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Leiden/Amsterdam Center for Drug Research, Department of Medicinal Chemistry, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands (R.M.V.R., K.S., R.A.B., R.L.).; and School of Biological & Biomedical Sciences, Durham University, Durham, United Kingdom (F.C.S., P.L.C.)
In this study, we report the homo- and hetero-oligomerization of the human histamine H4R by both biochemical (Western blot and immobilized metal affinity chromatography) and biophysical [bioluminescence resonance energy transfer and time-resolved fluorescence resonance energy transfer (tr-FRET)] techniques. The H4R receptor is the most recently discovered member of the histamine family of G-protein-coupled receptors. Using specific polyclonal antibodies raised against the C-terminal tail of the H4R, we demonstrate the presence of H4R oligomers in human embryonic kidney 293 and COS-7 cells heterologously overexpressing H4Rs and putative native H4R oligomers in human phytohaemagglutinin blasts endogenously expressing H4Rs. Moreover, we show that H4R homo-oligomers are formed constitutively, are formed at low receptor densities (300 fmol/mg of protein), and are present at the cell surface, as detected by tr-FRET. The formation of these oligomers is independent of N-glycosylation and is not modulated by H4R ligands, covering the full spectrum of agonists, neutral antagonists, and inverse agonists. Although we show H4R homo-oligomer formation at physiological expression levels, the detection of H1R-H4R hetero-oligomers was achieved only at higher H1R expression levels and are most likely not physiologically relevant.
Address correspondence to: Dr. R. Leurs, Leiden/Amsterdam Center for Drug Research, Department of Medicinal Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands. E-mail: r.leurs{at}few.vu.nl
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