Post-Transplant Lymphoproliferative Disease (PTLD) is a potentially fatal side effect of the immunosuppressive agents used to prevent allograft rejection. PTLD is associated with Epstein-Barr Virus (EBV) infection and can result in malignant B cell lymphoma. EBV lymphomagenesis is linked to the ability of the virus to usurp host cell pathways to promote cell survival. Indeed, the major oncogene of EBV, latent membrane protein 1 (LMP1), induces B cell resistance to multiple apoptotic pathways including Fas and TRAIL but the underlying mechanisms remain unknown. MicroRNAs (miRs) are small, non-coding RNAs that post-transcriptionally regulate gene expression for control of cellular events. Since aberrant expression of miRs is found in a variety of human malignancies, the goal of this study was to determine if cellular miRs modulated by EBV participate in the apoptotic resistance of host B cells induced by the virus.

We utilized microRNA array to establish that both EBV infection and LMP1 activation modulate B cell miRs and then validated the expression of individual miRs by qPCR. MicroRNA-194 expression was reduced in 5 of 6 EBV+ B cell lymphoma lines derived from patients with PTLD compared to B cell lines infected with the B95.8 strain of EBV, originally isolated from a patient with infectious mononucleosis (IM), or uninfected B cells. Using an inducible LMP1 signaling system expressed in an EBV negative B cell lymphoma line, BL41, we found that activation of LMP1 molecules isolated from PTLD patients markedly suppressed microRNA-194 expression compared to the IM form of LMP1. To determine the significance of microRNA-194 inhibition in PTLD-associated EBV infection, we used a lentiviral expression system to overexpress microRNA-194 in a panel of EBV+ PTLD-derived B cell lymphoma lines. Overexpression of microRNA-194 resulted in a significant increase (33-110%) in apoptotic B lymphoma cells as measured by Annexin V staining. Together these data demonstrate that EBV infection and LMP1 activation can alter host cell miR expression for cell survival through induction of apoptotic resistance. Thus, microRNA-194 may be a novel therapeutic candidate for inhibiting the survival of PTLD-associated EBV+ B cell lymphomas.

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