Vpu serine 52 dependent counteraction of tetherin is required for HIV-1 replication in macrophages, but not in ex vivo human lymphoid tissue.
BACKGROUND
The human immunodeficiency virus type 1 (HIV-1) Vpu protein degrades CD4 and counteracts a restriction factor termed tetherin (CD317; Bst-2) to enhance virion release. It has been suggested that both functions can be genetically separated by mutation of a serine residue at position 52. However, recent data suggest that the S52 phosphorylation site is also important for the ability of Vpu to counteract tetherin. To clarify this issue, we performed a comprehensive analysis of HIV-1 with a mutated casein kinase-II phosphorylation site in Vpu in various cell lines, primary blood lymphocytes (PBL), monocyte-derived macrophages (MDM) and ex vivo human lymphoid tissue (HLT).


RESULTS
We show that mutation of serine 52 to alanine (S52A) entirely disrupts Vpu-mediated degradation of CD4 and strongly impairs its ability to antagonize tetherin. Furthermore, casein-kinase II inhibitors blocked the ability of Vpu to degrade tetherin. Overall, Vpu S52A could only overcome low levels of tetherin, and its activity decreased in a manner dependent on the amount of transiently or endogenously expressed tetherin. As a consequence, the S52A Vpu mutant virus was unable to replicate in macrophages, which express high levels of this restriction factor. In contrast, HIV-1 Vpu S52A caused CD4+ T-cell depletion and spread efficiently in ex vivo human lymphoid tissue and PBL, most likely because these cells express comparably low levels of tetherin.


CONCLUSIONS
Our data explain why the effect of the S52A mutation in Vpu on virus release is cell-type dependent and suggest that a reduced ability of Vpu to counteract tetherin impairs HIV-1 replication in macrophages, but not in tissue CD4+ T cells.
Schindler
Michael
M
Heinrich-Pette-Institute for Experimental Virology and Immunology, Martinistrasse 52, 20251 Hamburg, Germany. michael.schindler@hpi.uni-hamburg.de
Rajan
Devi
D
Banning
Carina
C
Wimmer
Peter
P
Koppensteiner
Herwig
H
Iwanski
Alicja
A
Specht
Anke
A
Sauter
Daniel
D
Dobner
Thomas
T
Kirchhoff
Frank
F
D019943:Amino Acid Substitution; D015703:Antigens, CD; D015704:CD4 Antigens / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D058851:GPI-Linked Proteins; D015497:HIV-1 / Q000502:physiology*; D054298:Human Immunodeficiency Virus Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008264:Macrophages / Q000821:virology*; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors*; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000502:physiology; D013601:T-Lymphocytes / Q000821:virology*; D054334:Viral Regulatory and Accessory Proteins / Q000235:genetics / Q000502:physiology*; D057074:Virus Release; D014779:Virus Replication; D000074010:Bone Marrow Stromal Antigen 2; D000086082:Viroporin Proteins
D015703:Antigens, CD; D015704:CD4 Antigens; D058851:GPI-Linked Proteins; D054298:Human Immunodeficiency Virus Proteins; D008562:Membrane Glycoproteins; D050505:Mutant Proteins; D054334:Viral Regulatory and Accessory Proteins; C094572:BST2 protein, human; D000074010:Bone Marrow Stromal Antigen 2; C514859:vpu protein, Human immunodeficiency virus 1; D000086082:Viroporin Proteins