The anti-HIV pseudopeptide HE-19 forms a complex with the cell-surface-expressed nucleolin independent of heparan sulfate proteoglycans

The HB-19 pseudopeptide 5[K psi(CH2N)PR]-TASP, psi(CH2N) for reduced peptid e bond, is a specific inhibitor of human immunodeficiency virus (HIV) infec tion in different CD4(+) cell lines and in primary T-lymphocytes and macrop hages. Here, by using an experimental CD4(+) cell model to monitor HIV entr y and infection, we demonstrate that HB-19 binds the cell surface and inhib its attachment of HIV particles to permissive cells. At concentrations that inhibit HIV attachment, HB-19 binds cells irreversibly, becomes complexed with the cell-surface-expressed nucleolin, and eventually results in its de gradation, Accordingly, by confocal immunofluorescence microscopy, we demon strate the drastic reduction of the cell-surface-expressed nucleolin follow ing treatment of cells with HB-19, HIV particles can prevent the binding of HB-19 to cells and inhibit complex formation with nucleolin, Such a compet ition between viral particles and HB-19 is consistent with the implication of nucleolin in the process of HIV attachment to target cells. We show that another inhibitor of HIV infection, the fibroblast growth factor-2 (FGF-2) that uses cell-surface-expressed heparan sulfate proteoglycans as low affi nity receptors, binds cells and blocks attachment of HN to permissive cells , FG;F-S does not prevent the binding of HB-19 to cells and to nucleolin, a nd similarly HB-19 has no apparent effect on the binding of FGF-2 to the ce ll surface. The lack of competition between these two anti-HIV agents rules out the potential involvement of heparan sulfate proteoglycans in the mech anism of anti-HIV effect of HB-19, thus pointing out that nucleolin is its main target.