Search PubMed⌕ Search

Biomedical subjects

X Sun

Publications and source records attributed to X Sun.

At least 235 records · Page 13Linked to original sources
PubMed1999

p73 is regulated by tyrosine kinase c-Abl in the apoptotic response to DNA damage.

The protein p73 is a structural and functional homologue of the p53 tumour-suppressor protein but, unlike p53, it is not induced in response to DNA damage. The tyrosine kinase c-Abl is activated by certain DNA-damaging agents and contributes to the induction of programmed cell death (apoptosis) by p53-dependent and p53-independent mechanisms. Here we show that c-Abl binds to p73 in cells, interacting through its SH3 domain with the carboxy-terminal homo-oligomerization domain of p73. c-Abl phosphorylates p73 on a tyrosine residue at position 99 both in vitro and in cells that have been exposed to ionizing radiation. Our results show that c-Abl stimulates p73-mediated transactivation and apoptosis. This regulation of p73 by c-Abl in response to DNA damage is also demonstrated by a failure of ionizing-radiation-induced apoptosis after disruption of the c-Abl-p73 interaction. These findings show that p73 is regulated by a c-Abl-dependent mechanism and that p73 participates in the apoptotic response to DNA damage.

Animals↗
PubMed1999

Effects of serum on calcium mobilization in the submandibular cell line A253.

The effects of serum on inositol 1,4,5-trisphosphate (IP3) formation and Ca2+ mobilization in the human submandibular cell line A253 were studied. Exposure of A253 cells to fetal bovine serum (FBS) elicited a 3.3-fold increase in IP3 formation and a concentration-dependent transient increase in cytosolic free Ca2+ concentration ([Ca2+]i), which was similar in Ca2+-containing and Ca2+-free media. Newborn bovine serum (NBS), but not bovine serum albumin (BSA), induced a similar response. The Ca2+ release triggered by FBS was significantly (88%) reduced by the phospholipase C inhibitor U73122, indicating that Ca2+ release induced by FBS is through the PLC pathway. Pretreatment with the tyrosine kinase inhibitor genistein abolished the FBS- and NBS-induced Ca2+ release, suggesting that tyrosine kinase plays an important role in mediating the Ca2+ release. Pre-exposure to ATP or thapsigargin (TG) significantly reduced the FBS-induced [Ca2+]i increase, indicating that Ca2+ release caused by FBS is from the TG- or ATP-sensitive Ca2+ store. While FBS exposure elicited a large Ca2+ release, it reduced Ca2+ influx. Furthermore, FBS significantly inhibited the Ca2+ influx activated by the depletion of intracellular stores by ATP or TG. These results suggest that (1) serum elicits Ca2+ release from ATP- and TG-sensitive stores, which is mediated by IP3; (2) the serum-induced Ca2+ release may be modulated by a tyrosine kinase-associated process; and (3) serum strongly inhibits Ca2+ influxes including the store depletion-activated Ca2+ influx.

Animals↗
PubMed1999

RIP3, a novel apoptosis-inducing kinase.

RIP3 is a novel gene product containing a N-terminal kinase domain that shares extensive homology with the corresponding domain in RIP (receptor-interacting protein) and RIP2. Unlike RIP, which has a C-terminal death domain, and RIP2, which has a C-terminal caspase activation and recruitment domain, RIP3 has a unique C terminus. RIP3 binds RIP through its unique C-terminal segment and by virtue of this interaction is recruited to the tumor necrosis factor (TNF) receptor-1 signaling complex. Previous studies have shown that RIP mediates TNF-induced activation of the anti-apoptotic NF-kappaB pathway. RIP3, however, attenuates both RIP and TNF receptor-1-induced NF-kappaB activation. Overexpression studies revealed RIP3 to be a potent inducer of apoptosis, capable of selectively binding to large prodomain initiator caspases.

Amino Acid Sequence↗
PubMed1999

[Effects of aluminum on the number of neurons granulovacuolar degeneration in rats].

Effect of aluminum on neurobehavior and the number of neurons in different domains of brain as well as granulovacuolar degeneration (GVD) in hippocampus were observed in Sprague-Dawley rats by intraperitoneal injection with aluminum chloride for 60d. The injection of aluminum at the dosage of 4.0 or 10.0 mg/kg could decrease active avoidance response and spontaneous motor activity in the shuttle-box test and the open field test significantly. Sections from cerebrum, cerebellum and hippocampus were detected with microscope after HE staining. Aluminum(10.0 mg/kg) could result in the decrease of neurons in cerebrum, Pukinje cells in cerebellum and pyramidal neurons in hippocampus. GVD of nerve cells in hippocampus were observed in each group, while the dosages of Al injected was 4.0 and 10.0 mg/kg, the number of GVD cells increased significantly. The incidence of GVD per 300 nerve cells was significantly related to the dosage of aluminum.

Aluminum↗
PubMed1999

[A comparative study of HLA-A locus in northern and southern Chinese by means of PCR/SSOP typing]

OBJECTIVE: To compare the HLA-A locus in a population selected from Beijing (northern group) with that in a population selected from Guangzhou (southern group). METHODS: HLA typing was performed by using PCR/SSOP method. A pair of primer and 54 probes were used. RESULTS: In 18 alleles identified, the differences in gene frequency between northern and southern Chinese were found. In northern group, A*0205, 0210 and 2901 were absent, and the frequencies of A*2601, 3001 and 3101 were higher than those of southern group; while in southern group, A*3103, 3201 and 6801 were absent, the frequencies of A*0203 and 1101 were higher than those of northern group; and in addition, six subtypes of A2 serological specificity, namely A*0201, 0203, 0205, 0206, 0207 and 0210, were found, in which A*0201 predominated. CONCLUSION: There are some differences in the genetic background of northern and southern Chinese. A2 subtypes have important implications for unrelated-donor transplantation.

Journal Article↗
PubMed1999

Enhancement of amyloid beta 42 secretion by 28 different presenilin 1 mutations of familial Alzheimer's disease.

Families bearing mutations in the presenilin 1 (PS1) gene develop early onset familial Alzheimer's disease (FAD). Further, some PS1 mutants enhance secretion of the longer form of amyloid beta protein (Abeta42). We constructed cDNAs encoding human PS1 harboring 28 FAD-linked mutations, and examined the effects of the expressed PS1 mutants on Abeta42 secretion in beta amyloid precursor producing COS-1 cells. All the mutants significantly enhanced the ratio of Abeta42 to total Abeta compared with wild-type PS1. However, the increase in Abeta42 ratio in cells with each PS1 mutation did not correlate with the reported age of onset of FAD caused by that mutation. These results suggest that increased Abeta42 secretion is important for the development of Alzheimer's disease (AD), but may not be the only factor contributing to the onset of AD.

Age of Onset↗
PubMed1999

Analysis of differential effects of Pb2+ on protein kinase C isozymes.

Protein kinase C has been implicated as a cellular target for Pb2+ toxicity. We have previously proposed that Pb2+ modulates PKC activity by interacting with multiple sites within the enzyme. In order to further characterize the Pb-PKC interactions we compared the effects of Pb2+ on the CA-dependent and -independent protein kinase C isozymes using recombinant human PKC-alpha, PKC-epsilon, and PKC-zeta as well as the catalytic fragment of bovine brain protein kinase C, the PKC-M. The results demonstrate that, whereas at pM concentrations Pb2+ activates PKC-alpha half maximally (KAct approximately 2 pM), it has no effect on PKC-epsilon, PKC-zeta, or PKC-M activities. The activation of PKC-alpha by Pb2+ is additive with Ca2+ in a manner indicating interaction with half of the calcium activation sites. In the micromolar range of concentrations, Pb2+ inhibits all PKCs with estimated K0.5 of 1.0, 2.3, 28, and 93 microM for PKC-M, PKC-alpha, PKC-epsilon, and PKC-zeta, respectively. Examination of Pb2+ effects on PKC-M kinetics indicates a mixed type inhibition with respect to ATP and noncompetitive inhibition with respect to histone. Taken together with the results of our previous study (Tomsig and Suszkiw, J. Neurochem. 64, 2667-2673, 1995) and the evidence for the existence of two Ca2+ coordination sites Ca1 and Ca2 within the C2 domain (Shao et al., Science [Washington, D.C.] 273, 248-251, 1996), the results of the current study provide further support for a multisite Pb-PKC interaction scheme wherein lead (1) partially activates the enzyme through pM-affinity interactions with the Ca1 site and inhibits the divalent cation-dependent activity through nM-affinity interactions with Ca2 site in the C2 domain and (2) inhibits the constitutive kinase activity through microM-affinity interactions with the catalytic domain. The concentration dependence of the differential effects of Pb2+ on the calcium-dependent and -independent PKCs underscores the importance of the C2 motif as a high affinity molecular target for Pb2+.

Amino Acid Sequence↗
PubMed1999

[Effect of deoxynivalenol and aflatoxin G1 on apoptosis of human blood lymphocytes in vitro].

Effect of deoxynivalenol (DON) and aflatoxin G1 (AFG1) on human blood lymphocytes in culture were studied with flow cytometric DNA content analyses and DNA agarose gel electrophoresis. DON and AFG1 are two of the predominant mycotoxins contaminating foodstuffs or residents in a high incidence of esophageal cancer in Cixian County, Hebei province. A typical sub-diploid apoptosis peak was demonstrated in lymphocytes treated with DON and AFG1. A significant dose-effect response and time-effect correlation could be found between apoptosis rates and mycotoxin concentrations (DON: 50-2000 micrograms/L and AFG1: 3.12-2000 micrograms/L) and the treated time (DON: 2-72 hours and AFG1: 2-24 hours). The lymphocytes treated with DON and AFG1 showed characteristic 'ladder' pattern in agarose gel electrophoresis. All results confirmed that DON and AFG1 could induce and accelerate apoptosis in human peripheral blood lymphocytes.

Aflatoxins↗
PubMed1999

The t(8;21) fusion protein, AML1/ETO, transforms NIH3T3 cells and activates AP-1.

The 8;21 translocation is the most common cytogenetic abnormality in human acute myelogenous leukemia, joining the AML1 gene on chromosome 21, to the ETO gene on chromosome 8, forming the AML1/ETO fusion gene. The AMLI/ETO fusion protein has been shown to function mainly as a transcriptional repressor of AML1 target genes and to block AML1 function in vitro and in vivo. However, AML1/ETO can also activate the BCL-2 promoter and cause enhanced hematopoietic progenitor self-renewal in vitro, suggesting gain-of-functions unique to the fusion protein. We used NIH3T3 cells to determine the transforming capacity of AML1/ETO, and to further characterize its mechanism of action. Expression of AML1/ETO in NIH3T3 cells caused cell-type specific cell death, and cellular transformation, characterized by phenotypic changes, anchorage-independent growth, and tumor formation in nude mice. In contrast, neither expression of AML1A, AML1B or ETO altered the normal growth pattern of the cells. To investigate the mechanism of transformation by AML1/ETO, we analysed the levels of activated, phosphorylated c-Jun (ser63) and other constituents of the AP-1 complex, in the presence of various AML1/ETO related proteins. Expression of AML1/ETO increased the level of c-Jun-P (ser63), and activated AP-1 dependent transcription, which was inhibited by expression of a dominant-negative c-Jun protein. Mutational analysis revealed that the runt homology domain (RHD) and a C-terminal transcriptional repression domain in AML1/ETO are required for transformation, activation of c-Jun and increased AP-1 activity. These results establish the transforming potential of the t(8;21) fusion protein and link this gain-of-function property to modulation of AP-1 activity.

3T3 Cells↗
PubMed1999

Role of decay-accelerating factor in regulating complement activation on the erythrocyte surface as revealed by gene targeting.

Decay-accelerating factor (DAF) is a glycosylphosphatidylinositol (GPI)-anchored membrane protein that inhibits both the classical and the alternative pathways of complement activation. DAF has been studied extensively in humans under two clinical settings: when absent from the erythrocytes of paroxysmal nocturnal hemoglobinuria (PNH) patients, who suffer from complement-mediated hemolytic anemia, and in transgenic pigs expressing human DAF, which have been developed to help overcome complement-mediated hyperacute rejection in xenotransplantation. Nevertheless, the exact role of DAF in regulating complement activation in vivo on the cell surface and the species specificity of this molecule remain to be fully characterized. To address these issues, we have used gene targeting to produce mice lacking GPI-anchored DAF. We found that erythrocytes from mice deficient in GPI-anchored DAF showed no increase in spontaneous complement activation in vivo but exhibited impaired regulation of zymosan-initiated bystander and antibody-triggered classical pathway complement activation in vitro, resulting in enhanced complement deposition. Despite a high level of C3 fixation, no homologous hemolysis occurred. It is noteworthy that GPI-linked DAF knockout erythrocytes, when tested with human and guinea pig sera, were more susceptible to heterologous complement lysis than were normal erythrocytes. These results suggest that DAF is capable of regulating homologous as well as heterologous complement activation via the alternative or the classical pathway. They also indicate that DAF deficiency alone is not sufficient to cause homologous hemolysis. In contrast, when the assembly of the membrane-attack complex is not properly regulated, as in the case of heterologous complement activation or in PNH patients, impaired erythrocyte DAF activity and enhanced C3 deposition could lead to increased hemolytic reaction.

Animals↗
PubMed1999

Effect of interleukin-1 beta on the elevation of cytoplasmic free calcium of the cultured hippocampal neurons induced by L-glutamate.

To investigate the intracellular mechanism that interleukin-1 beta (IL-1 beta) facilitates epileptic seizure and neuronal damage, the effect of IL-1 beta alone or IL-1 beta plus glutamate (Glu) on the intracellular free calcium ([Ca2+]i) of single cultured hippocampal neuron was examined by using EPC-9 light-electricity measurement system. The results showed that IL-1 beta of different concentrations (5 x 10(3) U/L, 10 x 10(3) U/L, 20 x 10(3) U/L, 30 x 10(3) U/L, 50 x 10(3) U/L, 100 x 10(3) U/L) failed to affect the neuronal [Ca2+]i, but IL-1 beta could facilitate the augmentation of neuronal [Ca2+]i induced by Glu in a dose-dependent pattern. MK-801 inhibited the effect of Glu on [Ca2+]i, and also inhibited the effect of IL-1 beta on [Ca2+]i induced by Glu, while verapamil did not influence the effect of Glu or IL-1 beta. It is concluded that IL-1 beta, as a neuromodulator, can facilitate the activation of NMDA receptor by Glu, induce the increase of intracellular calcium, which enhances the excitement of neuron.

Animals↗
PubMed1999

RADHA--a new male germ line-specific chromosomal protein of Drosophila.

A new chromosomal protein - RADHA - of Drosophila is described that is specific for the male germ line. It is encoded by a single-copy gene, located in the region 96C-D of D. melanogaster polytene chromosomes. Transcription of the radha gene is restricted to the primary spermatocyte stage. The protein initially accumulates in some of the Y-chromosomal lampbrush loops. After meiosis it is found in the nuclei of spermatids and might be involved in chromatin rearrangement processes in the male germ line. RADHA is a basic protein with a C-terminal leucine zipper region and several segments capable of forming coiled-coil structures.

Amino Acid Sequence↗
PubMed1999

Activation of PKC increases Na+-K+ pump current in ventricular myocytes from guinea pig heart.

We have previously shown activation of alpha1-adrenergic receptors increases Na+-K+ pump current (Ip) in guinea pig ventricular myocytes, and the increase is eliminated by blockers of phosphokinase C (PKC). In this study we examined the effect of activators of PKC on Ip. Phorbol 12-myristate 13-acetate (PMA), a PKC activator, increased IP at each test potential without shifting its voltage dependence. The concentration required for a half-maximal response (K0.5) was 6 microM at 15 nM cytosolic [Ca2+] ([Ca2+]i) and 13 nM at 314 nM [Ca2+]i. The maximal increase at either [Ca2+]i was about 30%. Another activator of PKC, 1, 2-dioctanoyl-sn-glycerol (diC8), increased Ip similarly. The effect of PMA on IP was eliminated by the PKC inhibitor staurosporine, but not by the peptide PKI, an inhibitor of protein kinase A (PKA). PMA and alpha1-adrenergic agonist effects both were sensitive to [Ca2+]i, blocked by PKC inhibitors, unaffected by PKA inhibition, and increased Ip uniformly at all voltages. However, they differed in that alpha1-activation caused a maximum increase of 15% vs 30% via PMA, and alpha1-effects were less sensitive to [Ca2+]i than PMA effects. These results demonstrate that activation of PKC causes an increase in Ip in guinea pig ventricular myocytes. Moreover, they suggest that the coupling of alpha1-adrenergic activation to Ip is entirely through PKC, however alpha1-activation may be coupled to a specific population of PKC whereas PMA is a more global agonist.

Algorithms↗
PubMed1999

Inhibition of Ca2+ influx by pentoxifylline in NR8383 alveolar macrophages.

Pentoxifylline (PTF), a phosphodiesterase (PDE) inhibitor, can prevent inflammation and tissue damage in animal and in vitro human studies. However, the underlying mechanism remains unclear. Since Ca2+ is a critical signal regulating the release of inflammatory mediators in macrophages, the effects of PTF on Ca2+ influx were examined in NR8383 alveolar macrophages (AMs). PTF induced a dose-dependent inhibition on Ca2+ influx activated by zymosan and by protein kinase C (PKC) activators 1,2-dioctanoyl-sn-glycerol (DOG) or phorbol-12-myristate 13-acetate (PMA). The inhibition appeared to be specifically on the receptor-operated Ca2+ entry. The capacitative Ca2+ entry was not affected by PTF. The inhibition was not due to altered cAMP levels since the zymosan-activated Ca2+ influx was not affected by the adenylate cyclase activator forskolin, nor by dibutyryl cAMP. Pretreatment with protein tyrosine kinase (PTK) inhibitor genistein abolished zymosan-induced, but not DOG-induced Ca2+ influx, suggesting that PTK is an upstream element of the signaling cascade and not the target of PTF. The Ca2+ entry activated by zymosan and by PKC activators was inhibited by the mitogen-activated protein kinase (MAPK) inhibitor PD98059. Moreover, activation of MAPK by C6-ceramide (C6C) triggered a similar Ca2+ influx as elicited by zymosan and PKC activators, suggesting that MAPK is an element of the pathway. The C6C-induced Ca2+ influx was also inhibited by PTF. These results indicate that PTF blocks the receptor-operated Ca2+ influx in NR8383 AMs by inhibiting PDE which may acts as a downstream element of the signaling pathway or by direct interaction with Ca2+ channels.

Animals↗
PubMed1999

Mutations in the heatshock cognate 70 protein (hsc4) modulate Notch signaling.

In our effort to dissect the Notch signaling mechanism we have conducted a screen for mutations that reduce Notch signaling activity. We recovered nine complementation groups as modifiers of the hypomorphic Notch allele notchoid. Apart from the known Notch signaling modulators Notch, Delta and mastermind we isolated alleles in vestigial, wingless, scalloped and clipped, genes known to affect wing morphogenesis. In addition, we identified mutations in Bag, the gene encoding clathrin heavy chain and a dominant mutation of the cytosolic 70 kDa heatshock cognate protein encoded by the hsc4 gene, as Notch signaling modifier. We focused our attention on the latter mutation because it displays dramatic genetic interactions with mutations of the Notch receptor as well as several additional Notch signaling pathway elements. We discuss how hsc4, a gene thought to be involved in subcellular trafficking, may affect the number of functional Notch receptors on the cell surface.

Alleles↗
PubMed1999

Twenty-nine missense mutations linked with familial Alzheimer's disease alter the processing of presenilin 1.

1. Full-length form of human presenilin 1 (PS1) is processed and an N-terminal fragment (28 KD) and C-terminal fragment (19 KD) are generated. To elucidate the possible role of presenilin mutations in Alzheimer's disease (AD), the authors analyze the effects of AD-linked mutations on PS1 processing in cultured cells. 2. Complementary DNAs encoding genes for human PS1 harboring twenty-nine missense mutations linked with familial Alzheimer's disease (FAD) were introduced into PC12 cells. Human PS1 exogenously expressed in the cells was detected by immunoblotting using a monoclonal antibody that recognized the N-terminal region of human PS1. The amounts of full-length form (48 KD) and N-terminal fragment (28 KD) of PS1 was quantified by densitometrical analysis. 3. The ratio of the N-terminal fragment to total PS1 was reduced by twenty-nine mutations. The specific effects on PS1 processing varied according to mutation. 4. These results suggest that AD-linked missense mutations of PS1 are involved in neurodegeneration via inhibition of PS1 processing.

Alzheimer Disease↗