Abstract
Epstein-Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV) are classified as class I carcinogens and persistently infect B cells, significantly contributing to B cell lymphomagenesis. The AICDA/APOBEC and ADAR deaminase families are integral to the cellular innate immune response against viruses, becoming upregulated upon infection. While AICDA/APOBEC and ADAR enzymes are known to target various components of EBV and KSHV, including viral DNA genomes, miRNAs, or lncRNAs, these viruses encode proteins and miRNAs to counteract or modulate their functions. Beyond their viral restriction role, these cellular editors are highly upregulated in cancer tissues, where their mutation signatures contribute to cancer progression. However, the precise involvement of AICDA/APOBEC and ADAR in EBV and KSHV infections and the subsequent development of virus-induced B cell lymphomas remains incompletely understood. Furthermore, individuals infected with HIV have a higher risk of developing EBV and KSHV-associated B cell lymphomas such as Burkitt’s Lymphoma (BL) and Primary Effusion Lymphoma (PEL), respectively. The HIV Tat protein, secreted by infected cells, promotes AICDA-mediated somatic hypermutation (SHM) and genome instability in B cells and has been shown to contribute to KSHV-associated Kaposi’s sarcoma (KS). However, its role in promoting KSHV-associated B cell lymphomas remains to be fully elucidated. RNA sequencing of primary human B cells infected with EBV and EBV/KSHV in vitro was conducted to examine AICDA/APOBEC and ADAR gene expression during both initial and latent infection stages. These findings were corroborated using cell lines derived from humanised mice (huNSG) infected with EBV and EBV/KSHV. The impact of individual viral proteins on AICDA-mediated mutagenesis was investigated using a Ramos reporter cell assay. Furthermore, the role of the HIV-1 Tat protein on the development of B cell tumours derived from EBV and EBV/KSHV infections was assessed in vivo, utilising huNSG mice. This study provides comprehensive insights into the gene expression dynamics of AICDA/APOBEC and ADAR genes throughout the course of initial and persistent γ-herpesvirus infection. It confirms the upregulation of AICDA expression during early EBV/KSHV versus EBV infection, likely influenced by KSHV vIL-6 within a specific temporal window. The distinct B cell phenotypic variances observed between EBV and EBV/KSHV infected cells suggest a potential role of KSHV in enhancing germinal centre and plasma cell phenotypes during early B cell infection. Additionally, this research uncovers a novel finding that KSHV vIL-6, in addition to its reported role in promoting class switch recombination (CSR), also amplifies AICDA-mediated somatic hypermutation (SHM). Surprisingly, this enhancement of SHM by KSHV vIL-6 is only observed in a paracrine manner. Although there is evidence of an additive effect of HIV Tat protein and KSHV vIL-6 on AICDA-mediated mutagenesis, in vivo studies suggest a potential detrimental impact on B cell tumorigenesis. Overall, our findings elucidate the effect of EBV and KSHV infections on AICDA/APOBEC and ADAR expression and provide insights into the potential roles of KSHV vIL-6 and AICDA in virus-associated B cell malignancies.
Gramalla-Schmitz, Anna