Flaviviruses Exploit the Lipid Droplet Protein AUP1 to Trigger Lipophagy and Drive Virus Production.

Ubiquitylation is one of the most versatile protein post-translational modifications and is frequently altered during virus infections. Here we employed a functional proteomics screen to identify host proteins that are differentially ubiquitylated upon dengue virus (DENV) infection. Among the several differentially modified proteins identified in infected cells was AUP1, a lipid droplet-localized type-III membrane protein, which exists predominantly in the mono-ubiquitylated form. AUP1 associated with DENV NS4A and relocalized from lipid droplets to autophagosomes upon infection. Virus production was abolished in cells deleted for AUP1 or expressing an AUP1 acyltransferase domain mutant. Ubiquitylation disrupted the AUP1-NS4A interaction, resulting in inhibited acyltransferase activity, defective lipophagy, and attenuated virus production. Our results show that DENV-NS4A exploits the acyltransferase activity of AUP1 to trigger lipophagy, a process regulated by ubiquitylation. This mechanism appears to be a general phenomenon in biogenesis of flaviviruses and underscores the critical role of post-translational modifications in virus infections.