Tumor-derived Variants of Epstein-Barr Virus Latent Membrane Protein 1 Induce Sustained Erk Activation and c-Fos

Abstract

Latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV) is a proven oncogene that is essential for transformation LMP14 is an EBV-encoded oncoprotein that is essential for transformation of human B lymphocytes (1-3). In B cells LMP1 mimics the CD40 receptor, although unlike CD40, LMP1 functions in a ligand-independent manner and is constitutively active (4). LMP1 activates several cellular signaling pathways culminating in expression of downstream genes involved in cell transformation, survival, and proliferation. Thus, LMP1 plays a central role in EBV-associated tumorigenesis.LMP1 is composed of a short cytoplasmic N-terminal tail required for insertion into the membrane, six membrane-spanning domains that facilitate oligomerization of the protein, and a C-terminal cytoplasmic tail. Within the C terminus of LMP1 are two major signaling domains, C-terminal activation region 1 (CTAR1) and CTAR2. The CTAR interact with tumor necrosis factor receptor-associated factors (TRAFs) and TRAF-associated death domain protein (TRADD) molecules and potentially other adapter molecules to activate NF-B, Jun N-terminal kinase (JNK), p38 mitogen-activated protein (MAP) kinase, extracellular signal-regulated kinase (Erk), and phosphoinositide 3-kinase (PI3K). Several key sites within the C terminus of LMP1 are necessary for proper signaling including the PXQXT motif in the CTAR1 region which mediates binding of TRAFs 1, 2, 3, and 5, and tyrosines 384 and 385 of CTAR2 that are essential for TRADD interaction, the recruitment of TRAF2, and association of receptor-interacting protein (5-11).Activation of NF-B by LMP1 is critical to the survival of EBV-infected B cells. NF-B activation is highly regulated through association with the IB complex that prevents nuclear localization of NF-B. In EBV-infected B cells the activation of NF-B is initiated through interaction of LMP1 with TRAF2 at CTAR1 and TRAF6 at CTAR2, allowing for activation of the IB kinase (12, 13). IB kinase phosphorylates IB␣, thereby targeting it for proteasomal degradation. NF-B is then free to translocate to the nucleus and to activate transcription of downstream genes that promotes cell survival (14,15). Similar to the NF-B pathway, interaction of the adapter protein TRAF2 with both CTAR1 and CTAR2 (indirectly through TRADD) is required for p38 MAPK activation by LMP1 (16). We (17) and others (18) have shown that activation of p38 by LMP1 contributes to the induction of IL-10, an important autocrine growth factor for EBV-infected B cells.Whereas CTAR1 and CTAR2 both contribute to signaling of NF-B and p38, the activation of JNK, PI3K/Akt, and Erk rely on a single CTAR. Specifically, the CTAR2 domain of LMP1 participates in activation of the JNK pathway through interaction with TRAF6, TRAF2, and TRADD (19 -21). JNK kinase

Epstein-Barr Virus Infection Induces Indoleamine 2,3-Dioxygenase Expression in Human Monocyte-Derived Macrophages through p38/Mitogen-Activated Protein Kinase and NF-κB Pathways: Impairment in T Cell Functions

“…These results are consistent with previous studies that described HIV-induced IDO expression in dendritic cells and WNV-in- duced IDO expression in MDMs that predominantly depended on the activation of the MAPK/p38 and NF-B pathways (20,30). It has been confirmed that EBV infection activates the PI3K, JNK, and MAPK/p38 pathways and both the canonical and noncanonical NF-B signaling pathways (35)(36)(37). Activation of the p38, JNK, ERK, and NF-B pathways leads to the production of IDO-inducing cytokines such as TNF-␣ and IL-6, which act in an autocrine manner to stimulate the MAPK and NF-B pathways.…”

Using Epstein-Barr Viral Load Assays To Diagnose, Monitor, and Prevent Posttransplant Lymphoproliferative Disorder

“…Recently, there is increased acknowledgment of the role of host cytokine polymorphisms (e.g., mutated gamma interferon [IFN-␥], transforming growth factor ␤ [TGF-␤], and interleukin-10 [IL-10]) in defense against EBV and other viral pathogens (13,80,108,179). Likewise, EBV genomic polymorphism is emerging as a potential contributor to tumorigenesis (51,74,118,165,199). Variants in viral LMP1 gene sequence have been linked to pathogenesis and severity of lymphoid neoplasia (74,165).…”

Post-Transplant Lymphoproliferative Disease – PTLD

“…These cellular signaling pathways are responsible for the oncogenic function of the virus. It has been shown that tumor derived LMP-1 contains unique mutations, in position 212 and 366 (Vaysberg et al, 2008). Also, the wild type form of LMP-1 expressed on the B cell induces only a transient activation, known as benign or weakly oncogenic.…”

“…(Nepomuceno et al, 2003) Also, mTOR inhibitors provide an option of switching immunosuppression while providing some anti-tumor effect as an alternative to removal of immunosuppression. (Vaysberg et al, 2007 andKrams et al, 2008) A promising therapeutic option to control B-cell proliferation is anti-B-cell antibody therapy. Expression of B-cell antigens is variable in PTLD, most likely because of the dysregulation by EBV infection.…”