Introduction: The pathogenesis HIV-associated lymphomas involve a complex interplay of biological factors, including the immerging role of HIV encoded proteins. These proteins have been shown to have oncogenic potential and to enhance the pathogenesis of HIV-associated malignancies. However, very little is known about the molecular mechanisms involved in this interaction. Here, we investigate the effect of HIV protein Negative Factor (Nef) on the expression of c-MYC and activation-induced cytidine deaminase (AID) in lymphoblasts and lymphoma cells.
Methods: Native histidine-tagged HIV Nef was produced in a bacterial system and used to treat (1) an EBV-immortalized B lymphoblastoid cell line (L1439A) and (2) the established lymphoma cell line Ramos, at various concentrations and for various time points. Changes in the expressions of c-MYC and AID were measured at both the mRNA and proteins levels using qPCR and western blotting respectively. The ability of Nef to regulate the promoter of these two genes was determined using luciferase reporter assays. Furthermore, confocal microscopy was used to investigate the downstream effects of Nef exposure.
Results: In L1439A cells, a general decrease in the expression of c-MYC and AID was observed. After 1 and 3 hours of exposure to HIV-Nef both c-MYC and AID mRNA levels reduced by approximately 0.5-fold. In contrast, the expressions of both genes increased significantly upon these treatments in the lymphoma cell line Ramos. After 3 hours of exposure, c-MYC expression increased by ~1.9-fold, while AID expression increased up to 4.6-fold. The protein expression followed a similar pattern, as indicated by western blotting. Furthermore, luciferase reporter assays showed that the effect on c-MYC expression is likely to be direct since the activity of the c-MYC promoter increased in a dose-dependent manner in the presence of Nef. c-MYC translocated to the nucleus, which is indicative of an active protein. Furthermore, an increase in gamma H2AX foci on DNA, indicative of double strand breaks, shows that the increase in AID lead to genomic instability.
Conclusion: This study demonstrates a differential effect of HIV Nef on normal immortalized lymphoblasts versus lymphoma cells. More importantly, it shows for the first time that HIV Nef may enhance the pathogenesis of lymphomas by triggering pathways and mechanisms which increase the expression of c-MYC and AID.
Citation Format: Shaheen Mowla, Nontlantla Mdletshe. The role of HIV protein Nef in the development of HIV/AIDS-associated lymphomas [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr B31.