Search PubMed⌕ Search

Biomedical subjects

Y Xiong

Publications and source records attributed to Y Xiong.

At least 163 records · Page 9Linked to original sources
PubMed1995

Role of phosphodiesterase isoenzymes in regulating intracellular cyclic AMP in adenosine-stimulated smooth muscle cells.

Three phosphodiesterase (PDE) isoenzymes were separated by Mono Q h.p.l.c. column chromatography from the soluble fraction of a homogenate of pig aortic smooth muscle cells. The first peak of PDE activity was stimulated by calmodulin in the presence of calcium. The second broad peak contained at least two activities, which were sensitive to inhibition by CI-930 or rolipram respectively. The distribution of total cellular enzyme activity in different subcellular fractions was also determined. The majority (78%) of the total activity was present in the cytosolic fraction, 18% of activity was in a membrane-bound form and 4% of activity was associated with the cytoskeleton. Rolipram-sensitive PDE was present predominantly in the cytosolic fraction, whereas cyclic GMP-inhibited, CI-930-sensitive PDE was evenly distributed between the cytosolic and particulate fractions. All of the calmodulin-dependent PDE activity was found in the soluble fraction. CI-930 and rolipram enhanced, by 2-fold and 3-4-fold respectively, the adenosine-stimulated rise in cellular cyclic AMP level. The increase in cyclic AMP levels due to CI-930 or rolipram was dose-dependent. Removal of adenosine once cyclic AMP had risen resulted in a rapid fall in cyclic AMP levels even in the presence of rolipram and CI-930. M&B 22,948, the calmodulin-dependent PDE inhibitor, caused less than a 25% increase of the adenosine-stimulated cyclic AMP levels by itself, but it contributed substantially to controlling the cyclic AMP levels after the removal of adenosine when used together with CI-930 and rolipram. These phenomena suggested that all three PDE isoenzymes participated in modulating cellular cyclic AMP levels after adenosine stimulation, and that differential importance of the individual isoenzymes depends on cellular cyclic AMP levels.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1995

Chromosomal mapping of the genes for the human cell cycle proteins cyclin C (CCNC), cyclin E (CCNE), p21 (CDKN1) and KAP (CDKN3).

Many gene products associated with the cdk cell cycle kinases are thought to regulate the active kinase complex and thus regulate the transition points of the cell cycle. Genes encoding these proteins may potentially function as oncogenes or tumor suppressor genes. We describe the chromosomal mapping by FISH of the genes for several cdk-associated proteins including human CCNC (cyclin C) to 6q21, CCNE (cyclin E) to 19q12-->q13, CDKN1 (p21) to 6p21.2 and CDKN3 (KAP to 14q22). Some of these sites are near chromosomal translocations or LOH sites common to a variety of human tumors. The potential role for each of these genes in neoplasia is discussed.

Cell Cycle Proteins↗
PubMed1995

Evidence that diazoxide promotes calcium influx in mouse keratinocyte cultures by membrane hyperpolarization.

We have used fura-2/AM to investigate the effect of diazoxide on the cytosolic calcium concentration (Cai) in primary mouse keratinocyte cultures. Treatment of keratinocytes with 100 microM diazoxide induced a transient peak in Cai, followed by a sustained elevation. Depletion of medium calcium by addition of EGTA abolished the diazoxide-induced Cai response, indicating that the agent promoted calcium influx without release of calcium from intracellular stores. The diazoxide-induced rise in Cai was inhibited both by addition of 60 mM KCl to the assay buffer and by preincubation with glibenclamide, a specific K+ channel blocker. In addition, studies with the membrane potential-sensitive fluorescent probe bis-oxonol demonstrated that diazoxide hyperpolarized keratinocyte membranes. These findings suggest that keratinocytes possess K+ channels, and that the previously reported proliferation effects of K+ channel openers such as diazoxide on keratinocytes may result from hyperpolarization-induced elevation of Cai.

Animals↗
PubMed1995

Signaling properties of mouse and human corticotropin-releasing factor (CRF) receptors: decreased coupling efficiency of human type II CRF receptor.

CRF is the primary neuroregulator of the function of the hypothalamic-pituitary-adrenal axis. We have recently cloned a mouse CRF receptor (mCRF-R) complementary DNA (cDNA) from an AtT-20 cell cDNA library by polymerase chain reaction. To compare the functions of mCRF-R to those of the human type I and type II CRF receptors (hCRF-RI and hCRF-RII), cDNAs were cloned into the expression vector pcDNA1 and transfected into COS-7 cells. CRF binding and CRF-stimulated cAMP accumulation as well as phosphoinositide hydrolysis were measured. Scatchard analysis of the binding of 125I-labeled [Tyr0]r/hCRF ([125I]CRF) to COS-7 cells expressing mCRF-R and hCRF-RI cDNAs revealed the same apparent Kd (9 nM). In contrast, the apparent binding Kd for hCRF-RII was 20 nM CRF. Maximal stimulatory concentrations (1 microM) of rat/human CRF-(1-41) (r/hCRF) increased cAMP accumulation in COS-7 cells transfected with mCRF-R, hCRF-RI, and hCRF-RII cDNA plasmid (10 micrograms each) from basal values of 8-19 pmol/10(5) cells.15 min to 84 +/- 10, 87 +/- 16, and 45 +/- 16 pmol/10(5) cells.15 min, respectively. The EC50 values of r/hCRF-stimulated cAMP accumulation in COS-7 cells expressing mCRF-R and hCRF-RI cDNAs were similar at 0.4 +/- 0.2 and 0.7 +/- 0.2 nM, respectively. Conversely, the EC50 of r/hCRF-stimulated cAMP accumulation in hCRF-RII-transfected COS-7 cells was 47.5 +/- 18.9 nM. As the level of expression of hCRF-RII was lower than that of hCRF-RI, we compared r/hCRF-stimulated cAMP accumulation in COS-7 cells expressing low and high levels of hCRF-RI. The EC50 for r/hCRF-stimulated cAMP accumulation in COS-7 cells transfected with hCRF-RI did not change when receptor expression was varied by a factor of 1- to 8.4-fold. In contrast, the EC50 for r/hCRF-stimulated cAMP accumulation mediated by hCRF-RII was at least 100-fold higher than that mediated by the hCRF-RI in COS-7 cells, which suggests poor coupling between hCRF-RII and adenylate cyclase. Inositol phosphate (IP) levels were also determined in mCRF-R, hCRF-RI, and hCRF-RII cDNA-transfected COS-7 cells stimulated with increasing concentrations of r/hCRF. r/hCRF-stimulated IPs accumulation was dose dependent in COS-7 cells expressing mCRF-R and hCRF-RI using 100 and 1000 nM r/hCRF. Concentrations of 10 (or less) nM r/hCRF had no effect on IP generation. hCRF-RII did not mediate stimulation of IP even at 1000 nM r/hCRF.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

[The effectiveness of combined insulin and sulfonylurea in treating non-insulin dependent diabetic patients].

The effectiveness of combined therapy with insulin and sulfonylurea in non-insulin dependent diabetes mellitus (NIDDM) patients has, for decades, been a debated issue. In order to probe this question, we studied 33 diabetes mellitus patients aged 40 years and over, having a history of this disease for more than 5 years, treated with one of the sulfonylureas at maximal dosage for three weeks but without effect. These 33 cases were divided into three groups randomly: group A: treated with glurenorm and insulin. B insulin and C glurenorm. The treatment lasted 4 months. During the course of the trial, estimation of the free-insulin, C-peptide, blood glucose etc. was carried out three times i.e. one before the trial and then 2, 4 months after the trial. The data were dealed with U-test and comparison was made before and after the trial and between the three groups. It is shown that combined therapy with sulfonylurea and insulin is effective in NIDDM patients, especially in those with secondary failure of beta-cell function and the combined therapy may be used in NIDDM patients during the transitional period from treatment with sulfonylurea alone to traditional insulin cure.

Adult↗
PubMed1995

[Genes and the modulation of learning and memory].

Recently, progress in the study of the relationship between gene and the modulation of learning and memory was noticeable. The studies showed that: (1) The expression of immediate early genes (IEGs), especially the c-fos, is a necessary prerequisite for the formation of memory; the induction of long term potentiation (LTP) is accompanied by an increase of IEGs expression; (2) Mice with deficiency of alpha-Calcium-Calmodulin Kinase II (alpha-CaMK II), or neural-cell adhesion molecules (N-CAM) or tyrosine kinase gene (fyn) generated by gene targeting appear deficits in spatial learning and memory, mutation of alpha-CaMK II and N-CAM gene can also interfere with the induction and maintenance of LTP; (3) The single-gene mutants of Drosophilia (dnc, rut) showed significant decrease of the ability of memory. The mechanism is related to the altered synaptic plasticity, and the mushroom body may be the memory center of Drosophila.

Animals↗
PubMed1994

Growth suppression by p18, a p16INK4/MTS1- and p14INK4B/MTS2-related CDK6 inhibitor, correlates with wild-type pRb function.

The D-type cyclin-dependent kinases CDK4 and CDK6 are complexed with many small cellular proteins (p14, p15, p16, p18, and p20). We have isolated cDNA sequences corresponding to the MTS2 genomic fragment that encodes the CDK4- and CDK6-associated p14 protein. By use of a yeast interaction screen to search for CDK6-interacting proteins, we have also identified an 18-kD human protein, p18, that is a homolog of the cyclin D-CDK4 inhibitors p16 (INK4A/MTS1) and p14 (MTS2/INK4B). Both in vivo and in vitro, p18 interacts strongly with CDK6, weakly with CDK4, and exhibits no detectable interaction with the other known CDKs. Recombinant p18 inhibits the kinase activity of cyclin D-CDK6. Distinct from the p21/p27 family of CDK inhibitors that form ternary complexes with cyclin-CDKs, only binary complexes of p14, p16, and p18 were found in association with CDK4 and/or CDK6. Ectopic expression of p18 or p16 suppresses cell growth with a correlated dependence on endogenous wild-type pRb.

Amino Acid Sequence↗
PubMed1994

Transcriptional repression of the D-type cyclin-dependent kinase inhibitor p16 by the retinoblastoma susceptibility gene product pRb.

Progression of the eukaryotic cell division cycle is regulated by a series of structurally related serine/threonine protein kinases known as cyclin-dependent kinases (CDKs). The D-type cyclin-dependent kinases, CDK4 and CDK6, have been strongly implicated in the control of G1 progression and the phosphorylation of the retinoblastoma protein, pRb. The formation of complexes and enzymatic activity of cyclin D-CDK4 and cyclin D-CDK6 kinases is negatively regulated by p16INK4 (MTS1/CDK4I/CDKN2) via its specific interaction with CDK4 and CDK6 catalytic subunits. Here we report that the p16 mRNA accumulates to a high level in cells lacking pRb function and transcription of p16 is repressed by pRb. Our results provide evidence supporting a feedback regulatory loop involving pRb, p16, and cyclin-dependent kinases.

Cyclin-Dependent Kinase 4↗
PubMed1994

Neuronal expression of Fos protein in the paraventricular nucleus of the hypothalamus after i.p. injection of ulcergenic cinchophen.

The purpose of this study was to identify the CNS neurons that express Fos protein after i.p. injection of ulcergenic drug cinchophen (300 mg/kg). This was done in unanesthetized Wistar rats with careful physiological controls. The population of Fos-immunoreactive (Fos-ir) neurons was the largest in the medial parvicellular part of the paraventricular nucleus of the hypothalamus (PVH). Distribution of Fos-ir neurons in the PVH corresponds with that of the parvicellular neurons in the PVH which secrete corticotropin-releasing hormone (CRH). This study strongly suggests that the cinchophen-induced peptic ulcer may originate in excitation of the CRH-secreting neurons in the parvicellular part of the PVH.

Animals↗
PubMed1994

Regulation of fos-lacZ fusion gene expression in primary mouse epidermal keratinocytes isolated from transgenic mice.

The expression of a fos-lacZ fusion gene was studied in primary mouse epidermal keratinocytes obtained from transgenic mice. This gene construct contains the entire upstream regulatory sequence of c-fos, and expression of the endogenous and fusion gene was shown by Northern analysis to correlate upon induction with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). Using a chromogenic substrate of beta-galactosidase, we also demonstrated that expression of the fusion gene product, like that of Fos, was localized to the cell nucleus. In addition, we showed that epidermal keratinocytes responded to dialysed fetal bovine serum (FBS), TPA and high-calcium medium with enhanced Fos-lacZ expression and an inhibition of proliferation. The time course of induction of Fos-lacZ expression was similar for dialysed FBS and TPA, with a peak approximately 2 h after exposure. Exposure for approximately 24 h to an elevated extracellular calcium concentration was required to elicit an increase in Fos-lacZ expression. The lack of an immediate effect of raising medium calcium levels on Fos-lacZ expression contrasted with the rapidity of its effect on DNA synthesis, which was significantly inhibited within 6-8 h. In addition, we found that the protein kinase C inhibitor Ro 31-7549 blocked Fos-lacZ expression induced by TPA but had little or no effect on that elicited by high calcium levels. Thus, although our results indicate that the fos gene product may be involved in mediating epidermal keratinocyte growth arrest in response to differentiative agents such as FBS, TPA and high medium calcium levels, the exact role of this gene product remains unclear.

Animals↗
PubMed1994

Increase of an endogenous inhibitor of nitric oxide synthesis in serum of high cholesterol fed rabbits.

In the present study, the concentration of NG,NG-dimethylarginine (DMA), an endogenous inhibitor of nitric oxide synthesis, was measured with high-performance liquid chromatography, and the effect of hypercholesterolemia on DMA level was investigated in the high fat, high cholesterol fed rabbit. After 6 weeks on a high fat, high cholesterol diet, serum total cholesterol, triglycerides, and lipid peroxides were increased, and atherosclerosis was shown by means of morphological examination. In these rabbits with atherosclerosis, serum level of DMA was significantly raised, while serum creatine level remained normal. This study suggests that chronic hypercholesteremia may stimulate DMA production through elevation of lipid peroxides. The present results implicate endogenous DMA as a contributor to the development of atherosclerosis.

Animals↗
PubMed1994

Influence of humoral control peptides on medullary vasomotor control neurons: microstimulation and double-labeling studies using SHR and WKY rats.

To study the influence of humoral control peptides on medullary vasomotor control neurons, angiotensin II (AII), arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) were microinjected into three vasomotor control areas, i.e., the area postrema (AP), the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM), of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY), and the evoked cardiovascular response was observed. Unlike the injection areas, the threshold dose of one peptide for the cardiovascular response was similar, but the threshold dose differed from peptide to peptide. The threshold dose was lower for AII (0.15-0.29 pmol), in-between for ANP (0.9-1.5 pmol) and higher for AVP (14-30 pmol). No significant difference in the threshold dose was observed between SHR and WKY, suggesting that hypertension in SHR may not be due to the abnormal sensitivity to the three peptides of the vasomotor control neurons in the AP, NTS, and RVLM. The structural basis of the results of the microstimulation experiment was supported by the double-labeling study. The NTS neurons were innervated by (1) the AII-immunoreactive (ir) neurons in both sides of the lateral hypothalamic area (LH), the RVLM and the caudal ventrolateral medulla, and (2) the ANP-ir neurons in both sides of the paraventricular nucleus (Pa) and the LH. The RVLM neurons were innervated by (1) the AII-ir neurons in both sides of the LH and ipsilateral side of the lateral parabrachial nucleus (Pbl) and (2) the ANP-ir neurons in the ipsilateral Pbl. There was no evidence that the AVP-ir neurons in the Pa and the supraoptic nucleus innervate the NTS and the RVLM neurons, or that the AII, ANP or AVP-ir neurons innervate the AP neurons. This study suggests that in common with SHR and WKY rats AII and ANP may influence both the NTS and RVLM not by the humoral pathway but by the neural pathway, and AVP may not influence the three vasomotor control areas by the neural pathway.

Angiotensin II↗
PubMed1994

Recognition of rotavirus antigens by mouse L3T4-positive T helper cells.

A lymphocyte proliferation assay was used to examine the helper T cell response to rotavirus in mice following parenteral immunization with the UK strain of bovine rotavirus. Mixed populations of lymphocytes prepared from spleen or peripheral lymph nodes were tested for proliferation in the presence of UK strain rotaviruses, prepared as cell culture lysates, ultracentrifuged (pelleted) lysates, sucrose-purified virus and caesium chloride-purified virus. Live rotavirus induced non-specific stimulation of lymphocytes, which was not observed in response to inactivated virus. Putative helper T cells of the L3T4+ phenotype were prepared as an enriched population from UK strain-immunized mice or grown in vitro as a polyclonal T cell line. The response of L3T4(+)-enriched cells from mice immunized with inactivated virus was dependent on antigen-presenting cells (APCs). Cells obtained following immunization with live virus did not require further addition of APCs. The response of the L3T4+ T cell line was wholly dependent on APCs. UK strain-specific L3T4+ cells responded to whole UK rotavirus and to isolated VP6 of both UK and C486 rotavirus strains. The results indicate that virus-specific L3T4+ T cells are induced following rotavirus immunization and can respond to epitopes on VP6. UK strain-primed L3T4+ cells also responded to an avian rotavirus strain, Ch2, which shares only minimal serological cross-reactivity with the UK strain. T cell recognition of rotavirus may thus be broadly cross-reactive.

Animals↗
PubMed1994

Repression of cyclin D1: a novel function of MYC.

Constitutive expression of human MYC represses mRNA levels of cyclin D1 in proliferating BALB/c-3T3 fibroblasts. We expressed a series of mutant alleles of MYC and found that downregulation of cyclin D1 is distinct from previously described properties of MYC. In particular, we found that association with Max is not required for repression of cyclin D1 by MYC in vivo. Conversely, the integrity of a small amino-terminal region (amino acids 92 to 106) of MYC is critical for repression of cyclin D1 but dispensable for transformation of established RAT1A cells. Runoff transcription assays showed that repression occurs at the level of transcription initiation. We cloned the promoter of the gene for human cyclin D1 and found that it lacks a canonical TATA element. Transcription starts at an initiator element similar to that of the adenovirus major late promoter; this element can be directly bound by USF in vitro. Expression of MYC represses the cyclin D1 promoter via core promoter elements and antagonizes USF-mediated transactivation. Taken together, our data define a new pathway for gene regulation by MYC and show that the cyclin D1 gene is a target gene for repression by MYC.

3T3 Cells↗