Drosophila Argonaute2 turnover is regulated by the ubiquitin proteasome pathway

Argonaute (AGO) proteins play a central role in the RNA interference (RNAi) pathway, which is a cytoplasmic mechanism important for post-transcriptional regulation of gene expression. In Drosophila, AGO2 also functions in the nucleus to regulate chromatin insulator activity and transcription. Although there are a number of studies focused on AGO2 function, the regulation of AGO2 turnover is not well understood. We found that mutation of T1149 or R1158 in the conserved PIWI domain causes AGO2 protein instability, but only T1149 affects RNAi activity. Mass spec analysis shows that several proteasome components co-purify with both wildtype and mutant AGO2, and knockdown of two proteasome pathway components results in AGO2 protein accumulation. Finally, AGO2 protein levels increase after treatment with the proteasome inhibitor MG132. Our results indicate that the ubiquitin-proteasome pathway is involved in AGO2 protein turnover.