Interaction of endothelin-1 with porcine thyroid cells in culture: a possible autocrine factor regulating iodine metabolism.
Although endothelins were originally discovered as peptides with vasoconstrictor activity, recent studies have indicated a number of endothelin (ET)-induced hormonal functions in various tissues. We have studied the interaction of endothelins with porcine thyroid cells in culture. Specific binding of 125I-labelled ET-1 was demonstrated in porcine thyroid cells. The binding was displaced equally by unlabelled ET-1 and ET-2, but receptor affinity for ET-3 was lower than that for ET-1 and -2. Scatchard analysis of the data revealed a single class of high-affinity ET-1 receptors with a Kd of 0.45 nmol/l and a binding capacity of 2100 sites/cell. SDS-PAGE and autoradiography of 125I-labelled ET-1 cross-linked with thyroid cell membranes demonstrated ET-1 binding sites with an apparent molecular weight of 50 kDa. These results indicated that ET-1 receptors in thyroid cells are type A ET receptors. In association with the presence of ET-1 receptors, porcine thyroid cells responded to ET-1 and ET-2 with an increase in c-fos mRNA expression. Although ET-1 did not affect DNA synthesis stimulated by either EGF or IGF-I, it dose-dependently inhibited TSH-induced iodide uptake and also inhibited iodide uptake stimulated by forskolin and 8-bromo-cAMP. ET-1 had no effect on TSH-stimulated cAMP production. Thus, ET-1 inhibited TSH-induced iodine metabolism by acting at the steps distal to cAMP production. In agreement with a recent report, immunoreactive ET-1 was detected in medium conditioned by porcine thyroid cells. Antibody to ET-1 was found to increase TSH-induced iodide uptake.(ABSTRACT TRUNCATED AT 250 WORDS)
Tsushima
T
T
Department of Medicine 2, Tokyo Women's Medical College, Japan.
Arai
M
M
Isozaki
O
O
Nozoe
Y
Y
Shizume
K
K
Murakami
H
H
Emoto
N
N
Miyakawa
M
M
Demura
H
H
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D016232:Endothelins / Q000378:metabolism*; D007455:Iodine / Q000378:metabolism*; D007457:Iodine Radioisotopes; D017466:Receptors, Endothelin / Q000378:metabolism; D013268:Stimulation, Chemical; D013552:Swine; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology
D016232:Endothelins; D007457:Iodine Radioisotopes; D017466:Receptors, Endothelin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D013972:Thyrotropin; D007455:Iodine