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The murine gammaherpesvirus immediate-early Rta synergizes with IRF4, targeting expression of the viral M1 superantigen to plasma cells.

O'Flaherty BM, Soni T, Wakeman BS, Speck SH - PLoS Pathog. (2014)

Bottom Line: In addition, we show that M1 gene transcription is regulated by both the essential viral immediate-early transcriptional activator Rta and cellular interferon regulatory factor 4 (IRF4), which together potently synergize to drive M1 gene expression.Finally, we show that IRF4, a cellular transcription factor essential for plasma cell differentiation, can directly interact with Rta.The latter observation raises the possibility that the interaction of Rta and IRF4 may be involved in regulating a number of viral and cellular genes during MHV68 reactivation linked to plasma cell differentiation.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, United States of America; Emory Vaccine Center, Emory University School of Medicine, Atlanta, Georgia, United States of America.

ABSTRACT
MHV68 is a murine gammaherpesvirus that infects laboratory mice and thus provides a tractable small animal model for characterizing critical aspects of gammaherpesvirus pathogenesis. Having evolved with their natural host, herpesviruses encode numerous gene products that are involved in modulating host immune responses to facilitate the establishment and maintenance of lifelong chronic infection. One such protein, MHV68 M1, is a secreted protein that has no known homologs, but has been shown to play a critical role in controlling virus reactivation from latently infected macrophages. We have previous demonstrated that M1 drives the activation and expansion of Vβ4+ CD8+ T cells, which are thought to be involved in controlling MHV68 reactivation through the secretion of interferon gamma. The mechanism of action and regulation of M1 expression are poorly understood. To gain insights into the function of M1, we set out to evaluate the site of expression and transcriptional regulation of the M1 gene. Here, using a recombinant virus expressing a fluorescent protein driven by the M1 gene promoter, we identify plasma cells as the major cell type expressing M1 at the peak of infection in the spleen. In addition, we show that M1 gene transcription is regulated by both the essential viral immediate-early transcriptional activator Rta and cellular interferon regulatory factor 4 (IRF4), which together potently synergize to drive M1 gene expression. Finally, we show that IRF4, a cellular transcription factor essential for plasma cell differentiation, can directly interact with Rta. The latter observation raises the possibility that the interaction of Rta and IRF4 may be involved in regulating a number of viral and cellular genes during MHV68 reactivation linked to plasma cell differentiation.

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Model of M1 gene regulation upon differentiation of latently infected B cells to plasma cells and ensuing virus reactivation.During infection MHV68 M2 regulates the expression of cellular IRF4, a critical transcription factor in plasma cell differentiation. M2 has also been shown to be critical for viral reactivation in the plasma cell reservoir. Increased levels of Rta and IR4 during viral reactivation in infected plasma cells lead to increased expression of M1, which is mediated through protein:protein interactions between Rta and IRF4, as well as binding through cis-elements within the M1 promoter. Shown are 3 possible mechanism for how Rta synergizes with IRF4 to activate transcription of the M1 gene: (i) Rta binds to the novel RRE and interaction with IRF4 is mediated by a cellular and/or viral factor that binds both Rta and IRF4; (ii) Rta interacts with a cellular and/or viral factor bound to the RRE and also directly binds to IRF4; and (iii) Rta binds to the RRE and interacts directly with IRF4.
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ppat-1004302-g011: Model of M1 gene regulation upon differentiation of latently infected B cells to plasma cells and ensuing virus reactivation.During infection MHV68 M2 regulates the expression of cellular IRF4, a critical transcription factor in plasma cell differentiation. M2 has also been shown to be critical for viral reactivation in the plasma cell reservoir. Increased levels of Rta and IR4 during viral reactivation in infected plasma cells lead to increased expression of M1, which is mediated through protein:protein interactions between Rta and IRF4, as well as binding through cis-elements within the M1 promoter. Shown are 3 possible mechanism for how Rta synergizes with IRF4 to activate transcription of the M1 gene: (i) Rta binds to the novel RRE and interaction with IRF4 is mediated by a cellular and/or viral factor that binds both Rta and IRF4; (ii) Rta interacts with a cellular and/or viral factor bound to the RRE and also directly binds to IRF4; and (iii) Rta binds to the RRE and interacts directly with IRF4.

Mentions: Our findings demonstrate that the M1 promoter is regulated by MHV68 Rta, a viral transcription factor that is essential for induction of viral reactivation. Rta activation of the M1 promoter synergizes with IRF4, a transcription factor that plays a critical role in both plasma cell differentiation and immunoglobulin class switch recombination. Furthermore, we show that this interaction is likely mediated through both DNA-protein interactions with the M1 promoter sequence, as well as protein-protein interactions between Rta and IRF4. We propose that during MHV68 latency, the viral latency-associated gene product M2 is expressed in a sub-population of latently infected germinal center and memory B cells [21] leading to expression of high levels of IRF4 [50]. M2 appears to play an important role in virus reactivation from latency: (i) MHV68 M2 mutants exhibit a profound reactivation defect from B cells, but not latently infected macrophages [51], [52]; (ii) exogenous expression of M2 in primary B cells results in acquisition of a pre-plasma memory phenotype [53]; (iii) M2 can drive B cell differentiation of a B lymphoma cell line in vitro[27]; (iv) M2 is required for efficient immunoglobulin class switch in infected B cells in vivo[27]; and (v) plasma cells are the primary source of viral reactivation from the spleen [27]. Taken together these data suggest that MHV68 is capable of driving plasma cell differentiation, and concurrent with this differentiation, viral reactivation. As a result of this transition, the increased expression of the transcription factors Rta and IRF4 lead to induction of M1 expression in plasma cells (Figure 11).


The murine gammaherpesvirus immediate-early Rta synergizes with IRF4, targeting expression of the viral M1 superantigen to plasma cells.

O'Flaherty BM, Soni T, Wakeman BS, Speck SH - PLoS Pathog. (2014)

Model of M1 gene regulation upon differentiation of latently infected B cells to plasma cells and ensuing virus reactivation.During infection MHV68 M2 regulates the expression of cellular IRF4, a critical transcription factor in plasma cell differentiation. M2 has also been shown to be critical for viral reactivation in the plasma cell reservoir. Increased levels of Rta and IR4 during viral reactivation in infected plasma cells lead to increased expression of M1, which is mediated through protein:protein interactions between Rta and IRF4, as well as binding through cis-elements within the M1 promoter. Shown are 3 possible mechanism for how Rta synergizes with IRF4 to activate transcription of the M1 gene: (i) Rta binds to the novel RRE and interaction with IRF4 is mediated by a cellular and/or viral factor that binds both Rta and IRF4; (ii) Rta interacts with a cellular and/or viral factor bound to the RRE and also directly binds to IRF4; and (iii) Rta binds to the RRE and interacts directly with IRF4.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4125235&req=5

ppat-1004302-g011: Model of M1 gene regulation upon differentiation of latently infected B cells to plasma cells and ensuing virus reactivation.During infection MHV68 M2 regulates the expression of cellular IRF4, a critical transcription factor in plasma cell differentiation. M2 has also been shown to be critical for viral reactivation in the plasma cell reservoir. Increased levels of Rta and IR4 during viral reactivation in infected plasma cells lead to increased expression of M1, which is mediated through protein:protein interactions between Rta and IRF4, as well as binding through cis-elements within the M1 promoter. Shown are 3 possible mechanism for how Rta synergizes with IRF4 to activate transcription of the M1 gene: (i) Rta binds to the novel RRE and interaction with IRF4 is mediated by a cellular and/or viral factor that binds both Rta and IRF4; (ii) Rta interacts with a cellular and/or viral factor bound to the RRE and also directly binds to IRF4; and (iii) Rta binds to the RRE and interacts directly with IRF4.
Mentions: Our findings demonstrate that the M1 promoter is regulated by MHV68 Rta, a viral transcription factor that is essential for induction of viral reactivation. Rta activation of the M1 promoter synergizes with IRF4, a transcription factor that plays a critical role in both plasma cell differentiation and immunoglobulin class switch recombination. Furthermore, we show that this interaction is likely mediated through both DNA-protein interactions with the M1 promoter sequence, as well as protein-protein interactions between Rta and IRF4. We propose that during MHV68 latency, the viral latency-associated gene product M2 is expressed in a sub-population of latently infected germinal center and memory B cells [21] leading to expression of high levels of IRF4 [50]. M2 appears to play an important role in virus reactivation from latency: (i) MHV68 M2 mutants exhibit a profound reactivation defect from B cells, but not latently infected macrophages [51], [52]; (ii) exogenous expression of M2 in primary B cells results in acquisition of a pre-plasma memory phenotype [53]; (iii) M2 can drive B cell differentiation of a B lymphoma cell line in vitro[27]; (iv) M2 is required for efficient immunoglobulin class switch in infected B cells in vivo[27]; and (v) plasma cells are the primary source of viral reactivation from the spleen [27]. Taken together these data suggest that MHV68 is capable of driving plasma cell differentiation, and concurrent with this differentiation, viral reactivation. As a result of this transition, the increased expression of the transcription factors Rta and IRF4 lead to induction of M1 expression in plasma cells (Figure 11).

Bottom Line: In addition, we show that M1 gene transcription is regulated by both the essential viral immediate-early transcriptional activator Rta and cellular interferon regulatory factor 4 (IRF4), which together potently synergize to drive M1 gene expression.Finally, we show that IRF4, a cellular transcription factor essential for plasma cell differentiation, can directly interact with Rta.The latter observation raises the possibility that the interaction of Rta and IRF4 may be involved in regulating a number of viral and cellular genes during MHV68 reactivation linked to plasma cell differentiation.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, United States of America; Emory Vaccine Center, Emory University School of Medicine, Atlanta, Georgia, United States of America.

ABSTRACT
MHV68 is a murine gammaherpesvirus that infects laboratory mice and thus provides a tractable small animal model for characterizing critical aspects of gammaherpesvirus pathogenesis. Having evolved with their natural host, herpesviruses encode numerous gene products that are involved in modulating host immune responses to facilitate the establishment and maintenance of lifelong chronic infection. One such protein, MHV68 M1, is a secreted protein that has no known homologs, but has been shown to play a critical role in controlling virus reactivation from latently infected macrophages. We have previous demonstrated that M1 drives the activation and expansion of Vβ4+ CD8+ T cells, which are thought to be involved in controlling MHV68 reactivation through the secretion of interferon gamma. The mechanism of action and regulation of M1 expression are poorly understood. To gain insights into the function of M1, we set out to evaluate the site of expression and transcriptional regulation of the M1 gene. Here, using a recombinant virus expressing a fluorescent protein driven by the M1 gene promoter, we identify plasma cells as the major cell type expressing M1 at the peak of infection in the spleen. In addition, we show that M1 gene transcription is regulated by both the essential viral immediate-early transcriptional activator Rta and cellular interferon regulatory factor 4 (IRF4), which together potently synergize to drive M1 gene expression. Finally, we show that IRF4, a cellular transcription factor essential for plasma cell differentiation, can directly interact with Rta. The latter observation raises the possibility that the interaction of Rta and IRF4 may be involved in regulating a number of viral and cellular genes during MHV68 reactivation linked to plasma cell differentiation.

Show MeSH
Related in: MedlinePlus