RESEARCH ARTICLE Cellular MicroRNA Let-7a Suppresses KSHV Replication through Targeting MAP4K4 Signaling Pathways

Background Kaposi’s sarcoma (KS)-associated herpesvirus (KSHV) is the etiologic agent of KS, the most common AIDS-related malignancy. The majority of KS tumor cells harbor latent KSHV virus but only a small percentage undergoes spontaneous lytic replication. Viral reactivation from latency is crucial for the pathogenesis and development of KS, but the cellular mecha-nisms underlying the switch between viral latency and replication are not well understood. Methods The level of let-7 miRNAs and MAP4K4 in KSHV infected 293T cells were quantified by real-time PCRs. Let-7 expression was silenced by the miRNA sponge technique. In let-7a transfected 293T cells, the expression of MAP4K4 was measured by real-time PCR and western blot. Luciferease expression was employed to examine the effect of let-7a on the 3’-untranslated region (UTR) of theMAP4K4 gene in 293T cells. Real-time PCR was used to quantify the KSHV copy numbers in BC-3 cells in which the expression of let-7a and/or MAP4K4 were altered. Finally, ERK, JNK and p38 protein production and their phosphoryla