The biological effects of HIV-1 Nef on the development of B-cell Lymphoma

Ahmed, Riyaadh

The biological effects of HIV-1 Nef on the development of B-cell Lymphoma

Master Thesis

2022

Abstract

The incidence of HIV-associated cancers is significantly higher within the South African population compared to elsewhere in the world due to South Africa having one of the highest HIV burdens compared to the rest of the world. Burkitt lymphoma (BL) is an extremely aggressive cancer that is considered to be a highly prevalent subtype of Non-Hodgkin Lymphoma (NHL) affiliated with chronic HIV infection. While the immunosuppressive aspect of HIV remains a primary cause for the increased occurrence of cancer amongst HIV positive patients, new research demonstrates that the virus can have direct oncogenic effects, often through the action of specific virally-encoded proteins. The latter can act alone or collaboratively with cellular proteins, as well as with oncoproteins of established oncogenic viruses such as the Kaposi's Sarcoma-associated Herpes Virus (KSHV), or with Epstein-Barr Virus (EBV). To date, convincing evidence assign oncogenic activity to the HIV viral proteins Trans-activator of Transcription (Tat) and p17 in the progression of B-cell lymphomagenesis. Of particular interest to this study is the HIV-1 viral protein Nef (Negative Factor) which has been reported to have an oncogenic role in several cancer types including Kaposi's Sarcoma (KS) and Non-Small Cell Lung Cancer (NSCLC). However, the role of HIV-1 Nef in B-cell lymphoma, including BL, remains largely unexplored. Previous work performed in our research laboratory demonstrated that HIV-1 Nef protein could enhance the expression of two key lymphoma promoting factors, c-MYC and Activation Induced Cytidine Deaminase (AID), in BL cells and promoted genomic instability. The current study aimed to further explore the oncogenic effects of HIV-1 protein Nef in the development of BL. Furthermore, the potential internalization of recombinant Nef protein by B-cells during extracellular exposure was examined. Herein, we utilized cellular-based assays to examine alterations in the proliferation, the cell cycle and apoptosis of BL cells that have been extracellularly exposed to recombinant Nef protein. Our findings reveal that the proliferation of BL cells was enhanced in response to Nef exposure. Furthermore, the expression of the cyclin proteins A, B1 and E2 were found to be increased in Nef-exposed BL cells, which could account for the enhanced proliferation. No major changes in the cell cycle profile of BL cells were noted upon exposure to Nef. While a sub-G1 peak was noted during cell cycle analysis, Annexin V/7-Amino-actinomycin (7-AAD) staining confirmed that this observation was an anomaly, confirming that the Nef protein did not enhance apoptosis in BL cells. Additionally, the Nef protein did not provide any protective effect against apoptosis in BL cells exposed to the chemotherapeutic agent Doxorubicin. Finally, investigation of the potential internalization of the Nef protein by B-cells indicated that Nef may be trafficked to both the cytoplasm and the nucleus. However, this remains inconclusive due to Nef being detected in negative control samples. Overall, this study generated novel data on the oncogenic role of HIV-1 protein Nef in the development of BL, demonstrating that this viral protein has the ability to enhance proliferation of BL cells. Additionally, Nef was shown to alter the expression of cellular cyclin proteins, which could be one of the mechanisms via which proliferation is enhanced. This data allows for a better understanding of the oncogenic role of Nef in the development of B-cell lymphoma, and contributes to our observation of enhanced disease severity and progression in HIV infected people who develop BL. Future studies will focus on further defining the oncogenic potential of Nef in aggressive B-cell lymphomas by examining its effect on other oncogenic processes/pathways which define hallmarks of cancer, including cell migration and invasion, autophagy and angiogenesis, as well as its effect on oncogenic signalling pathways. In addition to this, further optimization of the experimental design used to assess the potential internalization of the Nef protein by BL-cells is recommended for future work. Ultimately, more research must be undertaken to further elucidate the oncogenic role of HIV-1 Nef protein in HIV-associated lymphomas such as BL.

Keywords

Haematology

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