Activity of α- and θ-Defensins against Primary Isolates of HIV-1

Abstract

θ-Defensins are lectin-like, cyclic octadecapeptides found in the leukocytes of nonhuman primates. They are also homologues of the more familiar α-defensins expressed by humans and certain other mammals. This study compares the ability of six θ-defensins (hominid retrocyclins 1–3 and rhesus θ-defensins 1–3) and four human α-defensins (human neutrophil peptides (HNPs) 1–4) to bind gp120 and CD4. In addition, we compared the ability of these θ-defensins and HNP-1 to protect J53-BL cells (an indicator cell line) from primary HIV-1 isolates that varied in subtype and coreceptor usage. The most potent θ-defensin, retrocyclin-2, bound with exceptionally high affinity to gp120 (KD, 9.4 nM) and CD4 (KD, 6.87 nM), and its effectiveness against subtype B isolates (IC50, 1.05 ± 0.28 μg/ml; 520 ± 139 nM) was approximately twice as great as that of HNP-1 on a molar basis. We also show, for the first time, that human α-defensins, HNPs 1–3, are lectins that bind with relatively high affinity to gp120 (KD range, 15.8–52.8 nM) and CD4 (KD range, 8.0–34.9 nM). Proteins found in human and FBS bound exogenous HNP-2 and retrocyclin-1, and competed with their ability to bind gp120. However, even the low concentrations of α-defensins found in normal human serum suffice to bind over half of the gp120 spikes on HIV-1 and a higher percentage of cell surface CD4 molecules. Although this report principally concerns the relationship between carbohydrate-binding and the antiviral properties of α- and θ-defensins, the lectin-like behavior of defensins may contribute to many other activities of these multifunctional peptides.

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

“…Several recent reports have shown that ␣-defensins act as natural inhibitors of HIV-1 infection, 6,15,23,24 but the mechanisms of such inhibition are still incompletely understood. In this study, we provide evidence that ␣-defensins inhibit the earliest stages of the HIV-1 infectious cycle as shown by blockade of envelope-mediated cell fusion, a process that closely mimics fusion between the viral and cellular membranes during the virus-entry process.…”

“…Because various proteins present in bovine serum (eg, fetuin, ␣2-macroglobulin) are known to bind and sequester ␣-defensins, 6,31,32 we tested the influence of serum on fusion inhibition by ␣-defensins by performing parallel tests in the presence and absence of bovine serum. Figure 1A shows that the antiviral activity of ␣-defensins was dramatically increased in the absence of bovine serum (IC 50 , 2.0 M for IIIB, 3.1 M for BaL, and 3.5 M for MN), demonstrating that serum proteins impair the capacity of ␣-defensins to inhibit the early events of the HIV-1 infectious cycle.…”

“…21,22 What remains undisputed, nevertheless, is that ␣-defensins are active against HIV-1, as recently confirmed by several authors. 6,15,23,24 ␣-defensins have been identified as in vivo correlates of protection in mother-to-child transmission, with a significant association between high ␣-defensin concentrations and a decreased risk of intrapartum and postnatal HIV transmission. 25 The mechanism of ␣-defensin-mediated HIV-1 inhibition is still uncertain.…”

“…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 structure.…”

“…on March 21, 2019. by guest www.bloodjournal.org From endotoxin concentrations we tested LPS in the HIV-1 envelopemediated cell fusion and observed no inhibitory effects at doses up to 1 g/mL (data not shown). Because envelope-mediated cell fusion closely mimics the molecular events leading to viral entry, these results demonstrated that ␣-defensins block HIV-1 infection at its earliest stages, before the viral entry step.Because various proteins present in bovine serum (eg, fetuin, ␣2-macroglobulin) are known to bind and sequester ␣-defensins, 6,31,32 we tested the influence of serum on fusion inhibition by ␣-defensins by performing parallel tests in the presence and absence of bovine serum. Figure 1A shows that the antiviral activity of ␣-defensins was dramatically increased in the absence of bovine serum (IC 50 , 2.0 M for IIIB, 3.1 M for BaL, and 3.5 M for MN), demonstrating that serum proteins impair the capacity of ␣-defensins to inhibit the early events of the HIV-1 infectious cycle.…”