HIV-1 Tat protein induces aberrant activation of AICDA in human B-lymphocytes from peripheral blood

Compensatory reactions of B cells in response to chronic HIV-1 Tat exposure

Patients infected with human immunodeficiency virus-1 (HIV-1) have an increased incidence of B-cell lymphoma, even though HIV-1 does not infect B cells. The development of B-cell lymphomas appears to be related to the action of the HIV-1 transactivator protein (Tat), which is released from HIV-infected cells and penetrates uninfected B cells, affecting host cell gene expression. Upon chronic HIV-1 infection, Tat acts on the cells for a long time, probably allowing the cells to adapt to the presence of the viral protein. The aim of this work was to identify and study the mechanism of adaptation of cells to prolonged (chronic) exposure to HIV-1 Tat. We performed a comparative analysis of cells expressing Tat under the action of either an inducible promoter or a constitutive promoter, allowing us to model acute and chronic Tat effects, respectively. We found that the acute action of Tat leads to the suppression of cell proliferation, probably due to the downregulation of genes associated with replication and protein synthesis. In the case of chronic action of Tat, cell proliferation was restored and the expression of genes associated with the implementation of protective (antiviral) functions of the cell was increased. Analysis using proteasome inhibitors showed that in the case of chronic action, intense Tat proteolysis occurred, which could be the main mechanism of B-cell adaptation. Thus, B cells have a powerful mechanism to adapt to the entry of HIV-1 Tat, the efficiency of which may determine the frequency of lymphomagenesis in HIV-1-infected patients.

Immune Characteristics and Immunotherapy of HIV-Associated Lymphoma

In the era of antiretroviral therapy (ART), mortality among people living with the human immunodeficiency virus (HIV) has significantly decreased, yet the population of people living with HIV remains substantial. Among people living with HIV (PLWH), HIV-associated lymphoma (HAL) has surpassed Kaposi's sarcoma to become the most common tumor in this population in developed countries. However, there remains a dearth of comprehensive and systematic understanding regarding HIV-associated lymphomas. This review aims to shed light on the changes in the immune system among PLWH and the characteristics of the immune microenvironment in HIV-associated lymphoma, with a specific focus on the immune system's role in these individuals. Additionally, it seeks to explore recent advancements in immunotherapy for the treatment of HIV-associated lymphoma, intending to enhance strategies for immunotherapy in this specific population.

Virus-driven dysregulation of the BCR pathway: a potential mechanism for the high prevalence of HIV related B-cell lymphoma

In people living with HIV (PLWH), the susceptibility to malignancies is notably augmented, with lymphoma emerging as a predominant malignancy. Even in the antiretroviral therapy (ART) era, aggressive B-cell lymphoma stands out as a paramount concern. Yet, the pathogenesis of HIV related lymphoma (HRL) largely remains an enigma. Recent insights underscore the pivotal role of the dysregulated B cell receptor (BCR) signaling cascade, evidencing its oncogenic potential across a spectrum of lymphomas. Intricate interplays between HIV and BCR structural-functional integrity have been identified in PLWH. In this review, we elucidated the mechanism by which the BCR signaling pathway is involved in HRL, mainly including the following aspects: HIV can reshape BCR structure by modulating of activation-induced cytidine deaminase (AID) and recombination-activating gene (RAG) dynamics; HIV can act as a chronic antigen to activate the BCR signaling pathway, such as upregulating PI3K and MAPK signaling pathway and reducing the expression of CD300a; HIV co-infection with other oncogenic viruses may also influence tumor formation mediated by the BCR signaling pathway. This review aims to elucidate the intricate regulation of the BCR signaling pathway by HIV in B cell lymphoma, providing a novel perspective on the pathogenesis of lymphoma in HIV-affected environments.

Immune dysregulation as a leading principle for lymphoma development in diverse immunological backgrounds

Lymphoma is a heterogeneous group of malignancies arising from lymphocytes, which poses a significant challenge in terms of diagnosis and treatment due to its diverse subtypes and underlying mechanisms. This review aims to explore the shared and distinct features of various forms of lymphoma predisposing conditions, with a focus on genetic, immunological and molecular aspects. While diseases such as autoimmune disorders, inborn errors of immunity and iatrogenic immunodeficiencies are biologically and immunologically distinct, each of these diseases results in profound immune dysregulation and a predisposition to lymphoma development. Interestingly, the increased risk is often skewed towards a particular subtype of lymphoma. Patients with inborn errors of immunity in particular present with extreme forms of lymphoma predisposition, providing a unique opportunity to study the underlying mechanisms. External factors such as chronic infections and environmental exposures further modulate the risk of lymphoma development. Common features of conditions predisposing to lymphoma include: persistent inflammation, recurrent DNA damage or malfunctioning DNA repair, impaired tumor surveillance and viral clearance, and dysregulation of fundamental cellular processes such as activation, proliferation and apoptosis. Our growing understanding of the underlying mechanisms of lymphomagenesis provides opportunities for early detection, prevention and tailored treatment of lymphoma development.

Ectopic expression of HIV-1 Tat modifies gene expression in cultured B cells: implications for the development of B-cell lymphomas in HIV-1-infected patients

An increased frequency of B-cell lymphomas is observed in human immunodeficiency virus-1 (HIV-1)-infected patients, although HIV-1 does not infect B cells. Development of B-cell lymphomas may be potentially due to the action of the HIV-1 Tat protein, which is actively released from HIV-1-infected cells, on uninfected B cells. The exact mechanism of Tat-induced B-cell lymphomagenesis has not yet been precisely identified. Here, we ectopically expressed either Tat or its TatC22G mutant devoid of transactivation activity in the RPMI 8866 lymphoblastoid B cell line and performed a genome-wide analysis of host gene expression. Stable expression of both Tat and TatC22G led to substantial modifications of the host transcriptome, including pronounced changes in antiviral response and cell cycle pathways. We did not find any strong action of Tat on cell proliferation, but during prolonged culturing, Tat-expressing cells were displaced by non-expressing cells, indicating that Tat expression slightly inhibited cell growth. We also found an increased frequency of chromosome aberrations in cells expressing Tat. Thus, Tat can modify gene expression in cultured B cells, leading to subtle modifications in cellular growth and chromosome instability, which could promote lymphomagenesis over time.

High expression of HIV-1 matrix protein p17 in both lymphoma and lymph node tissues of AIDS patients

BACKGROUND

HIV-1 matrix protein p17 was found to be associated with lymphoma development in vitro. This study aimed to elucidate the pathogenetic roles of HIV-1 p17 in AIDS-related lymphoma.

METHODS

Expression of HIV-1 proteins p17, p24, nef and tat were evaluated in tumor tissue samples from 60 lymphoma patients and lymph node samples from 23 non-lymphoma patients with HIV-1 infection by immunohistochemistry. Microvascular density (MVD) determined by CD34 were also assessed in tumor tissues. Clinicopathological data of AIDS patients with lymphoma were collected retrospectively.

RESULTS

The subtypes of lymphoma among sixty AIDS patients were diffuse large B-cell lymphoma (32 cases), Burkitt lymphoma (23 cases), Hodgkin's lymphoma (4 cases), and plasmablastic lymphoma (1 case). The expression rate of HIV-1 p17 in lymphoma and non-lymphoma group was 63 % (38/60) and 61 % (14/29) respectively, with no significant difference (p = 0.835). The positive expression rate of p17 in both groups was significantly higher than that of p24, nef and tat (p < 0.05). The expression of p17 was associated with a higher MVD in the lymphoma group (p < 0.05). There were no significant differences in the 2-years overall survival between p17 positive and negative group (61 % vs. 50 %, p = 0.525).

CONCLUSION

The common expression of HIV-1 matrix protein p17 in both lymphoma and lymph node tissues of AIDS patients and the association between p17 expression and the higher MVD suggest that the accumulation and persistence of p17 in tissues may play a role in lymphoma development.

Modulation of Cellular MicroRNA by HIV-1 in Burkitt Lymphoma Cells-A Pathway to Promoting Oncogenesis

Viruses and viral components have been shown to manipulate the expression of host microRNAs (miRNAs) to their advantage, and in some cases to play essential roles in cancer pathogenesis. Burkitt lymphoma (BL), a highly aggressive B-cell derived cancer, is significantly over-represented among people infected with HIV. This study adds to accumulating evidence demonstrating that the virus plays a direct role in promoting oncogenesis. A custom miRNA PCR was used to identify 32 miRNAs that were differently expressed in Burkitt lymphoma cells exposed to HIV-1, with a majority of these being associated with oncogenic processes. Of those, hsa-miR-200c-3p, a miRNA that plays a crucial role in cancer cell migration, was found to be significantly downregulated in both the array and in single-tube validation assays. Using an in vitro transwell system we found that this downregulation correlated with significantly enhanced migration of BL cells exposed to HIV-1. Furthermore, the expression of the ZEB1 and ZEB2 transcription factors, which are promotors of tumour invasion and metastasis, and which are direct targets of hsa-miR-200c-3p, were found to be enhanced in these cells. This study therefore identifies novel miRNAs as role players in the development of HIV-associated BL, with one of these miRNAs, hsa-miR-200c-3p, being a candidate for further clinical studies as a potential biomarker for prognosis in patients with Burkitt lymphoma, who are HIV positive.

New insights into pathogenesis point to HIV-1 Tat as a key vaccine target

Despite over 30 years of enormous effort and progress in the field, no preventative and/or therapeutic vaccines against human immunodeficiency virus (HIV) are available. Here, we briefly summarize the vaccine strategies and vaccine candidates that in recent years advanced to efficacy trials with mostly unsatisfactory results. Next, we discuss a novel and somewhat contrarian approach based on biological and epidemiological evidence, which led us to choose the HIV protein Tat for the development of preventive and therapeutic HIV vaccines. Toward this goal, we review here the role of Tat in the virus life cycle as well as experimental and epidemiological evidence supporting its key role in the natural history of HIV infection and comorbidities. We then discuss the preclinical and clinical development of a Tat therapeutic vaccine, which, by improving the functionality and homeostasis of the immune system and by reducing the viral reservoir in virologically suppressed vaccinees, helps to establish key determinants for intensification of combination antiretroviral therapy (cART) and a functional cure. Future developments and potential applications of the Tat therapeutic vaccine are also discussed, as well as the rationale for its use in preventative strategies. We hope this contribution will lead to a reconsideration of the current paradigms for the development of HIV/AIDS vaccines, with a focus on targeting of viral proteins with key roles in HIV pathogenesis.

HIV-1 Transactivator of Transcription (Tat) Co-operates With AP-1 Factors to Enhance c-MYC Transcription

HIV-1 infection often leads to the development of co-morbidities including cancer. Burkitt lymphoma (BL) is one of the most over-represented non-Hodgkin lymphoma among HIV-infected individuals, and displays a highly aggressive phenotype in this population group, with comparatively poorer outcomes, despite these patients being on anti-retroviral therapy. Accumulating evidence indicates that the molecular pathogenesis of HIV-associated malignancies is unique, with components of the virus playing an active role in driving oncogenesis, and in order to improve patient prognosis and treatment, a better understanding of disease pathobiology and progression is needed. In this study, we found HIV-1 Tat to be localized within the tumor cells of BL patients, and enhanced expression of oncogenic c-MYC in these cells. Using luciferase reporter assays we show that HIV-1 Tat enhances the c-MYC gene promoter activity and that this is partially mediated via two AP-1 binding elements located at positions -1128 and -1375 bp, as revealed by mutagenesis experiments. We further demonstrate, using pull-down assays, that Tat can exist within a protein complex with the AP-1 factor JunB, and that this complex can bind these AP-1 sites within the c-MYC promoter, as shown by in vivo chromatin immunoprecipitation assays. Therefore, these findings show that in HIV-infected individuals, Tat infiltrates B-cells, where it can enhance the expression of oncogenic factors, which contributes toward the more aggressive disease phenotype observed in these patients.

HIV Lymphoma and Burkitts Lymphoma

Despite widely available antiretroviral therapy, lymphoma remains the leading cause of death for human immunodeficiency virus (HIV)-infected persons in economically developed countries. Even a few months of drug interruptions can lead to drops in the CD4 cell count, HIV viremia, and an increased risk of lymphoma. Currently, good HIV control facilitates intensive therapies appropriate to the lymphoma, including autologous and even allogeneic hematopoietic stem cell transplantation. Nonetheless, HIV-related lymphomas have unique aspects, including pathogenetic differences driven by the presence of HIV and often coinfection with oncogenic viruses. Future therapies might exploit these differences. Lymphoma subtypes also differ in the HIV-infected population, and the disease has a higher propensity for advanced-stage, aggressive presentation and extranodal disease. Other unique aspects include the need to avoid potential interactions between antiretroviral therapy and chemotherapeutic agents and the need for HIV-specific supportive care such as infection prophylaxis. Overall, the care of these patients has progressed sufficiently that recent guidelines from the American Society of Clinical Oncology advocate the inclusion of HIV-infected patients alongside HIV-negative patients in cancer clinical trials when appropriate. This article examines HIV lymphoma and includes Burkitt lymphoma in the general population.

HIV-1 Tat Activates Akt/mTORC1 Pathway and AICDA Expression by Downregulating Its Transcriptional Inhibitors in B Cells

HIV-1 infects T cells, but the most frequent AIDS-related lymphomas are of B-cell origin. Molecular mechanisms of HIV-1-induced oncogenic transformation of B cells remain largely unknown. HIV-1 Tat protein may participate in this process by penetrating and regulating gene expression in B cells. Both immune and cancer cells can reprogram communications between extracellular signals and intracellular signaling pathways via the Akt/mTORC1 pathway, which plays a key role in the cellular response to various stimuli including viral infection. Here, we investigated the role of HIV-1 Tat on the modulation of the Akt/mTORC1 pathway in B cells. We found that HIV-1 Tat activated the Akt/mTORC1 signaling pathway; this leads to aberrant activation of activation-induced cytidine deaminase (AICDA) due to inhibition of the AICDA transcriptional repressors c-Myb and E2F8. These perturbations may ultimately lead to an increased genomic instability and proliferation that might cause B cell malignancies.

HIV Nef enhances the expression of oncogenic c-MYC and activation-induced cytidine deaminase in Burkitt lymphoma cells, promoting genomic instability

Background

Non-Hodgkin lymphoma is of high prevalence among HIV-infected people. In particular, the incidence of HIV-associated Burkitt lymphoma (BL) remains high despite the advent of Highly Active Anti-Retroviral Therapy. Recent evidence shows that serum-soluble HIV proteins can enhance oncogenesis, particularly in lymphoid tissues. This study sought to define the role of HIV protein Negative regulatory factor (Nef) in BL development by assessing its effect on key lymphoma driver genes.

Methods

A recombinant Nef protein was used to assess changes in expressions of activation-induced cytidine deaminase (AICDA/AID) and c-MYC in B lymphocytes exposed extracellularly to the protein. Additionally, changes in the promoter activities of these genes were measured using a Nef-expressing cellular model and reporter assays. Confocal microscopy was used to observe c-MYC and AID expression and localization, and genomic integrity via the recruitment of phosphorylated γ-H2AX, in Nef-exposed cells.

Results

mRNA transcription of c-MYC and AICDA were significantly enhanced in lymphoma cells, up to 2-fold for c-MYC and up to 4-fold for AICDA, when exposed to varying concentrations of Nef (0–1000 ng/ml) and for different periods of time (3, 6 and 12 h). The protein expressions of AID and c-MYC followed a similar pattern and these effects were specific to BL but not lymphoblastoid cells. While the promoter activity of c-MYC was enhanced in the presence of Nef in a dose-dependent manner, the same was not observed for AICDA. Both AID and c-MYC accumulated within the cytoplasmic and nuclear spaces of Nef-exposed lymphoma cells, with a concomitant increase in DNA double strand breaks within the genome.

Conclusions

Exposure to HIV Nef leads to significant increases in AID and c-MYC, leading to genomic instability, potentially enhancing the oncogenic potential of Burkitt lymphoma. Our findings align with that of others to show that HIV proteins can directly contribute to the development and pathogenesis of HIV-associated lymphoma and accounts for the elevated incidence of BL observed in the HIV-infected population.

HIV-associated Burkitt lymphoma

Burkitt lymphoma is a rare and aggressive non-Hodgkin lymphoma with three classifications: endemic, sporadic, and immunodeficiency-related. High-intensity chemotherapeutic regimens have considerably improved overall survival for patients with Burkitt lymphoma. In this Review of HIV-associated Burkitt lymphoma, we summarise expert opinion and provide general recommendations for the treatment of Burkitt lymphoma in patients with HIV on the basis of retrospective and prospective studies, taking into consideration immune status, CD4 cell counts, the presence of systemic disease, and the risk of CNS involvement or relapse. We also discuss the role of rituximab and antiretroviral therapy. We highlight the reasons behind the possible different mechanisms of lymphomagenesis in HIV-associated Burkitt lymphoma and endemic Burkitt lymphoma, which indicate that HIV might have either a direct or indirect oncogenic role in Burkitt lymphoma. We discuss the possible mechanisms by which HIV and HIV proteins could directly contribute to lymphomagenesis. Identifying these mechanisms might lead to the development of therapies that have fewer toxic effects than high-intensity chemotherapeutic regimens.

Activation-induced cytidine deaminase: in sickness and in health

Activation Induced cytidine Deaminase (AID) is an essential enzyme of the adaptive immune system. Its canonical activity is restricted to B lymphocytes, playing an essential role in the diversification of antibodies by enhancing specificity and changing affinity. This is possible through its DNA deaminase function, leading to mutations in DNA. In the last decade, AID has been assigned an additional function: that of a powerful DNA demethylator. Adverse cellular conditions such as chronic inflammation can lead to its deregulation and overexpression. It is an important driver of B-cell lymphoma due to its natural ability to modify DNA through deamination, leading to mutations and epigenetic changes. However, the deregulation of AID is not restricted to lymphoid cells. Recent findings have provided new insights into the role that this protein plays in the development of non-lymphoid cancers, with some research shedding light on novel AID-driven mechanisms of cellular transformation. In this review, we provide an updated narrative of the normal physiological functions of AID. Additionally, we review and discuss the recent research studies that have implicated AID in carcinogenesis in varying tissue types including lymphoid and non-lymphoid cancers. We review the mechanisms, whereby AID promotes carcinogenesis and highlight important areas of future research.

Oncogenic Properties of the EBV ZEBRA Protein

Epstein Barr Virus (EBV) is one of the most common human herpesviruses. After primary infection, it can persist in the host throughout their lifetime in a latent form, from which it can reactivate following specific stimuli. EBV reactivation is triggered by transcriptional transactivator proteins ZEBRA (also known as Z, EB-1, Zta or BZLF1) and RTA (also known as BRLF1). Here we discuss the structural and functional features of ZEBRA, its role in oncogenesis and its possible implication as a prognostic or diagnostic marker. Modulation of host gene expression by ZEBRA can deregulate the immune surveillance, allow the immune escape, and favor tumor progression. It also interacts with host proteins, thereby modifying their functions. ZEBRA is released into the bloodstream by infected cells and can potentially penetrate any cell through its cell-penetrating domain; therefore, it can also change the fate of non-infected cells. The features of ZEBRA described in this review outline its importance in EBV-related malignancies.

Effects of HIV on the Tumor Microenvironment

Oncomodulatory viruses can affect the tumor microenvironment (TME) by triggering inflammation, suppressing apoptosis, initiating angiogenesis, altering tumor metabolism, and stimulating tumor cell signaling pathways, leading to tumor growth, proliferation, and invasion. The higher incidence of malignancies among people with HIV (PWH), despite the widespread use of antiretroviral therapy (ART), suggests a more complex relation than HIV-associated immune deregulation. Viral cooperation can have synergistic effect on tumorigenesis. The most relevant oncogenes involved in viral cooperation include the HIV-1-related Tat and Vpu genes, EBV LMP-1 and EBNA-2 genes, and Kaposi's sarcoma herpesvirus (KSHV) KIE2, Rta, and LANA genes. The TME in HIV-related malignancies is highly angiogenic and characterized by high microvessel density compared to sporadic cases. Tat protein, found in patients with HIV infection regardless of their immune status, has been widely implicated in the increased angiogenesis and has been a target of interest for therapeutic strategies. Similarly, HIV-1 matrix protein p17 can be detected in the plasma and tissues of PWH, including those treated with ART. Studies have found that p17 can cause dysregulation of the biological activity of different immune cells, is involved in aberrant angiogenesis, and exhibits an IL8 chemokine activity, activating multiple intracellular signaling pathways, promoting angiogenic responses in endothelial cells, and forming capillary like structures. In addition, several studies have demonstrated difference in the cellular immune components within the TME in patients with or without HIV infection, as well as cases in pre- and post-ART era. In this chapter, we review the existing literature about the role tumor microenvironment plays in the pathogenesis of HIV-related malignancies. Understanding the functions of each component of the TME and determining how these cellular and noncellular components contribute to tumorigenesis will impact the advancement of interventions and treatment in clinical oncology among PWH.