Biomedical subjects

Khanhky Phamluong

Publications and source records attributed to Khanhky Phamluong.

8 recordsLinked to original sources

PubMed2006

The dopamine D3 receptor is part of a homeostatic pathway regulating ethanol consumption.

We recently identified a homeostatic pathway that inhibits ethanol intake. This protective pathway consists of the scaffolding protein RACK1 and brain-derived neurotrophic factor (BDNF). RACK1 translocates to the nucleus after exposure of neurons to ethanol and increases expression of BDNF (McGough et al., 2004). We also found that increasing the levels of BDNF via systemic administration of RACK1 expressed as a Tat-fusion protein (Tat-RACK1) reduces ethanol consumption, whereas reduction of BDNF levels augments this behavior (McGough et al., 2004). Based on these results, we hypothesized that activation of the BDNF receptor TrkB is necessary for the effects of BDNF on ethanol intake and that gene products downstream of BDNF negatively regulate ethanol consumption. Here, we show that inhibition of the BDNF receptor TrkB increases voluntary ethanol consumption in wild-type mice but not in mice lacking one copy of the BDNF gene (BDNF(+/-)). We also find that increases in the levels of BDNF, mediated by ethanol or RACK1, lead to increased dorsal striatal levels of the dopamine D3 receptor (D3R), a gene downstream of BDNF, via activation of the TrkB receptor. Finally, we show that the Tat-RACK1-mediated reduction of ethanol consumption is attenuated by coinjection with either the Trk inhibitor K252a or the dopamine D3R-prefering antagonist U-99194A [5, 6-dimethoxy-2-(di-n-propylamino)indan], suggesting that activation of the BDNF pathway via RACK1 leads to increased expression of the dopamine D3R, which in turn mediates the attenuation of ethanol consumption.

Alcohol Drinking↗

PubMed2005

Ethanol alters trafficking and functional N-methyl-D-aspartate receptor NR2 subunit ratio via H-Ras.

The N-methyl-D-aspartate receptor (NMDAR) plays a critical role in synaptic plasticity and is one of the main targets for alcohol (ethanol) in the brain. Trafficking of the NMDAR is emerging as a key regulatory mechanism that underlies channel activity and synaptic plasticity. Here we show that exposure of hippocampal neurons to ethanol increases the internalization of the NR2A but not NR2B subunit of the NMDAR via the endocytic pathway. We further observed that ethanol exposure results in NR2A endocytosis through the activation of H-Ras and the inhibition of the tyrosine kinase Src. Importantly, ethanol treatment alters functional subunit composition from NR2A/NR2B- to mainly NR2B-containing NMDARs. Our results suggest that addictive drugs such as ethanol alter NMDAR trafficking and subunit composition. This may be an important mechanism by which ethanol exerts its effects on NMDARs to produce alcohol-induced aberrant plasticity.

Adaptor Protein Complex 2↗

PubMed2005

Glial cell line-derived neurotrophic factor mediates the desirable actions of the anti-addiction drug ibogaine against alcohol consumption.

Alcohol addiction manifests as uncontrolled drinking despite negative consequences. Few medications are available to treat the disorder. Anecdotal reports suggest that ibogaine, a natural alkaloid, reverses behaviors associated with addiction including alcoholism; however, because of side effects, ibogaine is not used clinically. In this study, we first characterized the actions of ibogaine on ethanol self-administration in rodents. Ibogaine decreased ethanol intake by rats in two-bottle choice and operant self-administration paradigms. Ibogaine also reduced operant self-administration of ethanol in a relapse model. Next, we identified a molecular mechanism that mediates the desirable activities of ibogaine on ethanol intake. Microinjection of ibogaine into the ventral tegmental area (VTA), but not the substantia nigra, reduced self-administration of ethanol, and systemic administration of ibogaine increased the expression of glial cell line-derived neurotrophic factor (GDNF) in a midbrain region that includes the VTA. In dopaminergic neuron-like SHSY5Y cells, ibogaine treatment upregulated the GDNF pathway as indicated by increases in phosphorylation of the GDNF receptor, Ret, and the downstream kinase, ERK1 (extracellular signal-regulated kinase 1). Finally, the ibogaine-mediated decrease in ethanol self-administration was mimicked by intra-VTA microinjection of GDNF and was reduced by intra-VTA delivery of anti-GDNF neutralizing antibodies. Together, these results suggest that GDNF in the VTA mediates the action of ibogaine on ethanol consumption. These findings highlight the importance of GDNF as a new target for drug development for alcoholism that may mimic the effect of ibogaine against alcohol consumption but avoid the negative side effects.

Alcoholism↗

PubMed2004

RACK1 and brain-derived neurotrophic factor: a homeostatic pathway that regulates alcohol addiction.

Alcoholism is a devastating disease that manifests as uncontrolled drinking. Consumption of alcohol is regulated by neurochemical systems within specific neural circuits, but endogenous systems that may counteract and thus suppress the behavioral effects of ethanol intake are unknown. Here we demonstrate that BDNF plays a role in reducing the behavioral effects of ethanol, including consumption, in rodents. We found that decreasing the levels of BDNF leads to increased behavioral responses to ethanol, whereas increases in the levels of BDNF, mediated by the scaffolding protein RACK1, attenuate these behaviors. Interestingly, we found that acute exposure of neurons to ethanol leads to increased levels of BDNF mRNA via RACK1. Importantly, acute systemic administration of ethanol and voluntary ethanol consumption lead to increased levels of BDNF expression in the dorsal striatum. Taken together, these findings suggest that RACK1 and BDNF are part of a regulatory pathway that opposes adaptations that lead to the development of alcohol addiction.

Alcohol Drinking↗

PubMed2004

Spatial and temporal regulation of RACK1 function and N-methyl-D-aspartate receptor activity through WD40 motif-mediated dimerization.

Efficient signaling requires accurate spatial and temporal compartmentalization of proteins. RACK1 is a scaffolding protein that fulfils this role through interaction of binding partners with one of its seven WD40 domains. We recently identified the kinase Fyn and the NR2B subunit of the N-methyl-D-Aspartate receptor (NMDAR) as binding partners of RACK1. Scaffolding of Fyn near its substrate NR2B by RACK1 inhibits Fyn phosphorylation of NR2B and thereby negatively regulates channel function. We found that Fyn and NR2B share the same binding site on RACK1; however, their binding to RACK1 is not mutually exclusive (Yaka, R., Thornton, C., Vagts, A. J., Phamluong, K., Bonci, A., and Ron, D. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 5710-5715). We therefore tested the hypothesis that RACK1 forms a homodimer that allows the simultaneous binding of Fyn and NR2B. We found that RACK1 binds to itself both in vitro and in the brain. Deletion analyses identified a RACK1-RACK1 dimer-binding site within the 4th WD40 repeat, and application of the 4th WD40 repeat or a peptide derivative to hippocampal slices inhibited NMDAR activity. We further found that in hippocampal slices, both RACK1 and NR2B associated with another WD40 protein, the beta-subunit of G protein (Gbeta), previously shown to heterodimerize with RACK1 in vitro (Dell, E. J., Connor, J., Chen, S., Stebbins, E. G., Skiba, N. P., Mochly-Rosen, D., and Hamm, H. E. (2002) J. Biol. Chem. 277, 49888-49895). However, activation of the pituitary adenylate cyclase polypeptide (1-38) G protein-coupled receptor, previously found to induce the dissociation of RACK1 from the NMDAR complex (Yaka, R., He, D. Y., Phamluong, K., and Ron, D. (2003) J. Biol. Chem. 278, 9630-9638), attenuated the association of Gbeta with RACK1 and NR2B. Based on these results, we propose that WD40-mediated homo- and heterodimerization of RACK1 mediate the formation of a transient signaling complex that includes the NMDAR, a G protein and Fyn.

Amino Acid Sequence↗

PubMed2003

Scaffolding of Fyn kinase to the NMDA receptor determines brain region sensitivity to ethanol.

Alcohol (ethanol) abuse is a major societal problem. Although ethanol is a structurally simple, diffusible molecule, its sites of action are surprisingly selective, and the molecular mechanisms underlying specificity in ethanol actions are not understood. The NMDA receptor channel is one of the main targets for ethanol in the brain. We report here that the brain region-specific compartmentalization of Fyn kinase determines NMDA receptor sensitivity to ethanol. We demonstrate that, in the hippocampus but not in the cerebral cortex, Fyn is targeted to the NR2B subunit of the NMDA receptor by the scaffolding protein RACK1. During acute exposure to ethanol, RACK1 is dissociated from the complex, thereby facilitating Fyn-mediated phosphorylation of NR2B, which enhances channel activity, counteracting the inhibitory actions of ethanol. In this way, the selective scaffolding can account for the ethanol-induced acute tolerance of NMDA receptor activity that is detected in the hippocampus but not in the cerebral cortex. The phosphorylation-dependent, region-specific activities of ethanol on the NMDA receptor provide a compelling molecular explanation that accounts for the selective activities of ethanol and may have important implications for elucidating pathways leading to alcohol addiction.

Animals↗

PubMed2003

Pituitary adenylate cyclase-activating polypeptide (PACAP(1-38)) enhances N-methyl-D-aspartate receptor function and brain-derived neurotrophic factor expression via RACK1.

We recently identified a novel mechanism for modulation of the phosphorylation state and function of the N-methyl-d-aspartate (NMDA) receptor via the scaffolding protein RACK1. We found that RACK1 binds both the NR2B subunit of the NMDA receptor and the nonreceptor protein-tyrosine kinase, Fyn. RACK1 inhibits Fyn phosphorylation of NR2B and decreases NMDA receptor-mediated currents in CA1 hippocampal slices (Yaka, R., Thornton, C., Vagts, A. J., Phamluong, K., Bonci, A., and Ron, D. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 5710-5715). Here, we identified the signaling cascade by which RACK1 is released from the NMDA receptor complex and identified the consequences of the dissociation. We found that activation of the cAMP/protein kinase A pathway in hippocampal slices induced the release of RACK1 from NR2B and Fyn. This resulted in the induction of NR2B phosphorylation and the enhancement of NMDA receptor-mediated activity via Fyn. We identified the neuropeptide, pituitary adenylate cyclase activating polypeptide (PACAP(1-38)), as a ligand that induced phosphorylation of NR2B and enhanced NMDA receptor potentials. Finally, we found that activation of the cAMP/protein kinase A pathway induced the movement of RACK1 to the nuclear compartment in dissociated hippocampal neurons. Nuclear RACK1 in turn was found to regulate the expression of brain-derived neurotrophic factor induced by PACAP(1-38). Taken together our results suggest that activation of adenylate cyclase by PACAP(1-38) results in the release of RACK1 from the NMDA receptor and Fyn. This in turn leads to NMDA receptor phosphorylation, enhanced activity mediated by Fyn, and to the induction of brain-derived neurotrophic factor expression by RACK1.

Adenylyl Cyclases↗

PubMed2002

NMDA receptor function is regulated by the inhibitory scaffolding protein, RACK1.

Phosphorylation regulates the function of ligand-gated ion channels such as the N-methyl d-aspartate (NMDA) receptor. Here we report a mechanism for modulation of the phosphorylation state and function of the NMDA receptor via an inhibitory scaffolding protein, RACK1. We found that RACK1 binds both the NR2B subunit of the NMDA receptor and the nonreceptor protein tyrosine kinase, Fyn. RACK1 inhibits Fyn phosphorylation of NR2B and decreases NMDA receptor-mediated currents in CA1 hippocampal slices. Peptides that disrupt the interactions between RACK1, NR2B, and Fyn induce phosphorylation and potentiate NMDA receptor-mediated currents. Therefore, RACK1 is a regulator of NMDA receptor function and may play a role in synaptic plasticity, addiction, learning, and memory.

Amino Acid Sequence↗