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Specific activation of the thyrotropin receptor by trypsin
J Van Sande1, C Massart, S Costagliola
1Institute of Interdisciplinary Research, School of Medicine, Free University of Brussels, Belgium.
Molecular and Cellular Endocrinology
|May 31, 1996
Summary
Mild trypsin treatment of the TSH receptor mimics TSH action by relieving a negative constraint, suggesting its extracellular domain maintains this inhibition.
Area of Science:
- Endocrinology
- Molecular Biology
- Cell Signaling
Background:
- Activating mutations in the TSH receptor are linked to hyperthyroidism.
- These mutations suggest the wild-type TSH receptor may exist in a constrained conformation.
Purpose of the Study:
- To investigate the effect of mild proteolysis on TSH receptor signaling.
- To explore the concept of a constrained conformation in the TSH receptor.
Main Methods:
- Mild trypsin treatment of cells expressing human or dog TSH receptors.
- Measurement of cyclic AMP and inositol-phosphate accumulation.
- Antibody-based epitope mapping of the TSH receptor.
Main Results:
- Trypsin treatment specifically increased cyclic AMP, mimicking TSH action.
- This effect was specific to the TSH receptor and trypsin proteolysis.
- Trypsin removed a specific epitope (residues 354-359) from the extracellular domain.
Conclusions:
- Mild proteolysis can activate the TSH receptor, suggesting relief of a negative constraint.
- The C-terminal portion of the extracellular domain may maintain this constraint.
- Receptor activation, by various means, might involve overcoming inherent inhibitory forces.