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Dai H Chung

Publications and source records attributed to Dai H Chung.

At least 19 recordsLinked to original sources
PubMed2006

MYCN silencing induces differentiation and apoptosis in human neuroblastoma cells.

MYCN amplification strongly correlates with unfavorable outcomes in patients with neuroblastoma. The aim of this study was to investigate the role of MYCN in neuroblastoma cell differentiation and apoptosis. We used the technique of RNA interference to inhibit MYCN gene expression in neuroblastoma cells with variable expression of MYCN. Our results showed that inhibition of MYCN gene expression in MYCN amplified cells induced apoptosis and suppressed cell growth; neuronal differentiation also occurred after MYCN gene silencing. Moreover, N-myc downregulation was associated with decreased Bcl-xL protein levels and caspase-3 activation. These data show that small interfering RNA directed to MYCN, which plays a crucial role in neuroblastoma cell survival, may provide a potential novel therapeutic option for aggressive neuroblastomas.

Apoptosis↗
PubMed2006

Oxidative stress-induced intestinal epithelial cell apoptosis is mediated by p38 MAPK.

Free oxygen radicals are involved in the pathogenesis of necrotizing enterocolitis (NEC) in premature infants. The stress-activated p38 mitogen-activated protein kinase (MAPK) has been implicated in gut injury. Here, we found that phosphorylated p38 was detected primarily in the villus tips of normal intestine, whereas it was expressed in the entire mucosa in NEC. H(2)O(2) treatment resulted in a rapid phosphorylation of p38 MAPK and subsequent apoptosis of rat intestinal epithelial (RIE)-1 cells; this induction was attenuated by treatment with SB203580, a selective p38 MAPK inhibitor, or transfection with p38alpha siRNA. Moreover, SB203580 also blocked H(2)O(2)-induced PKC activation. In contrast, the PKC inhibitor (GF109203x) did not affect p38 activation, indicating that p38 MAPK activation occurs upstream of PKC activation in H(2)O(2)-induced apoptosis. H(2)O(2) treatment also decreased mitochondrial membrane potential; pretreatment with SB203580 attenuated this response. Our study demonstrates that the p38 MAPK/PKC pathway plays an important role as a pro-apoptotic cellular signaling during oxidative stress-induced intestinal epithelial cell injury.

Animals↗
PubMed2006

Gut mucosal homeostasis and cellular mediators after severe thermal trauma and the effect of insulin-like growth factor-I in combination with insulin-like growth factor binding protein-3.

Increased small bowel epithelial cell apoptosis and decreased cell proliferation lead to impairment of gut mucosal integrity and function after thermal injury. Impairment of gut integrity is associated with increased bacterial translocation and incidence of sepsis. The purpose of this study was to determine whether IGF-I/IGF binding protein (IGFBP)-3 can improve small bowel homeostasis after injury and by which cellular mechanisms these changes occur and to identify changes in apoptosis-related genes after burn and the effect of bile acid on small bowel epithelial cell apoptosis after burn. Rats sustained a thermal injury and received saline or the IGF-I/IGFBP-3 complex. Serum and small intestine were taken at 1, 2, 5, and 7 d after injury and serum inflammatory cytokines and mucosal apoptosis, proliferation, villous morphology, and apoptotic and proliferative mediators were measured. Apoptosis-related gene expression and the bile acid pool were determined in separate experiments up to 6 h after burn. Gut epithelial cell apoptosis as well as apoptosis-related genes were increased after the thermal injury, whereas bile acid secretion was significantly decreased (P < 0.05). IGF-I/IGFBP-3 significantly improved villous height and cells per villous by decreasing small bowel epithelial cell apoptosis and increasing proliferation (P < 0.05). Decreased apoptosis was associated with decreased Fas, Fas-ligand, and TNF when compared with saline (P < 0.05). A severe thermal injury caused an up-regulation of apoptosis and apoptosis-related genes and down-regulation of bile acid secretion. IGF-I/IGFBP-3 decreases small bowel epithelial cell apoptosis through down-regulation of the Fas pathway, which improves gut mucosal integrity after a severe thermal injury.

Animals↗
PubMed2006

IGF-1 protects intestinal epithelial cells from oxidative stress-induced apoptosis.

BACKGROUND: Reactive oxygen species (ROS) are involved in the pathogenesis of necrotizing enterocolitis (NEC) in premature infants. We have recently found that activation of multiple cellular signaling transduction pathways occurs during ROS-induced intestinal cell apoptosis; the phosphatidylinositol 3-kinase (PI3-K) pathway plays an anti-apoptotic role during this process. Insulin-like growth factor (IGF)-1 activates PI3-K pathway to promote cell survival; however, the effects of IGF-1 treatment during gut injury are not clearly defined. The purpose of this study was to determine whether IGF-1 protects intestinal cells from ROS-induced apoptosis. MATERIALS AND METHODS: Rat intestinal epithelial (RIE)-1 cells were treated with either IGF-1 (100 nm), hydrogen peroxide (H2O2; 500 microm), or combination. Western blotting was performed to assess phosphorylation of Akt, a downstream effector of PI3-K. Cell Death Detection ELISA, DCHF, and JC-1 assays were performed to demonstrate protective effects of IGF-1. Wortmannin, an inhibitor of PI3-K, was used to show PI3-K-dependent mechanism of action for IGF-1. RESULTS: H2O2 treatment resulted in increased intestinal epithelial cell apoptosis with intracellular ROS generation and mitochondrial membrane depolarization; IGF-1 pre-treatment attenuated this response without affecting ROS production. H2O2-induced phosphorylation of Akt was further increased with IGF-1 treatment; wortmannin abolished these effects in RIE-1 cells. CONCLUSIONS: PI3-K pathway is activated during ROS-induced intestinal epithelial cell injury; IGF-1 exerted an anti-apoptotic effect during this response by PI3-K activation. A better understanding of the exact role of IGF-1-mediated activation of PI3-K may allow us to facilitate the development of novel therapy against NEC.

Animals↗
PubMed2006

Inhibition of transforming growth factor-beta/Smad signaling by phosphatidylinositol 3-kinase pathway.

Gastrin-releasing peptide (GRP) activates phosphatidylinositol 3-kinase (PI3-K)/Akt, an important cell survival signaling pathway, to stimulate growth of various cell types. Transforming growth factor (TGF) superfamily ligands activate intracellular Smad signaling to regulate cell growth, differentiation and apoptosis; dysregulation of the TGF-beta/Smad pathway has been noted in cancer cells. Therefore, we sought to determine whether a potential cross-talk exists between the TGF-beta/Smad and PI3-K pathways in the regulation of neuroblastoma cell growth. Increased Smad DNA binding was noted in SK-N-SH human neuroblastoma cells when treated with LY294002, an inhibitor of PI3-K, by transcription factor/DNA array analysis and electrophoretic mobility shift assay. LY294002 treatment resulted in Smad2 accumulation in the nuclei and an increased Smad binding element (SBE)-luciferase activity. These findings were corroborated by co-transfection with pCGNN-Deltap85 plasmid, which expresses a PI3-K mutant p85 subunit. In contrast, GRP treatment decreased Smad binding activity in neuroblastoma cells. Our findings demonstrate that the PI3-K pathway negatively regulates TGF-beta/Smad signaling in neuroblastoma cells. GRP-induced activation of PI3-K, resulting in neuroblastoma cell growth promotion, is potentiated by down-regulation of TGF-beta/Smad signaling.

Cell Proliferation↗
PubMed2006

Protein kinase D protects against oxidative stress-induced intestinal epithelial cell injury via Rho/ROK/PKC-delta pathway activation.

Protein kinase D (PKD) is a novel protein serine kinase that has recently been implicated in diverse cellular functions, including apoptosis and cell proliferation. The purpose of our present study was 1) to define the activation of PKD in intestinal epithelial cells treated with H2O2, an agent that induces oxidative stress, and 2) to delineate the upstream signaling mechanisms mediating the activation of PKD. We found that the activation of PKD is induced by H2O2 in both a dose- and time-dependent fashion. PKD phosphorylation was attenuated by rottlerin, a selective PKC-delta inhibitor, and by small interfering RNA (siRNA) directed against PKC-delta, suggesting the regulation of PKD activity by upstream PKC-delta. Activation of PKD was also blocked by a Rho kinase (ROK)-specific inhibitor, Y-27632, as well as by C3, a Rho protein inhibitor, demonstrating that the Rho/ROK pathway also mediates PKD activity in intestinal cells. In addition, H2O2-induced PKC-delta phosphorylation was inhibited by C3 treatment, further suggesting that PKC-delta is downstream of Rho/ROK. Interestingly, H2O2-induced intestinal cell apoptosis was enhanced by PKD siRNA. Together, these results clearly demonstrate that oxidative stress induces PKD activation in intestinal epithelial cells and that this activation is regulated by upstream PKC-delta and Rho/ROK pathways. Importantly, our findings suggest that PKD activation protects intestinal epithelial cells from oxidative stress-induced apoptosis. These findings have potential clinical implications for intestinal injury associated with oxidative stress (e.g., necrotizing enterocolitis in infants).

Animals↗
PubMed2005

Caudal anesthesia for vascular access procedures in two extremely small premature neonates.

With advances in neonatology, there is an increasing need for central vascular access in extremely small (<1,000 g) premature infants. Although the use of peripherally inserted central venous lines have become common practice, surgeons still frequently perform central venous line placements via cut-down in difficult access patients. The advantages of general anesthesia for vascular access procedures are obvious for optimal pain control and ideal operative exposure; however, extremely premature infants are at significant risk for prolonged endotracheal intubation with postoperative apneas. We report two cases where regional caudal anesthesia with bupivacaine and clonidine without intubation was successfully utilized at bedside during central venous line placements in premature infants weighing <600 g. The operative field was ideal with adequate motor and sensory block with caudal anesthesia and both infants received only oxygen by nasal cannula.

Anesthesia, Caudal↗
PubMed2005

Pertussis with severe pulmonary hypertension and leukocytosis treated with extracorporeal membrane oxygenation.

Pertussis, or "whooping cough," is a highly communicable disease caused by the coccobacillus Bordetella pertussis. Pertussis remains one of the most common causes of death from infectious diseases worldwide. We describe a 5-week-old infant girl who presented with severe pertussis infection associated with extreme leukocytosis and required prolonged extracorporeal membrane oxygenation (ECMO). Nitric oxide therapy resolved the pulmonary hypertension, and she was successfully weaned from ECMO and discharged home after 3 months. We report successful application of ECMO for severe pertussis-induced respiratory failure despite multiple grave prognostic indicators (<1 year age, leukocytosis, pulmonary hypertension) and discuss the role of extracorporeal life support in treating pertussis.

Extracorporeal Membrane Oxygenation↗
PubMed2005

Role of gastrointestinal hormones in neuroblastoma.

As a neuroendocrine tumor, neuroblastoma expresses various gastrointestinal (GI) hormones, such as vasoactive intestinal peptide, gastrin-releasing peptide (GRP), neurotensin, and somatostatin, which exert diverse cellular functions in neuroblastoma. In particular, we have recently found that GRP and its cell surface receptor, GRP-R, are abundantly expressed in neuroblastomas. Moreover, more advanced-stage neuroblastomas demonstrated an increased level of GRP-R, suggesting an important role of GRP in aggressive tumor behavior. This review describes the role of several GI hormones commonly expressed in neuroblastoma and discusses in depth the mitogenic actions of GRP in neuroblastoma. In addition, the molecular mechanisms involved in the GRP-induced stimulation of neuroblastoma cell growth are discussed. Our study results demonstrate a role of GRP as an autocrine/paracrine growth factor and elucidate involvement of specific intracellular signaling, the phosphatidylinositol 3-kinase pathway, in the growth regulation of neuroblastoma.

Biomarkers↗
PubMed2005

Ischemic preconditioning at a distance: altered gene expression in mouse heart and other organs following brief occlusion of the mesenteric artery.

Remote ischemic preconditionining (IPC) has been defined as a brief episode of ischemia/reperfusion in an organ that protects another remote organ from the damage induced by subsequent and prolonged ischemia. As yet, no study has been conducted with the purpose of elucidating a precise association between remote IPC and patterns of gene-transcription in cardiac tissue. In this study, using a cDNA microarray, we analyzed the gene expression profile in murine heart at 24h after brief cycles of occlusion of the superior mesenteric artery. The profile revealed that IPC induces significant levels of expression of many genes known to be associated with the stress response, redox regulation, growth and metabolism, DNA repair and other functions. The result of cDNA microarray profile from heart was also compared with those from other organs (lung, kidney and intestine). The genes identified in the expression profile may be associated with remote IPC induced late phase organ protection.

Animals↗
PubMed2005

Gastrin-releasing peptide-induced down-regulation of tumor suppressor protein PTEN (phosphatase and tensin homolog deleted on chromosome ten) in neuroblastomas.

OBJECTIVES: To evaluate whether aggressive, undifferentiated neuroblastomas express tumor suppressor protein PTEN (phosphatase and tensin homolog deleted on chromosome ten) and to examine the effects of gastrin-releasing peptide (GRP) on PTEN gene and protein expression. SUMMARY BACKGROUND DATA: We have previously shown that neuroblastomas secrete GRP, which binds to its cell surface receptor (GRP-R) to stimulate cell growth in an autocrine fashion. However, the effects of GRP on expression of the tumor suppressor gene PTEN have not been elucidated in neuroblastomas. METHODS: Paraffin-embedded sections from human neuroblastomas were analyzed for PTEN and phospho-Akt protein expression by immunohistochemistry. Human neuroblastoma cell lines (SK-N-SH and SH-SY5Y) were stably transfected with the plasmid pEGFP-GRP-R to establish GRP-R overexpression cell lines, and the effects of GRP on PTEN gene and protein expression were determined. RESULTS: A decrease in the ratio of PTEN to phospho-Akt protein expression was identified in poorly differentiated neuroblastomas. An increase in GRP binding capacity was confirmed in GRP-R overexpressing cells, which demonstrated an accelerated constitutive cell growth rate. PTEN gene and protein expression was significantly decreased in GRP-R overexpressing cells when compared with controls. CONCLUSIONS: Our findings demonstrate decreased expression of the tumor suppressor protein PTEN in more aggressive undifferentiated neuroblastomas. An increase in GRP binding capacity, as a result of GRP-R overexpression, down-regulates PTEN expression. These findings suggest that an inhibition of the tumor suppressor gene PTEN may be an important regulatory mechanism involved in GRP-induced cell proliferation in neuroblastomas.

Cell Differentiation↗
PubMed2005

A survey for pain and sedation medications in pediatric patients during extracorporeal membrane oxygenation.

Routine administration of large amounts of pain and sedative medication is common to critically ill pediatric patients undergoing extracorporeal membrane oxygenation (ECMO) for cardiopulmonary failure. It has been our experience that pediatric patients are the most difficult age group in which to achieve an ideal pain and sedative control due to the narrow margin of safety. The purpose of this study was to determine the general practice guideline used for pain and anxiolytic pharmacotherapy for pediatric patients at ECMO centers. We sent a survey questionnaire to all ECMO centers in the USA that treat pediatric respiratory failure patients. Of the 46 responding centers (including telephone follow-ups), 37 (80%) centers had an active pediatric ECMO programs for patients with severe respiratory failure. Fentanyl was the most commonly used pain medication and continuous infusion, administered directly to the patient, was preferred. Subjective effectiveness of various pharmacological agents was variable without clear consensus; however, midazolam was considered to be the most effective agent used.

Anesthetics↗
PubMed2005

Signal transduction pathways involved in oxidative stress-induced intestinal epithelial cell apoptosis.

Necrotizing enterocolitis (NEC) is a devastating inflammatory condition of the gut that occurs in premature infants. Ischemia-reperfusion gut injury with production of reactive oxygen species (ROS) is thought to contribute to NEC; the exact cellular mechanisms involved are largely unknown. The purpose of this study was to determine the intracellular signaling transduction pathways involved in oxidative stress-induced intestinal epithelial cell apoptosis. H2O2 treatment resulted in rat intestinal epithelial cell apoptosis in a dose- and time-dependent manner; the caspase inhibitor, zVAD-fmk, blocked this response. Western blotting was performed to determine phosphorylation of kinases and ELISA was used to assess DNA fragmentation, as a measure of apoptosis. A rapid increase in phosphorylation of extracellular signal-related kinase (ERK)1/2, c-Jun N-terminal kinase (JNK)1/2, and Akt was noted. Inhibition of ERK and JNK decreased H2O2-induced apoptosis. Additionally, inhibition of protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI3-K) attenuated and enhanced H2O2-mediated apoptosis and mitochondrial membrane potential decrease, respectively. Furthermore, activation of PKC reduced the Akt phosphorylation, whereas inhibition of PKC attenuated H2O2-mediated activation of caspase-3 and enhanced the H2O2-induced Akt phosphorylation. This study shows that activation of multiple signaling transduction pathways occurs during oxidative stress-induced intestinal epithelial cell injury. In contrast to ERK, JNK, and PKC, PI3-K/Akt may play an important role as a protective cellular signaling pathway during this process.

Animals↗
PubMed2004

Phosphatidylinositol 3-kinase inhibition down-regulates survivin and facilitates TRAIL-mediated apoptosis in neuroblastomas.

BACKGROUND/PURPOSE: Recent findings have correlated neuroblastoma development with aberration of apoptosis. In particular, increased levels of survivin, a member of the inhibitor of apoptosis protein (IAP) family, have been associated with increased resistance to apoptosis in neuroblastomas. The purpose of this study was to determine whether the phosphatidylinositol 3-kinase (PI3K)/Akt pathway can alter the expression of survivin and facilitate tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in neuroblastoma cells. METHODS: Human neuroblastoma cells (SK-N-SH, BE[2]C, LAN-1 and IMR-32) were treated with LY294002 or wortmannin, inhibitors of PI3K, for 24 hours. Transient transfection of a dominant negative PI3K expression plasmid, pCGNN-Deltap85, was performed to inhibit PI3K activation. Cells were treated with TRAIL, caspase-3, or pan-caspase inhibitors. RNase protection assay was performed to assess mRNA changes in IAP family members, including survivin. Western blot analysis was performed to measure changes in the levels of procaspases and survivin. Apoptosis was assessed by a DNA fragmentation ELISA assay. RESULTS: The authors found that survivin and cIAP1 mRNA as well as protein expression were decreased after PI3K inhibition. Combination treatment with LY294002 and TRAIL increased apoptosis of SK-N-SH cells compared with TRAIL alone; these results were further corroborated by complete inhibition of apoptosis by caspase-3 or pan-caspase inhibitor. CONCLUSIONS: The authors report that PI3K pathway inhibition down-regulates survivin expression and enhances TRAIL-mediated apoptosis in neuroblastomas. PI3K pathway may play a crucial role in neuroblastoma cell survival; therefore, treatment with inhibitors of PI3K may provide potential novel therapeutic options.

Androstadienes↗
PubMed2004

Interferon-gamma induces caspase-8 in neuroblastomas without affecting methylation of caspase-8 promoter.

BACKGROUND: The expression of caspase-8, a cysteine protease that is crucial for the apoptotic cascade, is absent in a high percentage of neuroblastomas, the most frequent extracranial solid tumor of infants and children. Resistance of neuroblastomas to death-receptor (eg, tumor necrosis factor alpha (TNF-alpha) receptor)--mediated apoptosis is thought to be caused by loss of caspase-8 expression. Gene silencing by hypermethylation of caspase-8 promoter has been proposed for the loss of caspase-8 expression in neuroblastoma cells. METHODS: To further evaluate the role of caspase-8 in neuroblastoma, we assessed the induction of caspase-8 expression in neuroblastoma cells by treating the cells with a physiologic agent such as interferon-gamma. RESULTS: The authors found that interferon-gamma induces caspase-8 expression in neuroblastoma cells irrespective of the gene silenced by hypermethylation of caspase-8 promoter. The authors show that interferon-gamma also regulates other apoptosis related gene expression. Moreover, they show that interferon-gamma treatment in combination with TNF-alpha decreases neuroblastoma cell proliferation. CONCLUSIONS: Interferon-gamma induces procaspase-8 expression in neuroblastoma cells, and this induction is not dependent on demethylation of the caspase-8 promoter. Therapies aimed at inducing caspase-8 expression by adjunctive treatment, such as interferon-gamma, may increase the effectiveness of current chemotherapeutic regimens.

Apoptosis↗
PubMed2004

Ets transcriptional regulation of gastrin-releasing peptide receptor in neuroblastomas.

BACKGROUND: We have demonstrated that gastrin-releasing peptide (GRP) binds specifically to its cell surface receptor, GRP-R, to act as an autocrine/paracrine growth factor for neuroblastomas (NBs); an increased expression of GRP-R was found in more advanced-stage NBs. Ets family proteins are nuclear targets for intracellular kinase pathways that can lead to cell proliferation; however, a potential role of Ets in the expression of GRP-R in NBs is unknown. Therefore, the purpose of our study was to determine whether Ets regulates transcriptional activity of GRP-R in NBs. METHODS: We identified multiple DNA-binding sites for various nuclear transcription factors in the proximal (ie, 263 bp) GRP-R promoter. Luciferase assay was performed to measure GRP-R promoter activity that contained site-specific mutations of various binding elements. Electrophoretic mobility shift assay was performed to determine transcription factor-binding activity. RESULTS: Mutation of a consensus Ets-binding site in the GRP-R promoter significantly decreased GRP-R promoter activity. Electrophoretic mobility shift assay demonstrated a decrease in Ets nuclear protein-binding activity. Furthermore, overexpression of Ets1 resulted in upregulation of GRP-R promoter activity. CONCLUSIONS: Our results demonstrate that Ets is a transcription factor that significantly contributes to the GRP-R transcription in NBs. This finding may allow us to develop novel molecular tools to downregulate expression of GRP-R and hence inhibit mitogenic effects of GRP in NBs.

DNA↗