Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously isolated etoposide/teniposide-resistant cell lines from human cancer KB cells, designated KB/VP-2 and KB/VM-4, respectively, and we found that decreased expression of topoisomerase II alpha was associated with the acquisition of etoposide/teniposide resistance in both resistant cell lines. In this study, we studied how the expression of the DNA topoisomerase II alpha gene is regulated in drug-resistant cell lines at the transcriptional level. We first examined whether the decreased topoisomerase II alpha mRNA level was due to a shorter lifetime of mRNA molecules in drug-resistant cell lines. A comparison of the degradation kinetics of topoisomerase II alpha mRNA demonstrated that there was no difference in mRNA stability between both resistant cell lines and their parental counterpart. A run-on experiment with isolated nuclei showed that the transcriptional activity of topoisomerase II alpha gene of both resistant cell lines constituted less than 20% of the parental KB cells. The activity of DNA topoisomerase II alpha promoter in resistant cells was also less than 20% of that in KB cells when transient transfection assays were performed with the promoter-driven bacterial chloramphenicol acetyltransferase gene. Among the several transcription factors that might be involved in DNA topoisomerase II alpha gene expression, expression of Sp3, an inhibitory member of the Sp1 family, was elevated to about 3-fold higher in both resistant cell lines than their parental counterpart. These results indicated that the expression of DNA topoisomerase II alpha gene decreased at the transcriptional level through the enhanced expression of Sp3 in our two etoposide/teniposide-resistant cell lines.
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PMID:DNA topoisomerase II alpha gene expression under transcriptional control in etoposide/teniposide-resistant human cancer cells. 764 Dec 5

We have investigated the possibility of overcoming the resistance of human brain tumour cells (HBT20) to etoposide by transferring the normal human topoisomerase II alpha (H-topo II) gene into these cells. H-topo II in a mammalian expression vector containing a glucocorticoid-inducible mouse mammary tumour virus (MMTV) promoter was transfected into etoposide-resistant HBT20 cells (HBT20-hTOP2MAM). HBT20 cells transfected with pMAMneo vector alone served as control cells (HBT20-MAM). These were stable transfections. Following a 2 h dexamethasone treatment, H-topo II mRNA expression, protein production, etoposide-induced DNA-protein complex formation and sensitivity to etoposide were increased in HBT20-hTOP2MAM cells compared with control HBT20-MAM cells and with HBT20-hTOP2MAM cells not treated with dexamethasone. However, mRNA and protein levels and cell sensitivity returned to baseline when incubation with dexamethasone was continued for 24 h. This decrease from the 2 h values could not be explained by a loss of the MMTV promoter response to dexamethasone. (H-topo II alpha promoter)-(chloramphenicol acetyltransferase) constructs containing regions -559-0 and -2400-0 were significantly down-regulated in HBT20-hTOP2MAM cells treated for 24 h with dexamethasone compared with dexamethasone-treated control cells. H-topo II mRNA stability after 24 h of dexamethasone treatment was not altered compared with that in control cells. Our data indicate that the exogenously produced H-topo II may have a negative-feedback effect on the endogenous topoisomerase II promoter, causing down-regulation of the endogenous gene.
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PMID:Transfection of human topoisomerase II alpha into etoposide-resistant cells: transient increase in sensitivity followed by down-regulation of the endogenous gene. 887 Jun 83

We have previously shown that the DNA topoisomerase II alpha (topo II alpha) gene is down-regulated in VP16/VM26-resistant cells at the transcriptional level. To determine the DNA elements responsible for down-regulation, the transcriptional activities of luciferase reporter constructs containing various lengths of the promoter sequences were investigated by transient transfection of two resistant cell lines, KB/VP2 and KB/VM4. The transcriptional activities of the full-length promoter (-295 to +85) and of three deletion constructs (-197, -154 and -74 to +85) were significantly down-regulated in resistant cells. In contrast, the transcriptional activity of the minimal promoter (-20 to +85) in resistant cells was similar to that in parental KB cells. Furthermore, introduction of a mutation in ICE1 abolished the down-regulation of the topo II alpha promoter activity in drug-resistant cells. In vivo footprinting analysis of topo II alpha gene promoter revealed several specific protein-binding sites, a GC box, ICE1, ICE2 and ICE3. In vivo footprinting analysis also identified a cluster of hypersensitive sites. However, there was no marked difference in protein-binding sites between parental and resistant cells. To confirm our previous results, we have established the VP16-resistant cell lines T12-VP1 and T12-VP2 from T12 cells derived from human bladder cancer T24 cells stably transfected with the chloramphenicol acetyltransferase reporter gene driven by the topo II alpha gene promoter. The expression to topo II alpha was down-regulated in both cell lines. We also found that CAT gene expression was significantly decreased to one-fifth of that in T12 parental cells. These results suggest that the expression of the topo II alpha gene requires the binding of multiple factors to the core promoter and is down-regulated at the transcriptional level, probably through binding of a negative factor to ICE1 in drug-resistant cells.
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PMID:Structural and functional analysis of the control region of the human DNA topoisomerase II alpha gene in drug-resistant cells. 1040 35