RT Journal Article SR Electronic T1 Modified Receptor Internalization upon Coexpression of 5-HT1B Receptor and 5-HT2B Receptors JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 1463 OP 1474 DO 10.1124/mol.106.032656 VO 71 IS 6 A1 Agnes Janoshazi A1 Maud Deraet A1 Jacques Callebert A1 Vincent Setola A1 Silke Guenther A1 Bruno Saubamea A1 Philippe Manivet A1 Jean-Marie Launay A1 Luc Maroteaux YR 2007 UL http://molpharm.aspetjournals.org/content/71/6/1463.abstract AB Serotonin 5-HT2B receptors are often coexpressed with 5-HT1B receptors, and cross-talk between the two receptors has been reported in various cell types. However, many mechanistic details underlying 5-HT1B and 5-HT2B receptor cross-talk have not been elucidated. We hypothesized that 5-HT2B and 5-HT1B receptors each affect the others' signaling by modulating the others' trafficking. We thus examined the agonist stimulated internalization kinetics of fluorescent protein-tagged 5-HT2B and 5-HT1B 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-HT2B and 5-HT1B receptors displayed distinct half-lives. Upon coexpression, serotonin-induced internalization of 5-HT2B receptors was accelerated 5-fold and was insensitive to a 5-HT2B receptor antagonist. In this context, 5-HT2B receptors did internalize in response to a 5-HT1B receptor agonist. In contrast, co-expression did not render 5-HT1B receptor internalization sensitive to a 5-HT2B 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-HT1B receptors (expressed alone) was entirely clathrin-independent and Caveolin1-dependent, whereas that of 5-HT2B receptors (expressed alone) was Caveolin1-independent and clathrin-dependent. Upon coexpression, serotonin-induced 5-HT2B receptor internalization became partially Caveolin1-dependent, and serotonin-induced 5-HT1B receptor internalization became entirely Caveolin1-independent in a protein kinase Cϵ-dependent fashion. In conclusion, these data demonstrate that coexpression of 5-HT1B and 5-HT2B receptors influences the internalization pathways and kinetics of both receptors. The American Society for Pharmacology and Experimental Therapeutics