Lipid droplet protein AUP1 is exploited by Flaviviruses during infection
Yun Lan1, Jingshu Zhang1, Mingyuan Li1, Sumana Sanyal1，2,
1 HKU-Pasteur Research Pole, School of Public Health, 2 School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
Zika infection is a mosquito-borne disease caused by Zika virus (ZIKV). ZIKV belongs to Flaviviridae family of small enveloped RNA viruses, which include some important human and veterinary pathogens, such as hepatitis C (HCV) and dengue virus (DENV). Lacking an appropriate lipid biosynthetic machinery of their own, flaviviruses often hijack the host's lipid metabolism to acquire essential lipid components for their survival and replication. As a central regulator for lipid storage, metabolism, and transportation, lipid droplets (LDs) play essential roles at different steps of the intracellular life cycle of flaviviruses.
Using a functional proteomics screening approach, we identified several host LD proteins that were differentially ubiquitin modified during DENV infection. Among which, ancient ubiquitous protein 1 (AUP1), a monotopic membrane protein localized to both LDs and ER membranes, was identified as a key component in the replication and maturation of DENV particles by regulating lipophagy. AUP1-mediated lipophagy was not a unique characteristic of DENV infection, but rather a universal phenomenon observed during flavivirus infections. Our results demonstrated that ZIKV-infected cells contained fewer LDs compared to mock-infected cells. The expression of AUP1 was up-regulated in the early stages of infection, and was down-regulated in the late stages, while induction of autophagy increased as measured by conversion of LC3-I to LC3-II using Western blotting or HeLa-Difluo™ hLC3 reporter cells. Moreover, deletion of AUP1 using CRISPR/Cas9 strategy led to attenuated ZIKV production. Interestingly, while virus particles released into the supernatant was significantly reduced in AUP1 deficient cells, more viral particles were found accumulated inside host cells, implying that AUP1 may play an essential role in the assembly and egress of ZIKV particles.