Nucleophosmin Phosphorylation by v-Cyclin-CDK6 Controls KSHV Latency

Abstract

Nucleophosmin (NPM) is a multifunctional nuclear phosphoprotein and a histone chaperone implicated in chromatin organization and transcription control. Oncogenic Kaposi's sarcoma herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma, primary effusion lymphoma (PEL) and multicentric Castleman disease (MCD). In the infected host cell KSHV displays two modes of infection, the latency and productive viral replication phases, involving extensive viral DNA replication and gene expression. A sustained balance between latency and reactivation to the productive infection state is essential for viral persistence and KSHV pathogenesis. Our study demonstrates that the KSHV v-cyclin and cellular CDK6 kinase phosphorylate NPM on threonine 199 (Thr199) in de novo and naturally KSHV-infected cells and that NPM is phosphorylated to the same site in primary KS tumors. Furthermore, v-cyclin-mediated phosphorylation of NPM engages the interaction between NPM and the latency-associated nuclear antigen LANA, a KSHV-encoded repressor of viral lytic replication. Strikingly, depletion of NPM in PEL cells leads to viral reactivation, and production of new infectious virus particles. Moreover, the phosphorylation of NPM negatively correlates with the level of spontaneous viral reactivation in PEL cells. This work demonstrates that NPM is a critical regulator of KSHV latency via functional interactions with v-cyclin and LANA.

Kaposi's Sarcoma-Associated Herpesvirus-Encoded LANA Contributes to Viral Latent Replication by Activating Phosphorylation of Survivin

“…These studies suggested that KSHV can maintain its latency through regulation of the levels and activities of HATs and HDACs. Phosphorylation of the cellular protein nucleophosmin can control KSHV latency (89). The results obtained in our study also showed that a LANA and AK-B complex can enhance phosphorylation of survivin during KSHV latent replication (89).…”

“…Phosphorylation of the cellular protein nucleophosmin can control KSHV latency (89). The results obtained in our study also showed that a LANA and AK-B complex can enhance phosphorylation of survivin during KSHV latent replication (89). Therefore, the stabilization and activation of survivin can create an environment for hyperacetylation of histones in KSHV latently infected cells.…”

Histone Deacetylase Classes I and II Regulate Kaposi's Sarcoma-Associated Herpesvirus Reactivation

“…In particular, H3K27 methyltransferase (EZH2) activity, depletion of which reactivates KSHV (20,22), has been shown to require HDACs (48). Also, the viral protein LANA inhibits reactivation and forms multiprotein complexes with HDAC1 (73,74).…”

The Kaposi's Sarcoma-Associated Herpesvirus (KSHV)-Induced 5-Lipoxygenase-Leukotriene B4 Cascade Plays Key Roles in KSHV Latency, Monocyte Recruitment, and Lipogenesis

“…Nucleophosmin (NPM), a multifunctional nuclear phosphoprotein and a histone chaperone implicated in chromatin organization and transcription control, has been reported to be a novel link between LANA/vCyclin and KSHV latency. NPM phosphorylation by the vCyclin-cyclindependent kinase 6 complex supports its interaction with LANA and enables the transcriptional silencing of the KSHV lytic genes needed for latency (96). Interestingly, NPM phosphorylation has been shown to be regulated by lipoxygenases (97).…”