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H Han

Publications and source records attributed to H Han.

At least 181 records · Page 10Linked to original sources
PubMed1992

Cloning, pharmacological characterization, and chromosome assignment of the human dopamine transporter.

We have screened a human substantia nigra cDNA library with probes derived from the rat dopamine transporter. A 3.5-kilobase cDNA clone was isolated and its corresponding gene was located on the distal end of chromosome 5 (5p15.3). This human clone codes for a 620-amino acid protein with a calculated molecular weight of 68,517. Hydropathicity analysis suggests the presence of 12 putative transmembrane domains, a characteristic feature of sodium-dependent neurotransmitter carriers. The rat and the human dopamine transporters are 92% homologous. When permanently expressed in mouse fibroblast Ltk- cells, the human clone is able to induce a saturable, time- and sodium-dependent, dopamine uptake. This transport is blocked by psychostimulant drugs (cocaine, l- and d-amphetamine, and phenyclidine), neurotoxins (6-hydroxydopamine and N-methyl-4-phenylpyridine (MPP))+), neurotransmitters (epinephrine, norepinephrine, gamma-aminobutyric acid, and serotonin), antidepressants (amitriptyline, bupropion, desipramine, mazindol, nomifensine, and nortriptyline), and various uptake inhibitors (mazindol, GBR 12783, GBR 12909, and amfonelic acid). The rank orders of the Ki values of these substances at the human and the rat dopamine transporters are highly correlated (r = 0.998). The cloning of DNA human dopamine transporter gene has allowed establishment of a cell line stably expressing the human dopamine transporter and, for the first time, an extensive characterization of its pharmacology. Furthermore, these newly developed tools will help in the study of the regulation of dopamine transport in humans and in the clarification of the potential role of the dopamine transporter in a variety of disease states.

Amino Acid Sequence↗
PubMed1991

Role of divalent cations in the 3',5'-exonuclease reaction of DNA polymerase I.

X-ray studies of the proofreading 3',5'-exonuclease site of the large (Klenow) fragment of DNA polymerase I have detected a binuclear metal complex consisting of a pentacoordinate metal (site A) which shares a ligand, Asp-355, with an octahedral metal (site B) [Freemont, P. S., Friedman, J. M., Beese, L. S., Sanderson, M. R., & Steitz, T. A. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 8924-8928; Beese, L. S., & Steitz, T. A. (1991) EMBO J. 10, 25-33]. Kinetic studies of the activation of the 3',5'-exonuclease reaction by Co2+, Mn2+, or Mg2+, at low concentrations of DNA, reveal sigmoidal activation curves for the three metal ions with Hill coefficients of 2.3-2.4 and K0.5 values of 16.6 microM, 4.2 microM, and 343 microM, respectively. The binding of Co2+ to the enzyme results in the appearance of an intense visible absorption spectrum of the metal ion with maxima at 633, 570, and 524 nm and extinction coefficients of 190, 194, and 150 M-1 cm-1, respectively, suggesting the formation of a pentacoordinate Co2+ complex. Optical titration with Co2+ yields a sigmoidal titration curve which is best fit by assuming the cooperative binding of three Co2+ ions with a K0.5 of 39.9 microM, comparable to the value of 16.6 microM obtained kinetically. Displacement of Co2+ by 1 equiv of Zn2+, which binds tightly to the A site of the 3',5'-exonuclease, shifts the optical spectrum to 524 nm and lowers the extinction coefficient to 30 -1 cm-1, indicative of octahedral coordination.2+ the formation of the binuclear complex.

Binding Sites↗
PubMed1991

Trans-splicing as a possible molecular mechanism for the multiple isotype expression of the immunoglobulin gene.

We analyzed the molecular mechanism for the immunoglobulin (Ig) multiple isotype expression using a transgenic mouse (TG.SA) model system. Though most of the endogenous mu chain expression was excluded by the expression of the human rearranged mu transgene in the TG.SA mouse, a significant portion of splenic B lymphocytes could express the transgenic human IgM and endogenous mouse IgG simultaneously after stimulation with lipopolysaccharide and interleukin 4. The fluorescence-activated cell sorter-purified population of the human IgM+/mouse IgG+ cells expressed mRNA that consisted of properly spliced sequences of the transgenic VHDJH and the endogenous mouse C gamma genes (trans-mRNA), together with the transgenic human mu mRNA and germline transcripts of the mouse C gamma gene, without apparent rearrangement of the transgene. We also found that a lymphoma tumor, derived from the cross between the TG.SA mouse and another transgenic mouse carrying Ig H chain enhancer-driven c-myc oncogene, expressed about equal levels of the trans-mRNA and the transgenic mu mRNA without DNA rearrangement in either the transgene or the endogenous mouse switch region. These findings strongly support our previous proposal that the trans-splicing can account for the multiple isotype expression in this transgenic model and also suggest that novel molecular mechanism(s) might be involved in this reaction.

Animals↗
PubMed1991

Chronobiologic approach to beat-to-beat variations of cultured murine myocardial cells.

An earlier demonstration of a circadian rhythm in rat atria by others is complemented herein by observations in culture: A single murine myocardial cell and two sets of grouped cells beating in culture for several days reveal several features of an anticipated, presumably built-in spectrum of multifrequency rhythms and trends, the chronome. Circadian and about 12-h (circasemidian) components are modulated by an approximately 84-h (circasemiseptan) component, which cannot be separated from trends in view of the brevity of the series. The circumstance under which the culture is aging and in which fibroblasts proliferate is a further complication that limits the findings to a single cycle reproduced in three separate cultures. Whether it is a rhythm that repeats itself of a response to placement into culture, an approximately 3.5-d component in the beating of myocardial cells in culture is to be aligned with a very prominent similar component found in the incidence of 85,819 human myocardial infarctions.

Animals↗
PubMed1991

Regulated expression of immunoglobulin trans-mRNA consisting of the variable region of a transgenic mu chain and constant regions of endogenous isotypes.

Our previous work demonstrated that chimeric immunoglobulin mRNAs (trans-mRNAs) composed of a transgenic VHDJH region and endogenous CH sequences could be synthesized, most likely by a trans-splicing mechanism, in a transgenic line carrying a rearranged human membrane-type mu chain gene. In this study we further investigated regulation of trans-mRNA expression. Regulated expression of different gamma subclasses of trans-mRNA was similar to that of class switching: IL-4 together with lipopolysaccharide (LPS) predominantly increased the amount of gamma 1 trans-mRNA whereas LPS alone mainly induced gamma 3 and gamma 2b trans-mRNAs. Expression of the gamma class trans-mRNAs was preceded by germline transcription from the corresponding CH genes, but the co-existence of such germline transcripts and transgene transcripts was not sufficient for trans-mRNA production. Transforming growth factor-beta induced germline transcripts of the alpha chain CH gene but had no obvious effects on alpha trans-mRNA induction. Both C alpha gene alleles were used in trans-mRNA but in different frequencies. We could also detect trans-mRNA expression in another transgenic mouse line which carries a rearranged mouse VHDJH-C mu gene. These results indicate that trans-mRNA synthesis is not restricted to either a particular transgenic line or an isotype, but is a general mechanism to express a second isotype with the VH regions of rearranged mu chain transgenes.

Animals↗
PubMed1990

Cyclosporin A suppresses cisplatin-induced oncogene expression in human cancer cells.

Most cancer chemotherapeutic agents are designed to damage DNA directly or indirectly. One mechanism of cellular resistance to these agents is enhanced DNA repair. Human ovarian carcinoma cells resistant to cisplatin (A2780DDP) respond to cisplatin treatment with a 3-6-fold increase in gene expression for oncogenes, DNA repair enzymes and enzymes necessary for the synthesis of thymidine. Cyclosporin A has been shown to reverse drug resistance, but its mechanism of action is unclear. In this study, weekly exposures of A2780DDP cells to cyclosporin A resulted in the evolution of a revertant cell line A2780DDP/CSA that was sensitive to cisplatin again and suppressed the induction of genes necessary for the repair of drug-induced DNA damage.

Cisplatin↗
PubMed1990

Diminished superoxide production of synovial fluid neutrophils in patients with rheumatoid arthritis following piroxicam treatment.

Superoxide production by polymorphonuclear leukocytes (PMNs) and macrophages was inhibited by piroxicam and other non-steroidal anti-inflammatory drugs both in vitro and in vivo. Hitherto, data have only been available on blood PMNs and macrophages. In order to investigate the situation in the joint, PMNs were isolated from synovial fluid before and after 24 h of piroxicam treatment in patients with rheumatoid arthritis. Isolated PMNs were stimulated with PMA and serum-treated zymosan. The capacity of synovial fluid PMNs to produce superoxide decreased by 30% after piroxicam treatment. A similar decrease was found for blood PMNs. No difference in superoxide production was found between blood PMNs and synovial fluid PMNs which were obtained simultaneously. From the fact that the piroxicam concentration in synovial fluid was 40% of the serum value, it can be concluded that piroxicam probably became bound to PMNs before they entered the joint cavity. These results indicate that at the site of the inflammation the superoxide production by PMNs is inhibited by piroxicam treatment. The inhibition of superoxide production is probably important in the effect of piroxicam and other non-steroidal anti-inflammatory drugs in rheumatoid arthritis.

Arthritis, Rheumatoid↗
PubMed1989

RFLP analysis of HLA-DR beta and -DQ beta genes in the Korean patients with insulin-dependent diabetes mellitus.

Human genomic DNA samples from 19 Korean patients and 31 controls of known serological DR antigen specificity were studied for insulin-dependent diabetes mellitus (IDDM)-associated variation in HLA-DR beta and -DQ beta restriction fragment length polymorphisms (RFLPs). Genotyping allowed for accurate assignment of HLA-DR types. For HLA-DRw6, a 12kb/DR beta/Taq I fragment was decreased in Korean IDDM (p less than 0.05). However, we could not find an increased frequency of a 12kb/DQ beta/Bam HI fragment or decreased frequency of a 3.7kb/DQ beta/Bam HI fragment in Korean IDDM. These results suggest a possible protective role of the HLA-DRw6 specificity in IDDM, irrespective of ethnic background, the absence of a specific DQ beta RFLP pattern associated with IDDM in Koreans, and the difference of the Korean population in the genetic of IDDM, compared to the Caucasoid population.

Asian People↗
PubMed1989

[The blocking and partial agonistic actions of jatrorrhizine on alpha-adrenoceptors].

Jatrorrhizine (Jat) competitively antagonised the effects of phenylephrine on rabbit aortic rings and clonidine on electrically stimulated rat vas deferens with pA2 values of 5.73 and 5.86, respectively. It (5 mg/kg iv) also diminished the pressor responses induced by either thoracic sympathetic stimulation (T7-T9) or noradrenaline (2 micrograms/kg iv) in pithed rats. Furthermore the dose-response curves for methoxamine and B-HT 920 were shifted parallely to the right by iv Jat 10 mg/kg. Below 1 mumol/L, Jat alone showed the depression of the contraction of rat vas deferens stimulated electrically. This effect, however, was less evident at higher concentrations of Jat and was reversed by yohimbine (0.1 mumol/L). Similarly, at very low concentration (1 nmol/L), Jat shifted the dose-response curves for clonidine parallely to the left. In pithed rats, the increase of heart rate evoked with electrical stimulation of spinal segment (C7-T1) was attenuated by Jat (1 mg/kg) and clonidine (30 micrograms/kg), but argumented by large doses of Jat (10 mg/kg) and yohimbine (50 micrograms/kg). The above results showed that: firstly, Jat has blocking actions on both alpha 1- and alpha 2-adrenoceptors, which may be relevant to its hypotensive and anti-arrhythmic actions; secondly, the demonstration of dualistic actions of Jat on adrenoceptors, which has never been documented before, may be also present in other homologues of the protoberberines.

Adrenergic alpha-Agonists↗
PubMed1988

Complement (C3) metabolism in rheumatoid arthritis in relation to the disease course.

Metabolic turnover studies of the third component of complement, C3, were performed in 23 patients with rheumatoid arthritis (RA) to get a direct insight in the dynamics of complement synthesis and catabolism. Results of these turnover studies were related to the serum level of the total amount of C3 as well as to that of the activation product C3d. A hypercatabolism of C3 was observed in 12 of the 23 patients studied. Six of these 12 patients showed signs of extra-articular RA; only one patient with extra-articular manifestations had a normal catabolism of C3. Decreased serum levels of C3 were not found in any of the patients with a hypercatabolism of C3, indicating that the accelerated turnover was compensated by an increased synthesis. In RA patients levels of the activation product C3d could not correlate with the turnover of C3. However, in selected RA patients without signs of nodules or extra-articular manifestations, they could. Thus, our results indicate that serum levels of C3 and C3d do not reflect C3 metabolism in RA patients. Furthermore, the existence of extra-articular manifestations is accompanied by a more pronounced activation of the complement system.

Arthritis, Rheumatoid↗
PubMed1988

Significance of the HLA molecular structure to transplantation.

1. Residues in the first, second, and third domains of HLA-A,B,C, and the first domain of DR beta, DQ alpha, and DQ beta molecule have been assigned to unique A,B,C or DR specificities from the known amino acid sequences. Antibodies were noted to correlate with most of these variable amino acid residues. 2. We therefore conclude that most of the variable residues in the first domain function as immunogens against which the antibodies had been elicited. 3. If the variants at these positions are immunogens, then it follows that matching for transplantation should be done by considering mismatched amino acids rather than the private specificities, as performed today. 4. Molecular matching cannot be performed immediately for the HLA-A,B,C specificities since many specificities are not yet sequenced. For the DR and DQ specificities, the sequences are established, but antisera identifying the subtypes of DR and DQ are only now becoming available. Once patients are typed for the 23 DR beta alleles, 8 DQ alpha alleles and 13 DQ beta alleles, matching should be feasible. 5. Molecular matching combines both public and private specificity matching since it assumes that both types of antigens are distinct. A single extended DR mismatch may involve as many as 76 amino acid residues of mismatch. 6. True cross-reactivity of the HLA molecules can eventually be established through structural studies. Most of the previously described "cross-reactivities" are likely to be shared determinants.

Amino Acid Sequence↗
PubMed1987

An analysis of the levels of complement components in the synovial fluid in rheumatic diseases.

A linear relationship between the synovial fluid to serum concentration ratios and log molecular weight was found for six plasma proteins, which are largely synthesized by the liver. Production or utilization of a given protein in the joint can, therefore, be determined by its deviation from the calculated diffusion line. Based on this diffusion model the role of the complement system was investigated in the joint effusions of 48 patients with rheumatoid arthritis (RA), 6 patients with osteoarthritis (OA) and 7 patients with meniscus lesions (ML). Among these three groups quantitative differences were found in the metabolism or utilization of several complement components, based on the fact that the ratios were lower than expected for diffusion of proteins of similar molecular weight. The ratios for the RA group were the lowest. In the three patient groups, results showed increased consumption mainly of C3 and C4 locally in the joint. The existence of a real complement activation in the joints of the three different patient groups was further proved by the elevated levels of C3 breakdown products (C3d). Overall this kind of calculation provides us with a method for studying the role of other proteins which may be important in the inflammatory process of the joint.

Arthritis, Rheumatoid↗