Biomedical subjects

X Zhan

Publications and source records attributed to X Zhan.

At least 73 records · Page 4Linked to original sources

PubMed1994

Cardiorespiratory responses elicited by right atrial injections of iodinated contrast media. Comparative evaluation of four agents.

RATIONALE AND OBJECTIVES: The purpose of this study is three-fold: 1) to quantify the cardiorespiratory responses to rapid right atrial injections of meglumine/sodium diatrizoate, ioxaglate, iotrolan, and iopamidol; 2) to compare the effects of each contrast medium to that of its corresponding vehicle and saline; and 3) to evaluate the role of the vagus nerve in the cardiorespiratory responses. METHODS: Seventeen anesthetized dogs, breathing spontaneously, were used. Injections of 2.0 mL/kg were given into the right atrium in 2 seconds. Each contrast medium, along with its vehicle and saline, was tested on 4 dogs (5 dogs for diatrizoate). Blood pressure, air flow, tidal volume, upper airway pressure, esophageal pressure, mean arterial pressure and heart rate, breathing frequency, dynamic lung compliance, upper airway resistance, and total lung resistance were recorded or calculated. RESULTS: Diatrizoate and its vehicle caused a significant increase in blood pressure, tidal volume, esophageal pressure, and a decrease in mean arterial pressure with an increase in heart rate. These responses were not mediated by vagal afferents. Ioxaglate and iotrolan, but not their vehicles, increased breathing frequency; this response was abolished by vagal block. Ioxaglate decreased mean arterial pressure and increased heart rate; the decrease in mean arterial pressure was still present during vagal block. Iopamidol and its vehicle did not alter respiratory parameters. Iopamidol, but not its vehicle, caused only a minimal and transient increase in mean arterial pressure before and during vagal block. None of the contrast media changed upper airway resistance, total lung resistance, and dynamic lung compliance. CONCLUSION: Both diatrizoate and its vehicle elicited the largest changes in respiratory and cardiovascular functions, not mediated by vagal afferents and caused by osmolality of the solution. Ioxaglate, iotrolan, and iopamidol induced smaller cardiorespiratory changes, mediated by vagal afferents. Their respective vehicles did not cause any effects, which suggests that the chemical structure plays a role. Nonionic contrast media elicited only minor and transient cardiorespiratory alterations.

Airway Resistance↗

PubMed1993

Murine cortactin is phosphorylated in response to fibroblast growth factor-1 on tyrosine residues late in the G1 phase of the BALB/c 3T3 cell cycle.

We have previously reported that BALB/c 3T3 cells require a prolonged exposure to fibroblast growth factor (FGF)-1 for the stimulation of maximal DNA synthesis, and this event correlates with the tyrosine phosphorylation of novel proteins late in G1 including a protein termed p80/p85 (Zhan, X., Hu, X., Friesel, R., and Maciag, T. (1993) J. Biol. Chem. 268, 9611-9620). We have purified, sequenced, and cloned the cDNA encoding p80/p85 and report that it is the murine homolog of the chicken cortactin gene and a member of the human hematopoietic specific-1 gene family. Immunochemical analysis of m-cortactin-tyrosine phosphorylation in response to FGF-1 demonstrates a biphasic phosphorylation pattern both as a weak immediate-early and strong mid to late G1 response protein. Because the chicken cortactin gene was originally isolated as a substrate for v-Src, FGF-1 may influence the enzymatic activity of other cell-associated tyrosine kinases which utilize p80/p85 (cortactin) as a polypeptide substrate.

3T3 Cells↗

PubMed1993

Identification of a nuclear localization sequence within the structure of the human interleukin-1 alpha precursor.

Recent studies have suggested that the signal peptide-less cytokine, interleukin (IL)-1 alpha, may play a role as an intracellular regulator of human endothelial cell proliferation in vitro (Garfinkel, S., Haines, D. S., Brown, S., Wessendorf, J., Gillespie, D. H., and Maciag, T. (1992) J. Biol. Chem. 267, 24375-24378). In order to determine the intracellular locale of the IL-1 alpha precursor, we fused the open reading frame of the IL-1 alpha precursor to the reporter gene beta-galactosidase (Gal) and studied the cellular distribution of the chimera in NIH 3T3 cells after transfection. Immunological and enzymatic analysis demonstrated that the IL-1 alpha:beta-Gal fusion protein was associated with the nucleus. To further define the region responsible for this activity, we ligated the mature form of IL-1 alpha (IL-1 alpha 113-271) and the IL-1 alpha precursor domain (IL-1 alpha 1-112) to beta-Gal. Analysis of the intracellular distribution of these chimeric polypeptides following transfection demonstrated a differential distribution of IL-1 alpha 1-112:beta-Gal in the nucleus and IL-1 alpha 113-271:beta-Gal in the cytosol. Because the IL-1 alpha precursor domain contains a sequence that resembles a nuclear translocation signal (KVLKKRRL, residues 79-86), we prepared an IL-1 alpha precursor point mutant in which Lys82 was replaced by Glu. Transfection of NIH 3T3 cells with the IL-1 alpha precursor point mutant (IL-1 alpha 1-271 Glu82:beta-Gal) resulted in a significant reduction in the ability of the IL-1 alpha precursor to associate with the nucleus and similar data were obtained as a result of Lys82 mutagenesis in the IL-1 alpha precursor domain (IL-1 alpha 1-112 Glu82:beta-Gal). These data suggest that the IL-1 alpha precursor contains a functional nuclear localization sequence within the structure of the precursor domain and Lys82 is critical for its function.

3T3 Cells↗

PubMed1993

Long term growth factor exposure and differential tyrosine phosphorylation are required for DNA synthesis in BALB/c 3T3 cells.

The importance of growth factor-mediated immediate-early cellular events to the cell cycle has influenced the development and identity of oncogenes and tumor suppressor genes as well as the concept that growth factors commit mammalian cells to enter a biochemical program that ultimately yields DNA synthesis. However, the mid and late events involved in the regulation of growth factor-induced signal transduction remain largely unknown. In this report we demonstrate that BALB/c 3T3 cells require continuous exposure to fibroblast growth factor (FGF)-1 for a minimum of 12 h to achieve near maximal DNA synthesis. This correlates with the continuous internalization of radiolabeled FGF-1 into the cytosol and nucleus of BALB/c 3T3 cells and the maintenance of a low level of FGF receptors on the cell surface during the entire G1 phase of the cell cycle. Further analysis demonstrates the maintenance of a continuous series of differential FGF-1-induced tyrosine phosphorylation events including the phosphorylation of phospholipase C-gamma as well as novel FGF receptor polypeptide substrates, p60, p85, p90, and p130 throughout the G1 phase of the BALB/c 3T3 cell cycle. The tyrosine phosphorylation events are biphasic during the 12-h period after the administration of FGF-1, and the second phase is characterized by hyper-tyrosine phosphorylation of p60, p85, and p130. Interestingly, NIH 3T3 cells which overexpress the FGF receptor-1 polypeptide demonstrate exaggerated tyrosine phosphorylation of p60 and p85 but not p90 and exhibit growth factor-independent cell proliferation. These results suggest that the initiation of DNA synthesis in BALB/c 3T3 cells by FGF-1 is regulated by a complex biochemical program that involves the continuous tyrosine phosphorylation of known and novel polypeptides throughout the G0 to G1 transition period of the cell cycle.

3T3 Cells↗

PubMed1993

Recombinant fibroblast growth factor-1 promotes intimal hyperplasia and angiogenesis in arteries in vivo.

The prototype members of the heparin-binding fibroblast growth factor (FGF) family, acidic FGF (FGF-1) and basic FGF (FGF-2), are among the growth factors that act directly on vascular cells to induce endothelial cell growth and angiogenesis. In vivo, the role of the FGF prototypes in vascular pathology has been difficult to determine. We report here the introduction, by direct gene transfer into porcine arteries, of a eukaryotic expression vector encoding a secreted form of FGF-1. This somatic transgenic model defines gene function in the arterial wall in vivo. FGF-1 expression induced intimal thickening in porcine arteries 21 days after gene transfer, in contrast to control arteries transduced with an Escherichia coli beta-galactosidase gene. Where there was substantial intimal hyperplasia, neocapillary formation was detected in the expanded intima. These findings suggest that FGF-1 induces intimal hyperplasia in the arterial wall in vivo and, through its ability to stimulate angiogenesis in the neointima, FGF-1 could stimulate neovascularization of atherosclerotic plaques. Potentially, gene transfer of FGF-1 could also be used as a genetic intervention to improve blood flow to ischaemic tissues in selected clinical settings.

Animals↗

PubMed1993

The activity of the coat protein promoter of chloris striate mosaic virus is enhanced by its own and C1-C2 gene products.

DNA fragments from the bidirectional promoter region of the geminivirus chloris striate mosaic virus (CSMV) were cloned into the pUC18-based vector, pG1 producing transcriptional fusions with the beta-glucuronidase (GUS) gene and nopaline synthase terminator sequence. The relative activity of each promoter construct was analyzed by a GUS expression assay of extracts from Zea mays (maize) Black Mexican Sweet protoplasts coelectroporated with the GUS reporter constructs and constructs in which individual CSMV open reading frames (ORFs) were placed under control of a cauliflower mosaic virus 35 S promoter. Weak promoter activity was observed for the promoter of the C1 and C2 ORFs (C1-C2 gene) and for the promoter of the V1 ORF. The activity of these promoters was unaffected by coelectroporation with the CSMV ORF constructs. Moderate activity was observed for the promoter of the V2 ORF (coat protein gene) which was enhanced by coelectroporation of the C1-C2 ORF construct. Sequences within the C1-C2 gene responsible for transactivation of the V2 ORF promoter were mapped close to the A site of a conserved NTP-binding sequence pattern within the C2 ORF. To a lesser extent activity for the promoter of the V2 ORF was enhanced by the V2 ORF construct providing evidence for positive autoregulation of the CSMV coat protein gene.

Base Sequence↗

PubMed1992

Analysis of endogenous and exogenous nuclear translocation of fibroblast growth factor-1 in NIH 3T3 cells.

Nuclear localization of fibroblast growth factors (FGF) have been reported by many laboratories. We demonstrate here that FGF-1, the precursor for acidic FGF contains a putative nuclear translocation sequence (NTS) NYKKPKL, which is able to direct the expression of the bacterial beta galactosidase (beta gal) gene to the nucleus of transfected NIH 3T3 cells. However, this NTS is unable to target either FGF-1 itself or a FGF-1-beta gal fusion protein into the nucleus, suggesting that FGF-1 may contain an additional sequence which prevents endogenously expressed FGF-1 from being translocated into the nucleus. Indeed, when FGF-1 was fused to the NTS derived from the yeast histone 2B gene, the chimeric construct also failed to be transported into the nucleus either by itself or as a beta gal fusion protein. Interestingly, when 125I-FGF-1 was used to stimulate quiescent NIH 3T3 cells, a significant amount of internalized 125I-FGF-1 (approximately 10%) was found within the nucleus and the nuclear localization of FGF-1 through the exogenous pathway could be significantly reduced by suramin, an inhibitor of the interaction of FGF-1 with its receptor. These data suggest that while FGF-1 contains a NTS, nuclear translocation requires an exogenous and not an endogenous pathway.

3T3 Cells↗

PubMed1992

Heat shock induces the release of fibroblast growth factor 1 from NIH 3T3 cells.

Fibroblast growth factor 1 (FGF-1) is a potent angiogenic and neurotrophic factor whose structure lacks a classical signal sequence for secretion. Although the initiation of these biological activities involves the interaction between FGF-1 and cell surface receptors, the mechanism responsible for the regulation of FGF-1 secretion is unknown. We report that murine NIH 3T3 cells transfected with a synthetic gene encoding FGF-1 secrete FGF-1 into their conditioned medium in response to heat shock. The form of FGF-1 released by NIH 3T3 cells in response to increased temperature (42 degrees C, 2 hr) in vitro is not biologically active and does not associate with either heparin or the extracellular NIH 3T3 monolayer matrix. However, it was possible to derive biologically active FGF-1 from the conditioned medium of heat-shocked NIH 3T3 cell transfectants by ammonium sulfate fractionation. The form of FGF-1 exposed by ammonium sulfate fractionation is similar in size to cytosolic FGF-1 and can bind and be eluted from immobilized heparin similarly to the recombinant human FGF-1 polypeptide. Further, the release of FGF-1 by NIH 3T3 cell transfectants in response to heat shock is reduced significantly by both actinomycin D and cycloheximide. These data indicate that increased temperature may upregulate the expression of a factor responsible for the secretion of FGF-1 as a biologically inactive complex that requires an activation step to exhibit the biological activity of the extracellular polypeptide mitogen.

3T3 Cells↗

PubMed1992

Discordant regulation of human type I collagen genes by prostaglandin E2.

We examined the expression of type I collagen genes in prostaglandin E2 (PGE2)-treated human lung fibroblast cultures. Addition of PGE2 to fibroblast cultures inhibited alpha 1(I) mRNA levels by approx. 25% after 6 h and 60% after 24 h. Further studies showed that dibutyryl cAMP did not inhibit alpha 1(I) mRNA levels and that cycloheximide blocked the inhibitory effect of PGE2. In contrast, PGE2 treatment with or without cycloheximide did not affect alpha 2(I) mRNA levels. Moreover, in vitro translation of RNA derived from untreated and PGE2-treated cells yielded similar amounts of alpha 2(I) collagen peptides. Taken together, these results suggest that PGE2 induces a protein which inhibits alpha 1(I) transcription through distinct regulatory elements not under the control of cAMP and provide further evidence that the type I collagen genes can be discordantly regulated.

Blotting, Northern↗

PubMed1992

The nucleotide sequence of the infectious cloned DNA component of tobacco yellow dwarf virus reveals features of geminiviruses infecting monocotyledonous plants.

An infectious clone of the Australian geminivirus tobacco yellow dwarf virus (TobYDV) was constructed from virus-specific double-stranded DNA isolated from infected tobacco and used to demonstrate a single-component genome. The nucleotide sequence of TobYDV DNA comprises 2580 nucleotides. TobYDV DNA has three coding regions, two in the virion sense and one in the complementary sense, homologous to those identified for other geminiviruses, particularly those infecting monocotyledonous (monocot) plants. The complementary sense coding region is comprised of two overlapping reading frames, with an intron of 86 nucleotides. Efficient splicing of the mRNA for this coding region was observed in the infected dicotyledonous (dicot) hosts bean and tobacco despite the intron having an A + U content (57%) more typical of geminiviruses of monocot plants. TobYDV encapsidates a small oligonucleotide able to prime synthesis of the complementary DNA strand in vitro. The TobYDV genome organization, low A + U intron, and encapsidated oligonucleotide primer resemble those of the monocot-infecting geminiviruses. These results strongly suggest that TobYDV is a monocot geminivirus which has become adapted to dicot hosts.

Base Sequence↗

PubMed1992

Regulation of the activities of African cassava mosaic virus promoters by the AC1, AC2, and AC3 gene products.

DNA fragments comprising each of the promoter regions from the geminivirus African cassava mosaic virus (ACMV) were cloned into the pUC18-based vector, pG1, producing transcriptional fusions with the beta-glucuronidase gene (GUS) and nopaline synthase terminator sequence. The relative activity of each promoter construct was analyzed by a GUS expression assay of extracts from Nicotiana clevelandii protoplasts coelectroporated with the GUS reporter constructs and constructs in which individual ACMV open reading frames (ORFs) were placed under control of a cauliflower mosaic virus 35 S promoter. Results suggest repression of the AC1 gene by its gene product, which is required for ACMV DNA synthesis. The promoter activity observed for the single promoter for the DNA A genes encoding functions of spread and the regulation of replication (AC2 and AC3 ORFs) was unaffected by coelectroporation with any of the ACMV ORF constructs. Promoters for the AV1 (coat protein) gene and the two DNA B genes (BV1 and BC1) were activated by electroporation of the AC2 ORF construct. To a lesser extent promoters for the AV1 and BV1 genes were activated with the AC3 ORF construct. The same pattern of promoter repression and activation was observed when transgenic N. benthamiana plants expressing the GUS reporter constructions were inoculated with ACMV DNA A.

DNA-Directed DNA Polymerase↗

PubMed1992

[Effect of prefrontal cortex on the neuronal activity of the nucleus raphe magnus in rats].

The unit discharge of neurons in nucleus raphe magnus (NRM) were recorded with glass microelectrodes in 33 waking and tubocurarine-immobilized rats. It is observed that effects of the noxious stimulation and prefrontal cortex (PFC) stimulation on spontaneous discharges of NRM neurons and effects of PFC stimulation on noxious-evoked discharges of NRM neurons by stimulating sural nerve. The results indicated that noxious stimulation and PFC stimulation could increase spontaneous discharge of most (68.18% and 60.82% respectively) NRM neurons. It was also noted that most (49/80) NRM neurons altered their spontaneous discharge in response to noxious stimulation and PFC stimulation in a similar manner. The remainder (31/80) opposite manners. PFC stimulation could alter the response of NRM neurons to noxious stimulation. PFC stimulation could enhance or reduce noxious-evoked discharge in NRM neurons which alter their spontaneous discharge in response to noxious stimulation and PFC stimulation in a similar manner. PFC stimulation could reduce noxious-evoked discharge in NRM neurons which alter their spontaneous discharge in opposite manners. The above results suggest that PFC and NRM have a functional relation. PFC could modulate nociceptive response and it might be partly responsible for influence on activity of neurons in NRM.

Animals↗

PubMed1991

Biosynthesis of human fibroblast growth factor-5.

We have analyzed the biosynthesis of human fibroblast growth factor-5 (FGF-5) at the translational and posttranslational levels. FGF-5 RNA synthesized in vitro can be translated in rabbit reticulocyte lysates to yield a 29,500-Da protein, which is consistent with the molecular weight predicted from the coding sequence. The efficiency of FGF-5 translation is dramatically enhanced if an upstream open reading frame (ORF-1) in the RNA is deleted or if both AUG codons in ORF-1 are destroyed by point mutations, while partial enhancement is achieved by individual mutation of either ORF-1 AUG codon. These data suggest that FGF-5 synthesis requires the scanning of ribosomes past the two ORF-1 AUG codons. The introduction of these ORF-1 mutations into a eukaryotic FGF-5 expression vector increases its capacity to transform mouse NIH 3T3 cells up to 50-fold upon transfection. FGF-5 is secreted from transfected 3T3 cells and from human tumor cells as glycoproteins containing heterogeneous amounts of sialic acid. Glycosidase treatments suggest that the growth factor bears both N-linked and O-linked sugars.

Amino Acid Sequence↗

PubMed1991

[Effect of prefrontal cortex stimulation on the activity of pain-related neurons in parafascicular nucleus of thalamus in rats].

The effects of PFC stimulation on spontaneous and evoked discharges of neurons of parafascicular nucleus of thalamus were observed in rats. The results show that after PFC stimulation spontaneous of 78.7% PEN (48/61) and evoked discharges on noxious stimulation of 76.6% PEN (46/60) were decreased; spontaneous discharges of 72% PIN (18/25) were increased; inhibition response on noxious stimulation of 70.8% PIN (17/24) were decreased; and spontaneous discharges of 66.7% CON (6/9) and evoked discharges on noxious stimulation of 55.6% CON (5/9) were decreased. The results suggest that PFC might have analgesia action which was accomplished by modulating electric activities of pain-related neurons of parafascicular nucleus in thalamus.

Animals↗

PubMed1990

Recovery of mitogenic activity of a growth factor mutant with a nuclear translocation sequence.

Heparin-binding growth factor-1 (HBGF-1) is an angiogenic polypeptide mitogen for mesoderm- and neuroectoderm-derived cells in vitro and remains biologically active after truncation of the amino-terminal domain (HBGF-1 alpha) of the HBGF-1 beta precursor. Polymerase chain reaction mutagenesis and prokaryotic expression systems were used to prepare a mutant of HBGF-1 alpha lacking a putative nuclear translocation sequence (amino acid residues 21 to 27; HBGF-1U). Although HBGF-1U retains its ability to bind to heparin, HBGF-1U fails to induce DNA synthesis and cell proliferation at concentrations sufficient to induce intracellular receptor-mediated tyrosine phosphorylation and c-fos expression. Attachment of the nuclear translocation sequence from yeast histone 2B at the amino terminus of HBGF-1U yields a chimeric polypeptide (HBGF-1U2) with mitogenic activity in vitro and indicates that nuclear translocation is important for this biological response.

Amino Acid Sequence↗

PubMed1988

The human FGF-5 oncogene encodes a novel protein related to fibroblast growth factors.

We previously described the isolation of a human oncogene which had acquired transforming potential by a DNA rearrangement accompanying transfection of NIH 3T3 cells with human tumor DNA (X. Zhan, A. Culpepper, M. Reddy, J. Loveless, and M. Goldfarb, Oncogene 1:369-376, 1987). We now term this oncogene the FGF-5 gene, since it specifies the fifth documented protein related to fibroblast growth factors (FGFs. Two regions of the FGF-5 sequence, containing 122 of its 267 amino acid residues, were 40 to 50% homologous to the sequences of acidic and basic FGFs as well as to the sequences of the FGF-related oncoproteins int-2 and hst/KS3. The FGF-5 gene bears the three exon structures typical for members of this family. FGF-5 was found to be expressed in the neonatal brain and in 3 of the 13 human tumor cell lines examined. Several experiments strongly suggested that FGF-5 is a growth factor with properties common to those of acidic and basic FGFs. The rearrangement which activated the FGF-5 gene during DNA transfection had juxtaposed a retrovirus transcriptional enhancer just upstream from the native promoter of the gene.

Amino Acid Sequence↗

PubMed1987

Human oncogenes detected by a defined medium culture assay.

Oncogenes in DNAs from human tumor cell lines have been detected by a new transformation assay. Cellular DNAs are transfected into NIH3T3 murine fibroblasts, and transformed cells are selected by maintaining cell cultures in a defined medium lacking platelet-derived or fibroblast growth factors. DNAs from eight of 17 human tumor cell lines have yielded transformants by this method. Activated cellular ras genes account for three of the transforming activities. The SAOS2 osteosarcoma cell line contains an activated oncogene distinct from 18 known oncogenes. Another cellular oncogene was detected as the consequence of a fortuitous transfection-mediated DNA rearrangement.

Animals↗

PubMed1986

Growth factor requirements of oncogene-transformed NIH 3T3 and BALB/c 3T3 cells cultured in defined media.

We report conditions for the efficient growth of NIH 3T3 and BALB/c 3T3 cells cultured in a defined medium supplemented with either platelet-derived growth factor (PDGF) or pituitary-derived fibroblast growth factor (FGF). The oncogenes v-mos, v-src, v-sis, and c-H-ras Val 12 can induce morphological transformation of these cells and can release them from the mitogen requirement for growth, while the oncogene v-fos cannot abrogate the PDGF-FGF requirement. The radically different behavior of normal and transformed NIH 3T3 cells in PDGF-FGF-free defined medium can form the basis of a sensitive new fibroblast transformation assay.

Animals↗