Biomedical subjects

V A Spencer

Publications and source records attributed to V A Spencer.

11 recordsLinked to original sources

PubMed2001

Dynamically acetylated histone association with transcriptionally active and competent genes in the avian adult beta-globin gene domain.

In chicken immature erythrocytes, class 1 acetylated histones are rapidly tri- and tetra-acetylated and rapidly deacetylated. Class 2 acetylated H3 and H4 are rapidly acetylated to mono- and di-acetylated isoforms and slowly deacetylated. Our previous studies suggested that class 1 acetylated histones were primarily associated with transcriptionally active DNA (beta(A)-globin) but not competent DNA (epsilon-globin). Chromatin salt solubility (chromatin fiber oligomerization) is directly influenced by hyperacetylation. In this study we investigated the association of class 1 histones with beta(A)- and epsilon-globin DNA by measuring their loss of solubility rates in 150 mm NaCl and 3 mm MgCl(2) as a function of hyperacetylated histone deacetylation. Expressed and competent chromatin was associated with class 1 acetylated histones. As most active chromatin and hyperacetylated histones are associated with the low salt-insoluble residual nuclear material containing the nuclear matrix, we investigated whether hyperacetylated histones are bound to the beta(A)- and epsilon-globin DNA in this fraction. In chromatin immunoprecipitation assays, we found that the beta(A)- and epsilon-globin coding regions are bound to hyperacetylated H3 and H4. Our observations are consistent with a model in which nuclear matrix-associated histone acetyltransferases and deacetylases mediate a dynamic attachment between active and competent chromatin and the nuclear matrix.

Acetylation↗

PubMed2001

Altered profiles in nuclear matrix proteins associated with DNA in situ during progression of breast cancer cells.

Nuclear matrix proteins (NMPs) show promise as informative biomarkers in following the pathogenesis of breast cancer. The nuclear matrix is a dynamic RNA-protein network involved in the organization and expression of chromatin. Cisplatin, which preferentially cross-links nuclear matrix proteins to DNA in situ, may be used to identify NMPs that organize and/or regulate the processing of DNA. In this study, we analyzed the nuclear matrix proteins from an estrogen receptor-positive breast cancer cell line panel consisting of MCF-7, MIII, LCC1, and LCC2 cell lines. This cell line panel reflects the stages of malignant progression in breast cancer. Proteins isolated from nuclear matrices and proteins cross-linked to nuclear DNA in situ with cisplatin were analyzed by two-dimensional gel electrophoresis. Specific changes in nuclear matrix proteins bound to nuclear DNA were identified. In concordance with estrogen independence and antiestrogen insensitivity, a loss in cisplatin cross-linking of specific NMPs to nuclear DNA was observed. Our results suggest that progression of breast cancer is accompanied by a reorganization of chromosomal domains, which may lead to alterations in gene expression.

Antigens, Nuclear↗

PubMed2001

Signal transduction pathways and the modification of chromatin structure.

Mechanical and chemical signaling pathways are involved in transmitting information from the exterior of a cell to its chromatin. The mechanical signaling pathway consists of a tissue matrix system that links together the three-dimensional skeletal networks, the extracellular matrix, cytoskeleton, and karyoskeleton. The tissue matrix system governs cell and nuclear shape and forms a structural and functional connection between the cell periphery and chromatin. Further, this mechanical signaling pathway has a role in controlling cell cycle progression and gene expression. Chemical signaling pathways such as the Ras/mitogen-activated protein kinase (MAPK) pathway can stimulate the activity of kinases that modify transcription factors, nonhistone chromosomal proteins, and histones. Activation of the Ras/MAPK pathway results in the alteration of chromatin structure and gene expression. The tissue matrix and chemical signaling pathways are not independent and one signaling pathway can affect the other. In this chapter, we will review chromatin organization, histone variants and modifications, and the impact that signaling pathways have on chromatin structure and function.

Acetyltransferases↗

PubMed2000

Nuclear matrix proteins associated with DNA in situ in hormone-dependent and hormone-independent human breast cancer cell lines.

The nuclear matrix is a dynamic RNA-protein complex that organizes chromatin and regulates nuclear DNA metabolism. Nuclear matrix proteins informative in the diagnosis of cancer have been identified. Here, the nuclear matrix breast cancer proteins (NMBCs) cross-linked to nuclear DNA in situ with cisplatin in human breast cancer cell lines were analyzed by two-dimensional gel electrophoresis. We identified NMBCs that were differentially associated with nuclear DNA of hormone-dependent and -independent breast cancer cell lines. Three DNA cross-linked NMBCs were found to be exclusive to estrogen receptor-positive, hormone-dependent breast cancer cells, whereas two NMBCs were observed only in estrogen receptor-negative, hormone-independent breast cancer cells. Changes in these NMBCs were observed when hormone-dependent breast cancer cells became hormone independent. Furthermore, we show that the intermediate filament protein vimentin is associated with the nuclear DNA of MDA-MB-231 breast cancer cells, an estrogen receptor-negative, hormone-independent breast cancer cell line with high metastatic potential. These nuclear matrix DNA-binding proteins may play important roles in breast tumorigenesis.

Breast↗

PubMed2000

Signal transduction pathways and chromatin structure in cancer cells.

Molecular mechanisms controlling gene expression include cell shape, mechanical and chemical signal transduction pathways, chromatin remodeling, and DNA methylation. In this article, we will review the contribution of these molecular mechanisms and structural alterations in the malignant transformation of cells. The mechanical signaling pathway consists of the tissue matrix system that links together the three-dimensional skeletal networks, the extracellular matrix, cytoskeleton, and nuclear matrix. The cytoskeleton array is a dynamic system that transmits signals from the cell exterior to nuclear DNA. The composition and function of this mechanical signaling pathway is altered in cancer cells. Chemical signaling pathways such as the Ras/mitogen-activated protein kinase (MAPK) pathway stimulate the activity of kinases that modify transcription factors, histones, and chromatin remodeling factors. Oncoproteins deregulating this signaling pathway set in motion a series of events that cumulate to chromatin remodeling and aberrant gene expression. J. Cell. Biochem. Suppl. 35:27-35, 2000.

Animals↗

PubMed1999

Role of covalent modifications of histones in regulating gene expression.

DNA is organized into a hierarchy of structures, resulting in the level of compaction required to pack 2m of DNA into a nucleus with a diameter of 10 micrometer. The orderly packaging of DNA in the nucleus plays an important role in the functional aspects of gene regulation. A small percentage of chromatin is made available to transcription factors and the transcription machinery, while the remainder of the genome is in a state that is essentially invisible to the RNA polymerases. Modification of histones has a key role in altering chromatin higher order structure and function. In this review, we will present the latest developments in the study of histone modifications (ubiquitination, acetylation, methylation, and phosphorylation) and the enzymes involved in these processes.

Acetylation↗

PubMed1999

Control of histone modifications.

A role for histone modifications in transcription processes and the remodeling of chromatin structure has been established. This review highlights the recent advances made in studies on histone acetyltransferases, histone deacetylases, histone kinases, and protein phosphatases, as well as their roles in transcriptional activation and repression. Coactivators with histone acetyltransferase activity stimulate transcription, whereas corepressors with histone deacetylase activity repress transcription. Families of histone acetyltransferases and deacetylases have been identified. We have learned that their substrates are not limited to histones but also include transcription factors and architectural proteins. Studies on the composition of multiprotein complexes with histone acetyltransferase or histone deacetylase have revealed mechanisms by which these complexes are recruited to specific genomic sites that are transcriptionally active, silenced, or being repaired. A new and exciting development, presented in this review, is the role of signal transduction pathways in the phosphorylation of histone H3 and the expression of immediate-early genes. J. Cell. Biochem. Suppls. 32/33:141-148, 1999.

Acetylation↗

PubMed1999

Organization of chromatin in cancer cells: role of signalling pathways.

The role of mechanical and chemical signalling pathways in the organization and function of chromatin is the subject of this review. The mechanical signalling pathway consists of the tissue matrix system that links together the three-dimensional skeletal networks, the extracellular matrix, cytoskeleton, and nuclear matrix. Intermediate filament proteins are associated with nuclear DNA, suggesting that intermediate filaments may have a role in the organization of chromatin. In human hormone-dependent breast cancer cells, the interaction between cytokeratins and chromatin is regulated by estrogens. Transcription factors, histone acetyltransferases, and histone deacetylases, which are associated with the nuclear matrix, are components of the mechanical signalling pathway. Recently, we reported that nuclear matrix-bound human and chicken histone deacetylase 1 is associated with nuclear DNA in situ, suggesting that histone deacetylase has a role in the organization of nuclear DNA. Chemical signalling pathways such as the Ras/mitogen-activated protein kinase (Ras/MAPK) pathway stimulate the activity of kinases that modify transcription factors, nonhistone chromosomal proteins, and histones. The levels of phosphorylated histones are increased in mouse fibroblasts transformed with oncogenes, the products of which stimulate the Ras/MAPK pathway. Histone phosphorylation may lead to decondensation of chromatin, resulting in aberrant gene expression.

Amino Acid Sequence↗

PubMed1998

Estrogen regulates the association of intermediate filament proteins with nuclear DNA in human breast cancer cells.

In a previous study we showed that the levels of the intermediate filament proteins, cytokeratins 8, 18, and 19, in the nuclear matrix-intermediate filament (NM-IF) fraction from the hormone-dependent and estrogen receptor (ER)-positive human breast cancer cell line T-47D5 were regulated by estrogens. In contrast, estrogens did not regulate the cytokeratins in the NM-IF fraction of the hormone-independent and ER-positive cell line, T5-PRF. In this study, human breast cancer cells were treated with cis-diamminedichloroplatinum to cross-link protein to nuclear DNA in situ, and proteins bound to DNA were isolated. We show that cytokeratins 8, 18, and 19 of T-47D5 and T5-PRF were associated with nuclear DNA in situ. The levels of the cytokeratins 8, 18, and 19 bound to nuclear DNA or associated with the cytoskeleton of T-47D5 human breast cancer cells decreased when estrogens were depleted or the pure antiestrogen ICI 164,384 was added. In contrast, the cytokeratin levels associated with nuclear DNA or cytoskeleton were not significantly affected by estrogen withdrawal or antiestrogen administration in T5-PRF cells. These observations suggest that estrogen regulates the organization of nuclear DNA by rearrangement of the cytokeratin filament network in hormone-dependent, ER-positive human breast cancer cells and that this regulation is lost in hormone-independent, ER-positive breast cancer cells.

Breast Neoplasms↗

PubMed1998

In situ cross-linking by cisplatin of nuclear matrix-bound transcription factors to nuclear DNA of human breast cancer cells.

Cisplatin is an antitumor drug that is used to treat several types of cancers. In this study, we analyzed the proteins that were cross-linked to DNA in situ in MCF-7 human breast cancer cells incubated with cisplatin. We show that cisplatin cross-links nuclear matrix proteins to DNA. In immunoblotting experiments, we found that nuclear matrix-associated transcription factors and cofactors (estrogen receptor, HET/SAF-B, hnRNP K, and histone deacetylase 1) were cross-linked to nuclear DNA. These transcription factors and cofactors have essential roles in the regulation of genes involved in the proliferation of breast cancer cells and in the organization and structure of chromatin. We applied a novel protocol to demonstrate that the nuclear matrix-bound transcription factors/cofactors were cross-linked to DNA fragments attached to the nuclear matrix. These results suggest that the cross-linking of nuclear matrix-associated transcription factors and cofactors to DNA may be one of the mechanisms by which cisplatin inhibits transcription and replication processes.

Antigens, Nuclear↗

PubMed1998

Chromatin, nuclear matrix and the cytoskeleton: role of cell structure in neoplastic transformation (review).

Aberrant nuclear and cellular structures are hallmarks of malignant transformation. Thus it is not surprising that the three-dimensional structure of the cell both affects and is affected by changes in gene expression. Here we review the role of the cytoskeleton, nuclear matrix, and chromatin structure in the genesis of cancer. The shape of a cell is governed by a dynamic tissue matrix, which includes extracellular matrix, cytoskeleton and nuclear matrix. Mechanical and chemical signals are transmitted to the nucleus, resulting in alterations in the three-dimensional chromatin organization of genes. The signal transduction pathways affect histone modifications, such as acetylation and phosphorylation, resulting in a relaxed chromatin structure observed in oncogene-transformed cells.

Animals↗