Reversible role of MIR654/3P and MIR9/3P in pathogenesis of Epstein-Barr virus-negative, but not Epstein-Barr virus-positive, Burkitt lymphoma.

The role of MIR654 in Burkitt lymphoma (BL) and whether it impacts expression of MYC and its downstream activated MIR9 is not known. Expression of MYC, MYCN, MYCL, MIR9/3P, MIR654/5P, and MIR654/3P was assessed by quantitative reverse-transcription polymerase chain reaction in biopsy samples from Epstein-Barr virus-negative (EBV-) and EBV+ BL patients and BL cell lines. Effects of modulation of MIR9/3P and MIR654/3P on cell proliferation, apoptosis, and chemosensitivity were evaluated. Luciferase reporter assay was performed to validate the putative target of MIR654/5P. Effects of MIR9/3P and MIR654/3P on tumor burden and disease outcome were evaluated using xenograft model of BL. Expression of MYC, MYCN, and MIR9/3P was higher in all BL patient samples and cell lines. Expression of MIR654/3P was downregulated in EBV- BL patient samples and cell lines compared with either noncancer lymphoid-reactive hyperplasia or EBV+ samples and cell lines. Additionally, MIR654/3P overexpression inhibited cell proliferation, induced apoptosis, and increased chemosensitivity in EBV- BL cell lines. Luciferase reporter assay confirmed that MYC is a target of MIR654/3P in both EBV- and EBV+ BL cell lines; however, the effect of MIR654/3P-mediated targeting of MYC is overridden in EBV+ cells. Administration of MIR654/3P mimic or MIR9/3P antagomir in the xenograft model decreased tumor burden and increased survival. Combined intervention with MIR654/3P mimic and MIR9/3P antagomir had synergistic action on decreasing tumor burden and improving disease outcome. MIR654/3P, as a putative tumor suppressor in EBV- BL, collaborating with MIR9/3P might serve as a therapeutic agent to treat EBV- BL patients in combination with existing chemotherapy and immunotherapy regimes.