Functional characterization of alternatively spliced 5-HT2 receptor isoforms from the pharynx and muscle of the parasitic nematode, Ascaris suum.
Serotonin (5-HT) receptors play key regulatory roles in nematodes and alternatively spliced 5-HT2 receptor isoforms have been identified in the parasitic nematode, Ascaris suum. 5-HT2As1 and 5-HT2As2 contain different C-termini, and 5-HT2As1Delta4 lacks 42 amino acids at the C-terminus of the third intracellular loop. 5-HT2As1 and 5-HT2As2 exhibited identical pharmacological profiles when stably expressed in human embryonic kidney (HEK) 293 cells. Both 5-HT2As isoforms had higher affinity for 5-HT than their closely related Caenorhabditis elegans homolog (5-HT2Ce). This increased 5-HT affinity was not related to the substitution in 5-HT2As1 of F120 for Y in the highly conserved DRY motif found in the second intracellular loop of other 5-HT receptors, since a 5-HT2As1F120Y mutant actually exhibited increased 5-HT affinity compared with that of 5-HT2As1. As predicted, cells expressing either 5-HT2As1 or 5-HT2As2 exhibited a 5-HT-dependent increase in phosphatidylinositol (PI) turnover. In contrast, although 5-HT2As1Delta4 displayed a 10-fold higher affinity for 5-HT and 5-HT agonists than either 5-HT2As1 or 5-HT2As2, 5-HT2As1Delta4 did not couple to either PI turnover or adenyl cyclase activity. Based on RT-PCR, 5-HT2As1 and 5-HT2As2 were more highly expressed in pharynx and body wall muscle and 5-HT2As1Delta4 in nerve cord/hypodermis. This is the first report of different alternatively spliced 5-HT2 receptor isoforms from any system.
Huang
Xinyan
X
Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606, USA.
Xiao
Hong
H
Rex
Elizabeth B
EB
Hobson
Robert J
RJ
Messer
William S
WS
Komuniecki
Patricia R
PR
Komuniecki
Richard W
RW
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D017165:Ascaris suum / Q000378:metabolism*; D001667:Binding, Competitive / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008969:Molecular Sequence Data; D009132:Muscles / Q000737:chemistry / Q000378:metabolism*; D009928:Organ Specificity; D010614:Pharynx / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D010802:Phylogeny; D011485:Protein Binding / Q000502:physiology; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011985:Receptors, Serotonin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014162:Transfection
D010716:Phosphatidylinositols; D020033:Protein Isoforms; D011985:Receptors, Serotonin