Activation of HIV-1 from Latent Infection via Synergy of RUNX1 Inhibitor Ro5-3335 and SAHA

Abstract

A major barrier to the elimination of HIV-1 infection is the presence of a pool of long-lived, latently infected CD4+ memory T-cells. The search for treatments to re-activate latent HIV to aid in clearance is hindered by the incomplete understanding of the mechanisms that lead to transcriptional silencing of viral gene expression in host cells. Here we identify a previously unknown role for RUNX1 in HIV-1 transcriptional latency. The RUNX proteins, in combination with the co-factor CBF-β, are critical transcriptional regulators in T-cells. RUNX1 strongly modulates CD4 expression and contributes to CD4+ T-cell function. We show that RUNX1 can bind DNA sequences within the HIV-1 LTR and that this binding represses transcription. Using patient samples we show a negative correlation between RUNX1 expression and viral load. Furthermore, we find that pharmacologic inhibition of RUNX1 by a small molecule inhibitor, Ro5-3335, synergizes with the histone deacetylase (HDAC) inhibitor SAHA (Vorinostat) to enhance the activation of latent HIV-1 in both cell lines and PBMCs from patients. Our findings indicate that RUNX1 and CBF-β cooperate in cells to modulate HIV-1 replication, identifying for the first time RUNX1 as a cellular factor involved in HIV-1 latency. This work highlights the therapeutic potential of inhibitors of RUNX1 to re-activate virus and aid in clearance of HIV-1.

Author Summary

Since it was first discovered in the early 1980s, Human Immunodeficiency Virus 1 (HIV-1), the causative agent of Acquired Immunodeficiency Syndrome (AIDS), has been the focus of intense research. In untreated individuals, the number of CD4+ T-cells in the blood slowly drops over time and the patient eventually succumbs to an opportunistic infection. Although current therapies are capable of managing the virus; they do not represent a true cure. As a retrovirus, HIV-1 incorporates itself into the host genome and survives in the long-lived population of memory T-cells found in the human host. In this study, we examine the roll of a T-cell specific transcription factor (RUNX1) in the control of HIV-1 replication. Through various molecular studies, we show that RUNX1 represses HIV-1 replication in T-cells. By examining samples from patients with HIV-1, we are able to show a negative correlation between viral replication and RUNX1 expression. Finally, we show that an inhibitor of RUNX1 synergizes with Vorinostat, a current lead compound in the quest to re-active HIV-1 and purge the latent pool.