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Role of CD4 endocytosis in human immunodeficiency virus infection
A Pelchen-Matthews1, P Clapham, M Marsh
1Medical Research Council Laboratory for Molecular Cell Biology, University College London, United Kingdom.
Insights
Human immunodeficiency virus (HIV) entry into cells does not require CD4 endocytosis. Laboratory-adapted HIV strains infect cells most efficiently when CD4 uptake is limited, suggesting plasma membrane fusion is the primary entry mechanism.
Area of Science:
- Virology
- Cell Biology
Background:
- CD4 receptor is crucial for human immunodeficiency virus (HIV) entry.
- The mechanism of CD4 receptor internalization during HIV infection is not fully understood.
Purpose of the Study:
- To investigate the role of CD4 endocytosis in HIV entry.
- To determine if CD4 internalization is a prerequisite for HIV infection.
Main Methods:
- Analyzing infection levels of HeLa cells with varying CD4 endocytosis rates using a quantitative infectious focus assay.
- Utilizing a modified assay with prebinding, synchronized entry, and neutralization to assess HIV-1LAI infection.
- Employing hypertonic medium to inhibit CD4 endocytosis and observing its effect on infection.
Main Results:
- Cells with limited CD4 endocytosis showed the highest infection rates for laboratory-adapted HIV-1 and HIV-2 strains.
- Efficient CD4 uptake correlated with poor infectability, indicating internalization is not required for entry.
- Inhibition of CD4 endocytosis did not alter the rate or extent of HIV infection.
Conclusions:
- HIV infection does not necessitate CD4 endocytosis.
- Laboratory-adapted HIV strains likely enter HeLa-CD4 cells via fusion at the plasma membrane.
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-1LAI to HeLa-CD4 cells at 4 degrees C, synchronized virus entry during warming to 37 degrees 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.