Search PubMed⌕ Search

Biomedical subjects

Z Liu

Publications and source records attributed to Z Liu.

At least 1,225 records · Page 68Linked to original sources
PubMed1993

Carbohydrate regulation of the rat L-type pyruvate kinase gene requires two nuclear factors: LF-A1 and a member of the c-myc family.

Transcription of the L-type pyruvate kinase (L-PK) gene is induced in response to increased carbohydrate metabolism in the liver. We have demonstrated previously that a segment of the 5'-flanking region of the L-PK gene between -183 and -96 is necessary and sufficient for the glucose response in primary hepatocytes. To explore the protein factors that are involved in carbohydrate regulation, we have performed mutational analyses and in vitro binding studies of this segment. Sequences critical for the glucose response were mapped from -171 to -124. This segment contains the consensus binding sites for two nuclear transcription factors: LF-A1 and MLTF. Both factors are capable of binding to the corresponding L-PK sites in vitro. Mutational and functional analyses indicated that LF-A1 is indeed involved in glucose induction of the L-PK gene. The PK MLTF-like site consists of two imperfect CACGTG motifs, the core binding site for a family of transcription factors related to c-myc. Unexpectedly, mutations in either motif that resulted in defective glucose stimulation retained in vitro binding to MLTF. Furthermore, an authentic MLTF binding site from the adenovirus major late promoter was not functionally interchangeable with the natural sequence. These data indicate that binding of MLTF, in presence of LF-A1, is not capable of supporting the glucose response. Conversion of either imperfect motif to CACGTG within the context of the mutations disrupting the opposite site restored the response to elevated glucose. Thus, the factor that recognizes the PK MLTF-like site and participates in mediating the carbohydrate response of the L-PK gene appears to be a member of the c-myc family distinct from MLTF.

Animals↗
PubMed1993

Contribution of direct and indirect recognition pathways to T cell alloreactivity.

T cells from an HLA-DR11/DR12 responder were stimulated in mixed lymphocyte culture with cells carrying the DR1 antigen. After priming, T cells proliferated in response to both DR1-positive-stimulating cells and a peptide derived from a polymorphic region of the HLA-DR beta 1*0101 chain presented by responder's antigen-presenting cells (APC). The dominant epitope recognized by the primed T cells corresponded to residue 21-42 and was presented by the responder's HLA-DR12 antigen. The DR1 peptide-reactive T cells express T cell receptor V beta 3. The results demonstrate that allopeptides derived from the processing and presentation of donor major histocompatibility complex molecules by host-derived APC trigger alloreactivity. The frequency of T cells engaged in the indirect pathway of allorecognition is about 100-fold lower than that of T cells participating in the direct recognition of native HLA-DR antigen. However, indirect allorecognition may play an important role in chronic allograft rejection, a phenomenon that is mediated by the activation of T helper cells and of alloantibody-producing B cells.

Alleles↗
PubMed1993

Identification and characterization of a nuclease activity specific for G4 tetrastranded DNA.

We have identified a nuclease activity that is specific for G4 tetrastranded DNA. This activity, found in a partially purified fraction for a yeast telomere-binding protein, binds to DNA molecules with G4 tetrastranded structure, regardless of their nucleotide sequences, and cleaves the DNA in a neighboring single-stranded region 5' to the G4 structure. Competition with various G4-DNA molecules inhibits the cleavage reaction, suggesting that this nuclease activity is specific for G4 tetrastranded DNA. The existence of this enzymatic activity that reacts with G4 DNAs but not with single-stranded or Watson-Crick duplex DNAs suggests that tetrastranded DNA may have a distinct biological function in vivo.

Base Sequence↗
PubMed1993

Limited usage of T cell receptor V beta genes by allopeptide-specific T cells.

T cell reactivity to alloantigens results from direct and indirect recognition of allogeneic MHC molecules and/or peptides. Although direct recognition is not self-MHC restricted, indirect recognition, the result of alloantigen processing and presentation by host APC, is restricted by the self (responder) MHC molecule to which the allopeptide has bound. We have studied the MHC restriction and TCR usage in T cell alloreactivity to a synthetic peptide corresponding to amino acid residues 21-42 of the DR beta 1*0101 molecule. T cell lines were developed by in vitro immunization of T cells from three responders carrying the DR beta 1*1101 allele with this peptide. In all three responders, reactivity to peptide 21-42 was restricted by the DR11 molecule. A limited usage of V beta genes was found in these T cell lines, all of which shared the expression of V beta 13.2. Because indirect recognition of allopeptide may play an important role in chronic, antibody-mediated allograft rejection, study of the TCR gene usage may contribute to the development of specific immunosuppression therapy.

Antibodies, Monoclonal↗
PubMed1993

The products of the E5, E6, or E7 open reading frames of RhPV 1 can individually transform NIH 3T3 cells or in cotransfections with activated ras can transform primary rodent epithelial cells.

Rhesus papillomavirus (RhPV) type 1 was recently shown to cooperate with the activated ras oncogene to transform primary rodent epithelial cells at a level comparable to HPV 16. In similar cotransfection studies, subgenomic portions of RhPV 1 driven by either their natural or a strong heterologous promoter were used in primary baby rat kidney cells to demonstrate that transforming properties of RhPV 1 could be localized individually to the E5, E6, and E7 open reading frames. Fully transformed cells were observed when either E5 or E7 were downstream of a strong heterologous promoter. Similarly, either E6 or E6 and E7 downstream of the native promoter fully transformed these cells as determined by immortalization, anchorage independent growth and tumorigenicity studies.

3T3 Cells↗
PubMed1993

Expression of heat shock proteins during development of barley.

Barley heat shock proteins have been cloned, characterized by hybrid release translation and sequenced. Clones coding for proteins of 17, 18, 30, 32 and 70 kDa have been obtained. Out of these the 32 and 30 kDa proteins have been characterized as precursors to plastidic proteins of 26 kDa by posttranslational transport and by cDNA sequencing. The coding regions of these two transcribed genes are highly homologous. Accumulation of the plastid HSP as well as of HSP 70 as well as their corresponding mRNAs has been studied in 2- to 6-day old seedlings and in the 7-day old barley leaf. The mRNA for all investigated proteins were only found after a heat shock; the mRNA levels increase towards the tip of the leaf and with development. Furthermore, under the conditions used the mRNAs for all investigated heat shock proteins accumulate in parallel. Unexpectedly, both proteins, HSP 70 and HSP 26, are found by western blotting in the 2-day old control plants in the absence of any inducing heat shock. At later stages of development and in the leaf gradient only immunoreactivity with HSP 70 was observed. In contrast to the levels of their mRNAs the highest levels of HSP 30-26 and 70 have been observed in the basal segments indicating that translational control plays a role during HSP expression. Under severe heat shock a protein of 30 kDa is induced whose identity is not known but which reacts with the antibody to HSP 30-26 and might represent the accumulating precursors of the plastidic proteins.

Amino Acid Sequence↗
PubMed1993

Myelin formation by mouse glia in myelin-deficient rats treated with cyclosporine.

Previous attempts to generate myelin in the myelin-deficient rat spinal cord by transplanting mouse glia were not successful. In order to determine whether this result was due to graft rejection or to interspecies mismatch of cellular or molecular components at the axoglial junction, we have repeated the experiment in cyclosporine-treated rats. Our results show that in the immunosuppressed hosts, foetal glial xenografts form an abundance of myelin within the dorsal columns at or near the injection site about two weeks after the operation. In some cases, myelination extends virtually across the entire width of the dorsal columns. Ultrastructurally, the myelin sheaths are normal in all respects, including the presence of the 'radial component'. The lateral edges of the myelin lamellae form typical paranodal axoglial junctions, some displaying periodic 'transverse bands'. We infer that previous mouse to rat xenograft failures reflect host immune response rather than mismatch of heterologous junctional components. We also compared foetal, early post-natal and adult xenografts. Foetal donor cells, containing an abundance of precursors but virtually no mature oligodendrocytes, are more effective than neonatal donor cells in forming myelin, and after adult grafts, we found no myelin formation. Thus, in xenografts, as in allografts, foetal precursor cells are far more suitable than glia from mature donors in generating significant amounts of myelin.

Animals↗
PubMed1993

Regulation of expression of transgenes in developing fish.

The transcriptional regulatory elements of the beta-actin gene of carp (Cyprinus carpio) have been examined in zebrafish and goldfish harbouring transgenes. The high sequence conservation of the putative regulatory elements in the beta-actin genes of animals suggested that their function would be conserved, so that transgenic constructs with the same transcriptional control elements would promote similar levels of transgene expression in different species of transgenic animals. To test this assumption, we analysed the temporal expression of a reporter gene under the control of transcriptional control sequences from the carp beta-actin gene in zebrafish (Brachydanio rerio) and goldfish (Carrasius auratus). Our results indicated that, contrary to expectations, combinations of different transcriptional control elements affected the level, duration, and onset of gene expression differently in developing zebrafish and goldfish. The major differences in expression of beta-actin/CAT (chloramphenicol acetyltransferase) constructs in zebrafish and goldfish were: (1) overall expression was almost 100-fold higher in goldfish than in zebrafish embryos, (2) the first intron had an enhancing effect on gene expression in zebrafish but not in goldfish, and (3) the serum-responsive/CArG-containing regulatory element in the proximal promoter was not always required for maximal CAT activity in goldfish, but was required in zebrafish. These results suggest that in the zebrafish, but not in the goldfish, there may be interactions between motifs in the proximal promoter and the first intron which appear to be required for maximal enhancement of transcription.

Actins↗
PubMed1993

Major histocompatibility complex-restricted recognition of autologous chronic lymphocytic leukemia by tumor-specific T cells.

From the peripheral blood of a patient with chronic lymphocytic leukemia (CLL) we generated a T-cell line and clones which recognized autologous CLL. The line comprised T-cell clones which responded to the CLL as well as to autologous Epstein-Barr virus (EBV)-transformed B cells in an HLA-DR-restricted fashion. In addition, the line comprised clones which were CLL-specific and showed no reactivity against EBV-transformed B cells and against autologous peripheral blood mononuclear cells obtained during remission. The proliferative response of the CLL-specific T-cell clone was inhibited by monoclonal antibodies to HLA-DR11, the major histocompatibility complex (MHC)-restrictive element. These results indicate that the MHC class-II molecule of CLL binds a tumor-specific peptide which is recognized by autologous T cells in an MHC class-II-restricted fashion. Such a peptide may serve as a target for immunotherapy.

Amino Acid Sequence↗
PubMed1993

On nonaxisymmetric entry flow at very low Reynolds numbers.

The eigensolution of nonaxisymmetric entry flow of a Newtonian viscous fluid with very small Reynolds number in a semiinfinite rigid circular pipe is obtained. Leading eigenvalues are computed for steady flow and two periodic cases. The result shows that the entry length for nonaxisymmetric flows should be longer than the entry length for axisymmetric flows.

Animals↗
PubMed1993

Insulin and glucose suppress hepatic glycogenolysis by distinct enzymatic mechanisms.

Both insulin and hyperglycemia can effectively suppress hepatic glucose output (HGO). We examined whether insulin and hyperglycemia specifically suppress liver net glycogen breakdown in a rat model in which glycogen is the major source of HGO. We further examined whether insulin and hyperglycemia act by similar or distinct enzymatic mechanisms. HGO, the rate of net glycogen loss, and glycogen phosphorylase and synthase activities were measured in fed, anesthetized rats infused with saline or insulin (7 mU/min/kg) while either maintaining plasma glucose at basal (7.8 +/- 0.2 mmol/L, euglycemic clamp [EC]) or at 10 mmol/L above basal (18 +/- 0.4 mmol/L, hyperglycemic clamp [HC]). During the basal period, the rate of HGO in each group was comparable to the rate of net glycogen breakdown, averaging 76 +/- 9 and 75 +/- 5 mumol/min/kg, respectively. Thus glycogen breakdown appeared to be a major source of ongoing HGO. Over the last 60 minutes of the experimental period, the rate of glycogenolysis averaged 69 +/- 8 mumol/min/kg in saline-treated rats; this could account for about 80% of the total HGO. During both EC and HC studies, HGO was suppressed (5.5 +/- 3 and -3.6 +/- 10 mumol/min/kg, respectively; P < .001 for each). Net glycogen breakdown decreased by 50% in EC rats (P < .05) and ceased in HC rats (P < .001). Glycogen synthase was predominantly in the active form in all three experimental groups (87% +/- 2%, 89% +/- 2%, and 95% +/- 3% in saline, EC, and HC rats, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Enzyme-linked DNA oligotyping. A practical method for clinical HLA-DNA typing.

The use of PCR and oligonucleotide hybridization has increased the accuracy and resolution of typing for HLA class II alleles, but current procedures, performed in batches, take too long and are not suited for testing single samples. We have developed a typing method using enzyme-linked oligonucleotides and PCR products immobilized in 96-well trays. Trays preloaded with typing probes, covalently linked with alkaline phosphatase, have been kept for weeks at 4 degrees C without loss of enzyme-probe activity. Bound alkaline phosphatase was detected using a color reaction with enzymatic amplification which produces readings in 30 minutes. Coupled with a quick DNA preparation method, results can be obtained in about 4 hours. This method can be easily performed in small laboratories. It is accurate, reproducible, and sensitive, and will make oligotyping for HLA alleles more convenient for testing clinical samples.

Alkaline Phosphatase↗
PubMed1993

A novel method for detection of nitric oxide binding sites by using a chemiluminescence-headspace gas technique.

Nitric oxide (NO) is important in many physiological, pharmacological, and pathological processes. According to current concepts, guanylyl cyclase is considered to be a receptor for NO in vascular and nonvascular smooth muscle and other tissues. Since there are no suitable radioisotopes of oxygen and nitrogen available for conventional radioligand-receptor binding studies for NO, a novel method was developed to identify NO binding site(s). A chemiluminescence-headspace gas assay was utilized to measure the sequestration of NO in biological systems, and this was used as an index of NO binding. In the present report, myoglobin (a hemoprotein, Mb) was used as a prototype macromolecule to develop the binding assay for subsequent application to studies of putative NO receptors. Solutions containing various concentrations of Mb were incubated with NO in sealed micro-Fernbach flasks at 37 degrees C in an argon atmosphere for 30 min; NO remaining in the headspace gas was analyzed by means of the chemiluminescence assay. The magnitude of NO sequestration was dependent on Mb concentration, and 5 nM Mb was the lowest Mb concentration for which NO sequestration was measurable. Application of the method to the measurement of NO sequestration by bovine serum albumin (BSA) and pulmonary artery medial layer homogenate (BPA-M) revealed that the lowest BSA concentration at which NO sequestration was measurable was 1.6 microM, which was 320 times greater than that for Mb. Applicability of the method to address the question of putative NO receptors was indicated by significant NO sequestration after incubation with 20% (w/v) homogenate of BPA-M, which is responsive to NO and putative NO prodrugs.

Animals↗
PubMed1993

Interleukin-6 production during chronic experimental infection.

The appearance of interleukin-6 (IL-6) in serum of mice was monitored during the course of chronic infection with either Brucella abortus vaccine strain 19 or a virulent Mycobacterium avium Complex (MAC) isolate. Serum IL-6 during brucella infection was higher than during infection with MAC, despite similar numbers of bacteria. Furthermore, IL-6 titres decreased after the peak of infection, falling to baseline levels before these chronic infections were eradicated. The ability of peritoneal cells or spleen cell suspensions to produce IL-6 under either specific or non-specific stimulus was greatly enhanced by infection. While production of IL-6 by these cultures was apparently mostly independent of T cells, T cells from infected mice could produce an IL-6 response. Thus CD4+ T lymphocytes prepared from mice which had recovered from B. abortus infection, cultured with antigen and antigen presenting cells, resulted in IL-6 production, which was not observed in similarly cultured CD8+ T cells, indicating a role for T cells.

Animals↗