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Biomedical subjects

J Lim

Publications and source records attributed to J Lim.

At least 127 records · Page 7Linked to original sources
PubMed1999

Decreased prevalence of retinopathy of prematurity in an inner-city hospital.

BACKGROUND AND OBJECTIVE: Improvements in care of low birth weight preterm infants has led to an increased survival of this population. It is not known whether the improved care has decreased the prevalence of retinopathy of prematurity (ROP), or whether the survival of even smaller infants has increased the prevalence. The purpose of this study was to determine the prevalence of ROP in an inner-city hospital during two time periods to determine whether the prevalence is changing. PATIENTS AND METHODS: The frequency and characteristics of ROP were compared between a 10-month observation period in 1995-1996 and published data from a similar time period in 1988-1989. RESULTS: There were fewer cases of ROP per live births less than 1500 g during 1995-1996 compared with 1988-1989 (P< .0001). This included both mild and severe ROP. When the two racial subgroups were examined separately, there was a statistically significant decline for the black (P < .001) but not the Hispanic population (P = .12). The Mantel-Haenszel chi2 test confirmed that the decline was statistically significant when the two groups were combined (P < .001). CONCLUSIONS: In this population, the prevalence of ROP appears to have decreased between 1995-1996 and 1988-1989. The subgroup experiencing the biggest decline was black infants. Other studies should be performed to investigate whether the frequency of ROP has also declined in other settings.

California↗
PubMed1998

Urea inhibits the Na-K pump in human erythrocytes.

Recent studies have established that urea alters the activity of several volume-sensitive cation transport pathways. However, it has remained unclear whether urea has any effect on transport pathways that are not volume-sensitive. We examined the effect of urea on Na-K pump in the human erythrocytes. In cells from nine subjects, 500 mM urea inhibited 52 +/- 10% of the pump activity measured as the ouabain-sensitive (OS) K influx. Urea inhibited the OS K influx reversibly, in a concentration-dependent manner. [3H] oubain binding, a measure of the number of Na-K pump sites remained unchanged with urea. Urea decreased the Vmax for ouabain-sensitive K influx, but did not alter the apparent K(m) for external K. Furthermore, urea did not alter the apparent K(m) for intracellular Na. The ion turnover per pump site was decreased in the presence of urea. Thus, physiologically relevant urea concentration inhibit the Na-K pump in human erythrocyte. The inhibition of the Na-K pump by urea suggests that the effects of urea may not be limited to volume-sensitive transporters, but may be more widespread.

Biological Transport↗
PubMed1998

NRP/B, a novel nuclear matrix protein, associates with p110(RB) and is involved in neuronal differentiation.

The nuclear matrix is defined as the insoluble framework of the nucleus and has been implicated in the regulation of gene expression, the cell cycle, and nuclear structural integrity via linkage to intermediate filaments of the cytoskeleton. We have discovered a novel nuclear matrix protein, NRP/B (nuclear restricted protein/brain), which contains two major structural elements: a BTB domain-like structure in the predicted NH2 terminus, and a "kelch motif" in the predicted COOH-terminal domain. NRP/B mRNA (5.5 kb) is predominantly expressed in human fetal and adult brain with minor expression in kidney and pancreas. During mouse embryogenesis, NRP/B mRNA expression is upregulated in the nervous system. The NRP/B protein is expressed in rat primary hippocampal neurons, but not in primary astrocytes. NRP/B expression was upregulated during the differentiation of murine Neuro 2A and human SH-SY5Y neuroblastoma cells. Overexpression of NRP/B in these cells augmented neuronal process formation. Treatment with antisense NRP/B oligodeoxynucleotides inhibited the neurite development of rat primary hippocampal neurons as well as the neuronal process formation during neuronal differentiation of PC-12 cells. Since the hypophosphorylated form of retinoblastoma protein (p110(RB)) is found to be associated with the nuclear matrix and overexpression of p110(RB) induces neuronal differentiation, we investigated whether NRP/B is associated with p110(RB). Both in vivo and in vitro experiments demonstrate that NRP/B can be phosphorylated and can bind to the functionally active hypophosphorylated form of the p110(RB) during neuronal differentiation of SH-SY5Y neuroblastoma cells induced by retinoic acid. Our studies indicate that NRP/B is a novel nuclear matrix protein, specifically expressed in primary neurons, that interacts with p110(RB) and participates in the regulation of neuronal process formation.

Adult↗
PubMed1998

Where's the point?

Explore the source record for details and available documents.

Anesthetics, Local↗
PubMed1998

Arabidopsis gls mutants and distinct Fd-GOGAT genes. Implications for photorespiration and primary nitrogen assimilation.

Ferredoxin-dependent glutamate synthase (Fd-GOGAT) plays a major role in photorespiration in Arabidopsis, as has been determined by the characterization of mutants deficient in Fd-GOGAT enzyme activity (gls). Despite genetic evidence for a single Fd-GOGAT locus and gene, we discovered that Arabidopsis contains two expressed genes for Fd-GOGAT (GLU1 and GLU2). Physical and genetic mapping of the gls1 locus and GLU genes indicates that GLU1 is linked to the gls1 locus, whereas GLU2 maps to a different chromosome. Contrasting patterns of GLU1 and GLU2 expression explain why a mutation in only one of the two genes for Fd-GOGAT leads to a photorespiratory phenotype in the gls1 mutants. GLU1 mRNA was expressed at the highest levels in leaves, and its mRNA levels were specifically induced by light or sucrose. In contrast, GLU2 mRNA was expressed at lower constitutive levels in leaves and preferentially accumulated in roots. Although these results suggest a major role for GLU1 in photorespiration, the sucrose induction of GLU1 mRNA in leaves also suggests a role in primary nitrogen assimilation. This possibility is supported by the finding that chlorophyll levels of a gls mutant are significantly lower than those of the wild type when grown under conditions that suppress photorespiration. Both the mutant analysis and gene regulation studies suggest that GLU1 plays a major role in photorespiration and also plays a role in primary nitrogen assimilation in leaves, whereas the GLU2 gene may play a major role in primary nitrogen assimilation in roots.

Amino Acid Oxidoreductases↗
PubMed1998

Implications of rRNA operon copy number and ribosome content in the marine oligotrophic ultramicrobacterium Sphingomonas sp. strain RB2256.

Sphingomonas sp. strain RB2256 is a representative of the dominant class of ultramicrobacteria that are present in marine oligotrophic waters. In this study we examined the rRNA copy number and ribosome content of RB2256 to identify factors that may be associated with the relatively low rate of growth exhibited by the organism. It was found that RB2256 contains a single copy of the rRNA operon, in contrast to Vibrio spp., which contain more than eight copies. The maximum number of ribosomes per cell was observed during mid-log phase; however, this maximum content was low compared to those of faster-growing, heterotrophic bacteria (approximately 8% of the maximum ribosome content of Escherichia coli with a growth rate of 1. 5 h-1). The low number of ribosomes per cell appears to correlate with the low rate of growth (0.16 to 0.18 h-1) and the presence of a single copy of the rRNA operon. However, on the basis of cell volume, RB2256 appears to have a higher concentration of ribosomes than E. coli (approximately double that of E. coli with a growth rate of 1.5 h-1). Ribosome numbers reached maximum levels during mid-log-phase growth but decreased rapidly to 10% of maximum during late log phase through 7 days of starvation. The cells in late log phase and at the onset of starvation displayed an immediate response to a sudden addition of excess glucose (3 mM). This result demonstrates that a ribosome content 10% of maximum is sufficient to allow cells to immediately respond to nutrient upshift and achieve maximum rates of growth. These data indicate that the bulk of the ribosome pool is not required for protein synthesis and that ribosomes are not the limiting factor contributing to a low rate of growth. Our findings show that the regulation of ribosome content, the number of ribosomes per cell, and growth rate responses in RB2256 are fundamentally different from those characteristics in fast-growing heterotrophs like E. coli and that they may be characteristics typical of oligotrophic ultramicrobacteria.

Alaska↗
PubMed1997

High-performance liquid chromatographic determination and stability of 5-(3-methyltriazen-1-yl)-imidazo-4-carboximide, the biologically active product of the antitumor agent temozolomide, in human plasma.

5-(3-Methyltriazen-1-yl)-imidazo-4-carboximide (MTIC) is a highly unstable compound which is believed to be the biologically active degradation product of the antitumor agent temozolomide. An HPLC method has been developed and validated for the analysis of MTIC in human plasma. Because of the instability of MTIC, sample processing was kept to minimal. The method involved precipitation of plasma protein with methanol followed by analysis of the supernatant using reversed-phase column and UV detection at 316 nm. The linearity (r>0.99), precision (C.V.<9%) and accuracy (bias<5%) were satisfactory. The lower limit of quantitation (LOQ) was 10 ng/ml. The recovery of MTIC and internal standard was > or = 86.7%. MTIC was stable in plasma though three freeze-thaw cycles, and was stable at 4 degrees C for 1 h and at -80 degrees C for at least 70 days. MTIC may be unstable at 10 degrees C in processed samples; therefore, samples were placed in the autosampler (10 degrees C) immediately prior to injection. By using this analytical method, MTIC was quantified in plasma of cancer patients (n=12) within 0.25-12 h after oral administration of temozolomide at 150 mg/m2. The mean maximum plasma concentration (Cmax) was 211 ng/ml which was observed at a mean Tmax of 1.88 h post dose. MTIC disappeared rapidly from plasma with an apparent in vivo half-life (t1/2) of 1.9 h similar to that of temozolomide. Following in vitro incubation of MTIC in human plasma at 25 degrees C, MTIC disappearance was bioexponential with estimated t1/2 values of 25 and 60 min for the first and second phases, respectively. Therefore, the elimination t1/2 of MTIC in human in vivo (1.9 h) was controlled by the rate of its formation from temozolomide.

Administration, Oral↗
PubMed1997

Evaluation of some fluorogenic substrates for continuous assay of aminopeptidase P.

Three potential fluorogenic substrates for assay of aminopeptidase P (AP-P) have been prepared and evaluated, using enzyme purified from porcine kidney. They are based on internal quenching of the synthetic, fluorescent amino acid (R, S)-2-amino-3-(7-methoxy4-coumaryl)propanoic acid ((R,S)-Amp) by a 2, 4dinitrophenyl (DNP) group. The compounds are X-Pro-Pro-(R, S)-Amp-NH2, where X is H-Lys(epsilon-DNP), H-Orn(delta-DNP), or L-2-amino-3-(DNP)aminopropionic acid. The first two were found to be excellent substrates for AP-P, with respective Km values of 4.8 and 5.2 microM. An advantageous feature is that under the conditions of assay, using 4-mm2 cells, the substrates are without noticeable quenching effect on the fluorescence of Pro-Pro-(R,S)-Amp-NH2 (the product liberated by the action of AP-P). At concentrations greater than about 30-50 microM, both substrates appear to inhibit the enzyme, but this has little practical consequence since assays can be carried out at substrate concentrations, giving up to approximately 80% of Vmax without this inhibitory effect being noticeable. The Lys derivative was found to be a very useful substrate for a continuous assay for AP-P and equally good in a discontinuous assay of multiple samples using microtiter plates. The racemic center at the Amp residue did not prevent total hydrolysis of the Lys derivative, suggesting that subsite specificity in AP-P does not extend as far as the P3' position.

Aminopeptidases↗
PubMed1997

A novel splice site mutation in the androgen receptor gene results in exon skipping and a non-functional truncated protein.

Mutations of the androgen receptor (AR) gene and protein are associated with complete androgen insensitivity syndromes (CAIS) in individuals with XY genotypes causing them to develop as phenotypic females. Splice site mutations of the AR gene are very rare and in this report we describe the consequences of a novel G --> A mutation at the exon 7/intron 7 splice junction of the AR gene that resulted in CAIS in two siblings. Reverse transcriptase-polymerase chain reaction (RT-PCR) of the AR transcript in patient's fibroblasts was performed and sequencing of the product showed omission of exon 7, with exon 6 being spliced directly to exon 8. This resulted in a shift of the reading frame and the introduction of a premature stop codon 10 amino acids into exon 8. Immunoblot analyses showed that the resultant AR protein was partially deleted in its C-terminal region and was approximately 1.5 kDa smaller than the wild type. This truncated AR was non-functional as it was unable to bind its physiological ligand (dihydrotestosterone) in androgen-binding assays. This is the first documentation of a point mutation in the AR gene which causes exon skipping and proves that the mutation is the cause of CAIS in our two subjects.

Androgens↗
PubMed1997

Synthesis and anti-HIV-1 activity of a series of 1-alkoxy-5-alkyl-6-(arylthio)uracils.

A series of 1-alkoxy-5-alkyl-6-(arylthio)uracils was synthesized and tested for their ability to inhibit HIV-1 replication. Treatment of 2-alkyl-3,3-bis(methylthio)acryloyl chlorides (5a-e) with AgOCN in benzene followed by reaction of the resulting isocyanates 6a-e with an appropriate alkoxyamine gave N-alkoxy-N'-((2-alkyl-3,3-bis(methylthio)acryloyl)ureas (10a-z) in good to excellent yields. Cyclization of 10a-z in AcOH containing a catalytic amount of p-TsOH produced 1-alkoxy-5-alkyl-6-(methylthio)uracils (11a-z). Oxidation of 11a-z with 3-chloroperoxybenzoic acid in CH2Cl2 resulted in high yields of 1-alkoxy-5-alkyl-6-(methylsulfonyl)uracils (12a-x and 12z) and 1-(benzyloxy)-6-(methylsulfinyl)thymine (12y), which were subsequently reacted with an appropriate arenethiol in ethanolic NaOH solution to afford 1-alkoxy-5-alkyl-6-(arylthio)uracils (14-49). Substitution at the 3- and 5-positions of the C-6-(phenylthio) ring by two methyl groups significantly increased its original anti-HIV-1 activity (EC50: 6-((3,5-dimethylphenyl)thio)-5-isopropyl-1-propoxyuracil (18), 0.064 microM; 6-((3,5-dimethylphenyl)thio)-1-(3-hydroxypropoxy)-5-isopropyluracil++ + (23), 0.19 microM). Among the various alkoxy substituents at the N-1, the propoxy group was the most beneficial for improving the anti-HIV-1 activity. The 1-propoxy derivative 18 proved to be the most potent inhibitor of HIV-1 replication, followed by the 1-(3-hydroxypropoxy) derivative 23. Introduction of an isopropyl group at C-5 of the uracil base also remarkably enhanced the activity. When compound 18 was incubated with a rat liver homogenate preparation, no metabolite was observed, thus confirming the metabolic stability of the N-O bond in these 1-alkoxyuracils.

Animals↗
PubMed1997

A second type of rod opsin cDNA from the common carp (Cyprinus carpio).

A second type of rhodopsin cDNA from carp (cRh-II) shared 97.2% polynucleotide identity with the previously reported cRh-I. The deduced amino acid sequences of cRh-I and cRh-II exhibited 98.6% identity. The key difference between these two types of cRh is that valine at position 169 of cRh-I was replaced by glutamic acid in cRh-II. Southern blot analysis of genomic DNA showed that there were two types of cRh gene. These two rod opsin genes were proven to be expressed in carp retinas by using RT-PCR with type-specific primers.

Amino Acid Sequence↗
PubMed1997

Isolation of murine and human homologues of the fission-yeast dis3+ gene encoding a mitotic-control protein and its overexpression in cancer cells with progressive phenotype.

To investigate genes involved in metastasis, we used a differential display method to compare the levels of gene expression in three cell lines derived from murine colon-adenocarcinoma 26 that show different metastatic potentials. The results, and subsequent Northern analyses, confirmed that one gene was expressed most strongly in NL17, the cell line with the highest experimentally metastatic potential to the lung; strongly in NL22, the line with moderately metastatic potential; and very weakly in NL4, which has no metastatic potential in recipient mice. Using this fragment as a probe, we isolated the murine cDNA as well as its human homologue and determined their DNA sequences. The cDNA sequences from both species contained open reading frames of 2874 nucleotides, encoding peptides of 958 amino acids with calculated molecular weights of approximately 109,000; the murine and human nucleotide sequences were 90% identical. The deduced amino acid sequences of these cDNAs revealed significant homology (45% identity) to the dis3+ gene product of Schizosaccharomyces pombe, a protein thought to be essential for mitotic control in the yeast. We therefore termed the murine and human genes hmc (homologue to the mitotic-control gene) and HMC, respectively. In 7 of 13 patients with colorectal cancers and liver metastases, expression of HMC was increased up to 38-fold in primary tumors and metastatic foci as compared to adjacent normal colorectal mucosa. An increase in expression of HMC, its novel product likely to belong to a structurally distinct family of mitotic-control proteins, may be associated with malignant phenotypes of some colorectal cancers.

Adenocarcinoma↗
PubMed1997

Association of csk-homologous kinase (CHK) (formerly MATK) with HER-2/ErbB-2 in breast cancer cells.

Protein-tyrosine kinases, such as HER-2/ErbB-2, have been specifically linked to breast cancer. The Csk-homologous kinase (CHK), formerly MATK, is a tyrosine kinase that contains the Src homology 2 and 3 (SH2 and SH3) domains and demonstrates homology ( approximately 50%) to the Csk tyrosine kinase. Like Csk, CHK is able to phosphorylate and inactivate Src family kinases. In this report, we investigated whether CHK is expressed in breast cancer tissues and whether it participates in the ErbB-2 signaling pathway in T47D and MCF-7 breast cancer cell lines. Immunostaining of the CHK protein in breast tissues demonstrated that primary invasive ductal carcinomas, stage II (13 of 15 cases) and stage I (8 of 15 cases), expressed the CHK protein, while this protein was not detected in the adjacent normal tissues from the same patients. To study the role of CHK in the ErbB-2 signaling pathway, glutathione S-transferase fusion proteins containing the SH2 and SH3 domains of CHK were generated. CHK-SH2 and CHK-SH3-SH2, but not CHK-SH3 or CHK-NH2-SH3, precipitated the tyrosine-phosphorylated ErbB-2 upon stimulation with heregulin. EGF or interleukin-6 stimulation of T47D cells failed to induce CHK-SH2 association with ErbB-2, the EGF-receptor, or the interleukin-6 receptor. In vivo association of the tyrosine-phosphorylated ErbB-2 with CHK was observed in co-immunoprecipitation studies with anti-CHK antibodies. EGF-R, ErbB-3, and ErbB-4 were not detected in the CHK immunoprecipitates or in the precipitates of the GST-SH2 fusion proteins of CHK, suggesting that the association of CHK with ErbB-2 upon heregulin stimulation is receptor-specific (ErbB-2) and ligand-specific (heregulin). These results indicate that CHK might participate in signaling in breast cancer cells by associating, via its SH2 domain, with ErbB-2 following heregulin stimulation.

Glycoproteins↗
PubMed1997

An Arabidopsis photolyase mutant is hypersensitive to ultraviolet-B radiation.

Photolyases are DNA repair enzymes that use energy from blue light to repair pyrimidine dimers. We report the isolation of an Arabidopsis thaliana mutant (uvr2-1) that is defective in photorepair of cyclobutylpyrimidine dimers (CPDs). Whereas uvr2-1 is indistinguishable from wild type in the absence of UV light, low UV-B levels inhibit growth and cause leaf necrosis. uvr2-1 is more sensitive to UV-B than wild type when placed under white light after UV-B treatment. In contrast, recovery in darkness or in light lacking photoreactivating blue light results in equal injury in uvr2-1 and wild type. The uvr2-1 mutant is unable to remove CPDs in vivo, and plant extracts lack detectable photolyase activity. This recessive mutation segregates as a single gene located near the top of chromosome 1, and is a structural gene mutation in the type II CPD photolyase PHR1. This mutant provides evidence that CPD photolyase is required for plant survival in the presence of UV-B light.

Apoenzymes↗