Pleiotrophin inhibits HIV infection by binding the cell surface‐expressed nucleolin

Abstract

The human immunodeficiency virus (HIV) infects target cells by the capacity of its envelope glycoproteins gp120-gp41 to attach cells and induce the fusion of virus to cell membranes, a process which leads to virus entry. The receptor complex essential for HIV entry consists of the CD4 molecule and at least one of the members of the chemokine receptor family: CCR5 or CXCR4 [1,2]. Contrary to the virus entry process, the attachment of HIV particles to cells can occur even independently of CD4. We have previously demonstrated that HIV attachment is inhibited by the pseudopeptide HB-19 that binds specifically the C-terminal tail of nucleolin, a cell-surface-expressed protein identified to be implicated in HIV attachment [3][4][5]. Consequently, we have suggested that HIV attachment is achieved by the coordination of at least two events implicating on the one hand heparan sulfate proteoglycans [6,7] and on the other hand the cell surfaceexpressed nucleolin [4]. In the search for natural ligands of nucleolin that exhibit a potential inhibitory activity against HIV infection, other than midkine [8] and lactoferrin [9], here we show that pleiotrophin The growth factor pleiotrophin (PTN) has been reported to bind heparan sulfate and nucleolin, two components of the cell surface implicated in the attachment of HIV-1 particles to cells. Here we show that PTN inhibits HIV-1 infection by its capacity to inhibit HIV-1 particle attachment to the surface of permissive cells. The b-sheet domains of PTN appear to be implicated in this inhibitory effect on the HIV infection, in particular the domain containing amino acids 60-110. PTN binding to the cell surface is mediated by high and low affinity binding sites. Other inhibitors of HIV attachment known to bind specifically surface expressed nucleolin, such as the pseudopeptide HB-19 and the cytokine midkine prevent the binding of PTN to its low affinity-binding site. Confocal immunofluorescence laser microscopy revealed that the cross-linking of surface-bound PTN with a specific antibody results in the clustering of cell surface-expressed nucleolin and the colocalization of both PTN and nucleolin signals. Following its binding to surface-nucleolin, PTN is internalized by a temperature sensitive mechanism, a process which is inhibited by HB-19 and is independent of heparan and chondroitin sulfate proteoglycans. Nevertheless, proteoglycans might play a role in the concentration of PTN on the cell surface for a more efficient interaction with nucleolin. Our results demonstrate for the first time that PTN inhibits HIV infection and suggest that the cell surfaceexpressed nucleolin is a low affinity receptor for PTN binding to cells and it is also implicated in PTN entry into cells by an active process.Abbreviations ALK, anaplastic lymphoma kinase; AZT, azidothymidine; CHO, Chinese hamster ovary; HARP, heparin affin regulatory peptide; HB-GAM, heparin-binding growth-associated molecule; HBNF, heparin-binding neurite-promoting factor; MK, midkine; PTN, pleiotrophin; RPTP, receptor-type t...

RNA-binding protein nucleolin in disease

“…For example, HIV inhibitors such as pleiotrophin (PTN), the pseudopeptide HB-19, and the cytokine midkine bind specifically to cell surface-expressed nucleolin and inhibit HIV entry, indicating that nucleolin facilitates viral entry to the host cell. 94 In addition, nucleolin plays an important ligand-binding role in Francisella tularensis bacterial infection, facilitating host tissue invasion. 95 Regulation of nucleolin by phosphorylation.…”

“…HIV inhibitors such as pleiotrophin (PTN), the pseudopeptide HB-19, 69 and the cytokine midkine bind specifically to cell surface-expressed nucleolin and inhibit HIV entry, indicating that nucleolin facilitates viral entry into host cells. 94 A receptor for human RSV, nucleolin reduction by RNA interference (RNAi)-mediated knockdown lowered RSV infection in mice. 68 …”

Midkine, a cytokine that inhibits HIV infection by binding to the cell surface expressed nucleolin

“…The fact that HIV attachment is inhibited by two agents which do not compete, illustrates that virus attachment should be coordinated on one hand by heparan sulfate proteoglycans, and on the other hand by nucleolin. Consistent with the critical role of surface nucleolin in the initial steps of HIV infection, the HB-19 pseudopeptide and several physiological ligands of nucleolin (Midkine, Pleiotrophin, lactoferrin) inhibit HIV infection by blocking HIV particle attachment to CD4+ target cells [2][3][4][5][6].…”

“…In contrast to the high affinity receptors, the cell-surface expressed nucleolin is the only known low affinity receptor of MK [4]. Besides MK, surface nucleolin serves as a low affinity receptor for PTN [5] and lactoferrin [6].…”

Modulation of HIV Binding to Epithelial Cells and HIV Transfer from Immature Dendritic Cells to CD4 T Lymphocytes by Human Lactoferrin and its Major Exposed LF-33 Peptide

“…However, although both CD4 and coreceptors are essential for HIV-1 entry process, the initial association of HIV-1 particles to cells could occur in the absence of these receptors. Several observations pointed out that the attachment of HIV-1 particles to the cell surface occurs through interactions with heparan-sulfate proteoglycans and with the cell surface-expressed nucleolin [14][15][16], suggesting their possible involvement in HIV-1 attachment inhibition on epithelial cells by hLF. Thus, LF likely could exert its effect at the level of viral adsorption or penetration, in accordance with its highest effectiveness when administered before or simultaneous with the viral inoculum, as it occurs in vivo during breastfeeding and sexual transmission of HIV-1 [6].…”