RasGRP1 agonists stimulate P-TEFb biogenesis via MEK-ERK-mTORC1 signaling to reverse HIV latency with minimal CD4 downregulation

Reactivation of latent HIV to facilitate clearance of persisting infected cells requires identifying non-toxic latency-reversing agents (LRAs) that activate P-TEFb, a cellular transcription factor essential for efficient HIV RNA synthesis. Diacylglycerol (DAG)-mimicking PKC agonists induce P-TEFb to reverse HIV latency mainly through a PKC-independent RasGRP1-Ras-Raf-MEK-ERK1/2 pathway, but also elicit global T-cell activation and a drastic downregulation of CD4 receptors. Here, we demonstrate that synthetic DAG-indololactones, which preferentially bind RasGRP1 over PKC by up to 60-fold, strongly induce posttranscriptional P-TEFb expression in memory CD4+ T cells via MEK-ERK1/2-mTORC1 signaling without triggering T-cell activation markers and with minimal CD4 loss. Elevation of T-cell activation markers by natural and synthetic PKC agonists proceeds through MEK-ERK1/2 but is independent of mTORC1 activity. Combinations of the DAG-indololactone 2A127 and HDAC inhibitors synergistically reactivate latent HIV in a primary T-cell model and CD4+ T cells from treated individuals. These findings suggest that a combination LRA approach targeting P-TEFb production through RasGRP1-ERK1/2-mTORC1 signaling and the epigenetic activation of proviral HIV can efficiently and safely reverse HIV latency.