Functional significance of the thyrotropin receptor germline polymorphism D727E.
In a toxic thyroid adenoma we identified a novel somatic mutation that constitutively activates the thyrotropin receptor (TSHR). Two heterozygous point mutations at adjacent nucleotides led to a substitution of alanine with asparagine at codon 593 (A593N) in the fifth transmembrane helix of TSHR. This somatic mutation resided on the same TSHR allele with the germline polymorphism D727E. The functional characteristics of the single TSHR mutants A593N and D727E and of the double mutant A593N/D727E were studied in transiently transfected COS-7 cells. The TSHR mutants A593N and A593N/D727E constitutively activated the cAMP cascade, whereas the D727E mutant did not differ from the wild-type TSHR. Surprisingly, the double mutant's specific constitutive activity was 2.3-fold lower than the A593N mutant. Thus, the polymorphism significantly ameliorates G(alphas) protein activation in the presence of the gain-of-function mutation A593N, although it is functionally inert in the context of the wild-type TSHR.
Sykiotis
Gerasimos P
GP
Department of Biochemistry, School of Medicine, University of Patras, 26110, Patras, Greece.
Neumann
Susanne
S
Georgopoulos
Neoklis A
NA
Sgourou
Argyro
A
Papachatzopoulou
Adamantia
A
Markou
Kostas B
KB
Kyriazopoulou
Venetsana
V
Paschke
Ralf
R
Vagenakis
Apostolos G
AG
Papavassiliou
Athanasios G
AG
D000236:Adenoma / Q000235:genetics; D000483:Alleles; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D000242:Cyclic AMP / Q000096:biosynthesis; D004273:DNA, Neoplasm / Q000235:genetics; D018095:Germ-Line Mutation; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D011110:Polymorphism, Genetic; D011989:Receptors, Thyrotropin / Q000235:genetics* / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000235:genetics; D013972:Thyrotropin / Q000494:pharmacology; D014162:Transfection
D004273:DNA, Neoplasm; D011989:Receptors, Thyrotropin; D013972:Thyrotropin; D000242:Cyclic AMP; D020962:Heterotrimeric GTP-Binding Proteins