Membrane Trafficking, Ubiquitin and Signalling
Endocytosis is a fundamental cellular process that regulates the presence and abundance of proteins at the plasma membrane, such as receptors or transporters.
After binding to their ligand (hormone, growth factor), plasma membrane receptors engage into specific signalling activities. This is generally followed by their endocytosis, which allows to dampen this response. Defects in endocytosis lead to aberrant signalling and can cause several pathologies including cancer.
Endocytosis also regulates the presence of nutrient transporters at the plasma membrane with respect to the availability of nutrients in the medium and their fluctuations. It is therefore a central component of the cellular adaptation to its environment.
Transporters are usually ubiquitylated prior to being endocytosed. This post-translational modification acts as a molecular signal that allows transporter progression into the endocytic pathway.
In yeast, transporter ubiquitylation involves the ubiquitin ligase, Rsp5 (a member of the Nedd4 family: 9 members in human). It also relies on a set of Rsp5 adaptor proteins related to beta/visual-arrestins of metazoans, named ARTs (Arrestin-Related Trafficking adaptors – about 15 members in yeast).
In human, the orthologues of ARTs (termed ARRDCs) perform similar functions, and some act as tumor suppressors.
Our aim is to understand how extracellular signals control transporter ubiquitylation and, consequently,transporter endocytosis and cell adaptation.
The model organism currently used in the lab is the budding yeast Saccharomyces cerevisiae, which has largely contributed to the understanding of conserved cellular mechanisms, including endocytosis.
As a case study, we aim to understand the mechanisms driving cell adaptation to variations in the glucose concentration of the medium. Indeed, variations in glucose availability lead to a remodelling of the landscape of transporters present at the plasma membrane. For instance, glucose deprivation triggers the removal of most glucose transporters from the cell surface (eg. Hxt3; Figure 1). On the opposite, glucose addition to cells growing a medium containing alternative carbon sources induces the ubiquitylation and subsequent endocytosis of the corresponding transporters, to ensure that glucose is the only carbon source used when available (eg. Jen1; Figure 1; see also movie 1).
In our lab, we delineated some of the molecular mechanisms at stake in these regulations. In particular, we found that nutrient signalling pathways modulate the post-translational modifications of ART proteins and their activity. The regulation of ART activity by nutrient availability explains why transporter ubiquitylation and endocytosis is triggered only in a specific physiological condition.
Keywords: Endocytosis, , Membranes, Trafficking, Nutrient transporters, Glucose metabolism and signaling, AMPK / Snf1, Ubiquitin , Nedd4 / Rsp5, Arrestin-related proteins (ARTs, ARRDCs), Yeast, Cell imaging, Proteomics, Cancer metabolism
Selection of Publications
Hovsepian J, Albanèse V, Becuwe M, Ivashov V, Teis D, Léon S. (2018) The yeast arrestin-related protein Bul1 is a novel actor of glucose-induced endocytosis. Mol Biol Cell. 29:1012-1020)
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Hovsepian J, Defenouillère Q, Albanèse V, Váchová L, Garcia C, Palková Z, Léon S. (2017) Multilevel regulation of an α-arrestin by glucose depletion controls hexose transporter endocytosis. J Cell Biol. 216: 1811-1831.
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Becuwe M*, Vieira N*, Lara D, Gomes-Rezende J, Soares-Cunha C, Casal M, Haguenauer-Tsapis R, Vincent O, Paiva S*, Léon S*. (2012) A molecular switch on an arrestin-like protein relays glucose signaling to transporter endocytosis.
J Cell Biol. 196(2):247-59.
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