Cloning, expression and pharmacology of a truncated splice variant of the human 5-HT7 receptor (h5-HT7b).
1. The rat 5-hydroxytryptamine (5-HT)7 receptor displays two splice variations, a long form, and a truncated splice isoform, arising from the introduction of a stop codon near the carboxy-terminus. The human-5HT7 receptor gene contains at least two introns and encodes a 445 amino acid 5-HT receptor. 2. A truncated splice variation in the human 5-HT7 receptor was isolated from a human placental cDNA library. In accordance with current NC-IUPHAR nomenclature guidelines, it is suggested that this receptor be donated as the h5-HT7b receptor and the long form of the receptor as h5-HT7a. 3. The h5-HT7b receptor was stably expressed in HEK 293 cells and ligand affinities were determined by displacement of [3H]-5-carboxyamidotryptamine (5-CT; Kd = 0.28 +/- 0.6 nM, Bmax = 7.3 +/- 17 pmol mg-1 protein). The rank order of affinities (pKi) for a series of ligands was: 5-carboxamidotryptamine (5-CT, 9.65) > 5-hydroxytryptamine (5-HT, 9.41) > methiothepin (8.87) > mesulergine (7.87) > 8-hydroxy-2 (di-n-propylamino)tetralin (8-OH-DPAT, 6.85) > ketanserin (6.44). 4. The h5-HT7b receptor coupled positively to adenylyl cyclase in HEK 293 cells. This response was elicited by a number of agonists with the following order of potency (pEC50): 5-CT (8.7 +/- 0.11) > 5-MeOT (5-methoxytryptamine; 8.1 +/- 0.20) > 5-HT (7.5 +/- 0.13) tryptamine (5.6 +/- 0.36) > 8-OH-DPAT (5.3 +/- 0.28) > 5-methoxytryptamine (5.0 +/- 0.06). This rank order was comparable to that observed in the radioligand binding studies. 5. In a similar fashion to that described for the 5-HT7a receptor, PCR studies suggested that the 5-HT7b receptor mRNA is found in great abundance throughout the brain, in the small intestine and aorta. 6. It is concluded that the h5-HT7 receptor, like the rat receptor, exists as splice variants exhibiting similar pharmacology, signal transduction and distribution. It is thus likely that there exists a complex physiological role for alternate splicing products of the 5-HT7 receptor gene.
Jasper
J R
JR
Center for Biological Research, Roche Bioscience, Palo Alto, CA 94304, USA.
Kosaka
A
A
To
Z P
ZP
Chang
D J
DJ
Eglen
R M
RM
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D010920:Placenta / Q000737:chemistry; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011985:Receptors, Serotonin / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D018076:DNA, Complementary; D012333:RNA, Messenger; D011985:Receptors, Serotonin; C104425:serotonin 7 receptor; D000242:Cyclic AMP