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Function of latent protein 2B in EBV-positive Burkitt's lymphoma


Rechsteiner, M. Function of latent protein 2B in EBV-positive Burkitt's lymphoma. 2008, University of Zurich, Faculty of Science.

Abstract

Epstein-Barr virus (EBV) is a human γ-herpesvirus that, following primary infection, persists latently in the host’s memory B-cell pool for life and may periodically reactivate to lytic infection. EBV is linked to malignancies including Burkitt’s lymphoma (BL), Hodgkin’s
lymphoma (HL), and post-transplant lymphoproliferative diseases where it expresses different patterns of latency genes. Among these genes, latent membrane protein (LMP)2A and LMP2B seem to be involved in the regulation of EBV latency. LMP2A blocks the signalling from the B-cell receptor (BCR) after its engagement, which results otherwise in switching from latent to lytic EBV infection and induction of apoptosis. Therefore, LMP2A contributes
to ensuring the persistence of EBV in the latently infected B-cell. By contrast, the function of LMP2B, a splice variant of LMP2A, and its interaction with LMP2A is still not resolved. Thus, the investigation of the function of LMP2B and its contribution to latent and lytic EBV
infection was the main goal of my PhD thesis. To study switching of latent to lytic EBV the EBV-harboring BL cell line Akata was employed. BL Akata cells can easily be induced to switch latent to lytic EBV upon engagement of their BCR through cross-linking using anti-human immunoglobulin antibodies. BL Akata cells with silenced LMP2A, silenced LMP2B, overexpressed LMP2A, or overexpressed LMP2B were generated. The establishment of these cell lines revealed for the first time that silencing of LMP2B in EBV-harboring BL cells resulted in reduced expression of the initiator of lytic EBV, i.e.,
immediate-early lytic BZLF1 EBV gene mRNA and late lytic gp350/220 protein upon BCR cross-linking. Similarly, reduction of lytic EBV activation was observed in BL Akata cells overexpressing LMP2A. By contrast, silencing of LMP2A and LMP2B overexpression in BL Akata cells resulted in higher lytic EBV mRNA and protein expression upon BCR crosslinking. We could further demonstrate that LMP2A and LMP2B physically interact and that LMP2B resides predominantly in intracellular compartments, whereas LMP2A was detected on the plasma membrane as well as in intracellular compartments. In conclusion, these observations indicate a role for LMP2B distinct from LMP2A in regulation of lytic EBV activation in the host cell and support the hypothesis that LMP2B exhibits a negative regulatory effect on the ability of LMP2A to maintain latent EBV by preventing the switch to lytic EBV.

Abstract

Epstein-Barr virus (EBV) is a human γ-herpesvirus that, following primary infection, persists latently in the host’s memory B-cell pool for life and may periodically reactivate to lytic infection. EBV is linked to malignancies including Burkitt’s lymphoma (BL), Hodgkin’s
lymphoma (HL), and post-transplant lymphoproliferative diseases where it expresses different patterns of latency genes. Among these genes, latent membrane protein (LMP)2A and LMP2B seem to be involved in the regulation of EBV latency. LMP2A blocks the signalling from the B-cell receptor (BCR) after its engagement, which results otherwise in switching from latent to lytic EBV infection and induction of apoptosis. Therefore, LMP2A contributes
to ensuring the persistence of EBV in the latently infected B-cell. By contrast, the function of LMP2B, a splice variant of LMP2A, and its interaction with LMP2A is still not resolved. Thus, the investigation of the function of LMP2B and its contribution to latent and lytic EBV
infection was the main goal of my PhD thesis. To study switching of latent to lytic EBV the EBV-harboring BL cell line Akata was employed. BL Akata cells can easily be induced to switch latent to lytic EBV upon engagement of their BCR through cross-linking using anti-human immunoglobulin antibodies. BL Akata cells with silenced LMP2A, silenced LMP2B, overexpressed LMP2A, or overexpressed LMP2B were generated. The establishment of these cell lines revealed for the first time that silencing of LMP2B in EBV-harboring BL cells resulted in reduced expression of the initiator of lytic EBV, i.e.,
immediate-early lytic BZLF1 EBV gene mRNA and late lytic gp350/220 protein upon BCR cross-linking. Similarly, reduction of lytic EBV activation was observed in BL Akata cells overexpressing LMP2A. By contrast, silencing of LMP2A and LMP2B overexpression in BL Akata cells resulted in higher lytic EBV mRNA and protein expression upon BCR crosslinking. We could further demonstrate that LMP2A and LMP2B physically interact and that LMP2B resides predominantly in intracellular compartments, whereas LMP2A was detected on the plasma membrane as well as in intracellular compartments. In conclusion, these observations indicate a role for LMP2B distinct from LMP2A in regulation of lytic EBV activation in the host cell and support the hypothesis that LMP2B exhibits a negative regulatory effect on the ability of LMP2A to maintain latent EBV by preventing the switch to lytic EBV.

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Additional indexing

Item Type:Dissertation
Referees:Nadal D, Jiricny J, Greber U
Communities & Collections:04 Faculty of Medicine > University Children's Hospital Zurich > Medical Clinic
Dewey Decimal Classification:610 Medicine & health
Date:2008
Deposited On:03 Mar 2009 12:46
Last Modified:05 Apr 2016 13:08
Related URLs:http://opac.nebis.ch/F/?local_base=NEBIS&con_lng=GER&func=find-b&find_code=SYS&request=005722460

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