Constitutive dimerization of human serotonin 5‐HT4 receptors in living cells

Abstract
Serotonin 5‐HT4 receptor isoforms are G protein‐coupled receptors (GPCRs) with distinct pharmacological properties and may represent a valuable target for the treatment of many human disorders. Here, we have explored the process of dimerization of human 5‐HT4 receptor (h5‐HT4R) by means of co‐immunoprecipitation and bioluminescence resonance energy transfer (BRET). Constitutive h5‐HT4(d)R dimer was observed in living cells and membrane preparation of CHO and HEK293 cells. 5‐HT4R ligands did not influence the constitutive energy transfer of the h5‐HT4(d)R splice variant in intact cells and isolated plasma membranes. In addition, we found that h5‐HT4(d)R and h5‐HT4(g)R which structurally differ in the length of their C‐terminal tails were able to form constitutive heterodimers independently of their activation state. Finally, we found that coexpression of h5‐HT4R and β2‐adrenergic receptor (β2AR) led to their heterodimerization. Given the large number of h5‐HT4R isoforms which are coexpressed in a same tissue, our results points out the complexity by which this 5‐HTR sub‐type mediates its biological effects.

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