RESUMO
The dopamine transporter (DAT) is responsible for sequestration of extracellular dopamine (DA). The psychostimulant amphetamine (AMPH) is a DAT substrate, which is actively transported into the nerve terminal, eliciting vesicular depletion and reversal of DA transport via DAT. Here, we investigate the role of the DAT C terminus in AMPH-evoked DA efflux using cell-permeant dominant-negative peptides. A peptide, which corresponded to the last 24 C-terminal residues of DAT (TAT-C24 DAT) and thereby contained the Ca(2+)-calmodulin-dependent protein kinase IIα (CaMKIIα) binding domain and the PSD-95/Discs-large/ZO-1 (PDZ)-binding sequence of DAT, was made membrane-permeable by fusing it to the cell membrane transduction domain of the HIV-1 Tat protein (TAT-C24WT). The ability of TAT-C24WT but not a scrambled peptide (TAT-C24Scr) to block the CaMKIIα-DAT interaction was supported by co-immunoprecipitation experiments in heterologous cells. In heterologous cells, we also found that TAT-C24WT, but not TAT-C24Scr, decreased AMPH-evoked 1-methyl-4-phenylpyridinium efflux. Moreover, chronoamperometric recordings in striatum revealed diminished AMPH-evoked DA efflux in mice preinjected with TAT-C24WT. Both in heterologous cells and in striatum, the peptide did not further inhibit efflux upon KN-93-mediated inhibition of CaMKIIα activity, consistent with a dominant-negative action preventing binding of CaMKIIα to the DAT C terminus. This was further supported by the ability of a peptide with perturbed PDZ-binding sequence, but preserved CaMKIIα binding (TAT-C24AAA), to diminish AMPH-evoked DA efflux in vivo to the same extent as TAT-C24WT. Finally, AMPH-induced locomotor hyperactivity was attenuated following systemic administration of TAT-C24WT but not TAT-C24Scr. Summarized, our findings substantiate that DAT C-terminal protein-protein interactions are critical for AMPH-evoked DA efflux and suggest that it may be possible to target protein-protein interactions to modulate transporter function and interfere with psychostimulant effects.
Assuntos
Anfetamina/farmacologia , Peptídeos Penetradores de Células/farmacologia , Estimulantes do Sistema Nervoso Central/farmacologia , Corpo Estriado/metabolismo , Proteínas da Membrana Plasmática de Transporte de Dopamina/farmacologia , Dopamina/metabolismo , Anfetamina/efeitos adversos , Animais , Benzilaminas/farmacologia , Peptídeos Penetradores de Células/metabolismo , Estimulantes do Sistema Nervoso Central/efeitos adversos , Proteínas da Membrana Plasmática de Transporte de Dopamina/farmacocinética , Humanos , Masculino , Camundongos , Atividade Motora/efeitos dos fármacos , Domínios PDZ , Proteína Quinase C-alfa/antagonistas & inibidores , Proteína Quinase C-alfa/metabolismo , Inibidores de Proteínas Quinases/farmacologia , Sulfonamidas/farmacologiaRESUMO
The dopamine transporter mediates reuptake of dopamine from the synaptic cleft. The cellular mechanisms controlling dopamine transporter levels in striatal nerve terminals remain poorly understood. The dopamine transporters contain a C-terminal PDZ (PSD-95/Discs-large/ZO-1) domain-binding sequence believed to bind synaptic scaffolding proteins, but its functional significance is uncertain. Here we demonstrate that two different dopamine transporter knock-in mice with disrupted PDZ-binding motifs (dopamine transporter-AAA and dopamine transporter+Ala) are characterized by dramatic loss of dopamine transporter expression in the striatum, causing hyperlocomotion and attenuated response to amphetamine. In cultured dopaminergic neurons and striatal slices from dopamine transporter-AAA mice, we find markedly reduced dopamine transporter surface levels and evidence for enhanced constitutive internalization. In dopamine transporter-AAA neurons, but not in wild-type neurons, surface levels are rescued in part by expression of a dominant-negative dynamin mutation (K44A). Our findings suggest that PDZ-domain interactions are critical for synaptic distribution of dopamine transporter in vivo and thereby for proper maintenance of dopamine homoeostasis.