Open AccessIn Chinese Hamster Ovary K1 Cells Dog and Human Thyrotropin Receptors Activate Both the Cyclic AMP and the Phosphatidylinositol 4,5‐Bisphosphate Cascades in the Presence of Thyrotropin and the Cyclic AMP Cascade in Its Absence
Author(s) -
Sande Jacqueline,
Swillens Stéphane,
Gerard Catherine,
Allgeier Anouk,
Massart Claude,
Vassart Gilbert,
Dumont Jacques E.
Publication year - 1995
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1995.0338k.x
Subject(s) - thyrotropin receptor , chinese hamster ovary cell , medicine , endocrinology , phosphatidylinositol , receptor , ovary , luteinizing hormone , chemistry , biology , signal transduction , hormone , microbiology and biotechnology , thyroid , graves' disease
Thyrotropic hormone, through its human thyrotropin receptor, activates both the cyclic AMP and the phosphatidylinositol 4,5‐bisphosphate‐phospholipase‐C cascades in human thyroid cells and in Chinese hamster ovary cells (CHO‐K1) expressing this receptor. However, thyrotropin only activates the cyclic ‐AMP cascade in dog thyroid cells. In order to establish whether this different pattern of responses reflects a different structure of the human and dog thyrotropin receptors, CHO‐K1 cells were permanently transfected with a plasmid coding for one or the other receptor. For various levels of receptor expression, CHO‐K1 cells expressing either receptor presented qualitatively similar cyclic AMP and inositol phosphates responses to thyrotropin. This suggests that the difference in the response of the dog and human thyroid to thyrotropin involves elements of the phosphatidylinositol 4,5‐bisphosphate cascade downstream of the receptor. In CHO‐K1 cells overexpressing the thyrotropin receptor, the basal level of cyclic AMP was raised, suggesting a constitutive activity of the wild‐type receptor. This was confirmed in COS‐7 cells transiently expressing the human or dog thyrotropin receptors, the basal cyclic AMP levels of these cells increased in parallel with thyrotropin binding. This spontaneous activity of the thyrotropin receptor may have physiological and pathological consequences.