David Barbie
Harvard University, Medicine, Faculty Member
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Using methods that conserve nuclear architecture, we have reanalyzed the spatial organization of the initiation of mammalian DNA synthesis. Contrary to the commonly held view that replication begins at hundreds of dispersed nuclear sites,... more
Using methods that conserve nuclear architecture, we have reanalyzed the spatial organization of the initiation of mammalian DNA synthesis. Contrary to the commonly held view that replication begins at hundreds of dispersed nuclear sites, primary fibroblasts initiate synthesis in a limited number of foci that contain replication proteins, surround the nucleolus, and overlap with previously identified internal lamin A/C structures. These foci are established in early G(1)-phase and also contain members of the retinoblastoma protein family. Later, in S-phase, DNA replication sites distribute to regions located throughout the nucleus. As this progression occurs, association with the lamin structure and pRB family members is lost. A similar temporal progression is found in all the primary cells we have examined but not in most established cell lines, indicating that the immortalization process modifies spatial control of DNA replication. These findings indicate that in normal mammalian ...
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Small cell lung cancer (SCLC) is an aggressive disease with high mortality, and the identification of effective pharmacological strategies to target SCLC biology represents an urgent need. Using a high-throughput cellular screen of a... more
Small cell lung cancer (SCLC) is an aggressive disease with high mortality, and the identification of effective pharmacological strategies to target SCLC biology represents an urgent need. Using a high-throughput cellular screen of a diverse chemical library, we observe that SCLC is sensitive to transcription-targeting drugs, in particular to THZ1, a recently identified covalent inhibitor of cyclin-dependent kinase 7. We find that expression of super-enhancer-associated transcription factor genes, including MYC family proto-oncogenes and neuroendocrine lineage-specific factors, is highly vulnerability to THZ1 treatment. We propose that downregulation of these transcription factors contributes, in part, to SCLC sensitivity to transcriptional inhibitors and that THZ1 represents a prototype drug for tailored SCLC therapy.
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Research Interests: Cell Cycle, DNA damage, Multidisciplinary, Mice, Nuclear Structure, and 13 moreAnimals, T cells, Phenotype, Protein Function, Retinoblastoma, Cell nucleus, Cell Cycle regulation, Multienzyme complexes, Cysteine endopeptidases, Cell Proliferation, Cell Cycle Arrest, Human Fibroblasts, and retinoblastoma protein (RB1).
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Retinoblastoma (RB) tumor suppressor family pocket proteins induce cell cycle arrest by repressing transcription of E2F-regulated genes through both histone deacetylase (HDAC)-dependent and -independent mechanisms. In this study we have... more
Retinoblastoma (RB) tumor suppressor family pocket proteins induce cell cycle arrest by repressing transcription of E2F-regulated genes through both histone deacetylase (HDAC)-dependent and -independent mechanisms. In this study we have identified a stable complex that accounts for the recruitment of both repression activities to the pocket. One component of this complex is RBP1, a known pocket-binding protein that exhibits both HDAC-dependent and -independent repression functions. RB family proteins were shown to associate via the pocket with previously identified mSIN3-SAP30-HDAC complexes containing exclusively class I HDACs. Such enzymes do not interact directly with RB family proteins but rather utilize RBP1 to target the pocket. This mechanism was shown to account for the majority of RB-associated HDAC activity. We also show that in quiescent normal human cells this entire RBP1-mSIN3-SAP30-HDAC complex colocalizes with both RB family members and E2F4 in a limited number of discrete regions of the nucleus that in other studies have been shown to represent the initial origins of DNA replication following growth stimulation. These results suggest that RB family members, at least in part, drive exit from the cell cycle by recruitment of this HDAC complex via RBP1 to repress transcription from E2F-dependent promoters and possibly to alter chromatin structure at DNA origins.
Research Interests: Cellular Biology, Cell Cycle, DNA replication, Transcription Factors, Biological Sciences, and 15 moreCell line, Molecular and cellular biology, Humans, HIstone Deacetylase, Enzyme, Chromatin structure, Retinoblastoma, Cell nucleus, Cell Cycle Arrest, Cell Cycle Proteins, Protein Binding, DNA binding proteins, Histone deacetylases, Interphase, and retinoblastoma protein (RB1).
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Research Interests: Biological Sciences, RNA interference, Humans, Mutation, Mice, and 4 moreAnimals, Cell, Neoplasms, and Cell Survival
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Chromosomal rearrangements involving the H3K4 methyltransferase mixed-lineage leukemia (MLL) trigger aberrant gene expression in hematopoietic progenitors and give rise to an aggressive subtype of acute myeloid leukemia (AML). Insights... more
Chromosomal rearrangements involving the H3K4 methyltransferase mixed-lineage leukemia (MLL) trigger aberrant gene expression in hematopoietic progenitors and give rise to an aggressive subtype of acute myeloid leukemia (AML). Insights into MLL fusion-mediated leukemogenesis have not yet translated into better therapies because MLL is difficult to target directly, and the identity of the genes downstream of MLL whose altered transcription mediates leukemic transformation are poorly annotated. We used a functional genetic approach to uncover that AML cells driven by MLL-AF9 are exceptionally reliant on the cell-cycle regulator CDK6, but not its functional homolog CDK4, and that the preferential growth inhibition induced by CDK6 depletion is mediated through enhanced myeloid differentiation. CDK6 essentiality is also evident in AML cells harboring alternate MLL fusions and a mouse model of MLL-AF9-driven leukemia and can be ascribed to transcriptional activation of CDK6 by mutant MLL. Importantly, the context-dependent effects of lowering CDK6 expression are closely phenocopied by a small-molecule CDK6 inhibitor currently in clinical development. These data identify CDK6 as critical effector of MLL fusions in leukemogenesis that might be targeted to overcome the differentiation block associated with MLL-rearranged AML, and underscore that cell-cycle regulators may have distinct, noncanonical, and nonredundant functions in different contexts.
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The recent development of technologies for whole-genome sequencing, copy number analysis and expression profiling enables the generation of comprehensive descriptions of cancer genomes. However, although the structural analysis and... more
The recent development of technologies for whole-genome sequencing, copy number analysis and expression profiling enables the generation of comprehensive descriptions of cancer genomes. However, although the structural analysis and expression profiling of tumors and cancer cell lines can allow the identification of candidate molecules that are altered in the malignant state, functional analyses are necessary to confirm such genes as oncogenes or tumor suppressors. Moreover, recent research suggests that tumor cells also depend on synthetic lethal targets, which are not mutated or amplified in cancer genomes; functional genomics screening can facilitate the discovery of such targets. This review provides an overview of the tools available for the study of functional genomics, and discusses recent research involving the use of these tools to identify potential novel drug targets in cancer.