Downregulation of receptor signaling is mediated by a series of membrane trafficking steps including ubiquitin-mediated endocytosis, ESCRT-mediated sorting and packaging into vesicles that bud into the lumen of the endosome, and endosome-lysosome fusion that delivers sorted receptors into the lumen of the lysosome where degradation occurs. Failure to attenuate plasma membrane (PM) signaling processes by endocytic downregulation can lead to hyperproliferation and cancer. To better understand endocytic downregulation, we are interested in deciphering how the ubiquitin conjugation machinery is targeted to specific proteins at the PM and how this targeting is regulated.
In Saccharomyces cerevisiae, ubiquitination mediated by Rsp5, the yeast Nedd4 homolog, is known to be required for the endocytic downregulation of numerous PM proteins. Previously, we identified and characterized a family of arrestin-related trafficking adaptors, or ARTs, which recruit the Rsp5 ubiquitin ligase to specific targets at the PM. Recent research from several groups has demonstrated that ART proteins are key determinants of target selection during ubiquitin-mediated endocytosis. Our goal is to understand how cargo selectivity and stimulus-dependent activation of ART proteins is achieved. We have found that Art1 undergoes a phosphoregulatory cycle and that dephosphorylation of Art 1 triggers its activation and recruitment to PM cargo. Using genetics, quantitative mass spectrometry and biochemistry, we have shown that this phosphoregulatory cycle is mediated by a TORC1-Npr1 kinase signaling cascade. In addition to phosphorylation/dephosphorylation, ARTs are also subject to ubiquitination. Present work focuses on dissecting the roles of deubiquitinases (DUB’s) in the localization, stability, activity and protein-protein interactions of Rsp5 and the ARTs.
Key Publications
1. Baile, M., E. Guiney, E. Sanford, M. Smolka, and S.D. Emr. (2019). “Disordered insertions in the yeast Art1 arrestin domain regulate its localization and activity.” Mol. Biol. Cell, 30:3057-3072.
2. Zhao Y, Macgurn JA, Liu M, S.D. Emr. (2013). The ART-Rsp5 ubiquitin ligase network comprises a plasma membrane quality control system that protects yeast cells from proteotoxic stress. eLife2:e00459.
3. MacGurn JA, Hsu PC, Smolka MB, S.D. Emr. (2011). TORC1 Regulates Endocytosis via Npr1-Mediated Phosphoinhibition of a Ubiquitin Ligase Adaptor. Cell 147(5): 1104-17.
4. Lin CH, MacGurn JA, Chu T, Stefan CJ, S.D. Emr. (2008). Arrestin-related ubiquitin-ligase adaptors regulate endocytosis and protein turnover at the cell surface. Cell. 135: 714-725.
