Abstract 3793: Understanding the function of LMP1 CTAR3 in EBV-associated lymphomas

Abstract

Abstract Background: Our present study aims to determine the function of the repetitive elements in the biology of Epstein-Barr virus (EBV) Latent Membrane Protein-1 (LMP1). Latent EBV infection is associated with distinct lymphoid and epithelial malignancies, and LMP1 is the principal oncoprotein of the virus. LMP1 has three C-terminal activating regions (CTARs) that induce multiple signal transduction pathways resulting in sustained cellular proliferation, increased cellular survival, and its oncogenic nature. CTAR1 and CTAR2 have been extensively characterized, but CTAR3 is much less studied. CTAR3 contains the LMP1 repetitive elements, which consist of 11-amino acid repeats and PxxPxP/Jak-interacting motifs. Analysis of over 200 clinical isolates revealed that there is significant variability in the number of 11-aaR (1.5-7.5 repeats) and PxxPxP-motives (1-2 repeats), but the exact function of these elements in oncogenesis is unknown. The findings of the study will greatly add to the understanding of the oncogenic nature of LMP1 and help to elucidate a specific purpose for the repetitive elements found within CTAR3. Methods: Using EBV B95.8 as our wild type strain, we constructed GFP-tagged LMP1 expression constructs that contain (1) wild type CTAR3; (2) PxxPxP only (no 11-aaR); (3) 11-aaR only (no PxxPxP); and (4) ΔCTAR3 (no 11-aaR or PxxPxP). These expression constructs were transfected into HEK 293 cells to assess the effect of the repeats on the trafficking and oncogenic potential of LMP1. Results: Findings suggest that the 11-aaR are necessary for correct intracellular and extracellular trafficking of LMP1. Loss of the 11-aaRs results in decreased plasma membrane-expressed LMP1 and the accumulation of LMP1 in intracellular membranes. Further, loss of the 11-aaR inhibits LMP1-induced cell migration, which suggests that the 11-aaR contribute to the oncogenic nature of LMP1. Conclusions: The number of 11-aaR found in LMP1 CTAR3 is variable in nature. Here we show that loss of the 11-aaR inhibits the normal biology of the oncoprotein, in that LMP1 trafficking is altered and the ability of the oncoprotein in promote cell migration is abrogated. Therefore, we propose that the CTAR3 11-aaR are essential to the oncogenic nature of LMP1. The role of these repeats during the transformation process and during tumorigenesis will be determined. Ultimately, further appreciation of the role of LMP1 CTAR3 in the biology of the virus may help identify potential targets for therapeutic interventions for EBV-associated malignancies. Citation Format: Tabithia Ross, Gretchen L. Bentz. Understanding the function of LMP1 CTAR3 in EBV-associated lymphomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3793.