Involvement of histone methyltransferase GLP in HIV-1 latency through catalysis of H3K9 dimethylation

► We have established an in vitro model of HIV-1 latency.
► The integration sites of most clonal cell lines favor in active gene regions.
► Hypomethylation occurs in CpG islands of HIV 5′LTR in all four clonal cell lines.
► MTA can reactivate latent HIV-1 by decreasing the level of H3K9 me2 in C11 cells.
► HMT GLP may play a significant role in the maintenance of HIV-1 latency.

Understanding the mechanism of HIV-1 latency is crucial to eradication of the viral reservoir in HIV-1-infected individuals. However, the role of histone methyltransferase (HMT) G9a-like protein (GLP) in HIV-1 latency is still unclear. In the present work, we established four clonal cell lines containing HIV-1 vector. We found that the integration sites of most clonal cell lines favored active gene regions. However, we also observed hypomethylation of CpG of HIV 5′LTR in all four clonal cell lines. Additionally, 5′-deoxy-5′-methylthioadenosine (MTA), a broad-spectrum histone methyltransferase inhibitor, was used to examine the role of histone methylation in HIV-1 latency. MTA was found to decrease the level of H3K9 dimethylation, causing reactivation of latent HIV-1 in C11 cells. GLP knockdown by small interfering RNA clearly induced HIV-1 LTR expression. Results suggest that GLP may play a significant role in the maintenance of HIV-1 latency by catalyzing dimethylation of H3K9.