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The comparison of amino acid sequences of the SRG3 with SWI3 and its human homologues, BAF155 and BAF170. The YFK7, another yeast homologue of SWI3, is also presented. The regions showing highest homology are shown by rectangles with distinctive fillings (A). The SRG3 and human homologues of SWI3 protein contain the proline- and glutamine-rich domains that lack in the yeast SWI3. Amino acid comparisons of the three regions (Region I, II, and III) are shown in B and C. The three homologous regions of SRG3 and SWI3 protein displayed 33–47% identity and 61–64% similarity. The amino acids that are identical to consensus sequences are indicated as dots (C).
Source publication
We isolated a new mouse gene that is highly expressed in thymocytes, testis, and brain. This gene, SRG3, showed a significant sequence homology to SWI3, a yeast transcriptional activator, and its human homolog BAF155. SRG3 encodes 1,100 amino acids and has 33–47% identity with SWI3 protein over three regions. The SRG3 protein contains an acidic NH2...
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Citations
... The SWI/SNF chromatin remodeling complex is an ATP-dependent remodeler that drives conformational changes of nucleosomes by using the energy from ATP hydrolysis. The SWI/SNF complex is a multisubunit complex composed of at least 12 different subunits including Brg1, a core subunit containing the ATPase activity, and Srg3/mBaf155 (hereafter referred to as Srg3), a core subunit that controls the stability of this complex (8)(9)(10)(11). Whereas the SWI/SNF complex has been known to be essential for gene activation, increasing evidence also indicates its involvement in gene repression (12)(13)(14). ...
Significance
Germinal center (GC) response is central for generation of memory B cells and plasma cells that produce high-affinity antibodies, which are crucial for protective immunity against various foreign antigens. Even though key genetic factors for the GC formation are known, it is largely unknown how this process is controlled by epigenetic factors. Here we have demonstrated that the activity of SWI/SNF chromatin remodeling complex is required for the development of both GC B cells and follicular helper T cells. The SWI/SNF complex modulates Bcl-6–mediated Blimp-1 repression, and thus plays as a key mediator in the GC response. Our results provide fundamental insights into the epigenetic regulation in the GC reaction.
... The SWI/SNF complex has been shown to both augment and disrupt the function of essentially all steroid receptors, depending upon whether the BRG1 and BRM subunits are operational or disabled, respectively. The functional dependence upon SWI/SNF of estrogen receptors (ER) in breast cancer [98][99][100], glucocorticoid receptors (GR) in lymphoma and leukemia [101][102][103][104] and retinoids in digestive cancers suggests that an impairment of the SWI/ SNF complex, through the loss of BRG1 and/or BRM, could cause resistance to these steroids [25,105]. Like other steroid receptors, the androgen receptors (AR) [106][107][108][109] are also known to be SWI/SNF dependent. ...
... The glucocorticoid function is clearly SWI/SNF dependent [101,103,[116][117][118]; hence, a possible mechanism of glucocorticoid resistance that can occur in both lymphomas and leukemia could arise by SWI/SNF dysfunction through the loss of inactivation of one or more subunits. To this end, Pottier et al. [119] showed in all cells a statistically significant correlation between decreased expression of genes for core BRG1, BAF250 and BAF47 and resistance to prednisolone and dexamethasone, and knock down of BRG1-induced resistance to prednisolone in vitro. ...
The SWI/SNF complex is a key catalyst for gene expression and regulates a variety of pathways, many of which have anticancer
roles. Its central roles in cellular growth control, DNA repair, differentiation, cell adhesion and development are often
targeted, and inactivated, during cancer development and progression. In this review, we will discuss what is known about
how SWI/SNF is inactivated, and describe the potential impact of abrogating this complex. BRG1 and BRM are the catalytic subunits
which are essential for SWI/SNF function, and thus, it is not surprising that they are lost in a variety of cancer types.
As neither gene is mutated when lost, the mechanism of suppression, as well as the impact of potential gene activity restoration,
are reviewed.
KeywordsBrahma related gene 1 (BRG1)-Brahma (BRM)-SWI/SNF complex-Tumor suppressor-Epigenetic-Retinoblastoma protein-Subunits-Cancer progression
... Most notably, inhibition of mTOR signaling with rapamycin can reverse glucocorticoid resistance in leukemic lymphoblasts inducing posttranscriptional downregulation of MCL1 20 , however, we failed to detect changes in the protein levels of this antiapoptotic factor in cells treated with CompE plus dexamethasone (data not shown). Similarly, we did not detect changes in the differentiation arrest of T-ALL cells that could be linked to differential glucocorticoid sensitivity or transcriptional changes in the SRG3 gene (data not shown), two mechanisms proposed to reduce the sensitivity to glucocorticoid-induced apoptosis downstream of NOTCH1 activation in mouse primary thymocytes [24][25][26][27] . ...
SRG3 plays essential roles both in early mouse embryogenesis, and in extra-embryonic vascular development. In addition, As one of the core components of the SWI/SNF-like BAF complex, SRG3 serves as the scaffold protein, and its protein level controls the stability of the BAF complex, which controls diverse physiological processes through transcriptional regulation. However, little is known about how the protein level of SRG3 is regulated in mammalian cells. Previously, we identified a murine ubiquitin ligase Wwp2 and demonstrated that it interacts with pluripotency associated key transcription factor Oct4 and RNA polymerase II large subunit Rpb1, promoting their ubiquitination and degradation. Here, we report that Wwp2 acts as an ubiquitin ligase of SRG3. Our results show that Wwp2 and SRG3 form protein complexes and co-localize in the nucleus in mammalian cells. The interaction is mediated through the WW domain of Wwp2 and the PPPY motif of SRG3, respectively. Importantly, Wwp2 promotes ubiquitination and degradation of SRG3 through the ubiquitin-proteasome system. The expression of a catalytically inactive mutant of Wwp2 abolishes SRG3 ubiquitination. Collectively, our study opens up a new avenue to understand how the protein level of SRG3 is regulated in mammalian cells.
Mammalian SWI/SNF complexes are evolutionary conserved, ATP-dependent chromatin remodeling units. BAF155 in the SWI/SNF complex contains several highly conserved domains, including SANT, SWIRM, and leucine zipper domains. The biological roles of the SWIRM domain remain unclear; however, both structural and biochemical analyses of this domain have suggested that it could mediate protein-protein or protein-DNA interactions during the chromatin remodeling process. The human BAF155 SWIRM domain was cloned into the Escherichia coli expression vector pMAL-c2X and purified using affinity chromatography for structural analysis. We report the backbone 1H, 15N, and 13C resonance assignments and secondary structure of this domain using nuclear magnetic resonance (NMR) spectroscopy and the TALOS+ program. The secondary structure consists of five α-helices that form a typical histone fold for DNA interactions. Our data suggest that the BAF155 SWIRM domain interacts with nucleosome DNA (K
d = 0.47 μM).
Mouse T cells overexpressing the SRG3 protein displayed morphological changes; the cells were enlarged and their shapes were irregular compared to the normal parental cells. In addition, growth rate of the cells was dramatically reduced and their DNA contents were increased. The increased DNA contents were due to an increase in number of chromosomes in these cells. We have observed similar results in S. cerevisiae cells overexpressing the yeast SWC protein. Yeast cells overexpressing SWC protein displayed the phenotypes of highly elongated buds and 2C DNA content. These results suggest that the SRG3/SWC protein plays an important role in cell growth and cell cycle progression.
We have cloned Af10, the murine homologue of the MLL partner gene AF10. The predicted open reading frame of Af10 contains 1069 aa which are 90% identical to those of AF10. Af10 contains an N-terminal cysteine-rich region with a LAP/PHD finger, a leucine zipper domain and a glutamine-rich region at the C-terminus, features also found in the human proteins AF10 and AF17. A single 5.5-kb transcript was detected in murine tissues with the highest level of expression in the testes. A polyclonal antibody raised to the cysteine-rich region of AF10 was able to identify a double band of 140 kDa on Western analysis in mouse testicular extracts. After subcellular separation Af10 was identified in both the nuclear and cytoplasmic extracts, again as a double band of 140 kDa in size. In situ hybridisation studies were performed with sense and antisense digoxigenin-labelled oligonucleotides. High levels of expression were noted in postmeiotic germ cells, especially in spermatids from around stage VI to stage VIII. High levels of expression were also seen in the white matter of the cerebellum, extending into the granular layer. The expression in differentiated rather than in proliferating cells suggests that the role of Af10 may lie in the suppression of proliferation rather than in differentiation. Since the LAP/PHD finger domains are lost in the MLL–AF10 fusion, arguably such a function could be carried out by this domain.
Involvement of glucocorticoids (GCs) in the homeostasis of immune system has been extensively studied. However, numerous questions remain unresolved, including the role played by these hormones in the physiology of thymus gland, a central, key organ involved in T-cell maturation. In this study, we review the available information on the relationships between GCs and thymus gland with special emphasis on glucocorticoid receptor (GR) expression in the organ, the presumptive endogenous production of GCs in the thymus gland, and the role played by GCs in the development of thymocytes, thymic epithelial cells, and thymic dendritic cells (DCs). Our review concludes (1) the lack of correlation between GR expression on thymocyte subsets and sensitivity to GCs; (2) however, GCs could affect the maturation of lymphocyte progenitors which colonize the thymic primordium during early ontogeny; (3) furthermore, GCs affect also the development of main thymic stromal components, including epithelium and DCs; (4) the involvement of GCs in the determination of intrathymic T-cell repertoire is an important matter of discussion although recent data support a lack of effects of GCs on those processes.
During the process of B cell development, transcription factors, such as E2A and Ebf1, have been known to play key roles. Although transcription factors and chromatin regulators work in concert to direct the expression of B lineage-specific genes, little is known about the involvement of regulators for chromatin structure during B lymphopoiesis. In this article, we show that deletion of Srg3/mBaf155, a scaffold subunit of the SWI/SNF-like BAF complex, in the hematopoietic lineage caused defects at both the common lymphoid progenitor stage and the transition from pre-pro-B to early pro-B cells due to failures in the expression of B lineage-specific genes, such as Ebf1 and Il7ra, and their downstream target genes. Moreover, mice that were deficient in the expression of Brg1, a subunit of the complex with ATPase activity, also showed defects in early B cell development. We also found that the expression of Ebf1 and Il7ra is directly regulated by the SWI/SNF-like BAF complex. Thus, our results suggest that the SWI/SNF-like BAF complex facilitates early B cell development by regulating the expression of B lineage-specific genes.
SRG3 (SWI3-related gene) is a core subunit of mouse SWI/SNF complex and is known to play a critical role in stabilizing the SWI/SNF complex by attenuating its proteasomal degradation. SWI/SNF chromatin remodeling complex is reported to act as an important endogenous regulator in the proliferation and differentiation of mammalian neural stem cells. Because limited expression of SRG3 occurs in the brain and thymus during mouse embryogenesis, it was hypothesized that the altered SRG3 expression level might affect the process of adult hippocampal neurogenesis. Due to the embryonic lethality of homozygous knockout mice, this study focuses on dissecting the effect of overexpressed SRG3 on adult hippocampal neurogenesis. The BrdU incorporation assay, immunostaing with neuronal markers for each differentiation stage, and imunoblotting analysis with intracellular molecules involved in survival in adult hippocampal neurogenesis found no alteration, suggesting that the overexpression of SRG3 protein in mature neurons had no effect on the entire process of adult hippocampal neurogenesis including proliferation, differentiation, and survival.
