Skip to content

Advertisement

  • Poster presentation
  • Open Access

HLA-C increases fusion efficiency between the HIV-1 envelope and the cell membrane and is part of the fusion complex

  • 1,
  • 1,
  • 1,
  • 2,
  • 2,
  • 1 and
  • 1Email author
Retrovirology20063 (Suppl 1) :P70

https://doi.org/10.1186/1742-4690-3-S1-P70

  • Published:

Keywords

  • Viral Infectivity
  • Fusion Process
  • Primary Isolate
  • Syncytium Formation
  • Fusion Index

Background

The HIV-1 viral envelope originates from the cell membrane and contains different cellular proteins such as MHC class I molecules, which play a role in modulating viral infectivity. HLA-C is known to enhance viral infectivity and reduce sensitivity to neutralizing antibodies by inducing gp120/41 conformational changes that may increase fusion efficiency and viral infectivity [1]. In this work we studied the effect of HLA-C on syncytia formation and of its association with the HIV-1 gp120/41 and with the CD4/CCR5 receptors in purified fusion complexes.

Materials and methods

Syncytia were formed by co-cultivating HeLa cells expressing the HIV-1 gp120/41 of different laboratory and primary isolates with target cells expressing HIV-1 receptors (3T3.T4.CCR5; 3T3.T4.CXCR4; HeLa-P4.2; TZM-bl; CHO-CD4-CCR5). HLA-C expression was silenced using the RNA interference technique (Dharmacon SMARTpool siRNAs) and verified by Western blot and cytofluorimetry. Fusion efficiency was determined by calculating the fusion index, and, with TZM-bl cells, by using the β-gal and the luciferase quantitative assays. Fusion complexes formed by co-cultivating CHO-gp120/41-HLA-C and CHO-CD4-CCR5 cells, and by co-cultivating CHO-gp120/41 and CHO-CD4-CCR5-HLA-C cells were purified and analyzed by Western blot and dot-blot as described [2].

Results

The level of syncytia formation between HLA-C silenced HeLa-ADA and 3T3.T4.CCR5 cells or HeLa-LAI and 3T3.T4.CXCR4 cells was significantly lower (p < 0.01) than between non silenced control and target receptor cells. The R5-tropic gp120/41 ADA was sensitive to HLA-C presence when fusing with 3T3.T4.CXCR4 cells (p < 0.01), whereas the X4-tropic gp120/41 LAI was not affected by HLA-C presence when fusing with 3T3.T4.CCR5 cells. Similarly, fusion efficiency was significantly lower (p < 0.01) using HLA-C silenced cells expressing HIV-1 gp120/41s with either HeLa-P4.2 or TZM-bl cells. No difference was evident using gp120/41 of the NDK isolate, confirming a previous report [1]. When HLA-C was expressed on target receptors cells, a similar positive effect on fusion efficiency was observed for all gp120/41s tested, including NDK. HLA-C molecules were detected in purified fusion complexes, either associated with the gp120/41 or with the receptors.

Conclusion

HLA-C silencing by RNA interference reduces fusion efficiency of X4 and R5-tropic gp120/41s, highlighting its role in increasing viral infectivity. The fusion efficiency of R5-tropic gp120/41 with CD4-CXCR4 cells is enhanced by HLA-C presence, whereas the X4-tropic gp120/41 LAI is not sensitive to HLA-C presence when fusing with CD4-CCR5 cells, suggesting that HLA-C might play a role in the transition from R5 to X4-tropism during the course of natural infection. The NDK env fusion capacity is not influenced by HLA-C presence when co-expressed with the gp120/41, but it is enhanced when HLA-C is co-expressed with the receptors, suggesting a different mechanism of action for HLA-C molecules in enhancing viral infectivity, whether they are expressed on the same membrane that contains the gp120/41 or expressed with the receptors. The comparison between HLA-C sensitive and insensitive gp120/41 sequences may help elucidating the role of HLA-C in the fusion process by indicating a possible interaction and/or association between these molecules. The co-purification of HLA-C with the fusion complex suggests its association either with gp120/41 or with HIV-1 cellular receptor/co-receptor, resulting in an increased efficiency of the fusion process and thus a greater infectivity of viral particles that include HLA-C in their envelope.

Authors’ Affiliations

(1)
Section of Biology and Genetics, University of Verona, Italy
(2)
San Raffaele Scientific Institute, Milan, Italy

References

  1. Cosma A, Blanc D, Braun J, Quillent C, Barassi C, Moog C, Klasen S, Spire B, Scarlatti G, Pesenti E, Siccardi AG, Beretta A: Enhanced HIV infectivity and changes in GP120 conformation associated with viral incorporation of human leucocyte antigen class I molecules. AIDS. 1999, 13: 2033-2042. 10.1097/00002030-199910220-00005.View ArticlePubMedGoogle Scholar
  2. Zipeto D, Matucci A, Ripamonti C, Scarlatti G, Rossolillo P, Turci M, Sartoris S, Tridente G, Bertazzoni U: Induction of human immunodeficiency virus neutralizing antibodies using fusion complexes. Microbes Infect. 2006, 8: 1424-1433. 10.1016/j.micinf.2006.03.001.View ArticlePubMedGoogle Scholar

Copyright

Advertisement