EBV-Encoded miR-BART20-5p and miR-BART8 Inhibit the IFN-γ-STAT1 Pathway Associated with Disease Progression in Nasal NK-Cell Lymphoma

Nasal NK-cell lymphoma (NNL) is an Epstein-Barr virus (EBV) associated Lymphoma of cytotoxic natural killer (NK) cell origin. Because normal NK cells secrete the principal cytotoxic cytokine IFN-gamma to suppress both tumor growth and viral replication, we investigated how EBV may have used miRNAs of viral origin to inhibit the IFN-gamma-STAT1 pathway to facilitate viral replication and tumor growth. In EBV- Jurkat cells, transfection of miR-BART20-5p and miR-BART8 inhibited translation of luciferase IFN-gamma-3'-UTR and luciferase STAT1-3'-UTR, respectively. In EBV+IFN-gamma(weak)/STAT1(strong) YT Leukemic cells and IFN-gamma-(strong)/STAT1(weak) NK92 cells, relative endogenous levels between miR-BART20-5p and IFN-gamma mRNAs or between miR-BART8 and STAT1 mRNAs determined expression of the targets. Chromatin immunoprecipitation studies showed that STAT1 regulates the transcription of the tumor suppressor TP53 (encoding p53) and miR-Let7a. Consistent with these findings, overexpression of miR-BART8 in YT cells or of miR-BART20-5p in NK92 cells inhibited p53 and increased resistance to doxorubicin. In 36 NNLs, the levels of miR-BART20-5p or miR-BART8 correlated inversely with the expression of STAT1. Additionally, in 46 NNLs, expression of both miR-BART20-5p and miR-BART8 identified a group of NNLs with decreased p53 mRNAs and evidence of disease progression. We conclude that miR-BART20-5p and miR-BART8 cause progression of nasal NK-cell lymphomas through inhibition of the IFN-gamma-STAT1 pathway.