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Biomedical subjects

T E White

Publications and source records attributed to T E White.

At least 19 recordsLinked to original sources
PubMed1998

Genetics and ovarian carcinoma.

Ovarian cancer is a disease that will affect approximately 1% of American women during their lifetime, and contributes to more than 14,000 deaths annually. If not detected early, this disease has a 5-year survival rate of less than 20%. Ovarian cancer develops predominantly from the malignant transformation of a single cell type, the surface epithelium. Although the biological mechanisms of transformation remain unclear, it is probably a multistep process requiring an accumulation of genetic lesions in a number of different gene classes. Several proto-oncogenes, such as AKT2 and Ki-RAS, are activated during ovarian cancer development, with putative oncogene-containing chromosomal regions showing imbalances and DNA amplifications. A number of chromosomal regions are also lost in ovarian tumors, indicating that the inactivation of tumor suppressor genes, such as TP53, may also contribute to cancer development. An important recent advancement in the field of ovarian cancer research is the identification of the breast/ovarian cancer susceptibility genes, BRCA1 and BRCA2. Mutations in these two tumor suppressor genes are responsible for the majority of heritable forms of epithelial ovarian cancers. A second class of genes involved in DNA mismatch repair (MMR) are responsible for most cases of hereditary nonpolyposis colorectal cancer (HNPCC). HNPCC or Lynch II cancer syndrome patients are also at an increased risk for developing ovarian cancer. Individuals in cancer-prone kindreds are currently being screened for germline mutations in BRCA1, BRCA2, and several MMR genes (eg, MSH2, MLH1), and mutant allele carriers counseled for cancer risks. Issues related to counseling and management of women at high risk for developing ovarian cancer are discussed. Although BRCA1, BRCA2, and a number of MMR genes have been identified, many more genes involved in gynecologic malignancies remain to be discovered and the clinical significance of the cancer genes already known is still in its infancy.

BRCA1 Protein↗
PubMed1995

Weanling female Sprague-Dawley rats are not sensitive to the antiestrogenic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

Investigators have shown that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) can inhibit certain estrogenic events in vivo and in vitro. To further investigate this phenomenon, the effects of estradiol (E2) alone or TCDD plus estradiol on several estrogen-dependent parameters were evaluated in weanling female Sprague-Dawley rats. E2 (10 micrograms/kg/day, Postnatal Days (PND) 21 and 22) caused significant increases in relative uterine weight and keratinization of the vaginal epithelium (PND 23). E2 significantly reduced uterine estrogen receptor (ER) protein levels and serum FSH levels, with a trend toward reduction of ER mRNA levels. None of these parameters were affected by pretreatment with 20, 40, or 80 micrograms/kg TCDD (PND 19). Uterine progesterone receptor levels were not affected by E2 or TCDD in the present study. In contrast, TCDD significantly decreased body weight (40 or 80 micrograms/kg) by PND 21, significantly decreased relative thymic weights, and significantly increased relative hepatic weights (20, 40, and 80 micrograms/kg, by PND 23). In addition, TCDD dramatically induced CYPIA1 hepatic mRNA levels, indicating that TCDD was properly delivered and could mediate other well-documented Ah receptor-dependent events. Thus, weanling female Sprague-Dawley rats are not sensitive to the antiestrogenic effects of TCDD at doses which cause overt toxicity. The results provide evidence that the previously reported antiestrogenic effects of TCDD are probably species, strain, and age dependent.

Animals↗
PubMed1993

The human estrogen receptor structural gene contains a DNA sequence that binds activated mouse and human Ah receptors: a possible mechanism of estrogen receptor regulation by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

TCDD decreases ER levels in vitro and in vivo, possibly through down-regulation of the ER structural gene, although the actual mechanism is unknown. We report the identification of six partial and two full length DREs in the 5' flanking and coding regions of the human ER gene. To test the ability of the coding region DRE (+102) to bind the activated AhR, two complementary oligonucleotides corresponding to the DRE-containing region of the human ER gene were synthesized, termed hERO, and used in a gel shift assay. TCDD-activated nuclear extracts from both mouse Hepa 1c1c7 cells and human MCF-7 cells specifically bound to the hERO with relative binding affinities of 15.5 nM and 5.6 nM, respectively. This binding was dependent upon a functional DRE. The hERO also specifically competed for AhR binding with a DRE-containing oligonucleotide from the mouse CYP1A1 gene. The results suggest a possible mechanism by which TCDD could be acting to modulate ER levels.

Animals↗
PubMed1993

The effects of elevated cyclic AMP levels on histamine-H1-receptor-stimulated inositol phospholipid hydrolysis and calcium mobilization in the smooth-muscle cell line DDT1MF-2.

The effects of raising cyclic AMP levels, by forskolin stimulation, beta-adrenoceptor activation or cyclic AMP phosphodiesterase inhibition, on inositol phospholipid hydrolysis and increases in intracellular free [Ca2+] ([Ca2+]i) elicited by a range of agonists have been investigated in the hamster vas deferens smooth-muscle cell line DDT1MF-2. Isoprenaline (log [EC50 (M)] = -7.7 +/- 0.2), forskolin and the type IV cyclic AMP phosphodiesterase inhibitor rolipram elicited significant increases in the accumulation of cyclic [3H]AMP. Pretreatment with forskolin (10 microM) attenuated histamine (100 microM)- and N6-cyclopentyladenosine (CPA; 300 nM)-induced release of intracellular Ca2+, observed when cells are stimulated in Ca(2+)-free buffer containing 0.1 mM EGTA. Forskolin had no effect on ATP (100 microM)- or bradykinin (1 microM)-stimulated release of intracellular Ca2+. Histamine-induced intracellular Ca2+ release was also inhibited by pretreatment with rolipram (100 microM) or the membrane-permeant cyclic AMP analogue (Sp)-adenosine 3',5'-monophosphothioate (100 microM). Isoprenaline (1 microM) pretreatment (in the presence of 10 microM rolipram, a concentration which on its own did not decrease the histamine response) attenuated histamine-induced intracellular Ca2+ release. Forskolin inhibited histamine (100 microM)- and CPA (100 nM) stimulated accumulation of [3H]-inositol phosphates, but was without effect on ATP or bradykinin responses. Addition of forskolin (in the presence of 100 microM rolipram) after the cells had been stimulated with histamine (in experiments initiated in Ca(2+)-free buffer) inhibited the rise in [Ca2+]i observed when extracellular Ca2+ (2 mM) was re-applied (owing to receptor-mediated Ca2+ influx). Finally, the refilling of intracellular Ca2+ stores (after receptor-mediated Ca2+ influx is blocked by mepyramine) can be demonstrated in the presence of raised cyclic AMP levels.

Animals↗
PubMed1993

Human trophoblast cultures: models for implantation and peri-implantation toxicology.

Implantation is the process that leads from blastocyst attachment to its embedding in the uterine wall. It is widely believed that failure of implantation is a common cause of pregnancy loss. Toxic agents can interfere directly with the process of implantation and therefore may account for unexplained implantation failures. Our knowledge of human implantation remains limited, mainly due to the lack of adequate experimental models. Studies of mechanisms underlying implantation in humans are by nature and for ethical reasons restricted to in vitro models. The aim of this review is to provide a critical evaluation of various in vitro models of implantation in humans, as well as essential background knowledge required for application of these models to the assessment of peri-implantation toxicity. Particular attention has been devoted to cell-cell and cell-matrix interactions as possible endpoints in the screening of toxic agents.

Animals↗
PubMed1993

Histamine H1-receptor-mediated inositol phospholipid hydrolysis in DDT1MF-2 cells: agonist and antagonist properties.

1. The effect of histamine H1-receptor stimulation on inositol phospholipid hydrolysis has been investigated in the hamster vas deferens smooth muscle cell line, DDT1MF-2. 2. Histamine (EC50 = 27 microM) stimulated the accumulation of [3H]-inositol phosphates in DDT1MF-2 cells prelabelled with [3H]-myo-inositol. 2-Thiazolylethylamine (EC50 42 microM) produced a maximal response of similar magnitude to histamine while the maximal response obtained with N alpha-methylhistamine (EC50 = 72 microM) and 2-pyridylethylamine (EC50 = 85 microM) were much lower (circa 65%, histamine = 100%). 3. The H1-selective agonists 2-(3-fluorophenyl)-histamine (2-FPH) and 2-(3-chlorophenyl)-histamine (2-CPH) both appeared to act as partial H1-agonists in this system. Both compounds produced maximal responses of only 30% (with respect to histamine = 100) and were able to antagonize the inositol phosphate response to histamine (estimated Kp = 10.4 and 18.9 microM for 2-FPH and 2-CPH respectively). 4. The response to histamine was antagonized by the H1-antagonists, mepyramine (KD 0.4 nM), (+)-chlorpheniramine (KD 1.2 nM) and promethazine (KD 0.3 nM). Furthermore, the (-)-isomer of chlorpheniramine was approx. three orders of magnitude less potent than the corresponding (+)-isomer. 5. The response to histamine (0.1 mM) was not altered by prior treatment of cells with pertussis toxin (100 ng ml-1; 24 h) whereas the inositol phosphate response to adenosine A1-receptor stimulation in this cell line was significantly attenuated under these conditions. 6. These data indicate that histamine-stimulated inositol phospholipid hydrolysis in DDT1MF-2 cells is mediated via a classical H1-receptor. Furthermore, the results also suggest that histamine HI- and adenosine A,-receptors activate phospholipase C in DDTMF-2 cells via two different G-protein-coupled pathways.

Animals↗
PubMed1992

Adenosine A1-receptor stimulation of inositol phospholipid hydrolysis and calcium mobilisation in DDT1 MF-2 cells.

1. The effect of adenosine receptor-stimulation on inositol phospholipid hydrolysis and calcium mobilization has been investigated in the hamster vas deferens smooth muscle cell line DDT1 MF-2. 2. Adenosine receptor stimulation increased the accumulation of total [3H]-inositol phosphates in DDT1 MF-2 cells prelabelled with [3H]-myo-inositol. The rank order of agonist potencies was N6-cyclopentyladenosine greater than 5'-N-ethylcarboxamidoadenosine greater than 2-chloroadenosine greater than adenosine. 3. The response to 2-chloroadenosine was antagonized by the antagonists 8-cyclopentyl-1,3-dipropylxanthine (KD 1.2 nM), PD 115,199 (KD 39 nM) and 8-phenyltheophylline (KD 31 nM). 4. The inositol phosphate response to 2-chloradenosine (10 microM) was not significantly altered when the extracellular Ca2+ ion concentration was reduced from 2.4 mM to 1.2 mM or 0.6 mM. Under calcium-free conditions, however, a reduced but still significant response to 2-chloroadenosine was evident (39 +/- 10% of the response in calcium-containing medium). 5. The 5-lipoxygenase inhibitor AA861 (10 and 100 microM) inhibited the inositol phosphate response to 2-chloroadenosine by 40 +/- 9% and 60 +/- 4% respectively. The cyclo-oxygenase inhibitor, indomethacin, however, was without significant effect at 1 microM. 6. 2-Chloroadenosine stimulated an increase in intracellular free Ca2+ ion concentration in fura-2 loaded DDT1 MF-2 cells in calcium-free medium containing 0.1 mM EGTA, which could be inhibited by the adenosine A1-receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (0.1 microM). 7. These data suggest that adenosine A1-receptor stimulation results in inositol phospholipid hydrolysis and calcium mobilization from intracellular stores in DDT1 MF-2 cells.

2-Chloroadenosine↗
PubMed1990

Central nervous system lesions in the Wistar rat fetus following direct fetal injections of cadmium.

During embryogenesis, maternal administration of cadmium (Cd) produces teratogenic effects, including hydrocephalus (HC), whereas later in gestation (during the fetal period), such effects have not been reported. Since there is little placental transfer of Cd late in gestation, such differences in response could be due to a lower Cd concentration in the fetus compared with the embryo after maternal Cd exposure, or could be due to a decreased sensitivity of the fetal central nervous system (CNS) to Cd. To test the susceptibility of the late gestational CNS to Cd, day 19 (sperm plug = day 0) rat fetuses were directly injected i.p. with CdCl2 (165, 100, 50 nmoles/fetus in 5 microliters saline). All fetuses in one horn were treated with Cd, while fetuses in the other horn were treated with saline. Fetuses were collected on day 21, grossly examined, weighed, fixed in Bouin's fixative, and later razor sectioned. Cd did not affect fetal viability or body weight. However, Cd caused a dose-dependent increase in hydrocephalus, with the total number of fetuses showing moderate to severe HC being 0/45, 0/11, 6/10, and 18/20 for controls, low, medium, and high doses, respectively. Mild HC was noted in one control and two low Cd fetuses. Brain necrosis was correlated with hydrocephalus, being observed in 0/45, 0/11, 5/10, and 16/20 fetuses, respectively. In medium-dose fetuses without HC or brain necrosis, extravasation of erythrocytes was noted histologically within the cortical parenchyma, suggesting that hemorrhaging may lead to brain necrosis and hydrocephalus in Cd-exposed fetuses. Thus, the fetal CNS is susceptible to the toxic effects of Cd.

Animals↗
PubMed1990

Human endometrial cells grown on an extracellular matrix form simple columnar epithelia and glands.

Normal human endometrial cells were grown on an extracellular matrix containing type IV collagen, laminin, heparan sulfate proteoglycan, and entactin (Matrigel). On the extracellular matrix, dispersed endometrial cells remained rounded, and aggregated to form mounds of cells, which continued to grow in this arrangement. At 10 d, light microscopy demonstrated that these mounds were comprised of an eosinophilic substance, containing individual fusiform stromal cells. About 50% of the mounds were covered with a single layer of polarized cuboidal to columnar cells with basal nuclei, whereas 60% contained columnar cells forming glandular structures with open lumina. These polarized cuboidal and columnar cells were epithelial, based on their positive staining for cytokeratins and the possession of microvilli, tonofilaments, abundant glycogen, ribosomes, and primitive junctional complexes. Kreyberg's stain showed the presence of mucin within the lumina of the glands, indicating that they were functional. Thus, human endometrial cells grown on an extracellular matrix form a simple cuboidal to columnar epithelium, a stromal component, and glandular structures, thereby mimicking the in vivo morphology of the endometrium.

Cell Division↗
PubMed1990

Thrombolamban, the 22-kDa platelet substrate of cyclic AMP-dependent protein kinase, is immunologically homologous with the Ras family of GTP-binding proteins.

Platelet inhibition by agents that increase intracellular levels of cAMP is associated with cAMP-dependent phosphorylation of specific intracellular proteins, including a membrane-associated 22-kDa microsomal protein called thrombolamban. In view of recent studies suggesting that platelets also contain 22-kDa GTP-binding proteins that are homologous with ras-encoded p21 proteins, the present work was undertaken to examine the possibility that thrombolamban and the Ras-like proteins were the same. Platelet microsomes were labeled with [gamma-32P]ATP and the labeled proteins were examined by autoradiography of sodium dodecyl sulfate/polyacrylamide gels. On Western blots of both one-dimensional and two-dimensional gels, thrombolamban immunoreacted with M90, a monoclonal antibody that recognizes the GTP-binding domain of Ras p21 proteins, but not with Y13-259, a monoclonal antibody that recognizes another domain and is specific for Ras proteins. Overlay experiments with unlabeled platelet microsomes demonstrated numerous low molecular weight proteins that bound [alpha-32P]GTP, although none could be identified as thrombolamban. Finally, thrombolamban was immunoprecipitated by M90. These studies show that thrombolamban is a low molecular weight protein that is immunologically related to the Ras family of GTP-binding proteins.

Adenosine Triphosphate↗
PubMed1989

Cyclic AMP-dependent protein kinase does not increase calcium transport in platelet microsomes.

Cyclic AMP inhibits platelet activation, at least in part, by reducing intracellular levels of ionic calcium. Previous studies using platelet microsomal fractions have suggested that one mechanism for this effect is stimulation by cyclic AMP and its protein kinase of calcium uptake into microsomal storage sites. In the present study, the effect of cyclic AMP and its protein kinase on calcium uptake by microsomal membranes has been re-examined using the active catalytic subunit of cyclic AMP-dependent protein kinase. The catalytic subunit increased calcium uptake two-fold, but this effect was not inhibited by boiling the catalytic subunit or by recombination with the regulatory subunit of cyclic AMP-dependent protein kinase, conditions that inhibited catalytic subunit activity. Conversely, dialysis of the catalytic subunit preparation against low phosphate buffer, which did not inhibit catalytic subunit activity, inhibited the stimulation of calcium uptake by the catalytic subunit preparation. Finally, the addition of high phosphate buffer, similar in phosphate concentration to that of the catalytic subunit preparation, stimulated calcium uptake. We conclude that the catalytic subunit does not directly stimulate calcium uptake by platelet microsomes.

Biological Transport↗
PubMed1989

The identification of sarcoplasmic reticulum terminal cisternae proteins in platelets.

Two new proteins with apparent molecular masses of 53 kDa and 190 kDa have been identified in both sarcoplasmic reticulum and human blood platelets using a monoclonal antibody, FII1b5. The sarcoplasmic reticulum FII1b5 antigens were present in the terminal cisternae fraction, but were absent from light sarcoplasmic reticulum. The platelet and skeletal muscle proteins were not sensitive to digestion with endoglycosidase H under conditions that removed carbohydrate from the 53 kDa glycoprotein in sarcoplasmic reticulum or GPIIIa in platelet microsomes and did not bind 45Ca in a nitrocellulose overlay calcium-binding assay. These results distinguished the FII1b5 antigens from the 53 kDa glycoprotein and calsequestrin of sarcoplasmic reticulum. The 190 kDa platelet and sarcoplasmic reticulum proteins were extracted from membranes with high concentrations of NaCl, indicating that the high molecular mass FII1b5 antigens are peripherally associated with the bilayers. In contrast, the platelet and muscle 53 kDa proteins remained membrane-bound in the presence of high salt concentrations, suggesting that they are integral proteins.

Acetylglucosaminidase↗
PubMed1987

A fluorescence investigation of the nucleotide binding sites of the Ca ATPase.

Competitive binding and fluorescence energy transfer experiments were used to examine the binding of 2'[3']-O-(2,4,6-trinitrophenyl) adenosine-5'-diphosphate (TNP-ADP) to the catalytic site of Ca ATPase. Fluorescein isothiocyanate (FITC), which is known to covalently bind near the catalytic site (13), was shown to exclude all TNP-ADP binding. TNP-ADP, in turn, will protect against FITC labeling of the Ca ATPase in its native state and in both phosphoenzyme forms. The competitive nature of these probes indicates that TNP-ADP binds to the catalytic site exclusively. Fluorescence energy transfer studies using TNP-ADP as an energy acceptor and 1,N6-ethenoadenosine-5'-diphosphate (epsilon-ADP) as an energy donor were used to estimate the distance between nucleotide binding sites in the enzyme complex. A lower limit for the distance measured was 44 A. This is interpreted to be the distance between catalytic sites on adjacent monomers of a dimer unit. The results of this work are consistent with a single nucleotide site per ATPase monomer.

Adenosine Diphosphate↗
PubMed1987

A guide to MPRO.

Explore the source record for details and available documents.

Michigan↗
PubMed1986

Presence of O6-methylguanine acceptor protein in the tissues of different classes of vertebrates and invertebrates.

We have measured the ability of extracts of tissues from several species of mammals, birds, reptiles, amphibia and fish to demethylate adducts of O6-methylguanine in exogenous DNA by transfer of the methyl group to an acceptor protein. Our study also encompassed tissues from a smaller number of invertebrates, from arthropods, molluscs and annelids. The vertebrate tissues used were liver, brain, spleen and kidney. In the case of the invertebrates we sampled liver, neural tissue, gonads, digestive tract and hepatopancreas. There was no consistent change in the amount of acceptor activity per unit of protein or DNA going from cold-blooded to warm-blooded vertebrates. Liver invariably had the highest amount; this finding was not unexpected since metabolic processes in the liver are high, and good cellular protective mechanism important. Inter-class comparisons within the vertebrates are highly speculative, and hindered by the fact that there is little information on carcinogenesis in animals other than rodents and humans. O6-methylguanine acceptor activity was found in all the invertebrate tissues tested. The amounts were variable, 0.003-0.0051 fmol/micrograms cellular DNA, but the values fell within the range of those found in the tissues of vertebrates.

Amphibians↗