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Journal of Virology, April 2007, p. 4226-4234, Vol. 81, No. 8
0022-538X/07/$08.00+0     doi:10.1128/JVI.01888-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Arginine Methylation of the Human Immunodeficiency Virus Type 1 Tat Protein by PRMT6 Negatively Affects Tat Interactions with both Cyclin T1 and the Tat Transactivation Region

Baode Xie,^1, Cédric F. Invernizzi,^1,4, Stéphane Richard,^2,3,4,5 and Mark A. Wainberg^1,4*

McGill University AIDS Centre,¹ Terry Fox Molecular Oncology Group,² Bloomfield Centre for Research on Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital,³ Departments of Medicine,⁴ Oncology, McGill University, Montréal, Québec, Canada⁵

Received 30 August 2006/ Accepted 24 January 2007

Arginine methylation has been shown to regulate signal transduction, protein subcellular localization, gene transcription, and protein-protein interactions that ultimately alter gene expression. Although the role of cellular protein arginine methyltransferases (PRMT) in viral gene expression is largely unknown, we recently showed that the Tat protein of human immunodeficiency virus type 1 (HIV-1) is a substrate for one such enzyme, termed PRMT6. However, the mechanism by which arginine methylation impairs the transactivation potential of Tat and the sites of arginine methylation within Tat remain obscure. We now show that Tat is a specific in vitro and in vivo substrate of PRMT6 which targets the Tat R52 and R53 residues for arginine methylation. Such Tat methylation led to decreased interaction with the Tat transactivation region (TAR) of viral RNA. Furthermore, arginine methylation of Tat negatively affected Tat-TAR-cyclin T1 ternary complex formation and diminished cyclin T1-dependent Tat transcriptional activation. Overexpression of wild-type PRMT6, but not a methylase-inactive PRMT6 mutant, reduced levels of Tat transactivation of HIV-1 long terminal repeat chloramphenicol acetyltransferase and luciferase reporter plasmids in a dose-dependent manner. In cell-based assays, knockdown of PRMT6 resulted in increased HIV-1 production and faster viral replication. Thus, PRMT6 can compromise Tat transcriptional activation and may represent a form of innate cellular immunity in regard to HIV-1 replication. Finding a way of inhibiting or stimulating PRMT6 activity might help to drive quiescently infected cells out of latency or combat HIV-1 replication, respectively.

Published ahead of print on 31 January 2007.

B.X. and C.F.I. contributed equally to this work.

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