title: Internalization of human 5-HT4a and 5-HT4b receptors is splice variant dependent.
abstract: The family of 5-HT4 receptors comprises 16 putative splice variants. We have previously shown that there are differences in signal transduction of the h5-HT(4a) and h5-HT(4b) receptors. In the present study, the internalization of these two splice variants following receptor stimulation was investigated with confocal microscopy on living cells. Chimeric receptors, h5-HT(4a)-GFP and h5-HT(4b)-GFP were generated by fusing the coding sequence of the 5-HT4 receptor with the coding sequence of the GFP. The agonist stimulation of fluorescent receptors resulted in a time-dependent internalization of the h5-HT(4b)-GFP receptor, but not of the h5-HT(4a)-GFP receptor. The h5-HT(4b) receptor displays a dual coupling to G(alpha)i,o and G(alpha)s proteins, in contrast to the h5-HT4a receptor, which couples to Galphas proteins only. We investigated whether the difference in internalization of the two splice variant receptors was related to their differential coupling. Therefore, we performed agonist-stimulation of the receptor following inhibition of the G(alpha)i,o protein coupling using PTX. The h5-HT(4b) receptor internalization is PTX insensitive. We co-transfected the fluorescent chimeric receptors with other wild-type variants, which did not produce an alteration of the receptor trafficking. These findings provide the first evidence of differential internalization between the two splice variants, 5-HT(4a) and 5-HT(4b) receptors.
authors.affiliation: Johnson & Johnson Pharmaceutical Research & Development, N.V. Turnhoutseweg 30, B-2340, Beerse, Belgium. armellepindon@yahoo.fr
authors.forename: Armelle
authors.initials: A
authors.lastname: Pindon
authors.forename: Geert
authors.initials: G
authors.lastname: Van Hecke
authors.forename: Katty
authors.initials: K
authors.lastname: Josson
authors.forename: Paul
authors.initials: P
authors.lastname: Van Gompel
authors.forename: Anne
authors.initials: A
authors.lastname: Lesage
authors.forename: Josee E
authors.initials: JE
authors.lastname: Leysen
authors.forename: Mirek
authors.initials: M
authors.lastname: Jurzak
mesh_terms: D017398:Alternative Splicing; D002460:Cell Line; D004705:Endocytosis / Q000502:physiology*; D006801:Humans; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011869:Radioligand Assay; D044422:Receptors, Serotonin, 5-HT4 / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D044422:Receptors, Serotonin, 5-HT4