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Human herpesvirus 8 interferon regulatory factor-mediated BH3-only protein inhibition via Bid BH3-B mimicry.

Choi YB, Sandford G, Nicholas J - PLoS Pathog. (2012)

Bottom Line: Consistent with this finding, direct BBD-dependent inactivation by vIRF-1 of Bid-induced mitochondrial permeabilization was demonstrable in vitro and isolated BBD sequences were also active in this assay.In addition to Bim and Bid BH3 domains, BH3s of BOPs Bik, Bmf, Hrk, and Noxa also were found to bind BBD, while those of both pro- and anti-apoptotic multi-BH domain Bcl-2 proteins were not.Together, our data demonstrate and characterize BH3 targeting and associated inhibition of BOP pro-apoptotic activity by vIRF-1 via Bid BH3-B mimicry, identifying a novel mechanism of viral evasion from host cell defenses.

View Article: PubMed Central - PubMed

Affiliation: Sidney Kimmel Comprehensive Cancer Center, Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.

ABSTRACT
Viral replication efficiency is in large part governed by the ability of viruses to counteract pro-apoptotic signals induced by infection of host cells. For HHV-8, viral interferon regulatory factor-1 (vIRF-1) contributes to this process in part via inhibitory interactions with BH3-only protein (BOP) Bim, recently identified as an interaction partner of vIRF-1. Here we recognize that the Bim-binding domain (BBD) of vIRF-1 resembles a region (BH3-B) of Bid, another BOP, which interacts intramolecularly with the functional BH3 domain of Bid to inhibit it pro-apoptotic activity. Indeed, vIRF-1 was found to target Bid in addition to Bim and to interact, via its BBD region, with the BH3 domain of each. In functional assays, BBD could substitute for BH3-B in the context of Bid, to suppress Bid-induced apoptosis in a BH3-binding-dependent manner, and vIRF-1 was able to protect transfected cells from apoptosis induced by Bid. While vIRF-1 can mediate nuclear sequestration of Bim, this was not the case for Bid, and inhibition of Bid and Bim by vIRF-1 could occur independently of nuclear localization of the viral protein. Consistent with this finding, direct BBD-dependent inactivation by vIRF-1 of Bid-induced mitochondrial permeabilization was demonstrable in vitro and isolated BBD sequences were also active in this assay. In addition to Bim and Bid BH3 domains, BH3s of BOPs Bik, Bmf, Hrk, and Noxa also were found to bind BBD, while those of both pro- and anti-apoptotic multi-BH domain Bcl-2 proteins were not. Finally, the significance of Bid to virus replication was demonstrated via Bid-depletion in HHV-8 infected cells, which enhanced virus production. Together, our data demonstrate and characterize BH3 targeting and associated inhibition of BOP pro-apoptotic activity by vIRF-1 via Bid BH3-B mimicry, identifying a novel mechanism of viral evasion from host cell defenses.

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vIRF-1 BBD resembles the BH3-related BH3-B domain of Bid.Alignments of the primary sequence of vIRF-1 BBD with those of Bid BH3-B and BOP BH3 domains and comparison of the predicted secondary structure of BBD with the BH3-B α-helix. Collinear hydrophobic residues are indicated by grey shading. For BBD and BH3-B sequences and helical wheels, collinear hydrophobic and basic residues are indicated by darkly and lightly shaded circles, respectively. Matched shading on helical wheels indicates hydrophobic (diamonds) and hydrophilic [basic (pentagons) and acidic (triangles)] residues, respectively. Helical wheels were drawn using web-based software created by Don Armstrong and Raphael Zidovetzki.
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ppat-1002748-g001: vIRF-1 BBD resembles the BH3-related BH3-B domain of Bid.Alignments of the primary sequence of vIRF-1 BBD with those of Bid BH3-B and BOP BH3 domains and comparison of the predicted secondary structure of BBD with the BH3-B α-helix. Collinear hydrophobic residues are indicated by grey shading. For BBD and BH3-B sequences and helical wheels, collinear hydrophobic and basic residues are indicated by darkly and lightly shaded circles, respectively. Matched shading on helical wheels indicates hydrophobic (diamonds) and hydrophilic [basic (pentagons) and acidic (triangles)] residues, respectively. Helical wheels were drawn using web-based software created by Don Armstrong and Raphael Zidovetzki.

Mentions: We noted previously the amphipathic α-helical structure of the Bim-binding domain (BBD, residues 170–187) of vIRF-1 [23]. This type of structure also is apparent in the so-called BH3-B domain of Bid, which interacts intramolecularly with the BH3 domain to effect inhibition of Bid activity [40]. Indeed, the sequences of BBD and BH3-B are similar to each other and to BH3 domains of other proteins (Fig. 1). Particularly noteworthy are the BH3-conserved hydrophobic and BH3-B-conserved basic residues of the BBD core sequence (Fig. 1). The structural similarities of BBD and BH3-B suggested the possibility that BBD might interact with Bim via its BH3 domain and that vIRF-1 might target Bid (and possibly other BOPs) in addition to Bim.


Human herpesvirus 8 interferon regulatory factor-mediated BH3-only protein inhibition via Bid BH3-B mimicry.

Choi YB, Sandford G, Nicholas J - PLoS Pathog. (2012)

vIRF-1 BBD resembles the BH3-related BH3-B domain of Bid.Alignments of the primary sequence of vIRF-1 BBD with those of Bid BH3-B and BOP BH3 domains and comparison of the predicted secondary structure of BBD with the BH3-B α-helix. Collinear hydrophobic residues are indicated by grey shading. For BBD and BH3-B sequences and helical wheels, collinear hydrophobic and basic residues are indicated by darkly and lightly shaded circles, respectively. Matched shading on helical wheels indicates hydrophobic (diamonds) and hydrophilic [basic (pentagons) and acidic (triangles)] residues, respectively. Helical wheels were drawn using web-based software created by Don Armstrong and Raphael Zidovetzki.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369933&req=5

ppat-1002748-g001: vIRF-1 BBD resembles the BH3-related BH3-B domain of Bid.Alignments of the primary sequence of vIRF-1 BBD with those of Bid BH3-B and BOP BH3 domains and comparison of the predicted secondary structure of BBD with the BH3-B α-helix. Collinear hydrophobic residues are indicated by grey shading. For BBD and BH3-B sequences and helical wheels, collinear hydrophobic and basic residues are indicated by darkly and lightly shaded circles, respectively. Matched shading on helical wheels indicates hydrophobic (diamonds) and hydrophilic [basic (pentagons) and acidic (triangles)] residues, respectively. Helical wheels were drawn using web-based software created by Don Armstrong and Raphael Zidovetzki.
Mentions: We noted previously the amphipathic α-helical structure of the Bim-binding domain (BBD, residues 170–187) of vIRF-1 [23]. This type of structure also is apparent in the so-called BH3-B domain of Bid, which interacts intramolecularly with the BH3 domain to effect inhibition of Bid activity [40]. Indeed, the sequences of BBD and BH3-B are similar to each other and to BH3 domains of other proteins (Fig. 1). Particularly noteworthy are the BH3-conserved hydrophobic and BH3-B-conserved basic residues of the BBD core sequence (Fig. 1). The structural similarities of BBD and BH3-B suggested the possibility that BBD might interact with Bim via its BH3 domain and that vIRF-1 might target Bid (and possibly other BOPs) in addition to Bim.

Bottom Line: Consistent with this finding, direct BBD-dependent inactivation by vIRF-1 of Bid-induced mitochondrial permeabilization was demonstrable in vitro and isolated BBD sequences were also active in this assay.In addition to Bim and Bid BH3 domains, BH3s of BOPs Bik, Bmf, Hrk, and Noxa also were found to bind BBD, while those of both pro- and anti-apoptotic multi-BH domain Bcl-2 proteins were not.Together, our data demonstrate and characterize BH3 targeting and associated inhibition of BOP pro-apoptotic activity by vIRF-1 via Bid BH3-B mimicry, identifying a novel mechanism of viral evasion from host cell defenses.

View Article: PubMed Central - PubMed

Affiliation: Sidney Kimmel Comprehensive Cancer Center, Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.

ABSTRACT
Viral replication efficiency is in large part governed by the ability of viruses to counteract pro-apoptotic signals induced by infection of host cells. For HHV-8, viral interferon regulatory factor-1 (vIRF-1) contributes to this process in part via inhibitory interactions with BH3-only protein (BOP) Bim, recently identified as an interaction partner of vIRF-1. Here we recognize that the Bim-binding domain (BBD) of vIRF-1 resembles a region (BH3-B) of Bid, another BOP, which interacts intramolecularly with the functional BH3 domain of Bid to inhibit it pro-apoptotic activity. Indeed, vIRF-1 was found to target Bid in addition to Bim and to interact, via its BBD region, with the BH3 domain of each. In functional assays, BBD could substitute for BH3-B in the context of Bid, to suppress Bid-induced apoptosis in a BH3-binding-dependent manner, and vIRF-1 was able to protect transfected cells from apoptosis induced by Bid. While vIRF-1 can mediate nuclear sequestration of Bim, this was not the case for Bid, and inhibition of Bid and Bim by vIRF-1 could occur independently of nuclear localization of the viral protein. Consistent with this finding, direct BBD-dependent inactivation by vIRF-1 of Bid-induced mitochondrial permeabilization was demonstrable in vitro and isolated BBD sequences were also active in this assay. In addition to Bim and Bid BH3 domains, BH3s of BOPs Bik, Bmf, Hrk, and Noxa also were found to bind BBD, while those of both pro- and anti-apoptotic multi-BH domain Bcl-2 proteins were not. Finally, the significance of Bid to virus replication was demonstrated via Bid-depletion in HHV-8 infected cells, which enhanced virus production. Together, our data demonstrate and characterize BH3 targeting and associated inhibition of BOP pro-apoptotic activity by vIRF-1 via Bid BH3-B mimicry, identifying a novel mechanism of viral evasion from host cell defenses.

Show MeSH
Related in: MedlinePlus