Research

Lysine methylation of HIV-1 Tat regulates transcriptional activity of the viral LTR

Rachel Van Duyne¹ , Rebecca Easley¹ , Weilin Wu¹ , Reem Berro¹ , Caitlin Pedati¹ , Zachary Klase¹ , Kylene Kehn-Hall¹ , Elizabeth K Flynn² , David E Symer³ and Fatah Kashanchi^1,4

¹  The George Washington University Medical Center, Department of Biochemistry and Molecular Biology, Washington, DC 20037, USA

²  Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA

³  Basic Research Laboratory, and Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA

⁴  W.M. Keck Institute for Proteomics Technology and Applications, Washington, DC 20037, USA

author email corresponding author email

Retrovirology 2008, 5:40doi:10.1186/1742-4690-5-40

Published:	22 May 2008

Abstract

Background

The rate of transcription of the HIV-1 viral genome is mediated by the interaction of the viral protein Tat with the LTR and other transcriptional machinery. These specific interactions can be affected by the state of post-translational modifications on Tat. Previously, we have shown that Tat can be phosphorylated and acetylated in vivo resulting in an increase in the rate of transcription. In the present study, we investigated whether Tat could be methylated on lysine residues, specifically on lysine 50 and 51, and whether this modification resulted in a decrease of viral transcription from the LTR.

Results

We analyzed the association of Tat with histone methyltransferases of the SUV39-family of SET domain containing proteins in vitro. Tat was found to associate with both SETDB1 and SETDB2, two enzymes which exhibit methyltransferase activity. siRNA against SETDB1 transfected into cell systems with both transient and integrated LTR reporter genes resulted in an increase in transcription of the HIV-LTR in the presence of suboptimal levels of Tat. In vitro methylation assays with Tat peptides containing point mutations at lysines 50 and 51 showed an increased incorporation of methyl groups on lysine 51, however, both residues indicated susceptibility for methylation.

Conclusion

The association of Tat with histone methyltransferases and the ability for Tat to be methylated suggests an interesting mechanism of transcriptional regulation through the recruitment of chromatin remodeling proteins to the HIV-1 promoter.