Protein methylation is required to maintain optimal HIV-1 infectivity.
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.


CONCLUSIONS
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.
Willemsen
Nicole M
NM
Division of Immunology and Infectious Disease, Queensland Institute of Medical Research, Brisbane, Queensland, 4006, Australia. nicoleW@qimr.edu.au
Hitchen
Eleanor M
EM
Bodetti
Tracey J
TJ
Apolloni
Ann
A
Warrilow
David
D
Piller
Sabine C
SC
Harrich
David
D
D000241:Adenosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology*; D002460:Cell Line; D015685:Fusion Proteins, gag-pol / Q000378:metabolism; D016336:Gene Products, vpr / Q000378:metabolism; D015497:HIV-1 / Q000187:drug effects / Q000472:pathogenicity* / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D008745:Methylation; D008780:Methyltransferases / Q000037:antagonists & inhibitors*; D010504:Periodic Acid / Q000494:pharmacology*; D011506:Proteins / Q000378:metabolism*; D013601:T-Lymphocytes / Q000821:virology; D014771:Virion / Q000187:drug effects / Q000378:metabolism; D054325:vpr Gene Products, Human Immunodeficiency Virus
D015685:Fusion Proteins, gag-pol; D016336:Gene Products, vpr; D011506:Proteins; D054325:vpr Gene Products, Human Immunodeficiency Virus; D010504:Periodic Acid; C009288:metaperiodate; D008780:Methyltransferases; D000241:Adenosine