Abstract
Background:Protein methylation is recognized as a major protein modification pathway regulating diverse cellular events such as protein trafficking, transcription, and signal transduction. More recently, protein arginine methyltransferase activity has been shown to regulate HIV-1 transcription via Tat. In this study, adenosine periodate (AdOx) was used to globally inhibit protein methyltransferase activity so that the effect of protein methylation on HIV-1 infectivity could be assessed.Results:Two cell culture models were used: HIV-1-infected CEM T-cells and HEK293T cells transfected with a proviral DNA plasmid. In both models, AdOx treatment of cells increased the levels of virion in culture supernatant. However, these viruses had increased levels of unprocessed or partially processed Gag-Pol, significantly increased diameter, and displayed reduced infectivity in a MAGI X4 assay. AdOx reduced infectivity equally in both dividing and non-dividing cells. However, infectivity was further reduced if Vpr was deleted suggesting virion proteins, other than Vpr, were affected by protein methylation. Endogenous reverse transcription was not inhibited in AdOx-treated HIV-1, and infectivity could be restored by pseudotyping HIV with VSV-G envelope protein. These experiments suggest that AdOx affects an early event between receptor binding and uncoating, but not reverse transcription.Conclusion:Overall, we have shown for the first time that protein methylation contributes towards maximal virus infectivity. Furthermore, our results also indicate that protein methylation regulates HIV-1 infectivity in a complex manner most likely involving the methylation of multiple viral or cellular proteins and/or multiple steps of replication.
Highlights
Protein methylation is recognized as a major protein modification pathway regulating diverse cellular events such as protein trafficking, transcription, and signal transduction
AdOx treatment results in increased virus production AdOx, an indirect inhibitor of protein methylation, was used in order to determine if this methyltransferase inhibitor affected human immunodeficiency virus (HIV)-1 infectivity
We have shown that protein methylation contributes towards maximal virus infectivity
Summary
Protein methylation is recognized as a major protein modification pathway regulating diverse cellular events such as protein trafficking, transcription, and signal transduction. Proteins can be methylated on the side chain nitrogens of arginine, lysine, and histidine residues or on the carboxyl groups of proteins [1]. Similar to other post-translational modifications, protein methylation is involved in regulating protein-protein interactions resulting in a plethora of effects during key cellular events, including regulation of transcription [6,7,8], stress response, ageing and protein repair [9], T-cell activation [10], nuclear transport [11], neuronal differentiation [12,13], ion channel function [14,15], and cytokine signaling [16]. PRMTs can modify arginine residues by adding one or two methyl groups resulting in three distinct forms of methylated arginine residues in eukaryotes, ω-NG-monomethylarginine (MMA), asymmetric (a) and symmetric (s) ω-NG, NGdimethylarginine (aDMA and sDMA). Examples of cellular events affected by arginine methylation include RNA binding and processing, regulation of transcription, signal transduction and DNA repair [18]
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