Herpes simplex virus type 2 tegument protein UL56 relocalizes ubiquitin ligase Nedd4 and has a role in transport and/or release of virions

Yoko Ushijima,Fumi Goshima,Yukihiro Nishiyama,Hiroshi Kimura

doi:10.1186/1743-422x-6-168

Abstract

BackgroundThe ubiquitin system functions in a variety of cellular processes including protein turnover, protein sorting and trafficking. Many viruses exploit the cellular ubiquitin system to facilitate viral replication. In fact, herpes simplex virus (HSV) encodes a ubiquitin ligase (E3) and a de-ubiquitinating enzyme to modify the host's ubiquitin system. We have previously reported HSV type 2 (HSV-2) tegument protein UL56 as a putative adaptor protein of neuronal precursor cell-expressed developmentally down-regulated 4 (Nedd4) E3 ligase, which has been shown to be involved in protein sorting and trafficking.ResultsIn this study, we visualized and characterized the dynamic intracellular localization of UL56 and Nedd4 using live-cell imaging and immunofluorescence analysis. UL56 was distributed to cytoplasmic vesicles, primarily to the trans-Golgi network (TGN), and trafficked actively throughout the cytoplasm. Moreover, UL56 relocalized Nedd4 to the vesicles in cells transiently expressing UL56 and in cells infected with HSV-2. We also investigated whether UL56 influenced the efficiency of viral replication, and found that extracellular infectious viruses were reduced in the absence of UL56.ConclusionThese data suggest that UL56 regulates Nedd4 and functions to facilitate the cytoplasmic transport of virions from TGN to the plasma membrane and/or release of virions from the cell surface.

Highlights

The ubiquitin system functions in a variety of cellular processes including protein turnover, protein sorting and trafficking
neuronal precursor cellexpressed developmentally down-regulated 4 (Nedd4) carboxyl-terminally tagged with EGFP (Nedd4-EGFP) and/or UL56 amino-terminally tagged with mRFP were transiently expressed in cells to visualize their distribution and movement
As previously observed in fixed cells, Nedd4-EGFP was diffusely distributed in the cytoplasm (Fig. 1A; additional file 1 [movie 1]) cells [13]. mRFP-UL56 was detected in a vesicular pattern and the puncta moved around the cytoplasm (Fig. 1B; additional file 2 [movie 2]). mRFP-UL56 puncta varied in size and moved in the different directions and at the different speeds

Summary

Introduction

The ubiquitin system functions in a variety of cellular processes including protein turnover, protein sorting and trafficking. We have previously reported HSV type 2 (HSV-2) tegument protein UL56 as a putative adaptor protein of neuronal precursor cellexpressed developmentally down-regulated 4 (Nedd4) E3 ligase, which has been shown to be involved in protein sorting and trafficking. The ubiquitin system is a key regulatory mechanism for a variety of cellular processes: protein turnover, protein sorting and trafficking, signal transduction and cell-cycle control [1]. Virology Journal 2009, 6:168 http://www.virologyj.com/content/6/1/168 members, is one of the main HECT E3 protein families. They are characterized by a unique domain architecture, with an amino-terminal C2 domain, two to four proteinprotein interacting WW domains and a carboxyl terminal catalytic HECT domain [4]

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