Role of the carboxyl-terminal half of the extracellular domain of the human thyrotropin receptor in signal transduction.
We studied the role of the carboxyl-terminus of the extracellular region of the human TSH receptor in signal transduction (cAMP generation). For this purpose, we introduced homologous substitutions of smaller segments within amino acids 261-418 (domains D and E) of the TSH receptor with the corresponding amino acids of the rat LH/CG receptor. Amino acids 317-366 were not investigated in view of previous data indicating their noninvolvement. Mutant TSH receptor cDNAs, in a eukaryotic expression vector, were stably transfected into Chinese hamster ovary cells. Eight of nine plasmid constructs expressed TSH receptors that could be detected by radiolabeled TSH binding; six of these were of high affinity similar to the wild-type receptor and, therefore, provided informative data on signal transduction. Despite high affinity TSH binding, five of six TSH receptor mutants displayed a diminished cAMP response to TSH stimulation, suggesting the involvement of broad segments of domains DE in signal transduction. Amino acids 270-278 and 287-297 were particularly important in this respect. The conformation conferred by these segments of the TSH receptor, therefore, appears to be involved in transducing a signal from the extracellular to the intracellular region of the receptor.
Nagayama
Y
Y
Thyroid Molecular Biology Unit, Veterans Administration Medical Center, San Francisco, California 94121.
Rapoport
B
B
D000595:Amino Acid Sequence; D000818:Animals; D001323:Autoantibodies; D016466:CHO Cells; D006224:Cricetinae; D000242:Cyclic AMP / Q000096:biosynthesis; D006111:Graves Disease / Q000276:immunology; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D051381:Rats; D011989:Receptors, Thyrotropin / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D013329:Structure-Activity Relationship; D013972:Thyrotropin / Q000378:metabolism; D014162:Transfection
D001323:Autoantibodies; D011989:Receptors, Thyrotropin; D013972:Thyrotropin; D000242:Cyclic AMP