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Biomedical subjects

Y Lu

Publications and source records attributed to Y Lu.

At least 811 records · Page 45Linked to original sources
PubMed1994

Evidence that the activation of an inactive pool of membrane-associated protein kinase C is linked to the IL-2-dependent survival of T lymphocytes.

The activation of protein kinase C (PKC) is believed to result from the translocation of inactive cytosolic enzyme to the lipid environment of membranes. However, by using a novel method for measuring PKC activity directly in isolated membranes, we have previously shown that a significant proportion of the PKC present in a variety of cells associates with membranes in an inactive state, and that this pool of inactive PKC can be stimulated specifically in cells in the absence of translocation. IL-2 did not stimulate the translocation of PKC to membranes in the IL-2-dependent mouse T cell line, CTLL-2. Nevertheless, a transient, two approximately threefold increase in membrane PKC activity was observed within 10 min of IL-2 addition to these cells. This increase was entirely caused by the activation of a pool of inactive membrane PKC previously associated with the membrane. The inhibition of PKC activity by the specific inhibitors bisindolylmaleimide (BIS) and 1-O-hexadecyl-2-O-methyl-rac-glycerol (AMG) blocked the ability of IL-2 to suppress the onset of apoptosis in IL-2 and serum-deprived CTLL-2 cells. The inhibition of this important function of IL-2 was most pronounced when the PKC inhibitors were added to the medium within 2 h of stimulating the cells with IL-2. The results suggest that transient activation of inactive membrane PKC is linked to the IL-2 receptor signaling, and may be an important step in the mechanism(s) by which the cytokine suppresses cell death in T lymphocytes.

Animals↗
PubMed1994

The human DNA-binding protein, PO-GA, is homologous to the large subunit of mouse replication factor C: regulation by alternate 3' processing of mRNA.

We have previously cloned a human gene encoding a 128-kDa protein which we termed PO-GA [Lu et al., Biochem. Biophys. Res. Commun. 193 (1993) 779-786]. In the present report, we compared PO-GA to recent DNA database entries and determined that PO-GA was 80% identical, at the amino-acid level, to the large subunit of replication factor C (activator 1) cloned from mouse [Burbelo et al., Proc. Natl. Acad. Sci. USA 91 (1994) in press]. This indicates that PO-GA probably represents the corresponding subunit of human replication factor C. In addition, PO-GA has high homology to a putative Drosophila transcription factor. All three proteins contain a nuclear translocation signal and an ATP/ADP-binding motif, and are highly conserved in regions with homology to Escherichia coli and yeast DNA ligases. We determined that PO-GA mRNA species of 5.3 and 4.5 kb can be detected in most human tissues, but levels are especially high in ovary. Analysis of the sequence of a new PO-GA cDNA clone that we obtained reveals a previously undetected 650-bp 3'-UTR extension. This region contains several A+U-rich regions potentially involved in regulation of mRNA stability. This fragment only hybridizes to the larger 5.3-kb mRNA. Comparison of cDNA sequences revealed that the two mRNA species arise as a result of alternate use of poly(A)-addition sites. Since the ratio of the two mRNA species is variable in different tissues, we speculate that alternative 3' processing of the PO-GA mRNA is utilized as a mechanism of regulating cellular levels of mRNA.

Amino Acid Sequence↗
PubMed1994

The influenza virus NS1 protein: a novel inhibitor of pre-mRNA splicing.

We have shown previously that the influenza virus NS1 protein inhibits the nuclear export of mRNAs. Here we demonstrate that the NS1 protein also regulates another post-transcriptional step: It inhibits pre-mRNA splicing both in vivo and in vitro. The mode by which the NS1 protein inhibits pre-mRNA splicing is novel. The pre-mRNA forms spliceosomes, but subsequent catalytic steps in splicing are inhibited. Affinity selection experiments establish that the NS1 protein is associated with the spliceosomes that are formed. The RNA-binding domain of the NS1 protein is required for the inhibition of splicing and for the interaction of the protein with spliceosomes. Because the NS1 protein is associated with U6 snRNA in influenza virus-infected cells as well as in splicing extracts from uninfected cells, it is likely that the NS1 protein also inhibits pre-mRNA splicing in infected cells. Surprisingly, the splicing of the viral ns1 mRNA, the very mRNA that encodes the NS1 protein, was resistant to inhibition by the NS1 protein. This resistance is conferred by sequences in ns1 mRNA.

Amino Acid Sequence↗
PubMed1994

The invariant arginine in motif 2 of Escherichia coli alanyl-tRNA synthetase is important for catalysis but not for substrate binding.

Structural motifs 2 and 3, located in the active site of class II aminoacyl-tRNA synthetases, each contain an invariant arginine thought to participate in interactions with ATP. For Escherichia coli alanyl-tRNA synthetase (AlaRS), sequence comparisons indicate that Arg-69 should be aligned with the invariant arginine in motif 2 of other class II synthetases. Site-directed random mutagenesis has been employed to generate a set of proteins containing amino acid substitutions in a portion of motif 2 of AlaRS. In this set, only mutations at position 69 caused the enzyme to lose ability to complement growth of an alaS deletion strain, and proteins containing substitutions at position 69 alone are undetectable in a Western blot assay. A mutant protein containing the transposition of Arg-69 with Gly-71 does not complement growth but does accumulate in vivo and has thus been purified. Michaelis and dissociation constants for the interaction of this protein with ATP are indistinguishable from those of the wild-type enzyme. However, this two-position displacement of the arginine causes a decrease in the kcat for the ATP-PPi exchange reaction by 2 orders of magnitude. These data suggest a role for the invariant arginine of motif 2 in stabilization of the transition state during alanyladenylate synthesis.

Alanine-tRNA Ligase↗
PubMed1994

Results of radical cystectomy for transitional cell carcinoma of the bladder and the effect of chemotherapy.

BACKGROUND: Radical cystectomy continues to be one of the primary modalities of treatment for locally advanced bladder cancer. However, long-term survival after cystectomy has improved only marginally in the last decade, and still, nearly half of the patients die from the disease within 5 years. Adjuvant treatments such as radiation therapy and chemotherapy have been used, but a clear advantage has not been demonstrated. METHODS: The authors reviewed 130 patients who underwent radical cystectomy by the same surgeon as treatment for transitional cell carcinoma of the bladder. Morbidity, postoperative mortality, overall survival time, and accuracy of clinical staging as well as the effect of perioperative chemotherapy were evaluated. RESULTS: The overall actuarial survival rate at 2, 5, and 10 years was 80%, 53%, and 45%, respectively. The survival rate based on T-classification at 5 years was 82%, 65%, and 28% for less than pT2, pT2, and greater than pT2, respectively. Regional lymph node status had a significant effect on survival. The 5-year survival rate for all patients with negative nodes was 65%, whereas patients with positive nodes had a 18% 5-year survival rate. The overall clinical staging error was 61.5%, with 41.5% of the cancers understaged. Of the patients with cTis, 60% were found to be of greater extent than pT1 tumors. No apparent survival advantage was noted for those patients who received perioperative chemotherapy when compared with patients who were followed conservatively or received chemotherapy upon relapse. These results, however, are not conclusive because this was an observation study and the number of patients was limited. CONCLUSIONS: Only a modest improvement in survival time after radical cystectomy has been observed in the last decade, despite the use of adjuvant treatments such as radiation and chemotherapy. The pathologic (pT) classification is the most accurate prognostic indicator. Clinical errors in classification are common and impair the evaluation of neoadjuvant treatments. A high incidence of invasive tumors of greater extent than pT1 was found among patients with clinical cTis; this supports an aggressive approach when these patients do not respond promptly to intravesical chemotherapy. Prospective randomized studies are needed to evaluate objectively the benefit of perioperative adjuvant treatment in locally advanced transitional cell carcinoma of the bladder.

Aged↗
PubMed1994

Dielectric properties of human red blood cells in suspension at radio frequencies.

Dielectric properties of human red blood cells (RBCs) in suspension (hematocrit 50%) from 243 healthy persons (120 males, 123 females) were measured at 25 degrees C in a frequency range of 1-500 MHz, with a coaxial transmission line reflection method (one-side measurement). The measuring system, controlled by an IBM-PC computer, was composed of a network analyzer (HP4195A), an impedance test adapter (HP41951-61001), a coaxial line sensor, and a temperature-controlling set. The data measured revealed a statistically significant age dependence, with a critical age of about 49 years, above which permittivity and conductivity of human RBCs in suspension decreased significantly.

Adult↗
PubMed1994

CD28 signal transduction: tyrosine phosphorylation and receptor association of phosphoinositide-3 kinase correlate with Ca(2+)-independent costimulatory activity.

The interaction of CD28 with its counter-receptor, B7, induces a cosignal in T cells required to prevent clonal anergy and to promote antigen-dependent interleukin-2 production. The molecular basis of the CD28 cosignal is not well understood but involves the activation of protein tyrosine kinase(s) (PTK). In this report we demonstrate that CD28 cross-linking on Jurkat T leukemic cells causes the activation of at least two PTK pathways. A CD28-induced, p56lck kinase-independent pathway causes tyrosine-phosphorylation of a 110-kDa substrate while recruitment of p56lck kinase activity is apparently required for CD28-induced tyrosine-phosphorylation of 97- and 68-kDa substrates as well as CD28-induced increases in intracellular calcium. The tyrosine phosphorylation of p110, but not p97 or p68, correlated with CD28 calcium-independent costimulatory activity. The pp110 molecule was tentatively identified as the catalytic subunit of phosphoinositide (PI)-3 kinase based upon its coimmunoprecipitation with the p85 regulatory subunit of PI-3 kinase. PI-3 kinase protein and catalytic activity were found complexed with the CD28 receptor if the receptor was "activated" by cross-linking on the surface of intact cells prior to detergent solubilization. The kinetics of association of PI-3 kinase with the "activated" CD28 receptor was rapid, occurring within 30 s of receptor cross-linking and was stable for at least 30 min. Analysis of the CD28 cytoplasmic peptide sequence revealed a putative PI-3 kinase src homology 2 binding motif and CD28 tyrosine phosphorylation site, DYMNM. Tyrosine phosphorylation of CD28 was detected in pervanadate-treated Jurkat B2.7 cells, but not untreated cells. Pervanadate-induced tyrosine phosphorylation of CD28 correlated with receptor association of PI-3 kinase in the absence of CD28 cross-linking, suggesting that CD28 association with PI-3 kinase uses a tyrosine phosphorylation-dependent mechanism. These data provide a model for CD28 signal transduction and support a role for PI-3 kinase in mediating the CD28 calcium-independent, cyclosporin A-insensitive costimulatory signal.

Amino Acid Sequence↗
PubMed1994

Far less frequent mutations in ras genes than in the p53 gene in skin tumors of xeroderma pigmentosum patients.

Mutations in Ha-ras, Ki-ras, and N-ras genes in squamous and basal cell carcinomas in patients with xeroderma pigmentosum (XP) were examined by the polymerase chain reaction followed by single-strand conformation polymorphism analysis and direct base sequencing. No mutation was detected in codons 12, 13, and 61 of the ras genes in XP skin tumors. This was in contrast with previous findings of a high frequency of mutation in the p53 gene in skin tumors in XP patients. A novel mutation in codon 6 of the Ki-ras gene was detected in a squamous cell carcinoma. The mutation was a C-->T transition at a dipyrimidine (5'-CT) sequence and could have been produced by solar ultraviolet light. The mutated ras gene did not have the ability to transform NIH/3T3 cells. In three tumors, multiple base substitutions were detected in exon 1 of the Ki-ras and N-ras genes. These results and our previous work on p53 gene mutations suggest that mutations in ras genes are far less frequent than in the p53 gene in the skin tumors in XP patients and that ras genes are less important in skin tumorigenesis in XP patients than is the p53 gene.

3T3 Cells↗
PubMed1994

GM-CSF and M-CSF expression is associated with macrophage proliferation in progressing and regressing rabbit atheromatous lesions.

Recent studies have documented that macrophages are a significant cell component of atherosclerotic lesions and may play a significant role in the pathogenesis of these lesions. It has also been documented that markers of cell proliferation (e.g., the proliferating cell nuclear antigen) can be expressed by macrophage subpopulations in atherosclerotic lesions, and there is great interest in identifying cell mediated factors which might be instrumental in macrophage proliferation in this context, perhaps accounting for the persistence of macrophages within this context. Important candidates for this function include granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF); the latter has been previously demonstrated to be expressed in human and rabbit atherosclerotic lesions. We have extended these studies by studying immunocytochemical localization of GM-CSF and M-CSF in progressing and regressing lesions of cholesterol-fed rabbits, documenting expression of these factors predominantly in macrophages, but also in some smooth muscle-cells and endothelial cells. The simultaneous documentation of macrophage subpopulations expressing the proliferating cell nuclear antigen in the same lesions provides evidence to support the hypothesis that macrophage GM-CSF and M-CSF production represents a factor underlying macrophage proliferation and accumulation in atherosclerotic lesions.

Animals↗
PubMed1994

Interaction of 2,3,7,8-tetrachlorodibenzo-p-dioxin and retinoic acid in MCF-7 human breast cancer cells.

Both retinoic acid (RA) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) elicit a number of common biochemical and toxic responses including teratogenic effects in mice and inhibition of cell proliferation of numerous cell lines. In mice, RA plus TCDD interact synergistically as teratogens, suggesting a link between the RA and aryl hydrocarbon receptor signal transduction pathways. In this study, it was shown that both RA and TCDD elicit a number of common responses in MCF-7 human breast cancer cells, including inhibition of estrogen-induced cell proliferation and [3H]thymidine uptake, inhibition of nuclear estrogen receptor (ER) ligand binding, and interactions with a consensus [32]estrogen-responsive element in a gel mobility shift assay. RA and TCDD also decrease steady-state ER mRNA levels in a time-dependent manner. Moreover, interactive studies in which cells were treated with both RA plus TCDD also resulted in decreased responses.

Analysis of Variance↗
PubMed1994

Effect of norfloxacin and clonidine on human trabecular meshwork cells in vitro.

We evaluated the effect of norfloxacin and clonidine on the morphology, DNA synthesis and phagocytic activity of cultured human trabecular meshwork cells in the 3rd-5th generations. Exposure to norfloxacin at a concentration of 1.5 x 10(-4) g ml-1 for 6 h led to retraction of cytoplasmic processes and rounding of cell profile, and exposure for 48 h caused cell death. Exposure to clonidine at 1.0 x 10(-3) g ml-1 for 12 h caused cell degeneration, and exposure for 72 h led to cell death. The morphologic changes were dose-time dependent. Tritiated thymidine incorporation was determined as an index of DNA synthesis, which was significantly inhibited by 1.5 x 10(-5) g ml-1 norfloxacin or 1.0 x 10(-3) g ml-1 clonidine, but obviously enhanced by 1.0 x 10(-4) and 1.0 x 10(-5) g ml-1 clonidine. Both drugs inhibited phagocytosis of latex microspheres in a dose-dependent mode. According to the presented results and the pharmacokinetic data reported in the literature, we suggest that the topical use of norfloxacin should not be too frequent or continued too long, especially when the corneal epithelium was not intact; clonidine has no deleterious effect on trabecular cells in its conventional use.

Cell Death↗
PubMed1994

Tumor cell surface beta 1-6 branched oligosaccharides and lung metastasis.

NIH3T3 cells transfected with an activated Ha-ras oncogene were treated with L-PHA, the leukoagglutinin from red kidney beans. Cell lines resistant to L-PHA-mediated cytotoxicity were isolated and found to contain reduced levels of L-PHA-binding oligosaccharides. The levels of N-acetylglucosaminyltransferase V, the enzyme responsible for the initiation of the beta 1-6 branch, were reduced in L-PHA-resistant cells. Tumorigenicity in nude mice was unchanged by the change in oligosaccharide expression, but the ability to form lung tumors after intravenous injection was significantly reduced. These results demonstrate that the ability of NIH3T3 cells transfected with an activated Ha-ras oncogene to form lung tumors after intravenous injection into nude mice is reduced in all six L-PHA selected cell lines containing a reduction in beta 1-6 branched Asn-linked oligosaccharides.

3T3 Cells↗
PubMed1994

Total and methyl mercury levels in human scalp hairs of typical populations in China by NAA, GC(EC), and other techniques.

The contents of total and methyl mercury in scalp hair samples of 1179 fishermen living in a typical Hg-polluted region in northeast China and 27 lying-in women and their newborns in Beijing have been determined by INAA, GC(EC), and other techniques. Only 18 of all fishermen had Hg contents above 5 micrograms/g, which indicates that the Hg pollution there has been substantially alleviated. The longitudinal Hg patterns of the lying-in women showed a gradually lowering tendency during pregnant period. Further, the Hg contents of the newborn babies generally were above or close to those of their mothers, confirming the mechanism that the methyl Hg, an organic species of Hg with high toxicity, is readily able to penetrate the placental barrier and to accumulate in the fetus. Thus, the mercury poison has occurred at the early stage of pregnancy.

China↗
PubMed1994

Estimating multiple tumor transition rates based on data from survival-sacrifice experiments.

The development of two types of tumors in an animal survival-sacrifice experiment can be described by a Markov illness-and-death process with four unknown tumor transition rates and four unknown death rates. Due to the occult nature of tumors, these transition rates cannot be identified through the use of a completely nonparametric model. We propose a semiparametric model that assumes that the four tumor transition rates are proportional to each other and can be described by a known parametric function. We show that these tumor transition rates can be estimated using an ECM algorithm and that inferences about these parameters can be drawn using the likelihood ratio test. We illustrate this model and the algorithm with data from the ED01 study.

Algorithms↗
PubMed1994

Retinoblastoma protein regulation of surface CD74 (invariant chain) expression in breast carcinoma cells.

The HLA class II genes encode heterodimeric cell surface proteins which bind peptide antigen recognized by T-cell receptors on CD4+ T-cells. The class II proteins are inducible by IFN-gamma, and this induction requires, or is strongly enhanced, by retinoblastoma protein (RB) in a series of breast carcinoma cell lines. Loading of peptide onto the class II protein appears to be regulated by CD74, which associates with class II during their transition to the endosomal compartment, where class II binds peptide. Class II proteins and CD74 are largely regulated in concert, provoking the question, is CD74 induction by IFN-gamma affected by RB? Results described here indicate that IFN-gamma induction of CD74 surface expression in a series of breast carcinoma lines is enhanced by RB, while RB has no effect on CD74 mRNA induction. Also, neither the class II nor the CD74 promoter regions are activated by RB in cotransfection experiments where RB activates the SV40 promoter.

Antigens, CD↗
PubMed1994

Mutagenic effects of heavy ion radiation in plants.

Genetic and developmental effects of heavy ions in maize and rice were investigated. Heavy particles with various charges and energies were accelerated at the BEVALAC. The frequency of occurrence of white-yellow stripes on leaves of plants developed from irradiated maize seeds increased linearly with dose, and high-LET heavy charged particles, e.g., neon, argon, and iron, were 2-12 times as effective as gamma rays in inducing this type of mutation. The effectiveness of high-LET heavy ion in (1) inhibiting rice seedling growth, (2) reducing plant fertility, (3) inducing chromosome aberration and micronuclei in root tip cells and pollen mother cells of the first generation plants developed from exposed seeds, and (4) inducing mutation in the second generation, were greater than that of low-LET gamma rays. All effects observed were dose-dependent; however, there appeared to be an optimal range of doses for inducing certain types of mutation, for example, for argon ions (400 MeV/u) at 90-100 Gy, several valuable mutant lines with favorable characters, such as semidwarf, early maturity and high yield ability, were obtained. Experimental results suggest that the potential application of heavy ions in crop improvement is promising. RFLP analysis of two semidwarf mutants induced by argon particles revealed that large DNA alterations might be involved in these mutants.

Argon↗