The natural mutation encoding a C terminus-truncated 5-hydroxytryptamine 2B receptor is a gain of proliferative functions.
Although potentially implicated in several physiological functions, few functional mutations have been identified in the human 5-hydroxytryptamine (HT)(2B) receptor gene. A heterozygous mutation R393X in the 5-HT(2B) receptor was recently identified in a patient diagnosed with pulmonary hypertension after intake of the anorexigenic dexfenfluramine. Although reported to generate a lack of function, this C terminus-truncated 5-HT(2B) receptor should somehow affect transduction pathways relevant to pulmonary hypertension. In our study, we investigated putative modifications in transduction of the R393X-mutated 5-HT(2B) receptor. In stably transfected cells, we confirmed the loss of inositol 1,4,5-trisphosphate stimulation caused by the G(alphaq) uncoupling, despite conserved ligand affinity between the normal and mutated receptors. We also observed a partial loss of nitric-oxide synthase stimulation. However, the truncated R393X receptor presented 1) a strong gain of efficacy in cell proliferation as assessed by mitogen-activated protein kinase activity and thymidine incorporation, 2) a preferential coupling to G(alpha13) as shown by blocking antiserum, and 3) an apparent lack of internalization upon agonist stimulation as observed by confocal microscopy. This work demonstrates that, in the 5-HT(2B) receptor, the C terminus, including the palmitoylation and phosphorylation sites, is absolutely required for proper transduction and internalization. For the first time, we show that the lack of C terminus can generate a switch of coupling to G(alpha13), a reduced NO synthase activation, and an increase in cell proliferation. All these modifications are relevant in pathophysiological vasoconstriction.
Deraet
Maud
M
INSERM U616 Hospital Pitié-Salpetrière, Batiment Pédiatrie, 47 boulevard de l'Hôpital, 75651 Paris Cedex 13, France.
Manivet
Philippe
P
Janoshazi
Agnes
A
Callebert
Jacques
J
Guenther
Silke
S
Drouet
Ludovic
L
Launay
Jean-Marie
JM
Maroteaux
Luc
L
D002460:Cell Line; D049109:Cell Proliferation; D004789:Enzyme Activation; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D011487:Protein Conformation; D044403:Receptor, Serotonin, 5-HT2B / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D013329:Structure-Activity Relationship
D044403:Receptor, Serotonin, 5-HT2B; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D020928:Mitogen-Activated Protein Kinases