Publication Date

2013-10-18

Availability

Open access

Embargo Period

2013-10-18

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Cancer Biology (Medicine)

Date of Defense

2013-09-30

First Committee Member

Glen N. Barber

Second Committee Member

Xiangxi Xu

Third Committee Member

Roland Jurecic

Fourth Committee Member

Edward Harhaj

Fifth Committee Member

Mark Pegram

Abstract

Innate immunity is characterized by production of type I interferon which is necessary for the stimulation of effective anti-viral host defense. Upon recognition of cytosol viral dsRNA species, RIG-I-Like Receptors (RLRs), as well as many co-regulators, are recruited to adaptor protein IPS-1 and trigger innate immune responses. FADD (Fas associated with death domain) and RIP1 (receptor-interacting protein 1), have been reported to be recruited to this IPS-1 complex during viral infection and essential for optimal RLR signaling. Here we reported a novel type I interferon inducible DExD/H family helicase DDX24, which was found and confirmed to specifically associate with FADD through yeast two hybrid system and co-immunoprecipitation. Overexpression of DDX24 negatively regulates dsRNA induced type I IFNs signaling, while knockdown of DDX24 by siRNA has the opposite effect. Moreover, Plaque assays of virus titer consistently demonstrate that DDX24 also negatively regulates the cellular antiviral response. Further studies demonstrated that DDX24 disrupted the recruitment of IRF7 to the signaling complex through RIP1 interaction, leading to the attenuated K63 linked ubituitination of IRF7 and subsequently decrease IRF7 dependent type I IFN production. Correlated with this, DDX24 was found to be induced by IFN and blocked the type I IFNs signaling more likely through IRF7 but not IRF3, suggesting a negative feedback role of DDX24 in RLR antiviral signaling. To evaluate the in vivo role of DDX24, DDX24 knockout mice were generated by gene trap technology. Although DDX24+/– mice appeared normal and were fertile, DDX24-/- mice died at as early as E7.5. Collectively, these results suggest an important role of DDX24 as a negative regulator in RLR dependent type I interferon production.

Keywords

Innate immunity: RIG-I

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