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S Chen

Publications and source records attributed to S Chen.

At least 1,207 records · Page 67Linked to original sources
PubMed1993

Effect of androstenedione on growth of untransfected and aromatase-transfected MCF-7 cells in culture.

Aromatase is present in human breast tumors and in breast cancer cell lines suggesting the possibility of in-situ estrogen production via the androstenedione to estrone and estradiol pathway. However, proof of the biologic relevance of aromatase in breast cancer tissue requires the demonstration that this enzyme mediates biologic effects on cell proliferation. Accordingly, we studied the effects of the aromatase substrate, androstenedione, on the rate of proliferation of wild-type and aromatase-transfected MCF-7 breast cancer cells. Androstenedione did not increase cell growth in wild-type MCF-7 cells which contained relatively low aromatase activity and produced 4-fold more estrone than estradiol. In contrast, aromatase-transfected cells contained higher amounts of aromatase, produced predominantly estradiol, and responded to androstenedione with enhanced growth. An aromatase inhibitor fadrozole hydrochloride, blocked the proliferative effects of androstenedione providing evidence for the role of aromatase in this process. As further evidence of the requirement for aromatase, cells transfected with the neomycin resistance expression plasmid but lacking the aromatase cDNA did not respond to androstenedione. These studies provide evidence that aromatase may have a biologic role for in-situ synthesis of estrogens in breast cancer tissue.

Analysis of Variance↗
PubMed1993

Aromatase gene is amplified in MCF-7 human breast cancer cells.

The levels of the aromatase gene and its expression in MCF-7 human breast cancer cells and seven additional cultured cells were investigated. Using normal human foreskin fibroblasts as the control, the aromatase gene appeared to be amplified in MCF-7 cells as shown by Southern and DNA slot blot analyses utilizing human placental aromatase cDNA as the probe. However, the promoter I.1 and the first exon of the aromatase gene were not amplified in MCF-7 cells based on results obtained from DNA slot blot analysis using oligonucleotide probes having sequences derived from those regions of human aromatase gene. Aromatase was expressed at a very low level in this cell line as indicated by Northern blot analysis to measure the level of aromatase mRNA, immunoprecipitation analysis to measure the level of aromatase protein, and aromatase activity measurement. Furthermore, nucleotide sequence analysis of the aromatase cDNA obtained from MCF-7 cells by PCR techniques, revealed no sequence difference from that of the enzyme expressed in placenta. These results lead us to conclude that the expression of aromatase in MCF-7 cells is under the control of an unusual promoter and aromatase gene expression is repressed at the transcriptional level in these cells.

Aromatase↗
PubMed1993

Modified longitudinal preputial island flap urethroplasty for repair of hypospadias: results in 60 patients.

We report the results of hypospadias repair in 60 children requiring urethral reconstruction using a longitudinal or oblique preputial island flap technique that includes the inner and outer surfaces of the prepuce to construct the neourethra. Mean patient age was 3.2 years and mean length of the repair was 3.1 cm. The cosmetic and functional results were satisfactory. The incidence of urethrocutaneous fistula was 8.3% and that of meatal stenosis was 5%. Thus, this modification offers good results with a low complication rate. The range of applications can be extended by combining the technique with a tube of midline scrotal skin in cases of scrotal or perineal hypospadias. The surgical technique is described in detail.

Child, Preschool↗
PubMed1993

Radical retropubic prostatectomy and postoperative adjuvant radiation for pathological stage C (PcN0) prostate cancer from 1976 to 1989: intermediate findings.

Between 1976 and 1989, 114 patients undergoing radical retropubic prostatectomy and bilateral pelvic lymph node dissection for prostatic adenocarcinoma were found to have stage PcN0 lesions. Postoperative adjuvant radiation therapy without hormonal treatment was given to 95 of these patients (83%): 26 (27%) with stage C1, 37 (39%) with stage C2 and 32 (34%) with stage C3 disease. The median radiation dose was 45 Gy. given at 180 cGy. daily. Median followup was 4.4 years (range 1.4 to 13.3). The overall 5 and 10-year actuarial rates for the patients were 94% and 70%, respectively. Disease-specific 5 and 10-year actuarial survival rates were 99% and 78%, respectively. At 5 and 10 years the chance of clinical recurrence was estimated as 6% and 13%, respectively, and the chance of recurrence (clinical or indicated by prostate specific antigen levels) was estimated to be 34% and 46%, respectively. Patients with high Gleason scores (8 to 10) and seminal vesicle involvement (stage C3) fared worst. There were 5 patients with clinical distant metastases, 1 with a clinical local recurrence and 1 with both conditions. Detectable elevation of prostate specific antigen without clinically evident recurrence was noted in 25 patients. Radiation therapy was well tolerated with minimal morbidity. Disease-specific survival and survival without clinical recurrence were improved over historical control in patients with stage PcN0 prostate cancer treated by radical prostatectomy alone. These data support a role for adjuvant radiation therapy in stage PcN0 prostate adenocarcinoma following radical prostatectomy.

Adenocarcinoma↗
PubMed1993

Molecular cloning and sequence analysis of two porcine seminal proteins, PSP-I and PSP-II: new members of the spermadhesin family.

Two full-length cDNAs encoding porcine seminal proteins, PSP-I and PSP-II, have been isolated from a porcine seminal vesicle cDNA library. Nucleotide sequence analysis of the 706-bp PSP-I cDNA predicts a precursor protein of 133 amino acid residues, which includes a 21-residue signal peptide and a 112-residue secreted protein. On the other hand, the complete sequence of the 686-bp PSP-II cDNA reveals a coding sequence for a 21-residue signal peptide and a 116-residue secreted protein. The predicted amino acid sequences agree very well with those determined by conventional amino acid sequence analysis. Alignment of the two cDNA sequences shows an overall 66% sequence homology throughout their entire length. However, the sequence homology is much higher in the 3' untranslated region (72%) than in the coding region (61%). This suggests that these two genes evolved by duplication and divergence from a common ancestral gene. They share about 50% amino acid sequence homology and a similar overall structure with three members of the spermadhesin family.

Amino Acid Sequence↗
PubMed1993

Role of digitalis-like substance in the hypertension of streptozotocin-induced diabetes in reduced renal mass rats.

We have previously reported that chronic hypertension develops consistently in Wistar rats with a 25% reduction in renal mass (RRM) following the induction of insulin dependent diabetes mellitus (IDDM) with streptozotocin (STZ, 65 mg/kg body weight, intravenously). In this study, we examined the role of the endogenous digitalis-like substance in the development of hypertension. Four groups of rats were studied: 1) 25% RRM rats with STZ-induced IDDM (25-DM), 2) normal rats with STZ-induced IDDM (2K-DM), 3) 25% RRM rats with vehicle treatment (25-V), and 4) normal rats with vehicle treatment (2K-V). In 25-DM rats, blood pressure progressively increased during the 3 weeks after STZ treatment and was associated with microalbuminuria, low plasma renin activity, and extracellular volume expansion. In contrast, the 2K-DM, 25-V, and 2K-V rats remained normotensive. Furthermore, the plasma and urine levels of digoxin-like immunoreactive factor (DIF), determined by digoxin radioimmunoassay (Baxter), were significantly higher in hypertensive 25-DM rats than in their controls. The same was the case for plasma digitalis-like substance (DLS), determined by exposing canine Na+,K(+)-ATPase to plasma fractions and observing the percent inhibition. Increased DIF and DLS in hypertensive 25-DM rats was associated with a significant decrease in Na+,K(+)-ATPase activity of microsomes prepared from the left and right ventricles, when compared with microsomes from normotensive 2K-DM animals. Microsomal 5'-nucleotidase, a plasma membrane marker, was unchanged. The DIF and DLS correlated significantly with each other and with myocardial Na+,K(+)-ATPase activity and mean blood pressure. These results suggest that increased endogenous digitalis-like substance, which inhibits cardiovascular muscle cell Na(+)-K(+)-pump activity, may be involved in the mechanism of hypertension associated with IDDM in 25% RRM rats.

Animals↗
PubMed1993

3-Methylcholanthrene-inducible liver cytochrome(s) P450 in female Sprague-Dawley rats: possible link between P450 turnover and formation of DNA adducts and I-compounds.

The hepatic cytochrome P450s are mixed-function oxidases which metabolize a wide variety of xenobiotics and endobiotics, and also bioactivate carcinogens such as 3-methyl-cholanthrene (MC) to reactive metabolites capable of forming DNA adducts. To investigate possible relationships between cytochrome P450 induction and covalent DNA modifications (adducts and I-compounds), female Sprague-Dawley rats were i.p. treated with MC (25 mg/kg) in corn oil (CO), once daily for 4 days. Controls received CO only. Animals were euthanized at 1, 8, 15, 28 and 45 days after the last MC treatment, and liver microsomal cytochrome P450, ethoxycoumarin O-deethylase (ECD) and ethoxyresorufin O-deethylase (EROD) activities were determined. Liver DNA adducts and I-compounds were analyzed by 32P-postlabeling. A significant induction of the levels of P450, ECD and EROD activities was noted in MC-treated rats, and elevated enzyme levels persisted for about 6 weeks after cessation of MC administration. Linear decay of total P450, ECD and EROD activities as a function of time was observed. MC induced 11 DNA adducts in liver, which were resolved by thin-layer chromatography (TLC) and persisted at high levels throughout the study. On the other hand, MC elicited a significant depletion of both non-polar and polar I-compounds (age-dependent DNA modifications detectable by 32P-postlabeling in rodent tissues without known exposure to carcinogens). Level of most I-compounds returned to normal at 45 days, and this paralleled the return of P450-related activities to normal. These results suggest a possible link between P450 turnover, DNA adduct formation, and I-compound depletion.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1993

TSF1 to TSF6, required for silencing the Saccharomyces cerevisiae GAL genes, are global regulatory genes.

The Saccharomyces cerevisiae GAL1 and GAL10 genes are controlled in response to the availability of galactose and glucose by multiple activating and repressing proteins bound at adjacent or overlapping sites in UASG. Negative control elements in UASG, designated GAL operators GALO1 to GALO6, are required to silence basal level transcription of GAL1 and GAL10 when galactose is absent. We isolated and characterized recessive mutations in six nuclear genes, TSF1 to TSF6, that impair silencing of GAL1 and GAL10 gene expression. Surprisingly, the results of several experiments suggest that the TSF genes encode global regulatory factors. tsf1 to tsf6 mutations derepressed expression from yeast CYC-GAL hybrid promoters (fused to lacZ) that harbor a variety of operator sequences, and caused pleiotropic defects in cell growth, mating, and sporulation. S1 mapping and Northern blot results for tsf3 suggest that the molecular defect is at the transcriptional level. Mutant phenotypes were additive in certain combinations of tsf double mutants, implying that more than one silencing pathway is involved in TSF1 to TSF6 function. Most significantly, mutations in all six TSF1 to TSF6 genes activated expression from GAL1 and CYC1 promoters (fused to lacZ) lacking upstream activating sequences. Combined, the simplest interpretation of these results is that TSF1 to TSF6 encode factors that control the function of the basic RNA polymerase II transcriptional machinery.

Base Sequence↗
PubMed1993

Role of ouabain-like factors in hypertension: effects of ouabain and certain endogenous ouabain-like factors in hypertension.

Several reports suggest the presence of sodium-potassium pump inhibitor in plasma and various tissues, particularly during volume-expanded state and low-renin hypertension. It has been hypothesized that by inhibiting the cardiovascular muscle-cell Na(+)-K+ pump, this inhibitor can constrict blood vessels, enhance vasoconstriction, and increase cardiac contractility, thereby raising blood pressure. Only two such endogenous inhibitors have been chemically characterized: the bufodienolide derivative, resibufogenin, obtained from toad skin and plasma; and a factor with the same structure (based on mass spectral analysis) as ouabain, from human plasma. However, unlike bufalin (aglycone), which is almost structurally identical to resibufogenin, neither ouabain nor ouabagenin (aglycone of ouabain) caused a sustained increase in blood pressure when infused in equimolar doses during a 30-min period in rats. Because the rat is 10(4)-fold less sensitive to ouabain than the human is, we wondered whether the absence of a response to ouabain was due to the short infusion time. Therefore, in new experiments ouabain was administered chronically during a 6- to 7-week period to two-kidney normal rats and rats with 70, 60, and 25% reduced renal mass. Reduced renal mass rats were used because these rats have decreased sodium excretion capacity, and thus we hoped the action of exogenous ouabain would be potentiated in these volume-expanded rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Role of digitalis-like substance in experimental insulin-dependent diabetes mellitus hypertension.

Hypertension is frequently associated with insulin-dependent diabetes mellitus, but the mechanism of the hypertension is unknown. An animal model of insulin-dependent diabetes mellitus hypertension could be helpful in determining the mechanism, but experimental insulin-dependent diabetes mellitus has been infrequently and irregularly associated with hypertension. In an attempt to develop a dependable model of insulin-dependent diabetes mellitus hypertension, we studied seven series of rats receiving either streptozotocin, surgical reduction of renal mass, or both. We found that superimposing streptozotocin 65 mg/kg body weight on 25% reduced renal mass regularly produced insulin-dependent diabetes mellitus and low-renin volume-expanded hypertension and that the animals remained healthy and hypertensive for as long as followed (13 weeks). Microalbuminuria correlated temporally with blood pressure. We used this dependable model to examine the role of endogenous digitalis-like substance in the development of hypertension in insulin-dependent diabetes mellitus. Plasma levels of digoxin-like immunoreactive factor (DIF), determined with a digoxin radioimmunoassay, were significantly higher in these hypertensive rats than in normotensive control rats (two-kidney diabetic rats, 25% reduced renal mass rats receiving vehicle for streptozotocin). This increase in plasma DIF was associated with a decrease in Na+, K(+)-ATPase activity in microsomes prepared from left or right ventricle. Microsomal 5'-nucleotidase, a plasma membrane marker, was unchanged. The plasma DIF level correlated inversely with myocardial Na+, K(+)-ATPase activity and positively with systolic blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effects of all-trans retinoic acid on glycosaminoglycan synthesis in photodamaged hairless mouse skin.

All-trans retinoic acid (tRA) was previously shown to be active in wrinkle reduction in the hairless mouse photoaging model. To address the questions of whether tRA also alters glycosaminoglycan (GAG) synthesis and whether observed wrinkle effacement can be attributed to changes in total GAG production, the effects of tRA on de novo GAG synthesis were examined in this model. Sulfated glycosaminoglycans (S-GAG) and the non-sulfated hyaluronic acid (HA) labeled with [3H]-glucosamine or [35S]-sulfate were found to diffuse differentially into the medium during the labeling period in the control animals (9% and 35% of total incorporated label for HA and S-GAG, respectively). Furthermore, the diffusion of HA into media was significantly changed after tRA treatment (from 9% to 24%), but no alteration was observed in the diffusion of S-GAG. Separation of epidermis and dermis indicated that the additional HA in medium after retinoid treatment primarily originated from the dermis. When incorporated label from the medium and skin fractions was combined, both labeling protocols revealed that 10 weeks of tRA treatment did not increase the total (medium plus skin) de novo synthesis of either HA or S-GAG. Wrinkle effacement as induced by retinoids in the photodamaged mouse skin therefore can not be related to an increased total GAG synthesis.

Animals↗
PubMed1993

Helicobacter pylori.

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Helicobacter Infections↗
PubMed1993

Pharmacological characterization of muscarinic receptor-activated cation channels in guinea-pig ileum.

1. The pharmacological properties of cationic currents activated by acetylcholine (ACh) (Icat) in guinea-pig ileal smooth muscle cells were investigated, with conventional single patch electrode or nystatin-perforated whole-cell recording. Cs-aspartate was used as the internal solution to allow selective measurement of Icat. 2. Well-known K channel blockers, tetraethylammonium (TEA), 4-aminopyridine (4-AP), procaine and quinine as well as a Ca releasing agent, caffeine, all produced concentration-dependent inhibition of Icat with rapid onset (time constant approximately 100 ms), when applied externally. The recovery from the inhibition on washout also occurred rapidly in the order of 100 ms except in the case of quinine. Approximate values of the half inhibitory concentrations (IC50) were 10 nM for TEA and caffeine, 1-5 mM for 4-AP and procaine, and 1 microM for quinine. The mode of inhibition was voltage-dependent, i.e., depolarization relieved the inhibition with no change in reversal potential. 3. Externally applied diphenylamine-2-carboxylate (DPC) derivatives, DCDPC and flufenamic acid, produced potent inhibition of Icat at micromolar concentrations (IC50s were < 30 microM for DCDPC and 32 microM for flufenamic acid). The onset of and recovery from inhibition occurred slowly and the degree of inhibition depended on the membrane potential only weakly, without any discernible change in the reversal potential. 4. All of the above-tested drugs exhibited comparable inhibitory actions on the voltage-dependent Ca current in the concentration ranges effective at inhibiting Icat. However, amongst them, quinine and flufenamic acid seemed to have several-fold better selectivity for the Icat channel than for the voltage-dependent Ca channel. 5. Internally dialysed GTPgammaS (100 microM) induced inward cationic currents. The effects of drugs on these currents were similar to their effects on the Icat current.6. These results clearly indicate that many drugs used as pharmacological tools in smooth muscle research exert considerable nonspecific effects on various types of channels. The mechanism of inhibition and the relevance to use of these drugs as blockers for the I cat channel are discussed.

4-Aminopyridine↗
PubMed1993

The regulation of intracellular Mg2+ in guinea-pig heart, studied with Mg(2+)-selective microelectrodes and fluorochromes.

Because of the reported presence of a Na(+)-Mg2+ exchanger in guinea-pig but not in ferret myocardium, the Mg2+ extrusion mechanism in guinea-pig myocardium has been reinvestigated using Mg(2+)- and Na(+)- selective microelectrodes and the fluorochromes mag-fura-2 and -5. The mean [Mg2+]i measured with microelectrodes in trabeculae or papillary muscles was 0.72 mmol/l (n = 22, thirteen experiments; range 0.42-1.23 mmol/l). Increasing [Mg2+]o from 0.5 mmol/l to either 10.5 or 20 mmol/l caused small increases in [Mg2+]i. Decreasing [Na+]o by 50% had no effect on the [Mg2+]i and there was no change in [Na+]i on increasing [Mg2+]o from 0.5 to 10.5 mmol/l. Varying pHo or changing pHi with NH4Cl did not influence the [Mg2+]i. In vitro calibration of mag-fura-2 and -5 using the ratio method gave values for K'd (experimentally determined dissociation constant) of 22.2 +/- 2.7 (mean +/- S.D., n = 7) and 25.7 +/- 1.3 (n = 4) mmol/l respectively. Mag-fura-2 reacted to physiological concentrations of Ca2+ and mag-fura-5 to changes in pH. In isolated myocytes, Na+ removal gave an apparent increase of [Mg2+]i with mag-fura-2 but not with mag-fura-5. However, when the pHi was altered with NH4Cl mag-fura-5 showed an apparent decrease in [Mg2+]i on application and an apparent increase on removal, with a time course similar to the pHi changes. It is concluded that Mg2+ extrusion in guinea-pig myocardium is not via a Na(+)-Mg2+ exchanger. The use of mag-fura-2 and -5 are limited in their application because of Ca2+ and H+ sensitivity respectively.

Animals↗