The 30 kb deletion in the APOBEC3 cluster decreases APOBEC3A and APOBEC3B expression and creates a transcriptionally active hybrid gene but does not associate with breast cancer in the European population

Genetic alteration of mRNA editing enzyme APOBEC3B in the pathogenesis of ovarian endometriosis

RESEARCH QUESTION

What are the specific genetic alterations and associated network in endometriotic cells responsible for the disease pathogenesis?

DESIGN

Case control experimental study involving 45 women with endometriosis who underwent laparoscopic surgery (case) and 45 normal samples from women undergoing total abdominal hysterectomy (control). The endometrial samples were subjected to whole exome sequencing (WES) of endometriotic tissue and copy number variation analysis. Validation of gene hits were obtained from WES using polymerase chain reaction techniques, immunological techniques, in-silico tools and transgenic cell line models.

RESULTS

Germline heterozygous deletion of mRNA editing enzyme subunit APOBEC3B was identified in about 96% of endometriosis samples. The presence of germline deletion was confirmed with blood, endometrium and normal ovary samples obtained from the same patient. APOBEC3B deletions resulted in a hybrid protein that activates A1CF. APOBEC3B deletion can be a major cause of changes in the endometriotic microenvironment, and contributes to the pathogenesis and manifestation of the disease. The effect of APOBEC3B deletion was proved by in-vitro experiments in a cell line model, which displayed endometriosis-like characteristics. APOBEC3B germline deletion plays a major role in the pathogenesis of endometriosis, which is evident by the activation of A1CF, an increase in epithelial to mesenchymal transition, cellular proliferation, inflammation markers and a decrease in apoptosis markers.

CONCLUSION

The deleterious effects caused by APOBEC3B deletion in endometriosis were identified and confirmed. These results might provide a base for identifying the complete pathogenetic mechanism of endometriosis, thereby moving a step closer to better diagnosis and treatment options.

The APOBEC3B c.783delG Truncating Mutation Is Not Associated with an Increased Risk of Breast Cancer in the Polish Population

The APOBEC3B gene belongs to a cluster of DNA-editing enzymes on chromosome 22 and encodes an activation-induced cytidine deaminase. A large deletion of APOBEC3B was associated with increased breast cancer risk, but the evidence is inconclusive. To investigate whether or not APOBEC3B is a breast cancer susceptibility gene, we sequenced this gene in 617 Polish patients with hereditary breast cancer. We detected a single recurrent truncating mutation (c.783delG, p.Val262Phefs) in four of the 617 (0.65%) hereditary cases by sequencing. We then genotyped an additional 12,484 women with unselected breast cancer and 3740 cancer-free women for the c.783delG mutation. The APOBEC3B c.783delG allele was detected in 60 (0.48%) unselected cases and 19 (0.51%) controls (OR = 0.95, 95% CI 0.56-1.59, p = 0.94). The allele was present in 8 of 1968 (0.41%) familial breast cancer patients from unselected cases (OR = 0.80, 95% CI 0.35-1.83, p = 0.74). Clinical characteristics of breast tumors in carriers of the APOBEC3B mutation and non-carriers were similar. No cancer type was more frequent in the relatives of mutation carriers than in those of non-carriers. We conclude the APOBEC3B deleterious mutation p.Val262Phefs does not confer breast cancer risk. These data do not support the hypothesis that APOBEC3B is a breast cancer susceptibility gene.

APOBEC3A/B Polymorphism Is Not Associated with Human Papillomavirus Infection and Cervical Carcinogenesis

The persistence of a high-risk Human papillomavirus (HPV-HR) infection of the cervix results in different manifestations of lesions depending on the immunologic capacity of the host. Variations in apolipoprotein B mRNA editing enzyme catalytic polypeptide (APOBEC)-like genes, such as the APOBEC3A/B deletion hybrid polymorphism (A3A/B), may contribute to cervical malignancy in the presence of HPV. The aim of this study was to investigate the association between the A3A/B polymorphism and HPV infection and the development of cervical intraepithelial lesions and cervical cancer in Brazilian women. The study enrolled 369 women, who were categorized according to the presence of infection and subdivided according to the degree of intraepithelial lesion and cervical cancer. APOBEC3A/B was genotyped by allele-specific polymerase chain reaction (PCR). As for the A3A/B polymorphism, the distribution of genotypes was similar between groups and among the analyzed subgroups. There were no significant differences in the presence of infection or development of lesions, even after exclusion of confounding factors. This is the first study to show that the A3A/B polymorphism is not associated with HPV infection and the development of intraepithelial lesions and cervical cancer in Brazilian women.

Involvement of APOBEC3A/B Deletion in Mouse Mammary Tumor Virus (MMTV)-like Positive Human Breast Cancer

The association between mouse mammary tumor virus (MMTV)-like sequences and human breast cancer (BC) is largely documented in the literature, but further research is needed to determine how they influence carcinogenesis. APOBEC3 cytidine deaminases are viral restriction factors that have been implicated in cancer mutagenesis, and a germline deletion that results in the fusion of the APOBEC3A coding region with the APOBEC3B 3'-UTR has been linked to increased mutagenic potential, enhanced risk of BC development, and poor prognosis. However, little is known about factors influencing APOBEC3 family activation in cancer. Thus, we hypothesized that MMTV infection and APOBEC3-mediated mutagenesis may be linked in the pathogenesis of BC. We investigated APOBEC3A/B genotyping, MMTV-like positivity, and clinicopathological parameters of 209 BC patients. We show evidence for active APOBEC3-mediated mutagenesis in human-derived MMTV sequences and comparatively investigate the impact of APOBEC3A/B germline deletion in MMTV-like env positive and negative BC in a Brazilian cohort. In MMTV-like negative samples, APOBEC3A/B deletion was negatively correlated with tumor stage while being positively correlated with estrogen receptor expression. Although APOBEC3A/B was not associated with MMTV-like positivity, samples carrying both MMTV-like positivity and APOBEC3A/B deletion had the lowest age-at-diagnosis of all study groups, with all patients being less than 50 years old. These results indicate that APOBEC3 mutagenesis is active against MMTV-like sequences, and that APOBEC3A/B deletion might act along with the MMTV-like presence to predispose people to early-onset BC.

APOBEC3A /B deletion polymorphism and endometrial cancer risk

BACKGROUND

A common 30 kb deletion affecting the APOBEC3A and APOBEC3B genes has been linked to increased APOBEC activity and APOBEC-related mutational signatures in human cancers. The role of this deletion as a cancer risk factor remains controversial.

MATERIALS AND METHODS

We genotyped the APOBEC3A/B deletion in a sample of 1,470 Norwegian endometrial cancer cases and compared to 1,918 healthy controls. For assessment across Caucasian populations, we mined genotypes of the SNP rs12628403, which is in strong linkage disequilibrium with the deletion, in a GWAS dataset of 4,274 cases and 18,125 healthy controls, through the ECAC consortium.

RESULTS

We found the APOBEC3A/B deletion variant to be significantly associated with reduced risk of endometrial cancer among Norwegian women (OR = 0.75; 95% CI = 0.62-0.91; p = 0.003; dominant model). Similar results were found in the subgroup of endometrioid endometrial cancer (OR = 0.64; 95% CI = 0.51-0.79; p = 3.6 × 10^-5 ; dominant model). The observed risk reduction was particularly strong among individuals in the range of 50-60 years of age (OR = 0.51; 95% CI = 0.33-0.78; p = 0.002; dominant model). In the different populations included in the ECAC dataset, the ORs varied from 0.85 to 1.05. Although five out of six populations revealed ORs <1.0, the overall estimate was nonsignificant and, as such, did not formally validate the findings in the Norwegian cohort.

CONCLUSION

The APOBEC3A/B deletion polymorphism is associated with a decreased risk of endometrial cancer in the Norwegian population.

Addressing the benefits of inhibiting APOBEC3-dependent mutagenesis in cancer

Mutational signatures associated with apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like (APOBEC)3 cytosine deaminase activity have been found in over half of cancer types, including some therapy-resistant and metastatic tumors. Driver mutations can occur in APOBEC3-favored sequence contexts, suggesting that mutagenesis by APOBEC3 enzymes may drive cancer evolution. The APOBEC3-mediated signatures are often detected in subclonal branches of tumor phylogenies and are acquired in cancer cell lines over long periods of time, indicating that APOBEC3 mutagenesis can be ongoing in cancer. Collectively, these and other observations have led to the proposal that APOBEC3 mutagenesis represents a disease-modifying process that could be inhibited to limit tumor heterogeneity, metastasis and drug resistance. However, critical aspects of APOBEC3 biology in cancer and in healthy tissues have not been clearly defined, limiting well-grounded predictions regarding the benefits of inhibiting APOBEC3 mutagenesis in different settings in cancer. We discuss the relevant mechanistic gaps and strategies to address them to investigate whether inhibiting APOBEC3 mutagenesis may confer clinical benefits in cancer.

APOBEC3: Friend or Foe in Human Papillomavirus Infection and Oncogenesis?

Human papillomavirus (HPV) infection is a causative agent of multiple human cancers, including cervical and head and neck cancers. In these HPV-positive tumors, somatic mutations are caused by aberrant activation of DNA mutators such as members of the apolipoprotein B messenger RNA-editing enzyme catalytic polypeptide-like 3 (APOBEC3) family of cytidine deaminases. APOBEC3 proteins are most notable for their restriction of various viruses, including anti-HPV activity. However, the potential role of APOBEC3 proteins in HPV-induced cancer progression has recently garnered significant attention. Ongoing research stems from the observations that elevated APOBEC3 expression is driven by HPV oncogene expression and that APOBEC3 activity is likely a significant contributor to somatic mutagenesis in HPV-positive cancers. This review focuses on recent advances in the study of APOBEC3 proteins and their roles in HPV infection and HPV-driven oncogenesis. Further, we discuss critical gaps and unanswered questions in our understanding of APOBEC3 in virus-associated cancers.

Prognostic value of an APOBEC3 deletion polymorphism for glioma patients in Taiwan

OBJECTIVE

The molecular pathogenesis of malignant gliomas, characterized by diverse tumor histology with differential prognosis, remains largely unelucidated. An APOBEC3 deletion polymorphism, with a deletion in APOBEC3B, has been correlated to risk and prognosis in several cancers, but its role in glioma is unclear. The authors aimed to examine the clinical relevance of the APOBEC3 deletion polymorphism to glioma risk and survival in a glioma patient cohort in Taiwan.

METHODS

The authors detected deletion genotypes in 403 glioma patients and 1365 healthy individuals in Taiwan and correlated the genotypes with glioma risk, clinicopathological factors, patient survival, and patient sex. APOBEC3 gene family expression was measured and correlated to the germline deletion. A nomogram model was constructed to predict patient survival in glioma.

RESULTS

The proportion of APOBEC3B-/- and APOBEC3B+/- genotypes was higher in glioblastoma (GBM) patients than healthy individuals and correlated with higher GBM risk in males. A higher percentage of cases with APOBEC3B- was observed in male than female glioma patients. The presence of APOBEC3B-/- was correlated with better overall survival (OS) in male astrocytic glioma patients. No significant correlation of the genotypes to glioma risk and survival was observed in the female patient cohort. Lower APOBEC3B expression was observed in astrocytic glioma patients with APOBEC3B-/- and was positively correlated with better OS. A 5-factor nomogram model was constructed based on male patients with astrocytic gliomas in the study cohort and worked efficiently for predicting patient OS.

CONCLUSIONS

The germline APOBEC3 deletion was associated with increased GBM risk and better OS in astrocytic glioma patients in the Taiwan male population. The APOBEC3B deletion homozygote was a potential independent prognostic factor predicting better survival in male astrocytic glioma patients.

Unfavorable prognosis and clinical consequences of APOBEC3B expression in breast and other cancers: A systematic review and meta-analysis

INTRODUCTION: Controversy exists regarding the association of apolipoprotein B mRNA editing enzyme catalytic subunit 3B APOBEC3B, (A3B) overexpression and poor prognosis, metastasis, and chemotherapy drug resistance in cancers. Here we conducted a systematic review and meta-analysis to determine its prognostic value and clinicopathological features in breast cancer and some other malignancies. MATERIALS AND METHODS: PubMed, Scopus, Cochrane Library, Web of Science, and EMBASE were searched up to Feb 2022 for the association of A3B with breast, ovarian, gastrointestinal and lung cancers. The pooled hazard ratios with 95% confidence interval (CI) were evaluated to assess disease-free survival (DFS), overall survival (OS), and recurrence-free survival (RFS) in cancers under study. RESULTS: Over 3700 patients were included in this meta-survey. Elevated levels of A3B were significantly related to low OS (pooled HR = 1.30; 95% CI:1.09–1.55, P < 0.01), poor DFS (pooled HR = 1.66; 95% CI:1.17–2.35, P < 0.01) and poor RFS (HR = 1.51, 95% CI:1.11–2.04, P = 0.01). Subgroup analysis revealed that high A3B expression was associated with poor OS in lung (HR = 1.85, 95% CI: 1.40–2.45), and breast cancers (HR = 1.38, 95% CI: 1.00–1.89). High expression of A3B did not display any significant association with clinicopathologic features. CONCLUSION: APOBEC3B overexpression is related to poor OS, DFS and RFS only in some cancer types and no generalized role could be predicted for all cancers.

Revisiting the MMTV Zoonotic Hypothesis to Account for Geographic Variation in Breast Cancer Incidence

Human breast cancer incidence varies by geographic location. More than 20 years ago, we proposed that zoonotic transmission of the mouse mammary tumor virus (MMTV) from the western European house mouse, Mus musculus domesticus, might account for the regional differences in breast cancer incidence. In the intervening years, several developments provide additional support for this hypothesis, including the limited impact of genetic factors for breast cancer susceptibility revealed by genome-wide association studies and the strong effect of antiretroviral therapy to reduce breast cancer incidence. At the same time, economic globalization has further expanded the distribution of M. m. domesticus to Asia, leading to a significant increase in breast cancer incidence in this region. Here, we revisit this evidence and provide an update to the MMTV zoonotic hypothesis for human breast cancer at a time when the world is recovering from the global COVID-19 zoonotic pandemic. We present evidence that mouse population outbreaks are correlated with spikes in breast cancer incidence in Australia and New Zealand and that globalization has increased the range of M. m. domesticus and MMTV. Given the success of global vaccination campaigns for HPV to eradicate cervical cancer, a similar strategy for MMTV may be warranted. Until breast cancer incidence is reduced by such an approach, zoonotic transmission of MMTV from mice to humans as an etiologic factor for breast cancer will remain controversial.

Variant identification in BARD1, PRDM9, RCC1, and RECQL in patients with ovarian cancer by targeted next-generation sequencing of DNA pools

Several ovarian cancer susceptibility genes have been discovered, but more are likely to exist. In this study, we aimed to analyze knowledge-based selected genes, i.e., BARD1, PRDM9, RCC1, and RECQL, in which pathogenic germline variants have been reported in patients with breast and/or ovarian cancer. As deep sequencing of DNA samples remains costly, targeted next-generation sequencing of DNA pools was utilized to screen the exons of BARD1, PRDM9, RCC1, and RECQL in ~400 Polish ovarian cancer cases. 25 pools of 16 samples (including several duplicated samples with known variants) were sequenced on the NovaSeq6000 and analyzed with SureCall (Agilent) application. The set of variants was filtrated to exclude spurious variants, and, subsequently, the identified rare genetic variants were validated using Sanger sequencing. No pathogenic mutation was found within the analyzed cohort of ovarian cancer patients. Validation genotyping of filtered rare silent and missense variants revealed that the majority of them were true alterations, especially those with a higher mutation quality value. The high concordance (R2=0.95) of population allele frequency for 44 common SNPs in the European control population (gnomAD) and our experiment confirmed the reliability of pooled sequencing. Mutations in BARD1, PRDM9, RCC1, and RECQL do not contribute substantially to the risk of ovarian cancer. Pooled DNA sequencing is a cost-effective and reliable method for the initial screening of candidate genes; however, it still requires validation of identified rare variants.

Impact of the APOBEC3A/B deletion polymorphism on risk of ovarian cancer

A germline 29.5-kb deletion variant removes the 3’ end of the APOBEC3A gene and a large part of APOBEC3B, creating a hybrid gene that has been linked to increased APOBEC3 activity and DNA damage in human cancers. We genotyped the APOBEC3A/B deletion in hospital-based samples of 1398 Norwegian epithelial ovarian cancer patients without detected BRCA1/2 germline mutations and compared to 1,918 healthy female controls, to assess the potential cancer risk associated with the deletion. We observed an association between APOBEC3A/B status and reduced risk for ovarian cancer (OR = 0.75; CI = 0.61–0.91; p = 0.003) applying the dominant model. Similar results were found in other models. The association was observed both in non-serous and serous cases (dominant model: OR = 0.69; CI = 0.50–0.95; p = 0.018 and OR = 0.77; CI = 0.62–0.96; p = 0.019, respectively) as well as within high-grade serous cases (dominant model: OR = 0.79; CI = 0.59–1.05). For validation purposes, we mined an available large multinational GWAS-based data set of > 18,000 cases and > 26,000 controls for SNP rs12628403, known to be in linkage disequilibrium with the APOBEC3A/B deletion. We found a non-significant trend for SNP rs12628403 being linked to reduced risk of ovarian cancer in general and similar trends for all subtypes. For clear cell cancers, the risk reduction reached significance (OR = 0.85; CI = 0.69–1.00).

Human APOBEC3 Variations and Viral Infection

Human APOBEC3 (apolipoprotein B mRNA-editing catalytic polypeptide-like 3) enzymes are capable of inhibiting a wide range of endogenous and exogenous viruses using deaminase and deaminase-independent mechanisms. These enzymes are essential components of our innate immune system, as evidenced by (a) their strong positive selection and expansion in primates, (b) the evolution of viral counter-defense mechanisms, such as proteasomal degradation mediated by HIV Vif, and (c) hypermutation and inactivation of a large number of integrated HIV-1 proviruses. Numerous APOBEC3 single nucleotide polymorphisms, haplotypes, and splice variants have been identified in humans. Several of these variants have been reported to be associated with differential antiviral immunity. This review focuses on the current knowledge in the field about these natural variations and their roles in infectious diseases.

Germline APOBEC3B deletion increases somatic hypermutation in Asian breast cancer that is associated with Her2 subtype, PIK3CA mutations and immune activation

A 30-kb deletion that eliminates the coding region of APOBEC3B (A3B) is >5 times more common in women of Asian descent compared to European descent. This polymorphism creates a chimera with the APOBEC3A (A3A) coding region and A3B 3'UTR, and it is associated with an increased risk for breast cancer in Asian women. Here, we explored the relationship between the A3B deletion polymorphism with tumour characteristics in Asian women. Using whole exome and whole transcriptome sequencing data of 527 breast tumours, we report that germline A3B deletion polymorphism leads to expression of the A3A-B hybrid isoform and increased APOBEC-associated somatic hypermutation. Hypermutated tumours, regardless of A3B germline status, were associated with the Her2 molecular subtype and PIK3CA mutations. Compared to nonhypermutated tumours, hypermutated tumours also had higher neoantigen burden, tumour heterogeneity and immune activation. Taken together, our results suggest that the germline A3B deletion polymorphism, via the A3A-B hybrid isoform, contributes to APOBEC mutagenesis in a significant proportion of Asian breast cancers. In addition, APOBEC somatic hypermutation, regardless of A3B background, may be an important clinical biomarker for Asian breast cancers.

APOBEC3B deletion polymorphism and lung cancer risk in the southern Chinese population

Background

Approximately 80–85% of lung cancer is the non-small cell lung cancer (NSCLC) subtype, which ranks as the leading cause of cancer deaths worldwide. APOBEC3B (A3B) was reported to be a key source of mutations in NSCLC. However, the role of the A3B deletion polymorphism in the etiology of NSCLC has not been well-documented.

Methods

A case-control study with 317 NSCLC patients and 334 healthy controls was conducted to explore the association between the A3B deletion polymorphism and the risk of NSCLC. The unconditional logistic regression model was performed to calculate the odds ratio (OR) and the 95% confidence interval (CI), and the confounding factors were adjusted, including age, gender, and smoking status, to estimate the risk. An analysis of gene-environment interactions was performed using multifactor dimensionality reduction (MDR) software.

Results

We found that the del/del genotype of A3B deletion significantly increased NSCLC risk. Compared with individuals carrying the ins/ins genotype of A3B deletion, individuals with the del/del genotype had a 2.36 times increased risk of developing NSCLC after adjusting for confounding factors (OR =2.71, 95% CI: 1.67–4.42, P<0.001). A 3-factor gene-environment (A3B deletion, gender, and smoking) interaction model was found for NSCLC (OR =4.407, 95% CI: 1.174–16.549, P=0.028).

Conclusions

We propose that the A3B deletion polymorphism can increase the risk of developing NSCLC, and their interactions with gender and smoking may contribute to the risk of NSCLC in the southern Chinese population.

Germline copy number variations in BRCA1/2 negative families: Role in the molecular etiology of hereditary breast cancer in Tunisia

Hereditary breast cancer accounts for 5-10% of all breast cancer cases. So far, known genetic risk factors account for only 50% of the breast cancer genetic component and almost a quarter of hereditary cases are carriers of pathogenic mutations in BRCA1/2 genes. Hence, the genetic basis for a significant fraction of familial cases remains unsolved. This missing heritability may be explained in part by Copy Number Variations (CNVs). We herein aimed to evaluate the contribution of CNVs to hereditary breast cancer in Tunisia. Whole exome sequencing was performed for 9 BRCA negative cases with a strong family history of breast cancer and 10 matched controls. CNVs were called using the ExomeDepth R-package and investigated by pathway analysis and web-based bioinformatic tools. Overall, 483 CNVs have been identified in breast cancer patients. Rare CNVs affecting cancer genes were detected, of special interest were those disrupting APC2, POU5F1, DOCK8, KANSL1, TMTC3 and the mismatch repair gene PMS2. In addition, common CNVs known to be associated with breast cancer risk have also been identified including CNVs on APOBECA/B, UGT2B17 and GSTT1 genes. Whereas those disrupting SULT1A1 and UGT2B15 seem to correlate with good clinical response to tamoxifen. Our study revealed new insights regarding CNVs and breast cancer risk in the Tunisian population. These findings suggest that rare and common CNVs may contribute to disease susceptibility. Those affecting mismatch repair genes are of interest and require additional attention since it may help to select candidates for immunotherapy leading to better outcomes.

The interesting relationship between APOBEC3 deoxycytidine deaminases and cancer: a long road ahead

Cancer is considered a group of diseases characterized by uncontrolled growth and spread of abnormal cells and is propelled by somatic mutations. Apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3 (APOBEC3) family of enzymes are endogenous sources of somatic mutations found in multiple human cancers. While these enzymes normally act as an intrinsic immune defence against viruses, they can also catalyse 'off-target' cytidine deamination in genomic single-stranded DNA intermediates. The deamination of cytosine forms uracil, which is promutagenic in DNA. Key factors to trigger the APOBEC 'off-target' activity are overexpression in a non-normal cell type, nuclear localization and replication stress. The resulting uracil-induced mutations contribute to genomic variation, which may result in neutral, beneficial or harmful consequences for the cancer. This review summarizes the functional and biochemical basis of the APOBEC3 enzyme activity and highlights their relationship with the most well-studied cancers in this particular context such as breast, lung, bladder, and human papillomavirus-associated cancers. We focus on APOBEC3A, APOBEC3B and APOBEC3H haplotype I because they are the leading candidates as sources of somatic mutations in these and other cancers. Also, we discuss the prognostic value of the APOBEC3 expression in drug resistance and response to therapies.

Molecular origins of APOBEC-associated mutations in cancer

The APOBEC family of cytidine deaminases has been proposed to represent a major enzymatic source of mutations in cancer. Here, we summarize available evidence that links APOBEC deaminases to cancer mutagenesis. We also highlight newly identified human cell models of APOBEC mutagenesis, including cancer cell lines with suspected endogenous APOBEC activity and a cell system of telomere crisis-associated mutations. Finally, we draw on recent data to propose potential causes of APOBEC misregulation in cancer, including the instigating factors, the relevant mutator(s), and the mechanisms underlying generation of the genome-dispersed and clustered APOBEC-induced mutations.

Single-nucleotide polymorphism of the DNA cytosine deaminase APOBEC3H haplotype I leads to enzyme destabilization and correlates with lung cancer

A number of APOBEC family DNA cytosine deaminases can induce mutations in tumor cells. APOBEC3H haplotype I is one of the deaminases that has been proposed to cause mutations in lung cancer. Here, we confirmed that APOBEC3H haplotype I can cause uracil-induced DNA damage in lung cancer cells that results in γH2AX foci. Interestingly, the database of cancer biomarkers in DNA repair genes (DNArCdb) identified a single-nucleotide polymorphism (rs139298) of APOBEC3H haplotype I that is involved in lung cancer. While we thought this may increase the activity of APOBEC3H haplotype I, instead we found through computational modeling and cell-based experiments that this single-nucleotide polymorphism causes the destabilization of APOBEC3H Haplotype I. Computational analysis suggests that the resulting K121E change affects the structure of APOBEC3H leading to active site disruption and destabilization of the RNA-mediated dimer interface. A K117E mutation in a K121E background stabilized the APOBEC3H haplotype I, thus enabling biochemical study. Subsequent analysis showed that K121E affected catalytic activity, single-stranded DNA binding and oligomerization on single-stranded DNA. The destabilization of a DNA mutator associated with lung cancer supports the model that too much APOBEC3-induced mutation could result in immune recognition or death of tumor cells.

Germline APOBEC3B deletion influences clinicopathological parameters in luminal-A breast cancer: evidences from a southern Brazilian cohort

PURPOSE

APOBEC3A and APOBEC3B cytidine deaminases have been implicated in the pathogenesis of multiple cancers, including breast cancer (BC). A germline deletion linking APOBEC3A and APOBEC3B loci (A3A/B) has been associated with higher APOBEC-mediated mutational burden, but its association with BC risk have been controversial. Therefore, this study investigated the association between A3A/B and BC susceptibility and clinical presentation in a Brazilian cohort.

METHODS

A3A/B deletion was evaluated through allele-specific PCR in 341 BC patients and 397 women without familial or personal history of neoplasia from Brazil and associations with susceptibility to BC subtypes were tested through age-adjusted logistic models while correlations with clinicopathological parameters were tested using Kendall's tests.

RESULTS

No association was found between A3A/B and BC susceptibility; however, in Luminal-A BCs, it was positively correlated with tumor size (Tau-c = 0.125) and Ki67 (Tau-c = 0.116) and negatively correlated with lymph node metastasis (LNM) (Tau-c = - 0.162). The negative association between A3A/B with LNM in Luminal-A BCs remained significant even after adjusting for tumor size and Ki67 in logistic models (OR = 0.22; p = 0.008).

CONCLUSION

These results show that although A3A/B may not modify BC susceptibility in Brazilian population, it may affect clinicopathological features in BC subtypes, promoting tumor cell proliferation while being negatively associated with LNM in Luminal-A BCs.

Association of APOBEC3 deletion with cancer risk: A meta-analysis of 26 225 cases and 37 201 controls

Previous studies have found inconsistent results regarding gene deletion in APOBEC3 (apolipoprotein B mRNA-editing catalytic polypeptide-like 3) and risk of cancer. We conducted a meta-analysis of all eligible case-control studies to find out the associations between APOBEC3 deletion and cancer risk by pooling the odds ratios (ORs) and corresponding 95% confidence intervals (CIs). Overall, the findings from 20 studies (13 articles) involving of a total of 26 225 cases and 37 201 controls revealed that DD genotype was associated significantly with increased cancer risk compared to II genotype (OR = 1.25, 95% CI = 1.01-1.56, P = 0.04). Stratified analysis from 10 studies including 14 757 cases and 17 930 controls revealed that I/D variant significantly increased the risk of breast cancer in heterozygous codominant (OR = 1.15, 95% CI = 1.03-1.28, P = 0.02, ID vs II), dominant (OR = 1.15, 95% CI = 1.01-1.31, P = 0.03, ID + DD vs II), overdominant (OR = 1.11, 95% CI = 1.05-1.25, P < 0.0001, ID vs DD + II) and allele (OR = 1.15, 95% CI = 1.13-1.25, P = 0.03, D vs I) inheritance models. In conclusion, the data propose that APOBEC3 deletion is significantly associated with increased susceptibility to cancer in overall and breast cancer. Our findings require well-designed replication in a larger independent genetic association study with larger sample sizes in diverse ethnicities.

The spectrum of APOBEC3 activity: From anti-viral agents to anti-cancer opportunities

The APOBEC3 family of cytosine deaminases are part of the innate immune response to viral infection, but also have the capacity to damage cellular DNA. Detection of mutational signatures consistent with APOBEC3 activity, together with elevated APOBEC3 expression in cancer cells, has raised the possibility that these enzymes contribute to oncogenesis. Genome deamination by APOBEC3 enzymes also elicits DNA damage response signaling and presents therapeutic vulnerabilities for cancer cells. Here, we discuss implications of APOBEC3 activity in cancer and the potential to exploit their mutagenic activity for targeted cancer therapies.

Integrative genomic analyses of APOBEC-mutational signature, expression and germline deletion of APOBEC3 genes, and immunogenicity in multiple cancer types

BACKGROUND

Although APOBEC-mutational signature is found in tumor tissues of multiple cancers, how a common germline APOBEC3A/B deletion affects the mutational signature remains unclear.

METHODS

Using data from 10 cancer types generated as part of TCGA, we performed integrative genomic and association analyses to assess inter-relationship of expressions for isoforms APOBEC3A and APOBEC3B, APOBEC-mutational signature, germline APOBEC3A/B deletions, neoantigen loads, and tumor infiltration lymphocytes (TILs).

RESULTS

We found that expression level of the isoform uc011aoc transcribed from the APOBEC3A/B chimera was associated with a greater burden of APOBEC-mutational signature only in breast cancer, while germline APOBEC3A/B deletion led to an increased expression level of uc011aoc in multiple cancer types. Furthermore, we found that the deletion was associated with elevated APOBEC-mutational signature, neoantigen loads and relative composition of T cells (CD8+) in TILs only in breast cancer. Additionally, we also found that APOBEC-mutational signature significantly contributed to neoantigen loads and certain immune cell abundances in TILs across cancer types.

CONCLUSIONS

These findings reveal new insights into understanding the genetic, biological and immunological mechanisms through which APOBEC genes may be involved in carcinogenesis, and provide potential genetic biomarker for the development of disease prevention and cancer immunotherapy.

Associations between the single nucleotide polymorphisms of APOBEC3A, APOBEC3B and APOBEC3H, and chronic hepatitis B progression and hepatocellular carcinoma in a Chinese population

The present study examined the relationships between the single nucleotide polymorphisms (SNPs) of three members of the apolipoprotein B mRNA‑editing catalytic polypeptide‑like 3 (A3) gene family, A3A, A3B and A3H, and hepatitis B virus (HBV) infection and hepatocellular carcinoma (HCC) in a Han Chinese population. A total of 654 patients were enrolled in the study between January 2012 and July 2016, including 104 patients with chronic HBV infection (CHB), 265 patients with HBV‑related liver cirrhosis and 285 patients with HBV‑related HCC. A total of two A3A SNPs (rs7286317 and rs7290153), three A3B SNPs (rs2267398, rs2267401 and rs2076109), and five A3H SNPs (rs56695217, rs139302, rs139297, rs139316 and rs139292) were genotyped using a MassArray system. Statistical analysis and haplotype estimation were conducted using Haploview and Unphased software. No significant associations were observed between the A3A, A3B and A3H SNPs and the development of CHB and HCC. Haplotype analysis revealed that the mutant haplotypes C‑T‑A, C‑T‑G, T‑G‑G and T‑T‑G from the A3B SNPs rs2267398‑rs2267401‑rs2076109 carried a lower risk of HCC than the reference haplotype. These findings suggested that there was no relationship between A3A, A3B and A3H SNPs and CHB progression or HCC development in the Han Chinese population.