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Biomedical subjects

M Lu

Publications and source records attributed to M Lu.

At least 289 records · Page 16Linked to original sources
PubMed1993

The human brain cholecystokinin-B/gastrin receptor. Cloning and characterization.

The predominant brain cholecystokinin receptor (CCK-B/gastrin) has been implicated in mediating many of the central effects of cholecystokinin, including anxiety, panic attacks, satiety, and analgesia, suggesting it is an important pharmacologic target. We now report the cloning and characterization of the cDNA encoding the human brain CCK-B/gastrin receptor. The cDNA was isolated from a human brain library by low stringency screening using the canine "gastrin" receptor cDNA as a hybridization probe. Nucleotide sequence analysis revealed an open reading frame encoding a 447-amino-acid protein with seven putative hydrophobic transmembrane domains and significant homology with other known members of the gastrin/cholecystokinin receptor family. Agonist and antagonist affinities of the recombinant human brain receptor expressed in COS-7 cells are consistent with a classical "CCK-B" receptor as defined by the literature. In COS-7 cells expressing the cloned receptor, CCK-8-stimulated phosphatidylinositol hydrolysis and intracellular Ca2+ mobilization suggesting second messenger signaling through phospholipase C. CCK-B/gastrin receptor transcripts were identified in human brain, stomach, and pancreas using high stringency Northern blot analysis. Southern blot hybridization analysis of human genomic DNA indicates that a single gene encodes both the brain and the stomach CCK-B/gastrin receptors. Our data suggest that the CCK-B and gastrin receptors are identical and that the long standing distinction between them may no longer apply.

Amino Acid Sequence↗
PubMed1993

Effect of thymine tract length on the structure and stability of model telomeric sequences.

DNA from the telomeres at the ends of eukaryotic chromosomes contains a stretch of simple tandemly repeated sequences in which clusters of G residues alternate with clusters of T/A sequences along one DNA strand. Model telomeric G-clusters form four-stranded structures in Na+ or K+, stabilized by Hoogsteen pairing between G bases. DNA containing a single copy of the G-cluster can self-associate to form tetramers, with a parallel-stranded, right-handed helical structure. Two copies of the 3'-terminal G strand form a folded-back hairpin that dimerizes to create an antiparallel quadruplex structure. We show here that the tetrameric structure is strongly influenced by the T residue flanking either side of the G-cluster. The parallel tetraplex formed by single copies of the sequences dTnG4 is most stable for n = 1 and least stable for n = 8, the longest tract we have studied. At least two thymine residues are required to allow formation of antiparallel folded-back hairpin dimers from two-copy oligomers of sequence d(TnG4)2 in Na+; additional T's destabilize this structure. In K+, the predominant structure formed is the four-stranded parallel tetramer in all cases. Kinetic analysis indicates that the quadruplex structure formed by Oxytricha telomeric DNA overhangs in the presence of Na+ arises by dimerization of two Hoogsteen base-paired hairpins, with a relatively low energy barrier.

Circular Dichroism↗
PubMed1993

Thermodynamics of G-tetraplex formation by telomeric DNAs.

Telomeres are structures at the ends of eukaryotic chromosomes, the DNA of which contains stretches of tandemly repeated sequences with G clusters along one strand. Model telomeric G-rich DNAs can form different tetraplex structures, stabilized by cyclic hydrogen bonding of four guanines in the presence of metal ions such as Na+ or K+. Oligonucleotides with a single copy of the Oxytricha sequence dT4G4 form a tetramer, with a parallel-stranded, right-handed helical structure. Additional copies favor folded-back structures that associate to form an antiparallel dimer. The parallel-stranded tetramer has all G's in the anti configuration, while the folded-back dimer has alternating syn and anti nucleotide conformations along each strand. Here we have constructed two G-tetraplex structures, containing identical G-tetrad base pairs, from oligonucleotides. One has the truncated telomeric sequence from Oxytricha, dG4T4G4, which forms an antiparallel G-quartet structure; the second is constrained to form a parallel G-strand arrangement by insertion of a 5'-p-5' linkage between two dT2G4 sequences. Each oligomer forms a defined G-tetraplex dimeric structure in the presence of Na+. The standard-state enthalpies, entropies, and free energy for formation of these tetraplexes have been determined. The parallel strand structure is thermodynamically more stable than the antiparallel one, primarily because of both greater enthalpy and entropy of formation. In addition, the two molecules differ in their interaction with sodium ions, reflecting a difference in ion binding and therefore in structure between the two forms.

Calorimetry, Differential Scanning↗
PubMed1993

Variability of the envelope regions of HCV in European isolates and its significance for diagnostic tools.

Following the original description of HCV in 1989 a tremendous amount of sequence data is now available. Based on the 8 complete nucleotide sequences published so far at least 4 genotypes can be distinguished. Partial sequences of additional HCV isolates indicate the existence of further genotypes. A serological typing is not yet possible. For detection of virus, reverse transcription and amplification of the 5' non coding region is most commonly performed. This region of the genome is highly conserved among all isolates. In this study we used regions of the E1 and E2 gene in order to classify HCV isolates. The nucleotide sequences of regions in E1 and E2 gene of different European isolates from Germany, Croatia, Hungary, and Rumania were determined and compared to recently published RNA sequences of American and Japanese HCV isolates. The cDNA, obtained by reverse transcription of viral RNA extracted from sera was amplified by nested PCR, cloned and sequenced. Within 564 nucleotides (nt) of E1 we found 87-90% homology (and 89-92% homology at aa level) compared to sequences of Japanese origin and 73-74% homology (77-81% at aa level) compared to the prototype HCV sequence (ptHCV-I). In all characterized isolates the sequence of E2 (643 nucleotides) showed a homology of about 83% at the nucleotide level as compared to genotype II sequences, and a homology of about 70% to genotype I. Our results confirm the existence of two hypervariable regions in the E2 gene of genotype II sequences. Our results also indicate together with other reports from European HCV isolates that genotype II is predominant in Europe.

Amino Acid Sequence↗
PubMed1993

The diagnosis of diabetic retinopathy. Ophthalmoscopy versus fundus photography.

PURPOSE: To compare fundus photography with ophthalmoscopy in the detection of diabetic retinopathy. METHODS: Ophthalmoscopy and fundus photographs with a nonmydriatic camera, both performed through dilated pupils, were compared to diagnose retinopathy in a cohort of 410 Oklahoma Indians with noninsulin-dependent diabetes mellitus. A total of 795 eyes were examined using both methods. The mean age of participants was 60.3 years, with a mean duration of diabetes of 17.3 years. RESULTS: An overall agreement of 86.3% with a kappa statistic kappa of 0.74 was found between ophthalmoscopy and fundus photography with a nonmydriatic camera. For the diagnosis of proliferative diabetic retinopathy, kappa = 0.84 with an agreement of 98.1%. With a total of 61 cases of proliferative retinopathy diagnosed by either method in our study, ophthalmoscopy alone detected 88.5% and fundus photography, 78.7%. When compared on a lesion-by-lesion basis, agreement between the two diagnostic methods was highest for nonproliferative retinopathy, as well as fibrous proliferation. CONCLUSION: The fundus photography with a nonmydriatic camera, performed with mydriasis, is comparable to ophthalmoscopy for the detection of retinopathy. It may prove to be a suitable, cost-effective method for routine screening in diabetes clinics, provided ophthalmologic referral is ensured for those with a diagnosis of any form of retinopathy, questionable retinopathy, nondiabetic retinopathy, those with poor quality photographs, as well as those with acute changes in visual acuity.

Diabetes Mellitus, Type 2↗
PubMed1993

The role of the free cytosolic calcium level in beta-cell signal transduction by gastric inhibitory polypeptide and glucagon-like peptide I(7-37).

Using the glucose-responsive hamster beta-cell line (hamster insulin tumor cells), we examined the cellular mechanisms by which gastric inhibitory polypeptide (GIP) and glucagon-like peptide I(7-37) (GLP-I) potentiate glucose-stimulated insulin secretion. Glucose alone increased insulin secretion and increased the free cytosolic calcium levels ([Ca2+]i) without altering cAMP content. When added to glucose-stimulated cells, GIP and GLP-I increased cAMP levels and further increased insulin secretion. At 4 mM but not 0.4 mM glucose, both peptides triggered a dose-dependent rise in [Ca2+]i with ED50s of 0.4 and 0.2 nM for GIP and GLP-I, respectively. The increase in [Ca2+]i was blocked by either chelation of extracellular Ca2+ with EGTA or nimodipine, the voltage-dependent Ca2+ channel blocker. Nimodipine also inhibited the potentiation of glucose-stimulated insulin secretion by GIP and GLP-I without inhibition of the stimulatory effect of these two peptides on cAMP accumulation. Neither peptide altered phosphoinositide metabolism, further underlining that the mobilization of intracellular Ca2+ from endoplasmic reticulum is not involved in the GIP and GLP-I signal transduction pathways. This study establishes that GIP and GLP-I potentiate glucose-stimulated insulin secretion by increasing extracellular Ca2+ influx through voltage-dependent Ca2+ channels.

Animals↗
PubMed1993

The mechanisms underlying the glucose dependence of arginine vasopressin-induced insulin secretion in beta-cells.

The mechanisms underlying the glucose dependence of arginine vasopressin (AVP)-stimulated insulin secretion were examined in a hamster insulin-secreting cell line (HIT cells). At 1.67 mM glucose, 100 nM AVP stimulated biphasic changes in free cytosolic Ca2+ ([Ca2+]i) and insulin secretion. The initial spike of [Ca2+]i came from an intracellular pool and was accompanied by parallel changes in the levels of inositol 1,4,5-trisphosphate. The following sustained increase in [Ca2+]i was associated with membrane depolarization and Ca2+ influx through voltage-dependent Ca2+ channels. The rapid phase of insulin secretion and the [Ca2+]i spike were resistant to the Ca2+ channel blocker nimodipine, whereas the sustained insulin secretion and the protracted increase in [Ca2+]i were inhibited by nimodipine. Thus, biphasic increases in [Ca2+]i mediated the biphasic insulin secretory pattern. In the absence of glucose, 100 nM AVP triggered a transient smaller spike in [Ca2+]i, but did not stimulate membrane depolarization, Ca2+ influx, or insulin secretion. However, the increase in inositol 1,4,5-trisphosphate was similar to that seen at 1.67 mM glucose. Both the AVP-induced [Ca2+]i spike and sustained [Ca2+]i increase were augmented by glucose. We concluded that the initial AVP receptor-mediated activation of phospholipase-C is not altered by glucose, but both intracellular Ca2+ release and extracellular Ca2+ influx through voltage-dependent Ca2+ channels triggered by AVP are glucose dependent and explain the sensitivity of AVP-stimulated insulin release to this metabolite.

Animals↗
PubMed1993

Functional expression of the rat glucagon-like peptide-I receptor, evidence for coupling to both adenylyl cyclase and phospholipase-C.

In man, glucagon-like peptide-I-(7-37) [GLP-I-(7-37)] is the most potent endogenous insulin-stimulating hormone. Although GLP-I-(7-37)-stimulated insulin secretion from the beta-cell is associated with an increase in cAMP accumulation, little is known about the signal transduction pathways used by this peptide. Using a cDNA encoding a high affinity rat GLP-I-(7-37) receptor [Kd = 4.1 nM for GLP-I-(7-37); Kd = 1 microM for GLP-I-(1-36) amide] expressed in a monkey kidney cell line (COS-7), we have demonstrated that the receptor is not only coupled to adenylyl cyclase, but is associated with an increase in the free cytosolic calcium level ([Ca2+]i). GLP-I-(7-37) increased both cAMP and [Ca2+]i in a dose-dependent manner and with equal potency (ED50 = 2.0 nM). The major source of the increased [Ca2+]i was found to be through the release of intracellular pools of Ca2+ associated with an increase in phosphoinositol turnover. Northern blot hybridization studies demonstrated that the GLP-I-(7-37) receptor gene was expressed in relatively high abundance in pancreatic islets and lung, but was also expressed at lower levels in the brain, liver, kidney, and skeletal muscle. This study establishes that a single GLP-I receptor species can mediate the effects of GLP-I-(7-37) through multiple G-protein-coupled signaling pathways, including the adenylyl cyclase system, phospholipase-C, and changes in [Ca2+]i.

Adenylyl Cyclases↗
PubMed1993

Lower-extremity amputation. Incidence, risk factors, and mortality in the Oklahoma Indian Diabetes Study.

Oklahoma Indians with NIDDM (n = 1012) underwent a baseline examination in 1972-1980. The incidence of and risk factors for first lower-extremity amputation were estimated. The mortality rates of amputees using data from 875 patients who had no previous history of amputation and who underwent follow-up examination between 1987 and 1991 are presented. The mean age of the 875 patients was 51.6 +/- 10.8 yr, and the mean duration of diabetes was 6.6 +/- 6.1 yr. After a mean follow-up time of 9.9 +/- 4.3 yr, the incidence rate of first LEA among diabetic Oklahoma Indians was 18.0/1000 person-yr. The incidence rate was two times higher in men than in women. In both sexes, significant risk factors (P < 0.05) were retinopathy and duration of diabetes. Fasting plasma glucose, use of insulin, and systolic blood pressure were significant for men only. For women, plasma cholesterol and diastolic blood pressure were additional risk factors. Compared with the mortality rate of 33.5/1000 person-yr among nonamputees, the rate among amputees was 55.5/1000 person-yr. The 5-yr survival rate after first amputation was 40.4%. For the amputees, the most common causes of death were diabetes (37.3%), cardiovascular disease (29.1%), and renal disease (7.3%). The incidence and mortality rates in diabetic Oklahoma Indians were higher than those reported in Pima Indians and other diabetic populations. To lower the incidence of lower-extremity amputation in this high-risk population, preventive action through education, foot care programs, and early detection of lesions must be intensified.

Adult↗
PubMed1993

Relative accuracy of the halothane challenge test and a molecular genetic test in detecting the gene for porcine stress syndrome.

Pietrain swine homozygous for the hal gene (n) associated with porcine stress syndrome (PSS) and a Pietrain-derivative breed, Near Pietrain (NP), with a frequency of .31 for n, were mated to produce reciprocal F1, F2, and purebred NP litters. The halothane challenge test was performed on all 40 parents and 240 progeny to predict their hal genotype and PSS susceptibility. The DNA-based assay for a C to T mutation at base pair 1,843 of the skeletal muscle ryanodine receptor (ryr1) cDNA, which is very highly correlated with PSS, was also determined for these animals. The predicted hal genotypes observed in the progeny differed significantly from the expected Mendelian ratios, and the halothane challenge test consistently overestimated the n/n hal genotype. However, the ryr1 genotypes observed in the progeny did not differ significantly from the expected Mendelian ratios, and this DNA-based assay apparently misidentified only one of the 40 parents. The results of this study indicate that the assay for the ryr1 mutation more accurately predicts both the homozygous and heterozygous forms of the PSS gene than does the halothane challenge test.

Animals↗
PubMed1993

The HOX-11 (TCL-3) homeobox proto-oncogene encodes a nuclear protein that undergoes cell cycle-dependent regulation.

Molecular analysis of the t(10;14) chromosomal translocation found in pediatric patients with T-cell acute lymphoblastic leukemia has led to the identification of the HOX-11 (TCL-3) protooncogene. The HOX-11 cDNA contains an open reading frame encoding a homeoprotein with features of DNA-binding. The majority of the t(10;14) chromosomal translocation breakpoints have been mapped to the 5' end of the HOX-11 gene, supporting the notion that deregulation of the HOX-11 gene by the t(10;14) chromosomal translocation contributed importantly to leukemia formation. To further define the role of the HOX-11 homeoprotein, we have prepared rabbit antiserum against a trpE-HOX-11 fusion protein. The purified anti-HOX-11 IgG immuno-precipitated a protein with apparent relative molecular mass of 40 kD. Biochemical fractionation demonstrated that the protein is localized in the nucleus. Furthermore, the HOX-11 RNA and protein appeared to be modulated during the cell cycle, with the highest level of expression at G1/S phase boundary. Taken together, these data suggest that the HOX-11 gene product may function as a transcription factor for G1 progression in the cell cycle.

Amino Acid Sequence↗
PubMed1993

Insect tolerance of transgenic Populus nigra plants transformed with Bacillus thuringiensis toxin gene.

Leaves and stem segments of Populus nigra were transformed with A. tumefaciens LBA4404 harboring a binary vector containing chimeric genes of NPT and 35S-omega-B.t. toxin-Nos. Nineteen regenerated kanamycin resistant plants were analyzed by DNA hybridization, out of which 10 were shown to be the candidates of transgenic plants. Insect tolerance tests showed that the transgenic plants were toxic to two lepidopteran pests, Lymantria dispar L. and Apocheimia cinerarius Erschoff. Based on the results of Southern blot of PCR products and the cluster analysis of their growth and insect resistance, three independent transgenic plants were selected, which were then propagated in the nursery field. This field test is currently in progress.

Agrobacterium tumefaciens↗
PubMed1993

[Epidemiological studies on human cryptosporidiosis in rural and urban areas of Jiangsu].

A survey of cryptosporidiosis in outpatients and inhabitants in Xuzhou city and 6 rural areas of Jiangsu Province was carried out from 1989 to 1991. Cryptosporidium oocysts (CSO) were found in 97 (1.6%) of 6,221 individuals as a whole, and were detected in 39 (3.3%) of 1,172 outpatients among the examinees. 39 cases were from 31 towns and villages of 8 counties near Xuzhou city. Among the 136 cases, 83 were males and 53 females, of them 89 (65.4%) were infants and young children. The incidence was evidently higher in the group of children under 4 than in that aged 4 to 15 (P < 0.01). Diarrhea, intermittent or persistent, was the main symptom of cryptosporidiosis, being present in 94 (69.1%) of the 136 positive cases, while the other 42 were asymptomatic carriers. The results of routine blood examination and immunoassay performed in a part of the infected children indicated that more than half of them had anemia and lessened cellular immunity. Stool examination of the domestic animals of the affected households showed that a pig and a dog were CSO positive.

Adolescent↗
PubMed1992

Bl4 and Dl4 decay.

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Journal Article↗
PubMed1992

Adenine affects the structure and stability of telomeric sequences.

Adenine occurs in the strand containing repeated G clusters in the telomeric DNA of a variety of organisms, including that of humans. The role of adenine has been investigated by constructing two sets of oligonucleotides each with one, two, or four copies of the telomeric sequence dTTTAGGG together with a control sequence in which T replaces the A residue, dTTTTGGG. Comparison of the stability and spectral properties of these two sequences in the presence of Na+ or K+ affords a basis for defining the role of adenine in these structures. In Na+, the A residue stabilizes the structure formed by each oligomer significantly, presumably by a base-pairing interaction with T. In K+, by contrast, there is little difference in stability. In two- and four-copy oligomers, the A sequence has a different structure from its T analog, as detected by CD spectroscopy. In the presence of either Na+ or K+, the tetraplexes of A and T interact with intercalators.

Adenine↗