Characterization of the functional domains and quantification in the cells of a steroid receptor-binding protein, SRB-RGS

We isolated the cDNA of a steroid receptor-binding protein, SRB-RGS, binding to the estrogen receptor (ER)α. SRB-RGS very efficiently suppressed the ERs-mediated transcriptional activities. SRB-RGS interacted with ER on DNA. SRB-RGS was localized in both the nucleus and cytoplasm in the cells. SRB-RGS induced cell death of HeLa cells. In the present paper, we examined the functional domains of SRB-RGS. The effects of SRB-RGS on the ERs-mediated transcriptional activities were exerted by the PDZ domain-containing region and/or the RGS domain-containing region of SRB-RGS. The nuclear localization signal (NLS) was in the RGS domain containing one basic region. Either the PDZ or RGS domains on SRB- RGS induced cell death. Either the PDZ or RGS domains on SRB-RGS were necessary for transcriptional suppression, subcellular localization and induction of the death in HeLa cells. The expression of SRB-RGS was observed in the cytoplasm or both the cytoplasm and nucleus of various types of cells by confocal laser-scanning microscopy after immunostaining of the cells. SRB-RGS was expressed in all types of cells examined by using real-time RT-PCR.