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

We investigated the mechanism of verapamil (VRP) effects on mdr1 gene expression in two leukemic multidrug-resistant (MDR) cell lines, K562/ADR and CEM VLB100. Exposure to VRP for 24 hr resulted in a decrease in mdr1 mRNA levels that was dose related at concentrations between 15 and 50 microM. The maximal decrease of mdr1 mRNA levels was found to be 6-fold in the K562/ADR cells and 3-fold in the CEM VLB100 cells. The effect of VRP on mdr1 mRNA levels was, however, biphasic. At 100 microM VRP, which strongly inhibited cell proliferation, a 2-fold increase of mdr1 mRNA levels was observed in the K562/ADR cells. To determine whether the decrease of mRNA levels resulted from post-transcriptional mechanisms, mRNA stability was studied after blocking of transcription with actinomycin D in VRP-treated cells and in control cells. This study revealed that mdr1 mRNA was stable in both cell lines and no increase in mdr1 mRNA degradation was observed in the 30 microM VRP-treated cells versus control cells (half-lives of 23 hr versus 14 hr for the K562/ADR cells and 15.5 hr versus 10.0 hr for the CEM VLB100 cells). The suggestion of a transcriptional mechanism was confirmed by nuclear run-on assays. A 4-fold decrease in the mdr1 gene transcription rate was observed in the 30 microM VRP-treated CEM VLB100 cells. The decreased transcription rate could be due to the decrease in mdr1 proximal promoter activity observed in CEM VLB100 cells transiently transfected with the mdr1 promoter fused to the chloramphenicol acetyltransferase gene. Indeed, after exposure to 30 microM VRP, chloramphenicol acetyltransferase activity was decreased by 2-fold. This study reports for the first time a down-regulation of mdr1 gene transcription by a pharmacological agent. These results provide further identification of the regulatory mechanisms involved in the overexpression of mdr1 in MDR cells and may help in the development of new strategies for MDR reversal.
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PMID:Evidence for transcriptional control of human mdr1 gene expression by verapamil in multidrug-resistant leukemic cells. 783 33

Non-P-glycoprotein multidrug resistance of HL60/ADR cells appears to be related to overexpression of the MRP gene. Recent studies suggest that this gene may play an important role in a new form of cell resistance to certain chemotherapeutic agents. To examine mechanisms regulating transcriptional activity of this gene, a 2.2-kilobase 5'-flanking sequence of MRP has been isolated from a genomic library prepared from HL60/ADR cells. The 2.2-kilobase DNA fragment linked to the chloramphenicol acetyltransferase (CAT) gene in a reporter plasmid was found to be capable of driving expression of this gene in transient transfection experiments. This DNA containing promoter activity has been sequenced in its entirety and found to contain multiple putative regulatory sites. A series of deletion mutants linked to the CAT reporter gene was used to examine functional domains of the 2.2-kilobase sequence. The results suggest that promoter activity is contained in nucleotides -91 to +103 in a GC-rich region of the MRP genome. Promoter activity contained within this sequence, however, is modulated by both positive and negative regulatory elements. Certain of the regulatory sites contain consensus sequences for positive and negative regulatory elements which have been found in the promoter regions of other genes. Primer extension analysis indicates the presence of multiple major transcriptional start sites from the MRP promoter. Sequence analysis of MRP genomic and complementary DNAs has defined the exon/intron boundaries and the organization of a portion of the 5'-end region of the MRP genome. The results of these studies thus provide new insight in site-specific domains which may function in the regulation of MRP gene expression.
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PMID:Cloning and sequence analysis of the promoter region of the MRP gene of HL60 cells isolated for resistance to adriamycin. 804

Doxorubicin (Dox, adriamycin), an antineoplastic agent that can cause dilated cardiomyopathy, selectively inhibits muscle-specific gene expression in rodent cardiac muscle cells. This study shows that Dox treatment of proliferating C2 myoblasts, an established cell line from mouse skeletal muscle, completely prevents both fusion and accumulation of muscle-specific gene transcripts without significantly altering non-muscle gene transcripts. When added to high density cultures, Dox only blocked myotube formation but did not inhibit induction of muscle-specific genes. Transient transfection into C2 myoblasts showed that the transcriptional expression of chloramphenicol acetyltransferase reporter plasmids regulated by either the cardiac alpha-actin promoter or the muscle creatine kinase enhancer, but not with a viral or beta-actin promoter, was significantly diminished by Dox in a dose-dependent manner. Moreover, exposure of C2 myoblasts to Dox had a profound effect on the expression of regulatory genes critical to the myogenic differentiation program; mRNAs for MyoD and myogenin were dramatically reduced and Id mRNA was concomitantly increased. In addition, there was diminished DNA binding activity of the muscle-specific transcription factor, MEF-2. These results suggest that Dox inhibits myogenesis by preventing muscle-specific gene expression, possibly through affecting the myogenic programs controlled by muscle-specific transcription factors.
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PMID:Antineoplastic agent doxorubicin inhibits myogenic differentiation of C2 myoblasts. 844 15