D sub(2)/D sub(3) Dopamine Receptor Heterodimers Exhibit Unique Functional Properties

• Published in: The Journal of biological chemistry 2001-08, Vol.276 (32), p.30308-30314
• Main Authors: Scarselli, M, Novi, F, Schallmach, E, Lin, R, Baragli, A, Colzi, A, Griffon, N, Corsini, GU, Sokoloff, P, Levenson, R, Vogel, Z, Maggio, R
• Format: Article
• Language: English
• ISSN: 0021-9258

Evidence for heterodimerization has recently been provided for dopamine D sub(1) and adenosine A sub(1) receptors as well as for dopamine D sub(2) and somatostatin SSTR sub(5) receptors. In this paper, we have studied the possibility that D sub(2) and D sub(3) receptors interact functionally by forming receptor heterodimers. Initially, we split the two receptors at the level of the third cytoplasmic loop into two fragments. The first, containing transmembrane domains (TM) I to V and the N-terminal part of the third cytoplasmic loop, was named D sub(2trunk) or D sub(3trunk), and the second, containing the C-terminal part of the third cytoplasmic loop, TMVI and TMVII, and the C-terminal tail, was named D sub(2tail) or D sub(3tail). Then we defined the pharmacological profiles of the homologous (D sub(2trunk)/D sub(2tail) and D sub(3trunk)/D sub(3tail)) as well as of the heterologous (D sub(2trunk)/D sub(3tail) and D sub(3trunk)/D sub(2tail)) cotransfected receptor fragments. The pharmacological profile of the cross- cotransfected fragments was different from that of the native D sub(2) or D sub(3) receptors. In most cases, the D sub(3trunk)/D sub(2tail) was the one with the highest affinity for most agonists and antagonists. Moreover, we observed that all of these receptor fragments reduced the expression of the wild type dopamine D sub(2) and D sub(3) receptors, suggesting that D sub(2) and D sub(3) receptors can form complexes with these fragments and that these complexes bind [ super(3)H]nemonapride less efficiently or are not correctly targeted to the membrane. In a second set of experiments, we tested the ability of the split and the wild type receptors to inhibit adenylyl cyclase (AC) types V and VI. All of the native and split receptors inhibited AC-V and AC-VI, with the exception of D sub(3), which was unable to inhibit AC-VI. We therefore studied the ability of D sub(2) and D sub(3) to interact functionally with one another to inhibit AC-VI. We found that with D sub(2) alone, R-(+)-7-hydroxydypropylaminotetralin hydrobromide inhibited AC-VI with an IC sub(50) of 2.05 plus or minus 0.15 nM, while in the presence of D sub(2) and D sub(3) it inhibited AC-VI with an IC sub(50) of 0.083 plus or minus 0.011 nM. Similar results were obtained with a chimeric cyclase made from AC-V and AC-VI. Coimmunoprecipitation experiments indicate that D sub(2) and D sub(3) receptors are capable of physical interaction.