HIV-1 Tat Protein-Induced Rapid and Reversible Decrease in [H-3]Dopamine Uptake: Dissociation of [H-3]Dopamine Uptake and [H-3]2 beta-Carbomethoxy-3-beta-(4-fluorophenyl)tropane (WIN 35,428) Binding in Rat Striatal Synaptosomes

Program in Behavioral Neuroscience, Department of Psychology, University of South Carolina, 1512 Pendleton St., Columbia, SC 29208, USA.
Journal of Pharmacology and Experimental Therapeutics (Impact Factor: 3.86). 04/2009; 329(3):1071-83. DOI: 10.1124/jpet.108.150144
Source: PubMed

ABSTRACT Human immunodeficiency virus (HIV)-1 Tat protein plays a key role in the pathogenesis of both HIV-1-associated cognitive-motor disorder and drug abuse. Dopamine (DA) transporter (DAT) function is strikingly altered in patients with HIV-1-associated dementia and a history of chronic drug abuse. This study is the first in vitro evaluation of potential mechanisms underlying the effects of Tat protein on DAT function. Rat striatal synaptosomes were incubated with recombinant Tat(1-86) protein, and [(3)H]DA uptake and the binding of [(3)H]2beta-carbomethoxy-3-beta-(4-fluorophenyl)tropane (WIN 35,428) and [(3)H]1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)-piperazine (GBR 12935) were determined. Tat decreased [(3)H]DA uptake, [(3)H]WIN 35,428 binding, and [(3)H]GBR 12935 binding in a time-dependent manner. The potency of Tat for inhibiting [(3)H]DA uptake (K(i) = 1.2 microM) was the same as that for inhibiting [(3)H]GBR 12935 binding but 3-fold less than that for inhibiting [(3)H]WIN 35,428 binding. Mutant Tat proteins did not alter [(3)H]DA uptake. Kinetic analysis of [(3)H]DA uptake revealed that Tat (1 or 10 microM) decreased the V(max) value and increased the K(m) value in a dose-dependent manner. The V(max) value, decreased by Tat (1 microM), returned to the control level after washout of Tat, indicating that the inhibitory effect of Tat on DA uptake was reversible. Saturation studies revealed that Tat decreased the B(max) value and increased the K(d) value of [(3)H]WIN 35,428 binding, whereas Tat decreased the B(max) value of [(3)H]GBR 12935 binding, without a change in the K(d) value. These findings provide new insight into understanding the pharmacological mechanisms of Tat-induced dysfunction of the DAT in the dopaminergic system in HIV-infected patients.

Download full-text


Available from: David Wallace, Aug 12, 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: As a major neuropathogenic factor associated with human immunodeficiency virus (HIV) infection, HIV-1 Tat protein is known to synergize with psychostimulant drugs of abuse to cause neurotoxicity and exacerbate the progression of central nervous system pathology. However, the functional consequences of the interaction between HIV-1 Tat and abused drugs on behavior are little known. We tested the hypothesis that HIV-1 Tat expression in brain would modulate the psychostimulant effects of cocaine. Using the GT-tg bigenic mouse model, where brain-selective Tat expression is induced by activation of a doxycycline (Dox) promotor, we tested the effects of Tat on cocaine (10 mg/kg, s.c.) induced locomotion and conditioned place preference (CPP). Compared to uninduced littermates or C57BL/6 J controls, cocaine-induced hyperlocomotion was sustained for a significantly longer duration among Tat-induced mice. Moreover, although all groups displayed similar saline-CPP, Tat-induced GT-tg mice demonstrated a 3-fold increase in cocaine-CPP over the response of either uninduced littermates or Dox-treated C57BL/6 J control mice. Induction of Tat also increased the magnitude of a previously-established cocaine-CPP after an additional cycle of cocaine place conditioning. Despite Tat-induced potentiation, extinction of place preference occurred within 21 days, commensurate with cocaine-extinction among saline-treated littermates and C57BL/6 J controls. Re-exposure to cocaine produced reinstatement of an equivalent place preference in Tat-induced GT-tg, or C57BL/6 J, mice; however, induction of Tat protein after the extinction of CPP also produced reinstatement without additional exposure to cocaine. Together, these data suggest that central HIV-1 Tat expression can potentiate the psychostimulant behavioral effects of cocaine in mice.Neuropsychopharmacology accepted article preview online, 15 August 2013. doi:10.1038/npp.2013.201.
    Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 08/2013; 39(2). DOI:10.1038/npp.2013.201 · 7.83 Impact Factor
  • Source
    Synapse 11/2011; 65(11):1251-4. DOI:10.1002/syn.20949 · 2.43 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Human immunodeficiency virus-associated neurological disease (HAND) still causes significant morbidity, despite success reducing viral loads with combination antiretroviral therapy. The dopamine (DA) system is particularly vulnerable in HAND. We hypothesize that early, "reversible" DAergic synaptic dysfunction occurs long before DAergic neuron loss. As such, aging human immunodeficiency virus (HIV)-infected individuals may be vulnerable to other age-related neurodegenerative diseases like Parkinson's disease (PD), underscoring the need to understand shared molecular targets in HAND and PD. Previously, we reported that the neurotoxic HIV-1 transactivating factor (Tat) acutely disrupts mitochondrial and endoplasmic reticulum calcium homeostasis via ryanodine receptor (RyR) activation. Here, we further report that Tat disrupts DA transporter (DAT) activity and function, resulting in increased plasma membrane (PM) DAT and increased DAT V(max), without changes in K(m) or total DAT protein. Tat also increases calpain protease activity at the PM, demonstrated by total internal reflection fluorescence microscopy of a cleavable fluorescent calpain substrate. Tat-increased PM DAT and calpain activity are blocked by the RyR antagonists ryanodine and dantrolene, the calpain inhibitor calpastatin, and by a specific inhibitor of GSK-3β. We conclude that Tat activates RyRs via a calcium- and calpain-mediated mechanism that upregulates DAT trafficking to the PM, and is independent of DAT protein synthesis, reinforcing the feasibility of RyR and GSK-3β inhibition as clinical therapeutic approaches for HAND. Finally, we provide key translational relevance for these findings by highlighting published human data of increased DAT levels in striata of HAND patients and by demonstrating similar findings in Tat-expressing transgenic mice.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 10/2010; 30(42):14153-64. DOI:10.1523/JNEUROSCI.1042-10.2010 · 6.75 Impact Factor