Abstract
Following inducible expression in HEK293 cells, the human
orexin-1 receptor was targeted to the cell surface but became
internalized following exposure to the peptide agonist orexin A.
By contrast, constitutive expression of the human cannabinoid
CB1 receptor resulted in a predominantly punctate, intracellular
distribution pattern consistent with spontaneous, agonistindependent
internalization. Expression of the orexin-1 receptor
in the presence of the CB1 receptor resulted in both
receptors displaying the spontaneous internalization phenotype.
Single cell fluorescence resonance energy transfer imaging
indicated the two receptors were present as heterodimers/oligomers
in intracellular vesicles. Addition of the CB1 receptor
antagonist SR-141716A to cells expressing only the CB1 receptor
resulted in re-localization of the receptor to the cell surface.
Although SR-141716A has no significant affinity for the
orexin-1 receptor, in cells co-expressing the CB1 receptor, the
orexin-1 receptor was also re-localized to the cell surface by
treatment with SR-141716A. Treatment of cells co-expressing
the orexin-1 and CB1 receptors with the orexin-1 receptor
antagonist SB-674042 also resulted in re-localization of both
receptors to the cell surface. Treatment with SR-141716A
resulted in decreased potency of orexin A to activate the mitogen-
activated protein kinases ERK1/2 only in cells co-expressing
the two receptors. Treatment with SB-674042 also reduced
the potency of a CB1 receptor agonist to phosphorylate ERK1/2
only when the two receptors were co-expressed. These studies
introduce an entirely novel pharmacological paradigm, whereby
ligands modulate the function of receptors for which they have
no significant inherent affinity by acting as regulators of receptor
heterodimers.
Original language | English |
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Pages (from-to) | 38812 - 38824 |
Number of pages | 13 |
Journal | Journal of Biological Chemistry |
Volume | 281 |
Issue number | 50 |
DOIs | |
Publication status | Published - 2006 |