Epstein-Barr virus (EBV)is associated with several human malignancies where it expresses limited subsets of latent proteins. Of the latent proteins, latent membrane protein 1 (LMP1) is a potent transforming protein that constitutively induces multiple cell signaling pathways and contributes to EBV-associated oncogenesis. Regulation of LMP1 expression has been extensively described during the type III latency of EBV. Nevertheless, in the majority of EBV-associated tumors, the virus is commonly found to display a type II latency program in which it is still unknown which viral or cellular protein is really involved in maintaining LMP1 expression. Here, we demonstrate that LMP1 activates its own promoter pLMP1 through the JNK signaling pathway emerging from the TES2 domain. Our results also reveal that this activation is tightly controlled by LMP1, since pLMP1 is inhibited by LMP1-activated NF-B signaling pathway. By using our physiological models of EBV-infected cells displaying type II latency as well as lymphoblastoid cell lines expressing a type III latency, we also demonstrate that this balanced autoregulation of LMP1 is shared by both latency programs. Finally, we show that this autoactivation is the most important mechanism to maintain LMP1 expression during the type II latency program of EBV.Epstein-Barr virus (EBV) is a widespread herpesvirus, found in more than 90% of healthy adults and persisting, in the vast majority of individuals, as a lifelong and asymptomatic infection. EBV classically infects B cells, causing sometimes a benign disease (infectious mononucleosis) but also malignant disorders, such as B-lymphoproliferative diseases, in patients with severe immunodeficiency. In immunocompetent hosts, EBV is also associated with other malignancies, including Burkitt's lymphoma, nasopharyngeal carcinoma, Hodgkin's disease, peripheral or nasal NK/T-cell lymphomas, and gastric, breast, and hepatocellular adenocarcinomas (46,50). In all EBV-associated tumors, the virus displays mainly a latency program of infection with a restricted pattern of gene expression, which can be classified in three types. Type I latency, during which only the EBV-encoded nuclear antigen 1 (EBNA1) is expressed, is found in Burkitt's lymphoma. Type II latency is characterized by coexpression of EBNA1 and latent membrane proteins LMP1, LMP2A, and LMP2B and is found in nasopharyngeal carcinoma, Hodgkin's disease, NK/T-cell lymphomas, and AIDS-related non-Hodgkin's lymphomas. Type III latency with expression of the five EBNAs and three latent membrane proteins is restricted to B lymphomas of immunodeficient patients (50).Cellular models allowing investigation of the roles of LMP1 during type II and type III latencies have been developed. In vitro, EBV can infect and immortalize resting B cells to yield permanent growth of lymphoblastoid cell lines (LCLs) displaying a full latency III program (27). We previously showed that EBV can also infect and transform T cells and monocytes. We have described and extensively characterized two cel...

The latent membrane protein-1 (LMP1) is an integral membrane molecule expressed by Epstein-Barr virus (EBV) during viral latency and displays properties of a constitutively activated member of the TNF receptor family. LMP1 is required for B-cell or monocyte immortalization induced by EBV and is sufficient to transform rodent fibroblasts. Transforming potential of LMP1 is mediated by its cytoplasmic C-terminal domain, which activates various cellular signaling pathways including NFjB and JNK. In this report, we constructed mutants of LMP1 with preserved membrane spanning domain but mutated in the C-terminal domain and a second truncated C-terminal LMP1 fused to the enhanced green fluorescent protein. This latter mutant, termed LMP1-CT, impairs signaling by ectopic LMP1 as well as endogenous EBVexpressed wild-type (wt) LMP1. In contrast to dominantnegative mutants of LMP1 with preserved membrane spanning domains, LMP1-CT was unable to bind wt LMP1 to form an inactive complex. Its dominant-negative effects were due to binding and sequestration of LMP1 adapters TRAF2 and TRADD as assessed by coimmunoprecipitation experiments and confocal analysis. The effect was selective since LMP1-CT did not inhibit IL1b-induced signaling, whereas it impaired TNF-triggered NFjB and JNK signals without affecting TNF-induced apoptosis. In addition and in contrast to LMP1 constructs with membrane localization, LMP-CT did not display cytostatic properties in noninfected cells. Importantly, LMP1-CT inhibited survival induced by LMP1 in an EBV-transformed T-cell line expressing the type II viral latency commonly found in the majority of EBVassociated human tumors. These data demonstrate that LMP1-CT is a new tool to explore the differences between LMP1 and TNF signaling and may facilitate the design of molecules with potential therapeutic roles.