Inhibition of Polo-like kinase 1 (PLK1) to facilitate the reactivation and elimination of latent gamma-herpesviruses.

Both Kaposis sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV) establish the persistent, life-long infection primarily at the latent status, and contribute to certain types of tumors, including B cell lymphomas, especially in immuno-compromised individuals, such as people living with HIV (PLWH). Lytic reactivation of these viruses can be employed to kill tumor cells harboring latently infected viral episomes, through the viral cytopathic effects and the subsequent antiviral immune responses. In this study, we identified that polo-like kinase 1 (PLK1) is induced by KSHV de novo infection as well as lytic switch from KSHV latency. We further demonstrated that PLK1 depletion or inhibition facilitates KSHV reactivation and promotes cell death of KSHV-reactivated lymphoma cells. Mechanistically, PLK1 regulates Myc that is critical to both maintenance of KSHV latency and support of cell survival, and preferentially affects the level of H3K27me3 inactive mark both globally and at certain loci of KSHV viral episomes. Lastly, we recognized that PLK1 inhibition synergizes with STAT3 inhibition to efficiently induce KSHV reactivation. Furthermore, we also confirmed that PLK1 depletion or inhibition yields the similar effect on EBV reactivation and cell death of EBV-reactivated lymphoma cells. Additionally, we noticed the PLK1 in B cells is elevated in the context of HIV infection and by HIV Nef protein, which would favor KSHV/EBV latency. Above all, our findings illustrated that PLK1 is a novel host target that can be inhibited to benefit the viral oncolysis to eliminate KSHV/EBV-infected lymphoma cells, particularly for PLWH.