The Cellular Peptidyl-Prolyl cis / trans Isomerase Pin1 Regulates Reactivation of Kaposi's Sarcoma-Associated Herpesvirus from Latency

Abstract

Kaposi's sarcoma-associated herpesvirus (KSHV) causes Kaposi's sarcoma and primary effusion lymphoma. KSHV-infected cells are predominantly latent, with a subset undergoing lytic reactivation. Rta is the essential lytic switch protein that reactivates virus by forming transactivation-competent complexes with the Notch effector protein RBP-Jk and promoter DNA. Strikingly, Rta homolog analysis reveals that prolines constitute 17% of conserved residues. Rta is also highly phosphorylated in vivo. We previously demonstrated that proline content determines Rta homotetramerization and function. We hypothesize that prolinedirected modifications regulate Rta function by controlling binding to peptidyl-prolyl cis/trans isomerases (PPIases). Cellular PPIase Pin1 binds specifically to phosphoserine-or phosphothreonine-proline (pS/T-P) motifs in target proteins. Pin1 dysregulation is implicated in myriad human cancers and can be subverted by viruses. Our data show that KSHV Rta protein contains potential pS/T-P motifs and binds directly to Pin1. Rta transactivation is enhanced by Pin1 at two delayed early viral promoters in uninfected cells. Pin1's effect, however, suggests a rheostat-like influence on Rta function. We show that in infected cells, endogenous Pin1 is active during reactivation and enhances Rta-dependent early protein expression induced by multiple signals, as well as DNA replication. Surprisingly, ablation of Pin1 activity by the chemical juglone or dominant-negative Pin1 enhanced late gene expression and production of infectious virus, while ectopic Pin1 showed inhibitory effects. Our data thus suggest that Pin1 is a unique, dose-dependent molecular timer that enhances Rta protein function, but inhibits late gene synthesis and virion production, during KSHV lytic reactivation.

Nuclear Innate Immune DNA Sensor IFI16 Is Degraded during Lytic Reactivation of Kaposi's Sarcoma-Associated Herpesvirus (KSHV): Role of IFI16 in Maintenance of KSHV Latency

“…To assess the effect of IFI16 KD on TPA-mediated KSHV lytic reactivation, BCBL-1 cells were transduced with a lentivirus containing ShIFI16 or a control lentivirus. Forty-eight hours later, cells were induced with TPA (20 ng/ml), and total RNA was isolated after 0, 3,6,9,12,24,36,48,72, and 96 h, as indicated (Fig. 3A).…”

“…The control of the latent and lytic phases of herpesviruses is a complex interplay and orchestration between viral and host factors. Host factors such as STAT3 (21), KAP1/TRIM28 (22), retinoblastoma (Rb) (23), and the cellular peptidyl-prolyl cis/trans isomerase Pin1 (24) were recently found to play very important roles in this latent-tolytic life cycle switch of herpesviruses.…”

KSHV Reactivation and Novel Implications of Protein Isomerization on Lytic Switch Control

“…In silico alignment analysis of the transcription activation factor (TAF) 50 superfamily revealed that Rta homologs share a consensus of 134 amino acids (residues conserved between KSHV Rta and at least one additional member). Proline consists of 38 of these amino acids, accounting for 16.7% of all of Rta’s conserved residues ( Figure 4 ) [ 40 , 166 ]. The high degree of conservation supported their putative functional significance.…”

“…In our report, we demonstrated an interaction between cellular isomerase Pin1 and KSHV lytic switch Rta. We showed that Pin1 is expressed and active in infected PEL cells after lytic cycle induction, and that Pin1 directly interacts with Rta in vitro and in infected cells, most likely at one of Rta’s putative conserved Pin1-recognition (pS/T-P) motifs [ 166 ]. Pin1 did not, however, interact with the essential Rta cofactor and Notch effector RBP-Jk by GST pulldown assay [ 166 ].…”

KSHV episomes: rugged individualists on the factory floor

“…The reasons for this fascinating conduct are unknown but likely involve viral chromatin compaction, epigenetic modifications [15,16,19] and interactions with host factors [33][34][35][36][37] . Consistent with our results, previous studies have vividly demonstrated that only a limited number of herpesviral genomes give rise to progeny virus in studies using a Brainbow cassette to trace the lineage of incoming viral herpesviral genomes during de novo lytic infections [38,39] .…”