Tetraspanins CD9 and CD81 Modulate HIV-1-Induced Membrane Fusion

Abstract

Protein organization on the membrane of target cells may modulate HIV-1 transmission. Since the tetraspanin CD81 is associated to CD4, the receptor of HIV-1 envelope protein (Env; gp120/gp41), we have explored the possibility that this molecule may modulate the initial steps of HIV-1 infection. On the other hand, CD81 belongs to the tetraspanin family, which has been described as organizers of protein microdomains on the plasma membrane. Therefore, the role of CD81 and other related tetraspanin, CD9, on the cell-to-cell fusion process mediated by HIV-1 was studied. We found that anti-tetraspanin Abs enhanced the syncytia formation induced by HIV-1 envelope proteins and viral entry in human T lymphoblasts. In addition, anti-CD81 Abs triggered its clustering in patches, where CD4 and CXCR4 were included. Moreover, the knocking down of CD81 and CD9 expression resulted in an increase in syncytia formation and viral entry. Accordingly, overexpression of CD81 and CD9 rendered cells less susceptible to Env-mediated syncytia formation. These data indicate that CD9 and CD81 have an important role in membrane fusion induced by HIV-1 envelope.

Actin-binding Protein Drebrin Regulates HIV-1-triggered Actin Polymerization and Viral Infection

“…Interestingly, new viral particles released from drebrin-depleted cells are more infective, suggesting not only that drebrin-depleted cells are more easily infected but also that new virions released are more infective, explaining why at day 6 the effect of drebrin silencing was amplified. In this sense, previous reports have shown that other host proteins that get incorporated into the viral particles, affect both viral entry and infectivity (15,66,67). In summary, our results identify a regulatory role for the CXCR4-binding protein drebrin during HIV-1 entry into target T cells, by modulating profilin accumulation and actin polymerization at Envdriven contacts.…”

“…At any rate, the plasma membrane is what the virus particle encounters first. Thus, the spatial organization of transmembrane proteins at the cell surface and the physical state of the lipid bilayer are critical regulators of HIV-1 entry (11,14,15,18,(53)(54)(55). Supporting this statement, there is an increasing number of studies showing that cellular proteins affecting either the clustering of viral receptors (such as tetraspanins, EWI-2, moesin, and filamin-A) or the subcortical actin cytoskeleton (such as syntenin-1, ␣-actinin, talin, vinculin, cofilin, profilin, WASp, WAVE-2, diaphanous-2, and Arp2/3) alter HIV-1 infection effectiveness (15, 18, 20, 24, 26, 30, 31, 56 -60).…”

“…Env-induced Cell Fusion Assay-A dual-fluorescence cell-fusion assay was performed as described previously (15). Briefly, CMTMR-loaded Env ϩ Jurkat-Hxbc2 cells were mixed with calcein-AM-loaded parental or GFP-transfected CEM-T4 cells for 16 h at 37°C.…”

“…Then, the supernatants were removed and cells were lysed with a Steady Glo luciferase assay system (Promega Corp.) and a 1450 Microbeta Luminescence Counter (Walax, Trilux). Replication-deficient luciferase-HIV-1 viral particles (X4-Luc and VSV-Luc) were kindly provided by Suryaram Gummuluru (Boston University, Boston, MA) and were described previously (15). Briefly, virus stocks were generated by PolyFect transient transfection of HEK293T cells (44).…”

The Tetraspanin CD9 Localizes to Platelet-Platelet Contacts and Regulates Thrombus Stability

“…Interestingly, multiple studies indicate CD9 clusters at cell-cell contacts in a variety of cell types (Gordon-Elonso 2006, Nakamura 1995. It is interesting that CD9 was not found to localize to platelet-matrix contact sites on any of the matrices studied (Fig 4.5).…”