Germline APOBEC3B deletion is associated with breast cancer risk in an Asian multi-ethnic cohort and with immune cell presentation

UL16‑binding protein 1 is a significant prognostic and diagnostic marker for breast cancer

The aim of the present study was to investigate the association between UL16 binding protein 1 (ULBP1) and the prognosis of patients with and immune cell infiltration in breast cancer (BRCA). The mRNA data of BRCA and immune-related genes were extracted from The Cancer Genome Atlas and were analyzed using bioinformatics tools. Subsequently, the results obtained by bioinformatics were validated through the collection of clinical patient data at the Zibo Central hospital (Zibo, China). The difference in the expression of the ULBP1 gene between BRCA tissues and normal precancerous tissues was analyzed, followed by validation using immunohistochemistry. By combining clinical data from patients with BRCA, the prognostic and diagnostic significance of the ULBP1 gene in patients with BRCA was analyzed. Gene enrichment analysis was conducted to gain insight into the molecular mechanisms underlying the regulatory role of ULBP1 in BRCA by analyzing its related functions and signaling pathways. Furthermore, single sample gene set enrichment analysis (ssGSEA) and Spearman's correlation analysis were performed to explore the correlation between ULBP1 as a target gene related with tumor immune cell infiltration. The data revealed that ULBP1 is a target gene associated with immunity and the prognosis of patients with BRCA. Patients with BRCA with a high expression of ULBP1 had a poorer prognosis. ULBP1 expression correlated with progesterone receptor expression, estrogen receptor expression and histological type in patients with BRCA; thus, it may serve as an independent predictor for the overall survival rate of patients. Functional enrichment analysis revealed a significant co-expression between ULBP1 and ULBP2, ULBP3, retinoic acid early transcript 1K, as well as a significant enrichment of pathways associated with carcinogenesis and immune suppression. ssGSEA and Spearman's correlation analysis demonstrated significant correlations between ULBP1 expression and tumor immune cells, as well as immune checkpoints. Overall, the present study demonstrated that ULBP1 was associated with BRCA immunity and might serve as a prognostic and diagnostic biomarker for patients with BRCA. In addition, it might also be a potential target for the immunotherapy of BRCA.

Genetic evaluation of patients with multiple primary cancers

Regarding inherited cancer predisposition, single gene carriers of pathogenic variants (PVs) have been extensively reported on in the literature, whereas the oligogenic coinheritance of heterozygous PVs in cancer-related genes is a poorly studied event. Currently, due to the increased number of cancer survivors, the probability of patients presenting with multiple primary cancers (MPCs) is higher. The present study included patients with MPCs aged ≤45 years without known PVs in common cancer predisposition genes. This study used whole exome sequencing (WES) of germline and tumoral DNA, chromosomal microarray analysis (CMA) of germline DNA (patients 1-7, 9 and 10), and a karyotype test of patient 8 to detect variants associated with the disease. The 10 patients included in the study presented a mean of 3 cancers per patient. CMA showed two microduplications and one microdeletion, while WES of the germline DNA identified 1-3 single nucleotide variants of potential interest to the disease in each patient and two additional copy number variants. Most of the identified variants were classified as variants of uncertain significance. The mapping of the germline variants into their pathways showed a possible additive effect of these as the cause of the cancer. A total of 12 somatic samples from 5 patients were available for sequencing. All of the germline variants were also present in the somatic samples, while no second hits were identified in the same genes. The sequencing of patients with early cancers, family history and multiple tumors is already a standard of care. However, growing evidence has suggested that the assessment of patients should not stop at the identification of one PV in a cancer predisposition gene.

Human and bats genome robustness under COSMIC mutational signatures

Carcinogenesis is an evolutionary process, and mutations can fix the selected phenotypes in selective microenvironments. Both normal and neoplastic cells are robust to the mutational stressors in the microenvironment to the extent that secure their fitness. To test the robustness of genes under a range of mutagens, we developed a sequential mutation simulator, Sinabro, to simulate single base substitution under a given mutational process. Then, we developed a pipeline to measure the robustness of genes and cells under those mutagenesis processes. We discovered significant human genome robustness to the APOBEC mutational signature SBS2, which is associated with viral defense mechanisms and is implicated in cancer. Robustness evaluations across over 70,000 sequences against 41 signatures showed higher resilience under signatures predominantly causing C-to-T (G-to-A) mutations. Principal component analysis indicates the GC content at the codon's wobble position significantly influences robustness, with increased resilience noted under transition mutations compared to transversions. Then, we tested our results in bats at extremes of the lifespan-to-mass relationship and found the long-lived bat is more robust to APOBEC than the short-lived one. By revealing robustness to APOBEC ranked highest in human (and bats with much more than number of APOBEC) genome, this work bolsters the key potential role of APOBECs in aging and cancer, as well as evolved countermeasures to this innate mutagenic process. It also provides the baseline of the human and bat genome robustness under mutational processes associated with aging and cancer.

APOBEC Mutagenesis in Cancer Development and Susceptibility

APOBEC cytosine deaminases are prominent mutators in cancer, mediating mutations in over 50% of cancers. APOBEC mutagenesis has been linked to tumor heterogeneity, persistent cell evolution, and therapy responses. While emerging evidence supports the impact of APOBEC mutagenesis on cancer progression, the understanding of its contribution to cancer susceptibility and malignant transformation is limited. We examine the existing evidence for the role of APOBEC mutagenesis in carcinogenesis on the basis of the reported associations between germline polymorphisms in genes encoding APOBEC enzymes and cancer risk, insights into APOBEC activities from sequencing efforts of both malignant and non-malignant human tissues, and in vivo studies. We discuss key knowledge gaps and highlight possible ways to gain a deeper understanding of the contribution of APOBEC mutagenesis to cancer development.

Clinical activity of nivolumab in combination with eribulin in HER2-negative metastatic breast cancer: A phase IB/II study (KCSG BR18-16)

AIM

We evaluated the efficacy and safety of nivolumab and eribulin combination therapy for metastatic breast cancer (BC) in Asian populations.

METHODS

In this parallel phase II study, adult patients with histologically confirmed recurrent/metastatic hormone receptor-positive/HER2-negative (HR+HER2-) or triple-negative BC (TNBC) were prospectively enroled from 10 academic hospitals in Korea (ClinicalTrials.gov Identifier: NCT04061863). They received nivolumab (360 mg) on day 1 plus eribulin (1.4 mg/m2) on days 1 and 8 every 3 weeks until disease progression or intolerable toxicity. The primary endpoint was the investigator-assessed 6-month progression-free survival (PFS) rate in each subtype. Secondary endpoints included investigator-assessed objective response rate (ORR) as per Response Evaluation Criteria in Advanced Solid Tumors version 1.1, disease control rate, overall survival, and treatment toxicity. The association between PD-L1 expression and efficacy was investigated.

RESULTS

Forty-five patients with HR+HER2- BC and 45 with TNBC were enroled. Their median age was 51 (range, 31-71) years, and 74 (82.2%) received one or two prior treatments before enrolment. Six-month PFS was 47.2% and 25.1% in the HR+HER2- and TNBC cohorts, respectively. Median PFS was 5.6 (95% confidence interval [CI]: 5.3-7.4) and 3.0 (95% CI: 2.1-5.2) months in the HR+HER2- and TNBC groups, respectively. ORRs were 53.3% (complete response [CR]: 0, partial response [PR]: 24) and 28.9% (CR: 1, PR: 12). Patients with PD-L1+ tumours (PD-L1 expression ≥1%) and PD-L1- tumours (ORR 50% versus 53.8% in HR+HER2-, 30.8% versus 29.0% in TNBC) had similar ORRs. Neutropenia was the most common grade 3/4 adverse event; the most common immune-related adverse events (AEs) were grades 1/2 hypothyroidism and pruritus. Five patients discontinued therapy because of immune-related AEs.

CONCLUSION

Nivolumab plus eribulin showed promising efficacy and tolerable safety in previously treated HER2- metastatic BC.

TRIAL REGISTRATION

NCT04061863.

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.

APOBEC3-mediated mutagenesis in cancer: causes, clinical significance and therapeutic potential

Apolipoprotein B mRNA-editing enzyme, catalytic polypeptides (APOBECs) are cytosine deaminases involved in innate and adaptive immunity. However, some APOBEC family members can also deaminate host genomes to generate oncogenic mutations. The resulting mutations, primarily signatures 2 and 13, occur in many tumor types and are among the most common mutational signatures in cancer. This review summarizes the current evidence implicating APOBEC3s as major mutators and outlines the exogenous and endogenous triggers of APOBEC3 expression and mutational activity. The review also discusses how APOBEC3-mediated mutagenesis impacts tumor evolution through both mutagenic and non-mutagenic pathways, including by inducing driver mutations and modulating the tumor immune microenvironment. Moving from molecular biology to clinical outcomes, the review concludes by summarizing the divergent prognostic significance of APOBEC3s across cancer types and their therapeutic potential in the current and future clinical landscapes.

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.

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.

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.

APOBEC3F expression in triple-negative breast cancer is associated with tumor microenvironment infiltration and activation of cancer immunity and improved survival

The apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like (APOBEC) causes a point mutation from cytidine to uracil in DNA and/or RNA. The role of APOBEC3A and APOBEC3B in breast cancer has been well described, whereas that of APOBEC3F remains unknown. To investigate the clinical relevance of APOBEC3F expression, we analyzed a total of 3000 breast cancer cases from multiple independent large patient cohorts including METABRIC, TCGA, GSE75688, and GSE114725. High expression of APOBEC3F was associated with improved disease-specific and overall survival in triple negative breast cancer (TNBC). APOBEC3F is not usually a reflection of cancer cell biology in TNBC or luminal breast cancer, except for homologous recombination deficiency in TNBC. In the TNBC homologous recombination deficiency group, APOBEC3F expression was not consistently associated with intratumor heterogeneity, mutation rates, or neoantigens. APOBEC3F expression did not correlate with response to any of the drugs tested in breast cancer cell lines in vitro. However, high APOBEC3F expression was associated with enrichment of several immune-related gene sets and immune activity. High APOBEC3F expression also accompanied higher infiltration of anti-cancer immune cell infiltration in TNBC. However, in luminal breast cancer, high APOBEC3F tumor significantly enriched not only immune-related gene sets, but also cell proliferation-, metastasis-, and apoptosis-related gene sets. Analysis of single-cell transcriptomes showed APOBEC3F exclusively expressed in immune cells and significantly associated with cytolytic activity of the immune cells, immune response, and immune cell proliferation. Expression of immune checkpoint genes was uniformly elevated in APOBEC3F-high tumors. We conclude that APOBEC3F is exclusively expressed in immune cells and this expression is associated with enhanced anti-cancer immune response as well as improved survival in TNBC.

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).

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.

Correlation Between APOBEC3B Expression and Clinical Characterization in Lower-Grade Gliomas

Background

As the most aggressive tumors in the central nervous system, gliomas have poor prognosis and limited therapy methods. Immunotherapy has become promising in the treatment of gliomas. Here, we explored the expression pattern of APOBEC3B, a genomic mutation inducer, in gliomas to assess its value as an immune biomarker and immunotherapeutic target.

Methods

We mined transcriptional data from two publicly available genomic datasets, TCGA and CGGA, to investigate the relevance between APOBEC3B and clinical characterizations including tumor classifications, patient prognosis, and immune infiltrating features in gliomas. We especially explored the correlation between APOBEC3B and tumor mutations. Samples from Xiangya cohort were used for immunohistochemistry staining.

Results

Our findings demonstrated that APOBEC3B expression level was relatively high in advanced gliomas and other cancer types, which indicated poorer prognosis. APOBEC3B also stratified patients’ survival in Xiangya cohort. APOBEC3B was significantly associated with infiltrating immune and stromal cell types in the tumor microenvironment. Notably, APOBEC3B was involved in tumor mutation and strongly correlated with the regulation of oncogenic genes.

Conclusion

Our findings identified that APOBEC3B could be a latent molecular target in gliomas.

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.

APOBEC: A molecular driver in cervical cancer pathogenesis

Cervical cancer is one of the foremost common cancers in women. Human papillomavirus (HPV) infection remains a major risk factor of cervical cancer. In addition, numerous other genetic and epigenetic factors also are involved in the underlying pathogenesis of cervical cancer. Recently, it has been reported that apolipoprotein B mRNA editing enzyme catalytic polypeptide like (APOBEC), DNA-editing protein plays an important role in the molecular pathogenesis of cancer. Particularly, the APOBEC3 family was shown to induce tumor mutations by aberrant DNA editing mechanism. In general, APOBEC3 enzymes play a pivotal role in the deamination of cytidine to uridine in DNA and RNA to control diverse biological processes such as regulation of protein expression, innate immunity, and embryonic development. Innate antiviral activity of the APOBEC3 family members restrict retroviruses, endogenous retro-element, and DNA viruses including the HPV that is the leading risk factor for cervical cancer. This review briefly describes the pathogenesis of cervical cancer and discusses in detail the recent findings on the role of APOBEC in the molecular pathogenesis of cervical cancer.

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APOBEC enzymes deaminate cytidine to uridine and control diverse biological processes including viral restriction.

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APOBEC3, DNA/RNA-editing enzyme plays an important role in the molecular pathogenesis of cervical cancer.

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APOBEC3-mediated DNA editing leads to the accumulation of somatic mutations in tumors and HPV genome.

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Deregulation of APOBEC3 family genes cause genomic instability and result in drug resistance, and immune-evasion in tumors.

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.

Identifying germline APOBEC3B deletion and immune phenotype in Korean patients with operable breast cancer

BACKGROUND

Apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3B (APOBEC3B) is implicated in anti-viral immune response and cancer mutagenesis. Germline APOBEC3B deletion is associated with increased susceptibility to breast cancer. We aimed to evaluate the association between germline APOBEC3B deletion and clinical phenotypes of breast cancer in Korean patients with operable breast cancer.

METHODS

Mononuclear blood cell DNA of 103 patients with operable breast cancer was collected at Seoul National University Bundang Hospital in 2009. The DNA was sequenced to analyze APOBEC3B deletion status. Further, tumor-infiltrating lymphocytes (TILs) and programmed cell death-ligand 1 (PD-L1) expression in tumor cells were measured using immunohistochemistry.

RESULTS

Median age of breast cancer diagnosis was 46 (25-72). In APOBEC3B deletion analysis, 10 (9.7%), 36 (35.0%), and 57 (55.3%) patients were identified as two-copy deletion (A3B^del/del), one-one copy deletion (A3B^del/wt), and no deletion (A3B^wt/wt), respectively. For other cancer susceptibility gene alterations, 9 (8.7%) patients were identified as pathogenic variants: RAD51D (n = 1), GJB2 (n = 1), BRCA1 (n = 1), BRCA2 (n = 2), ATM (n = 1), USH2A (n = 1), RET (n = 1), BARD1 (n = 1). We observed no significant association between germline APOBEC3B deletion with any clinicopathologic features of breast cancer, such as age, family history of cancer, and bilateral breast cancer. Further, according to follow-up observations, APOBEC3B deletion was not predictive of disease-free survival. In ER+ subtype, a trend toward better survival was observed in patients with A3B^del/del genotype as compared to patients with A3B^del/wt and A3B^wt/wt genotype (log-rank, P = 0.25). In patients with sufficient tumor samples for the assessment of TIL (n = 63) and PD-L1 (n = 71), the A3B^del/del genotype was significantly associated with high TILs (> 10%) than other tumor genotypes (6/7 patients in A3B^del/del vs. 13/24 in A3B^del/wt vs. 15/32 in A3B^wt/wt: Fisher's exact test, P = 0.029). However, PD-L1 expression was not associated with APOBEC3B deletion status (1/7 patients > 1% PD-L1 in A3B^del/del vs. 4/26 in A3B^del/wt vs. 8/38 in A3B^wt/wt: P = 0.901).

CONCLUSION

We identified germline APOBEC3B deletion in 9.7% of Korean patients with operable breast cancer. The relationship between A3B^del/del genotype and high TILs suggests that patients carrying this genotype could be potential candidates for immunotherapy.

Immune Cell Infiltration and Identifying Genes of Prognostic Value in the Papillary Renal Cell Carcinoma Microenvironment by Bioinformatics Analysis

Papillary renal cell carcinoma (PRCC) is one of the most common histological subtypes of renal cell carcinoma. Type 1 and type 2 PRCC are reported to be clinically and biologically distinct. However, little is known about immune infiltration and the expression patterns of immune-related genes in these two histologic subtypes, thereby limiting the development of immunotherapy for PRCC. Thus, we analyzed the expression of 22 immune cells in type 1 and type 2 PRCC tissues by combining The Cancer Genome Atlas (TCGA) database with the ESTIMATE and CIBERSORT algorithms. Subsequently, we extracted a list of differentially expressed genes associated with the immune microenvironment. Multichip mRNA microarray data sets for PRCC were downloaded from the Gene Expression Omnibus (GEO) to further validate our findings. We found that the immune scores and stromal scores were associated with overall survival in patients with type 2 PRCC rather than type 1 PRCC. Tumor-infiltrating M1 and M2 macrophages could predict the clinical outcome by reflecting the host's immune capacity against type 2 PRCC. Furthermore, CCL19/CCR7, CXCL12/CXCR4, and CCL20/CCR6 were shown to be potential new targets for tumor gene therapy in type 2 PRCC. Our findings provide valuable resources for improving immunotherapy for PRCC.

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.

APOBEC3B expression and its prognostic potential in breast cancer

Apolipoprotein B mRNA editing enzyme catalytic subunit 3B (APOBEC3B) mRNA expression is associated with the poor prognosis of estrogen receptor positive (ER+) breast cancer. However, the clinical relevance of APOBEC3B protein expression in patients with breast cancer remains unclear. The present study evaluated the association of APOBEC3B protein expression with clinicopathological features, as well as survival outcomes of patients with breast cancer. Furthermore, the association between APOBEC3B protein expression and tumor infiltrating lymphocytes (TILs) was investigated. APOBEC3B protein expression in 120 patients with breast cancer was evaluated via immunohistochemistry, using a constructed tumor microarray, and TILs were analyzed by hematoxylin and eosin staining. The relevance of APOBEC3B mRNA expression in breast cancer was assessed using a Kaplan-Meier Plotter online tool, as well as the Tumor Immune Estimation Response and The Cancer Genome Atlas databases. The present study assessed APOBEC3B expression in 116 patients with breast cancer and demonstrated that protein expression was significantly associated with ER and progesterone receptor expression, as well as different subtypes of breast cancer. Notably, APOEBC3B protein expression was significantly associated with TILs. Overall, high expression levels of APOBEC3B protein and high levels of TILs were indicative of longer disease-free survival rate. High APOBEC3B mRNA expression was associated with poor relapse-free survival rate, overall survival rate and distant metastasis-free survival rate in patients with breast cancer, particularly for the Luminal A subtype. APOBEC3B mRNA expression was also indicated to be associated with the immune status of patients with breast cancer. Overall, the results of the present study demonstrated that APOBEC3B mRNA and protein expression levels presented different prognostic values in the survival of patients with breast cancer. However, both APOBEC3B mRNA and protein expression levels were associated with TILs in breast cancer. Therefore, APOBEC3B may be a prognostic biomarker for breast cancer.

Clinical implications of APOBEC3A and 3B expression in patients with breast cancer

Background

We aimed to evaluate the expression of APOBEC3A (A3A), 3B (A3B) mRNA, and germline APOBEC3A/B deletion polymorphism in patients with breast cancers and to investigate the correlation between their expressions and clinicopathological characteristics.

Methods

RNA and DNA samples were extracted from 138 breast cancer tissues and adjacent normal breast tissues. The levels of A3A and A3B mRNA transcripts were determined using quantitative real-time polymerase chain reaction. Insertion and deletion PCR assays were performed to detect the A3B deletion allele. The serum concentrations of soluble programmed death-ligand 1 (sPD-L1) and interferon gamma were determined using enzyme-linked immunosorbent assays.

Results

A3B mRNA expression levels were significantly higher in triple-negative breast cancers compared to hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancers. Older age of the patient and high ki-67 expression were associated with increased expression levels of A3A and A3B mRNA. Advanced tumor stage, presence of lymph node involvement, and high histological grade were associated with increased expression levels of A3A mRNA. The APOBEC3A/B deletion allele was found in 77 (55.8%) patients. TP53 and PIK3CA mutations were detected in 62 (44.9%) and 31 (22.5%) patients, respectively. The presence of a PIK3CA mutation was associated with lower A3A mRNA expression levels. There was a weak positive relationship between A3A mRNA expression levels and serum sPD-L1 levels.

Conclusions

There was a difference in A3B mRNA expression levels according to breast cancer subtypes, and high levels of A3A and A3B mRNA expressions were associated with an aggressive phenotype. There was a high incidence of APOBEC3A/B deletion allele. Further studies are needed to identify the clinical significance of APOBEC in Asian patients with breast cancer.

Immune gene expression profiling reveals heterogeneity in luminal breast tumors

Background

Heterogeneity of immune gene expression patterns of luminal breast cancer (BC), which is clinically heterogeneous and overall considered as low immunogenic, has not been well studied especially in non-European populations. Here, we aimed at characterizing the immune gene expression profile of luminal BC in an Asian population and associating it with patient characteristics and tumor genomic features.

Methods

We performed immune gene expression profiling of tumor and adjacent normal tissue in 92 luminal BC patients from Hong Kong using RNA-sequencing data and used unsupervised consensus clustering to stratify tumors. We then used luminal patients from The Cancer Genome Atlas (TCGA, N = 564) and a Korean breast cancer study (KBC, N = 112) as replication datasets.

Results

Based on the expression of 130 immune-related genes, luminal tumors were stratified into three distinct immune subtypes. Tumors in one subtype showed higher level of tumor-infiltrating lymphocytes (TILs), characterized by T cell gene activation, higher expression of immune checkpoint genes, higher nonsynonymous mutation burden, and higher APOBEC-signature mutations, compared with other luminal tumors. The high-TIL subtype was also associated with lower ESR1/ESR2 expression ratio and increasing body mass index. The comparison of the immune profile in tumor and matched normal tissue suggested a tumor-derived activation of specific immune responses, which was only seen in high-TIL patients. Tumors in a second subtype were characterized by increased expression of interferon-stimulated genes and enrichment for TP53 somatic mutations. The presence of three immune subtypes within luminal BC was replicated in TCGA and KBC, although the pattern was more similar in Asian populations. The germline APOBEC3B deletion polymorphism, which is prevalent in East Asian populations and was previously linked to immune activation, was not associated with immune subtypes in our study. This result does not support the hypothesis that the germline APOBEC3B deletion polymorphism is the driving force for immune activation in breast tumors in Asian populations.

Conclusion

Our findings suggest that immune gene expression and associated genomic features could be useful to further stratify luminal BC beyond the current luminal A/B classification and a subset of luminal BC patients may benefit from checkpoint immunotherapy, at least in Asian populations.

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.

Insights Into Breast Cancer in the East vs the West: A Review

Importance

During the past few decades, the incidence of breast cancer (BC) has been increasing rapidly in East Asia, and BC is currently the most common cancer in several countries. The rising incidence is likely related to changing lifestyle and environmental factors in addition to the increase in early diagnosis with BC awareness and screening. The understanding and management of BC are generally based on research and data from the West. However, emerging differences in BC epidemiology and tumor and host biology in Asian populations may be clinically relevant.

Observations

A higher proportion of premenopausal BCs occur in Asia, although this factor is possibly an age-cohort effect. Although the relative frequencies of different immunohistochemical subtypes of BC may be similar between the East and West, the higher prevalence of luminal B subtypes with more frequent mutations in TP53 may be confounded by disparities in early detection. In addition, Asian BCs appear to harbor a more immune-active microenvironment than BCs in the West. The spectra of germline mutations in BC predisposition genes and single-nucleotide polymorphisms contributing to BC risk vary with ethnicity as well. Differences in tolerability of certain cytotoxic and targeted agents used in BC treatment may be associated with pharmacogenomic factors, whereas the lower body mass of the average woman in East Asia may contribute to higher toxicities from drugs administered at fixed doses. Phenotypic characteristics, such as lower breast volume, may influence the type of surgery performed in East Asian women. On the other hand, increased breast density may affect the sensitivity of mammography in detecting BCs, limiting the benefits of screening mammography.

Conclusions and Relevance

Breast cancer has become a major health problem in Asia. The inclusion of more women from Asia in clinical trials and epidemiologic and translational studies may help unravel the interethnic heterogeneity of BCs and elucidate the complex interplay between environmental and intrinsic factors in its pathogenesis. These insights may help to refine prevention, diagnosis, and management strategies for BC in the setting of ethnic diversity.

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.

The APOBEC3 genes and their role in cancer: insights from human papillomavirus

The interaction between human papillomaviruses (HPV) and the apolipoprotein-B mRNA-editing catalytic polypeptide-like (APOBEC)3 (A3) genes has garnered increasing attention in recent years, with considerable efforts focused on understanding their apparent roles in both viral editing and in HPV-driven carcinogenesis. Here, we review these developments and highlight several outstanding questions in the field. We consider whether editing of the virus and mutagenesis of the host are linked or whether both are essentially separate events, coincidentally mediated by a common or distinct A3 enzymes. We discuss the viral mechanisms and cellular signalling pathways implicated in A3 induction in virally infected cells and examine which of the A3 enzymes might play the major role in HPV-associated carcinogenesis and in the development of therapeutic resistance. We consider the parallels between A3 induction in HPV-infected cells and what might be causing aberrant A3 activity in HPV-independent cancers such as those arising in the bladder, lung and breast. Finally, we discuss the implications of ongoing A3 activity in tumours under treatment and the therapeutic opportunities that this may present.

Characterization of cancer genomic heterogeneity by next-generation sequencing advances precision medicine in cancer treatment

Cancer is a heterogeneous disease with unique genomic and phenotypic features that differ between individual patients and even among individual tumor regions. In recent years, large-scale genomic studies and new next-generation sequencing technologies have uncovered more scientific details about tumor heterogeneity, with significant implications for the choice of specific molecular biomarkers and clinical decision making. Genomic heterogeneity significantly contributes to the generation of a diverse cell population during tumor development and progression, representing a determining factor for variation in tumor treatment response. It has been considered a prominent contributor to therapeutic failure, and increases the likelihood of resistance to future therapies in most common cancers. The understanding of molecular heterogeneity in cancer is a fundamental component of precision oncology, enabling the identification of genomic alteration of key genes and pathways that can be targeted therapeutically. Here, we review the emerging knowledge of tumor genomics and heterogeneity, as well as potential implications for precision medicine in cancer treatment and new therapeutic discoveries. An analysis and interpretation of the TCGA database was included.

Viral subversion of APOBEC3s: Lessons for anti-tumor immunity and tumor immunotherapy

APOBEC3s (A3) are endogenous DNA-editing enzymes that are expressed in immune cells including T lymphocytes. A3s target and mutate the genomes of retroviruses that infect immune tissues such as the human immunodeficiency virus (HIV). Therefore, A3s were classically defined as host anti-viral innate immune factors. In contrast, we and others showed that A3s can also benefit the virus by mediating escape from adaptive immune recognition and drugs. Crucially, whether A3-mediated mutations help or hinder HIV, is not up to chance. Rather, the virus has evolved multiple mechanisms to actively and maximally subvert A3 activity. More recently, extensive A3 mutational footprints in tumor genomes have been observed in many different cancers. This suggests a role for A3s in cancer initiation and progression. On the other hand, multiple anti-tumor activities of A3s have also come to light, including impact on immune checkpoint molecules and possible generation of tumor neo-antigens. Here, we review the studies that reshaped the view of A3s from anti-viral innate immune agents to host factors exploited by HIV to escape from immune recognition. Viruses and tumors share many attributes, including rapid evolution and adeptness at exploiting mutations. Given this parallel, we then discuss the pro- and anti-tumor roles of A3s, and suggest that lessons learned from studying A3s in the context of anti-viral immunity can be applied to tumor immunotherapy.

Human APOBEC3B interacts with the heterogenous nuclear ribonucleoprotein A3 in cancer cells

Human APOBEC3B (A3B), like other APOBEC3 members, is a cytosine deaminase which causes hypermutation of single stranded genome. Recent studies have shown that A3B is predominantly elevated in multiple cancer tissues and cell lines such as the bladder, cervix, lung, head and neck, and breast. Upregulation and activation of A3B in developing tumors can cause an unexpected cluster of mutations which promote cancer development and progression. The cellular proteins which facilitate A3B function through direct or indirect interactions remain largely unknown. In this study, we performed LC-MS-based proteomics to identify cellular proteins which coimmunoprecipitated with A3B. Our results indicated a specific interaction of A3B with hnRNP A3 (heterogeneous nuclear ribonucleoprotein). This interaction was verified by co-immunoprecipitation and was found to be RNA-dependent. Furthermore, A3B and hnRNP A3 colocalized as evident from immunofluorescence analysis.

APOBEC3A/B deletion polymorphism and cancer risk

Activity of the apolipoprotein B mRNA editing enzyme, catalytic-polypeptide-like (APOBEC) enzymes has been linked to specific mutational processes in human cancer genomes. A germline APOBEC3A/B deletion polymorphism is associated with APOBEC-dependent mutational signatures, and the deletion allele has been reported to confer an elevated risk of some cancers in Asian populations, while the results in European populations, so far, have been conflicting. We genotyped the APOBEC3A/B deletion polymorphism in a large population-based sample consisting of 11 106 Caucasian (Norwegian) individuals, including 7279 incident cancer cases (1769 breast, 1360 lung, 1585 colon, and 2565 prostate cancer) and a control group of 3827 matched individuals without cancer (1918 females and 1909 males) from the same population. Overall, the APOBEC3A/B deletion polymorphism was not associated with risk of any of the four cancer types. However, in subgroup analyses stratified by age, we found that the deletion allele was associated with increased risk for lung cancer among individuals <50 years of age (OR 2.17, CI 1.19-3.97), and that the association was gradually reduced with increasing age (P = 0.01). A similar but weaker pattern was observed for prostate cancer. In support of these findings, the APOBEC3A/B deletion was associated with young age at diagnosis among the cancer cases for both cancer forms (lung cancer: P = 0.02; dominant model and prostate cancer: P = 0.03; recessive model). No such associations were observed for breast or colon cancer.

Inherited mutations in BRCA1 and BRCA2 in an unselected multiethnic cohort of Asian patients with breast cancer and healthy controls from Malaysia

BACKGROUND

Genetic testing for BRCA1 and BRCA2 is offered typically to selected women based on age of onset and family history of cancer. However, current internationally accepted genetic testing referral guidelines are built mostly on data from cancer genetics clinics in women of European descent. To evaluate the appropriateness of such guidelines in Asians, we have determined the prevalence of germ line variants in an unselected cohort of Asian patients with breast cancer and healthy controls.

METHODS

Germ line DNA from a hospital-based study of 2575 unselected patients with breast cancer and 2809 healthy controls were subjected to amplicon-based targeted sequencing of exonic and proximal splice site junction regions of BRCA1 and BRCA2 using the Fluidigm Access Array system, with sequencing conducted on a Illumina HiSeq2500 platform. Variant calling was performed with GATK UnifiedGenotyper and were validated by Sanger sequencing.

RESULTS

Fifty-five (2.1%) BRCA1 and 66 (2.6%) BRCA2 deleterious mutations were identified among patients with breast cancer and five (0.18%) BRCA1 and six (0.21%) BRCA2 mutations among controls. One thousand one hundred and eighty-six (46%) patients and 97 (80%) carriers fulfilled the National Comprehensive Cancer Network guidelines for genetic testing.

CONCLUSION

Five per cent of unselected Asian patients with breast cancer carry deleterious variants in BRCA1 or BRCA2. While current referral guidelines identified the majority of carriers, one in two patients would be referred for genetic services. Given that such services are largely unavailable in majority of low-resource settings in Asia, our study highlights the need for more efficient guidelines to identify at-risk individuals in Asia.

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

APOBEC3B, in addition to other members of the APOBEC3 gene family, has recently been intensively studied due to its identification as a gene whose activation in cancer is responsible for a specific pattern of massively occurring somatic mutations. It was recently shown that a common large deletion in the APOBEC3 cluster (the APOBEC3B deletion) may increase the risk of breast cancer. However, conflicting evidence regarding this association was also reported. In the first step of our study, using different approaches, including an in-house designed multiplex ligation-dependent probe amplification assay, we analyzed the structure of the deletion and showed that although the breakpoints are located in highly homologous regions, which may generate recurrent occurrence of similar but not identical deletions, there is no sign of deletion heterogeneity. This knowledge allowed us to distinguish transcripts of all affected genes, including the highly homologous canonical APOBEC3A and APOBEC3B, and the hybrid APOBEC3A/APOBEC3B gene. We unambiguously confirmed the presence of the hybrid transcript and showed that the APOBEC3B deletion negatively correlates with APOBEC3A and APOBEC3B expression and positively correlates with APOBEC3A/APOBEC3B expression, whose mRNA level is >10-fold and >1500-fold lower than the level of APOBEC3A and APOBEC3B, respectively. In the next step, we performed a large-scale association study in three different cohorts (2972 cases and 3682 controls) and showed no association of the deletion with breast cancer, familial breast cancer or ovarian cancer. Further, we conducted a meta-analysis that confirmed the lack of the association of the deletion with breast cancer in non-Asian populations.

Precancer Atlas to Drive Precision Prevention Trials

Cancer development is a complex process driven by inherited and acquired molecular and cellular alterations. Prevention is the holy grail of cancer elimination, but making this a reality will take a fundamental rethinking and deep understanding of premalignant biology. In this Perspective, we propose a national concerted effort to create a Precancer Atlas (PCA), integrating multi-omics and immunity - basic tenets of the neoplastic process. The biology of neoplasia caused by germline mutations has led to paradigm-changing precision prevention efforts, including: tumor testing for mismatch repair (MMR) deficiency in Lynch syndrome establishing a new paradigm, combinatorial chemoprevention efficacy in familial adenomatous polyposis (FAP), signal of benefit from imaging-based early detection research in high-germline risk for pancreatic neoplasia, elucidating early ontogeny in BRCA1-mutation carriers leading to an international breast cancer prevention trial, and insights into the intricate germline-somatic-immunity interaction landscape. Emerging genetic and pharmacologic (metformin) disruption of mitochondrial (mt) respiration increased autophagy to prevent cancer in a Li-Fraumeni mouse model (biology reproduced in clinical pilot) and revealed profound influences of subtle changes in mt DNA background variation on obesity, aging, and cancer risk. The elaborate communication between the immune system and neoplasia includes an increasingly complex cellular microenvironment and dynamic interactions between host genetics, environmental factors, and microbes in shaping the immune response. Cancer vaccines are in early murine and clinical precancer studies, building on the recent successes of immunotherapy and HPV vaccine immune prevention. Molecular monitoring in Barrett's esophagus to avoid overdiagnosis/treatment highlights an important PCA theme. Next generation sequencing (NGS) discovered age-related clonal hematopoiesis of indeterminate potential (CHIP). Ultra-deep NGS reports over the past year have redefined the premalignant landscape remarkably identifying tiny clones in the blood of up to 95% of women in their 50s, suggesting that potentially premalignant clones are ubiquitous. Similar data from eyelid skin and peritoneal and uterine lavage fluid provide unprecedented opportunities to dissect the earliest phases of stem/progenitor clonal (and microenvironment) evolution/diversity with new single-cell and liquid biopsy technologies. Cancer mutational signatures reflect exogenous or endogenous processes imprinted over time in precursors. Accelerating the prevention of cancer will require a large-scale, longitudinal effort, leveraging diverse disciplines (from genetics, biochemistry, and immunology to mathematics, computational biology, and engineering), initiatives, technologies, and models in developing an integrated multi-omics and immunity PCA - an immense national resource to interrogate, target, and intercept events that drive oncogenesis. Cancer Res; 77(7); 1510-41. ©2017 AACR.

Risks at the DNA Replication Fork: Effects upon Carcinogenesis and Tumor Heterogeneity

The ability of all organisms to copy their genetic information via DNA replication is a prerequisite for cell division and a biological imperative of life. In multicellular organisms, however, mutations arising from DNA replication errors in the germline and somatic cells are the basis of genetic diseases and cancer, respectively. Within human tumors, replication errors additionally contribute to mutator phenotypes and tumor heterogeneity, which are major confounding factors for cancer therapeutics. Successful DNA replication involves the coordination of many large-scale, complex cellular processes. In this review, we focus on the roles that defects in enzymes that normally act at the replication fork and dysregulation of enzymes that inappropriately damage single-stranded DNA at the fork play in causing mutations that contribute to carcinogenesis. We focus on tumor data and experimental evidence that error-prone variants of replicative polymerases promote carcinogenesis and on research indicating that the primary target mutated by APOBEC (apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like) cytidine deaminases is ssDNA present at the replication fork. Furthermore, we discuss evidence from model systems that indicate replication stress and other cancer-associated metabolic changes may modulate mutagenic enzymatic activities at the replication fork.

Assessment of an APOBEC3B truncating mutation, c.783delG, in patients with breast cancer

PURPOSE

APOBEC3B belongs to the family of DNA-editing enzymes. A copy number variant targeting the genomic APOBEC3A-APOBEC3B locus has a significant impact on breast cancer risk, but the relative contribution of APOBEC3B is uncertain. In this study, we investigate a loss-of-function mutation that selectively targets APOBEC3B, for its association with breast cancer risk.

METHODS

We performed exome sequencing on genomic DNA samples of 6 Byelorussian patients with familial breast cancer. We then studied through mutation-specific genotyping four hospital-based breast cancer case-control series from Belarus, Russia, Germany, and Iran, respectively, comprising a total of 3070 breast cancer patients and 2878 healthy females. Results were evaluated using fixed-effects meta-analyses.

RESULTS

Exome sequencing uncovered a frameshift mutation, APOBEC3B*c.783delG, that was recurrent in the study populations. Subsequent genotyping identified this mutation in 23 additional breast cancer cases and 9 healthy female controls, with an adjusted Odds Ratio 2.29 (95% CI 1.04; 5.03, P = 0.04) in the combined analysis. There was an enrichment of the c.783delG mutation in patients with breast cancer diagnosed below 50 years of age (OR 3.22, 95% CI 1.37; 7.56, P = 0.007).

CONCLUSIONS

APOBEC3B*c.783delG showed evidence of modest association with breast cancer and seemed to contribute to earlier onset of the disease. These results may need to be reconciled with proposals to consider APOBEC3B as a possible therapeutic target in breast cancer.

Leveraging premalignant biology for immune-based cancer prevention

Prevention is an essential component of cancer eradication. Next-generation sequencing of cancer genomes and epigenomes has defined large numbers of driver mutations and molecular subgroups, leading to therapeutic advances. By comparison, there is a relative paucity of such knowledge in premalignant neoplasia, which inherently limits the potential to develop precision prevention strategies. Studies on the interplay between germ-line and somatic events have elucidated genetic processes underlying premalignant progression and preventive targets. Emerging data hint at the immune system's ability to intercept premalignancy and prevent cancer. Genetically engineered mouse models have identified mechanisms by which genetic drivers and other somatic alterations recruit inflammatory cells and induce changes in normal cells to create and interact with the premalignant tumor microenvironment to promote oncogenesis and immune evasion. These studies are currently limited to only a few lesion types and patients. In this Perspective, we advocate a large-scale collaborative effort to systematically map the biology of premalignancy and the surrounding cellular response. By bringing together scientists from diverse disciplines (e.g., biochemistry, omics, and computational biology; microbiology, immunology, and medical genetics; engineering, imaging, and synthetic chemistry; and implementation science), we can drive a concerted effort focused on cancer vaccines to reprogram the immune response to prevent, detect, and reject premalignancy. Lynch syndrome, clonal hematopoiesis, and cervical intraepithelial neoplasia which also serve as models for inherited syndromes, blood, and viral premalignancies, are ideal scenarios in which to launch this initiative.

Human endogenous retroviruses and cancer

Human endogenous retroviruses (HERVs) are retroviruses that infected human genome millions of years ago and have persisted throughout human evolution. About 8% of our genome is composed of HERVs, most of which are nonfunctional because of epigenetic control or deactivating mutations. However, a correlation between HERVs and human cancer has been described and many tumors, such as melanoma, breast cancer, germ cell tumors, renal cancer or ovarian cancer, express HERV proteins, mainly HERV-K (HML6) and HERV-K (HML2). Although the causative role of HERVs in cancer is controversial, data from animal models demonstrated that endogenous retroviruses are potentially oncogenic. HERV protein expression in human cells generates an immune response by activating innate and adaptive immunities. Some HERV-derived peptides have antigenic properties. For example, HERV-K (HML-6) encodes the HER-K MEL peptide recognized by CD8+ lymphocytes. In addition, HERVs are two-edged immunomodulators. HERVs show immunosuppressive activity. The presence of genomic retroviral elements in host-cell cytosol may activate an interferon type I response. Therefore, targeting HERVs through cellular vaccines or immunomodulatory drugs combined with checkpoint inhibitors is attracting interest because they could be active in human tumors.