Retroviruses are major causes of disease in animals and humans. Retroviruses replicate by reversetranscribing viral RNA into DNA, using the virus-encoded transcriptase. Since uncoating as well as reversetranscription occur in the cytoplasm, there is the potential for recognition of ?foreign? viral RNA or DNA by hostsensors. Recently, a number of host sensors, including cGAS, DDX41 and the ALR IFI16, have beenimplicated in the recognition of cytosolic DNA. Using a mutant murine leukemia virus (MLV) with an unstablecapsid that induces a strong IFN? response, we found that reverse transcripts induced this response andidentified three sensors in mice required for recognition ? IFI203, DDX41 and cGAS - that signal via the STINGpathway leading to increased IFN?? Using APOBEC3 knockout and STING mutant mice and cells, we showedthat the host retroviral restriction factor APOBEC3 limits the levels of reverse transcripts that trigger cytosolicsensing. Moreover, we found that the role of nucleic acid sensing in vivo is to increased expression of IFN-regulated restriction factors like APOBEC3 that in turn reduce viral load. While the identification of sensors involved in recognition is an important first step, there as of yet manyunanswered questions. While we and others have shown that host sensing of retroviral nucleic acid isdependent on reverse transcription and therefore must include DNA detection, the involvement of at least 3different factors in the response to infection could mean that RNA or RNA/DNA are also recognized.Additionally, while it is well-accepted that DNA binding cGAS activates production of cyclic GMP-AMP and thatthis ligand in turn activates STING, whether IFI203 and DDX41 operate in the same or parallel pathways toinduce IFN is not known. Finally, the relative importance of the different host sensors in controlling viralinfection in vivo has yet to be elucidated. To address these questions, we propose to carry out the following aims:I. What retroviral nucleic acids serve as ligands for cGAS, IFI203 and DDX41?II. What role does each of the sensors play in in vivo control of infection?III. What is the pathway of action of cGAS, IFI203 and DDX41 in the response to retroviral infection?Understanding the initial host response to infection by retroviruses is critical to our ability to determine howthese viruses establish persistent infection as well the discovery of novel approaches to intervene in theseinfections. Using a combination of functional and genetic approaches, this proposal will delineate the molecularmeans by which retroviral nucleic acids are sensed by cells, as well as to determine the significance of thissensing in in vivo infection and pathogenesis.
|Effective start/end date||6/1/16 → 5/31/21|
- National Institutes of Health: $392,434.00
Murine Leukemia Viruses
DNA-Directed RNA Polymerases