Since work on this project began in February 2017, we have made a number of key advancements. Our preliminary work using rapamycin on transformed epithelial cell lines has revealed that mTOR inhibition confers a 4- to 20-fold enhancement of infection, depending on the nature of the virus challenge and, specifically, the route of virus entry into cells. Furthermore, we found that the rapamycin-dependent enhancement of infection is reversed by inhibitors of endosomal acidification (v-ATPase), revealing that the enhancement requires active degradation of cellular factors via the lysosomal pathway. Through a number of distinct approaches, we show that mTOR inhibition by multiple drugs leads to lysosomal degradation of IFITM3 in an autophage-independent manner. Instead, endocytic trafficking through multivesicular bodies is necessary to delivery of IFITM3 to lysosomes, as confirmed by a functional requirement of ESCRT member TSG101. By studying mutant IFITM3 constructs, we found that mTOR inhibition leads to clearance of IFITM2 and IFITM3 from endosomes in a manner that is dependent on endocytosis, ubiquitination, and lysosomal acidification. Furthermore, the complex including mTOR that functionally modulates IFITM3 levels is mTORC2. This work is the first instance to describe an interrelationship between mTOR, cell-intrinsic antiviral immunity, and virus entry into cells. These results have been published in 2018 (Shi et al., 2018). We have now extended the results to include impacts on HIV-1 infection, which involves the study of virus entry mediated by HIV-1 Env glycoprotein. We have assessed the impact of rapamycin and other drugs on various cell types that serve as HIV-1 targets in vivo and we found that IFITM3 is also downregulated in these cells. The loss of IFITM3 from T cells and macrophages, for example, allows greater degrees of infection by multiple HIV-1 strains.
