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David Warburton

Publications and source records attributed to David Warburton.

At least 37 records · Page 2Linked to original sources
PubMed2004

Genomic structure and promoter characterization of the human Sprouty4 gene, a novel regulator of lung morphogenesis.

The expression of Sprouty4 (Spry4), an intracellular FGF receptor antagonist, shows a temporally and spatially restricted pattern in embryonic lung and is induced by ERK signaling. To clarify the molecular mechanisms regulating Spry4 transcription, the genomic structure of the human Sprouty4 (hSpry4) gene was first determined by using the GenomeWalker kit. The hSpry4 gene spans > 14 kb and is organized in three exons and two introns. Multiple transcription start sites were subsequently mapped by 5'-rapid amplification of cDNA ends. Analysis of up to 4 kb of sequence in the 5'-flanking region of the gene showed the presence of multiple potential transcription factor binding sites but no TATA or CAAT boxes. Transient transfection using luciferase reporter gene constructs with progressive deletions of the hSpry4 5'-flanking region revealed that the core promoter activity is located within the proximal 0.4-kb region, whereas the minimal ERK-inducible promoter activity is between -69 and -31. Homology analysis further showed that the core promoter region of the hSpry4 gene exhibits significant similarity to the 5'-flanking region of the mouse gene.

Animals↗
PubMed2004

Fibroblast growth factor 10 (Fgf10) invalidation results in anorectal malformation in mice.

BACKGROUND/PURPOSE: Anorectal malformations occur in 1 per 4,000 live births and represent a surgical challenge. Although critically important, the basic mechanisms of normal anorectal union are incompletely understood. Fgf10 signaling is known to serve a key role in mesenchymal/epithelial interactions in many organ systems including the gastrointestinal tract (GIT). The authors therefore hypothesized that Fgf10 signaling has a central role in normal anorectal development. METHODS: Fgf10 expression in wild-type (Wt) embryos was evaluated using whole-mount in situ hybridization. Wt and Fgf10-/- embryos were harvested from timed pregnant mothers at E12.5 through E17.5 and were analyzed for anorectal phenotype. RESULTS: Wt development of union between anorectal structures is completed between E12.5 and E13.5 with luminal communication between distal rectal epithelium and anus. Fgf10 is discretely expressed at E12.5 in the distal rectum. Fgf10-/- mutants show failure of union of the rectum and anus at an early stage (E13.5) and near term (E17.5). CONCLUSIONS: Fgf10 is expressed in the rectum at the time when anorectal continuity is established, indicating a role in normal anorectal development. Fgf10 invalidation (Fgf10-/- mutant) results in a genetically reproducible anorectal malformation phenotype. Fgf10 function is critical for normal anorectal development.

Anal Canal↗
PubMed2004

Fibroblast growth factor receptor 2 IIIb invalidation--a potential cause of familial duodenal atresia.

BACKGROUND/PURPOSE: Duodenal atresia (DA) occurs in 1 in every 6,000 live births and represents a significant surgically correctable cause of intestinal obstruction in the neonate. Familial or congenital DA has been reported, implying that at least some cases of DA are the result of genetic, heritable abnormalities. The genes controlling duodenal development are incompletely understood. Fibroblast growth factor receptor 2IIIb (Fgfr2b) is known to play a critical role in the development of multiple organ systems including other gastrointestinal tract (GIT) structures. This study shows the key role of Fgfr2b in normal duodenal development and the pathogenesis of DA. METHODS: Wild type (Wt) and Fgfr2b-/- embryos were harvested from timed pregnant mothers at stage E18.5 and were analyzed for duodenal phenotype. RESULTS: Inactivation of Fgfr2b results in DA. DA is present in the Fgf2b-/- mutants with a 35% penetrance. The duodenal phenotype of the Fgf2b-/- mutants ranges from normal to a mucosal web, type I, and type III atresia. CONCLUSIONS: Fgfr2b is a critical regulatory gene in the development of the duodenum. Fgfr2b invalidation (Fgfr2b-/- mutant) results in a reproducible, autosomal recessive duodenal atresia phenotype with incomplete penetrance and a variable phenotype.

Animals↗
PubMed2004

Knock-on effect of anthrax lethal toxin on macrophages potentiates cytotoxicity to endothelial cells.

Herein we report the knock-on cytotoxic effect of lethal toxin (LeTx) on human umbilical vascular endothelial cells (HUVECs). HUVECs were treated either directly with LeTx or indirectly with LeTx conditioned medium (LeTxCM) prepared from RAW264.7 macrophage cells. Cytotoxicity assays were done on HUVECs and A549 cells using LeTx. HUVECs were more susceptible to LeTx (61-74% survivals) as compared to A549 cells (83-94% survivals, P < 0.005). However, LeTxCM from RAW264.7 further potentiated killing of HUVECs (37% survival) compared to the LeTxCM from A549 cells (up to 70-100% survivals). LeTxCM challenge induced an apoptotic cell death in HUVECs, and this was confirmed by reduction of BCL-2 levels to 54%. Protective antigen (PA) binding to macrophage cell line RAW264.7 > HUVECs >> A549 cells. Thus, we postulate that after the initial prodormal phase of pulmonary entry, LeTx causes not only significant direct damage to macrophages and endothelial cells, but also mediates additional indirect damage to endothelial cells mediated by a knock-on effect of LeTx on macrophages that causes apoptotic cell death in endothelial cells.

Animals↗
PubMed2004

The molecular genetics of lung morphogenesis and injury repair.

Lung development, as well as epithelial injury repair, is tightly coordinated by a fine balance between stimulatory versus inhibitory genes that appear to co-regulate the function of stem/progenitor cells in the lung. Recently, it has been noted that many of the same genes direct development of the respiratory organs (tracheae) in the fruit fly Drosophila as in mice and men. For example, FGF receptor tyrosine kinase signaling is essential for respiratory organogenesis in both fly and mouse and is negatively regulated by the sprouty genes, a family of inducible FGF pathway inhibitors. Additionally, FGF signaling is required for formation of new alveoli, protection of alveolar epithelial cells from injury, as well as migration and proliferation of putative alveolar stem/progenitor cells during lung repair. Conversely, TGFbeta receptor serine-threonine kinase signaling via Smads 2, 3 and 4 inhibits lung morphogenesis and can inhibit postnatal alveolar development, while excessive TGFbeta signaling via Smad3 causes interstitial fibrosis. On the other hand, BMP4 stimulates morphogenesis of intact embryonic lung, while inhibiting proliferation of isolated epithelium. We speculate that evolutionary-developmental, functional conservation of the FGF- FGFR-SPROUTY stimulatory pathway as well as of the TGFbeta/BMP-SMAD modulatory pathways identifies them as potential therapeutic targets for rational therapy. Novel therapy to activate lung stem/progenitor cells, ameliorate lung injury, augment lung repair and/or induce lung regeneration could be highly beneficial in both children and adults with intractable pulmonary insufficiency.

Animals↗
PubMed2004

Overexpression of Smurf1 negatively regulates mouse embryonic lung branching morphogenesis by specifically reducing Smad1 and Smad5 proteins.

Early embryonic lung branching morphogenesis is regulated by many growth factor-mediated pathways. Bone morphogenetic protein 4 (BMP4) is one of the morphogens that stimulate epithelial branching in mouse embryonic lung explant culture. To further understand the molecular mechanisms of BMP4-regulated lung development, we studied the biological role of Smad-ubiquitin regulatory factor 1 (Smurf1), an ubiquitin ligase specific for BMP receptor-regulated Smads, during mouse lung development. The temporo-spatial expression pattern of Smurf1 in mouse embryonic lung was first determined by quantitative real-time PCR and immunohistochemistry. Overexpression of Smurf1 in airway epithelial cells by intratracheal introduction of recombinant adenoviral vector dramatically inhibited embryonic day (E) 11.5 lung explant growth in vitro. This inhibition of lung epithelial branching was restored by coexpression of Smad1 or by addition of soluble BMP4 ligand into the culture medium. Studies at the cellular level show that overexpression of Smurf1 reduced epithelial cell proliferation and differentiation, as documented by reduced PCNA-positive cell index and by reduced mRNA levels for surfactant protein C and Clara cell protein 10 expression. Further studies found that overexpression of Smurf1 reduced BMP-specific Smad1 and Smad5, but not Smad8, protein levels. Thus overexpression of Smurf1 specifically promotes Smad1 and Smad5 ubiquitination and degradation in embryonic lung epithelium, thereby modulating the effects of BMP4 on embryonic lung growth.

Animals↗
PubMed2003

Functional analysis of the human Sprouty2 gene promoter.

Sprouty2 plays a key role in negatively modulating the fibroblast growth factor signaling pathway, which is required for early branching events in embryonic development. The expression of the murine Sprouty2 gene shows a temporally and spatially restricted pattern in developing lung. In order to clarify the molecular mechanisms governing the transcription of the Sprouty2 gene, we first characterized the genomic organization of the human Sprouty2 (hSpry2) gene and mapped its transcription start sites by 5'-rapid amplification of cDNA ends. Subsequently, a 4-kb sequence from the 5'-flanking region of the gene was cloned and determined to contain promoter activity. Detailed truncation analysis of the hSpry2 promoter revealed the presence of context-specific suppressor activity in the distal upstream region. More importantly, we demonstrated that all the elements necessary to achieve strong basal transcription activity were located within the proximal 0.4-kb region. Sequence analysis revealed that this functionally important proximal region contains neither TATA nor CAAT box but an initiator element around the transcription start site. Several cis-acting elements (including AP2, CREB, SP1 and Ets-1) were found to be present in the proximal region, and their interactions with specific nuclear proteins were confirmed by electrophoretic mobility shift assays. To our knowledge, this is the first promoter study of any mammalian Sprouty gene. We propose that the high-level basal expression of hSpry2 is controlled by multiple transcription factors binding to its proximal promoter.

5' Flanking Region↗
PubMed2003

TACE is required for fetal murine cardiac development and modeling.

Tumor necrosis factor-alpha converting enzyme (TACE) is a membrane-anchored, Zn-dependent metalloprotease, which belongs to the ADAM (a disintegrin and metalloprotease) family. TACE functions as a membrane sheddase to release the ectodomain portions of many transmembrane proteins, including the precursors of TNFalpha, TGFalpha, several other cytokines, as well as the receptors for TNFalpha, and neuregulin (ErbB4). Mice with TACE(DeltaZn/DeltaZn) null mutation die at birth with phenotypic changes, including failure of eyelid fusion, hair and skin defects, and abnormalities of lung development. Abnormal fetal heart development was not previously described. Herein, we report that TACE(DeltaZn/DeltaZn) null mutant mice by late gestation exhibit markedly enlarged fetal hearts with increased myocardial trabeculation and reduced cell compaction, mimicking the pathological changes of noncompaction of ventricular myocardium. In addition, larger cardiomyocyte cell size and increased cell proliferation were observed in ventricles of TACE(DeltaZn/DeltaZn) knockout mouse hearts. At the molecular level, reduced expression of epidermal growth factor receptor, attenuated protein cleavage of ErbB4, and changes in MAPK activation were also detected in TACE(DeltaZn/DeltaZn) knockout heart tissues. The data suggest that TACE-mediated cell surface protein ectodomain shedding plays an essential and a novel regulatory role during cardiac development and modeling.

ADAM Proteins↗
PubMed2003

Isolation of a putative progenitor subpopulation of alveolar epithelial type 2 cells.

Alveolar epithelial type 2 cells (AEC2) isolated from hyperoxia-treated animals exhibit increases in both proliferation and DNA damage in response to culture. AEC2 express the zonula adherens proteins E-cadherin, -, - and -catenin, desmoglein, and pp120, as demonstrated by Western blotting. Immunohistochemical analysis of cultured AEC2 showed expression of E-cadherin on cytoplasmic membranes varying from strongly to weakly staining. When cultured AEC2 placed in suspension were labeled with fluorescent-tagged antibodies to E-cadherin, cells could be sorted into at least two subpopulations, either dim or brightly staining for this marker. With the use of antibody to E-cadherin bound to magnetic beads, cells were physically separated into E-cadherin-positive and -negative subpopulations, which were then analyzed for differences in proliferation and DNA damage. The E-cadherin-positive subpopulation contained the majority of damaged cells, was quiescent, and expressed low levels of telomerase activity, whereas the E-cadherin-negative subpopulation was undamaged, proliferative, and expressed high levels of telomerase activity.

Adherens Junctions↗
PubMed2003

Growth factor signaling in lung morphogenetic centers: automaticity, stereotypy and symmetry.

Lung morphogenesis is stereotypic, both for lobation and for the first several generations of airways, implying mechanistic control by a well conserved, genetically hardwired developmental program. This program is not only directed by transcriptional factors and peptide growth factor signaling, but also co-opts and is modulated by physical forces. Peptide growth factors signal within repeating epithelial-mesenchymal temporospatial patterns that constitute morphogenetic centers, automatically directing millions of repetitive events during both stereotypic branching and nonstereotypic branching as well as alveolar surface expansion phases of lung development. Transduction of peptide growth factor signaling within these centers is finely regulated at multiple levels. These may include ligand expression, proteolytic activation of latent ligand, ligand bioavailability, ligand binding proteins and receptor affinity and presentation, receptor complex assembly and kinase activation, phosphorylation and activation of adapter and messenger protein complexes as well as downstream events and cross-talk both inside and outside the nucleus. Herein we review the critical Sonic Hedgehog, Fibroblast Growth Factor, Bone Morphogenetic Protein, Vascular Endothelial Growth Factor and Transforming Growth Factorbeta signaling pathways and propose how they may be functionally coordinated within compound, highly regulated morphogenetic gradients that drive first stereotypic and then non-stereotypic, automatically repetitive, symmetrical as well as asymmetrical branching events in the lung.

Aging↗
PubMed2003

Burkholderia cepacia-induced IL-8 gene expression in an alveolar epithelial cell line: signaling through CD14 and mitogen-activated protein kinase.

Burkholderia cepacia is a prevalent pulmonary pathogen in patients with cystic fibrosis (CF). The lung pathology observed in patients with CF is postulated to be due to an overexpression of chemokines. This study investigated the induction of the neutrophil chemoattractant chemokine IL-8 and the signaling pathways activated by B. cepacia-infected human lung epithelial A549 (HLE) cells. Cells were infected with B. cepacia (genomovar III of the B. cepacia complex), and reverse transcriptase-PCR and ELISA for the cytokines were performed. B. cepacia (multiplicity of infection > or =4:1) induced HLE cells to significantly secrete IL-8 in a more potent manner than the predominant CF pathogen Pseudomonas aeruginosa (multiplicity of infection > or =64:1). IL-8 secretion by B. cepacia-infected HLE cells was abrogated by the gene transcription inhibitor actinomycin D and the protein translation inhibitor cycloheximide, confirming that B. cepacia-induced IL-8 secretion was mediated through de novo protein synthesis. Treatment of B. cepacia with proteinase K failed to down-regulate IL-8 secretion; furthermore, IL-8 secretion by B. cepacia-infected HLE cells was abrogated by > or =80% in the presence of anti-CD14 [specific lipopolysaccharide (LPS) receptor] antibody, thus suggesting that the IL-8-inducing component of B. cepacia was LPS and therefore dependent on CD14. The p38 mitogen-activated protein kinase (MAPK) inhibitor and the extracellular signal-regulated kinase MAPK inhibitor significantly abrogated IL-8 secretion by B. cepacia-infected HLE cells (SB203580, > or =80% inhibition; PD98059, > or =30% inhibition). In conclusion, B. cepacia-induced IL-8 secretion in A549 airway epithelial cells is more potent than P. aeruginosa; is mediated through LPS, which is CD14 dependent; and involves activation of the p38 and ERK MAPK pathways.

Burkholderia cepacia↗
PubMed2003

Nongenomic estrogen action regulates tyrosine phosphatase activity and tuberin stability.

Estrogen action and tuberin function has been suggested to play a crucial role in the proliferation of lung smooth muscle-like cells and/or myofibroblasts in pulmonary lymphangioleiomyomatosis (LAM). Tuberin is a tumor suppressor phosphoprotein, which also regulates fluid phase endocytosis. Its activity, turnover and complex association with hamartin depends on its phosphorylation status. We have recently reported that nongenomic estrogen action regulates the phosphorylation status of several cytoplasmic proteins. Herein, we demonstrate that estrogen increases tyrosine phosphatase activity, which can be abrogated by antiestrogen ICI 182780 and tyrosine phosphatase inhibitor bpV(phen), but not by the protein synthesis inhibitor cyclohexamide. Furthermore, we show that estrogen transiently enhances the turnover of tuberin, which follows an inverse pattern to that observed for tyrosine phosphatase and endocytosis activity. We showed that tuberin phosphorylation protects it from degradation and induces its accumulation in female human lung fibroblasts and myofibroblasts. Our results suggest that nongenomic estrogen action induces tyrosine phosphatase activity that regulates stability of tyrosine phosphorylated proteins, including tuberin, which may play a crucial role in cellular specific functions such as endocytosis.

Cell Line↗
PubMed2003

Transfer of the active form of transforming growth factor-beta 1 gene to newborn rat lung induces changes consistent with bronchopulmonary dysplasia.

Bronchopulmonary dysplasia is a chronic lung disease of premature human infancy that shows pathological features comprising varying sized areas of interstitial fibrosis in association with distorted large alveolar spaces. We have previously shown that transfer of active transforming growth factor (TGF)-beta 1 (AdTGF beta 1(223/225)) genes by adenovirus vector to embryonic lungs results in inhibition of branching morphogenesis and primitive peripheral lung development, whereas transfer to adult lungs results in progressive interstitial fibrosis. Herein we show that transfer of TGF-beta1 to newborn rat pups results in patchy areas of interstitial fibrosis developing throughout a period of 28 days after transfer. These areas of fibrosis appear alongside areas of enlarged alveolar spaces similar to the prealveoli seen at birth, suggesting that postnatal lung development and alveolarization has been inhibited. In rats treated with AdTGF beta 1(223/225), enlarged alveolar spaces were evident by day 21, and by 28 days, the mean alveolar cord length was nearly twice that in control vector or untreated rats. Hydroxyproline measurements confirmed the presence of fibrosis. These data suggest that overexpression of TGF-beta 1 during the critical period of postnatal rat lung alveolarization gives rise to pathological, biochemical, and morphological changes consistent with those seen in human bronchopulmonary dysplasia, thus inferring a pathogenic role for TGF-beta in this disorder.

Animals↗
PubMed2002

Murine nitrofen-induced pulmonary hypoplasia does not involve induction of TGF-beta signaling.

BACKGROUND/PURPOSE: In the murine nitrofen-induced model of congenital diaphragmatic hernia (CDH), the lungs are primarily hypoplastic and immature even before diaphragmatic closure. Because excess transforming growth factor-beta (TGF-beta) signaling induces pulmonary hypoplasia, the authors hypothesized that primary hypoplasia after nitrofen exposure may be caused by aberrant signaling by the TGF-beta pathway. Therefore, abrogation of TGF-beta signaling might rescue the hypoplasia. METHODS: The authors performed intratracheal microinjections of a recombinant adenoviral vector encoding a dominant-negative TGF-beta type II receptor (AdIIR-DN) in nitrofen-exposed and control E12 mouse lungs, which then were cultured for 4 days in serumless chemically defined media. The mRNA expression of Smad2, 3, 4, and 7 in nitrofen-exposed and control E12 lungs after 4 days in culture were compared. RESULTS: ADIIR-DN increased terminal branching in control lungs by 28% compared with lungs injected with control virus (61.8 +/- 4.6 v. 48.4 +/- 4.7, P =.004). However, there was no difference between nitrofen-exposed lungs injected with ADIIR-DN and those injected with control virus. Compared with control lungs, Smad mRNA expression was decreased markedly in nitrofen-exposed lungs: Smad2 (40%, P =.16), Smad3 (29%, P =.02), Smad4 (25%, P =.07), and Smad7 (36%, P =.04). CONCLUSIONS: Because abrogation of TGF-beta signaling does not rescue the hypoplasia seen in the nitrofen model, and Smad expression is decreased in nitrofen-exposed lungs, the TGF-beta pathway does not appear to play a role in nitrofen-induced pulmonary hypoplasia.

Animals↗
PubMed2002

Nitrofen inhibition of pulmonary growth and development occurs in the early embryonic mouse.

BACKGROUND/PURPOSE: It was believed previously that pulmonary hypoplasia in congenital diaphragmatic hernia (CDH) was a consequence of the herniation of abdominal viscera into the chest. Using the murine nitrofen-induced model of CDH, the authors evaluated lung growth and development before diaphragm closure or herniation. METHODS: The authors examined nitrofen-exposed early embryonic lungs on embryonic day 12 (E12). Branching morphogenesis was quantified before and after 4 days in culture in serumless chemically defined media and compared with age-matched control lungs. The mRNA expression of proliferative and developmental markers in cultured lungs was then determined. RESULTS: Nitrofen-exposed lungs had 30% fewer total terminal branches than age-matched controls (9.3 +/- 1.9 nitrofen v 13.7 +/- 2.6 control; P <.001). Hypoplasia also was more profound in the left than the right lung. These effects persisted after culturing the lungs for 4 days in serumless chemically-defined media (31.7 +/- 6.8 nitrofen v 42.9 +/- 8.4 control, P <.001). Furthermore, the mRNA expression of proliferative and developmental markers was decreased in nitrofen-exposed E12 lungs cultured for 4 days (as a percentage of age-matched controls): cyclin A (69.28%; P =.04), Nkx2.1 (44.4%, 0.04), SP-A (24.1%; P =.008), SP-B (23.4%; P =.05), SP-C (20%; P =.06), and CC-10 (13.8%; P =.04). CONCLUSION: Nitrofen induces primary pulmonary hypoplasia and immaturity in the early embryonic mouse, and this effect persists in culture.

Animals↗