Dual role of alpha-defensin-1 in anti-HIV-1 innate immunity

Alpha-defensins are abundant antimicrobial peptides in polymorphonuclear leukocytes and play an important role in innate immunity. We have previously shown that alpha-defensin-1 can inhibit HIV-1 replication following viral entry. Here we examined the molecular mechanism(s) of alpha-defensin-1-mediated HIV-1 inhibition. Alpha-defensin-1 had a direct effect on HIV-1 virions at a low MOI in the absence of serum. The direct effect on HIV-1 virions was abolished by the presence of serum or an increase in virus particles. Studying the kinetics of the HIV life cycle revealed that alpha-defensin-1 inhibited steps following reverse transcription and integration. Analysis of PKC phosphorylation in primary CD4+ T cells in response to alpha-defensin-1 indicated that alpha-defensin-1 inhibited PKC activity. Pretreatment of infected CD4+ T cells with a PKC activator, bryostatin 1, partially reversed alpha-defensin-1-mediated HIV inhibition. Like alpha-defensin-1, the PKC isoform-selective inhibitor Go6976 blocked HIV-1 infection in a dose-dependent manner. Furthermore, kinetic studies and analysis of HIV-1 products indicated that alpha-defensin-1 and Go6976 blocked HIV-1 infection at similar stages in its life cycle, including nuclear import and transcription. Taken together, our studies demonstrate that, in the absence of serum, alpha-defensin-1 may act directly on the virus, but, in the presence of serum, its effects are on the cell, where it inhibits HIV-1 replication. At least 1 of the cellular effects associated with HIV inhibition is interference with PKC signaling in primary CD4+ T cells. Studying the complex function of alpha-defensin-1 in innate immunity against HIV has implications for prevention as well as therapeutics.