Abstract
Human and Simian Immunodeficiency virus (HIV-1, HIV-2, and SIV) encode an accessory protein, Nef, which is a pathogenesis and virulence factor. Nef is a multivalent adapter that dysregulates the trafficking of many immune cell receptors, including chemokine receptors (CKRs). Physiological endocytic itinerary of agonist occupied CXCR4 involves ubiquitinylation of the phosphorylated receptor at three critical lysine residues and dynamin-dependent trafficking through the ESCRT pathway into lysosomes for degradation. Likewise, Nef induced CXCR4 degradation was critically dependent on the three lysines in the C-terminal -SSLKILSKGK- motif. Nef directly recruits the HECT domain E3 ligases AIP4 or NEDD4 to CXCR4 in the resting state. This mechanism was confirmed by ternary interactions of Nef, CXCR4 and AIP4 or NEDD4; by reversal of Nef effect by expression of catalytically inactive AIP4-C830A mutant; and siRNA knockdown of AIP4, NEDD4 or some ESCRT-0 adapters. However, ubiquitinylation dependent lysosomal degradation was not the only mechanism by which Nef downregulated CKRs. Agonist and Nef mediated CXCR2 (and CXCR1) degradation was ubiquitinylation independent. Nef also profoundly downregulated the naturally truncated CXCR4 associated with WHIM syndrome and engineered variants of CXCR4 that resist CXCL12 induced internalization via an ubiquitinylation independent mechanism.
Publication types
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Research Support, N.I.H., Intramural
MeSH terms
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Amino Acid Motifs
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Chemokine CXCL12 / genetics
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Chemokine CXCL12 / metabolism
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Endocytosis
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Endosomal Sorting Complexes Required for Transport / antagonists & inhibitors
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Endosomal Sorting Complexes Required for Transport / genetics
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Endosomal Sorting Complexes Required for Transport / metabolism
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Gene Expression Regulation / drug effects*
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HIV-1 / chemistry*
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HIV-1 / genetics
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HeLa Cells
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Host-Pathogen Interactions
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Humans
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Jurkat Cells
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Molecular Sequence Data
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Monocytes / drug effects
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Monocytes / metabolism*
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Monocytes / virology
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Nedd4 Ubiquitin Protein Ligases
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Primary Cell Culture
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Proteolysis
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RNA, Small Interfering / genetics
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RNA, Small Interfering / metabolism
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Receptors, CXCR4 / genetics*
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Receptors, CXCR4 / metabolism
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Recombinant Proteins / pharmacology
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Repressor Proteins / antagonists & inhibitors
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Repressor Proteins / genetics
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Repressor Proteins / metabolism
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Signal Transduction
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Ubiquitin / genetics*
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Ubiquitin / metabolism
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Ubiquitin-Protein Ligases / antagonists & inhibitors
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Ubiquitin-Protein Ligases / genetics
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Ubiquitin-Protein Ligases / metabolism
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Ubiquitination
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nef Gene Products, Human Immunodeficiency Virus / genetics
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nef Gene Products, Human Immunodeficiency Virus / metabolism
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nef Gene Products, Human Immunodeficiency Virus / pharmacology*
Substances
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CXCL12 protein, human
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CXCR4 protein, human
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Chemokine CXCL12
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Endosomal Sorting Complexes Required for Transport
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RNA, Small Interfering
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Receptors, CXCR4
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Recombinant Proteins
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Repressor Proteins
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Ubiquitin
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nef Gene Products, Human Immunodeficiency Virus
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nef protein, Human immunodeficiency virus 1
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ITCH protein, human
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Nedd4 Ubiquitin Protein Ligases
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Nedd4 protein, human
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Ubiquitin-Protein Ligases