p300/CREB Binding Protein-Related Protein p270 Is a Component of Mammalian SWI/SNF Complexes

Abstract

p300 and the closely related CREB binding protein (CBP) are transcriptional adaptors that are present in intracellular complexes with TATA binding protein (TBP) and bind to upstream activators including p53 and nuclear hormone receptors. They have intrinsic and associated histone acetyltransferase activity, suggesting that chromatin modification is an essential part of their role in regulating transcription. Detailed characterization of a panel of antibodies raised against p300/CBP has revealed the existence of a 270-kDa cellular protein, p270, distinct from p300 and CBP but sharing at least two independent epitopes with p300. The subset of p300/CBP-derived antibodies that cross-reacts with p270 consistently coprecipitates a series a cellular proteins with relative molecular masses ranging from 44 to 190 kDa. Purification and analysis of various proteins in this group reveals that they are components of the human SWI/SNF complex and that p270 is an integral member of this complex.The cellular protein p300 is a direct target of the transforming functions of the adenovirus E1A gene (19, 51) and as such is implicated in the regulation of both cell cycle-specific and tissue-specific gene expression (18,27,38,43,46,52,54). p300 is highly homologous (about 64% identical) to the cyclic AMP response element binding protein (CREB) coactivator, CBP (CREB binding protein) (5,11,17,30,34). Both p300 and CBP are present in intracellular complexes with the TATA binding protein (TBP) (1, 13). Both act as cofactors for p53 (6,21,33,44) and nuclear hormone receptors (9,24,28). Both also contain intrinsic and associated histone acetyltransferase (HAT) activity (39, 53), suggesting that chromatin modification is an essential part of their role in regulating transcription.A recent detailed characterization of a panel of antibodies raised against a mixture of native p300 and CBP revealed the existence of a 270-kDa cellular protein, distinct from p300 and CBP but sharing at least two independent antigenic determinants with p300 (13). Four of the eleven antibodies in the panel recognize p270. The subset of p300/CBP-derived antibodies that recognizes p270 consistently coprecipitates a series of cellular proteins with relative molecular masses ranging from 44 to 190 kDa. Typical of these is the antibody designated NM1, whose immunoprecipitation pattern is shown in Fig. 1. TBPspecific antibodies coprecipitate a subset of these proteins including p300, CBP, and the phosphoprotein species indicated in Fig. 1 as p64 and p59 (1, 13). Because the TBP-specific antibodies do not coprecipitate all of the p300 family-associated proteins, it is likely that the array of proteins seen in Fig. 1 represents more than one intracellular complex.We have now identified four of the remaining p300/CBP/ p270-associated proteins as members of another important cellular complex: the mammalian SWI/SNF complex. The 190-kDa protein visible in the p300-related complex is BRG1, the human homolog of the yeast transcriptional activator, SWI2/ SNF2. The 170-and 155-k...

An integrated genomic approach identifies ARID1A as a candidate tumor-suppressor gene in breast cancer

“…Here we report the discovery of ARID1A as a candidate TSG in the T47D breast cancer cell line by using this approach. ARID1A encodes a human homolog of yeast SWI1, which contains a DNA-binding motif (AT-rich interactive domain, ARID) and is an integral member of the hSWI/SNF complex, an ATPdependent, chromatin-remodeling, multiple-subunit enzyme (Takeuchi et al, 1997(Takeuchi et al, , 1998Dallas et al, 1998Dallas et al, , 2000Wang et al, 2004;Wilsker et al, 2004;Patsialou et al, 2005). An increasing body of evidence has demonstrated that SWI/SNF complexes have important roles in gene regulation (Winston and Carlson, 1992;Carlson and Laurent, 1994;Hirschhorn et al, 1995;Kennison, 1995;Sudarsanam et al, 1999Sudarsanam et al, , 2000, cell proliferation (Nagl et al, 2005(Nagl et al, , 2006(Nagl et al, , 2007 and development (Carlson and Laurent, 1994;Kennison, 1995).…”

Expression of p270 (ARID1A), a component of human SWI/SNF complexes, in human tumors

“…16,17 BRG1-associated factor-155 (BAF155) is occasionally deficient in tumor cell lines, 10 and BAF155-null mouse embryos die at an early implantation stage, indicating the gene is required for normal development although neoplasia in BAF155 heterozygotes has not been examined. 18 Despite this background, there is very little information on expression of SWI/SNF complex components other than hSNF5 in primary human tumor tissue.Human SWI/SNF complex components include a large subunit designated p270 19,20 or BAF-250 21 (HUGO Gene Nomenclature Committee, http://www.gene.ucl.ac.uk/nomenclature/, and the Mouse Genomic Nomenclature Committee, http://www.informatics.jax.org/mgihome/nomen/index.shtml, recommend the official gene designations ARID1A in humans and Arid1a in mice). p270 contains a DNA-binding domain (the ARID) that distinguishes a family of at least 14 human proteins, all of which are implicated in the regulation of differentiation and tumorigenesis.…”

Papel de BRG1 e Brm, reguladores globais de transcrição, na reversão fenotípica de células ST1 pela ação de glicocorticóides

“…A transformação pelo oncogene ras leva à perda da expressão da proteína mBrm nesta linhagem , já a proteína mBRG (Kwon et al, 1994;Wang et al, 1996bWang et al, e Östlund et al, 1997, tendo um importante papel na liberação de regiões específicas do DNA para transcrição gênica. Este complexo pode apresentar uma composição variada de proteínas (Wang et al, 1996a e b;Dallas et al, 1998e de La Serna et al, 2000, o que está relacionado com uma função transcricional específica (Kadam et al, 2000). Mesmo Brm e BRG são intercambiáveis e a presença de um ou de outro no complexo parece fazer com que este exerça diferentes funções (Aalfs et al, 2001 (Wang et al, 1996a), as quais fazem parte deste complexo multiprotéico.…”

“…Muitas proteínas, conhecidas por exercerem papéis importantes na regulação do ciclo celular, são capazes de interagir fisicamente com este complexo multiprotéico, ou com suas proteínas componentes. Por exemplo, pode-se citar a proteína p300/CREB (Dallas et al, 1998); GR (Östlund Farrants et al, 1997 e Fryer andArcher, 1998) e pRb ou proteínas da família (Dunaief et al, 1994;Singh et al, 1995;Strober et al, 1996;Trouche et al, 1997Strobeck et al, 2000e Zhang et al, 2000 e c-Myc (Cheng et al, 1999 (Mercado, 1997). Outra hipótese é de que esta proteína poderia corresponder à BAF155 ("BRG/Brm associated factor" 155), proteína de aproximadamente 155 kDa, que faz parte do complexo SWI/SNF em mamífero (Wang et al, 1996a), ou alguma outra proteína que também pode fazer parte ou estar associada ao complexo.…”

“…Também possuem atividade intrínseca de histona acetiltransferase (HAT), sugerindo uma regulação da transcrição através de mudanças conformacionais da cromatina, sendo capazes de interagir com o complexo SWI/SNF (Dallas et al, 1998 das células P7, apresenta um comportamento anormal, pois esta célula apresenta uma alta concentração desta proteína. Muchardt et al (1996) mostraram que Brm, após fosforilação, é degradada nas células em divisão mitótica, sendo novamente sintetizada quando as células entram em G1, além de sofrer um acúmulo em G0.…”