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Biomedical subjects

Q Li

Publications and source records attributed to Q Li.

At least 883 records · Page 49Linked to original sources
PubMed1994

Attenuation of hormone responses to the 5-HT1A agonist ipsapirone by long-term treatment with fluoxetine, but not desipramine, in male rats.

The present study had two objectives: (1) to provide information on neuroendocrine challenge tests that can lead to diagnostic tests in humans; and (2) to confirm our previous observation that chronic fluoxetine selectively inhibits serotonin (5-HT1A) receptor function. We determined the effect of chronic fluoxetine and desipramine (DMI) on the hormone response to ipsapirone, a 5-HT1A agonist and a potential anxiolytic drug. Ipsapirone increased oxytocin, adrenocorticotropic hormone (ACTH), corticosterone, and prolactin, but not renin or vasopressin concentrations in plasma. Chronic fluoxetine, but not DMI, significantly inhibited the effect of ipsapirone on plasma oxytocin, ACTH and corticosterone concentrations. Chronic fluoxetine also reduced the Bmax for 3H-8-hydroxy-2-(dipropylamino) tetralin (3H-8-OH-DPAT) labelled 5-HT1A receptors in the midbrain. Neither antidepressant altered the density or affinity of 5-HT uptake sites. In conclusion, the present results confirm our previous results using 8-OH-DPAT as a challenge, and suggest that chronic 5-HT uptake inhibition results in adaptive changes leading to decreased function of the 5-HT1A receptor system. Finally, because ipsapirone may be administered to humans, it might be usable to evaluate 5-HT1A receptor function in depressed patients.

Adrenocorticotropic Hormone↗
PubMed1994

Hypersensitive site 5 of the human beta locus control region functions as a chromatin insulator.

The human beta locus control region (LCR) consists of five DNAse I hypersensitive sites (HS), four of which are erythroid specific and one, the further upstream located 5'HS5, is constitutive. To characterize the function of 5'HS5 we analyzed globin gene expression of various constructs containing HS3 as an enhancer, HS5, and the beta gene as a reporter. Expression was analyzed in stably transfected MEL cells. We found that the enhancing effect of hypersensitive site 3 is blocked when the HS5 is interposed between HS3 and the beta globin gene. These data suggest that the human 5'HS5 has the properties of a chromatin insulator.

Animals↗
PubMed1994

A cloned rat CD38-homologous protein and its expression in pancreatic islets.

Cyclic ADP-ribose recently has been suggested to be an important intracellular signal for insulin secretion. CD38, which was originally isolated from human lymphocytes as a surface marker, is active in the synthesis of cyclic ADP-ribose. We report here the cloning of a rat CD38-homologous protein (CD38H) which is expressed in pancreatic islets. The deduced amino acid sequence shows that rat CD38H is a protein of 303 amino acids (M(r), 34.4 kD) and contains one possible membrane-spanning domain, consistent with a type II transmembrane glycoprotein. The overall identity and similarity of the amino acid sequences between the human CD38 and the rat CD38H are 58% and 76%, respectively. RNA blot analysis showed a strong signal of 3.4 kb in rat brain, duodenum, and heart. CD38H also is shown to be expressed in pancreatic islets by the RT-PCR procedure, but its expression is not significantly different in Wistar and GK rats, a genetic model of non-insulin-dependent diabetes mellitus. The presence of rat CD38H in the pancreatic islets suggests that CD38H may be involved in insulin secretion by synthesizing cADP-ribose.

ADP-ribosyl Cyclase↗
PubMed1994

Protein kinase C activity is required for lipid oxidation of low density lipoprotein by activated human monocytes.

Our previous studies have shown that human monocytes can oxidize native low density lipoprotein (LDL) and transform it to a cytotoxin. We also found that intracellular Ca2+ levels are integrally involved in lipid oxidation of LDL by activated monocytes. In these studies, we investigated the protein kinase C (PKC) signaling pathway for its contribution to the process of monocyte oxidation of LDL lipids. We found substantial protein phosphorylation induced upon monocyte activation. Pharmacologic inhibition of PKC activity with the PKC inhibitors H-7 (1-100 microM), calphostin C (1-10 microM), and GF109203X (0.1-10 microM) caused a dose-dependent inhibition of cellular protein phosphorylation, including that of several previously identified PKC substrates. These inhibitors of PKC activity also substantially inhibited LDL lipid oxidation by activated monocytes. This inhibition was correlated with a profound suppression of superoxide anion production by these cells. In contrast, inhibition of cAMP-dependent protein kinase activity altered neither monocyte-mediated LDL lipid oxidation nor O2- production by activated monocytes. Delaying the addition of PKC inhibitors until after the peak production of O2-, which occurs during the respiratory burst, still resulted in inhibition of LDL lipid oxidation, suggesting roles for PKC in both early and late events. To corroborate these findings using other approaches, we used phorbol 12-myristate 13-acetate to down-regulate PKC activity and also used antisense oligonucleotides as specific PKC inhibitors. Results of both types of studies support the conclusion that PKC activity is required for activated monocytes to oxidize LDL lipids. Thus, PKC activation in this system is essential, one critical pathway regulated by PKC activity is the production of O2-, and continued PKC activity is required for optimal oxidation of LDL lipids.

Base Sequence↗
PubMed1994

Effect of arginine on cisplatin-induced acute renal failure in the rat.

The effect of arginine on the nephrotoxicity produced by cisplatin (6.0 mg/kg i.v.) was investigated in the rat. Intravenous administration of L-arginine at doses of 0.26-2.63 g/kg at the time of cisplatin injection produced significant protection of renal function as evidenced by reductions in plasma urea and creatinine concentrations, decreased polyuria and increases in the plasma clearance of [3H]inulin and [14C]-p aminohippurate. Administration of D-arginine (2.63 g/kg i.v.) also significantly ameliorated the renal dysfunction induced by cisplatin although this protective effect was not as great as produced by the same dose of L-arginine. D-arginine, by contrast to its L-isomer, is reported to have little or no effect on renal haemodynamics. Consequently, the results of this study indicate that the protective effect of L-arginine in cisplatin nephrotoxicity involves both haemodynamic and nonhaemodynamic components.

Acute Kidney Injury↗
PubMed1994

Genomic organization, 5'-upstream sequence, and chromosomal localization of an insulinoma-associated intronless gene, IA-1.

IA-1 is a novel cDNA originally isolated from a human insulinoma subtraction library (ISL-153). It encodes a protein containing both a zinc finger DNA-binding domain and a putative prohormone domain. IA-1 transcripts have been found thus far only in tumors of neuroendocrine origin. Clinical studies have shown that IA-1 is a sensitive marker for neuroendocrine differentiation of human lung tumors. In this study, we cloned and sequenced the entire IA-1 gene and its 5'-upstream region from a human liver genomic library. In situ hybridization localized the IA-1 gene to the short arm of human chromosome 20. Sequence analysis and restriction enzyme mapping showed that the IA-1 gene is uninterrupted and appears to be intronless. Evidence that IA-1 is an intronless gene that can translate into protein was obtained from in vitro translation studies that showed that both IA-1 cDNA and IA-1 genomic DNA yielded identical protein products of approximately 61,000 daltons. Examination of the 5'-upstream region (2090 base pairs) revealed several tissue-specific regulatory elements, including glucokinase upstream promoter elements and a Pit-1 factor binding site. The presence of several different upstream regulatory elements may account for IA-1 gene expression in different neuroendocrine tumors.

Base Sequence↗
PubMed1994

Accurate processing and secretion in the baculovirus expression system of an erythroid-cell-stimulating factor consisting of a chimaera of insulin-like growth factor II and an insect insulin-like peptide.

A synthetic gene encoding the signal peptide and the N-terminal sequence of bombyxin, an insect insulin-like peptide, and the 58 amino acids of the C-terminal sequence of human insulin-like growth factor II (IGF II) has been expressed using the baculovirus system. This synthetic chimaera was obtained by amplification of four overlapping oligonucleotides using Taq polymerase and cloning into the transfer vector pBluebac. The construct was integrated by homologous recombination into the Autographa californica nuclear polyhedrosis genome. Spodoptera frugiperda Sf9 insect cells infected with the recombinant baculovirus secreted an accurately processed peptide consisting of the ten N-terminal amino acids of bombyxin and the 58 C-terminal amino acids of IGF II. The N-terminal glutamine of bombyxin was changed to asparagine to facilitate sequencing of the synthetic peptide. The chimaera was five times more potent than human recombinant IGF II in its capacity to stimulate thymidine incorporation into erythroid cells of fetal bovine liver in a serum-free medium. It stimulated erythroid colony formation in the presence of 2 microunits/ml erythropoietin in cells cultured over a monolayer of stromal cells of fetal liver. Artificial chimaeras as described here may prove useful for the production of insulin, IGF I and other peptides as secreted proteins in insect cells.

Amino Acid Sequence↗
PubMed1994

Negative regulation of the human atrial natriuretic peptide gene by 1,25-dihydroxyvitamin D3.

We have examined the effect of 1,25-dihydroxyvitamin D3 on the promoter activity of the atrial natriuretic peptide (ANP) gene in cultured neonatal rat atrial myocytes. In acute transfection studies 1,25-dihydroxyvitamin D3 inhibited the expression of a human ANP (hANP) promoter-driven chloramphenicol acetyltransferase reporter (-1150 hANP CAT) in a dose-dependent fashion (10(-10)-10(-8) M). When an expression vector for the vitamin D receptor (VDR) (pSVL-VDR) was introduced together with the reporter plasmid, there was a significant ligand-dependent amplification of the vitamin D-dependent inhibition. Deletion analysis of the 5'-flanking sequence localized the suppressible promoter sequence to within 104 base pairs of the transcription start site of the hANP gene. Thyroid hormone, glucocorticoid, estrogen, and retinoic acid receptor were incapable of mimicking the VDR-dependent inhibition. Retinoid X receptor, on the other hand, effected a significant reduction in hANP promoter activity which was at least additive with that produced by the liganded VDR. The VDR-dependent inhibition displayed promoter selectivity. Both the SV40 promoter and a conventional vitamin D response element linked to a truncated SV40 promoter were activated by the liganded vitamin D receptor, whereas the Rous sarcoma virus promoter was unaffected. On the other hand, the cardiac-specific troponin T promoter was suppressed in a fashion similar to ANP. These findings imply a potentially important role for vitamin D3 in the regulation of gene transcription in myocardial cells.

Animals↗
PubMed1994

The substrate specificity of Saccharomyces cerevisiae myristoyl-CoA: protein N-myristoyltransferase. Polar probes of the enzyme's myristoyl-CoA recognition site.

Saccharomyces cerevisiae myristoyl-CoA:protein N-myristoyltransferase (Nmt1p) is a monomeric enzyme that is essential for vegetative growth. Nmt1p catalyzes the co-translational transfer of myristate from CoA to the amino-terminal Gly of cellular proteins in an ordered Bi Bi reaction mechanism that initially involves binding of myristoyl-CoA to the apoenzyme. Forty one fatty acid analogs were synthesized to define features in the acyl chain of myristoyl-CoA which are important determinants of its recognition by Nmt1p's acyl-CoA binding site as well as to help us deduce the structure of the binding site itself. These analogs included dicarboxylic acids, omega-nitrocarboxylic acids, analogs equivalent in length to C13:0-C15:0 which contain electronegative halogens at their omega-termini, hydroxytetradecanoic acids with hydrogen replaced by OH from C3 to C13, and azidophenyl-containing fatty acids with the linear azide unit attached either meta or para to phenyl and with variations in the length of their methylene chains. These compounds were converted to their CoA derivatives using Pseudomonas acyl-CoA synthetase and then surveyed as substrates for purified Nmt1p in an in vitro assay system that included an octapeptide derived from residues 1-8 of the human immunodeficiency virus Pr55gag polyprotein precursor. The results suggest that the myristoyl-CoA binding site contains a conical-shaped "receptor" that interacts with the omega-terminus of the bound acyl chain of acyl-CoAs. The acuteness of this cone determines the enzyme's capacity to accommodate steric bulk at the omega-terminus as well as Nmt1p's sensitivity to the distance between the eclipsed C5-C6 bond of a bound acyl chain and its omega-terminus. The activity profile of the various analog-CoAs also indicates that the enzyme's myristoyl-CoA binding site can accommodate fatty acid analogs with marked increases in polarity at their omega-terminus (compared to C14:0) as long as their chain length is equivalent to that of myristate.

Acyl Coenzyme A↗
PubMed1994

Preparation of unoccupied thyroid-hormone receptor.

Thyroid hormone (3,5,3'-tri-iodothyronine; T3) regulates gene expression through binding to its specific receptor in the nucleus. In euthyroid animals, roughly half of all receptors are occupied by the hormone. Nuclear extracts thus yield mixtures of occupied and unoccupied receptors. We present here a simple method for transforming occupied receptors into unoccupied ones. In vitro, the T3-receptor complex dissociated in a half-dissociation time exceeding 100 h at 0 degrees C, and at temperatures that accelerated the dissociation the receptor was quickly inactivated. Long-chain-fatty-acyl-CoAs, on the other hand, greatly accelerated the dissociation of T3-receptor complex at 0 degree C. The receptor was extracted from rat liver nuclei, incubated with oleoyl-CoA to release the bound hormone, and passed through a small column of Lipidex, which strongly adsorbed both oleoyl-CoA and the dissociated hormone. The receptor was recovered in the flow-through fraction in its unoccupied form, as seen by the results of DEAE-Sephadex column chromatography and the loss of all previously bound [125I]T3. The maximum T3-binding capacity of the unoccupied receptor was about 1.5-fold that of the untreated sample, and the dissociation constant was unaltered. The results suggest that most nuclear thyroid-hormone receptors occupied by the hormone were transformed into unoccupied ones. From the T3-binding capacity before and after oleoyl-CoA treatment, the in vivo T3 occupancy of the receptor was estimated. The procedure is easy to perform, and the method should be useful for studies of unoccupied receptors.

Acyl Coenzyme A↗
PubMed1994

Analysis of the developmental and transcriptional potentiation functions of 5'HS2 of the murine beta-globin locus control region in transgenic mice.

We analyze the role of 5'HS2 of the mouse beta-globin LCR in the transcriptional and developmental regulation of beta-globin gene expression. Previous studies have shown that the human beta-globin gene behaves as an adult gene in transgenic mice, being expressed in fetal liver and bone marrow-derived erythroblasts but not in yolk sac-derived embryonic erythroid cells. We show that linkage of mLCR5'HS2 to a human beta-globin gene alters this pattern of expression during ontogeny, resulting in expression of the linked beta-globin gene at all stages of murine erythroid development. Expression was independent of integration position and correlated with transgene copy number. Our results provide the first test of a phylogenetically homologous LCR in transgenic mice and demonstrate evolutionary conservation of both developmental and transcriptional potentiation functions between mammalian beta-globin LCRs.

Animals↗
PubMed1994

Corticosteroids enhance S-antigen expression in nonretinal ocular tissues of rats with experimental autoimmune uveitis.

S-antigen (S-Ag), a major protein on the retinal photoreceptor cell, can induce experimental autoimmune uveitis (EAU). We have previously detected S-Ag and its mRNA in irises of chronic uveitis patients receiving long-term steroid therapy. To further investigate the effect of steroid therapy on ocular tissue, we compared levels of S-Ag and its mRNA in EAU rats with and without steroid treatment. EAU was induced in 72 Lewis rats by two footpad injections of S-Ag. The rats were then treated with Depo-Medrol or phosphate-buffered saline by intramuscular injection. Eyes were collected at different time points. S-Ag mRNA was detected in the lens epithelium, trabecular meshwork, iris, and ciliary body of 47.2% of the steroid-treated group vs 22.2% of the controls. S-antigen was also detected in 30.6% of the eyes of the treated group vs 16.7% of the controls. S-Ag and its mRNA was found only in the retina of normal rats. These results support the hypothesis that prolonged corticosteroid therapy in uveitic patients might enhance the expression of S-Ag in nonretinal ocular tissues and might contribute to the ocular side effects of corticosteroid.

Animals↗
PubMed1994

Toxoplasma gondii: acquired ocular toxoplasmosis in the murine model, protective role of TNF-alpha and IFN-gamma.

DNA and mRNA amplification by the polymerase chain reaction (PCR), immunohistochemical, and histopathology were performed in the eyes and brains from C57BL/6 mice infected with an avirulent strain of Toxoplasma gondii (ME49). Focal ocular inflammation and retinal pigment epithelial involvement were commonly observed after 15 days of infection. Four weeks after infection a stable number of cysts was observed in the brain but rarely in the eye, and they did not elicit an inflammatory response. In most of the ocular lesions the presence of the parasite could not be demonstrated even with the PCR technique. B1 DNA fragments of T. gondii were detected in only 4 of 11 eyes tested by PCR and Southern blot hybridization. Treatment of mice with mAbs against T cells (CD4 plus CD8) or cytokines (IFN-gamma or TNF-alpha) resulted in a marked increase of ocular lesions, more often associated with the presence of the parasite and the severity of inflammatory response. This model and the techniques utilized here can improve our understanding of the respective roles of parasite proliferation and immune mechanisms involved in the pathogenesis of acquired ocular toxoplasmosis.

Animals↗