title: RGS12TS-S localizes at nuclear matrix-associated subnuclear structures and represses transcription: structural requirements for subnuclear targeting and transcriptional repression.
abstract: RGS12TS-S, an 1,157-amino-acid RGS protein (regulator of G protein signaling), is a nuclear protein that exhibits a unique pattern of subnuclear organization into nuclear foci or dots when expressed endogenously or ectopically. We now report that RGS12TS-S is a nuclear matrix protein and identify structural determinants that target this protein to the nuclear matrix and to discrete subnuclear sites. We also determine the relationship between RGS12TS-S-decorated nuclear dots and known subnuclear domains involved in control of gene expression and provide the first evidence that RGS12TS-S is functionally involved in the regulation of transcription and cell cycle events. A novel nuclear matrix-targeting sequence was identified that is distinct from a second novel motif needed for targeting RGS12TS-S to nuclear dots. RGS12TS-S nuclear dots were distinct from Cajal bodies, SC-35 domains, promyelocytic leukemia protein nuclear bodies, Polycomb group domains, and DNA replication sites. However, RGS12TS-S inhibited S-phase DNA synthesis in various tumor cell lines independently of Rb and p53 proteins, and its prolonged expression promoted formation of multinucleated cells. Expression of RGS12TS-S dramatically reduced bromo-UTP incorporation into sites of transcription. RGS12TS-S, when tethered to a Gal4 DNA binding domain, dramatically inhibited basal transcription from a Gal4-E1b TATA promoter in a histone deacetylase-independent manner. Structural analysis revealed a role for the unique N-terminal domain of RGS12TS-S in its transcriptional repressor and cell cycle-regulating activities and showed that the RGS domain was dispensable for these functions. These results provide novel insights into the structure and function of RGS12TS-S in the nucleus and demonstrate that RGS12TS-S possesses biological activities distinct from those of other members of the RGS protein family.
authors.affiliation: Department of Pharmacology, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
authors.forename: Tapan K
authors.initials: TK
authors.lastname: Chatterjee
authors.forename: Rory A
authors.initials: RA
authors.lastname: Fisher
mesh_terms: D000818:Animals; D022003:Cell Nucleus Structures / Q000378:metabolism*; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004261:DNA Replication; D006801:Humans; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D020710:RGS Proteins / Q000235:genetics / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D016160:Retinoblastoma Protein / Q000378:metabolism; D016196:S Phase; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D020710:RGS Proteins; C106375:RGS12 protein, human; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D004247:DNA