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M9480498.TXT
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1994-08-20
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Document 0498
DOCN M9480498
TI Human immunodeficiency virus type 1 Nef-induced down-modulation of CD4
is due to rapid internalization and degradation of surface CD4.
DT 9410
AU Rhee SS; Marsh JW; Laboratory of Molecular Biology, National Institute
of Mental; Health, Bethesda, Maryland 20892.
SO J Virol. 1994 Aug;68(8):5156-63. Unique Identifier : AIDSLINE
MED/94309182
AB Human immunodeficiency virus type 1 (HIV-1) Nef is a myristylated
protein with a relative molecular mass of 27 kDa, is localized to the
cytoplasmic surfaces of cellular membranes, and has been reported to
down-modulate CD4 in human T cells. To understand the mechanism of HIV-1
Nef-mediated down-modulation of cell surface CD4, we expressed Nef
protein in human T-cell line VB. Expression of HIV-1 Nef protein
down-modulated surface CD4 molecules. In pulse-chase experiments, CD4
molecules in Nef-expressing cells were synthesized at normal levels.
However, the bulk of newly synthesized CD4 protein was degraded with a
half-life of approximately 6 h, compared with the 24-h half-life in
control cells. This Nef-induced acceleration of CD4 turnover was
inhibited by lysosomotropic agents NH4Cl and chloroquine as well as by
the protease inhibitor leupeptin. Surface CD4 biotinylation experiments
demonstrated that CD4 molecules in Nef-expressing T cells are
transported to the plasma membrane with normal kinetics but are then
rapidly internalized. Therefore, HIV-1 Nef-induced down-modulation of
CD4 is due to rapid internalization of surface CD4 and subsequent
degradation by an acid-dependent process, potentially lysosomal.
Additionally, in a Nef-expressing cell, we find accelerated dissociation
of the T-cell tyrosine kinase p56lck and CD4 but only after the complex
reaches the plasma membrane. This implies that HIV-1 Nef protein might
play a role in triggering a series of T-cell activation-like events,
which contribute to p56lck dissociation and internalization of surface
CD4 molecules.
DE Antigens, CD4/*METABOLISM Biological Transport Cells, Cultured
Down-Regulation (Physiology) Gene Products, nef/*PHYSIOLOGY Human
HIV-1/IMMUNOLOGY/*PHYSIOLOGY Kinetics Phagocytosis Proto-Oncogene
Proteins/METABOLISM Support, U.S. Gov't, P.H.S.
T-Lymphocytes/CYTOLOGY/IMMUNOLOGY JOURNAL ARTICLE
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).