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Biomedical subjects

F Liu

Publications and source records attributed to F Liu.

At least 595 records · Page 33Linked to original sources
PubMed1994

Promoter targeting by adenovirus E1a through interaction with different cellular DNA-binding domains.

A puzzling property of the transcriptional activators encoded by several animal viruses is their ability to function promiscuously. The adenovirus E1a protein, for example, stimulates transcription of adenoviral genes as well as a wide variety of other viral and cellular genes. We show that E1a can interact with several classes of cellular DNA-binding domains and thereby be recruited to diverse promoters. Our results explain how a single protein can regulate transcription of multiple genes that lack a common promoter element.

Activating Transcription Factor 2↗
PubMed1994

Identification of serines-967/968 in the juxtamembrane region of the insulin receptor as insulin-stimulated phosphorylation sites.

A line of Chinese hamster ovary cells overexpressing protein kinase C alpha was transfected with cDNAs encoding either the wild-type human insulin receptor or one of two mutant insulin receptors with either Ser-967 and -968 or -974 and -976 in the juxtamembrane region changed to alanine. Both mutant receptors exhibited normal insulin-activated tyrosine kinase activity as assessed by either autophosphorylation or insulin-stimulated increases in anti-phosphotyrosine-precipitable phosphatidylinositol 3-kinase. The wild-type and mutant insulin receptors were also examined for serine and threonine phosphorylation in response to insulin and activation of protein kinase C. To visualize Ser/Thr-phosphorylation sites of the receptor better in response to insulin, the receptor from in vivo-labelled insulin-treated cells was first treated with a tyrosine-specific phosphatase to remove all tyrosine phosphorylation. Phosphopeptides from the three receptors were analysed by high-percentage polyacrylamide/urea gel electrophoresis and two-dimensional t.l.c. The mutant receptor lacking Ser-967 and -968 but not the mutant lacking Ser-974 and -976 was found to be missing phosphorylated peptides in response to insulin and, to a lesser extent, after activation of protein kinase C. However, the insulin-stimulated increase in anti-phosphotyrosine-precipitable phosphatidylinositol 3-kinase was inhibited to the same extent by activation of protein kinase C in cells expressing the two mutant receptors as in cells expressing the wild-type receptor. These results indicate that these four serine residues in the juxtamembrane region are not major regulatory sites of the intrinsic tyrosine kinase activity of the insulin receptor by protein kinase C, although Ser-967 and/or -968 appear to be phosphorylated in response to insulin.

Animals↗
PubMed1994

Simultaneous detection of multiple bone-related mRNAs and protein expression during osteoblast differentiation: polymerase chain reaction and immunocytochemical studies at the single cell level.

Messenger RNA expression analyzed by in situ hybridization and Northern analysis and protein expression analyzed biochemically or immunocytochemically have been used to study the developmental expression of various osteoblast (OB)-associated molecules. These approaches have shown that over a time course of OB differentiation in vivo and in vitro, the expression of macromolecules associated with OB cells changes. However, ambiguities in data from different approaches and in populations representative of cells at different developmental stages are extant. To begin to discriminate differentiation stages with more precision and to address intercellular heterogeneity, fetal rat calvaria cells were grown at low densities under conditions in which bone nodules form and mineralize and colonies were classified morphologically as fibroblastic or osteoblastic (early, intermediate, or mature). Whole discrete colonies and single cells from individual colonies were analyzed molecularly by a random amplification poly(A)-polymerase chain reaction (PCR) and for protein expression by immunocytochemistry; we analyzed the expression of known bone-related macromolecules (collagen type I, alkaline phosphatase, osteopontin, bone sialoprotein, and osteocalcin). Both PCR and immunocytochemistry revealed that different colony types were reproducibly distinguishable in their expression of either general (collagen type I) or bone-associated (alkaline phosphatase, osteopontin, bone sialoprotein, and osteocalcin) macromolecules, such that fibroblastic colonies were distinguishable from osteoblastic colonies and the latter could be subdivided into less mature or more mature osteoblastic colonies. While some aspects of the temporal differentiation sequence defined earlier were confirmed, several additional features were evident from these single cell-single colony studies. First, different repertoires of OB-associated markers were expressed in different cells, suggesting variation in the switch-on of the OB differentiation program and heterogeneity in the OB phenotype. Second, among colonies classified as fibroblastic on the basis of morphology heterogeneity was also evident and there were some cells expressing features consistent with their being osteoprogenitor cells. Our data support the hypothesis that individual fibroblastic and osteoblastic cells are heterogeneous in expression of marker molecules. We also conclude that individual cells and colonies analyzed by poly(A)-PCR will be useful in lieu of mass populations to extend investigation of stages in the progression of OB differentiation.

Alkaline Phosphatase↗
PubMed1994

Flexible vowel recognition by the generation of dynamic coherence in oscillator neural networks: speaker-independent vowel recognition.

We propose a new model for speaker-independent vowel recognition which uses the flexibility of the dynamic linking that results from the synchronization of oscillating neural units. The system consists of an input layer and three neural layers, which are referred to as the A-, B- and C-centers. The input signals are a time series of linear prediction (LPC) spectrum envelopes of auditory signals. At each time-window within the series, the A-center receives input signals and extracts local peaks of the spectrum envelope, i.e., formants, and encodes them into local groups of independent oscillations. Speaker-independent vowel characteristics are embedded as a connection matrix in the B-center according to statistical data of Japanese vowels. The associative interaction in the B-center and reciprocal interaction between the A- and B-centers selectively activate a vowel as a global synchronized pattern over two centers. The C-center evaluates the synchronized activities among the three formant regions to give the selective output of the category among the five Japanese vowels. Thus, a flexible ability of dynamical linking among features is achieved over the three centers. The capability in the present system was investigated for speaker-independent recognition of Japanese vowels. The system demonstrated a remarkable ability for the recognition of vowels very similar to that of human listeners, including misleading vowels. In addition, it showed stable recognition for unsteady input signals and robustness against background noise. The optimum condition of the frequency of oscillation is discussed in comparison with stimulus-dependent synchronizations observed in neurophysiological experiments of the cortex.

Auditory Cortex↗
PubMed1994

Milk is a useful test meal for measurement of small bowel transit time.

To improve and standardize the measurement of small bowel transit time, milk was employed for the test meal instead of the conventional lactulose meal. Although 92% of the subjects were lactase deficient, only 2% were milk intolerant and 13% were lactose intolerant. Small bowel transit time with milk (milk breath hydrogen test) was 113 +/- 9 min (mean +/- SE, n = 20); the normal range calculated from the mean +/- 2 SD was 31-195 min. The coefficient of variation in the milk hydrogen breath test was 13 +/- 4% (n = 6), whereas in the lactulose hydrogen breath test, it was 39 +/- 16% (n = 10). The frequency of non-hydrogen producers, the occurrence of discomfort, and the reproducibility were better, though not significantly so, in the milk hydrogen breath test than in the lactulose. Since lactase activity in the intestine is variable in lactase-deficient subjects, small bowel transit times for milk may change from subject to subject. However, individual reproducibility of the milk hydrogen breath test is good. It could be useful for pharmacological experiments using paired comparison, for screening tests, or for the follow up of diseases in which small bowel transit time is affected.

Aged↗
PubMed1994

Effects of stimulation of the vestibular nuclei on posterior hypothalamic neuron activity in guinea pigs.

To clarify the differences among the four main vestibular nuclei in the vestibulo-autonomic reflex, we examined the effects of electrical stimulation of superior, lateral, medial and descending vestibular nuclei (SVN, LVN, MVN and DVN) on posterior hypothalamic area (PHA) neurons in the guinea pig. Ipsi- and contralateral SVN stimulation produced excitation in 30% and 25% of the PHA neurons tested, respectively. Twenty percent of the PHA neurons showed an excitatory response to ipsilateral LVN stimulation while 60% of the neurons tested responded to contralateral LVN stimulation, including excitation of 36% and inhibition of 24%. MVN and DVN stimulation produced little change in PHA neuron activity. These findings suggest that vestibular information processed in the SVN and the LVN is conveyed to the hypothalamus and may then contribute to activation of the vestibulo-autonomic reflex.

Animals↗
PubMed1994

Cell cycle regulation of the p34cdc2 inhibitory kinases.

In cells of higher eukaryotic organisms the activity of the p34cdc2/cyclin B complex is inhibited by phosphorylation of p34cdc2 at two sites within its amino-terminus (threonine 14 and tyrosine 15). In this study, the cell cycle regulation of the kinases responsible for phosphorylating p34cdc2 on Thr14 and Tyr15 was examined in extracts prepared from both HeLa cells and Xenopus eggs. Both Thr14- and Tyr15- specific kinase activities were regulated in a cell cycle-dependent manner. The kinase activities were high throughout interphase and diminished coincident with entry of cells into mitosis. In HeLa cells delayed in G2 by the DNA-binding dye Hoechst 33342, Thr14- and Tyr15-specific kinase activities remained high, suggesting that a decrease in Thr14- and Tyr15- kinase activities may be required for entry of cells into mitosis. Similar cell cycle regulation was observed for the Thr14/Tyr15 kinase(s) in Xenopus egg extracts. These results indicate that activation of CDC2 and entry of cells into mitosis is not triggered solely by activation of the Cdc25 phosphatase but by the balance between Thr14/Tyr15 kinase and phosphatase activities. Finally, we have detected two activities capable of phosphorylating p34cdc2 on Thr14 and/or Tyr15 in interphase extracts prepared from Xenopus eggs. An activity capable of phosphorylating Tyr15 remained soluble after ultracentrifugation of interphase extracts whereas a second activity capable of phosphorylating both Thr14 and Tyr15 pelleted. The pelleted fraction contained activities that were detergent extractable and that phosphorylated p34cdc2 on both Thr14 and Tyr15. The Thr14- and Tyr15-specific kinase activities co-purified through three successive chromatographic steps indicating the presence of a dual-specificity protein kinase capable of acting on p34cdc2.

Animals↗
PubMed1994

TATA box-binding protein (TBP) is a constituent of the polymerase I-specific transcription initiation factor TIF-IB (SL1) bound to the rRNA promoter and shows differential sensitivity to TBP-directed reagents in polymerase I, II, and III transcription factors.

The role of the Acanthamoeba castellanii TATA-binding protein (TBP) in transcription was examined. Specific antibodies against the nonconserved N-terminal domain of TBP were used to verify the presence of TBP in the fundamental transcription initiation factor for RNA polymerase I, TIF-IB, and to demonstrate that TBP is part of the committed initiation complex on the rRNA promoter. The same antibodies inhibit transcription in all three polymerase systems, but they do so differentially. Oligonucleotide competitors were used to evaluate the accessibility of the TATA-binding site in TIF-IB, TFIID, and TFIIIB. The results suggest that insertion of TBP into the polymerase II and III factors is more similar than insertion into the polymerase I factor.

Acanthamoeba↗
PubMed1994

Insulin-like growth factor and growth hormone receptor in nephrotic rats.

In an attempt to elucidate the mechanism of growth retardation in the nephrotic syndrome, specific serum and hepatic growth factors were measured in Sprague-Dawley rats in which nephrotic syndrome was produced by administration of puromycin (1.5 mg.100 g body wt-1.day-1) for 12 days. On the 13th day, the results of these nephrotic animals were compared with those of an equal number of pair-fed and control animals: the mean dietary intake of the nephrotic group was 71% that of the control group (P < 0.001). Serum insulin-like growth factor (IGF) binding protein-3 was significantly reduced (P < 0.005) in the nephrotic rats, compared with the pair-fed and the control groups. Hepatic IGF-I mRNA in the nephrotic rats averaged 36% that of control (P < 0.001) and 46% that of the pair-fed animals (P < 0.001). Hepatic growth hormone receptor (GHr) mRNA in the nephrotic rats averaged 19% of that of the control (P < 0.001) and 27% of that of the pair-fed rats (P < 0.001). These results indicate that the growth retardation of the nephrotic rats may be associated with the significant decrease in IGF-I mRNA and reduction in GHr mRNA.

Animals↗
PubMed1994

Prostaglandin B2-induced pulmonary hypertension is mediated by TxA2/PGH2 receptor stimulation.

We investigated whether the physiological effects of prostaglandin B2 (PGB2) in the pulmonary circulation might be due to stimulation of thromboxane A2-prostaglandin H2 (TxA2/PGH2) receptors. In seven anesthetized rabbits, intravenous infusion of PGB2 (5.0 micrograms/kg) caused pulmonary hypertension as evidenced by increases in right ventricular systolic blood pressure. The magnitude of the pulmonary hypertension was comparable to that observed after infusion of the TxA2 mimetic U-46619 at a significantly lower dose (0.5 micrograms/kg), indicating that the effects of PGB2 in the intact animal are similar to TxA2 but less potent. Additionally, the TxA2/PGH2-receptor antagonist SQ-29548 blocked the pulmonary blood pressure responses elicited by PGB2. Receptor-binding studies using the TxA2 receptor ligand [3H]SQ-29548 indicated that PGB2 was a potent competitor for TxA2/PGH2 receptor binding. In agreement with the results from the intact animal, however, the efficacy of inhibition with PGB2 was significantly less than that measured for the TxA2 agonist U-46619. All of these results are consistent with the hypothesis that the physiological effects of PGB2 are mediated by stimulation of TxA2/PGH2 receptors.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1994

Mechanisms for the tachypneic response to the thromboxane A2 mimetic U-46,619 in rabbits.

These experiments were designed to determine if intravenous infusion of the thromboxane A2 mimetic, U-46,619, would elicit tachypnea in the rabbit, and if so whether the afferent signal was generated by receptors innervated by myelinated or unmyelinated vagal nerve fibers. Intravenous infusion of U-46,619 (0.5 microgram/kg delivered over 10 s) increased breathing frequency (26%) and right ventricular blood pressure (59%) in the anesthetized rabbit (n = 10). Systemic arterial blood pressure, heart rate, and tidal volume were unaffected by the infusion of U-46,619. When myelinated fiber conduction in the vagus nerve was eliminated by bilaterally cooling the nerve to 6 degrees C, the increase in breathing frequency was only 5% above baseline levels. The tachypneic response to U-46,619 was totally eliminated when both myelinated and unmyelinated fiber conduction was abolished by cooling the vagi to 0 degree C. The increase in right ventricular blood pressure after U-46,619 infusion was unaffected by vagal cooling. Because most (> 80%) of the tachypneic response to U-46,619 was eliminated by blockade of myelinated vagal fiber conduction, we conclude that the tachypneic response to U-46,619 is mediated mostly by receptors innervated by myelinated vagal afferent fibers in the anesthetized rabbit.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1994

Thromboxane A2 mimetic U-46619 induces systemic and pulmonary hypertension and delayed tachypnea in the goat.

Cardiorespiratory variables were measured continuously in five conscious goats before and after the infusion of U-46619 at a dose of either 2, 4, or 6 micrograms.kg-1.5 min-1. Infusion of U-46619 led to immediate increases in pulmonary arterial blood pressure (ABP) that were sustained for up to 15 min after the end of the infusion. Systemic ABP also increased, but the relative increase from control was less than the pulmonary pressor response. At the highest dose, U-46619 elicited a delayed tachypneic response that was greatest several minutes after the infusion was stopped. U-46619 was also infused simultaneously with sodium nitroprusside to clamp ABP pressure at baseline levels to determine whether stimulation of baroreceptors might contribute to the latency of the tachypneic response. Although sodium nitroprusside infusion prevented the increase in ABP, the increase in breathing frequency was still delayed 3-4 min from the start of the infusion. We conclude that U-46619 elicits pulmonary and systemic arterial hypertension in the conscious goat. At the higher dose U-46619 also elicits a delayed tachypnea that remains delayed even if ABP is normal.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1994

Biochemical mechanisms of insulin resistance.

The insulin receptor tyrosine kinase is required for insulin to elicit subsequent biological signalling. Recent studies have identified several endogenous substrates of the insulin receptor kinase, including one called insulin receptor substrate 1 (IRS-1). Tyrosine phosphorylation of this substrate results in its being bound by various proteins containing src homology 2 (SH2) sites, including a phosphatidylinositol 3-kinase and a ras activator complex containing GRB2 and son of sevenless (SOS) 1. Decreases in the insulin receptor tyrosine kinase activity have been observed in various insulin-resistant states, such as non-insulin-dependent diabetes mellitus. A model of insulin resistance has recently been described in which the insulin receptor is expressed in Chinese hamster ovary cells along with the phospholipid- and calcium-activated serine/threonine kinase called protein kinase C. In this model system, activation of protein kinase C is shown to interfere with insulin receptor signalling by inhibiting tyrosine phosphorylation of IRS-1 and its subsequent binding by phosphatidylinositol 3-kinase. Such a model system may be further utilized to determine the detailed biochemical basis for insulin resistance.

Animals↗
PubMed1994

Modification of pressure natriuresis by long-term losartan in spontaneously hypertensive rats.

The goal of this study was to determine how long-term treatment of spontaneously hypertensive rats with losartan affects the pressure-natriuresis curve. Rats were treated with losartan (12 to 15 mg.kg-1.d-1 in drinking water) starting at 4 to 5 weeks of age. At 8 to 9 weeks of age, pressure natriuresis was studied in treated and untreated anesthetized rats using a preparation involving volume expansion and fixed neural and hormonal influences on the kidney. In some untreated rats, losartan (10 or 30 mg.kg-1 i.v.) was given acutely. Average initial mean arterial pressure (+/- SEM) for untreated rats was 164 +/- 2 mm Hg (n = 13) and 131 +/- 3 mm Hg (n = 13) for rats treated chronically with losartan (P < .01). Short-term losartan did not alter arterial pressure significantly. Glomerular filtration rate was not altered significantly by losartan, and renal blood flow was increased modestly by long- and short-term (10 mg.kg-1) losartan at several levels of renal artery pressure. At renal artery pressures of 130 to 175 mm Hg, there were no significant differences between untreated and short-term losartan rats for urine flow, total and fractional sodium excretions, and renal interstitial hydrostatic pressure. The relation between renal artery pressure and urine flow, sodium excretion, or fractional sodium excretion was shifted to the left by long-term losartan treatment. At identical renal artery pressures, renal interstitial hydrostatic pressure was not significantly different among losartan-treated (short or long term) and respective control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1994

Insulin-like growth factor axis abnormalities in prostatic stromal cells from patients with benign prostatic hyperplasia.

Benign prostatic hyperplasia (BPH) is a common proliferative disorder of unknown etiology. To assess whether patients with BPH have alterations in their prostatic IGF axis, we measured the expression (by Northern blotting) and the production (by Western ligand blotting and RIA) of insulin-like growth factor-II (IGF-II) and IGF-binding proteins (IGFBPs) in prostatic epithelial and stromal cell strains grown from normal (n = 7), hyperplastic (n = 7), and malignant (n = 5) surgical specimens. Levels of IGF-II messenger ribonucleic acid (mRNA; normalized for actin expression) were 10-fold higher in BPH stromal cell strains compared to those in normal stromal cell strains (P < 0.0001). Western ligand blotting of conditioned medium (CM) from normal stromal cells demonstrated the presence of IGFBP-2, -3, and -4. In the CM of BPH stromal cells, IGFBP-2 levels were dramatically reduced to less than 20% of normal (P < 0.001). Additionally, IGFBP-5, which was not observed in significant amounts in normal stromal cell-CM, was found in large quantities in BPH stromal cell-CM. Northern blot analysis of mRNA from normal and BPH stromal cells demonstrated a 5-fold decrease in IGFBP-2 mRNA (P < 0.001) and a 4-fold increase in IGFBP-5 mRNA (P < 0.01) in BPH compared to normal cells. In prostate stromal cells from cancer specimens, no abnormalities were found. No abnormalities were observed in the IGF axis parameters evaluated in prostate epithelial cells from BPH or cancer strains. We conclude that prostatic stromal cell strains isolated from patients with BPH hyperexpress the mRNA for IGF-II and IGFBP-5 while expressing reduced amounts of IGFBP-2 mRNA. IGFBP, but not IGF-II, peptide levels in CM correspond to the mRNA differences. This is the first documentation of altered gene and protein expression in this common disease. We speculate that these abnormalities in the IGF axis may be important in the pathogenesis of BPH.

Blotting, Northern↗
PubMed1994

Immunoblot studies of the IGF-related acid-labile subunit.

Insulin-like growth factors I and II (IGF-I and II) are present in serum primarily within a ternary complex consisting of IGF, IGF-binding protein-3 (IGF-3) and acid-labile subunit (ALS). Relatively little is known about ALS as compared to the other components of the complex. We report immunoblot studies of ALS using a new rabbit antiserum to human ALS1-34. The antiserum shows high specificity for ALS, labelling only the intact 82-88 kDa doublet in whole serum. Treatment with endoglycosidase-F leads to only a partial deglycosylation of ALS in whole serum, while purified ALS is reduced to M(r) approximately 58 kDa. Acidification of both whole serum and purified ALS leads to a complete loss of ALS ability to bind to cross-linked IGFBP-3:[125I]IGF-II tracer; however, immunoblot studies show no change in the apparent M(r) of the major ALS band. Immunoblot studies of human serum shows that intact ALS is decreased in growth-hormone (GH) deficiency, increases with GH treatment, is elevated in GH excess and is unchanged with IGF-I treatment. These data provide new information regarding the characteristics of ALS and demonstrate the research utility of a highly-specific antiserum for this protein.

Acromegaly↗