The off-target effects of AID in carcinogenesis

Excessive activation?induced cytidine deaminase accumulated by proteasome inhibitors rescues abnormal class switch in activated B?cell?like diffuse large B?cell lymphoma

Activation-induced cytidine deaminase (AID) is an enzyme that plays a crucial role in mediating somatic hypermutation and class-switch recombination (CSR). It has been found to be associated with aberrant immunoglobulin CSR in activated B-cell-like diffuse large B-cell lymphoma (ABC-DLBCL). In the present study, MG132, a potent proteasome and calpain inhibitor, induced significant cell death in ABC-DLBCL cells and inhibited the growth of ABC-DLBCL cell xenograft tumors. The results also showed that MG132 induced AID accumulation by impairing proteasome degradation of AID. Excessive endogenous AID accumulation was observed in both AID-deficient and C57/BL6 wild-type mice treated with MG132, and apparent CSR of IgM to IgG1, IgG3 and IgE. Upon stimulation of cytokines such as LPS and/or IL-4, ABC-DLBCL cells also showed a noticeable increase in CSR of IgM to IgG1, IgG3 and IgE with decreased AID protein levels. The present study demonstrates that MG132 can induce AID accumulation, which in turn restores dysfunctional CSR in ABC-DLBCL. Using MG132 as a tool, the present study elucidates the anti-lymphoma effect of proteasome inhibitors on ABC-DLBCL by rescuing the abnormal AID-induced CSR.

Activation-induced cytidine deaminase in tertiary lymphoid structures: dual roles and implications in cancer prognosis

Activation-induced cytidine deaminase (AID) serves as a critical molecular orchestrator in the germinal center (GC) reaction within secondary lymphoid organs (SLOs), driving the production of high-affinity antibodies through somatic hypermutation. While its pathological implications are well-documented - including ectopic expression in non-B cell populations and transcriptional dysregulation linked to hematological malignancies and solid tumorigenesis - the cellular provenance of AID in solid tumors remains an unresolved paradox. This review advances two principal hypotheses: (1) AID may derive from tertiary lymphoid structures (TLSs), ectopic immune niches mirroring SLO organization, and (2) exhibits context-dependent transcriptional duality, capable of both potentiating and suppressing gene expression based on microenvironmental cues. Through systematic analysis of AID/GC involvement across cancer subtypes, we delineate mechanistic connections between lymphoid neogenesis and tumor progression. Our examination extends to TLS architecture, revealing three critical dimensions: (i) structural organization and cellular heterogeneity, (ii) developmental trajectories, and (iii) bidirectional interactions with tumor microenvironments. Crucially, we establish functional parallels between tumor-infiltrating B cells (TIL-Bs) in SLOs versus TLSs, while elucidating the differential roles of AID in canonical GC versus TLS-associated GC formation. This synthesis ultimately proposes that AID's functional dichotomy - acting as both oncogenic collaborator and tumor suppressor - underlies the paradoxical prognostic associations observed with TLS presence across malignancies. The review thereby provides a conceptual framework reconciling AID's dual functionality with the context-dependent immunobiology of tumor-associated lymphoid structures.

Epigenetic activation of JAG1 by AID contributes to metastasis of hepatocellular carcinoma

Metastasis is a major cause of fatality in hepatocellular carcinoma (HCC), although the precise mechanisms driving the metastatic process remain incompletely understood. In this study, we have made several important findings. Firstly, we have discovered that elevated activation-induced cytidine deaminase (AID) expression is positively correlated with Jagged 1 (JAG1) levels in clinically metastatic HCC patients. Moreover, we observed that depletion of either AID or JAG1 leads to a reduction in HCC metastasis. Secondly, we have identified AID acts as a transcriptional regulator that regulates JAG1 transcription by interacting with histone acetyltransferase 1 (HAT1) in metastatic HCC cells. Furthermore, our results demonstrate that any domains of AID can cooperate with HAT1 to enhance JAG1 transcription. Importantly, we have determined that the AID/HAT1 complex directly binds to specific regions within the JAG1 gene body, specifically -1.504 kb to -1.104 kb region, thereby influencing the epigenetic state of the JAG1 promoter through modulating histone methylation, histone acetylation, and DNA methylation. Furthermore, we have elucidated that the AID-JAG1/NOTCH-c-FOS axis plays a pivotal role in facilitating HCC metastasis. Consequently, the inhibitory effects of MG149 on both AID and JAG1 significantly mitigate the progression of HCC. This investigation uncovers a heretofore unappreciated function of AID as a transcriptional regulator in the metastasis of HCC, heralding a promising therapeutic approach.

AID in non-Hodgkin B-cell lymphomas: The consequences of on- and off-target activity

Activation induced cytidine deaminase (AID) is a key element of the adaptive immune system, required for immunoglobulin isotype switching and affinity maturation of B-cells as they undergo the germinal center (GC) reaction in peripheral lymphoid tissue. The inherent DNA damaging activity of this enzyme can also have off-target effects in B-cells, producing lymphomagenic chromosomal translocations that are characteristic features of various classes of non-Hodgkin B-cell lymphoma (B-NHL), and generating oncogenic mutations, so-called aberrant somatic hypermutation (aSHM). Additionally, AID has been found to affect gene expression through demethylation as well as altered interactions between gene regulatory elements. These changes have been most thoroughly studied in B-NHL arising from GC B-cells. Here, we describe the most common classes of GC-derived B-NHL and explore the consequences of on- and off-target AID activity in B and plasma cell neoplasms. The relationships between AID expression, including effects of infection and other exposures/agents, mutagenic activity and lymphoma biology are also discussed.

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.