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J Th'ng

Publications and source records attributed to J Th'ng.

6 recordsLinked to original sources
PubMed2006

Sensitivity of 5-fluorouracil-resistant cancer cells to adenovirus suicide gene therapy.

A promising approach for cancer gene therapy is the combination of adenovirus vectors (AdV) with the suicide gene cytosine deaminase and uracil phosphoribosyl transferase (CDColon, two colonsUPRT). While such vectors have been tested in tumor cell lines and xenograft models, it is not clear how these therapeutic vectors would perform in primary human tumors. We, thus, examined the effect of the combination of a recombinant adenovirus expressing the CDColon, two colonsUPRT (AdCU) with 5-fluorocytosine (5-FC) on primary cancer cells isolated from the ascites or pleural fluids of patients with metastatic cancers. In such models, we have found a direct correlation between the patients' response to 5-FU and the response shown by the cancer cells in vitro, confirming the clinical relevance of this methodology. Our findings demonstrated that this combination was able to kill primary tumor cells, including those that had developed resistance to 5-FU. Furthermore, while proliferating cells were more susceptible to 5-FU, the combination was effective in both rapid and slow proliferating samples. Our study demonstrated that this gene therapy approach could provide an effective therapeutic option for cancers and is not affected by acquired 5-FU resistance. Also of importance is the effectiveness of this gene therapy approach on slower proliferating cells that is typical of the majority of cancers in vivo. This suggests a greater likelihood that it will be effective in a clinical setting.

Adenoviridae↗
PubMed1999

HDAC4, a human histone deacetylase related to yeast HDA1, is a transcriptional corepressor.

Histone acetylation plays an important role in regulating chromatin structure and thus gene expression. Here we describe the functional characterization of HDAC4, a human histone deacetylase whose C-terminal part displays significant sequence similarity to the deacetylase domain of yeast HDA1. HDAC4 is expressed in various adult human tissues, and its gene is located at chromosome band 2q37. HDAC4 possesses histone deacetylase activity intrinsic to its C-terminal domain. When tethered to a promoter, HDAC4 represses transcription through two independent repression domains, with repression domain 1 consisting of the N-terminal 208 residues and repression domain 2 containing the deacetylase domain. Through a small region located at its N-terminal domain, HDAC4 interacts with the MADS-box transcription factor MEF2C. Furthermore, HDAC4 and MEF2C individually upregulate but together downmodulate c-jun promoter activity. These results suggest that HDAC4 interacts with transcription factors such as MEF2C to negatively regulate gene expression.

Amino Acid Sequence↗
PubMed1996

A small proline-rich protein, SPRR1, is upregulated early during tobacco smoke-induced squamous metaplasia in rat nasal epithelia.

Small proline-rich proteins, believed to be precursor proteins for the crosslinked envelope formation in cells undergoing squamous differentiation, are encoded by the SPRR genes. To further investigate the role of these proteins, the time course of increased synthesis of SPRR1 mRNA in nasal epithelia of rats exposed to cigarette smoke was determined, and the deduced amino acid sequence of the rat SPRR1 was compared with those of other species. Using the pig homologue (20K) antisense cRNA probe, high levels of SPRR1 transcript were detected by in situ hybridization in squamous epithelia that line the nasal vestibule and hard palate of the rat. Basal cells of both the vestibule and palate contained low levels of the transcript, and increasing amounts were detected in the squamous layers. In rats exposed to 250 mg/m3 (total particulate matter) cigarette smoke 6 h/day for 5 days, the number of small mucous cells increased in the respiratory epithelium of the nasal septum in the early stages of squamous differentiation, but were gradually replaced by squamous metaplastic cells. During this transition, hybridization of the 20K antisense cRNA probe increased in the epithelial and mesenchymal cells, indicating that SPRR1 protein could have roles in cellular differentiation other than as a building block of the crosslinked envelope. Similarly, high levels of SPRR1 transcript were detected in the nasal transitional epithelium lining internal walls and maxilloturbinates that had undergone squamous metaplasia after cigarette smoke exposure. At 5 days after the withdrawal of cigarette smoke exposure, the morphology of the midseptal epithelium returned to that of a pseudostratified mucociliary epithelium and the epithelia lining the maxilloturbinates to that of a transitional epithelium. Accompanying this change in morphology of the tissues, the levels of SPRR1 transcripts significantly decreased in the epithelia. However, in the mesenchyme no significant decrease was observed during this recovery. RNA prepared from the external nose surrounding the nasal vestibule contained a transcript of about 0.9 kb that hybridized to the 20K cDNA probe on Northern blot analysis. DNA sequence analysis of the transcript confirmed the identity as that of the SPRR mRNA with its characteristic repeat encoding the oligopeptide with the general consensus -EPC*PKVP-. However, the rat homologue rSPRR1 contained more repeats of the oligopeptide compared with those of higher mammals such as the rabbit, pig, and human, suggesting a possible inverse relation between number of repeats and evolution development. This finding suggests that the number of repeats in the protein may be redundant; however, the conserved sequence of the peptide indicates that this region is essential for the function of this protein.

Amino Acid Sequence↗
PubMed1994

Premature p34cdc2 activation required for apoptosis.

Activation of the serine-threonine kinase p34cdc2 at an inappropriate time during the cell cycle leads to cell death that resembles apoptosis. Premature activation of p34cdc2 was shown to be required for apoptosis induced by a lymphocyte granule protease. The kinase was rapidly activated and tyrosine dephosphorylated at the initiation of apoptosis. DNA fragmentation and nuclear collapse could be prevented by blocking p34cdc2 activity with excess peptide substrate, or by inactivating p34cdc2 in a temperature-sensitive mutant. Premature p34cdc2 activation may be a general mechanism by which cells induced to undergo apoptosis initiate the disruption of the nucleus.

Amino Acid Sequence↗
PubMed1990

The topoisomerase II inhibitor VM-26 induces marked changes in histone H1 kinase activity, histones H1 and H3 phosphorylation, and chromosome condensation in G2 phase and mitotic BHK cells.

We have examined the effects of topoisomerase inhibitors on the phosphorylation of histones in chromatin during the G2 and the M phases of the cell cycle. Throughout the G2 phase of BHK cells, addition of the topoisomerase II inhibitor VM-26 prevented histone H1 phosphorylation, accompanied by the inhibition of intracellular histone H1 kinase activity. However, VM-26 had no inhibitory effect on the activity of the kinase in vitro, suggesting an indirect influence on histone H1 kinase activity. Entry into mitosis was also prevented, as monitored by the absence of nuclear lamina depolymerization, chromosome condensation, and histone H3 phosphorylation. In contrast, the topoisomerase I inhibitor, camptothecin, inhibited histone H1 phosphorylation and entry into mitosis only when applied at early G2. In cells that were arrested in mitosis, VM-26 induced dephosphorylation of histones H1 and H3, DNA breaks, and partial chromosome decondensation. These changes in chromatin parameters probably reverse the process of chromosome condensation, unfolding condensed regions to permit the repair of strand breaks in the DNA that were induced by VM-26. The involvement of growth-associated histone H1 kinase in these processes raises the possibility that the cell detects breaks in the DNA through their effects on the state of DNA supercoiling in constrained domains or loops. It would appear that histone H1 kinase and topoisomerase II work coordinately in both chromosome condensation and decondensation, and that this process participates in the VM-26-induced G2 arrest of the cell.

Animals↗