Primate lentiviral Nef proteins deregulate T-cell development by multiple mechanisms.
BACKGROUND
A nef gene is present in all primate lentiviral genomes and is important for high viral loads and progression to AIDS in human or experimental macaque hosts of HIV or SIV, respectively. In these hosts, infection of the thymus results in a decreased output of naive T cells that may contribute to the development of immunodeficiency. We have previously shown that HIV-1 subtype B Nef proteins can block human T-cell development. However, the underlying mechanism(s) and the conservation of this Nef function between different groups of HIV and SIV remained to be determined.


RESULTS
We investigated whether reduction of thymic output is a conserved function of highly divergent lentiviral Nef proteins including those from both types of human immunodeficiency viruses (HIV-1 and HIV-2), their direct simian counterparts (SIVcpz, SIVgor and SIVsmm, respectively), and some additional SIV strains. We found that expression of most of these nef alleles in thymocyte progenitors impaired T-cell development and reduced thymic output. For HIV-1 Nef, binding to active p21 protein (Cdc42/Rac)-activated kinase (PAK2) was a major determinant of this function. In contrast, selective disruption of PAK2 binding did not eliminate the effect on T-cell development of SIVmac239 Nef, as was shown by expressing mutants in a newly discovered PAK2 activating structural motif (PASM) constituted by residues I117, H121, T218 and Y221, as well as previously described mutants. Rather, down-modulation of cell surface CD3 was sufficient for reduced thymic output by SIVmac Nef, while other functions of SIV Nefs contributed.


CONCLUSIONS
Our results indicate that primate lentiviral Nef proteins impair development of thymocyte precursors into T cells in multiple ways. The interaction of HIV-1 Nef with active PAK2 by HIV-1 seem to be most detrimental, and downregulation of CD3 by HIV-2 and most SIV Nef proteins sufficient for reduced thymic output. Since the reduction of thymic output by Nef is a conserved property of divergent lentiviruses, it is likely to be relevant for peripheral T-cell depletion in poorly adapted primate lentiviral infections.
Department of Clinical Chemistry, Microbiology, and Immunology, Ghent University, Ghent, Belgium. Bruno.Verhasselt@UGent.be.
Anouk
A
Van Nuffel
Kevin K
KK
Ariën
Veronique
V
Stove
Michael
M
Schindler
Eduardo
E
O'Neill
Jan
J
Schmökel
Inge
I
Van de Walle
Evelien
E
Naessens
Hanne
H
Vanderstraeten
Kathleen
K
Van Landeghem
Tom
T
Taghon
Kati
K
Pulkkinen
Kalle
K
Saksela
J Victor
JV
Garcia
Oliver T
OT
Fackler
Frank
F
Kirchhoff
Bruno
B
Verhasselt
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D051379:Mice; D016513:Mice, SCID; D009924:Organ Culture Techniques; D013601:T-Lymphocytes / Q000187:drug effects / Q000502:physiology*; D060168:Thymocytes / Q000187:drug effects / Q000502:physiology*; D013950:Thymus Gland; D054334:Viral Regulatory and Accessory Proteins / Q000378:metabolism*; D054311:nef Gene Products, Human Immunodeficiency Virus / Q000378:metabolism*
C429284:NEF protein, SIV; D054334:Viral Regulatory and Accessory Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; C514837:nef protein, Human immunodeficiency virus 1; C514838:nef protein, Human immunodeficiency virus 2