ADAP1 Promotes Latent HIV-1 Reactivation by Tuning the KRAS-ERK-AP-1 Signaling-Transcriptional Axis

Immune stimulation fuels cell signaling-transcriptional programs that induce biological responses to eliminate virus-infected cells. Yet, retroviruses that integrate into host cell chromatin, such as HIV-1, co-opt these programs to switch between latent and reactivated states. However, many regulatory mechanisms are still unfolding. As such, here I take advantage of the unique intrinsic reliance HIV-1 has on host cell signaling-transcriptional programs to discover undescribed cell signaling regulators. Specifically, I implemented a functional screening platform, given HIV-1 gene expression relies on CD4+ T cell activation state, to identify host factors modulating CD4+ T cell signaling-transcriptional axes and consequently HIV-1 fate. Among the hits, I focus on ADAP1 (ArfGAP with Dual PH Domains 1), a previously thought neuro-restricted factor, and discover it is an amplifier of select human CD4+ T cell signaling programs. Using physiological models, I characterize ADAP1 expression is low in naïve and memory CD4+ T cells, but largely induced upon immune stimulation where it interacts with the immune signalosome. Using complementary biochemical and cellular assays, I demonstrate ADAP1 directly stimulates the GTPase activity of KRAS to amplify CD4+ T cell signaling through targeted activation of ERK-AP-1 axis. In primary CD4+ T cells which I have genetically ablated ADAP1, I show loss of ADAP1 function blunts gene expression programs in response to stimulation thereby reducing CD4+ T cell expansion and dampening latent HIV-1 reactivation. Supporting the impact of these findings, I propose the reduced CD4+ T cell programs and proliferation upon ADAP1 loss validates Genome-wide Association Studies linking ADAP1 single nucleotide polymorphisms in non-coding enhancers to an altered T lymphocyte count trait, potentially attributed to ADAP1 haploinsufficiency. Through these combined experimental approaches, I was able to define ADAP1 as an unexpected tuner of CD4+ T cell activation programs and co-opted by HIV-1 to escape latency.