Presynaptic monoamine reuptake is a major factor that influences extraneuronal monoamine levels and terminates synaptic transmission. Monoamine transporters within the SL6 carrier gene family mediate reuptake and are the molecular targets for the addictive psychostimulants cocaine, amphetamines, and MDMA ("ecstasy"), as well as for the therapeutic agents: methylphenidate ("Ritalin") and buproprion ("Wellbutrin", "Zyban"). These agents potently inhibit monoamine transport, significantly elevating extracellular monoamine levels and enhancing downstream signaling. Thus, transporter cell surface availability is paramount to both normal synaptic transmission and psychoactive drug efficacy. Abundant evidence demonstrates that monoamine transporters dynamically traffic to and from the plasma membrane. Moreover, both amphetamine exposure and protein kinase C (PKC) activation change transporter surface availability by modulating transporter trafficking kinetics. Although regulated transporter trafficking is well documented, the cellular and molecular mechanisms governing transporter regulation and trafficking are not clearly defined. Given the pronounced effect pharmacological transporter blockade exerts on synaptic transmission, transporter sequestration is highly likely to significantly effect downstream neuronal signaling. Moreover, modulation of transporter availability is certain to have significant impact on the efficacy of psychoactive drugs. The major goals of this project are to elucidate the cellular and molecular mechanisms mediating acute transporter regulation and trafficking. Specifically, we hypothesize that (1) A brake mechanism controls constitutive and PKC-stimulated dopamine transporter (DAT) endocytosis;(2) Post-endocytic DAT trafficking differs from classical trafficking pathways;and (3) Amphetamine- and PKC-induced DAT sequestration are mechanistically distinct. These hypotheses are based on strong preliminary data demonstrating distinct endocytic motifs required for constitutive and PKC-regulated DAT internalization, novel DAT post-endocytic trafficking properties and PKC-independent properties of amphetamine-induced DAT sequestration. We will use site- directed mutagenesis to define constitutive, PKC-, and amphetamine-regulated DAT internalization and recycling signals. State-of-the-art live cellular imaging approaches will be used to define the mechanisms governing basal and regulated DAT endocytic trafficking. Finally, molecular and proteonomic approaches will define DAT-interacting proteins required for DAT endocytic trafficking. These approaches will provide a comprehensive picture of the mechanisms underlying regulated transporter trafficking. We expect our results will significantly impact future addiction and affective disorder treatment strategies. Moreover, the outcomes will greatly improve our understanding of the factors contributing to monoamine availability and signaling in the brain.
Mental illness and psychostimulant addiction are growing problems in the United States, reaching near epidemic proportions over the past several years. Despite numerous investigations into the mechanisms underlying these conditions, there are still large gaps in our knowledge. The current project will investigate the major targets in the brain for both psychostimulants and antidepressants, with the expectation that the forthcoming information may lead to novel therapeutic approaches for treating these disorders.
|Gabriel, Luke R; Wu, Sijia; Melikian, Haley E (2014) Brain slice biotinylation: an ex vivo approach to measure region-specific plasma membrane protein trafficking in adult neurons. J Vis Exp :|
|Gabriel, Luke R; Wu, Sijia; Kearney, Patrick et al. (2013) Dopamine transporter endocytic trafficking in striatal dopaminergic neurons: differential dependence on dynamin and the actin cytoskeleton. J Neurosci 33:17836-46|
|Navaroli, Deanna M; Stevens, Zachary H; Uzelac, Zeljko et al. (2011) The plasma membrane-associated GTPase Rin interacts with the dopamine transporter and is required for protein kinase C-regulated dopamine transporter trafficking. J Neurosci 31:13758-70|
|Navaroli, Deanna M; Melikian, Haley E (2010) Insertion of tetracysteine motifs into dopamine transporter extracellular domains. PLoS One 5:e9113|
|Gabriel, Luke; Stevens, Zachary; Melikian, Haley (2009) Measuring plasma membrane protein endocytic rates by reversible biotinylation. J Vis Exp :|
|Boudanova, Ekaterina; Navaroli, Deanna M; Melikian, Haley E (2008) Amphetamine-induced decreases in dopamine transporter surface expression are protein kinase C-independent. Neuropharmacology 54:605-12|
|Boudanova, Ekaterina; Navaroli, Deanna M; Stevens, Zachary et al. (2008) Dopamine transporter endocytic determinants: carboxy terminal residues critical for basal and PKC-stimulated internalization. Mol Cell Neurosci 39:211-7|
|Holton, Katherine L; Loder, Merewyn K; Melikian, Haley E (2005) Nonclassical, distinct endocytic signals dictate constitutive and PKC-regulated neurotransmitter transporter internalization. Nat Neurosci 8:881-8|
|Melikian, Haley E (2004) Neurotransmitter transporter trafficking: endocytosis, recycling, and regulation. Pharmacol Ther 104:17-27|
|Loder, Merewyn K; Melikian, Haley E (2003) The dopamine transporter constitutively internalizes and recycles in a protein kinase C-regulated manner in stably transfected PC12 cell lines. J Biol Chem 278:22168-74|