The Nef Protein of Human Immunodeficiency Virus Is a Broad-Spectrum Modulator of Chemokine Receptor Cell Surface Levels That Acts Independently of Classical Motifs for Receptor Endocytosis and GαiSignaling

Abstract

Chemokine receptors (CKRs) are important physiological mediators of immune defense, inflammatory responses, and angiogenesis, and they have also been implicated in a number of viral disease processes. Here, we report that the Nef protein of human immunodeficiency virus (HIV) reduces cell surface levels of eight different members of the CC- and CXC-family of CKRs by up to 92%. This broad-range activity required specific elements in HIV(SF2) Nef, including the proline-rich motif P73P76P79P82 as well as the acidic cluster motif E66E67E68E69, and Nef expression induced a marked perinuclear accumulation of CKRs. Surprisingly, receptor mutagenesis demonstrated that the cytoplasmic tail of CCR5 and CXCR4, which is critical for basal and ligand-mediated endocytosis, was completely dispensable for this Nef activity. In contrast, triple-mutation of the highly conserved DRY motif in the second intracellular CKR loop abolished the Nef-mediated down-regulation of CXCR4 independently of this motif's role in CKR binding to heterotrimeric G proteins and signaling via the Galphai subunit. Thus, we identify the lentiviral pathogenicity factor Nef as a unique and broad-range modulator of CKR cell surface levels. Nef uses a mechanism that is distinct from well-established pathways orchestrating CKR metabolism and offers an interesting tool to study the multifaceted biology of CKRs.