PubMed Health⌕ Search

Biomedical subjects

S C Brooks

Publications and source records attributed to S C Brooks.

At least 55 records · Page 3Linked to original sources
PubMed1993

Influence of estrogen structure on nuclear binding and progesterone receptor induction by the receptor complex.

The relationship between steroid structure, estrogen receptor (ER) binding affinity, nuclear binding of the ER complex, and induction of progesterone receptor (PgR) have been examined. The level of ER in membrane-free homogenates of MCF-7 cells was found to be 10.0 +/- 0.5 fmol/micrograms of DNA by utilizing an enzyme immunoassay (EIA). However, only 2.5 +/- 0.2 fmol of ER complex/micrograms of DNA was bound by nuclei during maximal stimulation of PgR synthesis (2.9 +/- 0.2 fmol of PgR/micrograms of DNA; measured by EIA) following a pulse with 10(-10) M E2. Except at micromolar concentrations, estratriene was an ineffective estrogen. The addition of a hydroxyl group to either position 3 or position 17 beta of estratriene yielded ligands which were capable of causing nuclear binding and processing of ER as well as PgR induction. D-ring regioisomers of estradiol (E2) had lower affinity for receptor than E2. However, receptor complexed with these estrogens was fully capable of binding to nuclear material, undergoing processing, and inducing PgR. On the other hand, A-ring regioisomers of E2 displayed significant differences in their ability to mediate nuclear binding of receptor complex and induction of PgR. Although 1-hydroxyestratrien-17 beta-ol was weakly bound by ER, this dihydroxyestrogen was capable of bringing about nuclear binding and processing of ER and the stimulation of PgR synthesis. In contrast, 2- and 4-hydroxyestratrien-17 beta-ol, which caused extensive nuclear binding of ER (5-7 fmol/micrograms of DNA), were incapable of significant PgR induction.(ABSTRACT TRUNCATED AT 250 WORDS)

Androstenediols↗
PubMed1993

Differential induction of pS2 and cathepsin D mRNAs by structurally altered estrogens.

The influence of structural alterations to the estradiol-17 beta (E2) molecule on the induction of pS2 and Cathepsin D (Cath D) mRNAs has been examined by Northern analysis of RNA extracted from MCF-7 cells. Exposure of cultures to estratriene did not affect the level of expression of these estrogen-responsive genes. Addition of one hydroxyl group to estratriene at either of the hydroxylated positions of E2 (3-phenolic or 17 beta) yielded monohydroxyestrogens which stimulated the synthesis of Cath D and pS2 mRNAs to a level comparable to that induced by 10(-10) M E2 and displayed a decrease in activity at the higher concentrations (10(-8) - 10(-7) M) similar to that of the parent estrogen. Both of these genes were induced maximally by estrogens with D-ring alterations. Movement of the phenolic hydroxyl group of E2 to other positions on the A-ring yielded ligands which were highly discriminatory in the induction of these messages. 1-Hydroxyestratrien-17 beta-ol was capable of stimulating maximal synthesis of both pS2 and Cath D mRNAs when added to cultures of MCF-7 cells at a concentration of 10(-8) M. Placement of the phenolic hydroxyl at position 4 greatly diminished the induction of these two estrogen-responsive genes. On the other hand, positioning the A-ring hydroxyl group on carbon 2 yielded a ligand which brought about the induction of one gene (pS2) but was marginally effective in the induction of Cath D mRNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1993

Effects of estradiol-17 beta analogues on activation of estrogen response element regulated chloramphenicol acetyltransferase expression.

These experiments were designed to examine the effect of structural modifications to the estradiol-17 beta (E2) molecule on the estrogen response element (ERE) dependent activation of the thymidine kinase (tk) promoter. Estrogen receptor (ER) positive MCF-7 cells were transfected with plasmids containing one or two vitellogenin EREs inserted upstream of the tk promoter in p(-37)tk. Transient expression of the CAT gene in these constructs was measured after cells had been maintained for 36-42 h in the presence of E2 or an E2 analogue. E2 induced CAT expression at levels as low as 10(-13) M, with maximum induction at 10(-11) M. CAT activity decreased at higher concentrations of E2. Estratriene, which has low affinity for ER, was active only at micromolar concentrations. 3-Hydroxyestratriene displayed maximal activity at 10(-9) M, with higher levels being less active. Still higher concentrations (10(-7) M) of estratrien-17 beta-ol were required to induce maximum CAT activity. All positional and conformational alterations in the D-ring hydroxyl group of E2 yielded active ligands. Movement of the phenolic hydroxyl group of E2 to other positions on the A-ring produced dihydroxyestrogens with varied capacities to activate CAT (2-hydroxyestratrien-17 beta-ol produced maximum CAT activation at 10(-11) M; 1-hydroxyestratrien-17 beta-ol required a 10(-8) M concentration for maximum activity; 4-hydroxyestratrien-17 beta-ol gave maximum CAT activation at 10(-6) M). Only those androstanediols or 5-androstenediols with a 3 beta-hydroxyl group were capable of activating CAT expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1990

Isolation and characterization of a spontaneously immortalized human breast epithelial cell line, MCF-10.

Two sublines of a breast epithelial cell culture, MCF-10, derived from human fibrocystic mammary tissue exhibit immortality after extended cultivation in low calcium concentrations (0.03-0.06 mM) and floating transfers in low calcium (MCF-10F), or by trypsin-Versene passages in the customary (normal) calcium levels, 1.05 mM (MCF-10A). Both sublines have been maintained as separate entities after 2.3 years (849 days) in vitro and at present have been in culture for longer than 4 years. MCF-10 has the characteristics of normal breast epithelium by the following criteria: (a) lack of tumorigenicity in nude mice; (b) three-dimensional growth in collagen; (c) growth in culture that is controlled by hormones and growth factors; (d) lack of anchorage-independent growth; and (e) dome formation in confluent cultures. Cytogenetic analysis prior to immortalization showed normal diploid cells; although later passages showed minimal rearrangement and near-diploidy, the immortal cells were not karyotypically normal. The emergence of an immortal culture in normal calcium media was not an inherent characteristic of the original tissue from which MCF-10 was derived since reactivated cryo-preserved cells from cultures grown for 0.3 and 1.2 years in low calcium were incapable of sustained growth in normal calcium.

Animals↗
PubMed1990

Binding, X-ray and NMR studies of the three A-ring isomers of natural estradiol.

The effect of the position of the phenolic hydroxyl on the conformations of the three A-ring isomers of estradiol, namely, estra-1,3,5(10)-trien-1,17 beta-diol (10), estra-1,3,5(10)-trien-2,17 beta-diol (3), and estra-1,3,5(10)-trien-4,17 beta-diol (6), has been analyzed by X-ray crystallography. The results of these analyses were correlated with the absorptions of the angular methyl groups in the [1H]NMR spectra of these isomers and natural estradiol (E2). It was observed that the changes in chemical shift of protons at C18 corresponded to skeletal modifications in the steroid structure which changed the anisotropic effect of the hydroxyl group at C17. Examination of the affinity of these A-ring isomers of E2 for the estrogen receptor has shown the 2-hydroxylated isomer 3 to retain 1/5th the affinity of E2 for its binding protein. The 1- and 4-hydroxylated derivatives (10 and 6, respectively) bound to a much lesser extent. The receptor affinities of these estrogen analogues may be related to the angle between the 18-methyl and the 17 beta-hydroxyl groups (or the dihedral angle between the planar A-ring and the angular C18 methyl) as well as the position of the A-ring hydroxyl group.

Chemical Phenomena↗
PubMed1990

Evaluation of analytical techniques for measurement of denture-base acrylic resin glass-transition temperature.

The glass-transition temperature of a range of acrylic resin materials used in prosthetic dentistry was determined. The techniques used to make the measurement included: thermal mechanical analysis, dynamic mechanical thermal analysis, and differential scanning calorimetry. It was found that the measuring techniques used yielded very similar results, and as a consequence it was concluded that: familiarity and easy availability of thermal mechanical analysis lead to the recommendation that this technique should be employed as the standard glass-transition evaluation technique for denture-base acrylic resins.

Acrylic Resins↗
PubMed1990

Monitoring progress in major trauma care using TRISS.

We report on the outcome of major trauma patients brought to the Kent and Canterbury Hospital in 1989 and compare it with 1987. There is an improvement which followed changes in the management of serious injuries.

Adult↗
PubMed1989

Role of porcine endometrial estrogen sulfotransferase in progesterone mediated downregulation of estrogen receptor.

Estrogen sulfotransferase (EST) is a progesterone (Pg) induced secretory endometrial enzyme which may effect estrogen receptor levels by esterifying estradiol-17 beta (E2) to an inactive, sulfate form. The effects of this enzyme were studied using specific inhibitors of EST that do not bind to estrogen receptor (ER): 4-nitroestrone 3-methyl ether and 4-fluoroestrone 3-methyl ether. A 1 h pulse with 4 nM E2 caused ERn (i.e. E2-bound, chromatin-bound receptor) to increase 40% in incubations of proliferative gilt endometrium (no EST activity), while the same E2 treatment of secretory endometrium (high EST activity) caused no increase in ERn. ERn accumulation was completely restored in these experiments by preincubating secretory endometrium with 4 microM 4-fluoroestrone 3-methyl ether. Gilt endometrial explants cultured 7 days with 1 nM E2 plus 1 microM Pg (which induced EST activity) possessed half the ERn as explants devoid of EST activity which were cultured in E2 alone. The addition of 10 microM 4-nitroestrone 3-methyl ester to the cultures of secretory endometrium restored ERn to the levels seen in minces cultured with E2 alone. Furthermore, ovariectomized gilts injected daily with 250 micrograms E2 plus 25 mg Pg had much lower ERn (0.06 fmol/micrograms DNA) than gilts injected with E2 only (0.21 fmol/microgram DNA). ERn was restored completely by supplementing the E2 plus Pg injections with 0.5 g 4-nitroestrone 3-methyl ether administered by vaginal suppositories.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Comparison of three- and four-point flexural strength testing of denture-base polymers.

Flexural failure of denture-base materials is considered the primary mode of clinical failure. However, there are several methods of conducting flexural tests, and none has been demonstrated to be the most appropriate. Three- and four-point bend-testing were compared, with four different dental polymers used. The values for modulus of elasticity determined by the two tests were not statistically different. However, the values for flexural strength from the three-point bend test were always greater, suggesting that that parameter is dependent on the testing procedure. Modifications to the existing denture-base material specification are suggested.

Dental Stress Analysis↗
PubMed1989

Rapid curing of acrylic denture-base materials.

A rapid-cure polymerization of cure, including a terminal boil, with respect to transparency, residual monomer, mechanical properties, and generation of gaseous porosity. It was found that in order for porosity-free resin to be produced during rapid curing, a low concentration (approximately 0.26%) of benzoyl peroxide initiator in the powder component is vital, and a very small concentration (approximately 0.025%) of the chemical activator dimethyl-p-toluidine in the monomer component is an advantage. Mechanical properties were only influenced where substantial porosity existed, but it was recognized that a material "tailor-made" for rapid curing would be most welcome.

Acrylic Resins↗
PubMed1989

Effect of water and artificial saliva on mechanical properties of some denture-base materials.

Two artificial saliva samples selected on the basis of being chemically and physically similar to natural saliva were used as saturation media so that we could investigate their effects on mechanical properties of four denture-base materials, and the results were compared with the effect of water on the same materials. Diffusion coefficients in the more viscous saliva were different from those in water but, in general, mechanical properties were similarly affected in all liquids, indicating that the aqueous phase of the artificial medium was a major factor influencing the results.

Acrylic Resins↗
PubMed1989

One year's trauma in a district general hospital: injury severity and survival.

We studied the accident department management and survival of all seriously injured patients brought to the Kent and Canterbury hospital over one year. The physiological state on arrival and the injuries of each patient were coded and probabilities of survival calculated by reference to the Trauma Score and Injury Severity Score (the TRISS method). This enabled a broad comparison with North American results but also drew attention to cases in which survival and prediction were inconsistent. We discuss the worth of the method as a tool for local audit of emergency care.

Adolescent↗
PubMed1988

Quantitative determination of nuclear estrogen receptors by an enzyme immunoassay: applicability and caveats.

A method is presented with which approx. 95% of nuclear estrogen receptors appear to be extracted from MCF-7 cells. Since both nuclear isolation and nuclear estrogen receptor extraction take place in a single test tube with only vortex mixing, loss of nuclear material is minimized. The amount of nuclear estrogen receptors in the nuclear extract was determined by direct [3H]estradiol labeling of monolayer cultures and with a commercially available estrogen receptor immunoassay (ER-EIA) kit. Since the ER-EIA kit was designed and calibrated for quantitative determination of cytosolic estrogen receptor isolated in low ionic strength buffer, the applicability of the ER-EIA to quantitative determination of estrogen receptor content in high ionic strength nuclear extraction buffer was tested. A linear relationship exists between the amount of nuclear estrogen receptor detected by the immunoassay, the amount of receptor present in serial dilutions of the nuclear extract and the amount of nuclear estrogen receptor detected in cells by [3H]estradiol labeling of monolayer cultures, the absolute amount of nuclear estrogen receptors determined by the immunoassay consistently exceeded the amount of receptor detected by [3H]estradiol labeling. The possibility that the enzyme immunoassay must be properly calibrated for the specific conditions of the nuclear estrogen receptor assay is discussed.

Blotting, Western↗
PubMed1988

Studies on type II progesterone receptor in MCF-7 cells.

These experiments demonstrate for the first time the existence of a Type II progesterone receptor (RpII) in MCF-7 human breast cancer cells. RpII was shown to have a lower affinity for tritiated progesterone ([3H]Pg) (Kd greater than or equal to 13 nM) than classical Rp (Kd less than or equal to 3 nM). RpII was detected by cytosolic, nuclear, and whole cell assays of MCF-7 cells. Scatchard analysis of [3H]Pg binding data revealed that classical Rp but not RpII could be recompartmentalized from the cytosolic to the nuclear pool by treating cells 1 h at 37 degrees C with 1 microM Pg. RpII levels were shown to be increased more than two-fold by growing MCF-7 cells for 4 days in 10 nM estradiol (E2) plus 100 nM Pg when compared to either untreated cells or to cells treated with only E2.

Breast Neoplasms↗
PubMed1988

The measurement of the setting characteristics of rigid autopolymerizing resins for direct use in the oral cavity.

Differential scanning calorimetry has been used with success to determine working and setting times of autopolymerizing denture and orthodontic base resins. The technique is considered to be far more suitable for this task than thermal methods which are influenced by specimen geometry and heat transfer. Since only a few milligrams of material are required the technique would be suitable for other dental materials whose setting characteristics are of interest.

Calorimetry↗