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Binding properties of somatostatin receptor subtypes
Metabolism: Clinical and Experimental
|August 1, 1996
Summary
Researchers identified key mutations in somatostatin receptor 2 (sst2) that alter ligand binding, potentially guiding the development of new selective sst ligands. They also found sst4 receptors predominantly expressed in lung tissue, with high affinity for somatostatin-28.
Area of Science:
- Pharmacology
- Molecular Biology
- Endocrinology
Background:
- Five somatostatin receptor (SRIF) subtypes (sst1-5) are G-protein-coupled receptors.
- Naturally occurring somatostatins bind with high affinity to all subtypes, while synthetic analogs primarily target sst2.
- Previous reports of selective SRIF analogs could not be confirmed.
Purpose of the Study:
- To investigate the ligand-binding specificities of SRIF receptor subtypes.
- To identify amino acids responsible for ligand selectivity in sst2 using mutagenesis.
- To explore the expression and function of SRIF receptors in non-classical tissues like the lung.
Main Methods:
- Site-directed mutagenesis was used to alter amino acids in sst subtypes.
- Binding affinities of SRIF analogs were tested on mutated human receptors expressed in CHO and COS-1 cells.
- RT-PCR and autoradiography were employed to detect sst subtype expression in lung tissue.
Main Results:
- A single Ser305Phe mutation in sst1 significantly increased affinity for SMS 201-995, with a further Gln291Asn mutation yielding almost full sst2-like binding.
- SRIF and its analogs showed binding affinities in rat lung tissue correlating with sst4.
- RT-PCR confirmed predominant sst4 mRNA expression in mouse, rat, and human lung tissue.
Conclusions:
- Mutations in transmembrane helix VII of sst1 can confer sst2-like binding properties, aiding in the design of selective sst ligands.
- sst4 receptors are highly expressed in lung tissue and exhibit high-affinity binding for somatostatin-28, suggesting a role in pulmonary function.