Uptake of extracellular double-stranded RNA by SID-2.
Ingested dsRNAs trigger RNA interference (RNAi) in many invertebrates, including the nematode Caenorhabditis elegans. Here we show that the C. elegans apical intestinal membrane protein SID-2 is required in C. elegans for the import of ingested dsRNA and that, when expressed in Drosophila S2 cells, SID-2 enables the uptake of dsRNAs. SID-2-dependent dsRNA transport requires an acidic extracellular environment and is selective for dsRNAs with at least 50 base pairs. Through structure-function analysis, we identify several SID-2 regions required for this activity, including three extracellular, positively charged histidines. Finally, we find that SID-2-dependent transport is inhibited by drugs that interfere with vesicle transport. Therefore, we propose that environmental dsRNAs are imported from the acidic intestinal lumen by SID-2 via endocytosis and are released from internalized vesicles in a secondary step mediated by the dsRNA channel SID-1. Similar multistep mechanisms may underlie the widespread observations of environmental RNAi.
Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Deborah L
DL
McEwan
Alexandra S
AS
Weisman
Craig P
CP
Hunter
D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D017173:Caenorhabditis elegans / Q000166:cytology / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004330:Drosophila / Q000166:cytology / Q000378:metabolism; D004705:Endocytosis; D006639:Histidine / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D018942:Macrolides / Q000494:pharmacology; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012330:RNA, Double-Stranded / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D013329:Structure-Activity Relationship; D053778:Thiazolidines / Q000494:pharmacology
D019086:Bridged Bicyclo Compounds, Heterocyclic; D029742:Caenorhabditis elegans Proteins; D018942:Macrolides; D008565:Membrane Proteins; D012330:RNA, Double-Stranded; C521940:SID-2 protein, C elegans; D053778:Thiazolidines; D006639:Histidine; C040929:bafilomycin A1; C037067:latrunculin A