SYT Associates with Human SNF/SWI Complexes and the C-terminal Region of Its Fusion Partner SSX1 Targets Histones

Abstract

A global transcriptional co-activator, the SNF/SWI complex, has been characterized as a chromatin remodeling factor that enhances accessibility of the transcriptional machinery to DNA within a repressive chromatin structure. On the other hand, mutations in some human SNF/SWI complex components have been linked to tumor formation. We show here that SYT, a partner protein generating the synovial sarcoma fusion protein SYT-SSX, associates with native human SNF/SWI complexes. The SYT protein has a unique QPGY domain, which is also present in the largest subunits, p250 and the newly identified homolog p250R, of the corresponding SNF/SWI complexes. The C-terminal region (amino acids 310 -387) of SSX1, comprising the SSX1 portion of the SYT-SSX1 fusion protein, binds strongly to core histones and oligonucleosomes in vitro and directs nuclear localization of a green fluorescence protein fusion protein. Experiments with serial C-terminal deletion mutants of SSX1 indicate that these properties map to a common region and also correlate with the previously demonstrated anchorage-independent colony formation activity of SYT-SSX in Rat 3Y1 cells. These data suggest that SYT-SSX interferes with the function of either the SNF/SWI complexes or another SYT-interacting co-activator, p300, by changing their targeted localization or by directly inhibiting their chromatin remodeling activities.The chromatin structure of active eukaryotic genes is subject to dynamic change by chromatin modifiers such as ATP-dependent chromatin remodeling factors (reviewed in Refs. 1-5). Homologs of a yeast prototype ATP-dependent remodeling complex, SNF/SWI, appear to be widely present in eukaryotes from yeast to humans (6 -8). Functions of the subunits of the SNF/ SWI complexes (9, 10) were first demonstrated by genetic studies in Saccharomyces cerevisiae, which showed that SWI1/ ADR6, SWI2/SNF2, SWI3, and SNF5 are required for the expression of a set of genes that include the HO, GAL1, SUC2, and ADH2 genes (11-13). In Drosophila melanogaster, the SWI2/SNF2 homolog brm was originally identified as a suppressor of Polycomb mutations (14). The Drosophila complex has been isolated, and some of the subunits have been characterized (15, 16), revealing that the SNF/SWI complexes are highly conserved in subunit composition and in primary structure among yeast, fruit fly, and human. A number of studies have described various biochemical properties of the human and yeast SNF/SWI complexes, as well as other ATP-dependent chromatin remodeling complexes (reviewed in Refs. 1-3, 17). For instance the SNF/SWI complexes are recruited by transcriptional activators to nucleosomal templates (18 -23), perturb nucleosome positioning, and facilitate binding of activator proteins to nucleosomes (24 -26). Mechanisms for this perturbation have been proposed to involve interconversion between two different nucleosomal states (27), sliding of histone octamers (28) or a change of DNA topology (29, 30).The human complexes are composed of at least nine subunits that include appar...

Human synovial sarcoma proto-oncogene Syt is essential for early embryonic development through the regulation of cell migration

“…6 In fact, SYT has been shown to bind to hBRM/hSNF2a, a major component of the SWI/SNFtype chromatin remodeling complex. 5,[7][8][9] Moreover, it was also shown that SYT interacts with the putative transcriptional factor AF10, histone acetyl transferase p300 and a component of histone deacetylase complex mSin3A. [10][11][12] Thus, it is possible that SYT regulates transcription through the binding to chromatin modifiers.…”

Mutations in the tyrosine kinase domain of the EGFR gene are rare in synovial sarcoma

“…Several reports have localized the SYT/SSX fusion protein to the nucleus and described its role in the regulation of chromatin remodelling. 20,21 Various groups have recently found mutations in the EGFR tyrosine kinase domain (exons 18-21) in non-small-cell lung carcinoma that sensitize tumor cells to the effects of gefitinib and appear to be associated with clinical responsiveness to this drug. The prevalence of missense mutations in these carcinomas varies from 20 to 40% in Asian countries (Taiwan, Korea, and Japan) to about 10% in non-east Asians.…”

The C terminus of the synovial sarcoma-associated SSX proteins interacts with the LIM homeobox protein LHX4

“…In line with the transcriptional repressor function(s) of the SSX proteins, PcG proteins form multi-protein complexes that maintain the repressed state of target genes by inducing changes in chromatin structure (Schuettengruber et al, 2007;Schwartz and Pirrotta, 2007). Through cellular colocalization studies, we and others have found that the SSXRD is responsible for (i) SSX nuclear localization, (ii) colocalization with PcG proteins, (iii) association with mitotic chromosomes, and (iv) association with core histones (dos Santos et al, 2000a;Kato et al, 2002). Through yeast two-hybrid screening, we have previously identified the SSX2IP (also known as ADIP) and RAB3IP proteins as in vivo interactors of the SSX KRAB-like domain .…”

“…Of these, the SNH domain directly interacts with the acute leukemia-associated transcription factor AF10 (de Bruijn et al, 2001a), the SWI/SNF ATPases BRM and BRG1 (Thaete et al, 1999;Perani et al, 2003;de Bruijn et al, 2006), the histone acetyltransferase p300 (Eid et al, 2000) and the corepressor mSin3A (Ito et al, 2004). Indirectly, the SS18 protein associates with yet another SWI/SNF protein, INI1 (Debernardi et al, 2002;Kato et al, 2002). The QPGY domain is a transcriptional coactivation domain and mediates multimerization of the SS18 protein (Brett et al, 1997;Thaete et al, 1999;Perani et al, 2003).…”