RESUMO
BACKGROUND: The Epstein-Barr virus is widespread in all human populations and is strongly associated with human disease, ranging from infectious mononucleosis to cancer. In infected cells the virus can adopt several different latency programs, affecting the cells' behaviour. Experimental results indicate that a specific genetic switch between viral latency programs, reprograms human B-cells between proliferative and resting states. Each of these two latency programs makes use of a different viral promoter, Cp and Qp, respectively. The hypothesis tested in this study is that this genetic switch is controlled by both human and viral transcription factors; Oct-2 and EBNA-1. We build a physico-chemical model to investigate quantitatively the dynamical properties of the promoter regulation and experimentally examine protein level variations between the two latency programs. RESULTS: Our experimental results display significant differences in EBNA-1 and Oct-2 levels between resting and proliferating programs. With the model we identify two stable latency programs, corresponding to a resting and proliferating cell. The two programs differ in robustness and transcriptional activity. The proliferating state is markedly more stable, with a very high transcriptional activity from its viral promoter. We predict the promoter activities to be mutually exclusive in the two different programs, and our relative promoter activities correlate well with experimental data. Transitions between programs can be induced, by affecting the protein levels of our transcription factors. Simulated time scales are in line with experimental results. CONCLUSION: We show that fundamental properties of the Epstein-Barr virus involvement in latent infection, with implications for tumor biology, can be modelled and understood mathematically. We conclude that EBNA-1 and Oct-2 regulation of Cp and Qp is sufficient to establish mutually exclusive expression patterns. Moreover, the modelled genetic control predict both mono- and bistable behavior and a considerable difference in transition dynamics, based on program stability and promoter activities. Both these phenomena we hope can be further investigated experimentally, to increase the understanding of this important switch. Our results also stress the importance of the little known regulation of human transcription factor Oct-2.
Assuntos
Linfócitos B/fisiologia , Linfócitos B/virologia , Antígenos Nucleares do Vírus Epstein-Barr/genética , Herpesvirus Humano 4/fisiologia , Modelos Genéticos , Fator 2 de Transcrição de Octâmero/genética , Latência Viral/genética , Linfócitos B/química , Células Cultivadas , Simulação por Computador , Antígenos Nucleares do Vírus Epstein-Barr/química , Herpesvirus Humano 4/química , Humanos , Modelos Químicos , Fator 2 de Transcrição de Octâmero/química , Regiões Promotoras Genéticas/genéticaRESUMO
POU domain proteins contain a bipartite DNA-binding element that can confer allosteric control of coactivator recruitment. Dimerization of Oct-1 and Oct-2 on palindromic response elements results in the conformational dependent inclusion or exclusion of the transcriptional coactivator OBF-1. In this paper, we demonstrate that Oct-1 and Oct-2 can function as transcriptional repressors by recruiting and physically interacting with members of the Grg/TLE family of corepressors. In accordance with a model of DNA induced cofactor assembly, and analogous to the recruitment of the OBF-1 coactivator, the different Grg/TLE members can discriminate between both Oct-1 and Oct-2, and the monomeric or dimeric nature of the POU/DNA complex.
