Id1 interacts and stabilizes the Epstein-Barr virus latent membrane protein 1 (LMP1) in nasopharyngeal epithelial cells.

Maria G Masucci,Pok Man Hau,Sai Wah Tsao,Michael S Y Huen,Chi Man Tsang,Yim Ling Yip

doi:10.1371/journal.pone.0021176

Abstract

The EBV-encoded latent membrane protein 1 (LMP1) functions as a constitutive active form of tumor necrosis factor receptor (TNFR) and activates multiple downstream signaling pathways similar to CD40 signaling in a ligand-independent manner. LMP1 expression in EBV-infected cells has been postulated to play an important role in pathogenesis of nasopharyngeal carcinoma. However, variable levels of LMP1 expression were detected in nasopharyngeal carcinoma. At present, the regulation of LMP1 levels in nasopharyngeal carcinoma is poorly understood. Here we show that LMP1 mRNAs are transcribed in an EBV-positive nasopharyngeal carcinoma (NPC) cell line (C666-1) and other EBV-negative nasopharyngeal carcinoma cells stably re-infected with EBV. The protein levels of LMP1 could readily be detected after incubation with proteasome inhibitor, MG132 suggesting that LMP1 protein is rapidly degraded via proteasome-mediated proteolysis. Interestingly, we observed that Id1 overexpression could stabilize LMP1 protein in EBV-infected cells. In contrary, Id1 knockdown significantly reduced LMP1 levels in cells. Co-immunoprecipitation studies revealed that Id1 interacts with LMP1 by binding to the CTAR1 domain of LMP1. N-terminal region of Id1 is required for the interaction with LMP1. Furthermore, binding of Id1 to LMP1 suppressed polyubiquitination of LMP1 and may be involved in stabilization of LMP1 in EBV-infected nasopharyngeal epithelial cells.

Highlights

Epstein-Barr virus (EBV, categorized as human herpesvirus type 4) is the first human oncogenic DNA virus isolated from Burkitt’s lymphoma capable to transform B cells in vitro [1]
The latent membrane protein 1 (LMP1) transcripts were readily detected in C666-1 which is an EBV-positive nasopharyngeal carcinoma cell line [7], and other cell lines infected with EBV including NP460-hTERT-EBV [20], HONE1-EBV, CNE2-EBV, HK1-EBV and AGS-EBV
LMP1 expression is commonly detected in nasopharyngeal carcinoma [6]

Summary

Introduction

Epstein-Barr virus (EBV, categorized as human herpesvirus type 4) is the first human oncogenic DNA virus isolated from Burkitt’s lymphoma capable to transform B cells in vitro [1]. EBV was later shown to be a prototype of gamma herpesvirus that infects the majority of population worldwide. EBV infection is associated with specific types of human malignancies, for example Burkitt’s lymphoma, Hodgkin’s lymphoma, nasopharyngeal carcinoma and gastric carcinoma [2]. Examination of the expression profile of EBV genes in EBVrelated malignancies and EBV-derived cell lines have defined four major types of EBV latent infection: Latency 0, 1, 2 and 3 each with distinct EBV gene expression. Nasopharyngeal carcinoma are shown to exhibit type II latency infection and the major EBV genes expressed are EBNA1, EBER, LMP1, LMP2A, LMP2B, BARF1 and BARTs. The LMP1 is well-documented to be an important oncoprotein of EBV. The LMP1 is well-documented to be an important oncoprotein of EBV It is a transmembrane protein which localizes at cholesterol-rich lipid raft [3,4]. LMP1 functions as constitutive active form of tumor necrosis factor receptor (TNFR) and activates multiple downstream signaling pathways similar to CD40 signaling mostly via its C-terminal activation domains (CTAR): CTAR1, CTAR2 and CTAR3 [5]

Methods

Results

Conclusion