ABSTRACT
Oncoprotein SS18-SSX is a hallmark of synovial sarcomas. However, as a part of the SS18-SSX fusion protein, SS18's function remains unclear. Here, we depict the structures of both human SS18/BRG1 and yeast SNF11/SNF2 subcomplexes. Both subcomplexes assemble into heterodimers that share a similar conformation, suggesting that SNF11 might be a homologue of SS18 in chromatin remodeling complexes. Importantly, our study shows that the self-association of the intrinsically disordered region, QPGY domain, leads to liquid-liquid phase separation (LLPS) of SS18 or SS18-SSX and the subsequent recruitment of BRG1 into phase-separated condensates. Moreover, our results show that the tyrosine residues in the QPGY domain play a decisive role in the LLPS of SS18 or SS18-SSX. Perturbations of either SS18-SSX LLPS or SS18-SSX's binding to BRG1 impair NIH3T3 cell transformation by SS18-SSX. Our data demonstrate that both LLPS and assembling into chromatin remodelers contribute to the oncogenic activity of SS18-SSX in synovial sarcomas.
Subject(s)
Proto-Oncogene Proteins , Repressor Proteins , Sarcoma, Synovial , Animals , Cell Transformation, Neoplastic , Humans , Mice , NIH 3T3 Cells , Oncogene Proteins, Fusion/genetics , Oncogene Proteins, Fusion/metabolism , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , Repressor Proteins/genetics , Repressor Proteins/metabolism , Sarcoma, Synovial/genetics , Sarcoma, Synovial/metabolism , Transcription Factors/genetics , Transcription Factors/metabolismABSTRACT
Chromatin remodelers are ATP (adenosine triphosphate)-powered motors that reposition nucleosomes throughout eukaryotic chromosomes. Remodelers possess autoinhibitory elements that control the direction of nucleosome sliding, but underlying mechanisms of inhibition have been unclear. Here, we show that autoinhibitory elements of the yeast Chd1 remodeler block nucleosome sliding by preventing initiation of twist defects. We show that two autoinhibitory elements-the chromodomains and bridge-reinforce each other to block sliding when the DNA-binding domain is not bound to entry-side DNA. Our data support a model where the chromodomains and bridge target nucleotide-free and ADP-bound states of the ATPase motor, favoring a partially disengaged state of the ATPase motor on the nucleosome. By bypassing distortions of nucleosomal DNA prior to ATP binding, we propose that autoinhibitory elements uncouple the ATP binding/hydrolysis cycle from DNA translocation around the histone core.
Subject(s)
Adenosine Triphosphatases/genetics , DNA-Binding Proteins/genetics , Nucleosomes/genetics , Saccharomyces cerevisiae Proteins/genetics , Adenosine Triphosphatases/chemistry , Adenosine Triphosphate/genetics , Chromatin Assembly and Disassembly/genetics , Chromosomes/genetics , DNA-Binding Proteins/chemistry , Histones/chemistry , Histones/genetics , Hydrolysis , Nucleosomes/chemistry , Protein Binding/genetics , Protein Domains/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae Proteins/chemistryABSTRACT
The SWI/SNF chromatin remodeling complex, which alters nucleosome positions by either evicting histones or sliding nucleosomes on DNA, is highly conserved from yeast to humans, and 20% of all human cancers have mutations in various subunits of the SWI/SNF complex. Here, we reported the crystal structure of the yeast Snf5-Swi3 subcomplex at a resolution of 2.65 Å. Our results showed that the Snf5-Swi3 subcomplex assembles into a heterotrimer with one Snf5 molecule bound to two distinct Swi3 molecules. In addition, we demonstrated that Snf5-Swi3 subcomplex formation is required for SWI/SNF function in yeast. These findings shed light on the important role of the Snf5-Swi3 subcomplex in the assembly and functional integrity of the SWI/SNF complex.
