Pertussis toxin enhances human immunodeficiency virus type 1 replication

Human Beta-Defensin 2 and 3 Inhibit HIV-1 Replication in Macrophages

Human beta-defensins (hBDs) are broad-spectrum antimicrobial peptides, secreted by epithelial cells of the skin and mucosae, and astrocytes, which we and others have shown to inhibit HIV-1 in primary CD4⁺ T cells. Although loss of CD4⁺ T cells contributes to mucosal immune dysfunction, macrophages are a major source of persistence and spread of HIV and also contribute to the development of various HIV-associated complications. We hypothesized that, besides T cells, hBDs could protect macrophages from HIV. Our data in primary human monocyte-derived macrophages (MDM) in vitro show that hBD2 and hBD3 inhibit HIV replication in a dose-dependent manner. We determined that hBD2 neither alters surface expression of HIV receptors nor induces expression of anti-HIV cytokines or beta-chemokines in MDM. Studies using a G-protein signaling antagonist in a single-cycle reporter virus system showed that hBD2 suppresses HIV at an early post-entry stage via G-protein coupled receptor (GPCR)-mediated signaling. We find that MDM express the shared chemokine-hBD receptors CCR2 and CCR6, albeit at variable levels among donors. However, cell surface expression analyses show that neither of these receptors is necessary for hBD2-mediated HIV inhibition, suggesting that hBD2 can signal via additional receptor(s). Our data also illustrate that hBD2 treatment was associated with increased expression of APOBEC3A and 3G antiretroviral restriction factors in MDM. These findings suggest that hBD2 inhibits HIV in MDM via more than one CCR thus adding to the potential of using β-defensins in preventive and therapeutic approaches.

Negative regulation of interferon-regulatory factor 3–dependent innate antiviral response by the prolyl isomerase Pin1

Recognition of double-stranded RNA activates interferon-regulatory factor 3 (IRF3)-dependent expression of antiviral factors. Although the molecular mechanisms underlying the activation of IRF3 have been studied, the mechanisms by which IRF3 activity is reduced have not. Here we report that activation of IRF3 is negatively regulated by the peptidyl-prolyl isomerase Pin1. After stimulation by double-stranded RNA, induced phosphorylation of the Ser339-Pro340 motif of IRF3 led to its interaction with Pin1 and finally polyubiquitination and then proteasome-dependent degradation of IRF3. Suppression of Pin1 by RNA interference or genetic deletion resulted in enhanced IRF-3-dependent production of interferon-beta, with consequent reduction of virus replication. These results elucidate a previously unknown mechanism for controlling innate antiviral responses by negatively regulating IRF3 activity via Pin1.

The B-oligomer of pertussis toxin inhibits human immunodeficiency virus type 1 replication at multiple stages

We have recently demonstrated that the binding subunit (B-oligomer) of pertussis toxin (PTX-B) deactivates CCR5 and inhibits entry of R5 human immunodeficiency virus type 1 (HIV-1) strains in activated primary T lymphocytes (M. Alfano et al., J. Exp. Med. 190:597-605, 1999). We now present evidence that PTX-B also affects a post-entry step of HIV-1 replication. While PTX-B inhibited fusion induced by R5 but not that induced by X4 envelopes, it blocked infection of T cells with recombinant HIV-1 particles pseudotyped with R5, X4, and even murine leukemia virus or vesicular stomatitis virus envelopes. It also suppressed HIV-1 RNA synthesis in cultures of infected peripheral blood mononuclear cells when new infections had been inhibited by zidovudine, and it reduced Tat-dependent expression of the luciferase reporter gene controlled by the HIV-1 long terminal repeat (LTR). Surprisingly, PTX-B did not affect expression from the cytomegalovirus promoter, nor did it reduce the basal (Tat-independent) expression from the LTR promoter. These results indicate that PTX-B inhibits HIV-1 infection at both the entry and the post-entry stages of viral replication, with the post-entry activity specifically affecting transcription or stability of Tat-stimulated HIV-1 mRNAs.