Project Summary
Ubiquitin is a 76 amino acid peptide that can be covalently conjugated to substrates to alter protein fate in
diverse ways, regulating protein degradation, trafficking, subcellular localization and protein-protein
interactions. Given its versatility, ubiquitin regulates many fundamental cellular processes, and its
dysregulation is associated with many human diseases ranging from neurodegeneration to cancer. Ubiquitin
networks include conjugating and deconjugating enzymes as well as effector pathways comprised of ubiquitin
binding proteins that direct the fate of ubiquitin-modified substrates. All of these elements work together to
“write”, “read”, and “edit” the ubiquitin code – which ultimately consists of ubiquitin polymers of different lengths
and topologies that determine which effector pathways are engaged. Here, we describe two main research
directions that will result in a deeper understanding of the ubiquitin code and how it regulates diverse cellular
functions, including stress signaling and membrane trafficking. The first research direction will address how
phosphorylation of ubiquitin at the Ser57 position regulates stress responses in yeast and human cells. The
proposed studies will build on our recent discovery of a small group of Ser57 ubiquitin kinases conserved from
yeast to humans and will include genetic, biochemical, and proteomic approaches. Specifically, we will
determine how these kinases and Ser57 phosphorylation of ubiquitin contribute to the cellular stress response,
and we will address how ubiquitin phosphorylation alters its interaction profile and engagement with effector
pathways. This research will contribute transformative new insights into the biology of ubiquitin and
proteostasis. The second research direction will address how human glucose transporters are regulated by
ubiquitin modification and endocytic trafficking. Glucose transporters of the GLUT family are key regulators of
cellular glucose homeostasis, and yet regulation of their trafficking and quality control remain poorly
characterized. Here, we describe lines of investigation based on our recent findings that GLUT1 endocytic
trafficking is regulated by specific ubiquitin modifications. These studies have important implications for cellular
glucose homeostasis and human diseases including GLUT1 Deficiency Syndrome and many types of cancer.
Together, these research directions will result in a deeper understanding of the ubiquitin code, membrane
trafficking, and stress responses in eukaryotic cells.