*Purpose: Malignancies attributable to EBV, such as post-transplant lymphoproliferative disorder (PTLD), represent 1.8% of global cancer deaths. PTLD occurs in 1-20% of transplant recipients and results in significant morbidity and mortality. The mechanisms the virus utilizes towards the development and progression of EBV⁺ B cell lymphomas like PTLD are poorly characterized. We previously demonstrated that EBV infection modulates expression of host B cell microRNAs (miRs), small non-coding RNAs that regulate gene expression. The purpose of this study was to determine how the EBV oncogene latent membrane protein 1 (LMP1) regulates expression of host cell miRs.

*Methods: We used EBV^– B lymphoma lines that express inducible, chimeric LMP1 molecules derived from the B95.8 lab strain of EBV or PTLD tumor variants previously defined to contain gain of function mutations at position 212 and 366 of LMP1, and assessed miR expression by qPCR.

*Results: miR-155 and miR-886-5p were significantly upregulated in B cells by EBV infection and both B95.8 and tumor variant LMP1[OH1] . However, while miR-193b was upregulated by EBV infection and B95.8 LMP1, it was not modulated by PTLD tumor variant LMP1. To evaluate the requirement for specific signal transduction pathways, we utilized small molecule inhibitors (SMI) to target NFκB, p38, ERK, mTOR or PI3K. NFκB and p38 signaling were required for miR-155, but not miR-193b or miR-886-5p upregulation. Notably, miR-155 upregulation was also significantly reduced by a PI3Kα,δ inhibitor and PI3Kα-specific inhibitor. Since miRNA can have cell intrinsic effects or could be exported via exosomes we compared the levels of these miRs in EBV⁺ B cell lymphomas and their associated exosomes. Compared to EBV^– B cell lymphoma cells and associated exosomes, miR-155 and miR-193b, but not miR-886-5p, is significantly elevated in EBV⁺ B cell lymphomas and associated exosomes.

*Conclusions: Our data suggests that host miR expression by LMP1 is altered in PTLD and that unique signaling pathways downstream of LMP1 are required to regulate the expression of each host miR. Finally, this is the first demonstration that LMP1 regulates miR-155 expression by the PI3K pathway, specifically the PI3Kα isoform. Thus, modulation of miRNA by SMI is a potential therapeutic approach for EBV+ PTLD and exosomal miR-155 and miR-193b may serve as biomarkers for EBV+ B cell lymphomas like PTLD.

« Back to 2019 American Transplant Congress