title: Modified receptor internalization upon coexpression of 5-HT1B receptor and 5-HT2B receptors.
abstract: Serotonin 5-HT(2B) receptors are often coexpressed with 5-HT(1B) receptors, and cross-talk between the two receptors has been reported in various cell types. However, many mechanistic details underlying 5-HT(1B) and 5-HT(2B) receptor cross-talk have not been elucidated. We hypothesized that 5-HT(2B) and 5-HT(1B) receptors each affect the others' signaling by modulating the others' trafficking. We thus examined the agonist stimulated internalization kinetics of fluorescent protein-tagged 5-HT(2B) and 5-HT(1B) receptors when expressed alone and upon coexpression in LMTK(-) murine fibroblasts. Time-lapse confocal microscopy and whole-cell radioligand binding analyses revealed that, when expressed alone, 5-HT(2B) and 5-HT(1B) receptors displayed distinct half-lives. Upon coexpression, serotonin-induced internalization of 5-HT(2B) receptors was accelerated 5-fold and was insensitive to a 5-HT(2B) receptor antagonist. In this context, 5-HT(2B) receptors did internalize in response to a 5-HT(1B) receptor agonist. In contrast, co-expression did not render 5-HT(1B) receptor internalization sensitive to a 5-HT(2B) receptor agonist. The altered internalization kinetics of both receptors upon coexpression was probably not due to direct interaction because only low levels of colocalization were observed. Antibody knockdown experiments revealed that internalization of 5-HT(1B) receptors (expressed alone) was entirely clathrin-independent and Caveolin1-dependent, whereas that of 5-HT(2B) receptors (expressed alone) was Caveolin1-independent and clathrin-dependent. Upon coexpression, serotonin-induced 5-HT(2B) receptor internalization became partially Caveolin1-dependent, and serotonin-induced 5-HT(1B) receptor internalization became entirely Caveolin1-independent in a protein kinase Cepsilon-dependent fashion. In conclusion, these data demonstrate that coexpression of 5-HT(1B) and 5-HT(2B) receptors influences the internalization pathways and kinetics of both receptors.
authors.affiliation: Centre National de la Recherche Scientifique UMR7104, Illkirch, France.
authors.forename: Agnes
authors.initials: A
authors.lastname: Janoshazi
authors.forename: Maud
authors.initials: M
authors.lastname: Deraet
authors.forename: Jacques
authors.initials: J
authors.lastname: Callebert
authors.forename: Vincent
authors.initials: V
authors.lastname: Setola
authors.forename: Silke
authors.initials: S
authors.lastname: Guenther
authors.forename: Bruno
authors.initials: B
authors.lastname: Saubamea
authors.forename: Philippe
authors.initials: P
authors.lastname: Manivet
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Launay
authors.forename: Luc
authors.initials: L
authors.lastname: Maroteaux
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004705:Endocytosis / Q000187:drug effects* / Q000502:physiology; D004789:Enzyme Activation; D015870:Gene Expression / Q000502:physiology*; D051379:Mice; D051744:Protein Kinase C-epsilon / Q000378:metabolism; D044302:Receptor, Serotonin, 5-HT1B / Q000235:genetics / Q000378:metabolism*; D044403:Receptor, Serotonin, 5-HT2B / Q000235:genetics / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*; D058829:Serotonin 5-HT1 Receptor Antagonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D015398:Signal Transduction; D013696:Temperature
chemical_list: D044302:Receptor, Serotonin, 5-HT1B; D044403:Receptor, Serotonin, 5-HT2B; D058829:Serotonin 5-HT1 Receptor Antagonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D051744:Protein Kinase C-epsilon