RESUMO
Regulation of ribosomal transcription is under tight control from environmental stimuli, and this control involves changes in the chromatin structure. The underlying mechanism of how chromatin changes in response to nutrient and energy supply in the cell is still unclear. The chromatin-remodeling complex B-WICH is involved in activating the ribosomal transcription, and we show here that knock down of the B-WICH component WSTF results in cells that do not respond to glucose. The promoter is less accessible, and RNA pol I and its transcription factors SL1/TIF-1B and RRN3/TIF-1A, as well as the proto-oncogene c-MYC and the activating deacetylase SIRT7 do not bind upon glucose stimulation. In contrast, the repressive chromatin state that forms after glucose deprivation is reversible, and RNA pol I factors are recruited. WSTF knock down results in an accumulation of the ATPase CHD4, a component of the NuRD chromatin remodeling complex, which is responsible for establishing a repressive poised state at the promoter. The TTF-1, which binds and affect the binding of the chromatin complexes, is important to control the association of activating chromatin component UBF. We suggest that B-WICH is required to allow for a shift to an active chromatin state upon environmental stimulation, by counteracting the repressive state induced by the NuRD complex.
Assuntos
Montagem e Desmontagem da Cromatina/genética , Cromatina/genética , Glucose/genética , Complexo Mi-2 de Remodelação de Nucleossomo e Desacetilase/genética , Ribossomos/genética , Transcrição Gênica/genética , Adenosina Trifosfatases/genética , Linhagem Celular , Linhagem Celular Tumoral , Proteínas de Ligação a DNA/genética , Células HEK293 , Células HeLa , Humanos , Proteínas Nucleares/genética , Proteínas Pol1 do Complexo de Iniciação de Transcrição/genética , Proto-Oncogene Mas , Proteínas Proto-Oncogênicas c-myc/genética , RNA Polimerase I/genética , Sirtuínas/genética , Fatores de Transcrição/genéticaRESUMO
The chromatin-remodelling complex B-WICH, comprised of William syndrome transcription factor, the ATPase SNF2h and nuclear myosin, specifically activates RNA polymerase III transcription of the 5S rRNA and 7SL genes. However, the underlying mechanism is unknown. Using high-resolution MN walking we demonstrate here that B-WICH changes the chromatin structure in the vicinity of the 5S rRNA and 7SL RNA genes during RNA polymerase III transcription. The action of B-WICH is required for the binding of the RNA polymerase machinery and the regulatory factors c-Myc at the 5S rRNA and 7SL RNA genes. In addition to the c-Myc binding site at the 5S genes, we have revealed a novel c-Myc and Max binding site in the intergenic spacer of the 5S rDNA. This region also contains a region remodelled by B-WICH. We demonstrate that c-Myc binds to both sites in a Max-dependent way, and thereby activate transcription by acetylating histone H3. The novel binding patterns of c-Myc and Max link transcription of 5S rRNA to the Myc/Max/Mxd network. Since B-WICH acts prior to c-Myc and other factors, we propose a model in which the B-WICH complex is required to maintain an open chromatin structure at these RNA polymerase III genes. This is a prerequisite for the binding of additional regulatory factors.
Assuntos
Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Montagem e Desmontagem da Cromatina , Proteínas Proto-Oncogênicas c-myc/metabolismo , RNA Polimerase III/metabolismo , Fatores de Transcrição/metabolismo , Ativação Transcricional , Sítios de Ligação , Cromatina/química , Células HeLa , Histona Acetiltransferases/metabolismo , Histonas/metabolismo , Humanos , Ligação Proteica , RNA Ribossômico 5S/genética , RNA Citoplasmático Pequeno/genética , Partícula de Reconhecimento de Sinal/genéticaRESUMO
Actin and nuclear myosin 1c (NM1) cooperate in RNA polymerase I (pol I) transcription. NM1 is also part of a multiprotein assembly, B-WICH, which is involved in transcription. This assembly contains the chromatin remodeling complex WICH with its subunits WSTF and SNF2h. We report here that NM1 binds SNF2h with enhanced affinity upon impairment of the actin-binding function. ChIP analysis revealed that NM1, SNF2h, and actin gene occupancies are cell cycle-dependent and require intact motor function. At the onset of cell division, when transcription is temporarily blocked, B-WICH is disassembled due to WSTF phosphorylation, to be reassembled on the active gene at exit from mitosis. NM1 gene knockdown and motor function inhibition, or stable expression of NM1 mutants that do not interact with actin or chromatin, overall repressed rRNA synthesis by stalling pol I at the gene promoter, led to chromatin alterations by changing the state of H3K9 acetylation at gene promoter, and delayed cell cycle progression. These results suggest a unique structural role for NM1 in which the interaction with SNF2h stabilizes B-WICH at the gene promoter and facilitates recruitment of the HAT PCAF. This leads to a permissive chromatin structure required for transcription activation.
Assuntos
Actinas , Pontos de Checagem do Ciclo Celular , Montagem e Desmontagem da Cromatina/genética , Miosina Tipo I , RNA Ribossômico , Acetilação , Actinas/genética , Actinas/metabolismo , Adenosina Trifosfatases/genética , Adenosina Trifosfatases/metabolismo , Núcleo Celular/metabolismo , Proteínas Cromossômicas não Histona/genética , Proteínas Cromossômicas não Histona/metabolismo , Células HEK293 , Células HeLa , Histona-Lisina N-Metiltransferase/metabolismo , Humanos , Miosina Tipo I/genética , Miosina Tipo I/metabolismo , Regiões Promotoras Genéticas , Ligação Proteica , RNA Polimerase I/metabolismo , RNA Ribossômico/genética , RNA Ribossômico/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Transcrição GênicaRESUMO
The chromatin remodelling complex B-WICH, which comprises the William syndrome transcription factor (WSTF), SNF2h, and nuclear myosin 1 (NM1), is involved in regulating rDNA transcription, and SiRNA silencing of WSTF leads to a reduced level of 45S pre-rRNA. The mechanism behind the action of B-WICH is unclear. Here, we show that the B-WICH complex affects the chromatin structure and that silencing of the WSTF protein results in a compaction of the chromatin structure over a 200 basepair region at the rRNA promoter. WSTF knock down does not show an effect on the binding of the rRNA-specific enhancer and chromatin protein UBF, which contributes to the chromatin structure at active genes. Instead, WSTF knock down results in a reduced level of acetylated H3-Ac, in particular H3K9-Ac, at the promoter and along the gene. The association of the histone acetyl-transferases PCAF, p300 and GCN5 with the promoter is reduced in WSTF knock down cells, whereas the association of the histone acetyl-transferase MOF is retained. A low level of H3-Ac was also found in growing cells, but here histone acetyl-transferases were present at the rDNA promoter. We propose that the B-WICH complex remodels the chromatin structure at actively transcribed rRNA genes, and this allows for the association of specific histone acetyl-transferases.