CD4 Independent Binding of HIV gp120 to Mannose Receptor on Human Spermatozoa

Department of Biochemistry, National Institute for Research in Reproductive Health, Indian Council of Medical Research, Parel, Mumbai, Maharashtra, India.
JAIDS Journal of Acquired Immune Deficiency Syndromes (Impact Factor: 4.56). 09/2008; 48(4):389-97. DOI: 10.1097/QAI.0b013e318179a0fb
Source: PubMed


To characterize the CD4-independent HIV-binding protein of 160 kDa on human spermatozoa.
The N-terminal amino acid sequence of the 160 kDa protein and its peptide obtained by tryptic digestion were determined. Polymerase chain reaction amplification of human testicular cDNA was performed using degenerate primers corresponding to peptide sequences of the 160 kDa protein. Localization of 160 kDa protein on sperm was performed using fluorescently labeled gp120, followed by inhibition experiments using antagonists to determine the specificity.
The partial cDNA sequence of the 160 kDa protein demonstrated 99% identity with human macrophage mannose receptor. Sequence of testicular mannose receptor was obtained and exhibited 99% identity with that of macrophage mannose receptor. Furthermore, mannose receptor protein from sperm extract was found to have a molecular weight of 160 kDa, congruent with that of 160 kDa HIV-binding protein. gp120 binding and mannose receptor expression were localized to the equatorial segment in 10% of ejaculated sperm, which increased after capacitation. Mannan at molar excess concentrations completely inhibited gp120 binding to sperm.
The 160 kDa, CD4-independent HIV-binding sperm protein has been identified as the human mannose receptor protein. The role of mannose receptor in HIV transmission and association with risk of sexual transmission merit further investigation.

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    • "Our data show that the interaction of sperm with HIV-1 can occur through the MR, given that in 75% of individuals evaluated, mannose pretreatment specifically inhibited HIV-1–sperm cell interaction. Moreover, a recent report indicated that the HIV-1 envelope gp120 interacts with the MR at the sperm cell membrane (Fanibunda et al., 2008). Since increasing concentrations of mannose were unable to block this interaction in one individual, the existence of alternative receptors at the sperm cell membrane that might also allow HIV-1–cell interaction cannot be excluded. "
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    ABSTRACT: Leukocytes are considered to be the main source of HIV-1 infection in semen. However, HIV-1 interaction with spermatozoa has also been demonstrated, suggesting that both spermatozoa and leukocytes might play a role during sexual transmission of HIV-1. The purpose of the present study was to evaluate if HIV-1 particles interact with sperm cells through the mannose receptor (MR), and then to determine the ability of "infected" sperm cells to transmit the virus to susceptible targets. The expression of classical HIV-1 receptor and co-receptors and the MR by sperm cells was determined by flow cytometry; the interaction in vitro between sperm and HIV-1 was evaluated by fluorescence microscopy. Additionally, the in vitro interaction of sperm cells and HIV-1 was determined detecting viral nucleic acids by PCR. D-Mannose was used to block HIV-1-sperm cell interaction. Sperm cells preincubated with HIV-1 particles and activated mononuclear cells were co-cultured to determine viral transmission. The presence of viral RNA was detected in 28% of the samples in which sperm cells were preincubated with HIV-1 particles. Mannose was able to block interaction in 75% of the cases. Finally, we demonstrated that "infected" sperm cells were able to transmit the HIV-1 infection to susceptible targets. In conclusion, these results indicate that the MR is involved in sperm cell-HIV-1 interaction. Our results also suggest that sperm cells could be an important source of infection.
    Full-text · Article · Dec 2011 · Journal of Reproductive Immunology
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    • "The reverse transcription was carried out at 55°C for 30 min, followed by denaturation at 94°C for 2 min. This was followed by 35 cycles of amplification, each cycle comprising denaturation at 94°C for 15 s, annealing at 58°C for 30 s and extension at 68°C for 30 s. cDNA was PCR amplified using hMR specific primers– FP: 5′ TAC-ACA-AAC-TGG-GGG-AAA-GG 3′ and RP 5′ TGT-TTG-AAT-CGT-TGC-TGG-AG 3′ as described earlier [17]. The amplification conditions included denaturation at 94°C for 15 s, annealing at 58°C for 30 s, extension at 68°C for 30 s, with a final extension at 68°C for 5 min. "
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    ABSTRACT: During sexual transmission of HIV in women, the virus breaches the multi-layered CD4 negative stratified squamous epithelial barrier of the vagina, to infect the sub-epithelial CD4 positive immune cells. However the mechanisms by which HIV gains entry into the sub-epithelial zone is hitherto unknown. We have previously reported human mannose receptor (hMR) as a CD4 independent receptor playing a role in HIV transmission on human spermatozoa. The current study was undertaken to investigate the expression of hMR in vaginal epithelial cells, its HIV gp120 binding potential, affinity constants and the induction of matrix metalloproteinases (MMPs) downstream of HIV gp120 binding to hMR. Human vaginal epithelial cells and the immortalized vaginal epithelial cell line Vk2/E6E7 were used in this study. hMR mRNA and protein were expressed in vaginal epithelial cells and cell line, with a molecular weight of 155 kDa. HIV gp120 bound to vaginal proteins with high affinity, (Kd = 1.2±0.2 nM for vaginal cells, 1.4±0.2 nM for cell line) and the hMR antagonist mannan dose dependently inhibited this binding. Both HIV gp120 binding and hMR exhibited identical patterns of localization in the epithelial cells by immunofluorescence. HIV gp120 bound to immunopurified hMR and affinity constants were 2.9±0.4 nM and 3.2±0.6 nM for vaginal cells and Vk2/E6E7 cell line respectively. HIV gp120 induced an increase in MMP-9 mRNA expression and activity by zymography, which could be inhibited by an anti-hMR antibody. hMR expressed by vaginal epithelial cells has high affinity for HIV gp120 and this binding induces production of MMPs. We propose that the induction of MMPs in response to HIV gp120 may lead to degradation of tight junction proteins and the extracellular matrix proteins in the vaginal epithelium and basement membrane, leading to weakening of the epithelial barrier; thereby facilitating transport of HIV across the vaginal epithelium.
    Full-text · Article · Nov 2011 · PLoS ONE
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    • "Another receptor allowing the CD4-independent binding and entry of HIV in other cell types (Liu et al., 2004), the mannose receptor , was identified in about 10% of ejaculated spermatozoa and shown to bind HIV gp120 (Fanibunda et al., 2008). No internalization of gp120 was observed and it is presently unknown whether this receptor can trigger the internalization of a whole virion (Fanibunda et al., 2008). "
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    ABSTRACT: Despite semen being the main vector of human immunodeficiency virus (HIV) dissemination worldwide, the origin of the virus in this bodily fluid remains unclear. It was recently shown that several organs of the male genital tract (MGT) are infected by HIV/simian immunodeficiency virus (SIV) and likely to contribute to semen viral load during the primary and chronic stages of the infection. These findings are important in helping answer the following questions: (i) does the MGT constitute a viral reservoir responsible for the persistence of virus release into the semen of a subset of HIV-infected men under antiretroviral therapy, who otherwise show an undetectable blood viral load? (ii) What is the aetiology of the semen abnormalities observed in asymptomatic HIV-infected men? (iii) What is the exact nature of the interactions between the spermatozoa, their testicular progenitors and HIV, an important issue in the context of assisted reproductive techniques proposed for HIV-seropositive (HIV+) men? Answers to these questions are crucial for the design of new therapeutic strategies aimed at eradicating the virus from the genital tract of HIV+ men--thus reducing its sexual transmission--and for improving the care of serodiscordant couples wishing to have children. This review summarizes the most recent literature on HIV infection of the male genital tract, discusses the above issues in light of the latest findings and highlights future directions of research.
    Full-text · Article · Jul 2009 · International Journal of Andrology
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