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Biomedical subjects

Y Xiong

Publications and source records attributed to Y Xiong.

At least 127 records · Page 7Linked to original sources
PubMed1997

Parathyroid tumor suppressor on 1p: analysis of the p18 cyclin-dependent kinase inhibitor gene as a candidate.

Loss of chromosome arm 1p DNA is the most common molecular defect thus far observed in human parathyroid adenomas, suggesting that 1p is the location of a putative tumor suppressor gene (or genes) whose inactivation contributes frequently to parathyroid tumorigenesis. To narrow the genomic location of this tumor suppressor gene, we analyzed 25 sporadic parathyroid adenomas for allelic loss of polymorphic DNA loci on chromosome 1 using 11 microsatellite markers not previously scored for this set of tumors. Allelic loss on chromosome arm 1p DNA was observed in 8 of 25 adenomas. Marker deletion patterns showed some complexity, with the regions most commonly deleted in these tumors being 1p36 and 1p35-p31. The 1p35-p31 region contains an excellent candidate tumor suppressor gene, p18, whose product is a cell cycle regulator that inhibits the cyclin D1-associated kinase CDK6. Given that cyclin D1 is a parathyroid oncogene, inactivation of an inhibitor of cyclin D1 function, like p18, might also cause excessive parathyroid growth. To examine the involvement of p18 in parathyroid tumorigenesis, we analyzed 25 parathyroid adenomas for mutations of the p18 coding exons by single strand conformational polymorphism analysis and sequencing. No point mutations were found in any of the 25 adenomas. These observations indicate that inactivating mutation of the p18 gene occurs uncommonly, if at all, in parathyroid adenomas. In addition, the data raise the important possibility that more than a single tumor suppressor gene on 1p could contribute to parathyroid neoplasia.

Adenoma↗
PubMed1997

Elevation of an endogenous inhibitor of nitric oxide synthase in diabetic rat serum.

AIM: To study the endogenous inhibitor of NO synthase NG,NG-dimethyl-arginine (DMA) in the diabetic rat serum. METHODS: In streptozocin-induced diabetic rats, the serum DMA level and endothelium-dependent vasorelaxation to acetylcholine (ACh) were determined. RESULTS: The serum DMA concentration was increased in the diabetic rats compared with their age-matched controls (5.4 +/- 1.0 vs 0.7 +/- 0.3 mumol.L-1, P < 0.01). The serum malondialdehyde (MDA) level was also increased in the diabetic rats compared with controls (2.5 +/- 0.3 vs 1.5 +/- 0.1 mumol.L-1, P < 0.01). Vasodilator response to ACh was impaired in diabetic thoracic aortas, which was improved by preincubation with L-arginine 1 mmol.L-1. CONCLUSION: Hyperglycemia elevated the endogenous DMA content, which contributed to attenuated endothelium-dependent vasorelaxation in streptozocin-induced diabetic rats.

Animals↗
PubMed1997

[Observation on the changes of lipid peroxidation in neonates with sclerema].

Thirty-six hospitalized newborn infants with sclerema (case group), which were divided into mild group(n = 18) and severe group(n = 18), and 28 normal neonates (normal control group) were selected to measure the changes of blood lipid peroxidation (LPO) and superoxide dismutase(SOD) so as to study the role of free radicals and lipid peroxide injury the pathogenesis of the entity. The results showed that the plasma LPO contents were significantly increased and SOD were significantly decreased in the case group when compared with those in the normal group (P < 0.01). The plasma LPO was significantly higher and SOD activity was significantly lower in the severe group than those in the mild group (P < 0.01). The study indicates that the free radicals produced in sclerema neonatorum are great in amount and suggests that free radicals possibly participate in the pathogenesis of the disease.

Erythrocytes↗
PubMed1997

[The anti-inflammatory effects of superoxide dismutase].

This paper reports the anti-inflammatory effects of superoxide dismutase (SOD) from pig blood on inflammatory animal models. The experimental results have shown that SOD has significant anti-inflammatory effects. It inhibited carrageenin-induced foot-edema and croton oil induced granulation tissue edema of rats. It also inhibited arthritis induced by egg serum and Freund's adjuvant in rats. The effects were significantly dose-dependent.

Animals↗
PubMed1997

[Immuno-enhancing effect of gebie oral liquid on mice].

Gebie Oral Liquid can increase the weight of thymus and spleen of the mouse, damaged by prednisone and cytoxan, enhance the phagocytosis of monocytes and DHT, and promote the blastogenesis of splenic lymphocytes as well as the activity of NK cells.

Animals↗
PubMed1997

[Studies on hydrolysis of anti-HRV IgY and its oral passive immunity effect to human rotavirus].

In this paper, hens of fine breed were immunized with human rotavirus (HRV), and the anti-HRV IgY was isolated and purified from their eggs collected daily. In addition, the resistance of anti-HRV IgY to hydrolysis of gastric juice and proteases in human digestive tract, the safety of IgY and the effectiveness of IgY in clinical use were observed as well. The results showed that anti-HRV IgY has a fairly good resistance to gastroinstestinal proteases. The safety of using anti-HRV IgY was affirmed by oral administration to mice of a solution of IgY. In clinical test the IgY has been proved to be anti-HRV and, therefore, effective against infections of infant diarrhea induced by HRV.

Administration, Oral↗
PubMed1996

Molecular analysis of the cyclin-dependent kinase inhibitor genes p15INK4b/MTS2, p16INK4/MTS1, p18 and p19 in human cancer cell lines.

Cyclin-dependent kinase-4 inhibitor genes (INK4) regulate the cell cycle and are candidate tumor-suppressor genes. To determine if alterations in the coding regions of the p18 and p19 genes, which are novel members of the INK4 family and if they correlate with the development of human cancer, 100 human cancer cell lines were analyzed. Two other INK4 gene family members, p15INK4b/MTS2 and p16INK4/MTS1 genes were also analyzed. Homozygous deletions of the p15INK4b/MTS2 gene were detected in 29 cancer cell lines. Thirty-five homozygous deletions and 7 intragenic mutations of the pl6INK4/MTS1 gene were also detected in these cell lines. Neither homozygous deletions nor intragenic mutations of the p18 and p19 genes were found except in an ovarian cancer cell line, SKOV3, harboring a single base pair deletion in exon 1 of p19. In p16INK4/MTS1 expression analysis, 5 cell lines with both authentic and alternative spliced p16INK4/MTS1 mRNA had no detectable p16INK4/MTS1 protein. These results suggest the hypotheses that either post-translational modification or enhanced degradation may be responsible for the lack of detection of the p16INK4/MTS1 protein. Using Western blot analysis, subsets of 26 human cancer cell lines were examined for p18 expression and 39 cell lines for p19 expression. All of these cell lines expressed the p18 or p19 protein, with the exception of SKOV3, which did not express p19. Therefore, the INK4 gene family may be divided into 2 groups. One group includes p15INK4b/MTS2 and p16INK4/MTS1, in which genetic and epigenetic alterations might contribute to the development of human cancers. The other group includes p18 and p19, in which somatic mutations are uncommon in many types of human cancer, and their role in human carcinogenesis and cancer progression is uncertain.

Carrier Proteins↗
PubMed1996

Involvement of the cyclin-dependent kinase inhibitor p16 (INK4a) in replicative senescence of normal human fibroblasts.

Human diploid fibroblasts (HDFs) can be grown in culture for a finite number of population doublings before they cease proliferation and enter a growth-arrest state termed replicative senescence. The retinoblastoma gene product, Rb, expressed in these cells is hypophosphorylated. To determine a possible mechanism by which senescent human fibroblasts maintain a hypophosphorylated Rb, we examined the expression levels and interaction of the Rb kinases, CDK4 and CDK6, and the cyclin-dependent kinase inhibitors p21 and p16 in senescent HDFs. Cellular p21 protein expression increased dramatically during the final two to three passages when the majority of cells lost their growth potential and neared senescence but p21 levels declined in senescent HDFs. During this period, p16 mRNA and cellular protein levels gradually rose with the protein levels in senescent HDFs reaching nearly 40-fold higher than early passage cells. In senescent HDFs, p16 was shown to be complexed to both CDK4 and CDK6. Immunodepletion analysis of p21 and p16 from the senescent cell extracts revealed that p16 is the major CDK inhibitor for both CDK4 and CDK6 kinases. Immunoprecipitation of CDK4 and CDK6 and their associated proteins from radiolabeled extracts from senescent HDFs showed no other CDK inhibitors. Based upon these results, we propose that senescence is a multistep process requiring the expression of both p21 and p16. p16 up-regulation is a key event in the terminal stages of growth arrest in senescence, which may explain why p16 but not p21 is commonly mutated in immortal cells and human tumors.

Carrier Proteins↗
PubMed1996

Lack of mutation in the cyclin-dependent kinase inhibitor, p19INK4d, in tumor-derived cell lines and primary tumors.

Inhibitors of cyclin-dependent kinases provide a major mechanism of negative regulation on cell cycle progression. Defects in the function of the CDK inhibitors may lead to uncontrolled cell proliferation and potentially facilitate tumorigenesis. The p16INK4 family of CDK inhibitors specifically prevent the phosphorylation of the retinoblastoma susceptibility gene product, pRb, by inhibiting the kinase activity of CDK4 and CDK6, thereby keeping pRb in its active form as a growth suppressor. The loss of p16INK4 inhibitory activity would, therefore, have the same consequence as the loss of pRb growth suppressing activity. The p16INK4 family currently includes four members, p15INK4b, pl6INK4a, pl8INK4c and p19INK4d. Two members, p15INK4b and pl6INK4a have been found to be deleted and mutated in a variety of human tumor-derived cell lines and primary tumors. In the present study we have examined the genomic status of the newly isolated p19INK4d gene in 75 tumor-derived cell lines; 13 immortalized, transformed or normal cell lines; 19 ovarian tumors and 18 acute myelogenous leukemias. No deletions or point mutations were observed in the pl9INK4d gene. A genetic polymorphism at codon 30 (CGC-->CGG) in exon 1 of the pl9INK4d gene was observed in 10% of the samples under investigation. In the same set of samples, p16INK4a was found to be homozygously deleted in 32% of the tumor derived cell lines. These results together with our previous data that showed a 22% deletion frequency in p15INK4b and rare alterations in the pl8INK4c gene, indicating that the p16INK4a and pl5INK4b, but not the p18INK4c and pl9INK4d genes, are frequently mutated in human tumors. Hence, members of the p16INK4 CDK inhibitor family, while evolutionary related and biochemically indistinguishable, carry out distinct biological functions.

Carrier Proteins↗
PubMed1996

Intragenic mutations of the p16(INK4), p15(INK4B) and p18 genes in primary non-small-cell lung cancers.

The p15(INK4B), p16(INK4) and p18 genes are members of the gene family coding for inhibitors of cyclin-dependent kinases 4 and 6. p15(INK4B) and p16(INK4) are located at 9p21, a chromosomal region frequently deleted in many human neoplasms. To examine the role of these 3 genes in lung carcinogenesis, somatic mutations within the genes were analyzed by single-strand conformation polymorphism and DNA sequencing in 71 non-small-cell lung cancer (NSCLC) samples. Six somatic mutations in the p16(INK4) gene and 3 cases with a polymorphic allele were observed. Loss of heterozygosity in the p18 gene was found in 1 sample. We did not find any intragenic mutations in the p15(INK4B) or p18 genes. We conclude that p16(INK4) mutations play a role in the formation of some NSCLCs, whereas the involvement of p15(INK4B) and p18 is uncommon.

Base Sequence↗
PubMed1996

Targeted in vivo expression of the cyclin-dependent kinase inhibitor p21 halts hepatocyte cell-cycle progression, postnatal liver development and regeneration.

The CDK inhibitor p21 (WAF-1/CIP-1/SDI-1) has been implicated in DNA damage-induced p53-mediated G1 arrest, as well as in physiological processes, such as cell differentiation and senescence, that do not involve p53 function. To determine the impact of p21 on normal development and cell-cycle regulation in vivo, we have generated transgenic mice that abundantly express p21 specifically in hepatocytes. During postnatal liver development, when transgenic p-21 protein becomes detectable, hepatocyte proliferation is inhibited dramatically. This disturbance causes a reduction in the overall number of adult hepatocytes, resulting in aberrant tissue organization, runted liver and body growth, and increased mortality. The transgenic p21 protein is associated with most, if not all, of the cyclin D1-CDK4 in liver but not significantly with other cyclin/CDK proteins, indicating the importance of cyclin D1-CDK4 function in normal liver development. The appearance of large polyploid nuclei in some hepatocytes indicates that p21 may also cause arrest during the G2 phase of the cell cycle. Significantly, partial hepatectomy failed to stimulate hepatocytes to proliferate in p21 transgenic animals. These results provide the first in vivo evidence that appropriate p21 levels are critical in normal development and further implicate p21 in the control of multiple cell-cycle phases.

Animals↗
PubMed1996

Mutational analysis of the p16 family cyclin-dependent kinase inhibitors p15INK4b and p18INK4c in tumor-derived cell lines and primary tumors.

The growth suppressing activity of the retinoblastoma suspectibility gene product, pRb, is down regulated by cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) whose kinase activity is negatively regulated by CDK inhibitors of the p16 family. We have examined the genomic status of two recently isolated p16-related CDK inhibitors, p15 and p18, in 15 normal and 73 tumor-derived cell lines established from 23 different tissues, as well as 26 invasive primary breast cancers and 20 acute myelogenous leukemias. p15 was found to be homozygously deleted in 22% of the tumor derived cell lines, but no point mutations were found in either the cultured cells or the two types of primary tumors. With the exception of one breast cancer cell line, no deletions or mutations were found in the p18 gene in either cultured cell lines or primary tumors. These results indicate that mutation of the p18 gene occurs rarely in human tumors. Thus, while they share a very similar biochemical mechanism of inhibiting the kinase activity of CDK4 and CDK6, members of the p16 gene family play different roles in controlling cell proliferation and suppressing tumor growth.

Amino Acid Sequence↗
PubMed1996

Biochemical characterization of the human cyclin-dependent protein kinase activating kinase. Identification of p35 as a novel regulatory subunit.

The activation of cyclin-dependent protein kinases (Cdks) is dependent upon site-specific phosphorylation and dephosphorylation reactions, as well as positive and negative regulatory subunits. The human Cdk-activating protein kinase (Cak1) is itself a Cdc2-related cyclin-dependent protein kinase that associates with cyclin H. The present study utilized specific anti-Cak1 antibodies and immunoaffinity chromatography to identify additional Cak1-associated proteins and potential target substrates. Immunoprecipitation of metabolically labeled human osteosarcoma cells revealed a number of Cak1-associated proteins, including p95, p37 (cyclin H), and a 35-kDa protein that was further characterized herein. Microsequence analysis obtained after limited proteolysis revealed peptide fragments that are similar, but not identical to, human and yeast cyclins, thus identifying p35 as a cyclin-like regulatory subunit. The greatest sequence similarity of human p35 is with Mcs2, a yeast cyclin that is essential for cell cycle progression. Immunoaffinity chromatography performed under nondenaturing conditions afforded the isolation of enzymatically active Cak1 from cell lysates, enabling studies of kinase autophosphorylation and comparative substrate utilization. Immunoaffinity-purified Cak1 phosphorylated monomeric Cdc2 and Cdk2, but not Cdk4; the phosphorylation of both Cdc2 and Cdk2 were increased in the presence of recombinant cyclin A. These studies indicate that the Cak1 catalytic subunit, like Cdc2 and Cdk2, associates with multiple regulatory partners and suggests that subunit composition may be an important determinant of this multifunctional enzyme.

Amino Acid Sequence↗
PubMed1996

Purification and crystallization of cyclin-dependent kinase inhibitor p21.

p21, a universal inhibitor of mammalian cyclin-dependent kinases (CDK), regulates cell cycle progression by forming various distinct protein complexes with cyclins, CDKs, and the proliferating cell nuclear antigen. We have overexpressed recombinant human p21 in E. coli and purified active p21 to near homogeneity on a large scale. Crystals of recombinant p21 have been grown in the space group P2(1) a = 157.4, b = 152.7, c = 90.6 A, and beta = 92.7 degrees. The diffraction data of the recombinant p21 have been collected to 2.5 and 3.5 A resolution for the native crystal and two heavy atom derivatives of mercury and iridium.

Crystallization↗
PubMed1996

The protective effects of ischemic and calcitonin gene-related peptide-induced preconditioning on myocardial injury by endothelin-1 in the isolated perfused rat heart.

This study was to investigate the effects of ischemic preconditioning on endothelin-1-induced myocardial injury and the role of calcitonin gene-related peptide (CGRP) played in such effects. The rat hearts were perfused in a Langendorff mode. Heart rates (HR), coronary flow (CF), left ventricular pressure (LVP) and its first derivative (LV dp/dtmax) were recorded and creatinine phosphate kinase (CPK) from coronary effluent was measured. There were no changes in HR, CF, LVP, or LV dp/dtmax throughout the experiment in the control hearts. Endothelin-1 (100 pmol) significantly decreased HR and CF, impaired the cardiac function, and increased the CPK release. However, the HR, CF, LVP and LV dp/dtmax were significantly improved, while the CPK release was decreased in the preconditioned hearts. CGRP8-37, a selective CGRP receptor antagonist, abolished the cardioprotection of ischemic preconditioning, such as the cardiac function and the CPK release. A similar cardioprotection was observed in the hearts pretreated with CGRP. However, the CGRP-induced preconditioning-like protection was abolished in the presence of CGRP8-17 or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, an inhibitor of protein kinase C. The present study suggests that the cardioprotective effect of ischemic preconditioning on endothelin-1-induced myocardial injury is mediated by CGRP, and that the cardioprotection of CGRP-induced preconditioning is related to the activation of protein kinase C.

Animals↗
PubMed1996

Lipid peroxidation of mitochondrial membrane induced by D1: an organic solvent extractable component isolated from a crude extract of burn eschar.

D1, an organic solvent extractable component of an extract from burn eschar was characterized and the mechanism of its inhibitory effect on mitochondrial respiratory functions was investigated. Using silicic acid column chromatography, it was found that D1 consisted of two parts: a toxic simple lipid and a non-toxic complex lipid. Six subunits were obtained by further silicic acid column chromatography, among them, the no. 4 and no. 6 were toxic. Infrared spectrometric studies showed that no. 4 consisted of esters, while no. 6 were peroxides. D1 also contained large amounts of malonaldehyde (MDA) and lipid hydroperoxides (ROOH). Vitamin E was found to prevent the inhibitory action of D1 on mitochondrial function and to reduce the amount of MDA produced. However, if vitamin E was introduced after the addition of D1 the inhibition could not be prevented, although there was still a reduction in MDA production; therefore, MDA per se was probably not the cause of the inhibition. D1 induced ROOH formation in mitochondrial membranes. Cumene hydroperoxide, an organic hydroperoxide, was capable of inhibiting the mitochondrial function. This inhibitor action was blocked by vitamin E. It is speculated that ROOH in D1 is probably the element that inhibits mitochondrial function. That D1 caused lipid peroxidation of membrane lipid was also proved by analysing the fatty acid composition of mitochondrial membranes before and after treatment with D1. It was found that the amount of polyunsaturated fatty acids decreased and that of saturated fatty acids increased after incubation with D1, a direct proof that lipid peroxidation has occurred. Lipid peroxidation of the membrane lipid was the result of the action of oxygen free radicals. This process was best shown by a chemiluminescence study. In this experiment, D1 induced chemiluminescence which was dose-dependently related to the amount of D1 used. This was probably the most direct proof that D1 caused lipid peroxidation of membrane lipid resulting in damage of the mitochondria.

Burns↗