Biomedical subjects

L Yen

Publications and source records attributed to L Yen.

At least 19 recordsLinked to original sources

PubMed2001

Upregulation of gap junctional intercellular communication and connexin 43 expression by cyclic-AMP and all-trans-retinoic acid is associated with glutathione depletion and chemosensitivity in neuroblastoma cells.

PURPOSE: Downregulation of gap junctional intercellular communication (GJIC) has been implicated in carcinogenesis. This is a result of altered expression of connexins, the proteins that mediate GJIC, including connexin 43 (Cx43). Our aim was to evaluate the effect of known inducers of Cx43 on the chemosensitivity of the human neuroblastoma cell line IMR-32 to chemotherapeutic agents. METHODS: We examined the effect of dibutyryl-cyclic AMP (db-cAMP) and all-trans-retinoic acid (tRA) on Cx43 and GJIC, glutathione (GSH) and gamma-glutamyl-cysteine-synthetase (gamma-GCS) levels, and glutathione S-transferase (GST) activity. Finally, we performed cell survival assays to measure the response of IMR-32 cells to the chemotherapeutic drugs doxorubicin, melphalan and bis-chloronitrosourea (BCNU), after treatment with db-cAMP and/or tRA. RESULTS: Exposure to db-cAMP led to the upregulation of GJIC and Cx43 expression and phosphorylation. On the other hand, exposure to tRA led to the upregulation of GJIC but Cx43 expression and phosphorylation were not greatly affected. The combination of both agents was more potent in inducing GJIC in comparison to treatment with db-cAMP or tRA alone. Treatment with db-cAMP, but not with tRA, was associated with a significant increase in the cytotoxic effects of the anticancer drugs doxorubicin, melphalan and BCNU as shown by a decrease in their IC50 values. Concomitant exposure to db-cAMP and tRA, however, had a more pronounced effect on cell sensitization to chemotherapy drugs (particularly doxorubicin) than exposure to db-cAMP or tRA alone. Under the db-cAMP and tRA treatment conditions (which upregulate GJIC and modulate drug response), GSH levels were significantly reduced while the levels of GST and gamma-GCS activities remained unchanged. CONCLUSIONS: This study suggests that GJIC plays a role in cellular drug resistance, and highlights the potential use of GJIC modulators in combination with chemotherapy. Also, this is the first study exploring the ability of both db-cAMP and tRA to enhance cell chemosensitivity.

Bucladesine↗

PubMed2001

By any other name: when will preschoolers produce several labels for a referent?

Two experiments investigated why preschool children sometimes produce multiple words for a referent (i.e. polynomy), but other times seem to allow only one word. In Experiment 1, 40 three- and four-year-olds completed a modification of Deák & Maratsos' (1998) naming task. Although social demands to produce multiple words were reduced, children produced, on average, more than two words per object. Number of words produced was predicted by receptive vocabulary. Lexical insight (i.e. knowing that a word refers to function or appearance) and metalexical beliefs (i.e. that a hypothetical referent has one label, or more than one) were not preconditions of polynomy. Polynomy was independent of bias to map novel words to unfamiliar referents. In Experiment 2, 40 three- and four-year-olds learned new words for nameable objects. Children showed a correction effect, yet produced more than two words per object. Children do not have a generalized one-word-per-object bias, even during word learning. Other explanations (e.g. contextual restriction of lexical access) are discussed.

Child Language↗

PubMed2001

Reduction of functional N-methyl-D-aspartate receptors in neurons by RNase P-mediated cleavage of the NR1 mRNA.

One approach to studying the functional role of individual NMDA receptor subunits involves the reduction in the abundance of the protein subunit in neurons. We have pursued a strategy to achieve this goal that involves the use of a small guide RNA which can lead to the destruction of the mRNA for a specific receptor subunit. We designed a small RNA molecule, termed 'external guide sequence' (EGS), which binds to the NR1 mRNA and directs the endonuclease RNase P to cleave the target message. This EGS has exquisite specificity and directed the RNase P-dependent cleavage at the targeted location within the NR1 mRNA. To improve the efficiency of this EGS, an in vitro evolution strategy was employed which led to a second generation EGS that was 10 times more potent than the parent molecule. We constructed an expression cassette by flanking the EGS with self-cleaving ribozymes and this permitted generation of the specified EGS RNA sequence from any promoter. Using a recombinant Herpes simplex virus (HSV), we expressed the EGS in neurons and showed the potency of the EGS to reduce NR1 protein within neurons. In an excitotoxicity assay, we showed that expression of the EGS in cortical neurons is neuroprotective. Our results demonstrate the utility of EGSs to reduce the expression of any gene (and potentially any splice variant) in neurons.

Animals↗

PubMed2000

Heregulin selectively upregulates vascular endothelial growth factor secretion in cancer cells and stimulates angiogenesis.

The interaction between the erbB tyrosine kinase receptors and their ligands plays an important role in tumor growth via the regulation of autocrine and paracrine loops. We report the effect of heregulin beta1, the ligand for erbB-3 and erbB-4 receptors, on the regulation of vascular endothelial growth factor (VEGF) expression, using a panel of breast and lung cancer cell lines with constitutive erbB-2 overexpression or engineered to stably overexpress the erbB-2 receptor. We demonstrate that heregulin beta1 induces VEGF secretion in most cancer cell lines, while no significant effect was observed in normal human mammary and bronchial primary cells. Overexpression of erbB-2 receptor results in induction of the basal level of VEGF and exposure to heregulin further enhances VEGF secretion. This is associated with increased VEGF mRNA expression. In contrast, VEGF induction is significantly decreased in a T47D cell line where erbB-2 is functionally inactivated. Conditioned media from heregulin-treated cancer cells, but not from normal cells, stimulates endothelial cell proliferation; this paracrine stimulation is inhibited by co-exposure to a specific VEGF neutralizing antibody. Furthermore, heregulin-mediated angiogenesis is observed in the in vivo CAM assay. This study reports the first evidence of VEGF regulation by heregulin in cancer cells. Oncogene (2000) 19, 3460 - 3469

Adenocarcinoma↗

PubMed1999

Sequence-specific cleavage of Huntingtin mRNA by catalytic DNA.

The selective loss of neurons in Huntington's disease (HD) is caused by the abnormal expansion of the CAG triplet (>36 repeats) of the HD gene. Although the molecular events that lead to neuronal death are not clear, it is most likely that mutant HD protein operates through a "gain-of-function" mechanism. One possible therapeutic approach that does not require definition of the toxic mechanism(s) involves reduction in the levels of mutant HD protein by decreasing the quantity of translatable HD mRNA. In this report, we demonstrate the first effective destruction of the HD mRNA, using a catalytic DNA--an oligodeoxynucleotide with RNA-cleaving enzymatic activity. We show that the cleavage of HD mRNA by the catalytic DNA occurs in a sequence-specific manner, and leads to significant reduction of HD protein expression in mammalian cells. The catalytic DNAs we have developed are a valuable research tool for studying HD, and may have the therapeutic potential of reducing cellular toxicity caused by mutant HD protein.

DNA, Catalytic↗

PubMed1999

Single-vessel arteriovenous revascularization of the amputated ear.

Successful single-vessel arteriovenous replantation of a completely amputated human ear is described. This result was followed by an experimental study using a rabbit model, to confirm that an amputated ear could survive replantation with only a single arteriovenous anastomosis. Fifteen animals were placed in one of two experimental groups: Group 1-arteriovenous replantation, no treatment (n = 6); and Group 2-arteriovenous replantation with medicinal leeching (n = 9). All ears demonstrated initial reperfusion of the replantation immediately following microanastomosis. Laser Doppler flow readings in the non-leeched replanted ears fell to zero by 8 hr and, by 12 hr, the non-leeched ears demonstrated signs of necrosis. All the leeched, replanted ears demonstrated perfusion and complete viability at the time of sacrifice. The case report, combined with the results from the experimental study, confirm that single-vessel arteriovenous replantation of an amputated ear is feasible.

Adult↗

PubMed1998

Dual effect of erbB-2 depletion on the regulation of DNA repair and cell cycle mechanisms in non-small cell lung cancer cells.

Overexpression of the erbB-2 tyrosine kinase receptor, p185erbB-2, is a common alteration in non-small cell lung cancer (NSCLC) and has been associated with poor prognosis and a tumor drug resistance phenotype. In this study, we have examined the consequences of erbB-2 depletion on DNA repair, cell cycle, and apoptosis using a panel of NSCLC cell lines constitutively overexpressing erbB-2 receptor. Depletion of the erbB-2 was achieved using the tyrosine kinase inhibitor CP127,374 which promotes erbB-2 degradation. Treatment with CP127,374 concentrations which deplete erbB-2 and inhibit tyrosine phosphorylation resulted in downregulation of DNA repair mechanisms and cell accumulation at G1 phase of the cell cycle. GI arrest was observed in cells with mutated p53 as well as cells lacking p53 protein, suggesting a p53-independent mechanisms. NSCLC cells which overexpress erbB-2 were more resistant to cisplatin-induced cytotoxicity in comparison to cells expressing low levels of erbB-2. Treatment with CP127,374 alone did not result in any induction of apoptosis. A combination of CP127,374 and cisplatin, however, was more potent in cell growth inhibition and induction of apoptosis compared to treatment with cisplatin alone. Together, our results further support a pivotal role of erbB-2 signaling in the regulatory balance between DNA repair, cell cycle checkpoints and apoptosis; all these mechanisms are essential determinants for tumor cell destiny following chemotherapy stress.

Apoptosis↗

PubMed1998

Health action zones.

Explore the source record for details and available documents.

Delivery of Health Care↗

PubMed1998

Effects of cisapride on QT interval in children.

Recent reports of torsade de pointes and heart block associated with prolonged QT interval in children receiving cisapride raise questions about its safety. We prospectively examined the effects of cisapride on the QT interval in children. Electrocardiography was performed on 30 children before and after cisapride was administered. An additional 71 children underwent electrocardiography only after starting cisapride. The incidence of a corrected QT (QTc) interval > 440 msec or a marked abnormality in T wave morphology was determined in all 101 children. Cisapride significantly lengthened the QTc with a mean increase of 15.5 +/- 4.6 msec (mean +/- SEM, p = 0.002 in the 30 children with baseline electrocardiographs. Twelve of the 101 patients were found to have a QTc > 440 msec, and one had a new prominent notched T wave in all leads. In these 13 (13%) patients with repolarization abnormalities, other factors that might contribute to a long QT were noted in 11 (85%) patients. We conclude that cisapride use in children is associated with a modest increase in QT interval. The incidence of QTc > 440 msec is low. Most children with long QTc have other factors that could compound the effects of cisapride.

Child↗

PubMed1998

The dorsal cutaneous branch of the ulnar nerve. An anatomic clarification with six case reports.

We studied the anatomy and pathology of the dorsal cutaneous branch of the ulnar nerve by dissecting 10 fresh cadaver upper limbs and reviewing 6 cases of injury or entrapment of the dorsal cutaneous branch of the ulnar nerve. In all of the cadavers and in our series of cases, several anatomical features were apparent: 1) the dorsal cutaneous branch of the ulnar nerve arises from the main ulnar nerve an average of 5.5 centimeters proximal to the head of the ulna; 2) the dorsal cutaneous branch of the ulnar nerve reaches the dorsum of the hand after coursing volar to the ulnar head; 3) there was no communication between the dorsal cutaneous branch of the ulnar nerve and the superficial sensory branch of the radial nerve; and 4) no volar branches were noted. Based on our experience, disorders of this nerve are more prevalent than previously reported. This clarification of the anatomy will help prevent unnecessary injury during surgery and will be valuable in the diagnosis of disorders of the dorsal cutaneous branch of the ulnar nerve.

Adult↗

PubMed1997

Regulation of cellular response to cisplatin-induced DNA damage and DNA repair in cells overexpressing p185(erbB-2) is dependent on the ras signaling pathway.

We have examined the role of erbB-2 expression in the modulation of cellular toxicity to cisplatin. We have demonstrated that treatment of NIH3T3-erbB-2 cells, which overexpress the p185(erbB-2) product of the human erbB-2 gene, with a monoclonal antibody directed against the extracellular domain (TAb-250), results in enhanced cisplatin cytotoxicity. A similar enhancement was obtained when cells were exposed to herbimycin A and its analogue CP127 374, both of which inhibit tyrosine kinase activity. Using the host cell reactivation (HCR) of reporter gene expression from cisplatin-damaged plasmid and unscheduled DNA synthesis (UDS) following cisplatin treatment of cells, we have found that modulation of erbB-2 by TAb-250 was associated with inhibition of DNA repair. TAb-250 alone, under conditions which modulate DNA repair, slightly reduces the S-phase of the cell cycle, while cisplatin induced arrest at S and G2 phases. Combination of TAb-250 and cisplatin only slightly prevented cisplatin-induced S and G2 blocks. Since the ras pathway is one of the major signaling components coupled to erbB-2, we have examined the role of ras in DNA repair regulation. Transient expression of a ras dominant negative mutant, Asn-17-ras(H), prevents DNA repair modulation by TAb-250, suggesting that the erbB-2 receptor regulates DNA repair mechanism(s), at least in part, through ras-coupled pathway(s).

3T3 Cells↗

PubMed1997

The role of ErbB-2 tyrosine kinase receptor in cellular intrinsic chemoresistance: mechanisms and implications.

The erbB family of tyrosine kinase receptors is involved in the regulation of a variety of vital functions including cell proliferation, cell differentiation, and stress response. Alteration in the expression of erbB receptors occurs in numerous tumor types and plays an important role in cancer development, cancer progression, and susceptibility to cell killing by anticancer agents. Of particular interest is the intrinsic drug resistance associated with overexpression of the erbB-2 receptor. In general, tumor cells overexpressing erbB-2 are intrinsically resistant to DNA-damaging agents such as cisplatin. While the molecular mechanisms by which erbB-2 induces drug resistance are not yet established, there is evidence that this may be a consequence of altered cell cycle checkpoint and DNA repair mechanisms and dysregulation of apoptotic pathway(s). The apoptotic signal induced by many anticancer drugs originates at a receptor on the cell membrane and is transduced through a signaling cascade to the nucleus. Drug-induced apoptosis is dependent on the balance between cell cycle checkpoints and DNA repair mechanisms. Blockade of erbB-2 signaling using erbB-2 antagonists, dominant negative mutants, or chemical inhibitors of erbB-2 tyrosine kinase activity induces cell cycle arrest, inhibits DNA repair, and (or) promotes apoptosis. Less understood are downstream signal transduction cascades by which erbB-2 affects these regulatory mechanisms. The diversity of erbB receptors results in an interconnected network of cell signaling pathways that determine tumor cell fate in response to chemotherapy stress. Further investigations on the role of erbB-coupled signaling in the regulation of stress responsive genes are critical to understand the mechanisms by which tumor cells escape cell death, and will contribute to the development of alternative therapeutic targets to overcome intrinsic drug resistance in clinical settings.

Animals↗

PubMed1995

In situ hybridization analysis of AMPA receptor subunit gene expression in the developing rat spinal cord.

In early postnatal life the acquisition of mature morphological and molecular features of motor neurons is influenced by synaptic activity within the spinal cord. Glutamatergic synaptic neurotransmission is believed to play a central role in this process. We hypothesize that the repertoire of glutamate receptors expressed by neurons in the young spinal cord differ from those expressed in adults and such receptors support activity-dependent developmental plasticity. To explore this idea, we used in situ hybridization histochemistry to determine the distribution, temporal expression, and potential subunit composition of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors in the developing rat spinal cord and compared these findings with those in adult rats. We find qualitative and quantitative changes in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit gene expression over the first month of postnatal life. alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit genes GluR1, 2 and 4 are expressed at greater levels throughout the spinal cord of the neonate versus the adult animals. The developmental down-regulation is most pronounced for GluR1 transcripts, less for GluR2 and GluR4 transcripts, and minimal for GluR3 transcripts. Analysis of flip and flop splice variants of each subunit show that receptors expressed by adult motor neurons are potentially composed of the subunits GluR1 flop, GluR2 flip, GluR3 flip and flop, and GluR4 flip. In neonatal motor neuron all subunits are potentially expressed (except GluR2 flop) with quantitatively the dominent subunits being the flip splice variants of GluR1, 2 and 4. Receptors in the substantia gelatinosa undergo equally dramatic, developmentally independent changes. Changes in the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit composition are likely to have an important effect on the electrophysiological properties of motor neurons and may form part of the molecular identity of neurons capable of undergoing activity-dependent developmental plasticity.

Animals↗

PubMed1995

Enhanced host cell reactivation capacity and expression of DNA repair genes in human breast cancer cells resistant to bi-functional alkylating agents.

Human breast carcinoma (MCF7-MLNr) cells resistant to the bifunctional drugs L-phenylalanine mustard (L-PAM, 5-fold resistance), mechlorethamine (9-fold), cisplatin (3-fold), and BCNU (3-fold) were used to investigate the role of DNA repair in the development of resistance to alkylating agents. We have previously shown that neither L-PAM transport and metabolism nor glutathione-associated enzymes were altered in MCF7-MLNr cells, compared to the sensitive cells MCF7-WT. This study shows that treatment of pRSV-CAT plasmid with L-PAM at concentrations up to 1 microM proportionally inhibit the expression of chloramphenicol acetyl transferase (CAT) activity, while higher concentrations abolished CAT activity. pRSV-CAT reactivation was significantly increased when plasmid was transfected into MCF7-MLNr cells, compared to MCF7-WT cells. This indicates that resistant cells have more efficient capacity to recognize and repair L-PAM induced DNA damage. The mRNA expression of DNA nucleotide excision repair genes ERCC1, XPD (ERCC2), XPB (ERCC3), and polymerase beta was found to be similar in both the MCF7-WT and MCF7-MLNr cells. Western blot analysis also reveals no difference in the expression of ERCC1, AP endonuclease, poly (ADP-ribose) polymerase, and alkyl-N-purine-DNA glycosylase proteins. The lack of correlation between enhanced host cell reactivation capacity in resistant cells, and the expression of these specific DNA repair genes suggests that proteins encoded by these genes are not rate limiting steps for resistance to bi-functional alkylating drugs in human breast cancer cells.

Adenocarcinoma↗

PubMed1995

Analysis of synaptic distribution within single retinal axonal arbors after chronic NMDA treatment.

Activation of the NMDA subtype of glutamate receptor has been implicated in structural synaptic plasticity in many developing sensory systems. In the frog retinotectal system, chronic exposure of the optic tectum to NMDA, which decreases the effectiveness of NMDA receptors (Debski et al., 1991), results in the pruning of the branches of retinal terminal arbors (Cline and Constantine-Paton, 1990). However, it is difficult from these studies to relate the involvement of NMDA receptors to changes in synapse distribution. In this study, we have developed an EM sampling procedure to quantitatively compare the amount and the distribution of synaptic contact within single retinal arbors. We report that within each retinal arbor, synaptic contact gradually increases from the main branches to the end branches of the arbor. Chronic NMDA treatment, however, significantly reduces the total amount of synaptic contact within each arbor. This reduced synaptic contact appears to be due to the pruning of the end branches, and the synapses these branches bear. The results are consistent with the hypothesis that NMDA receptor is an integral part of the mechanism that stabilizes coactive synapses, and that maintenance of an axonal branch requires a minimum density of synapses that are correlated with converging neighbors.

Animals↗

PubMed1992

A benefit-to-cost analysis of a work-site health promotion program.

An analysis of the benefit-to-cost ratio of a major health promotion program was conducted for the years 1986 through 1990, with projections to the year 2000. Program costs for personnel, capital expenses, materials, and rent were determined and compared with program benefits (discounted to account for increasing pension liability) for heath care cost savings, increased productivity, decreased absenteeism, decreased life insurance claims, and program-generated income. After adjusting future monies to net present value, a benefit-to-cost ratio of 3.4 was estimated for the program. Despite the limitations of the study design, the authors concluded that the program realizes a positive return on its investment. Several program recommendations are presented to increase the probability of achieving positive benefit-to-cost ratios in future program offerings.

Absenteeism↗

PubMed1985

Cost of orthopedic injuries sustained in motorcycle accidents.

Fifty-one serial admissions to the orthopedic services at the University of California, Davis, Medical Center, Sacramento, for motorcycle accident trauma with open fractures were reviewed. Fifty-five percent of those tested were alcohol intoxicated at the time of admission. Seventy-five percent carried no insurance of any kind, and for the total group, 72% of the cost of acute hospitalization (+17,704 per patient) was paid by the state of California, with an additional 10% paid by other tax-based sources. Care of motorcycle trauma consumes a substantial portion of public health care funds in California. This could be reduced by legislative action concerning helmet use, licensing, and rigid enforcement of compulsory insurance.

Accidents, Traffic↗

PubMed1985

A systematic approach for detecting high-frequency restriction fragment length polymorphisms using large genomic probes.

Thirteen phage clones containing low-copy sequences were isolated from a human DNA library and tested for their ability to detect restriction fragment length polymorphisms (RFLPs). Reported are the RFLPs revealed with each clone, all found in frequencies useful for linkage studies. Cytological data are available for five of the 13 clones, with regional assignments made for three of the markers by in situ hybridization. It is concluded that phage clones containing large unique DNA inserts detect multiple RFLPs with high efficiency. An analysis of the relative efficiency of 20 restriction enzymes for detecting single nucleotide changes is discussed by comparing the observed data to those expected on the basis of recognition and potential site frequencies, as computed from the dinucleotide distribution. Finally, in an effort to facilitate linkage studies using polymorphic DNA sequences, experiments were made with pools of probes from various sources.

Bacteriophages↗