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Multiple GPCR conformations and signalling pathways: implications for antagonist affinity estimates.

Baker JG, Hill SJ - Trends Pharmacol. Sci. (2007)

Bottom Line: As a consequence, changes in antagonist affinity values have been taken as initial evidence for the presence of novel receptor subtypes.Emerging evidence suggests, however, that receptors can possess multiple binding sites and the same receptor can show different antagonist affinity measurements under distinct experimental conditions.Here, we discuss several mechanisms by which antagonists have different affinities for the same receptor as a consequence of allosterism, coupling to different G proteins, multiple (but non-interacting) receptor sites, and signal-pathway-dependent pharmacology (where the pharmacology observed varies depending on the signalling pathway measured).

View Article: PubMed Central - PubMed

Affiliation: Institute of Cell Signalling, Medical School, Nottingham, NG7 2UH, UK.

ABSTRACT
Antagonist affinity measurements have traditionally been considered important in characterizing the cell-surface receptors present in a particular cell or tissue. A central assumption has been that antagonist affinity is constant for a given receptor-antagonist interaction, regardless of the agonist used to stimulate that receptor or the downstream response that is measured. As a consequence, changes in antagonist affinity values have been taken as initial evidence for the presence of novel receptor subtypes. Emerging evidence suggests, however, that receptors can possess multiple binding sites and the same receptor can show different antagonist affinity measurements under distinct experimental conditions. Here, we discuss several mechanisms by which antagonists have different affinities for the same receptor as a consequence of allosterism, coupling to different G proteins, multiple (but non-interacting) receptor sites, and signal-pathway-dependent pharmacology (where the pharmacology observed varies depending on the signalling pathway measured).

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5′-N-ethylcarboxamidoadenosine (NECA)-induced gene transcription mediated by the human A1 adenosine receptor. (a) Gi and Gs signalling pathways from the adenosine A1 receptor to CRE-mediated gene transcription in CHO cells expressing the human A1-receptor. Abbreviations: CREB, CRE-binding protein; PKA, protein kinase A. 6 × CRE–SPAP signifies a SPAP reporter gene containing six CRE elements. (b) Concentration–response curves for the effect of the agonist NECA on forskolin-stimulated CRE gene transcription in the presence and absence of increasing concentrations of DPCPX. Data are from Ref. [26].
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fig2: 5′-N-ethylcarboxamidoadenosine (NECA)-induced gene transcription mediated by the human A1 adenosine receptor. (a) Gi and Gs signalling pathways from the adenosine A1 receptor to CRE-mediated gene transcription in CHO cells expressing the human A1-receptor. Abbreviations: CREB, CRE-binding protein; PKA, protein kinase A. 6 × CRE–SPAP signifies a SPAP reporter gene containing six CRE elements. (b) Concentration–response curves for the effect of the agonist NECA on forskolin-stimulated CRE gene transcription in the presence and absence of increasing concentrations of DPCPX. Data are from Ref. [26].

Mentions: When expressed in CHO cells, the human adenosine A1 receptor couples to both Gi and Gs proteins [24,25]. When antagonist affinity measurements were made at both the Gi- and Gs-coupled forms of the A1 receptor, however, the antagonist affinities were found to be constant, regardless of the signalling cascade that was monitored (Gi or Gs) or the level at which the signalling cascade was evaluated (cAMP or CRE-mediated gene expression) [26] (Figure 2). Thus, in this study the fundamental pharmacological concept that antagonist affinities are indeed constant seems to hold true for the A1 receptor.


Multiple GPCR conformations and signalling pathways: implications for antagonist affinity estimates.

Baker JG, Hill SJ - Trends Pharmacol. Sci. (2007)

5′-N-ethylcarboxamidoadenosine (NECA)-induced gene transcription mediated by the human A1 adenosine receptor. (a) Gi and Gs signalling pathways from the adenosine A1 receptor to CRE-mediated gene transcription in CHO cells expressing the human A1-receptor. Abbreviations: CREB, CRE-binding protein; PKA, protein kinase A. 6 × CRE–SPAP signifies a SPAP reporter gene containing six CRE elements. (b) Concentration–response curves for the effect of the agonist NECA on forskolin-stimulated CRE gene transcription in the presence and absence of increasing concentrations of DPCPX. Data are from Ref. [26].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2169386&req=5

fig2: 5′-N-ethylcarboxamidoadenosine (NECA)-induced gene transcription mediated by the human A1 adenosine receptor. (a) Gi and Gs signalling pathways from the adenosine A1 receptor to CRE-mediated gene transcription in CHO cells expressing the human A1-receptor. Abbreviations: CREB, CRE-binding protein; PKA, protein kinase A. 6 × CRE–SPAP signifies a SPAP reporter gene containing six CRE elements. (b) Concentration–response curves for the effect of the agonist NECA on forskolin-stimulated CRE gene transcription in the presence and absence of increasing concentrations of DPCPX. Data are from Ref. [26].
Mentions: When expressed in CHO cells, the human adenosine A1 receptor couples to both Gi and Gs proteins [24,25]. When antagonist affinity measurements were made at both the Gi- and Gs-coupled forms of the A1 receptor, however, the antagonist affinities were found to be constant, regardless of the signalling cascade that was monitored (Gi or Gs) or the level at which the signalling cascade was evaluated (cAMP or CRE-mediated gene expression) [26] (Figure 2). Thus, in this study the fundamental pharmacological concept that antagonist affinities are indeed constant seems to hold true for the A1 receptor.

Bottom Line: As a consequence, changes in antagonist affinity values have been taken as initial evidence for the presence of novel receptor subtypes.Emerging evidence suggests, however, that receptors can possess multiple binding sites and the same receptor can show different antagonist affinity measurements under distinct experimental conditions.Here, we discuss several mechanisms by which antagonists have different affinities for the same receptor as a consequence of allosterism, coupling to different G proteins, multiple (but non-interacting) receptor sites, and signal-pathway-dependent pharmacology (where the pharmacology observed varies depending on the signalling pathway measured).

View Article: PubMed Central - PubMed

Affiliation: Institute of Cell Signalling, Medical School, Nottingham, NG7 2UH, UK.

ABSTRACT
Antagonist affinity measurements have traditionally been considered important in characterizing the cell-surface receptors present in a particular cell or tissue. A central assumption has been that antagonist affinity is constant for a given receptor-antagonist interaction, regardless of the agonist used to stimulate that receptor or the downstream response that is measured. As a consequence, changes in antagonist affinity values have been taken as initial evidence for the presence of novel receptor subtypes. Emerging evidence suggests, however, that receptors can possess multiple binding sites and the same receptor can show different antagonist affinity measurements under distinct experimental conditions. Here, we discuss several mechanisms by which antagonists have different affinities for the same receptor as a consequence of allosterism, coupling to different G proteins, multiple (but non-interacting) receptor sites, and signal-pathway-dependent pharmacology (where the pharmacology observed varies depending on the signalling pathway measured).

Show MeSH
Related in: MedlinePlus