ABSTRACT
The process of thymocyte development requires an exquisite regulation of many genes via transcription factors and chromatin remodeling activities. Even though the SWI/SNF chromatin remodeling complex has been thought to play important roles during thymocyte development, its known function is very limited. In this study, we show that the SWI/SNF chromatin remodeling activity is finely regulated during thymocyte maturation process, especially during thymocyte selections. We found that TCR signaling directly down-regulates mBRG1 and SWI3-related gene, the core components of murine SWI/SNF complex, during thymocyte maturation. Constitutive expression of SWI3-related gene in developing thymocytes attenuated the down-regulation of the SWI/SNF complex and resulted in a change in the expression of genes such as linker for activation of T cells and casitas B lineage lymphoma, which affected the TCR-mediated intracellular signaling pathway. The defects in TCR signaling resulted in the disruption of both positive and negative selections in specific TCR transgenic mice systems. Our results state, for the first time, that the chromatin remodeling activity needs to be finely controlled for proper thymocyte selection and maturation processes.
Subject(s)
Cell Differentiation/immunology , Chromatin/metabolism , Chromosomal Proteins, Non-Histone/antagonists & inhibitors , Down-Regulation/immunology , Receptors, Antigen, T-Cell/physiology , Signal Transduction/immunology , T-Lymphocyte Subsets/immunology , Thymus Gland/immunology , Transcription Factors/antagonists & inhibitors , Animals , Cell Differentiation/genetics , Cells, Cultured , Chromatin/genetics , Chromosomal Proteins, Non-Histone/physiology , Down-Regulation/genetics , Female , Growth Inhibitors/antagonists & inhibitors , Growth Inhibitors/biosynthesis , Growth Inhibitors/genetics , Male , Mice , Mice, Inbred A , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , Receptors, Antigen, T-Cell/antagonists & inhibitors , Receptors, Antigen, T-Cell/genetics , Repressor Proteins/antagonists & inhibitors , Repressor Proteins/biosynthesis , Repressor Proteins/genetics , Signal Transduction/genetics , T-Lymphocyte Subsets/cytology , T-Lymphocyte Subsets/metabolism , Thymus Gland/cytology , Thymus Gland/metabolism , Trans-Activators/antagonists & inhibitors , Trans-Activators/biosynthesis , Trans-Activators/genetics , Transcription Factors/physiologyABSTRACT
The mammalian SWI/SNF complex is an evolutionarily conserved ATP-dependent chromatin remodeling complex that consists of nine or more components. SRG3, a murine homologue of yeast SWI3, Drosophila MOIRA, and human BAF155, is a core component of the murine SWI/SNF complex required for the regulation of transcriptional processes associated with development, cellular differentiation, and proliferation. Here we report that SRG3 interacts directly with other components of the mammalian SWI/SNF complex such as SNF5, BRG1, and BAF60a. The SWIRM domain and the SANT domain were required for SRG3-SNF5 and SRG3-BRG1 interactions, respectively. In addition, SRG3 stabilized SNF5, BRG1, and BAF60a by attenuating their proteasomal degradation, suggesting its general role in the stabilization of the SWI/SNF complex. Such a stabilization effect of SRG3 was not only observed in the in vitro cell system, but also in cells isolated from SRG3 transgenic mice or knock-out mice haploinsufficient for the Srg3 gene. Taken together, these results suggest the critical role of SRG3 in the post-transcriptional stabilization of the major components of the SWI/SNF complex.
Subject(s)
Chromatin Assembly and Disassembly/physiology , Chromosomal Proteins, Non-Histone/metabolism , Proteasome Endopeptidase Complex/metabolism , Transcription Factors/metabolism , Animals , COS Cells , Cell Cycle Proteins/genetics , Cells, Cultured , Chlorocebus aethiops , Chromosomal Proteins, Non-Histone/genetics , DNA Helicases/genetics , DNA Helicases/metabolism , Drosophila , Drosophila Proteins/genetics , Mice , Mice, Knockout , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Proteasome Endopeptidase Complex/genetics , SMARCB1 Protein , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae Proteins/genetics , Sequence Homology, Amino Acid , Trans-Activators/genetics , Transcription Factors/deficiency , Transcription Factors/geneticsABSTRACT
Nitric oxide (NO) plays many roles in the immune system. It has been known that NO rescues thymocytes from glucocorticoid (GC)-induced apoptosis. However, the downstream target of NO in the protection from GC-induced thymocyte apoptosis has yet to be identified. We previously reported that GC sensitivity of developing thymocytes is dependent on the expression level of SRG3. In the present report, we found that NO repressed the SRG3 expression in both primary thymocytes and 16610D9 thymoma cells. Specifically, NO down-regulated the transcription of SRG3 via the inactivation of the transcription factor Sp1 DNA-binding activity to the SRG3 promoter. In addition, overexpression of SRG3 by a heterologous promoter reduced NO-mediated rescue of thymocytes from GC-induced apoptosis. These observations strongly suggest that NO may be involved in protecting immature thymocytes from GC-induced apoptosis by repressing the SRG3 expression in thymus.
