Expression of HIV-1 accessory protein Vif is controlled uniquely to be low and optimal by proteasome degradation.
While the Vif protein of human immunodeficiency virus type 1 (HIV-1) is essential for viral replication in non-permissive cells, it is rapidly degraded intracellularly. We have previously suggested that the rapid turn-over of Vif is biologically meaningful to prevent detrimental effects of this protein at high expression levels. We now studied the mechanism of Vif degradation by examining the blocking effect of protease inhibitors in pulse/chase experiments and by monitoring the extent of Vif ubiquitination. The rapid turn-over of Vif could be blocked by proteasome inhibitors, and Vif was highly ubiquitinated. Cytoskeletal Vif was found to be more stable than soluble cytosolic Vif. These degradation characteristics of Vif were cell type-independent and observed in both non-permissive and permissive cells. Characterization of a series of vif deletion mutants showed that amino acids predicted to be important for formation of beta-strand structures (amino acid nos. 63-70 and 86-89) were critical for maintaining a normal expression level of Vif and for viral infectivity. Finally, we performed comparative stability analysis of the four HIV-1 accessory proteins. Vif was unique in its short half-life and in the magnitude of the degradation. Taken together, we conclude that the proteasome degradation of HIV-1 Vif is a virologically important process and crucial for the function of Vif.
Fujita
Mikako
M
Department of Virology, The University of Tokushima, Graduate School of Medicine, 3-18-15 Kuaramoto-cho, Tokushima-shi Tokushima 770-8503, Japan. mfujita@basic.med.tokushima-u.ac.jp
Akari
Hirofumi
H
Sakurai
Akiko
A
Yoshida
Akiko
A
Chiba
Tomoki
T
Tanaka
Keiji
K
Strebel
Klaus
K
Adachi
Akio
A
D000595:Amino Acid Sequence; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D017353:Gene Deletion; D015967:Gene Expression Regulation, Viral; D016346:Gene Products, vif / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity* / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D054320:vif Gene Products, Human Immunodeficiency Virus
D016346:Gene Products, vif; D009097:Multienzyme Complexes; D054320:vif Gene Products, Human Immunodeficiency Virus; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex