ZIKV Induction of Tristetraprolin in Endothelial and Sertoli Cells Post-Transcriptionally Inhibits IFNβ/{lambda} Expression and Promotes ZIKV Persistence
Zika virus (ZIKV) is a mosquito-borne Flavivirus that persistently infects patients, enters protected brain, placental, and testicular compartments, is sexually transmitted, and causes fetal microcephaly in utero. ZIKV persistently infects brain microvascular endothelial cells (hBMECs) that form the blood-brain-barrier and Sertoli cells that form testicular barriers, establishing reservoirs that enable viral dissemination. ZIKV persistence requires inhibiting interferon (IFN) responses that direct viral clearance. We found that ZIKV induces IFN-{beta} and IFN-{lambda} in hBMECs but post-transcriptionally inhibits IFN-{beta}/{lambda} expression. IFN{beta}/{lambda} mRNAs contain AU-rich elements (AREs) in their 3 untranslated regions which regulate protein expression through interactions with ARE binding proteins (ARE-BPs). We found that ZIKV infection of primary hBMECs induces the expression of the ARE-BP tristetraprolin (TTP) and that TTP is a novel regulator of endothelial IFN secretion. In hBMECs, TTP knockout (KO) increased IFN-{beta}/{lambda}1 mRNA abundance and IFN-{beta}/{lambda}1 secretion in response to ZIKV infection and inhibited viral persistence. In contrast, TTP expression dramatically reduced IFN-{beta}/{lambda}1 secretion in hBMECs. IFN-{beta}/{lambda}1 mRNA stability was not significantly altered by TTP and is consistent with TTP inhibition of IFN-{beta}/{lambda}1 translation. TTP is similarly induced by ZIKV infection of Sertoli cells, and like hBMECs, TTP expression or KO inhibited or enhanced IFN-{beta}/{lambda} mRNA levels, respectively. These findings reveal a mechanism for ZIKV induced TTP to promote viral persistence in hBMECs and Sertoli cells by post-transcriptionally regulating IFN-{beta}/{lambda} secretion. Our results demonstrate a novel role for virally induced TTP in regulating IFN secretion in barrier cells that normally restrict viral persistence and spread to protected compartments. ImportanceOur findings define a novel role for ZIKV induced TTP expression in regulating IFN-{beta}/{lambda} production in primary hBMECs and Sertoli cells. These cells comprise key physiological barriers subverted by ZIKV to access brain and testicular compartments and serve as reservoirs for persistent replication and dissemination. We demonstrate for the first time that the ARE binding protein TTP is virally induced and post-transcriptionally regulates IFN-{beta}/{lambda} secretion. In ZIKV infected hBMEC and Sertoli cells, TTP knockout increased IFN-{beta}/{lambda} secretion, while TTP expression blocked IFN-{beta}/{lambda} secretion. The TTP directed blockade of IFN secretion permits ZIKV spread and persistence in hBMECs and Sertoli cells and may similarly augment ZIKV spread across IFN-{lambda} protected placental barriers. Our work highlights the importance of post-transcriptional ZIKV regulation of IFN expression and secretion in cells that regulate viral access to protected compartments and defines a novel mechanism of ZIKV regulated IFN responses which facilitate neurovirulence and sexual transmission.