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Tumor susceptibility gene 101 protein represses androgen receptor transactivation and interacts with p300
1Liem Sioe Liong Molecular Biology Laboratory, Department of Surgery, Stanford University School of Medicine, Stanford, California, USA.
Background:
Functional inactivation of the tsg101 gene in mouse fibroblasts leads to cell transformation and the ability to form metastatic tumors in nude mice. Abnormal TSG101 transcripts with highly-specific deletions in the protein-coding region have been identified in human tumor samples and cancer cell lines, including prostate and breast carcinomas, and have been attributed to alternative splicing of TSG101 mRNA. The function of the TSG101 protein is not known, although its predicted sequence has suggested that it may function as a transcription factor.
Methods:
Human TSG101 N-terminal (encoding amino acids 10-240) and C-terminal (encoding amino acids 230-391) fragments were cloned and used in both transient transfection and protein binding experiments. The transient transfections were carried in CV-1 cells. Protein-protein interactions were determined by both glutathione-S-transferase fusion protein binding and co-immunoprecipitation.
Results:
The N-terminal region of TSG101, when fused to the GAL4 DNA binding domain, can activate transcription; whereas the C-terminal region mediates transcriptional repression. Full-length TSG101 or its separated regions repressed ligand-dependent transcriptional activation by nuclear receptors, including androgen receptor and estrogen receptor, which play central roles in prostate carcinoma and breast carcinoma, respectively. In addition, a direct association between TSG101 and the transcriptional co-factor p300 was demonstrated in vitro and in vivo.
Conclusions:
These results indicate that TSG101 can function as a transcription modulator to affect nuclear receptor-mediated transcriptional activation, which raises the possibility that the tumor suppression by TSG101 observed previously may be mediated at least in part by its effects on nuclear receptor function.
Insights
Tumor suppressor gene TSG101 modulates nuclear receptor activity, potentially explaining its role in preventing metastasis. Its N-terminal domain activates transcription, while the C-terminal represses it, impacting cancer cell growth.
Area of Science:
- Molecular Biology
- Cancer Research
- Gene Regulation
Background:
- TSG101 gene inactivation in mice causes cell transformation and metastasis.
- Abnormal TSG101 transcripts due to alternative splicing are found in human cancers.
- The function of TSG101 protein, predicted to be a transcription factor, remains largely unknown.
Purpose of the Study:
- To investigate the functional role of the TSG101 protein.
- To determine TSG101's mechanism of action in transcriptional regulation.
- To explore TSG101's potential involvement in nuclear receptor-mediated transcription.
Main Methods:
- Cloning and expression of human TSG101 N-terminal and C-terminal fragments.
- Transient transfections in CV-1 cells to assess transcriptional activity.
- Protein-protein interaction studies using glutathione-S-transferase (GST) pull-down and co-immunoprecipitation assays.
Main Results:
- TSG101 N-terminus activates transcription; C-terminus represses transcription.
- Full-length TSG101 and its fragments inhibit ligand-dependent transcription by androgen and estrogen receptors.
- Direct interaction between TSG101 and the transcriptional co-activator p300 was confirmed.
Conclusions:
- TSG101 acts as a transcription modulator influencing nuclear receptor activity.
- TSG101's tumor suppressive function may be linked to its regulation of nuclear receptors.
- These findings offer insights into TSG101's role in prostate and breast cancer progression.