Biomedical subjects

H Li

Publications and source records attributed to H Li.

At least 19 recordsLinked to original sources

PubMed1992

Carboxamide group conformation in the nicotinamide and thiazole-4-carboxamide rings: implications for enzyme binding.

Ab initio computations (RHF/6-31G* parallel 3-21G*) were performed on the thiazole-4-carboxamide group found in the antitumor drug tiazofurin and its dehydrogenase-binding anabolite thiazole-4-carboxamide adenine dinucleotide (TAD). Results indicate that the carboxamide group is constrained in the conformation in which the amino group is cis-planar to the ring nitrogen. This finding is consistent with carboxamide conformations observed in crystal structures of the thiazole nucleosides. In contrast, ab initio computations on the nicotinamide and dihydronicotinamide rings found in the cofactors NAD+ and NADH indicate two stable conformations for the carboxamide group. This finding confirms previous computational studies and is consistent with results from a survey of the Cambridge Structural Database. Natural bond orbital analysis indicates that the low-energy carboxamide conformers of all three heterocycles are stabilized by a combination of electrostatic and charge transfer interactions. A survey of the Protein Data Bank indicates that the carboxamide group conformation in TAD is constrained to that favored by dehydrogenase-bound NAD(P)(H).

Adenine Nucleotides↗

PubMed1992

Casein kinase II protein kinase is bound to lamina-matrix and phosphorylates lamin-like protein in isolated pea nuclei.

A casein kinase II (CK II)-like protein kinase was identified and partially isolated from a purified envelope-matrix fraction of pea (Pisum sativum L.) nuclei. When [gamma-32P]ATP was directly added to the envelope-matrix preparation, the three most heavily labeled protein bands had molecular masses near 71, 48, and 46 kDa. Protein kinases were removed from the preparation by sequential extraction with Triton X-100, EGTA, 0.3 M NaCl, and a pH 10.5 buffer, but an active kinase still remained bound to the remaining lamina-matrix fraction after these treatments. This kinase had properties resembling CK II kinases previously characterized from animal and plant sources: it preferred casein as an artificial substrate, could use GTP as efficiently as ATP as the phosphoryl donor, was stimulated by spermine, was calcium independent, and had a catalytic subunit of 36 kDa. Some animal and plant CK II kinases have regulatory subunits near 29 kDa, and a lamina-matrix-bound protein of this molecular mass was recognized on immunoblot by anti-Drosophila CK II polyclonal antibodies. Also found associated with the envelope-matrix fraction of pea nuclei were p34cdc2-like and Ca(2+)-dependent protein kinases, but their properties could not account for the protein kinase activity bound to the lamina. The 71-kDa substrate of the CK II-like kinase was lamin A-like, both in its molecular mass and in its cross-reactivity with anti-intermediate filament antibodies. Lamin phosphorylation is considered a crucial early step in the entry of cells into mitosis, so lamina-bound CK II kinases may be important control points for cellular proliferation.

Amino Acid Sequence↗

PubMed1992

Chimeric DNA-RNA hammerhead ribozymes have enhanced in vitro catalytic efficiency and increased stability in vivo.

Subsequent to the discovery that RNA can have site specific cleavage activity, there has been a great deal of interest in the design and testing of trans-acting catalytic RNAs as both surrogate genetic tools and as therapeutic agents. We have been developing catalytic RNAs or ribozymes with target specificity for HIV-1 RNA and have been exploring chemical synthesis as one method for their production. To this end, we have chemically synthesized and experimentally analyzed chimeric catalysts consisting of DNA in the non-enzymatic portions, and RNA in the enzymatic core of hammerhead type ribozymes. Substitutions of DNA for RNA in the various stems of a hammerhead ribozyme have been analyzed in vitro for kinetic efficiency. One of the chimeric ribozymes used in this study, which harbors 24 bases of DNA capable of base-pairing interactions with an HIV-1 gag target, but maintains RNA in the catalytic center and in stem-loop II, has a sixfold greater kcat value than the all RNA counterpart. This increased activity appears to be the direct result of enhanced product dissociation. Interestingly, a chimeric ribozyme in which stem-loop II (which divides the catalytic core) is comprised of DNA, exhibited a marked reduction in cleavage activity, suggesting that DNA in this region of the ribozyme can impart a negative effect on the catalytic function of the ribozyme. DNA-RNA chimeric ribozymes transfected by cationic liposomes into human T-lymphocytes are more stable than their all-RNA counterparts. Enhanced catalytic turnover and stability in the absence of a significant effect on Km make chimeric ribozymes favorable candidates for therapeutic agents.

Amino Acid Sequence↗

PubMed1992

Genomic typing of hepatitis C viruses present in China.

Hepatitis C virus (HCV) genomic clones were obtained from the serum of Chinese HCV carriers using a polymerase chain reaction-based approach. Consensus sequences were derived from (1) the structural region (nt 1-1543) for one carrier, (2) the hypervariable region V (nt 1156-1233) from four carriers and (3) region V3 from four carriers. Region V3, located in the nonstructural domain NS5 (nt 7066-7137), has been previously shown to be a particularly good marker for the genomic typing of HCV isolates [Inchauspe et al., Proc. Natl. Acad. Sci. USA 88 (1991) 10292-10296]. Comparison of these sequences with sequences from geographically distinct HCV isolates indicates that Chinese HCV strains are closely related to, though distinguishable from, Japanese prototype strains. One amino acid motif, GGAA, located in region V, was found to be conserved only among Chinese isolates. This may define a new subgroup among HCV isolates.

Alanine Transaminase↗

PubMed1992

Gamma delta T-cell receptor repertoire in acute multiple sclerosis lesions.

Gamma delta T cells are a distinct lymphocyte population that can exhibit reactivity with heat shock proteins over-expressed at inflammatory sites. As gamma delta T cells may be involved in the central nervous system (CNS) inflammatory process in multiple sclerosis (MS), we examined T-cell populations in MS plaque tissue by quantitative immunohistochemistry and sequence analysis of T-cell antigen receptor (TCR) delta chains. Gamma delta T cells that express the variable (V) gene segments V delta 1, V delta 2, and V gamma 2 (V gamma 9) were found to accumulate in acute, demyelinating MS plaques and appeared to have undergone clonal expansion, most likely because of recognition of a specific CNS ligand. Further, 60-kDa and 90-kDa heat shock proteins (hsp60 and hsp90), which may be target antigens for autoreactive gamma delta T cells, were found to be expressed in normal CNS tissue and overexpressed in acute MS plaques. In acute plaques, hsp60 was found in foamy macrophages, while hsp90 was detected in reactive astrocytes. These results provide evidence for a role of gamma delta T cells in active stages of MS.

Base Sequence↗

PubMed1992

Cloning of two adult hamster globin cDNAs (alpha and beta major).

A cDNA library was prepared from poly(A) mRNA extracted from adult anemic hamster spleen erythroid cells. cDNA clones containing inserts coding for adult alpha and beta major globin chains were isolated. Their identity was confirmed by (a) translation of hybrid selected mRNA and (b) nucleotide sequence analysis of the inserts and comparison to the adult globin cDNAs of mouse, rabbit and human. Availability of sequences for embryonic (Li et al. (1992) Biochim. Biophys. Acta 1130, 218-220) and adult globin cDNAs (this report) will aid in investigations of the molecular mechanisms involved in the globin ontogeny of hamsters.

Amino Acid Sequence↗

PubMed1992

T cell receptor V alpha-V beta repertoire and cytokine gene expression in active multiple sclerosis lesions.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system with presumed autoimmune etiology. A recent study has suggested the presence of a restricted T cell receptor (TCR) V alpha repertoire in MS lesions. The presence of such a restricted TCR repertoire at the site of inflammation would have important consequences for the pathogenesis and the ultimate treatment of MS. To further characterize the TCR V alpha and V beta repertoire in MS plaque tissue, we examined a series of 26 histologically well-characterized central nervous system (CNS) tissue specimens from six MS patients as well as samples from five normal postmortem cases and a case of subacute sclerosing panencephalitis. RNA was extracted from frozen sections and cDNAs were amplified by polymerase chain reaction using primers for TCR V alpha (V alpha 1-18) and V beta (V beta 1-19) gene families. This analysis demonstrated a broad TCR V alpha-V beta repertoire in active lesions, while fewer TCR V genes were detected in chronic plaques and control samples. Even though a large number of TCR V alpha and V beta gene segments were present in the majority of active lesions, there were clear differences in the TCR repertoire between plaques from the same case, suggesting that local events influence the TCR repertoire at the level of T cell recruitment or T cell expansion. Examination of cytokine mRNAs demonstrated that IL-1 mRNA was present in the majority of acute and subacute plaques, while IL-2 and IL-4 mRNA were detected in only a few acute lesions. These data demonstrate that the TCR repertoire in MS plaques is polyclonal. However, autoreactive alpha/beta T cells thought to be critical in the initiation of the inflammatory process probably represent a minor fraction of T cells in active MS plaques and may use a limited number of TCR V gene segments for recognition of the autoantigen.

Acute Disease↗

PubMed1992

Cloning and sequence analysis of two embryonic beta-like globin cDNAs (y and z) of hamster.

A cDNA library was prepared from poly(A) mRNA extracted from 9-day hamster-yolk-sac erythroid cells. Two clones containing inserts coding for embryonic beta-like z or y globin-chains were isolated. Their identity was confirmed by (a) translation of hybrid selected mRNAs and (b) nucleotide sequence analysis of the inserts and comparison to the embryonic beta-like globin genes of Balb/c mouse. Availability of sequences for embryonic and adult globin cDNAs will aid in investigations of the molecular mechanisms of the globin switch in hamster YSEC.

Amino Acid Sequence↗

PubMed1992

Effects of p-chlorophenylalanine on thermoregulation and sleep in rats.

Sleep/waking and body temperature (Tb) were recorded in male rats in a 12:12 light-dark photoperiod at one of 3 ambient temperatures (Ta's): 20, 30, or 32 degrees C. After adaptation to the sleep recording chamber for at least 48 h, the rats were injected with saline at the beginning of lights-on (day S1). Twenty-four hours later (day P1), they were injected with PCPA (300 mg/kg, i.p.) and recordings continued for 4 more days (P2-P5). At these Ta's, hypothalamic 5-HT was depleted by 66-75% 30 h post-PCPA. Changes in both amplitude and acrophase of Tb depended on Ta. Compared to S1, amplitude was reduced on P2-P4 at 20 degrees C and on P3-P4 at 30 degrees C. Acrophase was advanced on P1-P3 at Ta 20 degrees C only. Sleep variables were generally independent of Ta and largely unchanged in the dark. In the light, amounts of slow-wave sleep (SWS) were depressed on P2-P4, number of bouts decreased on P3-P5 and percent nocturnality decreased on P2-P5. Bout length was depressed on P2 and lengthened on P4-P5. Acrophase was delayed on P2-P4 at Ta 30 degrees C. Amounts of rapid-eye-movement sleep (REMS) were depressed on P1-P3. REMS bout length decreased on P1-P3. The decreases in number of REMS bouts seen on P1-P3 depended on Ta. Changes in percent nocturnality and acrophase of REMS were minor. Waking----SWS transitions decreased on P3-P5 while SWS----REMS transitions were reduced on P1-P2. These results suggest that PCPA affects circadian aspects of both Tb and sleep, that 5-HT is important in the initiation of SWS bouts, and finally that the mechanisms by which 5-HT depletion affects Tb, SWS and REMS are different.

Animals↗

PubMed1992

Expression of growth hormone receptor by immunocytochemistry in rat molar root formation and alveolar bone remodeling.

Growth hormone (GH) may regulate tooth formation and bone remodeling associated with tooth eruption. This study reports the distribution of growth hormone receptor/binding protein in developing rat molars and adjacent alveolar bone by immunocytochemistry using well-characterized anti-growth hormone receptor monoclonal antibodies. These tissues represent an excellent model for studying the ontogenic changes that occur in odontogenic and osteogenic cells, as these cells are found in linear arrays displaying the various stages of morphological and functional differentiation, and differentiated function. Immunoreactivity was first seen in precementoblasts in contact with the epithelial root sheath, and preodontoblasts. However, growth hormone receptor immunoreactivity was associated primarily with the cytoplasm of odontogenic and osteogenic cells forming their respective matrices. Thus, cementoblasts and odontoblasts at sites of new matrix formation showed intense immunoreactivity whereas cementocytes and mature odontoblasts at later stages of tooth development were nonreactive. Osteoblasts engaged in intramembranous ossification in the alveolar bone were positive, although osteocytes and endosteal cells were immunonegative. Osteoclasts at sites of alveolar bone remodeling resorption were also immunopositive. These patterns of receptor expression parallel the ontogenic sequences of odontogenic and osteogenic cells and suggest that GH promotes the functional state of these cells. Our results also imply that GH may influence differentiation or differentiated functions associated with odontogenesis, osteogenesis, and bone remodeling independent of systemic insulin-like GF-I.

Alveolar Process↗

PubMed1992

Frequent spontaneous sister chromatid exchange in hepatocytes of transgenic mice harboring the SV40-T antigen gene.

In order to shed light on the causal mechanisms of hepatocarcinogenesis in the transgenic mouse into which the albumin-promotor-regulated SV40-T antigen gene has been introduced (T+ mouse), and especially on the frequent chromosomal aberrations seen in cultured hepatocytes and hepatocellular neoplasms derived from such animals, the frequency of sister chromatid exchange (SCE) and karyotype abnormalities were investigated in a hepatocyte primary culture system. Cells were obtained through collagenase perfusion from T+ mice at 16-18 days of age, when no morphological changes are apparent, and from nontransgenic littermates, and cultured in the presence of bromodeoxyuridine. SCE was seen in transgenic hepatocytes twice as frequently as in their normal counterparts. No karyotype abnormalities in terms of numerical change or gross aberration were detected at this phase. The results thus suggest mutagenic properties for the T antigen, which may play an important role in hepatocarcinogenesis in this transgenic mouse.

Animals↗

PubMed1992

Effects of surgical trauma on interleukin 2 production and interleukin 2 receptor expression.

To elucidate the mechanism of immunologic abnormalities induced by surgical trauma, we measured interleukin 2 (IL-2) production and IL-2 receptor expression in peripheral blood mononuclear cells from 16 patients with cholelithiasis. Compared with preoperative levels, IL-2 production and IL-2 receptor expression were significantly reduced on postoperative day 4, and the reduction was consistent with the suppression of lymphocyte proliferative response to phytohemagglutinin.

Adult↗

PubMed1992

Interleukin 2 production and its relationship with T lymphocyte subsets in patients with obstructive jaundice.

Sepsis remains a major risk in the high mortality and morbidity after surgery for obstructive jaundice. The reasons for the increased susceptibility to infection are unknown. This study examined interleukin 2 (IL-2) production and the lymphocyte response to PHA mitogen in 31 patients with obstructive jaundice. Among them, 18 patients were simultaneously investigated by enumeration of T lymphocyte subsets in peripheral blood with APAAP technique. The results showed that the patients had significantly decreased IL-2 production and lymphocyte response to PHA mitogen. The percentage of Leu 3a (helper/inducer T cell) in the patients was significantly lower than that in normal controls. Leu 3a/Leu 2a (suppressor/cytotoxic T cell) ratio was significantly lower in these patients. The reduction of IL-2 production correlated significantly with the suppression of lymphocyte proliferation but not with the percentage of Leu 3a cells. From these results, it may be suggested that the reduction of IL-2 production in the patients with obstructive jaundice is an important reason for the suppression of T lymphocyte proliferative response, not merely a reflection of the decrease of helper T cells.

Adult↗

PubMed1992

Hormonal profile of the menstrual cycle in Chinese women after tubal sterilization.

Ten women after tubal sterilization were studied for the hormonal profile of the menstrual cycle. They had undergone sterilization procedures, on the average 5.3 years (range 1.5-10 years) earlier. The serum concentrations of LH, FSH, prolactin, estradiol and progesterone were measured by RIA in daily blood samples of a complete menstrual cycle. Another ten normal women were studied at the same time and were used as the control group. There were no significant differences in the hormonal patterns of the menstrual cycle between the two groups. There was a significantly lower LH level in the early luteal phase of the tubal ligation group compared to the control group. Also, a significantly lower E2 luteal peak compared to the preovulatory peak was observed in the tubal ligation group. The physiological significance of these minor changes is not clear. Only one out of ten women in the tubal ligation group, who had undergone sterilization 1.5 years prior, showed a deficiency in luteal function, but her ovulatory function and menstrual cycle appeared normal. This study indicates that normal hormonal profiles are retained after tubal sterilization.

Adult↗

PubMed1992

Effect of chronic administration of dexfenfluramine on blood pressure in salt-sensitive rats.

Chronic administration of dexfenfluramine, at a relatively low daily dose, slowed the development of salt-induced elevation of blood pressure in salt-sensitive (Dahl DS and Rapp SS) rats. This effect could not be accounted for by drug-related anorexia alone. Elevated serotonin activity, possibly in the brain, may underlie this antihypertensive action of dexfenfluramine.

Animals↗

PubMed1992

Stage dependent development of intraocular cochlear grafts.

The intraocular grafting technique was employed to test whether the peripheral hearing organ, the cochlea, is capable of survival and an organized development in total isolation from the temporal bone. Rat cochleae obtained from gestation day 16, postnatal day 1 and 7 were chosen for transplantation into the anterior chamber of the eye of adult Sprague-Dawley rats. The grafts were maintained in the anterior chamber for 6, 10, or 15 weeks survival time. The salient features of this study is that 1) cochlear structures survive and, 2) the cochlear structures develop beyond their pre-grafted stage as determined from light and electron micrographs. In the present study, the grafts obtained at gestation day 16 (GD 16) and postnatal day 1 gave a much higher rate of survival and development than the postnatal day 7 grafts. In addition, grafts maintained for either 6 or 10 weeks had a better survival rate than those grafts left for 15 weeks. It is estimated from light and electron micrographs that the gestation day 16 otocysts that were maintained for 10 weeks, developed to the equivalent of a postnatal day 10 cochlea. The grafts obtained from postnatal day one rats developed to the equivalent of approximately 14 days after birth. Interestingly, in the absence of synaptic contact, the inner and outer hair cells were capable of survival, differentiation and maturation. It remains to be determined if the spiral ganglion cells require additional neurotrophic factors for survival in the anterior chamber of the eye.

Animals↗

PubMed1992

Gene-centromere linkage mapping by PCR analysis of individual oocytes.

We describe a general method of determining the recombination fraction between a polymorphic locus and the centromere in any species where single oocytes can be obtained. After removal of the first polar body, each oocyte is analyzed by PCR. The frequency of oocytes heterozygous at the polymorphic locus is used to estimate the recombination fraction. We estimate a recombination fraction of 0.15 between the mouse major histocompatibility complex (H-2) and the centromere of chromosome 17.

Animals↗

PubMed1992

A genetic linkage map of 96 loci on the short arm of human chromosome 3.

We constructed a genetic map of 96 loci on the short arm of human chromosome 3 (3p) in 59 families provided by the Centre d'Etude du Polymorphisme Humaine (CEPH). Twenty-nine continuously linked loci were placed on the map with likelihood support of at least 1000:1; one locus, D3S213, was placed on the map with likelihood support of 871:1; D3Z1, an alpha satellite centromeric repeat probe, was placed on the map with likelihood support of 159:1; 65 loci were assigned regional locations. The average heterozygosity of the uniquely ordered markers was 49%. The map extends from 3p26, the terminal band of 3p, to the centromere (from D3S211 to D3Z1). Multipoint linkage analysis indicated that the male, female, and sex-averaged maps extend for 102, 147, and 116 cM, respectively. The mean genetic distance between uniquely ordered loci on the sex-averaged map was 4.0 cM. Probe density was greatest for the region of 3p between D3F15S2e and the telomere. The sex-averaged map contained two intervals greater than 10 cM. Seventeen probes were localized by fluorescence in situ hybridization. The loci described in this report will be useful in building an integrated genetic and physical map of this chromosome.

Chromosome Mapping↗