Human immunodeficiency virus (HIV) infection is associated with B-cell malignancies in patients though HIV-1 is not able to infect B-cells. The rate of B-cell lymphomas in HIV-infected individuals remains high even under the combined antiretroviral therapy (cART) that reconstitutes the immune function. Thus, the contribution of HIV-1 to B-cell oncogenesis remains enigmatic. HIV-1 induces oxidative stress and DNA damage in infected cells via multiple mechanisms, including viral Tat protein. We have detected elevated levels of reactive oxygen species (ROS) and DNA damage in B-cells of HIV-infected individuals. As Tat is present in blood of infected individuals and is able to transduce cells, we hypothesized that it could induce oxidative DNA damage in B-cells promoting genetic instability and malignant transformation. Indeed, incubation of B-cells isolated from healthy donors with purified Tat protein led to oxidative stress, a decrease in the glutathione (GSH) levels, DNA damage and appearance of chromosomal aberrations. The effects of Tat relied on its transcriptional activity and were mediated by NF-κB activation. Tat stimulated oxidative stress in B-cells mostly via mitochondrial ROS production which depended on the reverse electron flow in Complex I of respiratory chain. We propose that Tat-induced oxidative stress, DNA damage and chromosomal aberrations are novel oncogenic factors favoring B-cell lymphomas in HIV-1 infected individuals.

With combined antiretroviral therapy (cART), the risk for HIV-infected individuals to develop a non-Hodgkin lymphoma is diminished. However, the incidence of Burkitt lymphoma (BL) remains strikingly elevated. Most BL present a t(8;14) chromosomal translocation which must take place at a time of spatial proximity between the translocation partners. The two partner genes, MYC and IGH, were found colocalized only very rarely in the nuclei of normal peripheral blood B-cells examined using 3D-FISH while circulating B-cells from HIV-infected individuals whose exhibited consistently elevated levels of MYC-IGH colocalization. In vitro, incubating normal B-cells from healthy donors with a transcriptionally active form of the HIV-encoded Tat protein rapidly activated transcription of the nuclease-encoding RAG1 gene. This created DNA damage, including in the MYC gene locus which then moved towards the center of the nucleus where it sustainably colocalized with IGH up to 10-fold more frequently than in controls. In vivo, this could be sufficient to account for the elevated risk of BL-specific chromosomal translocations which would occur following DNA double strand breaks triggered by AID in secondary lymph nodes at the final stage of immunoglobulin gene maturation. New therapeutic attitudes can be envisioned to prevent BL in this high risk group.

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Individuals infected with human immunodeficiency virus (HIV) are at increased risk for Burkitt lymphoma, a B‐cell malignancy which occurs after a chromosomal translocation rearranging the MYC oncogene with an immunoglobulin gene locus, usually the IGH heavy chain gene locus. We have previously reported that the HIV protein Tat which circulates in all HIV‐positive individuals whatever their immune status caused an increased rate of colocalization between IGH and MYC in B‐cells nuclei. We here present in vitro evidence that Tat activates the expression of the AICDA gene that encodes the activation‐induced cytidine deaminase whose physiological function is to create double‐strand breaks for immunoglobulin gene maturation. In the presence of Tat, DNA damage was observed concomitantly in both MYC and IGH, followed by DNA repair by nonhomologous end joining. AICDA was further found overexpressed in vivo in peripheral blood B‐cells from HIV‐infected individuals. Thus, the capacity of Tat to spontaneously penetrate B‐cells could be sufficient to favor the occurrence of MYC‐IGH oncogenic rearrangements during erroneous repair, a plausible cause for the increased incidence of Burkitt lymphoma in the HIV‐infected population.

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Burkitt lymphoma (BL) is a B cell malignancy associated with the Epstein−Barr virus (EBV). Most BL cases are characterized by a t(8;14) chromosomal translocation involving the MYC oncogene and the immunoglobulin heavy chain gene (IGH). The role of EBV in promoting this translocation remains largely unknown. Here we provide the experimental evidence that EBV reactivation from latency leads to an increase in the proximity between the MYC and IGH loci, otherwise located far away in the nuclear space both in B-lymphoblastoid cell lines and in patients' B-cells. Specific DNA damage within the MYC locus, followed by the MRE11-dependent DNA repair plays a role in this process. Using a CRISPR/Cas9-based B cell model to induce specific DNA double strand breaks in MYC and IGH loci, we have shown that the MYC-IGH proximity induced by EBV reactivation leads to an increased t(8;14) translocation frequency.

Recurrent chromosomal translocations are found in many blood and solid cancers. Balanced translocations, frequent in lymphoid malignancies, lead to the formation of two aberrant derivative (der) chromosomes. This event often leads to overexpression of an oncogene. In many cases, the expression of an oncogene is not enough to produce a malignant phenotype; however, most part of the studies focus on the events involving the chromosome where the oncogene is located, but rarely the other der chromosome where other oncogenic alterations may potentially arise. Mantle cell lymphoma (MCL), an aggressive B-cell non-Hodgkin lymphoma, is a perfect example of this. In 85% of the cases, it is characterized by the translocation t(11;14), which leads to the overexpression of cyclin D1 (CCND1) gene which results juxtaposed to the immunoglobulin heavy chain (IGH) gene on the der14 chromosome.This feature alone is not sufficient to induce oncogenesis. Here we focused on the der11 chromosome. We demonstrated that expression of 88 genes located in a 15mb region close to the translocation breakpoint on the der11 was deregulated both in the GRANTA-519 MCL cell line and in B-cells from MCL patients. We found that a large segment of der11containing deregulated genes was relocated from its normal position in the nuclear periphery towards the center of the nucleus in close proximity to the nucleolus where the abundant nucleolar protein nucleolin binds a subset of genes located close to the breakpoint and activates their expression. This finding allowed to identify new potential oncogenes involved in MCL and the mechanisms of their upregulation.

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