Counteracting effects of cellular Notch and Epstein-Barr virus EBNA2 : implications for stromal effects on virus-host interactions
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Colleges, School and Institutes
A number of diverse environmental cues have been linked to B lymphocyte differentiation and activation. One such cue, Notch-2, may be particularly relevant to the biology of Epstein Barr virus (EBV) infection which colonizes the B cell compartment. Activated Notch and EBV nuclear antigen, EBNA2, both function as transcriptional activators by virtue of their interactions with the transcription factor RBP-Jκ. Although EBNA2 and activated Notch appear to have partially overlapping functions, we now report that activated Notch counteracts a crucial EBNA2 function in both newly-infected primary B cells and in lymphoblastoid cell lines (LCLs). EBNA2 is directly responsible for the initiation of transcription of the majority of EBV proteins associated with type III latency, leading to the outgrowth of LCLs. One of the key proteins driving this outgrowth is latent membrane protein 1 (LMP1), which is regulated by an EBNA2-responsive element within its ED-L1 promoter. Activation of Notch-2 via Delta-like ligand-1 inhibits EBNA2 mediated initiation of LMP1 transcription. Furthermore, ligated Notch-2 also efficiently turns off LMP1 from the ED-L1 promoter in LCLs already expressing LMP1. Modulation of EBV gene expression by Notch was not confined to EBNA2-dependent events. Activated Notch-2 also inhibited EBV entry into lytic cycle in a B-cell non-Hodgkin lymphoma line by up-regulating the cellular transcription factor Zeb2, which represses transcription of BZLF1. These results support the concept that in vivo, cumulative signals from the microenvironment down-regulate EBV gene expression in B cells to the latency 0 gene expression profile observed in B cells entering the peripheral blood.
IMPORTANCE: Experimental infection of resting B cells by Epstein Barr virus leads to the growth transformation programme of virus gene expression and outgrowth of lymphoblastoid cell lines. Previous studies at the single cell level revealed complex cellular and viral signaling networks regulating transcription of the viral genome. This study demonstrates that viral gene expression can also be radically altered by molecules expressed on stromal cells in the microenvironment of lymphoid tissue; specifically, Delta-like ligand-1 on stromal cells ligating Notch-2 on infected B cells. Activation of Notch interferes with the transactivation function of EBNA2, downregulates expression of LMP1 and LMP2a, and inhibits activation of lytic virus replication in B-cell non-Hodgkin lymphoma line by preventing expression of BZLF1. The significance of these observations is that they indicate new mechanisms whereby the microenvironment in normal lymphoid tissue may facilitate the repression of viral gene expression enabling establishment of true latency in memory B cells.
|Journal||Journal of virology|
|Early online date||13 Aug 2014|
|Publication status||Published - Oct 2014|