The relative ability of cell autonomous HIV-1 restriction factors to interfere with the viral life cycle contributes to a host’s level of susceptibility to infection. Pharmacological enhancement of restriction factor efficacy would be a novel approach to treating HIV infection. However, the mechanistic basis for HIV blockage by restriction factors is not completely understood hampering efforts to employ restriction factor-based host directed therapies. The tripartite motif (TRIM) family of proteins consists of more than 70 members in humans, several of which have been identified as antiviral restriction factors. In this role, TRIMs can diminish viral replication directly by interfering with the viral life cycle or indirectly by fine tuning cellular innate immune responses. TRIM family member TRIM5α accomplishes both of these: first, it prevents retroviral infection of cells by a hitherto unexplained mechanism. Second, TRIM5α also acts as a pattern recognition receptor, promoting the establishment of an antiviral cellular state via the activation of inflammatory signaling pathways upon retroviral recognition. Although TRIMs appear to employ multiple approaches in antiretroviral defense, one strikingly common feature among the TRIM family is that many if not all TRIMs are involved in the regulation and execution of autophagy. In addition to its role as a known defense mechanism against intracellular pathogens (including HIV-1), autophagy is also increasingly recognized as a means of reducing or fine tuning inflammation. Here, we propose to test the hypothesis that autophagy underlies TRIM action in protecting cells against HIV-1 infection and in modulating the TRIM-dependent inflammatory signaling. The studies proposed here have several overarching goals. First, they seek to improve our understanding of the molecular mechanism whereby rhesus TRIM5α both regulates autophagy and directs the autophagic degradation of incoming HIV-1 capsids (Aim 1). Second, they will determine if modulations of the autophagy pathway affect TRIM5α-dependent activation of pro-inflammatory signaling upon lentiviral infection. Finally, they will address whether human TRIMs other than TRIM5α that restrict HIV also employ autophagy in their antiviral actions (Aim 2). We have assembled a team of autophagy and HIV experts to address these questions. Our studies have the potential to uncover the mode of action of several known antiretroviral proteins and lay the groundwork for our understanding of how TRIMs as a family can both positively and negatively affect inflammation. We expect these studies to show that autophagy is a unifying aspect of diverse TRIM actions in HIV defense. Since autophagy can be pharmacologically manipulated, our findings may indicate that modulations of autophagy could be a therapeutic approach to dealing with TRIM-related diseases including HIV/AIDS. Our expertise in TRIMs and autophagy, along with the financial and institutional support to be provided should the COBRE application be funded will ensure successful completion of these aims.

The function of T helper (TH) cells, the central organizers of adaptive immunity, is specified by the effector cytokines they produce. Regulation of TH cell cytokine secretion is not well understood and represents an important gap in our knowledge. Our recent data indicate that membrane- associated nucleic acid binding protein (Mnab, encoded by Rc3h2) is required for TH cell effector cytokine secretion. Mnab shares with its paralog Roquin (encoded by Rc3h1) a highly conserved N-terminus but possesses a unique hydrophobic C-terminus. Roquin is important for control of follicular helper T (Tfh) cell development through repression of Icos mRNA. Recently, Mnab was shown to play a redundant role with Roquin in Tfh cell development via repression of Icos and Ox40 mRNAs. Whether Mnab also targets other mRNAs and regulates function of other TH lineages is unclear. Our preliminary studies demonstrated that a Mnab deficiency led to profound defects in effector cytokine production in TH1, TH2 and TH17 cells, which differs from its known function, suggesting an important role of the distinct C-terminus of Mnab. Based on our preliminary data, we formulate a novel hypothesis: Mnab targets mRNAs encoding proteins in the stress response-autophagy pathway, a common pathway that is critical in TH cell effector cytokine production. The overall specific aims of this project are: Aim 1. Determine the role of Mnab and UPR-autophagy in TH cell function. Aim 2. Delineate the molecular mechanism whereby Mnab controls mRNA stability. Aim 3. Determine the role of Mnab in TH cell function in vivo using disease models. By addressing our hypothesis, these studies will reveal a novel post-transcription control mechanism of TH cell effector function. Manipulation of the corresponding pathways may be of therapeutic benefit in human disease, such as autoimmune and inflammatory disorders.