Novel brain-specific 5-HT4 receptor splice variants show marked constitutive activity: role of the C-terminal intracellular domain.
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 beta2-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.
Claeysen
S
S
Centre National de la Recherche Scientifique, Unité Propre de Recherche 9023, Montpellier, France.
Sebben
M
M
Becamel
C
C
Bockaert
J
J
Dumuis
A
A
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001921:Brain / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000096:biosynthesis; D017353:Gene Deletion; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000235:genetics; D011985:Receptors, Serotonin / Q000737:chemistry / Q000235:genetics*; D044422:Receptors, Serotonin, 5-HT4; D017386:Sequence Homology, Amino Acid; D012701:Serotonin / Q000378:metabolism
D011943:Receptors, Adrenergic, beta; D011985:Receptors, Serotonin; D044422:Receptors, Serotonin, 5-HT4; D012701:Serotonin; D000242:Cyclic AMP