RESUMO
Organization of chromatin by epigenetic mechanisms is essential for establishing and maintaining cellular identity in developing and adult organisms. A key question that remains unresolved about this process is how epigenetic marks are transmitted to the next cell generation during cell division. Here we provide a model to explain how trimethylated Lys 27 of histone 3 (H3K27me3), which is catalysed by the EZH2-containing Polycomb Repressive Complex 2 (PRC2), is maintained in proliferating cells. We show that the PRC2 complex binds to the H3K27me3 mark and colocalizes with this mark in G1 phase and with sites of ongoing DNA replication. Efficient binding requires an intact trimeric PRC2 complex containing EZH2, EED and SUZ12, but is independent of the catalytic SET domain of EZH2. Using a heterologous reporter system, we show that transient recruitment of the PRC2 complex to chromatin, upstream of the transcriptional start site, is sufficient to maintain repression through endogenous PRC2 during subsequent cell divisions. Thus, we suggest that once the H3K27me3 is established, it recruits the PRC2 complex to maintain the mark at sites of DNA replication, leading to methylation of H3K27 on the daughter strands during incorporation of newly synthesized histones. This mechanism ensures maintenance of the H3K27me3 epigenetic mark in proliferating cells, not only during DNA replication when histones synthesized de novo are incorporated, but also outside S phase, thereby preserving chromatin structure and transcriptional programs.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Epigênese Genética , Histonas/metabolismo , Modelos Biológicos , Fatores de Transcrição/metabolismo , Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Catálise , Linhagem Celular , Células Cultivadas , Cromatina/genética , Cromatina/metabolismo , Proteínas de Ligação a DNA/genética , Proteína Potenciadora do Homólogo 2 de Zeste , Fibroblastos/metabolismo , Fase G1/fisiologia , Genes Reporter , Histonas/genética , Humanos , Rim/citologia , Luciferases/metabolismo , Lisina/genética , Lisina/metabolismo , Metilação , Mutação , Proteínas de Neoplasias , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Complexo Repressor Polycomb 2 , Proteínas do Grupo Polycomb , Regiões Promotoras Genéticas , RNA Interferente Pequeno/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Fase S/fisiologia , Fatores de Transcrição/genética , TransfecçãoRESUMO
BACKGROUND: Brain natriuretic peptide (BNP) is increased in heart failure; however, the relative contribution of the right and left ventricles is largely unknown. AIM: To investigate if right ventricular function has an independent influence on plasma BNP concentration. METHODS: Right (RVEF), left ventricular ejection fraction (LVEF), and left ventricular end-diastolic volume index (LVEDVI) were determined in 105 consecutive patients by first-pass radionuclide ventriculography (FP-RNV) and multiple ECG-gated equilibrium radionuclide ventriculography (ERNV), respectively. BNP was analyzed by immunoassay. RESULTS: Mean LVEF was 0.51 (range 0.10-0.83) with 36% having a reduced LVEF (<0.50). Mean RVEF was 0.50 (range 0.26-0.78) with 43% having a reduced RVEF (<0.50). The mean LVEDVI was 92 ml/m2 with 22% above the upper normal limit (117 ml/m2). Mean BNP was 239 pg/ml range (0.63-2523). In univariate linear regression analysis LVEF, LVEDVI and RVEF all correlated significantly with log BNP (p<0.0001). In a multivariate analysis only RVEF and LVEF remained significant. The parameter estimates of the final adjusted model indicated that RVEF and LVEF influence on log BNP were of the same magnitude. CONCLUSION: BNP, which is a strong prognostic marker in heart failure, independently depends on both left and right ventricular systolic function. This might, at least in part, explain why BNP holds stronger prognostic value than LVEF alone.
Assuntos
Peptídeo Natriurético Encefálico/sangue , Disfunção Ventricular Esquerda/sangue , Disfunção Ventricular Direita/sangue , Adolescente , Adulto , Idoso , Biomarcadores/sangue , Feminino , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
Human papillomavirus type 16 (HPV-16) is the major risk factor for development of cervical cancer. The major oncoprotein E7 enhances cell growth control. However, E7 has in some reports been shown to induce apoptosis suggesting that there is a delicate balance between cell proliferation and induction of cell death. We have used the osteosarcoma cell line U2OS cells provided with E7 and the cdk2 inhibitor p21 (cip1/waf1) under inducible control, as a model system for the analysis of E7-mediated apoptosis. Our data shows that simultaneous expression of E7 and p21 proteins induces cell death, possibly because of conflicting growth control. Interestingly, E7/p21-induced cell death is associated with the activation of a newly identified mediator of apoptosis, namely cathepsin B. Activation of the cellular caspases is undetectable in cells undergoing E7/p21-induced apoptosis. To our knowledge, this is the first time a role for cathepsin B is reported in HPV-induced apoptotic signalling.
