Limits...
Viral induction of AID is independent of the interferon and the Toll-like receptor signaling pathways but requires NF-kappaB.

Gourzi P, Leonova T, Papavasiliou FN - J. Exp. Med. (2007)

Bottom Line: Here we show that AID is not an interferon responsive gene and abrogation of Toll-like receptor signaling does not diminish the AID response.However, we found that NF-kappaB was required for expression of virally induced AID.Since NF-kappaB binds and activates the AID promoter, these results mechanistically link viral infection with AID transcription.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Lymphocyte Biology, The Rockefeller University, New York, NY 10021, USA.

ABSTRACT
Activation-induced cytidine deaminase (AID) is expressed in germinal centers of lymphoid organs during immunoglobulin diversification, in bone marrow B cells after infection with Abelson murine leukemia retrovirus (Ab-MLV), and in human B cells after infection by hepatitis C virus. To understand how viruses signal AID induction in the host we asked whether the AID response was abrogated in cells deficient in the interferon pathway or in signaling via the Toll-like receptors. Here we show that AID is not an interferon responsive gene and abrogation of Toll-like receptor signaling does not diminish the AID response. However, we found that NF-kappaB was required for expression of virally induced AID. Since NF-kappaB binds and activates the AID promoter, these results mechanistically link viral infection with AID transcription. Thus, induction of AID by viruses could be the result of several signaling pathways that culminate in NF-kappaB activation, underscoring the versatility of this host defense program.

Show MeSH

Related in: MedlinePlus

NF-κB–p50 is recruited to the mouse AID promoter to directly activate AID expression during infection by Ab-MLV. (A) Occupancy of the NF-κB binding site present in the AID promoter is assessed by ChIP before (day 0) or during (day 6) infection of wild-type or NF-κB–p50–deficient animals. Occupancy of an NF-κB binding site present in the nearby APOBEC1 promoter was evaluated as a negative control. Threefold titrations are shown for input, anti–NF-κB immunoprecipitation, and isotype control immunoprecipitation samples. (B) AID promoter activity in infected cells, in the presence or absence of the κB binding site. Bone marrow cells were coinfected with Ab-MLV and with a retroviral luciferase reporter construct containing either the wild-type κB site (wt κB Luc) or a mutated κB site (mut κB Luc). Promoter activity for each construct was measured in relative light units per μg of protein lysate. Results are means ± SD (n = 3).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2118730&req=5

fig5: NF-κB–p50 is recruited to the mouse AID promoter to directly activate AID expression during infection by Ab-MLV. (A) Occupancy of the NF-κB binding site present in the AID promoter is assessed by ChIP before (day 0) or during (day 6) infection of wild-type or NF-κB–p50–deficient animals. Occupancy of an NF-κB binding site present in the nearby APOBEC1 promoter was evaluated as a negative control. Threefold titrations are shown for input, anti–NF-κB immunoprecipitation, and isotype control immunoprecipitation samples. (B) AID promoter activity in infected cells, in the presence or absence of the κB binding site. Bone marrow cells were coinfected with Ab-MLV and with a retroviral luciferase reporter construct containing either the wild-type κB site (wt κB Luc) or a mutated κB site (mut κB Luc). Promoter activity for each construct was measured in relative light units per μg of protein lysate. Results are means ± SD (n = 3).

Mentions: The human AID promoter contains two NF-κB binding sites, and nuclear extracts from human cell lines that are stimulated to express AID can supershift oligonucleotides containing both sites. These in vitro experiments have suggested that AID induction during CSR can be at least in part attributed to NF-κB (4). In contrast, a scan of the mouse AID promoter revealed a single NF-κB binding site (gaGGGActtgtc; capital letters refer to the core binding sequence), corresponding to positions −1447 to −1434 from the promoter. To directly confirm the link between viral AID induction and NF-κB activation, we asked whether this site was occupied in vivo by NF-κB–p50 after infection of B cells with Ab-MLV. Using chromatin immunoprecipitation we found that the site was not occupied by NF-κB before infection (Fig. 5, day 0). However, the site was clearly bound by NF-κB at day 6 after infection (Fig. 5 A), a time point which coincides with the initial peak of AID expression (Figs. 3 and 4 and reference 20). Thus, our experiments demonstrate that, in vivo, NF-κB is recruited to the AID promoter during infection, with kinetics that parallel those of AID induction.


Viral induction of AID is independent of the interferon and the Toll-like receptor signaling pathways but requires NF-kappaB.

Gourzi P, Leonova T, Papavasiliou FN - J. Exp. Med. (2007)

NF-κB–p50 is recruited to the mouse AID promoter to directly activate AID expression during infection by Ab-MLV. (A) Occupancy of the NF-κB binding site present in the AID promoter is assessed by ChIP before (day 0) or during (day 6) infection of wild-type or NF-κB–p50–deficient animals. Occupancy of an NF-κB binding site present in the nearby APOBEC1 promoter was evaluated as a negative control. Threefold titrations are shown for input, anti–NF-κB immunoprecipitation, and isotype control immunoprecipitation samples. (B) AID promoter activity in infected cells, in the presence or absence of the κB binding site. Bone marrow cells were coinfected with Ab-MLV and with a retroviral luciferase reporter construct containing either the wild-type κB site (wt κB Luc) or a mutated κB site (mut κB Luc). Promoter activity for each construct was measured in relative light units per μg of protein lysate. Results are means ± SD (n = 3).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2118730&req=5

fig5: NF-κB–p50 is recruited to the mouse AID promoter to directly activate AID expression during infection by Ab-MLV. (A) Occupancy of the NF-κB binding site present in the AID promoter is assessed by ChIP before (day 0) or during (day 6) infection of wild-type or NF-κB–p50–deficient animals. Occupancy of an NF-κB binding site present in the nearby APOBEC1 promoter was evaluated as a negative control. Threefold titrations are shown for input, anti–NF-κB immunoprecipitation, and isotype control immunoprecipitation samples. (B) AID promoter activity in infected cells, in the presence or absence of the κB binding site. Bone marrow cells were coinfected with Ab-MLV and with a retroviral luciferase reporter construct containing either the wild-type κB site (wt κB Luc) or a mutated κB site (mut κB Luc). Promoter activity for each construct was measured in relative light units per μg of protein lysate. Results are means ± SD (n = 3).
Mentions: The human AID promoter contains two NF-κB binding sites, and nuclear extracts from human cell lines that are stimulated to express AID can supershift oligonucleotides containing both sites. These in vitro experiments have suggested that AID induction during CSR can be at least in part attributed to NF-κB (4). In contrast, a scan of the mouse AID promoter revealed a single NF-κB binding site (gaGGGActtgtc; capital letters refer to the core binding sequence), corresponding to positions −1447 to −1434 from the promoter. To directly confirm the link between viral AID induction and NF-κB activation, we asked whether this site was occupied in vivo by NF-κB–p50 after infection of B cells with Ab-MLV. Using chromatin immunoprecipitation we found that the site was not occupied by NF-κB before infection (Fig. 5, day 0). However, the site was clearly bound by NF-κB at day 6 after infection (Fig. 5 A), a time point which coincides with the initial peak of AID expression (Figs. 3 and 4 and reference 20). Thus, our experiments demonstrate that, in vivo, NF-κB is recruited to the AID promoter during infection, with kinetics that parallel those of AID induction.

Bottom Line: Here we show that AID is not an interferon responsive gene and abrogation of Toll-like receptor signaling does not diminish the AID response.However, we found that NF-kappaB was required for expression of virally induced AID.Since NF-kappaB binds and activates the AID promoter, these results mechanistically link viral infection with AID transcription.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Lymphocyte Biology, The Rockefeller University, New York, NY 10021, USA.

ABSTRACT
Activation-induced cytidine deaminase (AID) is expressed in germinal centers of lymphoid organs during immunoglobulin diversification, in bone marrow B cells after infection with Abelson murine leukemia retrovirus (Ab-MLV), and in human B cells after infection by hepatitis C virus. To understand how viruses signal AID induction in the host we asked whether the AID response was abrogated in cells deficient in the interferon pathway or in signaling via the Toll-like receptors. Here we show that AID is not an interferon responsive gene and abrogation of Toll-like receptor signaling does not diminish the AID response. However, we found that NF-kappaB was required for expression of virally induced AID. Since NF-kappaB binds and activates the AID promoter, these results mechanistically link viral infection with AID transcription. Thus, induction of AID by viruses could be the result of several signaling pathways that culminate in NF-kappaB activation, underscoring the versatility of this host defense program.

Show MeSH
Related in: MedlinePlus