Vpu Is the Main Determinant for Tetraspanin Downregulation in HIV-1-Infected Cells

Abstract

Tetraspanins constitute a family of cellular proteins that organize various membrane-based processes. Several members of this family, including CD81, are actively recruited by HIV-1 Gag to viral assembly and release sites. Despite their enrichment at viral exit sites, the overall levels of tetraspanins are decreased in HIV-1-infected cells. Here, we identify Vpu as the main viral determinant for tetraspanin downregulation. We also show that reduction of CD81 levels by Vpu is not a by-product of CD4 or BST-2/ tetherin elimination from the surfaces of infected cells and likely occurs through an interaction between Vpu and CD81. Finally, we document that Vpu-mediated downregulation of CD81 from the surfaces of infected T cells can contribute to preserving the infectiousness of viral particles, thus revealing a novel Vpu function that promotes virus propagation by modulating the host cell environment. IMPORTANCEThe HIV-1 accessory protein Vpu has previously been shown to downregulate various host cell factors, thus helping the virus to overcome restriction barriers, evade immune attack, and maintain the infectivity of viral particles. Our study identifies tetraspanins as an additional group of host factors whose expression at the surfaces of infected cells is lowered by Vpu. While the downregulation of these integral membrane proteins, including CD81 and CD82, likely affects more than one function of HIV-1-infected cells, we document that Vpu-mediated lowering of CD81 levels in viral particles can be critical to maintaining their infectiousness. Tetraspanins are integral membrane proteins that span the lipid bilayer four times. The 33 members (in humans) of this protein family, by homo-and hetero-oligomerizing and by laterally interacting with other proteins and with lipids, form a web that serves as the basis for their involvement in the organization of membranes. When triggered by intra-or extracellular cues, socalled tetraspanin-enriched microdomains (TEMs) can form, and these platforms then support or modulate various membranebased processes, including cell adhesion, membrane fusion, signaling, and protein sorting. Consequently, tetraspanins play roles in a wide range of biological activities, such as fertilization, muscle formation and repair, generation of synaptic contacts at neuromuscular junctions, maintenance of skin integrity, and induction of immune responses (1-4). They are also implicated in pathologies, including cancer (e.g., metastasis [5]) and inherited disorders (6), as well as in the propagation and pathogenesis of numerous infectious agents (parasites, bacteria, and viruses) (7-11).While one member of the tetraspanin family (CD63) was shown more than 2 decades ago to be specifically acquired by HIV-1 particles released from infected cells (12)(13)(14), only during the past decade has work by several groups documented that tetraspanins play roles during different stages of the viral replication cycle (for recent reviews, see references 9 and 15). The tetraspanins CD9, CD53, CD63, CD81, CD...

HIV-1 Vpu Downmodulates ICAM-1 Expression, Resulting in Decreased Killing of Infected CD4 + T Cells by NK Cells

“…Consistent with this idea, Vpu has been shown to inhibit HIV-1 cell-to-cell transmission in both BST2-expressing (69) and BST2-deficient (70) cells and is selected against during long-term in vitro culture, perhaps resulting in enhanced cell-to-cell transmission (71). A similar evolutionary compromise has been proposed for the Vpu-targeted tetraspanin molecules (27). Tetraspanins are surface membrane proteins that have been reported to benefit HIV-1 by preventing the cell-to-cell fusion events that lead to the formation of syncytia (72) yet hinder HIV-1 by decreasing infectivity when packaged into virions (73).…”

“…They include immunoreceptors, such as human leukocyte antigen C (HLA-C) (20), NK-T-B antigen (NTB-A) (21), CD1d (22), and poliovirus receptor (PVR) (23); homing molecules, like CCR7 (24) and CD62L (25); sodium-coupled neutral amino acid transporter 1 (SNAT1) (26); and numerous members of the tetraspanin family (27). These downregulations lead to a wide array of immunomodulatory effects, including immune evasion and metabolic dysfunction.…”

The Antagonism of HIV-1 Nef to SERINC5 Particle Infectivity Restriction Involves the Counteraction of Virion-Associated Pools of the Restriction Factor

“…By virtue of this adaptor function, Nef affects many central processes in HIV target cells. This includes modulation of cellular transport pathways leading to downregulation of an array of receptors from the surface of infected cells (4)(5)(6), which, e.g., prevents superinfection (7,8) and lysis of productively infected cells by cytotoxic T or NK cells (9,10). HIV-1 Nef also alters the response of CD4 T lymphocytes to stimulation via the T cell receptor (TCR), and modulation of the resulting cellular signaling pathways is thought to increase virus replication in the infected host (11)(12)(13)(14)(15)(16)(17).…”

Various plus unique: Viral protein U as a plurifunctional protein for HIV-1 replication

“…Particularly, surface expression of tetraspanin protein family members, such as CD37, CD53, CD63, CD81, and CD231, was reduced by both Vpu and Nef. 75 Lambele et al 76 also demonstrated that two tetraspanin molecules, CD81 and CD82, are downmodulated by HIV-1 Vpu (strain NL4-3), and specifically, that CD81 is reduced independently of the serine residues at positions 53 and 57 ( Figure 1(b)). Interestingly, these tetraspanin proteins including CD37, CD53, CD63, CD81, and CD231 have the ability to modulate HIV-1 infectivity by incorporating into nascent released viral particles 77 and impair cell-to-cell HIV-1 infection.…”