Tumor susceptibility gene 101 protein represses androgen receptor transactivation and interacts with p300

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 th e protein-coding region have been identified in human tumor samples and can cer cell lines, including prostate and breast carcinomas, and have been att ributed 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-termin al (encoding amino acids 230-391) fragments were cloned and used in both tr ansient transfection and protein binding experiments. The transient transfe ctions were carried in CV-1 cells. Protein-protein interactions were determ ined by both glutathione-S-transferase fusion protein binding and co-immuno precipitation. RESULTS. The N-terminal region of TSG101, when fused to the GALA DNA bindin g domain, can activate transcription; whereas the C-terminal region mediate s transcriptional repression. Full-length TSG101 or its separated regions r epressed 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 d irect 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 transcrip tion modulator to affect nuclear receptor-mediated transcriptional activati on, which raises the possibility that the tumor suppression by TSG101 obser ved previously may be mediated at least in, part by its effects on nuclear receptor function. Cancer 1999;86:689-96. (C) 1999 American Cancer Society.