ABSTRACT
Cells establish and sustain structural and functional integrity of the genome to support cellular identity and prevent malignant transformation. In this review, we present a strategic overview of epigenetic regulatory mechanisms including histone modifications and higher order chromatin organization (HCO) that are perturbed in breast cancer onset and progression. Implications for dysfunctions that occur in hormone regulation, cell cycle control, and mitotic bookmarking in breast cancer are considered, with an emphasis on epithelial-to-mesenchymal transition and cancer stem cell activities. The architectural organization of regulatory machinery is addressed within the contexts of translating cancer-compromised genomic organization to advances in breast cancer risk assessment, diagnosis, prognosis, and identification of novel therapeutic targets with high specificity and minimal off target effects.
Subject(s)
Breast Neoplasms/genetics , Breast Neoplasms/prevention & control , Chromatin/genetics , Epigenesis, Genetic/genetics , Genome/genetics , Animals , Cell Line, Tumor , Epithelial-Mesenchymal Transition/genetics , Female , Humans , Mice , Neoplastic Stem CellsABSTRACT
Functional interrelationships between the intranuclear organization of nucleic acids and regulatory proteins are obligatory for fidelity of transcriptional activation and repression. In this article, using the Runx/AML/Cbfa transcription factors as a paradigm for linkage between nuclear structure and gene expression we present an overview of growing insight into the dynamic organization and assembly of regulatory machinery for gene expression at microenvironments within the nucleus. We address contributions of nuclear microenvironments to the convergence and integration of regulatory signals that mediate transcription by supporting the combinatorial assembly of regulatory complexes.
Subject(s)
Cell Nucleus/genetics , Cell Nucleus/metabolism , Gene Expression Regulation , Signal Transduction , Transcription Factors/genetics , Transcription Factors/metabolism , Active Transport, Cell Nucleus/physiology , Animals , Core Binding Factor Alpha 3 Subunit , Core Binding Factor alpha Subunits , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Gene Expression Regulation, Neoplastic , Neoplasm Proteins/genetics , Neoplasm Proteins/metabolism , Neoplasms/genetics , Nuclear Matrix/genetics , Nuclear Matrix/metabolism , Transcription, Genetic/physiologyABSTRACT
Key components of DNA replication and the basal transcriptional machinery as well as several tissue-specific transcription factors are compartmentalized in specialized nuclear domains. In the present study, we show that determinants of subnuclear targeting of the bone-related Runx2/Cbfa1 protein reside in the C-terminus. With a panel of C-terminal mutations, we further demonstrate that targeting of Runx2 to discrete subnuclear foci is mediated by a 38 amino acid sequence (aa 397-434). This nuclear matrix-targeting signal (NMTS) directs the heterologous Gal4 protein to nuclear-matrix-associated Runx2 foci and enhances transactivation of a luciferase gene controlled by Gal4 binding sites. Importantly, we show that targeting of Runx2 to the NM-associated foci contributes to transactivation of the osteoblast-specific osteocalcin gene in osseous cells. Taken together, these findings identify a critical component of the mechanisms mediating Runx2 targeting to subnuclear foci and provide functional linkage between subnuclear organization of Runx2 and bone-specific transcriptional control.
Subject(s)
Cell Nucleus/metabolism , Neoplasm Proteins , Osteocalcin/genetics , Osteocalcin/metabolism , Saccharomyces cerevisiae Proteins , Signal Transduction , Transcription Factors/genetics , Transcription Factors/metabolism , Transcriptional Activation , Amino Acid Sequence , Animals , Binding Sites , Blotting, Western , Core Binding Factor Alpha 1 Subunit , DNA-Binding Proteins , Fungal Proteins/metabolism , Genes, Reporter , HeLa Cells , Humans , In Situ Hybridization , Luciferases/metabolism , Microscopy, Fluorescence , Molecular Sequence Data , Mutation , Plasmids/metabolism , Protein Structure, Tertiary , Rats , Sequence Homology, Amino Acid , Transcription Factors/chemistry , Transcription, Genetic , Tumor Cells, CulturedABSTRACT
Runx (Cbfa/AML) transcription factors are critical for tissue-specific gene expression. A unique targeting signal in the C terminus directs Runx factors to discrete foci within the nucleus. Using Runx2/CBFA1/AML3 and its essential role in osteogenesis as a model, we investigated the fundamental importance of fidelity of subnuclear localization for tissue differentiating activity by deleting the intranuclear targeting signal via homologous recombination. Mice homozygous for the deletion (Runx2 Delta C) do not form bone due to maturational arrest of osteoblasts. Heterozygotes do not develop clavicles, but are otherwise normal. These phenotypes are indistinguishable from those of the homozygous and heterozygous null mutants, indicating that the intranuclear targeting signal is a critical determinant for function. The expressed truncated Runx2 Delta C protein enters the nucleus and retains normal DNA binding activity, but shows complete loss of intranuclear targeting. These results demonstrate that the multifunctional N-terminal region of the Runx2 protein is not sufficient for biological activity. We conclude that subnuclear localization of Runx factors in specific foci together with associated regulatory functions is essential for control of Runx-dependent genes involved in tissue differentiation during embryonic development.