Pokeweed Antiviral Protein Increases HIV-1 Particle Infectivity by Activating the Cellular Mitogen Activated Protein Kinase Pathway

Abstract

Pokeweed antiviral protein (PAP) is a plant-derived N-glycosidase that exhibits antiviral activity against several viruses. The enzyme removes purine bases from the messenger RNAs of the retroviruses Human immunodeficiency virus-1 and Human T-cell leukemia virus-1. This depurination reduces viral protein synthesis by stalling elongating ribosomes at nucleotides with a missing base. Here, we transiently expressed PAP in cells with a proviral clone of HIV-1 to examine the effect of the protein on virus production and quality. PAP reduced virus production by approximately 450-fold, as measured by p24 ELISA of media containing virions, which correlated with a substantial decline in virus protein synthesis in cells. However, particles released from PAP-expressing cells were approximately 7-fold more infectious, as determined by single-cycle infection of 1G5 cells and productive infection of MT2 cells. This increase in infectivity was not likely due to changes in the processing of HIV-1 polyproteins, RNA packaging efficiency or maturation of virus. Rather, expression of PAP activated the ERK1/2 MAPK pathway to a limited extent, resulting in increased phosphorylation of viral p17 matrix protein. The increase in infectivity of HIV-1 particles produced from PAP-expressing cells was compensated by the reduction in virus number; that is, virus production decreased upon de novo infection of cells over time. However, our findings emphasize the importance of investigating the influence of heterologous protein expression upon host cells when assessing their potential for antiviral applications.

Pokeweed antiviral protein alters splicing of HIV-1 RNAs, resulting in reduced virus production

“…1B). This decrease agreed with our previous p24 ELISA results illustrating a 450-fold reduction in virus production from cells expressing PAP (Mansouri et al 2012). To test whether the antiviral effect of PAP was due to cellular toxicity, cells were metabolically radiolabeled with […”

“…PAP expression in 293T cells results in 17% depurination of rRNA (Chan Tung et al 2008), and consistent with previous results, metabolic labeling of cells showed that this level of depurination is not sufficient to decrease the cellular translation rate (Mansouri et al 2009). We appreciate that our current study was conducted in a cell line and our future work needs to be confirmed in primary cells over a longer time frame; however, we and others have shown previously that expression or application of PAP is not toxic to cells more relevant to HIV-1 infection, such as MT-2, a lymphoblastoid T cell line, and CD4+ T cells (Zarling et al 1990;Mansouri et al 2012). Therefore, we suggest that changes in HIV-1 translation would not be due to a ribotoxic effect of PAP, but rather due to a more specific targeting of viral translation caused by damage to viral RNA.…”

Effectiveness of Herbicides for Control of Common Pokeweed (Phytolacca americana) in Corn and Soybean

“…Much of the recent scientific literature on pokeweed has focused on the plant’s medicinal and antiviral properties, and not its management as a weed in field crops (Baldwin et al 2009; Domashevskiy et al 2012; Maness et al 2012; Mansouri et al 2012). Most of the available literature on pokeweed as a weed is in non–peer-reviewed research reports and conference proceedings.…”

Verotoxin A Subunit Protects Lymphocytes and T Cell Lines against X4 HIV Infection in Vitro

“…Depurination of HIV-1 RNA long terminal repeats may hinder HIV integration [30]. However, RIPs can also activate the host MAP kinase pathway to counter this and increase infectivity [31]. VT has been shown to activate this pathway [32].…”