Project description:To explore how Myc and E2f3 might coordinate gene expression programs that drive normal cell cycles in wild type intestines and ectopic cell cycles in Rb-deficient small intestines, we compared Myc and E2f3 chromatin occupancy in these tissues.
Project description:Rb and E2F are thought to play antagonistic roles in celll proliferation. However, this model is based mostly from in vitro cell culture systems. We used small intestines to test this model in vivo. We found that deletion of E2f1-3 in the small intestine of mice suppressed the ectopic expression of E2F targets and cell proliferation caused by Rb-deficiency. Surprisingly, E2f1-3 deletion failed to arrest the proliferation of intestinal cells containing an intact Rb gene, and instead led to E2F target derepression and apoptosis. Experiment Overall Design: Total RNA of crypts and villi from wild-type, Rb-/-, E2f1-/-, E2f2-/-, E2f3-/-, E2f1-/-, E2f2-/-, and E2f3-/- small intestines. Small intestines were harvested 7 days after mice were injected intraperitoneally with beta-napthoflavone.
Project description:The LXCXE peptide motif facilitates interaction between the RB tumor suppressor and a large number of cellular proteins that are expected to impinge on diverse biological processes. In vitro and in vivo analyses demonstrated that LXCXE-binding function is dispensable for RB promoter association and control of basal gene expression. Dependence on this function of RB is unmasked after DNA damage, wherein LXCXE-binding is essential for exerting control over E2F3 and suppressing cell cycle progression in the presence of genotoxic stress. Gene expression profiling revealed that the transcriptional program coordinated by this specific aspect of RB is associated with progression of human hepatocellular carcinoma and poor disease outcome. Consistent with these findings, biological challenge revealed a requirement for LXCXE-binding in suppression of genotoxin-initiated hepatocellular carcinoma in vivo. Together, these studies establish an essential role of the LXCXE-binding motif for RB-mediated transcriptional control, response to genotoxic insult, and tumor suppression. Mice transgenic for Cre-recombinase under the albumin promoter contain indicated combinations of loxP sites flanking exon 19 of Rb1 (f), N750F mutation (NF) or wild-type (plus) genotypes. For gene expression microarray analysis, mice were aged to 14 days and treated for 24 hours with diethylnitrosamine (DEN) or saline as an M-bM-^@M-^\untreatedM-bM-^@M-^] control. Liver tissue was obtained from DEN treated livers and compared to normal liver tissue of saline treated littermates.
Project description:Identification of c-Myc, H3K4me3 and a set of skin differentiation specific TFs binding sites in the genome of normal or c-Myc overexpressed mouse epidermis
Project description:The E2F family consists of transcriptional repressors and activators that control cell proliferation. In the classic paradigm of cell cycle regulation, the three activators, E2F1, E2F2 and E2F3, are invariably depicted as the final components of a CDK/Rb signaling cascade that executes the transcriptional program necessary to commit cells to enter S phase. Unexpectedly, we find through analysis of Affymetrix expression array data that mature lens epithelial cells deficient for E2F1-3 fail to repress cell cycle-regulated genes (and other targets of E2F) and that this corresponds with subsequent apoptosis and cellular collapse in the lens. Murine lenses were collected at two stages of development for RNA extraction and hybridization on Affymetrix microarrays. Our aim was to determine key events that lead to cellular collapse of lenses triply deficient for E2F1, E2F2, and E2F3 in neonates.
Project description:Most E2F-binding sites repress transcription through the recruitment of Retinoblasoma (RB) family members until the end of the G1 cell-cycle phase. Although the MYB promoter contains an E2F-binding site, its transcription is activated shortly after the exit from quiescence, before RB family members inactivation, by unknown mechanisms. We had previously uncovered a nuclear factor distinct from E2F, Myb-sp, whose DNA-binding site overlapped the E2F element and had hypothesized that this factor might overcome the transcriptional repression of MYB by E2F-RB family members. We have purified Myb-sp and discovered that Myc-associated zinc finger proteins (MAZ) are major components. We show that various MAZ isoforms are present in Myb-sp and activate transcription via the MYB-E2F element. Moreover, while forced RB or p130 expression repressed the activity of a luciferase reporter driven by the MYB-E2F element, co-expression of MAZ proteins not only reverted repression, but also activated transcription. Finally, we show that MAZ binds the MYB promoter in vivo, that its binding site is critical for MYB transactivation, and that MAZ knockdown inhibits MYB expression during the exit from quiescence. Together, these data indicate that MAZ is essential to bypass MYB promoter repression by RB family members and to induce MYB expression.
Project description:The LXCXE peptide motif facilitates interaction between the RB tumor suppressor and a large number of cellular proteins that are expected to impinge on diverse biological processes. In vitro and in vivo analyses demonstrated that LXCXE-binding function is dispensable for RB promoter association and control of basal gene expression. Dependence on this function of RB is unmasked after DNA damage, wherein LXCXE-binding is essential for exerting control over E2F3 and suppressing cell cycle progression in the presence of genotoxic stress. Gene expression profiling revealed that the transcriptional program coordinated by this specific aspect of RB is associated with progression of human hepatocellular carcinoma and poor disease outcome. Consistent with these findings, biological challenge revealed a requirement for LXCXE-binding in suppression of genotoxin-initiated hepatocellular carcinoma in vivo. Together, these studies establish an essential role of the LXCXE-binding motif for RB-mediated transcriptional control, response to genotoxic insult, and tumor suppression.
Project description:We report here genome-wide analysis of the tumor suppressor p53 binding sites in normal human cells. 743 high-confidence ChIP-seq peaks representing putative genomic binding sites were identified in normal IMR90 fibroblasts using a reference chromatin sample. More than 40 % were located within 2 kb of a transcription start site (TSS), a distribution similar to that documented for individually studied functional p53 binding sites and to date not observed by previous genome-wide studies. Nearly half of the high-confidence binding sites in the IMR90 cells reside in CpG islands, in marked contrast to sites reported in cancer-derived cells. The distinct genomic features of the IMR90 binding sites do not reflect a distinct preference for specific sequences, since the de novo developed p53 motif based on our study is similar to those reported by genome-wide studies of cancer cells. More likely the different chromatin landscape in normal compared to cancer-derived cells influences p53 binding via modulating availability of the sites. We compared the IMR90 ChIP-seq peaks to the recently published IMR90 methylome1, and demonstrated that they are enriched at hypomethylated DNA. Our study represents the first genome-wide, de novo mapping of p53 binding sites in normal human cells and reveals that p53 binding sites reside in distinct genomic landscapes in normal and cancer-derived human cells. Identification of genomic p53 binding sites in normal human cells by ChIP-seq.