Project description:E2F-transcription factors activate many genes involved in cell cycle progression, DNA repair, and apoptosis. Hence, E2F-dependent transcription must be tightly regulated to prevent tumorigenesis, and therefore metazoan cells possess multiple E2F regulation mechanism. The best-known is the Retinoblastoma protein (RB), which is mutated in many cancers. Atypical E2Fs (E2F7 and -8) can repress E2F-target gene expression independently of RB and are rarely mutated in cancer. Therefore, they may act as emergency brakes in RB-mutated cells to suppress tumor growth. Currently it is unknown if and how RB and atypical E2Fs functionally interact in vivo. Here, we demonstrate that mice with liver-specific combinatorial deletion of Rb and E2f7/8 have reduced life spans compared to E2f7/8 or Rb deletion alone. This was associated with increased proliferation and enhanced malignant progression of liver tumors. Hence, atypical repressor E2Fs and RB cooperatively act as tumor suppressors in hepatocytes. We propose that the complex interactions between atypical E2Fs and RB on maintenance of genetic stability underlie this context-dependency.
Project description:Upon G1-S transition, cyclin-dependent kinases (CDKs) phosphorylate the retinoblastoma tumor suppressor protein (pRB) to release E2F transcription factors, which activate transcriptional programs, required for S-phase entry. Beyond the G1-S transition, pRB activity remains poorly understood. Our lab has discovered that hyperphosphorylated pRB (ppRB), found beyond G1, retains exclusive binding to E2F1 through an alternate E2F1-‘specific’ binding site at the pRB c-terminus. We have developed a gene-targeted mouse model that is defective for the E2F1-‘specific’ interaction. We are exploring the function of this complex through genome-wide expression profiling. Overall, this work suggests an alternate pRB-E2F1 complex persists beyond the G1-S transition to establish regions of constitutive heterochromatin
Project description:Upon G1-S transition, cyclin-dependent kinases (CDKs) phosphorylate the retinoblastoma tumor suppressor protein (pRB) to release E2F transcription factors, which activate transcriptional programs, required for S-phase entry. Beyond the G1-S transition, pRB activity remains poorly understood. Our lab has discovered that pRB retains exclusive binding to E2F1 through an alternate E2F1-‘specific’ binding site at the pRB c-terminus independent of CDK phosphorylation. We have developed a gene-targeted mouse model that is defective for the E2F1-‘specific’ interaction. We are exploring the function of this complex through genome-wide binding and expression profiling. Overall, this work suggests an alternate pRB-E2F1 complex persists independent of CDK phosphorylation to establish regions of constitutive heterochromatin
Project description:Upon G1-S transition, cyclin-dependent kinases (CDKs) phosphorylate the retinoblastoma tumor suppressor protein (pRB) to release E2F transcription factors, which activate transcriptional programs, required for S-phase entry. Beyond the G1-S transition, pRB activity remains poorly understood. Our lab has discovered that hyperphosphorylated pRB (ppRB), found beyond G1, retains exclusive binding to E2F1 through an alternate E2F1-‘specific’ binding site at the pRB c-terminus. We have developed a gene-targeted mouse model that is defective for the E2F1-‘specific’ interaction. We are exploring the function of this complex through genome-wide expression profiling. Overall, this work suggests an alternate pRB-E2F1 complex persists beyond the G1-S transition to establish regions of constitutive heterochromatin.
Project description:Upon G1-S transition, cyclin-dependent kinases (CDKs) phosphorylate the retinoblastoma tumor suppressor protein (pRB) to release E2F transcription factors, which activate transcriptional programs, required for S-phase entry. Beyond the G1-S transition, pRB activity remains poorly understood. Our lab has discovered that pRB retains exclusive binding to E2F1 through an alternate E2F1-‘specific’ binding site at the pRB c-terminus independent of CDK phosphorylation. We have developed a gene-targeted mouse model that is defective for the E2F1-‘specific’ interaction. We are exploring the function of this complex through genome-wide binding and expression profiling. Overall, this work suggests an alternate pRB-E2F1 complex persists independent of CDK phosphorylation to establish regions of constitutive heterochromatin.
Project description:The retinoblastoma protein (pRB) is best known for regulating cell proliferation through E2F transcription factors. In this report we investigate the properties of a targeted mutation that disrupts pRB interactions with the transactivation domain of E2Fs. Mice that carry this mutation endogenously (Rb1DeltaG) are defective in regulating E2F target genes. Surprisingly, cell cycle regulation in Rb1DeltaG/DeltaG MEFs strongly resembles that of wild type. In a serum deprivation induced cell cycle exit, Rb1DeltaG/DeltaG MEFs display a similar magnitude of E2F target gene derepression as Rb1-/-, even though Rb1DeltaG/DeltaG cells exit the cell cycle normally. Interestingly, cell cycle arrest in Rb1DeltaG/DeltaG MEFs is responsive to p16 expression, indicating that the DeltaG-pRB protein can be activated in G1 to arrest proliferation through non-E2F mechanisms. Some Rb1DeltaG/DeltaG mice die neonatally with a muscle degeneration phenotype, while the others live a normal lifespan with no evidence of spontaneous tumor formation. Histological analysis reveals discrete examples of hyperplasia in the mammary epithelium, but most tissues appear normal while being accompanied by derepression of pRB regulated E2F targets. This suggests that non-E2F, pRB dependent pathways may have a more relevant role in proliferative control than previously identified. Total RNA was extracted from littermate paired WT, DeltaG and null MEFs induced to enter quiencense by Serum deprivation. Expresssion levels were analyzed by Affymetrix GeneChip Mouse Gene 1.0ST Array. Relative expression was determined by BRB-Array Tools software to generate RMA values.
Project description:The activating E2F-transcription factors are best known for their dependence on the Retinoblastoma protein and their role in cellular proliferation. E2F3 is uniquely amplified in specific human tumours where its expression is inversely correlated with the survival of patients. Here, E2F3 interaction partners were identified by mass spectrometric analysis. We show that the SNF2-like HELLS interacts with E2F3 in vivo and cooperates with its oncogenic functions. Depletion of HELLS severely perturbs the induction of E2F-target genes, hinders cell cycle re-entry and growth. Using chromatin immmunoprecipitation coupled to sequencing we identified genome-wide targets of HELLS and E2F3. Our analysis revealed that HELLS binds near promoters of active genes, including the trithorax-related MLL1, and co-regulates E2F3-dependent genes. Our analysis is the first to link HELLS with E2F-controlled processes that are critical to establish a proliferative tumour circuitry. Strikingly, just as E2F3, HELLS is overexpressed in human tumours including prostate cancer, indicating that either factor may contribute to the malignant progression of tumours. Our work reveals that HELLS is important for E2F3 in tumour cell proliferation. Examination of E2F3, Hells, and H3K27me3 in 2 cell types.
Project description:The most frequent focal alterations in human retinoblastoma are RB mutation and MYCN amplification. Whether MYCN overexpression drives retinoblastoma has not been assessed in model systems. Here, we show that Rb inactivation collaborates strongly with MYCN overexpression to lead to retinoblastoma in mice. MYCN overexpression in the context of Rb inactivation increased the expression of MYC, E2F and ribosome related gene sets, promoted excessive proliferation and led to retinoblastoma with anaplastic changes. Part of our study compares expression profiles in Rbnull vs Rbnull/MYCN overexpressing retinas collected at 12 days after birth.
Project description:The retinoblastoma protein (pRB) is best known for regulating cell proliferation through E2F transcription factors. In this report we investigate the properties of a targeted mutation that disrupts pRB interactions with the transactivation domain of E2Fs. Mice that carry this mutation endogenously (Rb1∆G) are defective in regulating E2F target genes. Surprisingly, cell cycle regulation in Rb1∆G/∆G MEFs strongly resembles that of wild type. In a serum deprivation induced cell cycle exit, Rb1∆G/∆G MEFs display a similar magnitude of E2F target gene derepression as Rb1-/-, even though Rb1∆G/∆G cells exit the cell cycle normally. Interestingly, cell cycle arrest in Rb1∆G/∆G MEFs is responsive to p16 expression, indicating that the ΔG-pRB protein can be activated in G1 to arrest proliferation through non-E2F mechanisms. Some Rb1∆G/∆G mice die neonatally with a muscle degeneration phenotype, while the others live a normal lifespan with no evidence of spontaneous tumor formation. Histological analysis reveals discrete examples of hyperplasia in the mammary epithelium, but most tissues appear normal while being accompanied by derepression of pRB regulated E2F targets. This suggests that non-E2F, pRB dependent pathways may have a more relevant role in proliferative control than previously identified.