Ate1 downregulation impaired SQSTM1-mediated autophagy

Crieff, Scotland

Workshop; EMBO Workshop, Autophagy: From molecular principles to human diseases; 2019

EMBO

Two major pathways are responsible for regulating protein catabolism in eukaryotic cells, the ubiquitin-proteasome system and the autophagy-lysosomal system. Like the proteasomal pathway, the selective autophagic machinery recognizes and degrades polyubiquitinated proteins accumulated in aggregates through the signaling receptor, Sequestosome 1 (SQSTM1). Arginyltransferase (Ate1) an enzyme that mediates posttranslational arginylation of proteins, has been suggested to target proteins for proteasomal degradation and some substrates has been associated to the autophagic pathway. We hypothesized that Ate1 has a direct participation on autophagy by modulating SQSTM1 targeting to the autophagosome. To test this hypothesis, lysosomal flux was inhibited by Cloroquine and proteasomal flux using Bortezomib (BT) and MG132. Our studies indicated that SQSTM1-mediated autophagy is impaired in Ate1-knockdown cells under BT treatment. Upon Ate1 downregulation, these treated cells showed a higher accumulation of SQSTM1 together with polyubiquitinated proteins while LC3II protein levels indicates that autophagic flux was not altered. Furthermore, WT fibroblasts treated with MG132 showed accumulation of SQSTM1 and polyubiquitinated proteins around the nuclei (aggresomes), in which Ate1 showed partial colocalization. These results indicate a close association of Ate1 with SQSTM1, suggesting a putative function of both proteins modulating aggresome formation and consequently the flux of polyubiquitinated proteins degradation by autophagy.