Epstein-Barr virus latent membrane protein 2A activates beta-catenin signaling in epithelial cells.
The Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A) functions to maintain latency in EBV-infected B lymphocytes. Although LMP2A is nonessential for the immortalization of B lymphocytes by EBV, its expression in B lymphocytes prevents viral reactivation by blocking B-cell receptor activation and signaling. LMP2A also provides an antiapoptotic signal in transgenic mice that express LMP2A in B lymphocytes. LMP2A activates phosphatidylinositol 3-kinase (PI3K) and the serine/threonine kinase Akt in lymphocytes and epithelial cells. Here we show that EBV LMP2A activates the PI3K and beta-catenin signaling pathways in telomerase-immortalized human foreskin keratinocytes (HFK). LMP2A activated Akt in a PI3K-dependent manner, and the downstream Akt targets glycogen synthase kinase 3beta (GSK3beta) and the Forkhead transcription factor FKHR were phosphorylated and inactivated in LMP2A-expressing HFK cells. GSK3beta is a negative regulator of the Wnt signaling pathway, and inactivation of GSK3beta by LMP2A signaling led to stabilization of beta-catenin, the central oncoprotein of Wnt signaling. In LMP2A-expressing cells, beta-catenin accumulated in the cytoplasm and translocated into the nucleus via a two-step mechanism. The cytoplasmic accumulation of beta-catenin downstream of LMP2A was independent of PI3K signaling, whereas its nuclear translocation was dependent on PI3K signaling. In the nucleus, beta-catenin activated a reporter responsive to T-cell factor, and this activation was augmented by LMP2A coexpression. The Wnt pathway is inappropriately activated in 90% of colon cancers and is dysregulated in several other cancers, and these data suggest that activation of this pathway by LMP2A may contribute to the generation of EBV-associated cancers.
Morrison
J A
JA
Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Klingelhutz
A J
AJ
Raab-Traub
N
N
D021581:Active Transport, Cell Nucleus; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000502:physiology; D038362:Glycogen Synthase Kinase 3 / Q000502:physiology; D000071679:Glycogen Synthase Kinase 3 beta; D004854:Herpesvirus 4, Human / Q000472:pathogenicity; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D051821:Lymphoid Enhancer-Binding Factor 1; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000502:physiology*; D019098:Telomerase / Q000235:genetics; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000502:physiology; D014763:Viral Matrix Proteins / Q000502:physiology*; D051176:beta Catenin
D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D051821:Lymphoid Enhancer-Binding Factor 1; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019098:Telomerase; D015534:Trans-Activators; D014157:Transcription Factors; D014763:Viral Matrix Proteins; D051176:beta Catenin; C495270:CTNNB1 protein, human; C037662:EBV-associated membrane antigen, Epstein-Barr virus; C494918:AKT1 protein, human; C000605506:GSK3B protein, human; C000605507:Gsk3b protein, mouse