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M9630621.TXT
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1996-02-27
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Document 0621
DOCN M9630621
TI The human immunodeficiency virus type 1 Vpu protein: a potential
regulator of proteolysis and protein transport in the mammalian
secretory pathway.
DT 9603
AU Vincent MJ; Abdul Jabbar M; Department of Molecular Biology, Cleveland
Clinic Foundation,; Ohio 44195, USA.
SO Virology. 1995 Nov 10;213(2):639-49. Unique Identifier : AIDSLINE
MED/96074538
AB HIV-1 Vpu is a small transmembrane phosphoprotein of 16 kDa which
performs critical roles in CD4 proteolysis and virus release. Previous
studies have demonstrated that Vpu-induced degradation of CD4 occurs in
the endoplasmic reticulum (ER), and that the proteolytic process is
sequence specific requiring both the transmembrane and cytoplasmic
domains of CD4. In the present study, we investigated the effects of Vpu
expression on the intracellular membrane trafficking pathway of
mammalian cells. In singly transfected cells, the HIV envelope
glycoproteins and vesicular stomatitis virus glycoprotein (VSV G) were
properly transported to the cell surface undergoing oligosaccharide
modifications characteristic of their movement through the Golgi
complex. In contrast, the cell surface delivery of glycoproteins was
severely impeded in cells expressing Vpu. Biochemical analyses revealed
that Vpu expression blocked the transfer of proteins from the ER-Golgi
complex to the plasma membrane in a dose- and protein-dependent manner.
Soluble gp120 exhibited extreme transport defects in the presence of
Vpu, whereas transmembrane proteins (e.g., gp160, VSV) responded only
moderately to wild-type Vpu. To gain insight into Vpu-mediated transport
inhibition, we performed mutational analysis of the CK-2 phosphorylation
sites (serines at 52 and 56) in the Vpu protein. CK-2 phosphorylation of
Vpu has been shown to regulate the activity of the protein in reactions
that involve the proteolysis of CD4 in the ER. We demonstrate here that
the phosphorylation mutant is defective in both sequence-specific
degradation of VRE-containing substrates and the transport inhibition of
gp120 and VSV-G in the secretory pathway. Thus, these experiments have
revealed that Vpu-mediated proteolysis and transport inhibition are
mechanistically coupled requiring the same structural elements of the
Vpu protein in both processes. We propose that the primary effect of Vpu
expression is to impede the secretion process and then access
glycoproteins bearing the VRE for Vpu-mediated proteolysis in the ER of
mammalian cells.
DE Base Sequence Biological Transport Cell Membrane/*METABOLISM DNA
Primers Endoplasmic Reticulum/*METABOLISM Gene Products,
vpu/GENETICS/*METABOLISM Golgi Apparatus/*METABOLISM Hela Cells Human
HIV Envelope Protein gp120/*METABOLISM *HIV-1 Intracellular
Membranes/METABOLISM Molecular Sequence Data Phosphorylation
Protein-Serine-Threonine Kinases/METABOLISM Transfection Viral
Envelope Proteins/GENETICS/METABOLISM JOURNAL ARTICLE
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).