Epstein-Barr Virus Latent Membrane Protein-1 Effects on Junctional Plakoglobin and Induction of a Cadherin Switch

Latent membrane protein-1 (LMP1) is considered the major oncoprotein of Epstein-Barr virus and is frequently expressed in nasopharyngeal carcinoma (NPC). LMP1 promotes growth an migration of epithelial cells, and the loss of plakoglobin has been identified as a contributing factor to LMP1-induced migration. Plakoglobin is a junctional protein that can also serve as a transcription factor in Tcf/Lef signaling. To determine the effects of LMP1 on the molecular and functional properties of plakoglobin, LMP1 was overexpressed in the NPC cell line C666-1. LMP1 did not affect plakoglobin stability but did decrease plakoglobin transcription. The resultant decreased levels of nuclear plakoglobin did not affect Tcf/Lef activity or the amount of plakoglobin bound to Tcf4. Although LMP1 induced and stabilized beta-catenin, a protein with common binding partners to plakoglobin, the loss of plakoglobin did not affect its association with Tcf4. However, LMP1 did induce a cadherin switch from E- to N-cadherin, a process involved in cancer progression, and enhanced the association of junctional beta-catenin with N-cadherin. LMP1 decreased overall levels of junctional plakoglobin but the remaining junctional plakoglobin was found associated with the induced N-cadherin. This increased association of junctional plakoglobin wit N-cadherin was a distinguishing feature of LMP1-expressing cells that have reduced migration due to restoration of plakoglobin. Low levels of plakoglobin were also detected in human NPC tissues. These findings reveal that the effects of LMP1 on junctional plakoglobin and the initiation of a cadherin switch likely contribute to metastasis of NPC. [Cancer Res 2009;69(14):5734-42]