Viral whole genome sequencing reveals high variations in APOBEC3 editing between HPV risk categories.

High-risk human papillomavirus (HPV) infections are responsible for cervical cancer. However, little is known about the differences between HPV types and risk categories regarding their genetic diversity and particularly APOBEC3-induced mutations - which contribute to the innate immune response to HPV. Using a capture-based next-generation sequencing, 156 HPV whole genome sequences covering 43 HPV types were generated from paired cervical and anal swabs of 30 Togolese female sex workers (FSWs) sampled in 2017. Genetic diversity and APOBEC3-induced mutations were assessed at the viral whole genome and gene levels. Thirty-four pairwise sequence comparisons covering 24 HPV types in cervical and anal swabs revealed identical infections in the two anatomical sites. Differences in genetic diversity among HPV types was observed between patients. The E6 gene was significantly less conserved in low-risk HPVs (lrHPVs) compared to high-risk HPVs (hrHPVs) (p = 0.009). APOBEC3-induced mutations were found to be more common in lrHPVs than in hrHPVs (p = 0.005), supported by our data and by using large HPV sequence collections from the GenBank database. Focusing on the most common lrHPVs 6 and 11 and hrHPVs 16 and 18, APOBEC3-induced mutations were predominantly found in the E4 and E6 genes in lrHPVs, but were almost absent in these genes in hrHPVs. The variable APOBEC3 mutational signatures could contribute to the different oncogenic potentials between HPVs. Further studies are needed to conclusively determine whether APOBEC3 editing levels are associated to the carcinogenic potential of HPVs at the type and sublineage scales.

The genomic and transcriptomic landscape of metastastic urothelial cancer.

Metastatic urothelial carcinoma (mUC) is a lethal cancer, with limited therapeutic options. Large-scale studies in early settings provided critical insights into the genomic and transcriptomic characteristics of non-metastatic UC. The genomic landscape of mUC remains however unclear. Using Whole Exome (WES) and mRNA sequencing (RNA-seq) performed on metastatic biopsies from 111 patients, we show that driver genomic alterations from mUC were comparable to primary UC (TCGA data). APOBEC, platin, and HRD mutational signatures are the most prevalent in mUC, identified in 56%, 14%, and 9% of mUC samples, respectively. Molecular subtyping using consensus transcriptomic classification in mUC shows enrichment in neuroendocrine subtype. Paired samples analysis reveals subtype heterogeneity and temporal evolution. We identify potential therapeutic targets in 73% of mUC patients, of which FGFR3 (26%), ERBB2 (7%), TSC1 (7%), and PIK3CA (13%) are the most common. NECTIN4 and TACSTD2 are highly expressed regardless of molecular subtypes, FGFR3 alterations and sites of metastases.

RADD: A real-time FRET-based biochemical assay for DNA deaminase studies.

In recent years, the connection between APOBEC3 cytosine deaminases and cancer mutagenesis has become ever more apparent. This growing awareness and lack of inhibitory drugs has created a distinct need for biochemical tools that can be used to identify and characterize potential inhibitors of this family of enzymes. In response to this challenge, we have developed a Real-time APOBEC3-mediated DNA Deamination (RADD) assay. The RADD assay provides a rapid, real-time fluorescence readout of APOBEC3 DNA deamination and serves as a crucial addition to the existing APOBEC3 biochemical and cellular toolkit. This method improves upon contemporary DNA deamination assays by offering a more rapid and quantifiable readout as well as providing a platform that is readily adaptable to a high-throughput format for inhibitor discovery. In this chapter we provide a detailed guide for the usage of the RADD assay for the characterization of APOBEC3 enzymes and potential inhibitors.

APOBEC family reshapes the immune microenvironment and therapy sensitivity in clear cell renal cell carcinoma.

Emerging evidence suggests that the APOBEC family is implicated in multiple cancers and might be utilized as a new target for cancer detection and treatment. However, the dysregulation and clinical implication of the APOBEC family in clear cell renal cell cancer (ccRCC) remain elusive. TCGA multiomics data facilitated a comprehensive exploration of the APOBEC family across cancers, including ccRCC. Remodeling analysis classified ccRCC patients into two distinct subgroups: APOBEC family pattern cancer subtype 1 (APCS1) and subtype 2 (APCS2). The study investigated differences in clinical parameters, tumor immune microenvironment, therapeutic responsiveness, and genomic mutation landscapes between these subtypes. An APOBEC family-related risk model was developed and validated for predicting ccRCC patient prognosis, demonstrating good sensitivity and specificity. Finally, the overview of APOBEC3B function was investigated in multiple cancers and verified in clinical samples. APCS1 and APCS2 demonstrated considerably distinct clinical features and biological processes in ccRCC. APCS1, an aggressive subtype, has advanced clinical stage and a poor prognosis. APCS1 exhibited an oncogenic and metabolically active phenotype. APCS1 also exhibited a greater tumor mutation load and immunocompromised condition, resulting in immunological dysfunction and immune checkpoint treatment resistance. The genomic copy number variation of APCS1, including arm gain and loss, was much more than that of APCS2, which may help explain the tired immune system. Furthermore, the two subtypes have distinct drug sensitivity patterns in clinical specimens and matching cell lines. Finally, we developed a predictive risk model based on subtype biomarkers that performed well for ccRCC patients and validated the clinical impact of APOBEC3B. Aberrant APOBEC family expression patterns might modify the tumor immune microenvironment by increasing the genome mutation frequency, thus inducing an immune-exhausted phenotype. APOBEC family-based molecular subtypes could strengthen the understanding of ccRCC characterization and guide clinical treatment. Targeting APOBEC3B may be regarded as a new therapeutic target for ccRCC.

Evolutionary trajectory and characteristics of Mpox virus in 2023 based on a large-scale genomic surveillance in Shenzhen, China.

The global epidemic of Mpox virus (MPXV) continues, and a local outbreak has occurred in Shenzhen city since June 2023. Herein, the evolutionary trajectory and characteristics of MPXV in 2023 were analyzed using 92 MPXV sequences from the Shenzhen outbreak and the available genomes from GISAID and GenBank databases. Phylogenetic tracing of the 92 MPXVs suggests that MPXVs in Shenzhen may have multiple sources of importation, and two main transmission chains have been established. The combination of phylogenetic relationships, epidemiological features, and mutation characteristics supports the emergence of a new lineage C.1.1. Together with the B.1 lineage diverging from the A.1 lineage, C.1.1 lineage diverging from the C.1 lineage may serve as another significant evolutionary events of MPXV. Moreover, increasing apolipoprotein B mRNA-editing catalytic polypeptide-like 3 (APOBEC3) related mutations, higher rate of missense mutations, and less mutations in the non-coding regions have been shown during MPXV evolution. Host regulation proteins of MPXV have accumulated considerable amino acid mutations since the B.1 lineage, and a lineage-defining APOBEC3-related mutation that disrupts the N2L gene encoding a viral innate immune modulator has been identified in the C.1.1 lineage. In summary, our study provides compelling evidence for the ongoing evolution of MPXV with specific features.

Hypomorphic mutation in the large subunit of replication protein A affects mutagenesis by human APOBEC cytidine deaminases in yeast.

Human APOBEC single-strand (ss) specific DNA and RNA cytidine deaminases change cytosines to uracils (U's) and function in antiviral innate immunity and RNA editing and can cause hypermutation in chromosomes. The resulting U's can be directly replicated, resulting in C to T mutations, or U-DNA glycosylase can convert the U's to abasic (AP) sites which are then fixed as C to T or C to G mutations by translesion DNA polymerases. We noticed that in yeast and in human cancers, contributions of C to T and C to G mutations depend on the origin of ssDNA mutagenized by APOBECs. Since ssDNA in eukaryotic genomes readily binds to replication protein A (RPA) we asked if RPA could affect APOBEC-induced mutation spectrum in yeast. For that purpose, we expressed human APOBECs in the wild-type (WT) yeast and in strains carrying a hypomorph mutation rfa1-t33 in the large RPA subunit. We confirmed that the rfa1-t33 allele can facilitate mutagenesis by APOBECs. We also found that the rfa1-t33 mutation changed the ratio of APOBEC3A-induced T to C and T to G mutations in replicating yeast to resemble a ratio observed in long persistent ssDNA in yeast and in cancers. We present the data suggesting that RPA may shield APOBEC formed U's in ssDNA from Ung1, thereby facilitating C to T mutagenesis through the accurate copying of U's by replicative DNA polymerases. Unexpectedly, we also found that for U's shielded from Ung1 by WT RPA, the mutagenic outcome is reduced in the presence of translesion DNA polymerase zeta.

Apobec-mediated retroviral hypermutation in vivo is dependent on mouse strain.

Replication of the complex retrovirus mouse mammary tumor virus (MMTV) is antagonized by murine Apobec3 (mA3), a member of the Apobec family of cytidine deaminases. We have shown that MMTV-encoded Rem protein inhibits proviral mutagenesis by the Apobec enzyme, activation-induced cytidine deaminase (AID) during viral replication in BALB/c mice. To further study the role of Rem in vivo, we have infected C57BL/6 (B6) mice with a superantigen-independent lymphomagenic strain of MMTV (TBLV-WT) or a mutant strain that is defective in Rem and its cleavage product Rem-CT (TBLV-SD). Compared to BALB/c, B6 mice were more susceptible to TBLV infection and tumorigenesis. Furthermore, unlike MMTV, TBLV induced T-cell tumors in B6 µMT mice, which lack membrane-bound IgM and conventional B-2 cells. At limiting viral doses, loss of Rem expression in TBLV-SD-infected B6 mice accelerated tumorigenesis compared to TBLV-WT in either wild-type B6 or AID-knockout mice. Unlike BALB/c results, high-throughput sequencing indicated that proviral G-to-A or C-to-T mutations were unchanged regardless of Rem expression in B6 tumors. However, knockout of both AID and mA3 reduced G-to-A mutations. Ex vivo stimulation showed higher levels of mA3 relative to AID in B6 compared to BALB/c splenocytes, and effects of agonists differed in the two strains. RNA-Seq revealed increased transcripts related to growth factor and cytokine signaling in TBLV-SD-induced tumors relative to TBLV-WT-induced tumors, consistent with another Rem function. Thus, Rem-mediated effects on tumorigenesis in B6 mice are independent of Apobec-mediated proviral hypermutation.

The role of distinct APOBEC/ADAR mRNA levels in mutational signatures linked to aging and ultraviolet radiation.

The APOBEC/AID family is known for its mutator activity, and recent evidence also supports the potential impact of ADARs. Furthermore, the mutator impacts of APOBEC/ADAR mutations have not yet been investigated. Assessment of pancancer TCGA exomes identified enriched somatic variants among exomes with nonsynonymous APOBEC1, APOBEC3B, APOBEC3C, ADAR, and ADARB1 mutations, compared to exomes with synonymous ones. Principal component (PC) analysis reduced the number of potential players to eight in cancer exomes/genomes, and to five in cancer types. Multivariate regression analysis was used to assess the impact of the PCs on each COSMIC mutational signature among pancancer exomes/genomes and particular cancers, identifying several novel links, including SBS17b, SBS18, and ID7 mainly determined by APOBEC1 mRNA levels; SBS40, ID1, and ID2 by age; SBS3 and SBS16 by APOBEC3A/APOBEC3B mRNA levels; ID5 and DBS9 by DNA repair/replication (DRR) defects; and SBS7a-d, SBS38, ID4, ID8, ID13, and DBS1 by ultraviolet (UV) radiation/ADARB1 mRNA levels. APOBEC/ADAR mutations appeared to potentiate the impact of DRR defects on several mutational signatures, and some factors seemed to inversely affect certain signatures. These findings potentially implicate certain APOBEC/ADAR mutations/mRNA levels in distinct mutational signatures, particularly APOBEC1 mRNA levels in aging-related signatures and ADARB1 mRNA levels in UV radiation-related signatures.

Potential Role of APOBEC3 Family Proteins in SARS-CoV-2 Replication.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has acquired multiple mutations since its emergence. Analyses of the SARS-CoV-2 genomes from infected patients exhibit a bias toward C-to-U mutations, which are suggested to be caused by the apolipoprotein B mRNA editing enzyme polypeptide-like 3 (APOBEC3, A3) cytosine deaminase proteins. However, the role of A3 enzymes in SARS-CoV-2 replication remains unclear. To address this question, we investigated the effect of A3 family proteins on SARS-CoV-2 replication in the myeloid leukemia cell line THP-1 lacking A3A to A3G genes. The Wuhan, BA.1, and BA.5 variants had comparable viral replication in parent and A3A-to-A3G-null THP-1 cells stably expressing angiotensin-converting enzyme 2 (ACE2) protein. On the other hand, the replication and infectivity of these variants were abolished in A3A-to-A3G-null THP-1-ACE2 cells in a series of passage experiments over 20 days. In contrast to previous reports, we observed no evidence of A3-induced SARS-CoV-2 mutagenesis in the passage experiments. Furthermore, our analysis of a large number of publicly available SARS-CoV-2 genomes did not reveal conclusive evidence for A3-induced mutagenesis. Our studies suggest that A3 family proteins can positively contribute to SARS-CoV-2 replication; however, this effect is deaminase-independent.

Replication timing alterations are associated with mutation acquisition during breast and lung cancer evolution.

During each cell cycle, the process of DNA replication timing is tightly regulated to ensure the accurate duplication of the genome. The extent and significance of alterations in this process during malignant transformation have not been extensively explored. Here, we assess the impact of altered replication timing (ART) on cancer evolution by analysing replication-timing sequencing of cancer and normal cell lines and 952 whole-genome sequenced lung and breast tumours. We find that 6%-18% of the cancer genome exhibits ART, with regions with a change from early to late replication displaying an increased mutation rate and distinct mutational signatures. Whereas regions changing from late to early replication contain genes with increased expression and present a preponderance of APOBEC3-mediated mutation clusters and associated driver mutations. We demonstrate that ART occurs relatively early during cancer evolution and that ART may have a stronger correlation with mutation acquisition than alterations in chromatin structure.

DNA mismatch and damage patterns revealed by single-molecule sequencing.

Mutations accumulate in the genome of every cell of the body throughout life, causing cancer and other diseases1,2. Most mutations begin as nucleotide mismatches or damage in one of the two strands of the DNA before becoming double-strand mutations if unrepaired or misrepaired3,4. However, current DNA-sequencing technologies cannot accurately resolve these initial single-strand events. Here we develop a single-molecule, long-read sequencing method (Hairpin Duplex Enhanced Fidelity sequencing (HiDEF-seq)) that achieves single-molecule fidelity for base substitutions when present in either one or both DNA strands. HiDEF-seq also detects cytosine deamination-a common type of DNA damage-with single-molecule fidelity. We profiled 134 samples from diverse tissues, including from individuals with cancer predisposition syndromes, and derive from them single-strand mismatch and damage signatures. We find correspondences between these single-strand signatures and known double-strand mutational signatures, which resolves the identity of the initiating lesions. Tumours deficient in both mismatch repair and replicative polymerase proofreading show distinct single-strand mismatch patterns compared to samples that are deficient in only polymerase proofreading. We also define a single-strand damage signature for APOBEC3A. In the mitochondrial genome, our findings support a mutagenic mechanism occurring primarily during replication. As double-strand DNA mutations are only the end point of the mutation process, our approach to detect the initiating single-strand events at single-molecule resolution will enable studies of how mutations arise in a variety of contexts, especially in cancer and ageing.

A real-time biochemical assay for quantitative analyses of APOBEC-catalyzed DNA deamination.

Over the past decade, the connection between APOBEC3 cytosine deaminases and cancer mutagenesis has become increasingly apparent. This growing awareness has created a need for biochemical tools that can be used to identify and characterize potential inhibitors of this enzyme family. In response to this challenge, we have developed a Real-time APOBEC3-mediated DNA Deamination assay. This assay offers a single-step set-up and real-time fluorescent read-out, and it is capable of providing insights into enzyme kinetics. The assay also offers a high-sensitivity and easily scalable method for identifying APOBEC3 inhibitors. This assay serves as a crucial addition to the existing APOBEC3 biochemical and cellular toolkit and possesses the versatility to be readily adapted into a high-throughput format for inhibitor discovery.

The implications of APOBEC3-mediated C-to-U RNA editing for human disease.

Intra-organism biodiversity is thought to arise from epigenetic modification of constituent genes and post-translational modifications of translated proteins. Here, we show that post-transcriptional modifications, like RNA editing, may also contribute. RNA editing enzymes APOBEC3A and APOBEC3G catalyze the deamination of cytosine to uracil. RNAsee (RNA site editing evaluation) is a computational tool developed to predict the cytosines edited by these enzymes. We find that 4.5% of non-synonymous DNA single nucleotide polymorphisms that result in cytosine to uracil changes in RNA are probable sites for APOBEC3A/G RNA editing; the variant proteins created by such polymorphisms may also result from transient RNA editing. These polymorphisms are associated with over 20% of Medical Subject Headings across ten categories of disease, including nutritional and metabolic, neoplastic, cardiovascular, and nervous system diseases. Because RNA editing is transient and not organism-wide, future work is necessary to confirm the extent and effects of such editing in humans.

Targeting APOBECs in cancer: It's about timing.

APOBEC3 cytidine deaminases have emerged as key drivers of mutagenesis in a wide spectrum of tumor types and are now appreciated to play a causal role in driving tumor evolution and drug resistance. As efforts to develop APOBEC3 inhibitors progress, understanding the timing and consequences of APOBEC3-mediated mutagenesis in distinct clinical contexts will be critical for guiding the development of anti-cancer therapeutic strategies.

APOBEC2 safeguards skeletal muscle cell fate through binding chromatin and regulating transcription of non-muscle genes during myoblast differentiation.

The apolipoprotein B messenger RNA editing enzyme, catalytic polypeptide (APOBEC) family is composed of nucleic acid editors with roles ranging from antibody diversification to RNA editing. APOBEC2, a member of this family with an evolutionarily conserved nucleic acid-binding cytidine deaminase domain, has neither an established substrate nor function. Using a cellular model of muscle differentiation where APOBEC2 is inducibly expressed, we confirmed that APOBEC2 does not have the attributed molecular functions of the APOBEC family, such as RNA editing, DNA demethylation, and DNA mutation. Instead, we found that during muscle differentiation APOBEC2 occupied a specific motif within promoter regions; its removal from those regions resulted in transcriptional changes. Mechanistically, these changes reflect the direct interaction of APOBEC2 with histone deacetylase (HDAC) transcriptional corepressor complexes. We also found that APOBEC2 could bind DNA directly, in a sequence-specific fashion, suggesting that it functions as a recruiter of HDAC to specific genes whose promoters it occupies. These genes are normally suppressed during muscle cell differentiation, and their suppression may contribute to the safeguarding of muscle cell fate. Altogether, our results reveal a unique role for APOBEC2 within the APOBEC family.

Protein Interaction Map of APOBEC3 Enzyme Family Reveals Deamination-Independent Role in Cellular Function.

Human APOBEC3 enzymes are a family of single-stranded (ss)DNA and RNA cytidine deaminases that act as part of the intrinsic immunity against viruses and retroelements. These enzymes deaminate cytosine to form uracil which can functionally inactivate or cause degradation of viral or retroelement genomes. In addition, APOBEC3s have deamination-independent antiviral activity through protein and nucleic acid interactions. If expression levels are misregulated, some APOBEC3 enzymes can access the human genome leading to deamination and mutagenesis, contributing to cancer initiation and evolution. While APOBEC3 enzymes are known to interact with large ribonucleoprotein complexes, the function and RNA dependence are not entirely understood. To further understand their cellular roles, we determined by affinity purification mass spectrometry (AP-MS) the protein interaction network for the human APOBEC3 enzymes and mapped a diverse set of protein-protein and protein-RNA mediated interactions. Our analysis identified novel RNA-mediated interactions between APOBEC3C, APOBEC3H Haplotype I and II, and APOBEC3G with spliceosome proteins, and APOBEC3G and APOBEC3H Haplotype I with proteins involved in tRNA methylation and ncRNA export from the nucleus. In addition, we identified RNA-independent protein-protein interactions with APOBEC3B, APOBEC3D, and APOBEC3F and the prefoldin family of protein-folding chaperones. Interaction between prefoldin 5 (PFD5) and APOBEC3B disrupted the ability of PFD5 to induce degradation of the oncogene cMyc, implicating the APOBEC3B protein interaction network in cancer. Altogether, the results uncover novel functions and interactions of the APOBEC3 family and suggest they may have fundamental roles in cellular RNA biology, their protein-protein interactions are not redundant, and there are protein-protein interactions with tumor suppressors, suggesting a role in cancer biology. Data are available via ProteomeXchange with the identifier PXD044275.

Expression and prognostic value of APOBEC2 in gastric adenocarcinoma and its association with tumor-infiltrating immune cells.

BACKGROUND: Apolipoprotein B mRNA editing enzyme catalytic polypeptide-like 2 (APOBEC2) is associated with nucleotide alterations in the transcripts of tumor-related genes which are contributed to carcinogenesis. Expression and prognosis value of APOBEC2 in stomach adenocarcinoma (STAD) remains unclear. METHODS: The APOBEC2 gene alteration frequency of STAD and APOBEC2 gene expression in STAD and normal tissues were investigated in cBioportal and GEPIA, respectively. We detected expression of APOBEC2, infiltration of CD66b+ tumor-associated neutrophils and CD163+ tumor-associated macrophages in tissue microarrays by immunohistochemistry. APOBEC2 gene expression was explored by western blot and qRT-PCR. Relationships between APOBEC2 and CD66b, CD163, and other clinicopathological characteristics were investigated. Associations among APOBEC2 expression status and patient survival outcome were further analyzed. RESULTS: APOBEC2 gene alteration frequency was 5%, and APOBEC2 gene was downexpressed in STAD compared to normal tissues (P < 0.05). APOBEC2 expression status were associated with the infiltration of CD66b+ TANs, differentiation grade, TNM stage, histological type and gender (all P < 0.05) in STAD. Little or no APOBEC2 expression was detected in STAD and adjacent normal tissues by western blot. We failed to show that APOBEC2 was an independent risk factor for OS (Hazard Ratio 0.816, 95%CI 0.574-1.161, P = 0.259) or DFS (Hazard Ratio 0.821, 95%CI 0.578-1.166, P = 0.270) in STAD by multivariate Cox regression analysis, but APOBEC2 negative subgroup has a worse OS and DFS among patients with adjuvant chemotherapy. CONCLUSIONS: APOBEC2 correlates with CD66b, differentiation grade, TNM stages, histological classification, and gender in STAD. APOBEC2 is not an independent prognostic factor for STAD, our results suggest that patients with positive APOBEC2 can benefit from postoperative chemotherapy, and combination of APOBEC2 and CD66b is helpful to further stratify patients into different groups with distinct prognoses.

Unraveling C-to-U RNA editing events from direct RNA sequencing.

In mammals, RNA editing events involve the conversion of adenosine (A) in inosine (I) by ADAR enzymes or the hydrolytic deamination of cytosine (C) in uracil (U) by the APOBEC family of enzymes, mostly APOBEC1. RNA editing has a plethora of biological functions, and its deregulation has been associated with various human disorders. While the large-scale detection of A-to-I is quite straightforward using the Illumina RNAseq technology, the identification of C-to-U events is a non-trivial task. This difficulty arises from the rarity of such events in eukaryotic genomes and the challenge of distinguishing them from background noise. Direct RNA sequencing by Oxford Nanopore Technology (ONT) permits the direct detection of Us on sequenced RNA reads. Surprisingly, using ONT reads from wild-type (WT) and APOBEC1-knock-out (KO) murine cell lines as well as in vitro synthesized RNA without any modification, we identified a systematic error affecting the accuracy of the Cs call, thereby leading to incorrect identifications of C-to-U events. To overcome this issue in direct RNA reads, here we introduce a novel machine learning strategy based on the isolation Forest (iForest) algorithm in which C-to-U editing events are considered as sequencing anomalies. Using in vitro synthesized and human ONT reads, our model optimizes the signal-to-noise ratio improving the detection of C-to-U editing sites with high accuracy, over 90% in all samples tested. Our results suggest that iForest, known for its rapid implementation and minimal memory requirements, is a promising tool to denoise ONT reads and reliably identify RNA modifications.