Cross-Receptor Interactions between Dopamine D_2L and Neurotensin NTS₁ Receptors Modulate Binding Affinities of Dopaminergics

Abstract

T he ability to form spatial complexes allowing molecular interactions between receptor protomers facilitates cooperative effects and tissue specific control of neuronal activity. Thus, heterodimerization is discussed as an integral feature of G-protein coupled receptor (GPCR) mediated signal transduction. 1À3 Intramembrane receptorÀreceptor interactions of associated protomers may modify binding and activating properties of GPCR ligands. 4À7 Using F€ orster resonance energy transfer (FRET) technique, a recent study on the interactions between R 2A -adrenergic and μ-opioid receptors demonstrated a transinhibitory effect between the protomers. In detail, morphine binding to the μ-opioid receptor triggered the conformational changes in the norepinephrine-occupied R 2A -adrenergic receptor leading to the inhibition of its signaling. 8 Physical interactions between δ-and μ-opioid receptors were suggested to modulate μ-mediated tolerance and dependence 9 when the development of bivalent ligands was constituted as a useful approach to investigate changes in receptor properties as a consequence to dimerization. 10,11 Heterodimerization is also a highly relevant phenomenon for dopamine receptor mediated signaling. 12,13 Demonstrating the development of a new complex with enhanced functional activity through hetero-oligomerization, the physical interaction between the dopamine D 2L and the somatostatin SST5 receptor was investigated via radioligand binding studies, functional assays, and FRET microscopy. 14 The heterooligomerization of D 2L and SST5, known for their colocalization in the central nervous system (CNS), led to a synergistic effect on binding and signaling as molecular cross-talk and the correlation between activated receptor function and oligomerization was stressed.Dopaminergic systems have been also described to functionally interact with the neuromodulatory peptide neurotensin (NT, pE-L-Y-E-N-K-P-R-R-P-Y-I-L) 15 which is suggested to play a role in the pathophysiology of brain diseases including schizophrenia, Parkinson's disease. and Morbus Alzheimer. 16À18 Thus, neurotensin was shown to negatively alter binding affinity of the dopamine receptor agonist [ 3 H]N-n-propyl-nor-apomorphine in specific brain areas. 19À25 However, biomolecular interactions and a putative heteromer formation between dopamine receptors and neurotensin receptors have not been investigated yet.Employing fluorescence detected coimmunoprecipitation and radioligand binding experiments, we herein demonstrate that coexpression of dopamine D 2L receptor and the neurotensin receptor subtype NTS 1 in human embryonic kidney cells (HEK293 cells) leads to physical interaction at a molecular level. In this in vitro system, a trans-inhibitory effect on the agonist binding affinity of D 2 was observed in the presence of neurotensin. A biochemical fingerprint 26 of the D 2L -NTS 1 heteromer was explored by investigating the effect of both neurotensin and NTS 1 on the D 2 receptor binding properties of different ABSTRACT: Dopaminergic systems ...

Neurotensin inhibits both dopamine- and GABA-mediated inhibition of ventral tegmental area dopamine neurons

“…Interestingly, we also found that the effects of neurotensin were not specific to the D2R IPSC as neurotensin also inhibited the GABA B IPSC to the same magnitude. This suggests that the effects of neurotensin are likely not due to modulation of D2R activity by direct heterodimer interactions with NTS1 as has been observed in HEK-293 cells (Borroto-Escuela et al 2013;Koschatzky et al 2011). Previously, it was reported that neurotensin does not block GABA-caused inhibition of DA neuronal firing (Shi and Bunney 1991).…”

“…Fibers containing neurotensin heavily innervate midbrain DA neurons (Hokfelt et al 1984;Woulfe and Beaudet 1989), and DA neurons of the VTA and SNc express neurotensin receptors, primarily the NTS1 receptor (Binder et al 2001;Fassio et al 2000;Lepee-Lorgeoux et al 1999;Nicot et al 1995;Palacios and Kuhar 1981;Szigethy and Beaudet 1989). Furthermore, D2Rs and NTS1 receptors have been shown to form heteromers in heterologous expression systems, which resulted in a decrease in D2R agonist binding and decreases in D2R signaling after treatment with neurotensin (Borroto-Escuela et al 2013;Koschatzky et al 2011). Previous research has shown that neurotensin modifies midbrain DA neuron activity through two NTS1 receptordependent mechanisms: increased DA neuron firing through activation of a nonselective cation channel Jiang et al 1994;Jomphe et al 2006;Shi and Bunney 1991;St-Gelais et al 2004;Werkman et al 2000) and a reduction in the inhibition of firing caused by D2R activation Nimitvilai et al 2012;Shi and Bunney 1990;Bunney 1991, 1992;Werkman et al 2000).…”

Selective Agonists for Dopamine/Neurotensin Receptor Heterodimers

“…[6] By the use of a recombinant in vitro test system, a cross-inhibitory effect on the agonist binding affinity of D 2 was observed in the presence of NT. Structurally diverse ligands were investigated to determine the relationship between the intrinsic activity of dopaminergics and the modulatory effect of NTS 1 -NT binding on the affinity of dopaminergics.…”

“…[6] Binding-deficient NTS 1 mutants were used to investigate the role of the active receptor conformation of NTS 1 as a prerequisite for the trans-modulatory effect between the D 3 receptors and NT receptors. Based on recent investigations revealing that N-arylamidobutyl-substituted dopaminergics have excellent D 3 receptor binding and activating properties, we synthesized the 7-OH-DPAT congeners of type A (Scheme 1).…”

“…Based on recent investigations revealing that N-arylamidobutyl-substituted dopaminergics have excellent D 3 receptor binding and activating properties, we synthesized the 7-OH-DPAT congeners of type A (Scheme 1). [6,7] Employing these novel test compounds, the influence of structural changes on the NT-induced decrease in affinity was investiThe neuromodulatory peptide neurotensin has been described to functionally interact with dopaminergic pathways of the human brain. We employed radioligand binding studies to investigate the physical interaction between co-expressed dopamine D 2L or D 3 and neurotensin NTS 1 or NTS 2 receptors.…”