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Modified Receptor Internalization upon Co-expression of 5-HT1B Receptor and 5-HT2B Receptors.
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Edité par CCSD ; American Society for Pharmacology and Experimental Therapeutics -
International audience. Serotonin 5-HT2B receptors are often co-expressed with 5-HT1B receptors, and crosstalk between the two receptors has been reported in various cell types. However, many mechanistic details underlying 5-HT1B and 5-HT2B receptors crosstalk have not been elucidated. We hypothesized that 5-HT2B and 5-HT1B receptors affect each other's signaling by modulating each other's trafficking. We thus examined the agonist stimulated internalization kinetics of fluorescent protein-tagged 5-HT2B and 5-HT1B receptors when expressed alone and upon co-expression in LMTK(-) murine fibroblasts. Time-lapse confocal microscopy and whole-cell radioligand binding analyses revealed that 5-HT2B and 5-HT1B receptors when expressed alone displayed distinct half-lives. Upon co-expression, serotonin-induced internalization of 5-HT2B receptors was accelerated five-fold, and 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 co-expression was likely not due to direct interaction as only low levels of co-localization were observed. Antibody knock-down experiments revealed that internalization of 5-HT1B receptors (expressed alone) was entirely clathrin-independent and Caveolin1-dependent, while that of 5-HT2B receptors (expressed alone) was Caveolin1-independent and clathrin-dependent. Upon co-expression, 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 Cepsilon-dependent fashion. In conclusion, these data demonstrate that co-expression of 5-HT1B and 5-HT2B receptors influences the internalization pathways and kinetics of both receptors.
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