Cloning and functional expression of a thyrotropin receptor cDNA from rat fat cells.
Thyrotropin receptor (TSH-R) has been thought to be thyroid-specific, but, by Northern blot analysis, we found that rat adipose tissue expressed TSH-R mRNAs in amounts approaching those in the thyroid. To investigate the function of TSH-R from adipose tissue, we screened a rat fat cell lambda gt11 cDNA library for TSH-R sequences using a 32P-labeled rat thyroid TSH-R cDNA as a probe. Among 10(6) plaques, we obtained four positive clones. Sequencing of these cDNAs has revealed that two of them (F alpha and F beta) contained both initiation and termination codons. Comparison of F alpha with the thyroid TSH-R cDNA sequence revealed that F alpha was almost identical to the thyroid TSH-R, except that nucleotides 1041 and 1277 were changed from A to G and from C to T, respectively. In contrast, we found that F beta contained 21 novel nucleotides between nucleotides 467 and 468 of the thyroid TSH-R cDNA, encoding an additional 7 amino acids. However, when we prepared mRNA from adipose tissue and transcribed it into cDNA, we failed to amplify the F beta type of TSH-R cDNA by polymerase chain reaction, suggesting that F beta mRNAs are rare in the tissue. We then ligated F cDNAs into pSG5 and transfected them with pSV2-neo into Chinese hamster ovary (CHO)-K1 cells. TSH stimulated cAMP formation in CHO-F alpha cells in a manner similar to that in CHO cells transfected with thyroid TSH-R cDNA. In contrast, no increase of cAMP was observed in CHO-F beta cells. IgG from patients with Graves' disease (n = 4) showed thyroid-stimulating antibody activity only in CHO-F alpha cells (1288-4582%). In addition, CHO-F alpha cells and CHO cells transfected with thyroid TSH-R showed similar 125I-TSH binding activity. These results indicate that the fat cell expresses high levels of a TSH-R whose function is indistinguishable from that in the thyroid and suggest that the TSH-R autoantibody plays an important role in the pathogenesis of the extrathyroidal manifestations of Graves' disease.
Endo
T
T
Third Department of Internal Medicine, University of Yamanashi Medical School, Japan.
Ohta
K
K
Haraguchi
K
K
Onaya
T
T
D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000737:chemistry; D018076:DNA, Complementary / Q000235:genetics; D004822:Epididymis; D015870:Gene Expression; D008053:Lipid Mobilization / Q000187:drug effects; D008297:Male; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011989:Receptors, Thyrotropin / Q000235:genetics*; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D013961:Thyroid Gland / Q000378:metabolism; D013972:Thyrotropin / Q000494:pharmacology
D017931:DNA Primers; D018076:DNA, Complementary; D012333:RNA, Messenger; D011989:Receptors, Thyrotropin; D013972:Thyrotropin