1 was evaluated by Kaplan-Meier survival analysis in our cohort and R2 database.

Results

APE1 expression is elevated in bladder cancer compared to normal adjacent tissues. Compared with low grade tumors, high grade tumors show a shift in the staining pattern including higher intensity and positive cytoplasmic staining. Carcinoma in situ has a similar staining pattern to high grade tumors. APE1 and SSRP1 staining intensity increases as tumor progresses with stage. There is a correlation between APE1 and SSRP1 staining in invasive bladder cancer (Spearman r = 0.5466, p < 0.0001). The increased expression of APE1 and SSRP1 is associated with poor survival in Kaplan-Meier analysis in our cohort and in R2-TCGA bladder cancer database.

Conclusions

The expression levels of APE1 and SSRP1 are significantly elevated in bladder cancer as compared to normal adjacent tissues. APE1 correlates with SSRP1 expression in high grade tumors. Overexpression of APE1 and SSRP1 is associated with poor survival in bladder cancer. This suggests the usage of FACT inhibitor curaxins in muscle invasive bladder cancer to target FACT complex and APE1 to improve chemosensitization after further validation.

Non-muscle invasive bladder cancer tissues have increased base excision repair capacity

The molecular mechanisms underlying the development and progression of bladder cancer (BC) are complex and have not been fully elucidated. Alterations in base excision repair (BER) capacity, one of several DNA repair mechanisms assigned to preserving genome integrity, have been reported to influence cancer susceptibility, recurrence, and progression, as well as responses to chemotherapy and radiotherapy. We report herein that non-muscle invasive BC (NMIBC) tissues exhibit increased uracil incision, abasic endonuclease and gap-filling activities, as well as total BER capacity in comparison to normal bladder tissue from the same patient (p < 0.05). No significant difference was detected in 8-oxoG incision activity between cancer and normal tissues. NMIBC tissues have elevated protein levels of uracil DNA glycosylase, 8-oxoguanine DNA glycosylase, AP endonuclease 1 and DNA polymerase β protein. Moreover, the fold increase in total BER and the individual BER enzyme activities were greater in high-grade tissues than in low-grade NMIBC tissues. These findings suggest that enhanced BER activity may play a role in the etiology of NMIBC and that BER proteins could serve as biomarkers in disease prognosis, progression or response to genotoxic therapeutics, such as Bacillus Calmette–Guérin.

Effects of APE1 Asp148Glu polymorphisms on OPMD malignant transformation, and on susceptibility to and overall survival of oral cancer in Taiwan

BACKGROUND

The associations between malignant transformation of oral potentially malignant disorders (OPMDs), oral cancer development and prognosis, and apurinic/apyrimidinic endonuclease 1 (APE1) functional polymorphisms are unclear.

METHODS

Patients with OPMDs, patients with oral cancer, and healthy controls from the community were recruited to determine the effects of APE1 polymorphisms on malignant transformation, overall survival, and genetic susceptibility, respectively.

RESULTS

The APE1 Asp148Glu polymorphisms significantly correlated with a high hazard ratio for OPMD malignant transformation (adjusted hazard ratio [AHR] = 2.29; 95% confidence interval [CI] = 1.44-3.74) and low overall survival in oral cancer patients (AHR = 1.71, 95% CI = 1.11-2.56) according to follow-up and survival analysis. However, APE1 polymorphisms did not significantly correlate with development of oral cancer in the case-control study and logistic regression analysis.

CONCLUSIONS

These results indicate that APE1 Asp148Glu polymorphisms may have indirect roles in increasing the OPMD malignant transformation rate and in decreasing overall survival in oral cancer patients.

Bu-Fei decoction and modified Bu-Fei decoction inhibit the growth of non-small cell lung cancer, possibly via inhibition of apurinic/apyrimidinic endonuclease 1

Human apurinic/apyrimidinic endonuclease 1 (APE1) is a ubiquitous multifunctional protein, which possesses DNA repair and redox activities. High levels of APE1 are associated with chemo‑ and radioresistance, and poor prognosis in various types of cancer, including non‑small cell lung cancer (NSCLC). Bu‑Fei decoction (BFD) is a traditional Chinese herbal formula, which is believed to supplement Qi, clear away heat and nourish the lungs. BFD and modified Bu‑Fei decoction (MBFD) have been used in China to treat patients with lung cancer. The present study aimed to evaluate the potential antitumor effects of BFD and MBFD on NSCLC in vitro and in vivo. In addition, the possible contribution of APE1 was examined. MTT assay was used to investigated the anti-tumor activity of BFD and MBFD on H1975 and H292 NSCLC cell lines. The DNA damage of cells in the control and the experimental groups was detected using comet assay. The in vivo anti-tumor effects of BFD and MBFD were evaluated in a NSCLC tumor nude mouse xenograft model. Polymerase chain reaction (PCR), reverse transcription‑quantitative PCR (RT‑qPCR) analysis and western blot analysis were applied to analyze the mRNA and protein expression levels of APE1 in H1975 and H292 cells, so as to the xenograft tumor tissues. The concentration of APE1 in mice plasma was determined using enzyme linked immunosorbent assay (ELISA). In vitro, BFD and MBFD inhibited the growth of cultured H1975 and H292 NSCLC cells. The results of a comet assay revealed that BFD and MBFD increased DNA damage. Furthermore, the expression levels of APE1 were decreased in response to BFD and MBFD at the mRNA and protein levels. In mice carrying NSCLC xenografts, BFD and MBFD inhibited tumor growth and decreased APE1 expression. In addition, in normal human lung bronchial epithelial BEAS‑2B cells, the half maximal inhibitory concentrations of BFD and MBFD were much higher compared with in NSCLC cells, and they had no effect on DNA damage. These results suggested that BFD and MBFD may inhibit the growth of NSCLC, possibly by inhibiting APE1 expression.

Relationship between XPD, RAD51, and APEX1 DNA repair genotypes and prostate cancer risk in the male population of Rio de Janeiro, Brazil

Susceptibility to cancer ensues in individuals carrying malfunctioning DNA repair mechanisms. The impact of Single Nucleotide Polymorphisms (SNPs) in key DNA repair mechanisms on risk for prostate cancer was investigated in this case-control study. Samples consisted of 110 patients with confirmed prostate cancer and 200 unaffected men, from Rio de Janeiro, Brazil. XPD/Lys751Gln (rs13181), APEX1/Asp148Glu (rs1130409), and RAD51/G135C (rs1801320) SNPs were analyzed by PCR-RFLP. Allelic and genotypic frequencies were calculated and compared by Chi-Square test. The association between SNPs and clinical/epidemiological data was considered significant by Odds Ratio analysis, with IC95% and a p-value≤0.05. Only the XPD/Lys751Gln SNP significantly increased susceptibility to disease in southeastern Brazilian men, with p≤0.001 [OR=2.36 (1.46-3.84)], with no association with APEX1 or RAD51 SNPs. Combined XPD+RAD51 SNPs were highly associated with the disease, p≤0.005 [OR=3.40 (1.32-9.20)]. A Chi-Square significant association between XPD/Lys751Gln and Gleason score was also observed (OR=9.31; IC95%=1.19–428.0; p=0.022). Epidemiological inquiries revealed that exposure to pesticides significantly impacted the risk for prostate cancer in this population. DNA repair dysfunctions seem to prevail among workers exposed to chemical byproducts to cancer in this specific tissue. Non-invasive genotyping SNPs may help assessment of prostate cancer risk in environmentally exposed populations.

Not breathing is not an option: How to deal with oxidative DNA damage

Oxidative DNA damage constitutes a major threat to genetic integrity, and has thus been implicated in the pathogenesis of a wide variety of diseases, including cancer and neurodegeneration. 7,8-dihydro-8oxo-deoxyGuanine (8-oxo-G) is one of the best characterised oxidative DNA lesions, and it can give rise to point mutations due to its miscoding potential that instructs most DNA polymerases (Pols) to preferentially insert Adenine (A) opposite 8-oxo-G instead of the correct Cytosine (C). If uncorrected, A:8-oxo-G mispairs can give rise to C:G→A:T transversion mutations. Cells have evolved a variety of pathways to mitigate the mutational potential of 8-oxo-G that include i) mechanisms to avoid incorporation of oxidized nucleotides into DNA through nucleotide pool sanitisation enzymes (by MTH1, MTH2, MTH3 and NUDT5), ii) base excision repair (BER) of 8-oxo-G in DNA (involving MUTYH, OGG1, Pol λ, and other components of the BER machinery), and iii) faithful bypass of 8-oxo-G lesions during replication (using a switch between replicative Pols and Pol λ). In the following, the fate of 8-oxo-G in mammalian cells is reviewed in detail. The differential origins of 8-oxo-G in DNA and its consequences for genetic stability will be covered. This will be followed by a thorough discussion of the different mechanisms in place to cope with 8-oxo-G with an emphasis on Pol λ-mediated correct bypass of 8-oxo-G during MUTYH-initiated BER as well as replication across 8-oxo-G. Furthermore, the multitude of mechanisms in place to regulate key proteins involved in 8-oxo-G repair will be reviewed. Novel functions of 8-oxo-G as an epigenetic-like regulator and insights into the repair of 8-oxo-G within the cellular context will be touched upon. Finally, a discussion will outline the relevance of 8-oxo-G and the proteins involved in dealing with 8-oxo-G to human diseases with a special emphasis on cancer.

Extreme Expression of DNA Repair Protein Apurinic/Apyrimidinic Endonuclease 1 (APE1) in Human Breast Cancer As Measured by Liquid Chromatography and Isotope Dilution Tandem Mass Spectrometry

Apurinic/apyrimidinic endonuclease 1 (APE1) is a DNA repair protein and plays other important roles. Increased levels of APE1 in cancer have been reported. However, available methods for measuring APE1 levels are indirect and not quantitative. We previously developed an approach using liquid chromatography and tandem mass spectrometry with isotope dilution to accurately measure APE1 levels. Here, we applied this methodology to measure APE1 levels in normal and cancerous human breast tissues. Extreme expression of APE1 in malignant tumors was observed, suggesting that breast cancer cells may require APE1 for survival. Accurate measurement of APE1 may be essential for the development of novel treatment strategies and APE1 inhibitors as anticancer drugs.