Abstract A30: High levels of STAT3 and Epstein-Barr virus latent membrane protein 1 are required for virus-driven proliferation and transformation of B cells
Authors: Koganti Siva , De la Paz Amanda , Freeman Alexandra , Hui-Yuen Joyce , Bhaduri-McIntosh Sumita 
Published: June 2012

Abstract
Epstein-Barr virus (EBV) is associated with lymphocyte and epithelial cell cancers in humans. EBV tumorigenesis requires expression of both viral genes, such as the oncoprotein latent membrane protein 1 (LMP1), and cellular genes. In previous tumorigenesis studies, we identified a B cell surface marker pattern (CD23hiCD58+) that predicts proliferation and subsequent transformation of B cells following EBV infection. To investigate the contribution of signal transducer and activator of transcription 3 (STAT3), a progrowth and survival signaling molecule, in EBV-driven proliferation and transformation of B cells, two approaches were taken: 1) Primary B cells from healthy donors were infected with EBV in the presence of AG490, which inhibits the function of STAT3 by interfering with Janus kinases, and 2) B cells from patients with autosomal-dominant hyper IgE syndrome (AD-HIES or Job syndrome) that have naturally occurring dominant negative mutations in the Stat3 gene were infected with EBV. The effects of chemical inhibition of STAT3 function and those of Stat3 mutations on EBV-driven B cell survival, proliferation, and transformation were examined.
Following exposure to EBV, LMP1 + cells and CD23hiCD58+ cells expressed activated STAT3 and high levels of total STAT3. Chemical inhibition of STAT3 activation by AG490 inhibited the emergence of the CD23hiCD58+ population by 10- to 30-fold as compared to control infection. This was accompanied by a fall in the fraction of B cells expressing LMP1 and increased apoptosis of CD23hiCD58+ and LMP1 + cells. A similar pattern was observed following infection of B cells from AD-HIES patients, further supporting a role for STAT3 in survival of B cells following EBV infection. Both AG490 treatment during infection of healthy B cells and infection of B cells from AD-HIES patients resulted in accumulation of extant LMP1 + cells in S phase of the cell cycle. Evaluation of nuclear morphology following AG490 treatment demonstrated an absence of LMP1 + mitotic nuclei but enrichment of LMP1 + cells with small dense nuclei consistent with cells in a resting state, supporting a proliferation defect. Only those cells expressing high levels of STAT3 in addition to high levels of LMP1 progressed to G2/M phase of the cell cycle. Cultures with reduced LMP1 expression or reduced CD23hiCD58+ population also failed to establish transformed cell lines. We conclude that proliferation and subsequent transformation of EBV-infected B cells is dependent on the presence of activated STAT3 and high levels of total STAT3 as well as high levels of LMP1. These findings support a possible role for STAT3 modulation in the treatment of EBV-related cancers, particularly those arising in the context of immunocompromise.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A30.