α-defensins block the early steps of HIV-1 infection: interference with the binding of gp120 to CD4

Abstract

␣-defensins are antibiotic peptides that act as natural inhibitors of HIV-1 infection. However, the mechanisms of such inhibition are still unclear. Here we demonstrate that ␣-defensins block the earliest steps in the viral infectious cycle, as documented using an HIV-1 envelopemediated cell-fusion assay. A broad-spectrum inhibitory activity was observed on primary and laboratory-adapted HIV-1 isolates irrespective of their coreceptor specificity and genetic subtype. A primary mechanism of such inhibition was identified as the ability of ␣-defensins to bind specifically both to the primary HIV-1 cellular receptor, CD4, and to the viral envelope glycoprotein, gp120. Moreover, treatment of CD4 ؉ T cells with ␣-defensins caused a dramatic downmodulation of CD4 expression. By monoclonal antibody competition, the regions of interaction with ␣-defensins were mapped to the D1 domain of CD4 and to a surface contiguous to the CD4-and coreceptorbinding sites of gp120. Consistent with these findings, ␣-defensins inhibited the binding of gp120 to CD4. These data demonstrate that ␣-defensins specifically block the initial phase of the HIV infectious cycle and modulate the expression of CD4, a critical receptor in the physiology of T-cell activation. IntroductionEvidence suggests that a concerted action of innate and adaptive immune responses is essential for the effective containment and, ultimately, the clearance of invading microorganisms. 1 The innate immune system is phylogenetically more archaic and constitutes the first line of antimicrobial defense, characterized by a rapid response time; however, it is limited in its target specificity. By contrast, the adaptive immune system has evolved refined molecular devices for the recognition of a wide variety of specific epitopes, but a lag time is required for its functional activation. Once activated, most of the cells involved in both innate and cognate immune responses secrete soluble factors, including cytokines, chemokines, antibiotic peptides, and others, which can directly antagonize infectious microorganisms and/or contribute to the recruitment and activation of other immune cells, thereby amplifying the cascade of defense mechanisms and bolstering their effectiveness. 2,3 In HIV infection, various host-derived soluble factors with antiviral activity have been described, which act by both specific and nonspecific mechanisms. These include chemokines such as RANTES, MIP-1␣, and MIP-1␤ 4 ; cytokines such as the interferons, IL-10, IL-13, IL-16, transforming growth factor-␤, and others 5 ; as well as, more recently, defensins. [6][7][8][9] Defensins are natural antibiotic peptides that play an important role in innate immune responses by acting as broad-spectrum antibacterial, antifungal, and antiviral effector molecules 10 as well as by enhancing certain adaptive immune responses. 11 ␣-defensins 1 to 3 are 3-to 4-kDa cationic peptides (29 to 30 amino acids [aa]) characterized by a conserved 6-cysteine motif, with 3 disulfide bonds that impose a characteristic ␤-sheet ...

Extracellular HIV-1 Tat Induces Human Beta-Defensin-2 Production Via NF-kappaB/AP-1 Dependent Pathways in Human B Cells

“…A variety of defensins, such as alpha-defensin, beta-defensin, and theta-defensin, have been shown to exert anti-HIV activity by multiple distinct mechanisms. Alpha-defensin-1 can inhibit HIV-1 replication via blockage of PKC signaling and inhibition of binding of gp120 and CD4 in CD4+ T cells (Chang et al, 2005;Furci et al, 2007). Beta-defensins such as hBD-2 have been shown to inhibit HIV-1 replication via direct interaction with virions and through down-modulation of the CXCR4 coreceptor (Quiñones-Mateu et al, 2003;Sun et al, 2005;Weinberg et al, 2006).…”

Human Defensins in HIV Infection: Friends or Foes?

“…The post-entry inhibitory effect of HIV infection occurs in primary CD4 + T cells and macrophages but not in several transformed T-cell lines (Chang et al, 2003;Chang et al, 2005). In the presence of serum, HNP1 did not affect expression of cellsurface CD4 and HIV-coreceptors on primary CD4+ T cells (Chang et al, 2005), whereas HNP2 down-regulates CD4 expression in the absence of serum (Furci et al, 2007). HNPs block HIVmediated cell-cell fusion and the early steps of HIV infection by interacting with HIVgp120 and CD4 through their lectin-like properties (Furci et al, 2007).…”

“…In the presence of serum, HNP1 did not affect expression of cellsurface CD4 and HIV-coreceptors on primary CD4+ T cells (Chang et al, 2005), whereas HNP2 down-regulates CD4 expression in the absence of serum (Furci et al, 2007). HNPs block HIVmediated cell-cell fusion and the early steps of HIV infection by interacting with HIVgp120 and CD4 through their lectin-like properties (Furci et al, 2007). In macrophages, HNP1 and HNP2 upregulate the expression of CC-chemokines, which could contribute to inhibition of HIV through competition for receptors (Guo et al, 2004).…”

“…HNPs1 -3 all have similar activities against HIV primary isolates , in contrast to their differential chemotactic activities on monocytes, where HNP3 has no effect (Territo et al, 1989). They can inhibit HIV-1 replication by a direct interaction with the virus as well by affecting multiple steps of HIV life cycle (Chang et al, 2003;Chang et al, 2005;Furci et al, 2007;Mackewicz et al, 2003;Wang et al, 2004). In the absence of serum, HNP1 has a direct effect on the virus prior to infection of a cell (Chang et al, 2005).…”

“…HNPs1-3 block HIV infection through multiple mechanisms (Furci et al, 2007;Zhang et al, 2002) (Chang et al, 2003;Mackewicz et al, 2003). HNPs1 -3 all have similar activities against HIV primary isolates , in contrast to their differential chemotactic activities on monocytes, where HNP3 has no effect (Territo et al, 1989).…”