Role of CD4 endocytosis in human immunodeficiency virus infection

Abstract

We have analyzed the role of CD4 endocytosis in human immunodeficiency virus (HIV) entry by measuring the infection of HeLa cells expressing various CD4 constructs with endocytosis rates of between 0.2 and 30%/min in a quantitative infectious focus assay. For a number of laboratory-adapted HIV-1 and HIV-2 strains, the highest levels of infection were found on cells with very limited CD4 endocytosis, while cells with efficient CD4 uptake were only poorly infectable, suggesting that CD4 internalization is not required for HIV entry. This was confirmed in a modified assay involving prebinding of HIV-1 LAI to HeLa-CD4 cells at 4؇C, synchronized virus entry during warming to 37؇C, and neutralization of virions remaining at the cell surface with anti-V3 loop antibodies. Warming cells in hypertonic medium inhibited CD4 endocytosis but did not affect the rate or the extent of infection. These studies confirm that HIV infection does not require endocytosis and that laboratory-adapted virus strains can enter HeLa-CD4 cells by fusion at the plasma membrane.

The molecular basis ofHIVentry

“…Electron micrographs of virions fusing at the cell surface might not represent complete fusion, let alone productive entry, by infectious virus (Stein et al, 1987;Grewe et al, 1990). Blocking the constitutive endocytosis of CD4 by deletions in its cytoplasmic tail does not reduce infection (Maddon et al, 1988;Pelchen-Matthews et al, 1995), but might still allow endocytosis of virions capping such mutated receptors. Furthermore, early studies attributed monocyte infection to receptor-mediated endocytosis (Pauza and Price, 1988), and also showed HIV virions fusing from within endosomes in T-lymphocytes and macrophages (Grewe et al, 1990).…”

Endocytosis in Viral Replication

“…vesicular stomatitis virus] and the non‐enveloped adenoviruses) require endocytosis to ensure delivery to acidic organelles, usually endosomes. By contrast, pH‐independent viruses (such as the majority of retroviruses, including the primate immunodeficiency viruses [HIV‐1, HIV‐2 and SIV]) are frequently assumed, and in some cases have been demonstrated, to undergo fusion or penetration at the cell surface [for references see [2,3]]. However, this distinction is by no means clear‐cut.…”

Hemagglutinin 1-Specific Immunoglobulin G and Fab Molecules Mediate Postattachment Neutralization of Influenza A Virus by Inhibition of an Early Fusion Event

“…PAN has been reported for a number of different virus systems, and it is evident that not all monoclonal antibodies (MAbs) that mediate STAN can also mediate PAN. Examples of PAN have been reported with enterovirus 71 (27), poliovirus (54), Venezuelan equine encephalitis virus (42), rotavirus (43), influenza A virus (25), respiratory syncytial virus (34), Newcastle disease virus (44), transmissible gastroenteritis virus (52), vesicular stomatitis virus (7), rabies virus (14), adenovirus (58), human cytomegalovirus (33), African swine fever virus (20), and human immunodeficiency virus type 1 (HIV-1) (1,3,4,11,26,29,31,37). Sensitivity to PAN has been used as a means of demonstrating the kinetics of virus endocytosis or of virus genome entry into the cell of viruses that fuse with the plasma membrane at neutral pH.…”