ID: 222 : The role of mTOR in TLR7/9 mediated signaling and cytokine production by human plasmacytoid dendritic cells

Abstract

The mammalian target of rapamycin (mTOR) integrates signals from growth factors, energy, and nutrients to regulate protein synthesis, cell growth, cell differentiation, and autophagy. Rapamycin is known to substantially inhibit IFN- α production in mouse pDC by blocking the interaction of TLR9 with MyD88. In contrast, in agreement with others, we observed that rapamycin only partially inhibited HSV-induced (TLR9) IFN- α production by human pDC. To understand how the mTOR pathway affects TLR-induced IFN- α expression in human pDC, we examined the activation of ribosome protein S6, the major substrate of mTORC1/p70S6K, in pDC in response to different stimuli. We found that phosphorylation of S6 was rapidly induced by HSV-1, influenza, CpG A, CpG B, LPS and imiquimod, as well as by the cytokines IFN- α , IFN- β , and TNF- α , but not in response to IFN- λ 1, IL-10 or IL-6. Using phospho-flow in combination with intracellular cytokine staining, we observed only p-S6-positive pDC produced IFN- α . Unexpectedly, cytokine-induced p-S6 was completely abolished in the presence of rapamycin, however, virus-induced p-S6-positive cells were partially affected. Interestingly, both HIV-1MN and AT2-inactivated HIV-1MN induced a delayed p-S6 compared to the other viruses, which is consistent with the delayed IFN- α induction by HIV-1. Given that mTORC1 function is regulated by the formation of hybrid compartments containing both early and late endosomes, the delay of p-S6 may indicate a perturbation of endocytic trafficking by HIV-1. Currently, the mechanism of how TLR7/9 engage with the mTOR pathway to shape the type, dynamics, and magnitude of pDC innate immune responses is under investigation.