Roles for trafficking and O-linked glycosylation in the turnover of model cell surface proteins [Membrane Biology]

June 2nd, 2014 by Karabasheva, D., Cole, N. B., Donaldson, J. G.

Proteins targeted to the plasma membrane (PM) of cells are degraded at different rates. Sorting motifs contained within the cytoplasmic domains of transmembrane proteins, posttranslational modifications (e.g. ubiquitination) and assembly into multi-protein or protein-lipid complexes all may affect the efficiency of endocytosis and recycling and influence the delivery to degradative compartments. Using the SNAP-tag labeling system, we have examined the turnover of a model PM protein, the alpha chain of the interleukin-2 receptor (Tac). The surface lifetimes of SNAP-Tac fusions were influenced by their mode of entry into cells (clathrin-dependent versus clathrin-independent), their orientation in the PM (transmembrane versus GPI anchored) and by ubiquitination in their cytosolic domains. In addition, shedding of SNAP-Tac into the medium was greatly influenced by its O-linked glycosylation status. For a number of PM proteins, delivery to lysosomes and ectodomain shedding represent distinct parallel mechanisms to determine protein half-life.