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A thyroid hormone receptor coactivator negatively regulated by the retinoblastoma protein
1Department of Molecular Medicine and Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 15355 Lambda Drive, San Antonio, TX 78245, USA.
Abstract:
The retinoblastoma protein (Rb) plays a critical role in cell proliferation, differentiation, and development. To decipher the mechanism of Rb function at the molecular level, we have systematically characterized a number of Rb-interacting proteins, among which is the clone C5 described here, which encodes a protein of 1,978 amino acids with an estimated molecular mass of 230 kDa. The corresponding gene was assigned to chromosome 14q31, the same region where genetic alterations have been associated with several abnormalities of thyroid hormone response. The protein uses two distinct regions to bind Rb and thyroid hormone receptor (TR), respectively, and thus was named Trip230. Trip230 binds to Rb independently of thyroid hormone while it forms a complex with TR in a thyroid hormone-dependent manner. Ectopic expression of the protein Trip230 in cells, but not a mutant form that does not bind to TR, enhances specifically TR-dependent transcriptional activity. Coexpression of wild-type Rb, but not mutant Rb that fails to bind to Trip230, inhibits such activity. These results not only identify a coactivator molecule that modulates TR activity, but also uncover a role for Rb in a pathway that responds to thyroid hormone.
Insights
Researchers identified Trip230, a protein that interacts with retinoblastoma protein (Rb) and thyroid hormone receptor (TR). Trip230 acts as a coactivator, modulating TR activity and revealing Rb
Area of Science:
- Molecular Biology
- Cellular Biology
- Endocrinology
Background:
- Retinoblastoma protein (Rb) is crucial for cell cycle regulation.
- Thyroid hormone receptors (TRs) mediate thyroid hormone signaling.
- Understanding protein interactions is key to deciphering molecular mechanisms.
Purpose of the Study:
- To identify and characterize novel retinoblastoma protein (Rb)-interacting proteins.
- To elucidate the molecular function of a newly identified protein, Trip230.
- To investigate the role of Rb and Trip230 in thyroid hormone response pathways.
Main Methods:
- Systematic characterization of Rb-interacting proteins.
- Gene cloning and protein expression analysis.
- Yeast two-hybrid assays and co-immunoprecipitation to study protein-protein interactions.
- Reporter gene assays to assess transcriptional activity.
Main Results:
- A novel protein, Trip230, was identified and characterized.
- Trip230 binds to both Rb and thyroid hormone receptor (TR) via distinct domains.
- Trip230 enhances TR-dependent transcription in a thyroid hormone-dependent manner.
- Rb modulates Trip230's effect on TR activity.
Conclusions:
- Trip230 functions as a coactivator for thyroid hormone receptor (TR).
- Retinoblastoma protein (Rb) plays a role in thyroid hormone signaling.
- This study uncovers a novel link between cell cycle control and hormone response pathways.