Regulation and Manipulation of Innate Immunity During HIV Infection

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PROJECT SUMMARY Innate immune sensing of microbes leads to activation of signal transduction cascades that trigger multiple transcription factors to rewire gene expression for host defense. However, the mechanisms that regulate this sophisticated response are not completely understood. This proposal addresses a novel transcriptional mechanism that regulates the innate response to HIV-1. Our preliminary data define a gene regulatory network that maps the innate immune response in monocyte-derived dendritic cells, and highlight new transcriptional circuitry that controls interferon signaling, which is highly relevant for HIV infection. Type I and type III interferon are known to block acute infection of HIV. However, dysregulated interferon signaling is a hallmark of pathogenesis and can increase virus replication and spread. Based on our network predictions and experimental validations, our data indicate that Core-Binding Factor Subunit Beta (CBFb, encoded by the gene CBFB) is a cell-type specific regulator of interferon and inflammation. Loss-of-function mutations in CBFb have been associated with breast cancer and acute myeloid leukemia, but a role in regulating antiviral responses through interferon signaling has not been described. We have found that perturbation of CBFb by CRISPR-Cas9 or RNA interference leads to spontaneous induction of specific interferon stimulated genes and inflammatory factors in myeloid cells but not T cells. CBFb is known to be hijacked by HIV-1 Vif in T cells to reduce expression of APOBEC3 family restriction factors, but our work suggests that CBFb’s impact on HIV is more complex than previously appreciated. Interestingly, our data indicate that HIV-1 replicates more efficiently in CBFb-depleted myeloid cells in single-cycle infections, but the virus fails to spread efficiently in replication-competent assays (and in this case, effects are independent of Vif). The experiments outlined in this proposal will provide a greater mechanistic understanding of how the transcription cofactor CBFb regulates innate immune responses and influences HIV-1 replication. With this project we aim to: 1) Determine the mechanism by which CBFb limits IFN responses in myeloid cells, 2) Determine the direct and indirect targets of CBFb and their impact on HIV infection, and 3) Validate roles for CBFb during maturation of primary immune cells. By systematically testing mutant CBFb constructs in rescue experiments, testing the roles of CBFb binding partners (such as RUNX family members), and testing CBFb-dependent genes that are known to impact HIV replication, we expect to uncover the molecular mechanism of how CBFb suppresses innate immune signaling and how dysregulation of this function is exploited during virus infection. Our long-term goals are to understand how cellular parameters can be manipulated to tune innate responses to HIV-1 and optimize our cell’s antiviral defenses. With this project, we seek to gain mechanistic insight into the transcriptional regulation of innate immunity, knowledge that could lead to new treatments to target the virus reservoir and engage anti-HIV immune responses.