TY - JOUR
T1 - TSH action on cAMP binding to the regulatory subunits of cAMP-dependent protein kinases in pig thyroid cell cultures
AU - Abdelkhalek, M. Ben
AU - Breton, M. F.
AU - Feliers, D.
AU - Haye, B.
AU - Pavlovic-Hournac, M.
N1 - Funding Information:
The authors are grateful to Mrs 0. Leg& for her expert technical assistance in the thyroid cell preparation and culture. They also thank the National Institute of Health (Bethesda) for donating the bTSH and Sobe-vir (Rethel) for providing porcine thyroid glands. This study was partially supported (B.H.1 by ‘Association de la Recherche sur le Cancer’ (ARC) and the ‘Fondation pour la Recherche Medicale’ (FRM). The financial aid to Mr M. Ben Abdelkhalek obtained through the international cooperation between CNRS and CNR MAROC is also acknowledged.
PY - 1994/2
Y1 - 1994/2
N2 - This study examines the mechanism of TSH action on the cAMP-dependent protein kinases (PKA) by measuring the catalytic activity of the two PKA isozymes (PKA I and PKA II) and their capacity to bind cAMP to the regulatory subunits (RI and RII) in thyroid cell cultures exposed for two days to different doses of TSH. In TSH-treated cell cultures a selective down regulation (up to 60%) of the catalytic activity was found; the PKA I was down regulated at lower TSH doses (0.1 mU/ml and even 0.05 mU/ml) than was the PKA II (1.0 mU/ml TSH). At the dose of 1.0 mU/ml the loss of the catalytic activity in PKA I and PKA II was respectively 60% and 40%. No free catalytic activity was found either in control or in TSH-treated cells. Binding of cAMP to regulatory subunits (R) measured under exchange conditions at 37°C, showed that no change in total regulatory subunit protein content occurs in TSH-treated cells. Binding of cAMP to R subunits at 4°C (when only free cAMP binding sites are measured) revealed an important endogenous occupancy of cAMP binding sites of RI and RII isoreceptors under basal conditions (40%) and a significantly increased occupancy after exposure of cells to TSH (60%). Pools of regulatory subunits with more than 50% of sites occupied, which were devoid of enzyme activity, were found both, in control and TSH-exposed cells. They were identified as RI subunits which represented a mixed population of native and partly degraded molecules. In summary, in thyroid cell cultures, TSH when chronically present, has an independent action on the catalytic and the regulatory subunits of PKAs. The catalytic subunit activity was down regulated in parallel with an increased residual cAMP binding to regulatory subunits, but with no change in total regulatory subunit protein. The increased fractional saturation of cAMP-binding sites in TSH-treated cells renders their PKAs more sensitive to further stimulations and may help understand the molecular mechanism of the tonic effect of TSH on thyroid cells in culture.
AB - This study examines the mechanism of TSH action on the cAMP-dependent protein kinases (PKA) by measuring the catalytic activity of the two PKA isozymes (PKA I and PKA II) and their capacity to bind cAMP to the regulatory subunits (RI and RII) in thyroid cell cultures exposed for two days to different doses of TSH. In TSH-treated cell cultures a selective down regulation (up to 60%) of the catalytic activity was found; the PKA I was down regulated at lower TSH doses (0.1 mU/ml and even 0.05 mU/ml) than was the PKA II (1.0 mU/ml TSH). At the dose of 1.0 mU/ml the loss of the catalytic activity in PKA I and PKA II was respectively 60% and 40%. No free catalytic activity was found either in control or in TSH-treated cells. Binding of cAMP to regulatory subunits (R) measured under exchange conditions at 37°C, showed that no change in total regulatory subunit protein content occurs in TSH-treated cells. Binding of cAMP to R subunits at 4°C (when only free cAMP binding sites are measured) revealed an important endogenous occupancy of cAMP binding sites of RI and RII isoreceptors under basal conditions (40%) and a significantly increased occupancy after exposure of cells to TSH (60%). Pools of regulatory subunits with more than 50% of sites occupied, which were devoid of enzyme activity, were found both, in control and TSH-exposed cells. They were identified as RI subunits which represented a mixed population of native and partly degraded molecules. In summary, in thyroid cell cultures, TSH when chronically present, has an independent action on the catalytic and the regulatory subunits of PKAs. The catalytic subunit activity was down regulated in parallel with an increased residual cAMP binding to regulatory subunits, but with no change in total regulatory subunit protein. The increased fractional saturation of cAMP-binding sites in TSH-treated cells renders their PKAs more sensitive to further stimulations and may help understand the molecular mechanism of the tonic effect of TSH on thyroid cells in culture.
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U2 - 10.1016/0303-7207(94)90152-X
DO - 10.1016/0303-7207(94)90152-X
M3 - Article
C2 - 7514548
AN - SCOPUS:0028147671
VL - 99
SP - 103
EP - 110
JO - Molecular and Cellular Endocrinology
JF - Molecular and Cellular Endocrinology
SN - 0303-7207
IS - 1
ER -