Biomedical subjects

Q Q Qiu

Publications and source records attributed to Q Q Qiu.

12 recordsLinked to original sources

PubMed2001

3D bone tissue engineered with bioactive microspheres in simulated microgravity.

Three-dimensional (3D) osteoblast cell cultures were obtained in rotating-wall vessels (RWV), simulating microgravity. Three types of bioactive microcarriers, specifically modified bioactive glass particles, bioceramic hollow microspheres, and biodegradable bioactive glass-polymer composite microspheres, were developed and used with osteoblasts. The surfaces of composite microspheres fully transformed into bone apatite after 2-wk immersion in simulated physiological fluid, which demonstrated their bone-bonding ability. The motion of microcarriers in RWVs was photographically recorded and numerically analyzed. The trajectories of hollow microspheres showed that they migrated and eventually stayed around at the central region of the RWV. At their surfaces, shear stresses were low. In contrast, solid glass or polymer particles moved toward and finally bounced off the outer wall of the RWVs. Cell culture studies in the RWV using bone marrow stromal cells showed that the cells attached to and formed 3D aggregates with the hollow microspheres. Extracellular matrix and mineralization were observed in the aggregates. Cell culture studies also confirmed the ability of the composite microspheres to support 3D bone-like tissue formation. These data suggest that the new hollow bioceramic microspheres and degradable composite microspheres can be used as microcarriers for 3D bone tissue engineering in microgravity. They also have potential applications as drug delivery systems.

Animals↗

PubMed2000

New bioactive, degradable composite microspheres as tissue engineering substrates.

Novel bioactive, degradable polymer/glass/ceramic composite microspheres were developed using a solid-in-oil-in-water (s/o/w) emulsion solvent removal method. Modified bioactive glass (MBG) powders were encapsulated into the polylactic acid (PLA) matrix. Scanning electron microscopy and energy-dispersive X-ray analyses revealed that the MBG powders were mostly embedded in the polymer matrix, and submicron-size pores were present at the surface. Immersion in simulated physiological fluid (SPF) was used to evaluate the surface reactivity of the microspheres. The polymeric surface was fully transformed into carbonated calcium hydroxyapatite (c-HA) after 3 weeks of immersion. In contrast, PLA microspheres showed no evidence of any calcium phosphate deposition. Ion concentration analyses revealed a decrease in Ca and P concentrations and an increase in Si concentration in the SPF immersed with composite microspheres during the 3-week period. The Ca and P uptake rates decreased after 2 days of incubation. This coincided with the decrease of the Si release rate. These data lend support to the suggestion that the Si released from the MBG powders present in the polymer matrix is involved in the formation of the Ca-P layer. Our results support the concept that these new bioactive, degradable composite microspheres may serve as microcarriers for synthesis of bone and other tissues in vitro and in vivo.

Biocompatible Materials↗

PubMed1999

Fabrication, characterization and evaluation of bioceramic hollow microspheres used as microcarriers for 3-D bone tissue formation in rotating bioreactors.

Novel bioactive ceramic hollow microspheres with an apparent density in the range 0.8-1.0 g cm(-3) have been developed as microcarriers for 3-D bone tissue formation in rotating-wall vessels (RWV). Hollow ceramic microspheres with a composition of 58-72% SiO2, 28-42% Al2O3 (wt%) and an apparent density 0.8-1.0 g cm(-3) were pretreated in 1.0 N NaOH for 2 h before being coated with synthesized calcium hydroxyapatite (HA) particulate sol. The HA-coated hollow microspheres were sintered for 1 h at 600, 800 and 1000 degrees C. SEM analysis revealed that the grain size and pore size of the calcium phosphate coating increased with the sintering temperature. FTIR analysis showed that crystalline calcium hydroxyapatite was present in the coatings sintered at 600 and 800 degrees C. When sintered at 1000 degrees C, the coating consisted of alpha-tricalcium phosphate. All the coatings adhered well, independent of sintering temperature. The trajectory analysis revealed that the hollow microsphere remained suspended in a rotating-wall vessel (RWV), and experienced a low shear stress (approximately 0.6 dyn cm(-2)). Cell culture studies using rat bone marrow stromal cells and osteosarcoma cells (ROS 17/2.8) showed that the cells attached to and formed 3-D aggregates with the hollow microspheres in a RWV. Extracellular matrix was observed in the aggregates. These data suggest that these hollow bioactive ceramic microspheres can be used as microcarriers for 3-D bone tissue formation in vitro, as well as for the study of the effects of microgravity on bone cell functions.

Animals↗

PubMed1998

17Beta-hydroxysteroid dehydrogenases in human bone cells.

Interconversion of estrogens by osteoblasts may play a role in regulating bone mass. As a first step toward exploring this possibility, we investigated the expression and activity of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) in cultured human osteoblasts (HOB) and osteoblast-like osteosarcoma cells (MG63, TE85, and SaOS-2). Significant 17beta-HSD activity was detected in cell-free extracts of all bone cells with oxidation of estradiol to estrone predominating over reduction. Reverse transcription-polymerase chain reaction (RT-PCR) experiments showed that the mRNA for 17beta-HSD I was detectable only in MG63 cells, albeit at low levels, while 17beta-HSD II was present in MG63, TE85, and HOB, but not SaOS-2, and 17beta-HSD III was absent from each bone cell type. 17Beta-HSD IV was the only isoform present in all bone cells analyzed. Further analysis of the expression of 17beta-HSD IV in these bone cells by immunoblotting revealed both the full-length 83 kDa protein and the proteolytic 38 kDa form. The kinetic parameters for estradiol oxidation by purified recombinant 17beta-HSD IV (Km = 49.7 microM, Vmax = 79.4 nmol/minute/mg of protein) and its HSD-domain (Km = 79.4 microM, Vmax = 476 nmol/minute/mg of protein) were significantly higher than previously reported, but consistent with the values obtained with crude cell-free extracts of SaOS-2 cells (Km = 98.8 microM, Vmax = 0.07 nmol/minute/mg of protein) which contain only 17beta-HSD IV based on RT-PCR. These studies show that bone cells have the capacity to interconvert circulating estrogens and suggest that bone cell 17beta-HSDs serve primarily to attenuate the continuing actions of estradiol through conversion to its less potent form, estrone, under certain conditions.

17-Hydroxysteroid Dehydrogenases↗

PubMed1996

Molecular cloning of the cDNA and chromosome localization of the gene for human ubiquitin-conjugating enzyme 9.

We report a novel human gene whose product specifically associates with the negative regulatory domain of the Wilms' tumor gene product (WT1) in a yeast two-hybrid screen and with WT1 in immunoprecipitation and glutathione S-transferase (GST) capture assays. The gene encodes a 17-kDa protein that has 56% amino acid sequence identity with yeast ubiquitin-conjugating enzyme (yUBC) 9, a protein required for cell cycle progression in yeast, and significant identity with other subfamilies of ubiquitin-conjugating enzymes. The human gene fully complements yeast that have a temperature-sensitive yUBC9 gene mutation to fully restore normal growth, indicating that we have cloned a functionally conserved human (h) homolog of yUBC9. Transcripts of hUBC9 of 4.4 kilobases (kb), 2.8 kb, and 1.3 kb were found in all human tissues tested. A single copy of the hUBC9 gene was found and localized to human chromosome 16p13.3. We conclude that hUBC9 retains striking structural and functional conservation with yUBC9 and suggest a possible link of the ubiquitin/proteosome proteolytic pathway and the WT1 transcriptional repressor system.

Amino Acid Sequence↗

PubMed1995

WT1, the Wilms' tumor suppressor gene product, represses transcription through an interactive nuclear protein.

The Wilms' tumor suppressor gene, wt1, encodes a transcription factor of the zinc finger family. Mutations in WT1 have been detected in subsets of Wilms' tumor and in patients with the Denys-Drash Syndrome. In order to determine how WT1 regulates transcription and perhaps the consequences that mutations in WT1 may have, we established that residues 85-124 and 181-250 of WT1 constitute domains that function independently with a DNA binding domain to repress or activate transcription, respectively, and function equally effectively with heterologous promoters, suggesting the activator and repressor domains interact with nuclear components of general importance. To seek evidence for such components, increasing concentrations of WT1 repressor domain without a zinc finger DNA binding domain were co-transfected with fixed concentrations of wild-type (wt) WT1 and PDGF A-chain promoter/reporter gene constructs. As levels of the repressor domain were increased, a progressive loss of wt WT1 repressor activity and a progressive increase in its activation were observed, suggesting that the repressor domain of WT1 competes with wt WT1 for an interactive protein that is an essential component of the repressor activity of wt WT1. Because the most common mutation associated with Denys-Drash Syndrome disrupts the zinc finger domains of WT1, the results also suggest that the mutant WT1 may have aberrant DNA binding activity and perhaps function as a dominant negative effector of wt WT1.

3T3 Cells↗

PubMed1995

Products of alternatively spliced transcripts of the Wilms' tumor suppressor gene, wt1, have altered DNA binding specificity and regulate transcription in different ways.

The Wilms' tumor susceptibility gene, wt1, encodes a transcription factor of the zinc finger protein family. Mutations in the WT1 gene product have been detected in both sporadic and familial Wilms' tumors, suggesting that alterations in WT1 may disrupt its normal function as a transcriptional regulator. The transcripts of wt1 are alternatively spliced; however, roles of the alternatively spliced forms have not been defined. The major transcript of wt1 encodes a WT1 protein [WT1(+KTS)+17AA] that contains three amino acids (+KTS) between the third and fourth zinc fingers and a serine-rich, 17 amino acid (+17AA) domain N-terminal to the zinc finger region. We now show that the WT1 (+KTS) forms functionally bind to a unique G+C-rich sequence within the PDGF A-chain promoter. We also show that WT1 (+KTS)+17AA functions as a strong transcriptional repressor and that +17AA alone fused to the zinc-finger domain of WT1 or to the heterologous DNA binding domain of GAL4 functions independently as a repressor. Deletion of four serine residues within +17AA abolishes the repressor activity of +17AA. These results indicate that wt1 products with +17AA contain an additional dominant repressor domain and that the presence or absence of +KTS determines alternative DNA binding specificity.

3T3 Cells↗

PubMed1994

An S1 nuclease-sensitive region in the first intron of human platelet-derived growth factor A-chain gene contains a negatively acting cell type-specific regulatory element.

The platelet-derived growth factor (PDGF) A-chain gene is expressed in a tissue- and developmental stage-specific manner. Here we identify an S1 nuclease sensitive region within the first intron that functions as a negative regulatory element in HeLa but not in human glioblastoma (A172) cells in transient transfection assays. A 147 bp DNA fragment that contains this element functions in a position and orientation independent manner to negatively regulate both the PDGF A-chain promoter and the heterologous herpes simplex virus thymidine kinase (TK) promoter. The cell-type specific effect of this 147 bp DNA fragment is seen when it is located downstream but not upstream of the reporter gene driven by either the PDGF A-chain or TK promoters. The negative regulatory element has been localized to a 24 bp DNA sequence within the S1 sensitive site that retains negative regulatory activity and recognizes a nuclear protein in HeLa but not in A172 cells. Furthermore, the 24 bp element functions as a cell type-specific negative element independent of its position. These results suggest that a functional silencer within the first intron exhibits a non-B-form DNA structure under superhelical stress in vitro and may contribute to the cell type-specific transcriptional regulation of PDGF A-chain gene in vivo.

Base Sequence↗

PubMed1994

An S1 nuclease sensitive region in the PDGFA-chain gene promoter contains a positive transcriptional regulatory element.

Homodimers of the platelet-derived growth factor (PDGF) A-chain are strong mitogens for cells of mesenchymal origin and appear to be functionally important during development and perhaps in phenotypic transformation. In order to understand mechanisms of the developmental regulation of the PDGF A-chain gene and its dysregulation in transformation, we used S1 nuclease to identify and map an S1 hypersensitive region that is located 482 to 513 base pairs upstream of the transcription initiation site of the PDGF A-chain gene. A single nuclear protein binds to this site in gel mobility shift assays. This site confers a 2-3 fold increase in transcriptional activity when inserted into a heterologous promoter and analysed in transient transfection assays. The results suggest that this region of DNA under torsional stress locally assumes a single stranded character and functions to upregulate promoter activity.

Base Sequence↗

PubMed1993

A second transcriptionally active DNA-binding site for the Wilms tumor gene product, WT1.

The putative Wilms tumor suppressor gene, wt1, encodes a zinc-finger protein that binds to the DNA sequence 5'-GCGGGGGCG-3'. We previously reported that WT1 has separable domains that function either to activate or suppress transcription. We now have identified a second WT1 binding sequence (5'-TCCTCCTCCTCCTCTCC-3') 3' to the transcription initiation site of the platelet-derived growth factor A-chain gene by DNase I footprinting and gel mobility shift assays. WT1 requires both 5' and 3' binding sites for transcriptional suppression; however, WT1 functions as a transcriptional activator when it binds to either the 5' or 3' site alone. This second WT1 binding sequence functions equally well as the previously identified 5'-GCGGGGGCG-3' sequence when analyzed in transient transfection assays. A core DNA sequence recognized by WT1 was defined by using related synthetic oligonucleotides. We also identified sequences similar to the WT1 binding site within the promoter regions of five other growth-related genes and demonstrated that each of these sequences also binds WT1 in gel mobility shift assays. These results thus identify a second WT1 binding site and suggest that additional growth-related genes may be transcriptionally influenced by WT1.

3T3 Cells↗

PubMed1993

The Wilms' tumor gene product WT1 activates or suppresses transcription through separate functional domains.

We recently reported that the putative tumor suppressor gene product WT1 interacts with a 5'-flanking DNA sequence 5'-GCGGGGGCG-3' within the platelet-derived growth factor A-chain gene and abolishes its promoter activity, suggesting that WT1 functions as a transcriptional suppressor of the platelet-derived growth factor A-chain gene. We now show that WT1 functions also as a transcriptional activator. Using chimeric reporter plasmids, we demonstrated that WT1 requires both 5' and 3' binding sites relative to transcription start site for transcriptional repression; however, when WT1 binds to either the 5' or the 3' site alone, WT1 functions to activate transcription. We truncated the wt1 gene and established that amino acid residues 84-179 are required for transcriptional suppression, whereas amino acid residues 180-294 contain a domain that mediates transcriptional activation. These results establish that WT1 has regulatory domains that function either to activate or suppress transcription and suggest the possibility that WT1 functions as an activator and not as a suppressor of selected gene transcription.

3T3 Cells↗

PubMed1992

Modulation of transcription of the platelet-derived growth factor A-chain gene by a promoter region sensitive to S1 nuclease.

Homodimers of the platelet-derived growth factor (PDGF) A-chain are strong mitogens for cells of mesenchymal origin. Differences in the levels of expression of the PDGF A-chain gene have been reported in both normal and transformed cell lines, suggesting that transcription of the PDGF A-chain gene is highly regulated. We have now identified two S1-hypersensitive sites which flank a 13-base pair oligo(dG).oligo(dC) sequence located 70-82 base pairs upstream of the transcription initiation site. Three lines of evidence suggest that these S1-sensitive sites contribute to optimum promoter activity. Nuclear protein(s) binding to these sites were detected in gel mobility shift assays. Deletion of the S1-sensitive sites results in a 2-3-fold decrease in the transcriptional activity and eliminated sensitivity to S1 nuclease. Deletions in the oligo(dG).oligo(dC) motif also eliminated sensitivity to S1 and resulted in a 2.5-fold decrease of the promoter activity in the stable transfection assays. The results suggest that the highly G+C-rich region in the PDGF A-chain gene promoter locally induces the formation of non-B-form DNA under torsional stress which appears to be important in the transcriptional regulation of the PDGF A-chain gene in vivo.

Base Sequence↗