Upregulation of Cellular Bcl-2 by the KSHV Encoded RTA Promotes Virion Production

Jianming Gao,Hem Chandra Jha,Erle S. Robertson,Qiliang Cai,Jie Lu,J. Pedro Simas

doi:10.1371/journal.pone.0023892

Jianming Gao, Hem Chandra Jha + Show 4 more

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https://doi.org/10.1371/journal.pone.0023892

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Journal: PloS one	Publication Date: Aug 25, 2011
Citations: 73	License type: CC BY 4.0

Affiliation: University of Pennsylvania

Abstract

Apoptosis of virus infected cells can restrict or dampen full blown virus propagation and this can serve as a protective mechanism against virus infection. Consequently, viruses can also delay programmed cell death by enhancing the expression of anti-apoptotic proteins. Human Bcl-2 is expressed on the surface of the mitochondrial membrane and functions as the regulator of the delicate balance between cell survival and apoptosis. In this report, we showed that the replication and transcription activator (RTA) encoded by KSHV ORF 50, a key regulator for KSHV reactivation from latent to lytic infection, upregulates the mRNA and protein levels of Bcl-2 in 293 cells, and TPA-induced KSHV-infected cells. Further analysis revealed that upregulation of the cellular Bcl-2 promoter by RTA is dose-dependent and acts through targeting of the CCN9GG motifs within the Bcl-2 promoter. The Bcl-2 P2 but not the P1 promoter is primarily responsive to RTA. The results of ChIP confirmed the direct interaction of RTA protein with the CCN9GG motifs. Knockdown of cellular Bcl-2 by lentivirus-delivered small hairpin RNA (shRNA) resulted in increased cell apoptosis and decreased virion production in KSHV-infected cells. These findings provide an insight into another mechanism by which KSHV utilizes the intrinsic apoptosis signaling pathways for prolonging the survival of lytically infected host cells to allow for maximum production of virus progeny.

Highlights

Kaposi’s Sarcoma-Associated Herpesvirus (KSHV), the etiological factor associated with Kaposi’s Sarcoma is known as human herpesvirus 8 (HHV 8)
KSHV viral genes are successively activated in the lytic replication phase which can be triggered by replication and transcription activator (RTA) [53]
RTA regulates the KSHV lytic phase to reactivate the virus from latency and so initiate replication [55,56,57]

Summary

Introduction

Kaposi’s Sarcoma-Associated Herpesvirus (KSHV), the etiological factor associated with Kaposi’s Sarcoma is known as human herpesvirus 8 (HHV 8). Several other malignancies such as primary effusion lymphoma, and multicentric Castleman’s disease have been known to associate with KSHV [1,2,3,4]. The virus establishes persistent infection and only a small subset of genes such as ORF73, K12, ORF72, ORF71 and K15 are typically expressed [9,10]. Under conditions of lytic reactivation such as hypoxia the virus spreads to new target cells and the viral genes are activated in cascade mode [11,12,13]. The switch to lytic reactivation is experimentally induced by a number of intracellular or extracellular motivators including the chemical agents 12-O-tetradecanoyl phorbol-13 acetate (TPA) and sodium butyrate [14,15]

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