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Genetics. 2017 Apr;205(4):1473-1488. doi: 10.1534/genetics.116.198903. Epub 2017 Feb 3.

Reliance of Wolbachia on High Rates of Host Proteolysis Revealed by a Genome-Wide RNAi Screen of Drosophila Cells.

Author information

1
Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, California 95064.
2
Department of Biological Sciences, Florida International University, Miami, Florida.
3
Biomolecular Sciences Institute, Florida International University, Miami, Florida 33199.
4
Institut Jacques Monod, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7592, University Paris Diderot, 75 205 Paris, France.
5
Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064.
6
Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, California 95064 wtsulliv@ucsc.edu.

Abstract

Wolbachia are gram-negative, obligate, intracellular bacteria carried by a majority of insect species worldwide. Here we use a Wolbachia-infected Drosophila cell line and genome-wide RNA interference (RNAi) screening to identify host factors that influence Wolbachia titer. By screening an RNAi library targeting 15,699 transcribed host genes, we identified 36 candidate genes that dramatically reduced Wolbachia titer and 41 that increased Wolbachia titer. Host gene knockdowns that reduced Wolbachia titer spanned a broad array of biological pathways including genes that influenced mitochondrial function and lipid metabolism. In addition, knockdown of seven genes in the host ubiquitin and proteolysis pathways significantly reduced Wolbachia titer. To test the in vivo relevance of these results, we found that drug and mutant inhibition of proteolysis reduced levels of Wolbachia in the Drosophila oocyte. The presence of Wolbachia in either cell lines or oocytes dramatically alters the distribution and abundance of ubiquitinated proteins. Functional studies revealed that maintenance of Wolbachia titer relies on an intact host Endoplasmic Reticulum (ER)-associated protein degradation pathway (ERAD). Accordingly, electron microscopy studies demonstrated that Wolbachia is intimately associated with the host ER and dramatically alters the morphology of this organelle. Given Wolbachia lack essential amino acid biosynthetic pathways, the reliance of Wolbachia on high rates of host proteolysis via ubiquitination and the ERAD pathways may be a key mechanism for provisioning Wolbachia with amino acids. In addition, the reliance of Wolbachia on the ERAD pathway and disruption of ER morphology suggests a previously unsuspected mechanism for Wolbachia's potent ability to prevent RNA virus replication.

KEYWORDS:

Drosophila; RNAi; Wolbachia; oocyte; ubiquitin; virus

PMID:
28159754
PMCID:
PMC5378107
[Available on 2018-04-01]
DOI:
10.1534/genetics.116.198903
[Indexed for MEDLINE]
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