Epstein-Barr virus-encoded EBNA2 downregulates ICOSL by inducing miR-24 in B-cell lymphoma

Blood. 2024 Feb 1;143(5):429-443. doi: 10.1182/blood.2023021346.

Abstract

Hematological malignancies such as Burkitt lymphoma (BL), Hodgkin lymphoma (HL), and diffuse large B-cell lymphoma (DLBCL) cause significant morbidity in humans. A substantial number of these lymphomas, particularly HL and DLBCLs have poorer prognosis because of their association with Epstein-Barr virus (EBV). Our earlier studies have shown that EBV-encoded nuclear antigen (EBNA2) upregulates programmed cell death ligand 1 in DLBCL and BLs by downregulating microRNA-34a. Here, we investigated whether EBNA2 affects the inducible costimulator (ICOS) ligand (ICOSL), a molecule required for efficient recognition of tumor cells by T cells through the engagement of ICOS on the latter. In virus-infected and EBNA2-transfected B-lymphoma cells, ICOSL expression was reduced. Our investigation of the molecular mechanisms revealed that this was due to an increase in microRNA-24 (miR-24) by EBNA2. By using ICOSL 3' untranslated region-luciferase reporter system, we validated that ICOSL is an authentic miR-24 target. Transfection of anti-miR-24 molecules in EBNA2-expressing lymphoma cells reconstituted ICOSL expression and increased tumor immunogenicity in mixed lymphocyte reactions. Because miR-24 is known to target c-MYC, an oncoprotein positively regulated by EBNA2, we analyzed its expression in anti-miR-24 transfected lymphoma cells. Indeed, the reduction of miR-24 in EBNA2-expressing DLBCL further elevated c-MYC and increased apoptosis. Consistent with the in vitro data, EBNA2-positive DLBCL biopsies expressed low ICOSL and high miR-24. We suggest that EBV evades host immune responses through EBNA2 by inducing miR-24 to reduce ICOSL expression, and for simultaneous rheostatic maintenance of proproliferative c-MYC levels. Overall, these data identify miR-24 as a potential therapeutically relevant target in EBV-associated lymphomas.

MeSH terms

  • Antagomirs
  • Epstein-Barr Virus Infections* / complications
  • Epstein-Barr Virus Infections* / genetics
  • Epstein-Barr Virus Infections* / metabolism
  • Epstein-Barr Virus Nuclear Antigens / genetics
  • Epstein-Barr Virus Nuclear Antigens / metabolism
  • Herpesvirus 4, Human / genetics
  • Hodgkin Disease* / complications
  • Humans
  • Ligands
  • Lymphoma, Large B-Cell, Diffuse* / metabolism
  • MicroRNAs* / genetics
  • Viral Proteins / metabolism

Substances

  • Antagomirs
  • Epstein-Barr Virus Nuclear Antigens
  • Ligands
  • MicroRNAs
  • MIRN24 microRNA, human
  • Viral Proteins
  • EBNA-2 protein, Human herpesvirus 4
  • ICOSLG protein, human