PubMed Health⌕ Search

Biomedical subjects

T H Tan

Publications and source records attributed to T H Tan.

At least 19 recordsLinked to original sources
PubMed1992

The c-rel protooncogene product c-Rel but not NF-kappa B binds to the intronic region of the human interferon-gamma gene at a site related to an interferon-stimulable response element.

Interferon-gamma (IFN-gamma) is an important immunoregulatory protein that is expressed usually only in large granular lymphocytes and T cells. The gene encoding IFN-gamma was previously found to contain an intronic enhancer element that was not tissue-specific in its activity, despite the restricted expression of the intact IFN-gamma-encoding gene. Using nuclear extracts from the human T-cell line Jurkat, we have now identified two protein-binding regions in this intronic enhancer element. One of the protected regions has strong partial identify to the NF-kappa B site present in the promoter region of the human interleukin 2-encoding gene. Based on this observation and recent reports of the interaction of the c-rel protooncogene product (c-Rel) with NF-kappa B sites, we determined whether c-Rel could interact with the intronic enhancer element in the human IFN-gamma genomic DNA. Most surprisingly, gel-shift analysis, using c-Rel expressed in Escherichia coli established that c-Rel binds specifically to the IFN-gamma intronic DNA but not to the interleukin 2-like NF-kappa B site. Additional studies with antibodies prepared against c-Rel peptides verified specificity of the interaction of c-Rel with this binding site. In addition, using an affinity-purified p50 subunit of the NF-kappa B complex, we observed that the p50 protein did not bind to this additional c-Rel-binding site. Furthermore, nucleotide sequence analysis of this DNA region revealed a strong similarity of the additional c-Rel-binding site to a previously identified IFN-stimulable response element. These data show that c-Rel can interact with DNA regions distinct from that recognized by NF-kappa B and may, in fact, be involved in transcriptional regulation of the IFN-stimulable genes via the IFN-stimulable response element.

Base Sequence↗
PubMed1992

Expression and characterization of the trans-activating protein Tax of human T-cell leukemia virus type I in Saccharomyces cerevisiae.

The trans-activator protein Tax of human T-cell leukemia virus type I (HTLV-I) stimulates transcription of the viral genome from the long terminal repeat. With a reporter HIS4TATA::lacZ fusion gene, the transcriptional activity of the Tax-responsive element in the long terminal repeat was tested in Saccharomyces cerevisiae. We found that fragments containing the 21-bp repeat of the HTLV-I enhancer stimulate synthesis of beta-galactosidase activity 15- to 20-fold. To test the ability of the Tax protein to trans activate the HTLV-I enhancer in yeast cells, the pX region of HTLV-I, encoding the Tax protein, was cloned under the control of the yeast GAL1 promoter. The expressed Tax protein is localized in the nucleus and associated with the yeast nuclear matrix fraction. In yeast cells that contained the integrated tax gene, two- to sixfold stimulation of expression from the HTLV-I enhancer was detected at the early stages of tax induction. This in vivo reconstitution system provides a new approach for examining the host factor(s), the signal transduction mechanism(s), and the role of nuclear architecture involved in Tax-mediated trans activation.

Blotting, Western↗
PubMed1992

Kappa B site-dependent activation of the interleukin-2 receptor alpha-chain gene promoter by human c-Rel.

The cis-acting control elements of the interleukin-2 receptor alpha-chain (IL-2R alpha) gene contain a potent kappa B-like enhancer whose activity can be induced by various mitogenic stimuli. Recent cloning of the p50 and p65 subunits of the kappa B-binding protein NF-kappa B complex revealed a striking sequence homology of these proteins with the c-rel proto-oncogene product (c-Rel). On the basis of this homology, we examined the potential role of c-Rel in controlling IL-2R alpha transcription. We now demonstrate that the recombinant human c-Rel protein binds to the kappa B element in the IL-2R alpha promoter and results in alteration of the DNA structure in the adjacent downstream regulatory elements containing the CArG box and the GC box. We found that human c-Rel can activate transcription from the IL-2R alpha promoter, but not the kappa B-containing human immunodeficiency virus type 1 promoter, upon cotransfection into Jurkat T cells. Furthermore, truncation of the carboxyl terminus of c-Rel results in a c-Rel mutant (RelNA) that (i) localizes exclusively in the nucleus and (ii) acts in synergy with wild-type c-Rel in activating transcription from the kappa B site of the IL-2R alpha promoter. Finally, induction of surface IL-2R alpha expression coincides with the induced levels of endogenous c-Rel and induced c-Rel binding to the IL-2R alpha kappa B site. Our study identified c-Rel as one component of the Rel/NF-kappa B-family proteins involved in the kappa B-dependent activation of IL-2R alpha gene expression. Furthermore, our results suggest that a Re1NA-like cellular factor (e.g., NF-kappa B p50 or p49 subunit) acts in synergy with c-Re1 during T-cell activation.

Base Sequence↗
PubMed1991

A nonradioactive screening method for cloning genes encoding sequence-specific DNA binding proteins.

We have developed a novel nonradioactive screening method for cloning genes encoding sequence-specific DNA binding proteins. This method is derived from previously described protocols developed for the same purpose by using radioactively labeled DNA probes containing protein recognition sequences. This nonradioactive strategy relies upon the use of a small hapten, digoxigenin. Fusion proteins expressed from the recombinant bacteriophage lambda gt11/lambda ZAP are immobilized on nitrocellulose filters and probed with digoxigenin-labeled double-stranded DNA as a ligand. The specifically bound DNA probes can be detected through sequential incubations with antibody-enzyme conjugate and enzyme substrates. This technique has been successfully utilized to isolate several cDNA clones encoding DNA binding proteins.

Bacteriophage lambda↗
PubMed1990

An evaluation of 1987 tuberculosis deaths in Singapore.

Tuberculosis was responsible for 177 deaths in 1987. This study evaluated the accuracy of tuberculosis death certification by hospital doctors and general practitioners in 111 cases where hospital case-notes were available for verification. It revealed that only 49 cases (44%) died of active tuberculosis, 12 (11%) died of late effects of tuberculosis and 41 (37%) died of causes unrelated to tuberculosis. There was no evidence of tuberculosis in 9 cases. Only 39 cases (56%) of active tuberculosis certified by hospital doctors were correct compared to 10 (24%) certified by general practitioners. Hospital doctors certified 6 out of 9 deaths which had no evidence of tuberculosis. The actual tuberculosis mortality rate was estimated to be between 1.9 and 4.9 per 100,000 instead of the officially published 6.8 per 100,000 for 1987.

Adolescent↗
PubMed1989

Utilization of signal transduction pathway by the human T-cell leukemia virus type I transcriptional activator tax.

The human T-cell leukemia virus type I (HTLV-I) trans-activator (tax)-inducible enhancer was localized to three copies of 21-base-pair repeats within the long terminal repeat. Interestingly, the TGACG motif found in the center of the 21-base-pair tax-responsive element (TRE) is also present in the cyclic AMP (cAMP)-responsive elements (CREs) and activating transcription factor (ATF)-binding sites. In this study, we demonstrate that the three TRE-binding proteins, TREB-1, TREB-2, and TREB-3, also bind to various CREs and ATF-binding sites and that the TREs can confer upon a heterologous promoter responsiveness to various inducing agents, including tax, cAMP, and E1a. Furthermore, the transcriptional activation of the HTLV-I promoter by tax can be inhibited by several protein kinase inhibitors, including sangivamycin. Our results indicate that the TREs, CREs, and ATF-binding sites are similar cis-acting elements and further suggest (i) that the transcriptional activation of the HTLV-I promoter by tax involves the action of a protein kinase and (ii) that induction by tax, cAMP, and E1a might be mediated by distinct factors or kinases.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Purification and characterization of multiple nuclear factors that bind to the TAX-inducible enhancer within the human T-cell leukemia virus type 1 long terminal repeat.

Within the human T-cell leukemia virus type I promoter, there are three copies of a 21-base-pair repeat (hereafter called the tax-responsive element [TRE]) that both contributes to basal promoter activity and mediates induction by the viral activator TAX. We have identified and separated three nuclear proteins that interact with the TRE. The TRE-binding protein designated TREB-3 bound more avidly to a multimerized TRE than to a single-copy TRE, while the other two TRE-binding proteins, TREB-1 and TREB-2, bound equally well to either TRE. TREB-1 has been purified to near homogeneity, and binding activity was localized to a protein of 35 to 43 kilodaltons. The affinity-purified TREB-1 activated transcription from the human T-cell leukemia virus type I promoter in vitro. The purified TREB-1 fraction contained activating transcription factor binding activity and showed a cooperative interaction with the TATA-binding factor (TFIID) on the adenovirus E4 promoter.

Base Sequence↗
PubMed1989

A comparative study of Japanese and British BCG vaccine strains in newborn infants.

A prospective study on the British and Japanese BCG vaccines in newborn infants was carried out in which 317 and 285 infants were randomly allocated and vaccinated with the British and Japanese BCG vaccines, respectively. Four follow-up examinations were carried out with an average of 98% of the study cohort attending all sessions. About half the infants did not produce any visible response at the end of the first week. All, by the end of the third month, had characteristic BCG scars with an average diameter of 4.6 mm. A Mantoux test was carried out at six months. A mean skin induration of 7.2 mm (SD 5.3 mm) was recorded. Significantly higher proportions of infants given Japanese BCG were found to be tuberculin convertors (74.7%) when compared to those given British BCG (51.4%). Breast-feeding practices and the mothers' tuberculin status did not influence markedly their infants response to tuberculin.

BCG Vaccine↗
PubMed1989

[Case report on the treatment of the Angle's Class III malocclusion using Wunderer Activator and multi-vertical loop arch wire].

Class III malocclusions are usually related to growth and mandibular posture, so we must detect the exact causes of mesioclusion i.e., functional, skeletal, or combind from the start. Functional mesioclusion is easily managed but skeletal mesioclusion is usually more difficult than functional cases. The author and coworkers treated this case using the Wunderer Activator and TMA multivertical loop arch wire. Therefore, we got good results and the results were as follows. 1. Anterior cross-bite was corrected, therefore facial profile was improved. 2. Posterior occlusal seating was improved. 3. Down and backward rotation of mandible occurred.

Activator Appliances↗
PubMed1989

Significance of the tuberculin test in Singapore.

The standard tuberculin test used by all Singapore government hospitals and institutions is the intradermal Mantoux test using 1 TU of PPD RT23 with Tween 80, and read 72 hours later. There is almost 100% BCG coverage in Singapore children for many years, and therefore the tuberculin skin reaction must be interpreted with special consideration. Taking 8 mm and above as positive, six month old infants vaccinated at birth gave a positive rate of 42% and a mean reaction size of 5.89 mm. The reaction appeared to wane rapidly and among 6 year old school children the positive rate dropped to 12% and the mean size to 2.38 mm. By the age of 11 years, the children showed a positive rate of 36% and a mean size of 6.27 mm. A further increase is observed in 15 year old children, the positive rate being 88% and mean size 13.28 mm. Among tuberculosis contacts, the positive rate and mean size of the tuberculin reaction are generally higher, especially in the younger age groups. Tuberculosis patients above 15 years old were observed to be practically all positive reactors with a mean size of at least 16 mm.

Adolescent↗
PubMed1988

Cellular transcription factors and regulation of IL-2 receptor gene expression by HTLV-I tax gene product.

Expression of the interleukin-2 receptor (IL-2R alpha) gene is activated by the transcriptional activator protein, Tax (previously referred to as the tat gene product), encoded by the human T-cell leukemia virus (HTLV-I). Multiple protein binding sites for specific DNA-protein interactions were identified over the upstream IL-2R alpha transcriptional regulatory sequences. However, only one region, which includes the sequence motif GGGGAATCTCCC, was required for activation by both the tax gene product and mitogenic stimulation. Remarkably, this sequence also bound the nuclear factor NF kappa B, which is important for induction of kappa-immunoglobulin gene expression. A model is presented whereby regulation of cellular gene expression by the HTLV-I tax gene product occurs via an indirect mechanism that may involve a post-translational modification of preexistent cellular transcription factors.

Base Sequence↗
PubMed1988

Activating mutations for transformation by p53 produce a gene product that forms an hsc70-p53 complex with an altered half-life.

The 11-4 p53 cDNA clone failed to transform primary rat fibroblasts when cotransfected with the ras oncogene. Two linker insertion mutations at amino acid 158 or 215 (of 390 amino acids) activated this p53 cDNA for transformation with ras. These mutant cDNAs produced a p53 protein that lacked an epitope, recognized by monoclonal antibody PAb246 (localized at amino acids 88 to 110 in the protein) and preferentially bound to a heat shock protein, hsc70. In rat cells transformed by a genomic p53 clone plus ras, two populations of p53 proteins were detected, PAb246+ and PAb246-, which did or did not bind to this monoclonal antibody, respectively. The PAb246- p53 preferentially associated with hsc70, and this protein had a half-life 4- to 20-fold longer than free p53 (PAb246+). These data suggest a possible functional role for hsc70 in the transformation process. cDNAs for p53 derived from methylcholanthrene-transformed cells transform rat cells in cooperation with the ras oncogene and produce a protein that bound with the heat shock proteins. Recombinant clones produced between a Meth A cDNA and 11-4 were tested for the ability to transform rat cells. A single amino acid substitution at residue 132 was sufficient to activate the 11-4 p53 cDNA for transformation. These studies have identified a region between amino acids 132 and 215 in the p53 protein which, when mutated, can activate the p53 cDNA. These results also call into question what the correct p53 wild-type sequence is and whether a wild-type p53 gene can transform cells in culture.

Amino Acid Sequence↗
PubMed1986

Identification of the p53 protein domain involved in formation of the simian virus 40 large T-antigen-p53 protein complex.

An expression vector utilizing the enhancer and promoter region of the simian virus 40 (SV40) DNA regulating a murine p53 cDNA clone was constructed. The vector produced murine p53 protein in monkey cells identified by five different monoclonal antibodies, three of which were specific for the murine form of p53. The murine p53 produced in monkey cells formed an oligomeric protein complex with the SV40 large tumor antigen. A large number of deletion mutations, in-frame linker insertion mutations, and linker insertion mutations resulting in a frameshift mutation were constructed in the cDNA coding portion of the p53 protein expression vector. The wild-type and mutant p53 cDNA vectors were expressed in monkey cells producing the SV40 large T antigen. The conformation and levels of p53 protein and its ability to form protein complexes with the SV40 T antigen were determined by using five different monoclonal antibodies with quite distinct epitope recognition sites. Insertion mutations between amino acid residues 123 and 215 (of a total of 390 amino acids) eliminated the ability of murine p53 to bind to the SV40 large T antigen. Deletion (at amino acids 11 through 33) and insertion mutations (amino acids 222 through 344) located on either side of this T-antigen-binding protein domain produced a murine p53 protein that bound to the SV40 large T antigen. The same five insertion mutations that failed to bind with the SV40 large T antigen also failed to react with a specific monoclonal antibody, PAb246. In contrast, six additional deletion and insertion mutations that produced p53 protein that did bind with T antigen were each recognized by PAb246. The proposed epitope for PAb246 has been mapped adjacent (amino acids 88 through 109) to the T-antigen-binding domain (amino acids 123 through 215) localized by the mutations mapped in this study. Finally, some insertion mutations that produced a protein that failed to bind to the SV40 T antigen appeared to have an enhanced ability to complex with a 68-kilodalton cellular protein in monkey cells.

Animals↗
PubMed1986

The bioavailability of isoniazid, rifampin, and pyrazinamide in two commercially available combined formulations designed for use in the short-course treatment of tuberculosis.

The bioavailability of isoniazid, rifampin, and pyrazinamide in 2 combined formulations of the 3 drugs (Rifater) for use primarily in the short-course chemotherapy of tuberculosis has been studied in Chinese patients in Singapore and Hong Kong. One formulation, containing 50 mg isoniazid, 120 mg rifampin, and 300 mg pyrazinamide per tablet is suitable for daily use, whereas the other, containing higher proportions of isoniazid and pyrazinamide, is designed for intermittent treatment, each tablet containing 125 mg isoniazid, 100 mg rifampin, and 375 mg pyrazinamide. Appropriate dosages for the Chinese patients, whose average weight was approximately 50 kg, were 5 and 6 tablets, respectively. Plasma concentrations of the 3 drugs after giving such dosages of the 2 combined formulations were compared in 16 patients, 8 in Singapore and 8 in Hong Kong, by means of a crossover study, with the concentrations obtained when identical doses of the 3 drugs were given using standard separate drug formulations. The concomitant urinary excretions of the drugs and their major metabolites were also estimated. Very similar results were obtained whether the drugs were given as the combined preparations or in their standard separate formulations, demonstrating the excellent bioavailability of all 3 drugs in each of the 2 combined formulations.

Acetylation↗