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{{for|the computer bus standard|VPX}}
{{for|the computer bus standard|VPX}}
'''Vpx''' is a virion-associated protein encoded by human immunodeficiency virus type 2 [[HIV-2]] and most [[Simian immunodeficiency virus|simian immunodeficiency virus (SIV)]] strains, but that is absent from [[HIV-1]]. <ref>{{cite journal|last=Vicenzi|first=E.|coauthors=Poli, G.|title=Novel factors interfering with human immunodeficiency virus-type 1 replication in vivo and in vitro|journal=Tissue Antigens|year=2013|month=February|volume=81|issue=2|pages=61-71|doi=10.1111|pmid=23330719|url=http://www.ncbi.nlm.nih.gov/pubmed/23330719}}</ref> It is similar in structure to the protein [[vpr|Vpr]] that is carried by SIV and HIV-2 as well as HIV-1.<ref name="fujita">{{cite journal|last=Fujita|first=M.|coauthors=Nomaguchi, M., Adachi, A., Otsuka, M.|title=SAMHD1-Dependent and -Independent Functions of HIV-2/SIV Vpx Protein|journal=Frontiers in Microbiology|date=10|year=2012|month=August|volume=3|issue=297|doi=10.3389|pmid=22908011|url=http://www.ncbi.nlm.nih.gov/pubmed/?term=SAMHD1-dependent+and+-independent+functions+of+HIV-2%2FSIV+Vpx+protein}}</ref> Vpx is one of five accessory proteins ([[Viral infectivity factor|Vif]], Vpx, [[Vpr]], [[Vpu]], and [[Nef (protein)|Nef]]) carried by lentiviruses that enhances viral replication by inhibiting host antiviral factors <ref name="fujita" />.
'''Vpx''' is a virion-associated protein encoded by human immunodeficiency virus type 2 [[HIV-2]] and most [[Simian immunodeficiency virus|simian immunodeficiency virus (SIV)]] strains, but that is absent from [[HIV-1]]. <ref>{{cite journal|last=Vicenzi|first=E.|coauthors=Poli, G.|title=Novel factors interfering with human immunodeficiency virus-type 1 replication in vivo and in vitro|journal=Tissue Antigens|year=2013|month=February|volume=81|issue=2|pages=61-71|doi=10.1111|pmid=23330719|url=http://www.ncbi.nlm.nih.gov/pubmed/23330719}}</ref> It is similar in structure to the protein [[vpr|Vpr]] that is carried by SIV and HIV-2 as well as HIV-1.<ref name="fujita">{{cite journal|last=Fujita|first=M.|coauthors=Nomaguchi, M., Adachi, A., Otsuka, M.|title=SAMHD1-Dependent and -Independent Functions of HIV-2/SIV Vpx Protein|journal=Frontiers in Microbiology|date=10|year=2012|month=August|volume=3|issue=297|doi=10.3389|pmid=22908011|url=http://www.ncbi.nlm.nih.gov/pubmed/?term=SAMHD1-dependent+and+-independent+functions+of+HIV-2%2FSIV+Vpx+protein}}</ref> Vpx is one of five accessory proteins ([[Viral infectivity factor|Vif]], Vpx, [[Vpr]], [[Vpu]], and [[Nef (protein)|Nef]]) carried by lentiviruses that enhances viral replication by inhibiting host antiviral factors. <ref name="fujita" />


Vpx enhances HIV-2 replication in humans by counteracting the host factor [[SAMHD1]] <ref name="LaguetteNadine">Laguette, Nadine, Nadia Rahm, Bijan Sobhian, Christine Chable-Bessia, Jan Munch, Joke Snoeck, Daniel Sauter, William M. Switzer, Walid Heneine, Frank Kirchhoff, Frederic Delsuc, Amalio Telenti, and Monsef Benkirane (2012), Evolutionary and functional analyses of the interaction between the myeloid restriction factor SAMHD1 and the lintiviral Vpx protein. Cell Host & Microbe, doi: 10.1016/j.chom.2012.01.007 (Volume 11, issue 2 pp. 205-217)</ref>. SAMHD1 is a host factor found in human myeloid cells, such as dendritic cells and macrophages, that restricts HIV-1 replication by depleting the cytoplasmic pool of deoxynucleoside triphosphates needed for viral DNA production <ref>Lahouassa, H., Daddacha, W., Hofmann, H., Ayinde, D., Logue, E. C., Dragin, L., Bloch, N., Maudet, C., Bertrand, M., Gramberg, T., Pancino, G., Priet, S., Canard, B., Laguette, N., Benkirane, M., Transy, C., Landau, N. R., Kim, B., and Margottin-Goguet, F. (2012). SAMHD1 restricts the replication of HIV-1 by depleting the intracellular pool of deoxynucleoside triphosphates. Nat. Immunol. 13, 223-228.</ref>. SAMHD1 does not, however, restrict HIV-2 replication in myeloid cells due to the presence of viral Vpx. Vpx counteracts restriction by inducing the ubiquitin-proteasome-dependent degradation of SAMHD1 <ref name="LaguetteNadine" />. Vpx-mediated degradation of SAMHD1 therefore decreases deoxynucleoside triphosphate hydrolysis, thereby increasing the availability of dNTPs for viral reverse transcription in the cytoplasm. It has been postulated that SAMHD1 degradation is required for HIV-2 replication because the HIV-2 reverse transcriptase (RT) is less active than the HIV-1 RT, which would be the reason for the absence of Vpx from HIV-1 <ref name="fujita" />. Because Vpx is required for HIV-2 reverse transcription and the early stages of the viral life cycle, it is packaged into virions in significant amounts <ref>Wu X., Conway J. A., Kim J., Kappes J. C. (1994) Localization of the Vpx packaging signal within the C terminus of the human immunodeficiency virus type 2 Gag precursor protein. J. Virol. 68:6161–6169.</ref><ref>Fujita,M.,Otsuka,M.,Miyoshi,M., Khamsri,B.,Nomaguchi,M.,and Adachi,A.(2008). Vpx is critical for reverse transcription of the human immune deficiency virus type 2 genome in macrophages. J. Virol. 82, 7752–7756.</ref>.
Vpx enhances HIV-2 replication in humans by counteracting the host factor [[SAMHD1]].<ref name='"LaguetteNadine"'>{{cite journal|last=Laguette|first=Nadine|coauthors=Nadia Rahm, Bijan Sobhian, Christine Chable-Bessia, Jan Munch, Joke Snoeck, Daniel Sauter, William M. Switzer, Walid Heneine, Frank Kirchhoff, Frederic Delsuc, Amalio Telenti, & Monsef Benkirane|title=Evolutionary and functional analyses of the interaction between the myeloid restriction factor SAMHD1 and the lintiviral Vpx protein|journal=Cell Host & Microbe|date=16|year=2012|month=February|volume=11|issue=2|pages=205-217|doi=10.1016|pmid=22305291|url=http://www.ncbi.nlm.nih.gov/pubmed/?term=Evolutionary+and+functional+analyses+of+the+interaction+between+the+myeloid+restriction+factor+SAMHD1+and+the+lintiviral+Vpx+protein}}</ref> SAMHD1 is a host factor found in human myeloid cells, such as dendritic cells and macrophages, that restricts HIV-1 replication by depleting the cytoplasmic pool of deoxynucleoside triphosphates needed for viral DNA production <ref>Lahouassa, H., Daddacha, W., Hofmann, H., Ayinde, D., Logue, E. C., Dragin, L., Bloch, N., Maudet, C., Bertrand, M., Gramberg, T., Pancino, G., Priet, S., Canard, B., Laguette, N., Benkirane, M., Transy, C., Landau, N. R., Kim, B., and Margottin-Goguet, F. (2012). SAMHD1 restricts the replication of HIV-1 by depleting the intracellular pool of deoxynucleoside triphosphates. Nat. Immunol. 13, 223-228.</ref>. SAMHD1 does not, however, restrict HIV-2 replication in myeloid cells due to the presence of viral Vpx. Vpx counteracts restriction by inducing the ubiquitin-proteasome-dependent degradation of SAMHD1 <ref name="LaguetteNadine" />. Vpx-mediated degradation of SAMHD1 therefore decreases deoxynucleoside triphosphate hydrolysis, thereby increasing the availability of dNTPs for viral reverse transcription in the cytoplasm. It has been postulated that SAMHD1 degradation is required for HIV-2 replication because the HIV-2 reverse transcriptase (RT) is less active than the HIV-1 RT, which would be the reason for the absence of Vpx from HIV-1 <ref name="fujita" />. Because Vpx is required for HIV-2 reverse transcription and the early stages of the viral life cycle, it is packaged into virions in significant amounts <ref>Wu X., Conway J. A., Kim J., Kappes J. C. (1994) Localization of the Vpx packaging signal within the C terminus of the human immunodeficiency virus type 2 Gag precursor protein. J. Virol. 68:6161–6169.</ref><ref>Fujita,M.,Otsuka,M.,Miyoshi,M., Khamsri,B.,Nomaguchi,M.,and Adachi,A.(2008). Vpx is critical for reverse transcription of the human immune deficiency virus type 2 genome in macrophages. J. Virol. 82, 7752–7756.</ref>.


Vpx is also involved in the nuclear import of the HIV-2/SIV genomes and associated proteins <ref name="AmelBaya">Amel Baya Bouzar, François Guiguen, Thierry Morin, Stephanie Villet, Claudie Fornazero, C.éline Garnier, Kathy Gallay, Françoise Gounel, Colette Favier, Jitka Durand, Sabine Balleydier, Jean Francois Mornex, Opendra Narayan, Yahia Chebloune, Specific G2 arrest of caprine cells infected with a caprine arthritis encephalitis virus expressing vpr and vpx genes from simian immunodeficiency virus, Virology, Volume 309, Issue 1, 25 April 2003, Pages 41-52, ISSN 0042-6822, 10.1016/S0042-6822(03)00014-X.</ref>, but the specific mechanisms and interactions are currently unknown. Interestingly, although Vpr and Vpx are similar in size (both are ~100 amino acids with 20-25% sequence similarity) and structure (both are predicted to have similar tertiary structure with three major helices), they serve very different roles in viral replication <ref name="fujita" />. Vpx targets a host restriction factor for proteasomal degradation, while Vpr arrests the host cell cycle in the G2 phase <ref name="fujita" />. However, they are both involved in the import of the viral preintegration complex into the host nucleus <ref name="AmelBaya" />.
Vpx is also involved in the nuclear import of the HIV-2/SIV genomes and associated proteins <ref name="AmelBaya">Amel Baya Bouzar, François Guiguen, Thierry Morin, Stephanie Villet, Claudie Fornazero, C.éline Garnier, Kathy Gallay, Françoise Gounel, Colette Favier, Jitka Durand, Sabine Balleydier, Jean Francois Mornex, Opendra Narayan, Yahia Chebloune, Specific G2 arrest of caprine cells infected with a caprine arthritis encephalitis virus expressing vpr and vpx genes from simian immunodeficiency virus, Virology, Volume 309, Issue 1, 25 April 2003, Pages 41-52, ISSN 0042-6822, 10.1016/S0042-6822(03)00014-X.</ref>, but the specific mechanisms and interactions are currently unknown. Interestingly, although Vpr and Vpx are similar in size (both are ~100 amino acids with 20-25% sequence similarity) and structure (both are predicted to have similar tertiary structure with three major helices), they serve very different roles in viral replication <ref name="fujita" />. Vpx targets a host restriction factor for proteasomal degradation, while Vpr arrests the host cell cycle in the G2 phase <ref name="fujita" />. However, they are both involved in the import of the viral preintegration complex into the host nucleus <ref name="AmelBaya" />.

Revision as of 00:13, 26 March 2013

For the computer bus standard, see VPX.

Vpx is a virion-associated protein encoded by human immunodeficiency virus type 2 HIV-2 and most simian immunodeficiency virus (SIV) strains, but that is absent from HIV-1. [1] It is similar in structure to the protein Vpr that is carried by SIV and HIV-2 as well as HIV-1.[2] Vpx is one of five accessory proteins (Vif, Vpx, Vpr, Vpu, and Nef) carried by lentiviruses that enhances viral replication by inhibiting host antiviral factors. [2]

Vpx enhances HIV-2 replication in humans by counteracting the host factor SAMHD1.[3] SAMHD1 is a host factor found in human myeloid cells, such as dendritic cells and macrophages, that restricts HIV-1 replication by depleting the cytoplasmic pool of deoxynucleoside triphosphates needed for viral DNA production [4]. SAMHD1 does not, however, restrict HIV-2 replication in myeloid cells due to the presence of viral Vpx. Vpx counteracts restriction by inducing the ubiquitin-proteasome-dependent degradation of SAMHD1 [5]. Vpx-mediated degradation of SAMHD1 therefore decreases deoxynucleoside triphosphate hydrolysis, thereby increasing the availability of dNTPs for viral reverse transcription in the cytoplasm. It has been postulated that SAMHD1 degradation is required for HIV-2 replication because the HIV-2 reverse transcriptase (RT) is less active than the HIV-1 RT, which would be the reason for the absence of Vpx from HIV-1 [2]. Because Vpx is required for HIV-2 reverse transcription and the early stages of the viral life cycle, it is packaged into virions in significant amounts [6][7].

Vpx is also involved in the nuclear import of the HIV-2/SIV genomes and associated proteins [8], but the specific mechanisms and interactions are currently unknown. Interestingly, although Vpr and Vpx are similar in size (both are ~100 amino acids with 20-25% sequence similarity) and structure (both are predicted to have similar tertiary structure with three major helices), they serve very different roles in viral replication [2]. Vpx targets a host restriction factor for proteasomal degradation, while Vpr arrests the host cell cycle in the G2 phase [2]. However, they are both involved in the import of the viral preintegration complex into the host nucleus [8].

References

  1. ^ Vicenzi, E. (2013). "Novel factors interfering with human immunodeficiency virus-type 1 replication in vivo and in vitro". Tissue Antigens. 81 (2): 61–71. doi:10.1111. PMID 23330719. {{cite journal}}: Check |doi= value (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  2. ^ a b c d e Fujita, M. (10). "SAMHD1-Dependent and -Independent Functions of HIV-2/SIV Vpx Protein". Frontiers in Microbiology. 3 (297). doi:10.3389. PMID 22908011. {{cite journal}}: Check |doi= value (help); Check date values in: |date= and |year= / |date= mismatch (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  3. ^ Laguette, Nadine (16). "Evolutionary and functional analyses of the interaction between the myeloid restriction factor SAMHD1 and the lintiviral Vpx protein". Cell Host & Microbe. 11 (2): 205–217. doi:10.1016. PMID 22305291. {{cite journal}}: Check |doi= value (help); Check date values in: |date= and |year= / |date= mismatch (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  4. ^ Lahouassa, H., Daddacha, W., Hofmann, H., Ayinde, D., Logue, E. C., Dragin, L., Bloch, N., Maudet, C., Bertrand, M., Gramberg, T., Pancino, G., Priet, S., Canard, B., Laguette, N., Benkirane, M., Transy, C., Landau, N. R., Kim, B., and Margottin-Goguet, F. (2012). SAMHD1 restricts the replication of HIV-1 by depleting the intracellular pool of deoxynucleoside triphosphates. Nat. Immunol. 13, 223-228.
  5. ^ Cite error: The named reference LaguetteNadine was invoked but never defined (see the help page).
  6. ^ Wu X., Conway J. A., Kim J., Kappes J. C. (1994) Localization of the Vpx packaging signal within the C terminus of the human immunodeficiency virus type 2 Gag precursor protein. J. Virol. 68:6161–6169.
  7. ^ Fujita,M.,Otsuka,M.,Miyoshi,M., Khamsri,B.,Nomaguchi,M.,and Adachi,A.(2008). Vpx is critical for reverse transcription of the human immune deficiency virus type 2 genome in macrophages. J. Virol. 82, 7752–7756.
  8. ^ a b Amel Baya Bouzar, François Guiguen, Thierry Morin, Stephanie Villet, Claudie Fornazero, C.éline Garnier, Kathy Gallay, Françoise Gounel, Colette Favier, Jitka Durand, Sabine Balleydier, Jean Francois Mornex, Opendra Narayan, Yahia Chebloune, Specific G2 arrest of caprine cells infected with a caprine arthritis encephalitis virus expressing vpr and vpx genes from simian immunodeficiency virus, Virology, Volume 309, Issue 1, 25 April 2003, Pages 41-52, ISSN 0042-6822, 10.1016/S0042-6822(03)00014-X.
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