Articles by Zachary Stevens in JoVE
Measuring Plasma Membrane Protein Endocytic Rates by Reversible Biotinylation Luke Gabriel1, Zachary Stevens1, Haley Melikian1 1University of Massachusetts Medical School Regulated endocytosis governs the cell surface expression levels of the majority of membrane proteins. Here we utilize reducible, membrane impermeant biotinylation reagents to measure the endocytic rate of the dopamine transporter (DAT), a polytopic membrane protein. The method facilitates a straightforward approach to measuring the endocytic rate of most plasma membrane proteins.
Other articles by Zachary Stevens on PubMed
Dopamine Transporter Endocytic Determinants: Carboxy Terminal Residues Critical for Basal and PKC-stimulated Internalization Molecular and Cellular Neurosciences. Oct, 2008 | Pubmed ID: 18638559 Dopamine (DA) reuptake terminates dopaminergic neurotransmission and is mediated by DA transporters (DATs). Acute protein kinase C (PKC) activation accelerates DAT internalization rates, thereby reducing DAT surface expression. Basal DAT endocytosis and PKC-stimulated DAT functional downregulation rely on residues within the 587-596 region, although whether PKC-induced DAT downregulation reflects transporter endocytosis mechanisms linked to those controlling basal endocytosis rates is unknown. Here, we define residues governing basal and PKC-stimulated DAT endocytosis. Alanine substituting DAT residues 587-590 1) abolished PKC stimulation of DAT endocytosis, and 2) markedly accelerated basal DAT internalization, comparable to that of wildtype DAT during PKC activation. Accelerated basal DAT internalization relied specifically on residues 588-590, which are highly conserved among SLC6 neurotransmitter transporters. Our results support a model whereby residues within the 587-590 stretch may serve as a locus for a PKC-sensitive braking mechanism that tempers basal DAT internalization rates.
The Plasma Membrane-associated GTPase Rin Interacts with the Dopamine Transporter and is Required for Protein Kinase C-regulated Dopamine Transporter Trafficking The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Sep, 2011 | Pubmed ID: 21957239 Dopaminergic signaling and plasticity are essential to numerous CNS functions and pathologies, including movement, cognition, and addiction. The amphetamine- and cocaine-sensitive dopamine (DA) transporter (DAT) tightly controls extracellular DA concentrations and half-life. DAT function and surface expression are not static but are dynamically modulated by membrane trafficking. We recently demonstrated that the DAT C terminus encodes a PKC-sensitive internalization signal that also suppresses basal DAT endocytosis. However, the cellular machinery governing regulated DAT trafficking is not well defined. In work presented here, we identified the Ras-like GTPase, Rin (for Ras-like in neurons) (Rit2), as a protein that interacts with the DAT C-terminal endocytic signal. Yeast two-hybrid, GST pull down and FRET studies establish that DAT and Rin directly interact, and colocalization studies reveal that DAT/Rin associations occur primarily in lipid raft microdomains. Coimmunoprecipitations demonstrate that PKC activation regulates Rin association with DAT. Perturbation of Rin function with GTPase mutants and shRNA-mediated Rin knockdown reveals that Rin is critical for PKC-mediated DAT internalization and functional downregulation. These results establish that Rin is a DAT-interacting protein that is required for PKC-regulated DAT trafficking. Moreover, this work suggests that Rin participates in regulated endocytosis.