Mechanistic Target of Rapamycin Signaling Activation Antagonizes Autophagy To Facilitate Zika Virus Replication.

Zika virus (ZIKV), a mosquito-transmitted flavivirus, is linked to microcephaly and other neurological defects in neonates and Guillain-Barré syndrome in adults. The molecular mechanisms regulating ZIKV infection and pathogenic outcomes are incompletely understood. Signaling by the mechanistic (mammalian) target of rapamycin (mTOR) kinase is important for cell survival and proliferation, and viruses are known to hijack this pathway for their replication. Here, we show that in human neuronal precursors and glial cells in culture, ZIKV infection activates both mTOR complex 1 (mTORC1) and mTORC2. Inhibition of mTOR kinase by Torin1 or rapamycin results in reduction in ZIKV protein expression and progeny production. Depletion of Raptor, the defining subunit of mTORC1, by small interfering RNA (siRNA) negatively affects ZIKV protein expression and viral replication. Although depletion of Rictor, the unique subunit of mTORC2, or the mTOR kinase itself also inhibits the viral processes, the extent of inhibition is less pronounced. Autophagy is transiently induced early by ZIKV infection, and impairment of autophagosome elongation by the class III phosphatidylinositol 3-kinase (PI3K) inhibitor 3-methyladenine (3-MA) enhances viral protein accumulation and progeny production. mTOR phosphorylates and inactivates ULK1 (S757) at later stages of ZIKV infection, suggesting a link between autophagy inhibition and mTOR activation by ZIKV. Accordingly, inhibition of ULK1 (by MRT68921) or autophagy (by 3-MA) reversed the effects of mTOR inhibition, leading to increased levels of ZIKV protein expression and progeny production. Our results demonstrate that ZIKV replication requires the activation of both mTORC1 and mTORC2, which negatively regulates autophagy to facilitate ZIKV replication.