Cyclin F Controls Cell-Cycle Transcriptional Outputs by Directing the Degradation of the Three Activator E2Fs.

E2F1, E2F2, and E2F3A, the three activators of the E2F family of transcription factors, are key regulators of the G1/S transition, promoting transcription of hundreds of genes critical for cell-cycle progression. We found that during late S and in G2, the degradation of all three activator E2Fs is controlled by cyclin F, the substrate receptor of 1 of 69 human SCF ubiquitin ligase complexes. E2F1, E2F2, and E2F3A interact with the cyclin box of cyclin F via their conserved N-terminal cyclin binding motifs. In the short term, E2F mutants unable to bind cyclin F remain stable throughout the cell cycle, induce unscheduled transcription in G2 and mitosis, and promote faster entry into the next S phase. However, in the long term, they impair cell fitness. We propose that by restricting E2F activity to the S phase, cyclin F controls one of the main and most critical transcriptional engines of the cell cycle.

Fosb Induction in Nucleus Accumbens by Cocaine Is Regulated by E2F3a.

The transcription factor ΔFosB has been proposed as a molecular switch for the transition from casual, volitional drug use into a chronically addicted state, but the upstream regulatory mechanisms governing ΔFosB expression are incompletely understood. In this study, we find a novel regulatory role for the transcription factor E2F3, recently implicated in transcriptional regulation by cocaine, in controlling ΔFosB induction in the mouse nucleus accumbens (NAc) following cocaine administration. We find that an E2F consensus sequence 500 bp upstream of the Fosb transcription start site is enriched for E2F3 specifically over other E2F isoforms. We further conclude that ΔFosB expression is regulated specifically by E2F3a, not E2F3b, that E2f3a expression is specific to D1 receptor-expressing medium spiny neurons, and that E2F3a overexpression in NAc recapitulates the induction of Fosb and ΔFosb mRNA expression observed after chronic cocaine exposure. E2F3a knockdown in NAc does not abolish ΔFosb induction by cocaine, a result consistent with previously published data showing that singular knockdown of upstream regulators of ΔFosB is insufficient to block cocaine-induced expression. Finally, to elucidate potential combinatorial epigenetic mechanisms involved in E2F3a's regulation of Fosb, we explore H3K4me3 enrichment at the Fosb promoter and find that it is not enhanced by E2F3a overexpression, suggesting that it may instead be a pre-existing permissive mark allowing for E2F3a to interact with Fosb. Together, these findings support a role for E2F3a as a novel, upstream regulator of the addiction-mediating transcription factor ΔFosB in NAc.

Transcription factor E2F3a regulates CASP8AP2 transcription and enhances sensitivity to chemotherapeutic drugs in acute lymphoblastic leukemia.

BACKGROUND: Low expression of E2F3a and caspase 8 associated protein 2 (CASP8AP2) are associated with poor prognosis of childhood acute lymphoblastic leukemia (ALL). METHODS: Dual-luciferase reporter assay and wild type as well as four mutated types of reporter plasmids were used to demonstrate the activation of E2F3a on CASP8AP2 transcription. The direct binding of E2F3a with the promoter of CASP8AP2 was shown by Chromatin Immunoprecipitation (ChIP). Cell proliferation activity and cell cycle were determined by MTS and flow cytometry in leukemic cells after treating with common chemotherapeutic drugs vincristine and daunorubicin. RESULTS: In this study, we found that up-regulation of E2F3a in leukemic cells led to increased fraction of cells in S and G2/M phase, accelerated proliferation, and enhanced sensitivity to vincristine and daunorubicin. ChIP and luciferase assay indicated that E2F3a could directly bind to two fragments in the wild type of CASP8AP2 promotor (- 206 to - 69 and - 677 to - 507), and activate its transcription activity which was reduced in mutated promotors. The effect of E2F3a on chemotherapeutic sensitivity of leukemic cells could be reversed by down-regulating CASP8AP2. CONCLUSIONS: E2F3a could promote transcription and expression of CASP8AP2. The effect of E2F3a on chemotherapeutic sensitivity of ALL cells was implemented by regulating CASP8AP2 expression to a great extent.

The role of combined analysis of E2F3a and CASP8AP2 expression in prognosis evaluation in pediatric acute lymphoblastic leukemia / 中华实用儿科临床杂志

Objective To investigate the role of combined analysis of E2F3a and CASP8AP2 expression in prognosis evaluation in pediatric acute lymphoblastic leukemia (ALL). Methods The study included 141 newly diag-nosed pediatric ALL patients enrolled at the Hematology Center,Beijing Children′s Hospital,Capital Medical Universi-ty between March 2008 and July 2010,including 97 boys and 44 girls(aged 1. 2 - 15. 5 years,median 5. 2 years). E2F3a and CASP8AP2 expressions were quantified in 141 children with ALL by adopting real - time quantitative poly-merase chain reaction (qPCR). Receiver operating characteristic (ROC)curve was used to find the best cut - off point to divide the patients into E2F3a or CASP8AP2 low - and high - expression groups,and the treatment outcome between the groups was compared. Cox regression was used to analyze the prognostic significance of the combined expression of E2F3a and CASP8AP2. Results The estimated 5 - year relapse free survival(RFS)rate,event free survival(EFS) rate and overall survival (OS)rate of patients with low - E2F3a and low - CASP8AP2 expression were (58. 9 ± 10. 0)％,(56. 0 ± 9. 9)％ and (72. 0 ± 9. 0)％,respectively. They were significantly lower than those of patients with high - E2F3a and high - CASP8AP2 expression,whose RFS,EFS and OS were (94. 9 ± 2. 5)％,(93. 7 ± 2. 7)％ and (96. 2 ± 2. 2)％,and the differences were all statistically significant(all P < 0. 05),respectively. Compared with other patients,the one with low expression of both E2F3a and CASP8AP2 had a poorer prognosis. In addition to MLL rear-rangements and minimal residual disease level at the end of remission induction,low expression of both E2F3a and CASP8AP2 remained as independent prognostic factors. Conclusion Low expressions of E2F3a and CASP8AP2 pre-dict poor prognosis in pediatric ALL. Combined assessment of E2F3a and CASP8AP2 expression could predict poor prognosis and relapse more accurately.

E2F3a gene expression has prognostic significance in childhood acute lymphoblastic leukemia.

OBJECTIVES: To study E2F3a expression and its clinical significance in children with acute lymphoblastic leukemia (ALL). METHODS: We quantified E2F3a expression at diagnosis in 148 children with ALL by real-time PCR. In the test cohort (n = 48), receiver operating characteristic (ROC) curve was used to find the best cut-off point to divide the patients into E2F3a low- and high-expression groups. The prognostic significance of E2F3a expression was investigated in the test cohort and confirmed in the validation cohort (n = 100). The correlations of E2F3a expression with the clinical features and treatment outcome of these patients were analyzed. RESULTS: ROC curve analysis indicated that the best cut-off point of E2F3a expression was 0.3780. In the test cohort, leukemia-free survival (LFS) and event-free survival (EFS) of the low-expression group were lower than those of the high-expression group (log rank: P = 0.026 for both). This finding was verified in the validation cohort. LFS, EFS, and overall survival were also lower in the low-expression group than in the high-expression group (log rank, P = 0.015, 0.008, and 0.002 respectively). E2F3a low expression was correlated with the existence of BCR-ABL fusion. An algorithm composed of E2F3a expression and minimal residual disease (MRD) could predict relapse or induction failure more precisely than current risk stratification. These results were still significant in the ALL patients without BCR-ABL fusion. CONCLUSIONS: Low expression of E2F3a was associated with inferior prognosis in childhood ALL. An algorithm composed of E2F3a expression and MRD could predict relapse or induction failure more precisely than that of the current risk stratification.