Search PubMed⌕ Search

Biomedical subjects

M K Bradley

Publications and source records attributed to M K Bradley.

At least 19 recordsLinked to original sources
PubMed2001

Programming the Drosophila embryo 2: from genotype to phenotype.

Although development is a single hierarchical process, scientists tend to study only one level at a time: molecular, cellular, or organismal. The data and theory are available to integrate molecular, cellular, and organismal levels into a series of maps for development of the Drosophila embryo. These maps link the transcriptional cascade with mitotic and phenotypic fate maps to trace hierarchical mechanisms of development from the genotype in the egg to the phenotype in the larva.

Animals↗
PubMed1998

Maternal shunt dependency: implications for obstetric care, neurosurgical management, and pregnancy outcomes and a review of selected literature.

OBJECTIVE: Because more women with cerebrospinal fluid shunts are surviving to child-bearing age, neurosurgeons, obstetricians, and other health care professionals require information about the care of these patients, especially during pregnancy and delivery. The purpose of this study was to gather comprehensive data from women with shunts regarding their clinical histories during and immediately after pregnancy. The following questions were addressed. 1) How does maternal shunt dependency influence the course of pregnancies and pregnancy outcomes? 2) What neurosurgical complications characterize this population of patients? 3) What complications of shunt dependency influence obstetric management, including prenatal testing and delivery? METHODS: A total of 37 respondents (age, 18-41 yr), accounting for 77 pregnancies, completed a questionnaire providing information on maternal background and medical history, shunt performance during pregnancy, management of delivery, pregnancy outcomes, and unusual complications. RESULTS: Fifty-six pregnancies resulted in live births; of these, 47 occurred in women with ventriculoperitoneal shunts. Three women underwent therapeutic abortions, 1 experienced preterm delivery, and 8 experienced 17 miscarriages. Four women experienced seizures during pregnancy, five reported third-trimester headaches, and eight described abdominal pains during the first and third trimesters. Four babies were diagnosed as having congenital defects. Shunt malfunctions and revisions occurred 10 times in 7 women, either during pregnancy or within 6 months after delivery. No acute malfunctions occurred during delivery. Forty-seven cases, representing 84% of all pregnancies, exhibited no shunt malfunctions or revisions. CONCLUSION: This study extends previous observations to a larger population of shunt-dependent mothers. The results suggest that maternal shunt dependency entails a relatively high incidence of complications but that proper care of these patients can lead to normal pregnancies and deliveries.

Adolescent↗
PubMed1997

An immortalized cell culture from a malignant mixed tumor of the lacrimal gland.

Tumor cells from a malignant mixed tumor of the lacrimal gland were maintained in tissue culture for more than 55 generations. Comparative immunohistochemical analysis was performed on whole tumor sections and on the tumor cell culture to define the origin of the cells in culture. The cultured cells expressed cytokeratin, smooth-muscle actin, S-100 protein, and vimentin and were negative for glial fibrillary acidic protein. Tumor sections expressed cytokeratin but were negative for muscle-specific actin, vimentin, and glial fibrillary acidic protein. Through tissue culture studies of salivary gland epithelial neoplasias, which are very similar to lacrimal gland epithelial neoplasias, pluripotential stem cells have been identified. Similar tissue culture analysis of lacrimal gland epithelial neoplasms can be a valuable tool for studying the origin of these uncommon tumors.

Antigens, Neoplasm↗
PubMed1996

A chromatin switch.

Cellular and molecular biological approaches that study eukaryotic gene regulation have led to separate models which describe structure and mechanism with differing precision. Using principles of combinatorial and cooperative interactions inherent in both models, we have extended concepts derived from a "genetic switch" for prokaryotes to a chromatin switch for eukaryotes composed of DNA, transactivators, nucleosomes and the nuclear matrix. We present a consensus model for gene regulation that uses a simple Monte Carlo method for simulating condensation and extension of chromatin. Such a chromatin switch can be modulated by known biochemical and molecular modifications, and the transactivator binding sites or enhancers within DNA domains can be organized into a hierarchy to control cell cycling and differentiation.

Animals↗
PubMed1996

Neuroectodermal antigens persist in benign and malignant salivary gland tumor cultures.

OBJECTIVE: To determine whether a heterogeneous collection of salivary gland tumors shared common antigenic characteristics and growth patterns in tissue culture. DESIGN: Cell cultures were derived from benign and malignant salivary gland neoplasms, cultured conservatively, and serially analyzed for epithelial, myoepithelial, and neuroectodermal antigens. SUBJECTS: Nineteen samples reflecting the spectrum of salivary tumor pathologic characteristics were established in tissue culture. Most were derived from benign pleomorphic adenomas, and several were from carcinomas, including carcinoma ex pleomorphic adenoma, and mucoepidermoid and adenoid cystic carcinoma. RESULTS: All cultures were epithelial as determined by morphologic and antigenic examination, using antibodies for cytokeratin. The phenotype of cells derived from benign tumors, especially the pleomorphic adenomas, resembled those in the original neoplasm. Those from carcinomas were similar, with less differentiated characteristics. Manipulation of growth conditions altered the phenotypes shown in culture. Some cultures contained cells expressing vascular smooth-muscle actin and glial fibrillary acidic protein or nestin. CONCLUSIONS: This model cell system containing proliferative cells from several tumor types is consistent with a stem-cell theory of salivary gland tumor origin. Our data were not consistent with the bicellular or multicellular theory. We hypothesize a neuroectodermal origin for this group of apparently heterogeneous tumors. These cultured cells will be valuable for in-depth investigation of the loss of proliferation controls in benign and malignant tumors of the salivary gland.

Antibodies, Monoclonal↗
PubMed1996

Aggressive papillary tumors of the temporal bone: an immunohistochemical analysis in tissue culture.

Aggressive papillary tumors of the temporal bone are neoplasms that are locally invasive and destructive. Previously classified on histologic study as middle ear adenomas or adenocarcinomas, observational evidence suggested that they arose from endolymphatic sac. To evaluate this hypothesis, we established a tissue culture from cells derived from such a papillary tumor and compared immunohistochemical stains of the original tumor with stains on endolymphatic epithelium. Similarities in expression of neuroectodermal antigens were observed. Similar staining antigens in cells derived from tumor and the endolymphatic sac provide evidence that epithelium from endolymphatic sac is the site of origin for these aggressive neoplasms. In tissue culture the cells remain contact inhibited and dependent on serum or growth factors with survival beyond the expected senescence at 30 to 50 generations. Therefore the cell culture technique provides a model for study of the disruption of growth control and invasive properties of this tumor.

Adenocarcinoma, Papillary↗
PubMed1996

An N-terminal deletion mutant of simian virus 40 (SV40) large T antigen oligomerizes incorrectly on SV40 DNA but retains the ability to bind to DNA polymerase alpha and replicate SV40 DNA in vitro.

A peptide encompassing the N-terminal 82 amino acids of simian virus 40 (SV40) large T antigen was previously shown to bind to the large subunit of DNA polymerase alpha-primase (I. Dornreiter, A. Höss, A. K. Arthur, and E. Fanning, EMBO J. 9:3329-3336, 1990). We report here that a mutant T antigen, T83-708, lacking residues 2 to 82 retained the ability to bind to DNA polymerase alpha-primase, implying that it carries a second binding site for DNA polymerase alpha-primase. The mutant protein also retained ATPase, helicase, and SV40 origin DNA-binding activity. However, its SV40 DNA replication activity in vitro was reduced compared with that of wild-type protein. The reduction in replication activity was accompanied by a lower DNA-binding affinity to SV40 origin sequences and aberrant oligomerization on viral origin DNA. Thus, the first 82 residues of SV40 T antigen are not strictly required for its interaction with DNA polymerase alpha-primase or for DNA replication function but may play a role in correct hexamer assembly and efficient DNA binding at the origin.

Adenosine Triphosphatases↗
PubMed1995

Morphologic, immunologic, biochemical, and cytogenetic characteristics of the human glioblastoma-derived cell line, SNB-19.

Human glioma-derived cell cultures and lines have proven to be of significant value in the study of the basic properties that contribute to the highly malignant, invasive and angiogenic phenotype of glioblastoma multiforme tumors. It is frequently difficult to establish lines that retain glial tumor properties in long term culture. The SNB-19 cell line has maintained and exhibited properties of transformation, differentiation, autocrine growth response, and tumorigenesis while remaining in culture for over 13 yr and undergoing over 200 passages. This human line has been utilized in a wide range of studies related to the basic properties of human glioblastoma multiforme. In this report, we summarize the immunologic, biochemical, and cytogenetic properties of this versatile cell line and its utility for additional mechanistic investigation into the pathophysiology of the progression of human malignant gliomas.

Animals↗
PubMed1995

Aggressive papillary tumors of the endolymphatic sac: clinical and tissue culture characteristics.

Aggressive papillary tumors of the temporal bone are neoplasms that were recently re-classified as tumors of the endolymphatic sac. They typically invade the mastoid bone and otic capsule and can grow into the petrous apex. The authors have treated three patients with this rare neoplasm and grown one of the tumors in tissue culture. This report reviews the clinical presentation in the three patients and the immunohistochemical staining characteristics of the tumor and tumor culture as compared to those of the endolymphatic sac. Findings support the hypothesis that aggressive papillary lesions of the temporal bone arise from the endolymphatic sac. Additionally, it is noted that the tumor culture maintains the characteristics of the original tumor and thus provides an exciting laboratory model for further study of this rare neoplasm.

Adenocarcinoma, Papillary↗
PubMed1993

The future of therapy for glioblastoma.

Effective therapy for malignant gliomas has centered on traditional approaches such as surgery and radiation therapy. Over the past two decades, more innovative approaches involving the use of chemotherapy and immunotherapy have been developed. Although these techniques have improved the quality of survival for many patients, the median survival following diagnosis and adjuvant treatment still remains only about a year. Recently, genetically engineered viruses for gene transduction and targeted cell killing have been used successfully in the experimental treatment of glioblastoma multiforme. We provide a review of the current and possible future therapies for malignant glioma with the belief that molecular biologic and genetic techniques offer the greatest hope of significantly altering the course of disease.

Combined Modality Therapy↗
PubMed1991

Specific mutation of a regulatory site within the ATP-binding region of simian virus 40 large T antigen.

In an attempt to distinguish simian virus 40 (SV40) large T antigen (T) binding to ATP from hydrolysis, specific mutations were made in the ATP-binding site of T according to our model for the site (M. K. Bradley, T. F. Smith, R. H. Lathrop, D. M. Livingston, and T. A. Webster, Proc. Natl. Acad. Sci. USA 84:4026-4030, 1987). Two acidic residues predicted to make contact with the magnesium phosphate were changed to alanines. The mutated T gene was completely defective for viral DNA synthesis and for virion production, and it was dominant defective for viral DNA replication. The defective T gene encoded a stable product (2905T) that oncogenically transformed mouse cell lines. 2905T, immunoprecipitated from transformed-cell extracts, bound SV40 origin DNA specifically and, surprisingly, it was active as an ATPase. A recombinant baculovirus was constructed for the production and purification of the mutant protein for detailed biochemical analyses. 2905T had only 10% of the ATPase and helicase of wild-type T. The Km of 2905T for ATP in ATPase assays was the same as the Km of wild-type T. ATP activated the ATPase activity of wild-type T, but not of 2905T. As tested by gel bandshift assay, 2905T bound to SV40 origin DNA and to individual sites I and II with affinities similar to that of the wild type. However, ATP did not modulate the DNA-binding activity of mutant T to site II. Therefore, this mutation in the ATP-binding site in T resulted in defects in the interaction between the protein and ATP that appeared to be responsible for the determination of the active state of T for DNA binding versus ATPase.

Adenosine Triphosphatases↗
PubMed1991

Use of the polymerase chain reaction for screening and evaluation of recombinant baculovirus clones.

We report the application of the PCR for screening and high-resolution characterization of recombinant baculovirus clones. Starting with less than 10 nanograms of viral DNA, it is possible to 1) demonstrate that the DNA sequence to be expressed has not been deleted or rearranged during the co-transfection or homologous recombination events, 2) test for the presence of wild-type virus in the isolate and 3) generate amplified DNA that can be used for nucleotide sequence analysis or high-resolution restriction analysis. The method is based upon PCR of genomic viral DNA prepared from primary amplified stocks of extracellular virus using a small-scale procedure. The approach has special relevance for definitive characterization of recombinant virus used to express point mutant proteins and for characterization of recombinant virus generated through use of mixed oligonucleotides or random mutagenesis.

Animals↗
PubMed1990

Activation of ATPase activity of simian virus 40 large T antigen by the covalent affinity analog of ATP, fluorosulfonylbenzoyl 5'-adenosine.

Fluorosulfonylbenzoyl 5'-adenosine (FSBA) bound to one site in simian virus 40 large T antigen (T) and covalently modified greater than 95% of the molecules in a complete reaction. This analog for ATP specifically cross-links to the Mg-phosphate pocket in ATP-binding sites. Cyanogen bromide cleavage and tryptic digestion of [14C]FSBA-labeled protein, paired with T-specific monoclonal antibody analyses, were used to map the site in T to a tryptic peptide just C terminal to the PAb204 epitope. The location of the FSBA linkage was consistent with the predicted tertiary structure of the ATP-binding region in T described previously (M. K. Bradley, T. F. Smith, R. H. Lathrop, D. M. Livingston, and T. A. Webster, Proc. Natl. Acad. Sci. USA 84:4026-4030, 1987). Binding of FSBA to T was cooperative, implying an interaction between two binding sites. This could occur if the protein formed a dimer, and it is known that the ATPase activity is associated with a dimeric T. Most interesting was the activation of the ATPase when up to 50% of T was bound by the analog. The effect was also produced by preincubation with millimolar concentrations of ATP or the nonhydrolyzable analog gamma beta-methylene 5'-adenosine diphosphate at elevated temperatures. When greater than 50% of T was modified by FSBA, the ATPase was inhibited as the analog cross-linked to the second, previously activated, binding site. These data support a dual function for the one ATP-binding site in T as both regulatory and catalytic.

Adenosine↗
PubMed1988

Purification and functional properties of simian virus 40 large and small T antigens overproduced in insect cells.

The insect baculovirus Autographa californica nuclear polyhedrosis virus was used as an expression vector for the simian virus 40 (SV40) small t (t) and large T (T) antigens. Spodoptera frugiperda (SF9) cells infected with recombinant viruses encoding these proteins produced approximately 1 to 2 micrograms of t and up to 30 micrograms of T per 3 X 10(6) cells. The former was highly soluble after Nonidet P-40 extraction of the infected cells, unlike its Escherichia coli-produced counterpart. Both SF9-produced proteins were of authentic size and could be readily immunoprecipitated by specific antibodies. Single-step immunoaffinity chromatography was used to purify the two proteins to near homogeneity, with yields averaging 70% in each case. Experiments to test the biological activity of the baculovirus SV40 proteins showed that SF9 t was capable of associating with two of the cellular proteins reported to bind to t in SV40-infected mammalian cells. Moreover, SF9 T had ATPase activity comparable to that of T produced in monkey cells, exhibited helicase activity and SV40 origin-specific DNA binding, and was active in the SV40 DNA replication assay in vitro. Thus, the SV40 T antigens produced in insect cells can be used in future studies of their biochemical roles in vitro and in vivo.

Adenosine Triphosphatases↗
PubMed1987

In vitro initiation of DNA replication in simian virus 40 chromosomes.

A soluble system has been developed that can initiate DNA replication de novo in simian virus 40 (SV40) chromatin isolated from virus-infected monkey cells as well as in circular plasmid DNA containing a functional SV40 origin of replication (ori). Initiation of DNA replication in SV40 chromatin required the soluble fraction from a high-salt nuclear extract of SV40-infected cells, a low-salt cytosol fraction, polyethylene glycol, and a buffered salts solution containing all four standard deoxyribonucleoside triphosphates. Purified SV40 large tumor antigen (T-ag) partially substituted for the high-salt nucleosol, and monoclonal antibodies directed against SV40 T-ag inhibited DNA replication. Replication began at ori and proceeded bidirectionally to generate replicating DNA intermediates in which the parental strands remained covalently closed, as observed in vivo. Partial inhibition of DNA synthesis by aphidicolin resulted in accumulation of newly initiated replicating intermediates in this system, a phenomenon not observed under conditions that supported completion of replication only. However, conditions that were optimal for initiation of replication repressed conversion of late-replicating intermediates into circular DNA monomers. Most surprising was the observation that p-n-butylphenyl-dGTP, a potent and specific inhibitor of DNA polymerase-alpha, failed to inhibit replication of SV40 chromatin under conditions that completely inhibited replication of plasmid DNA containing the SV40 ori and either purified or endogenous DNA polymerase-alpha activity. In contrast, all of these DNA synthesis activities were inhibited equally by aphidicolin. Therefore, DNA replication in mammalian cells is carried out either by DNA polymerase-alpha that bears a unique association with chromatin or by a different enzyme such as DNA polymerase-delta.

Antigens, Neoplasm↗
PubMed1987

Consensus topography in the ATP binding site of the simian virus 40 and polyomavirus large tumor antigens.

The location and sequence composition of a consensus element of the nucleotide binding site in both simian virus 40 (SV40) and polyomavirus (PyV) large tumor antigens (T antigens) can be predicted with the assistance of a computer-based pattern-matching system, ARIADNE. The latter was used to optimally align elements of T antigen primary sequence and predicted secondary structure with a "descriptor" for a mononucleotide binding fold. Additional consensus elements of the nucleotide binding site in these two proteins were derived from comparisons of T antigen primary and predicted secondary structures with x-ray structures of the nucleotide binding sites in four otherwise unrelated proteins. Each of these elements was predicted to be encompassed within a 110-residue segment that is highly conserved between the two T antigens residues 418-528 in SV40 T antigen and residues 565-675 in PyV). Results of biochemical and immunologic experiments on the nucleotide binding behavior of these proteins were found to be consistent with these predictions. Taken together, the latter have resulted in a topological model of the ATP binding site in these two oncogene products.

Adenosine Triphosphate↗
PubMed1987

The simian virus 40 large T antigen. A lot packed into a little.

Simian virus 40 (SV40) large T antigen is an 81,000 Mr, multifunctional viral phosphoprotein. Certain of its functions are essential to the viral replication process in monkey cells. Others, as yet undefined in biochemical terms, contribute to its neoplastic transforming activity. This review focuses on the known structure-function relationships of this protein and reflects upon the potential significance of its transforming properties in the natural host species of this virus.

Antigens, Viral, Tumor↗