Abstract
We have cloned new 5-Hydroxytryptamine 4 (5-HT4) receptor splice variants from mouse (m5-HT4(e)R and m5-HT4(f)R), rat (r5-HT4(e)R), and human brain tissue (h5-HT4(e)R) which differ, as do the previously described 5-HT4 receptor variants, in the length and composition of their intracellular C termini after the common splicing site (L358). These new variants have a unique C-terminal sequence made of two PV repeats and are only expressed in brain tissue. All of the 5-HT4 receptor splice variants have a high constitutive activity when expressed at low and physiological densities (<500 fmol/mg protein). At similar density, they showed a much higher constitutive activity than the native and the mutated β2-adrenergic receptors. The constitutive activity of the new splice variants with short C-terminal sequences (m5-HT4(e)R and m5-HT4(f)R) was higher than that of the long C-terminal sequence variants (m5-HT4(a)R and m5-HT4(b)R). This may indicate that the short variants have a higher capacity for isomerization from the inactive to the active conformation. Moreover, we further identified a sequence within the C-terminal tail upstream of L358, rich in serine and threonine residues, that played a crucial role in maintaining 5-HT4R under its inactive conformation.
Footnotes
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Send reprint requests to: Dr. Joël Bockaert, Centre National de la Recherche Scientifique, Unité Propre de Recherche 9023; 141 rue de la Cardonille, 34094 Montpellier cedex, 5 France. E-mail: bockaert{at}ccipe.montp.inserm.fr
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This work was supported by grants from the Fondation pour la Recherche Médicale and Roche Laboratories.
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1 This work was supported by grants from the Fondation pour la Recherche Médicale and Roche Laboratories.
- Abbreviations:
- GPCRs
- G protein coupled receptors
- 5-HT
- 5-hydroxytryptamine
- TSHR
- thyrotropin receptor
- RT-PCR
- reverse transcription polymerase chain reaction
- β2-AR
- β2-adrenergic receptor
- DMEM
- Dulbecco’s modified Eagle’s medium
- dFBS
- dialyzed fetal bovine serum
- R
- inactive receptor conformation
- R*
- active receptor conformation
- ON
- oligonucleotide
- CAM
- constitutively active mutant
- TM
- transmembrane domain
- i3
- third intracellular loop
- Gs
- G protein that stimulates adenylate cyclase
- Received November 11, 1998.
- Accepted January 27, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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