期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 104, 期 46, 页码 18303-18308出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0702857104
关键词
G protein; desensitization; G protein-coupled receptor; G protein-coupled receptor kinase; PKC
资金
- NIDDK NIH HHS [R01 DK019974, DK19974] Funding Source: Medline
The G protein-coupled thyrotropin (TSH)-releasing hormone (TRH) receptor forms homodimers. Regulated receptor dimerization increases TRH-induced receptor endocytosis. These studies test whether dimerization increases receptor phosphorylation, which could potentiate internalization. Phosphorylation at residues 355-365, which is critical for internalization, was measured with a highly selective phospho-site-specific antibody. Two strategies were used to drive receptor dimerization. Dimerization of a TRH receptor-FK506-binding protein (FKBP) fusion protein was stimulated by a dimeric FKBP ligand. The chemical dimerizer caused a large increase in TRH-dependent phosphorylation within 1 min, whereas a monomeric FKBP ligand had no effect. The dimerizer did not alter phoshorylation of receptors lacking the FKBP domain. Dimerization of receptors containing an N-terminal HA epitope also was induced with anti-HA antibody. Anti-HA IgG strongly increased TRI-induced phosphorylation, whereas monomeric Fab fragments had no effect. Anti-HA antibody did not alter phosphorylation in receptors lacking an HA tag. Furthermore, two phosphorylation-defective TRH receptors functionally complemented one another and permitted phosphorylation. Receptors with a D71A mutation in the second transmembrane domain do not signal, whereas receptors with four Ala mutations in the 355-365 region signal normally but lack phosphorylation sites. When D71A- and 4Ala-TRH receptors were expressed alone, neither underwent TRH-dependent phosphorylation. When they were expressed together, D71A receptor was phosphorylated by G protein-coupled receptor kinases in response to TRH. These results suggest that the TRH receptor is phosphorylated preferentially when it is in dimers or when preexisting receptor dimers are driven into microaggregates. Increased receptor phosphorylation may amplify desensitization.
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