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)

'Universal fuser' clones of a human papillomavirus type 16 positive cervical carcinoma cell line (SiHa) were established to study the effect of a non-tumorigenic fusion partner on the regulation of a stably integrated chloramphenicol acetyltransferase (CAT) gene controlled by the HPV18 upstream regulatory region under non-selective conditions. The CAT expressing cells were fused with both non-tumorigenic, spontaneously immortalized human keratinocytes (HaCaT) and non-modified SiHa cells. The resulting hybrids were characterized by restriction enzyme fragment length polymorphism analysis and flow cytometry. While the non-selectable, HPV18-driven indicator gene is constitutively expressed in SiHa cells, the CAT activity is extinguished in SiHa x HaCaT cells, but still present in SiHa x SiHa hybrids. Examination of the cytokeratin expression pattern reveals that the keratinocyte phenotype seems not only to be dominant in terms of the extinction of the HPV18 regulatory region but also by the conservation of most of the differentiation markers of the non-tumorigenic fusion partner. Cycloheximide treatment and intracellular competition experiments using the transient COS7 fusion-amplification technique are accompanied by the reactivation of the marker gene in previously CAT- SiHa x HaCaT hybrids. These data strongly suggest that trans-acting negative regulatory factors derived from the non-malignant human keratinocytes are responsible for the extinction phenomenon.
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PMID:Extinction of the HPV18 upstream regulatory region in cervical carcinoma cells after fusion with non-tumorigenic human keratinocytes under non-selective conditions. 170 93

The cytokeratins, which form the intermediate filaments (IFs) characteristic of epithelial cells, are encoded by a large family of genes whose members are differentially expressed in patterns different in the various kinds of epithelia. To identify possible cis-regulatory DNA elements involved in the cell-type-specific expression of these genes, we examined, in transfection assays, 5' upstream sequence intercepts of a certain cytokeratin gene, i.e. that for bovine cytokeratin IV* (CKIV*), in combination with the coding portions of either the chloramphenicol acetyltransferase (CAT) gene or other cytokeratin genes. A 5' upstream region located between the cap-site and nucleotide -605 was found to enhance the specific expression of these reporter genes in bovine mammary gland-derived BMGE + H cells, which express the endogenous gene, but not in bovine kidney epithelium-derived MDBK cells which synthesize cytokeratins other than IV*. This epithelium-type-specific expression was also observed in heterologous combinations, e.g. in murine keratinocytes, but not in other murine cell lines such as 3T3 fibroblasts. When a fragment located between -180 and -605 was coupled to the HSV-TK promoter it stimulated the expression of the reporter gene in a cell-type-specific manner. The enhancer character of this 425 nucleotide long region is also demonstrated. Moreover, the CKIV* promoter/enhancer complex was able to direct the expression of epidermal cytokeratins characteristic for suprabasal differentiation, i.e. bovine cytokeratins Ia and VIb, in cells that normally do not express these genes. We show that the newly synthesized cytokeratins integrate into the pre-existing cytokeratin IF system of the transfected cells and that the forced expression of one of these cytokeratins does not induce the endogenous gene encoding its normal pair partner.
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PMID:Enhancer elements directing cell-type-specific expression of cytokeratin genes and changes of the epithelial cytoskeleton by transfections of hybrid cytokeratin genes. 246 72

8-Cl-cAMP, a site-selective analogue of cAMP, decreased mdr-1 expression in multidrug-resistant human breast cancer cells. A sixfold reduction of mdr-1 mRNA expression by 8-Cl-cAMP began within 8 h of treatment and was associated with a decrease in the synthesis of P-glycoprotein and with an increase in vinblastine accumulation. A reduction in mdr-1 expression after 8-Cl-cAMP treatment was also observed in multidrug-resistant human ovarian cancer cell lines. 8-Cl-cAMP is known to change the ratio between the two regulatory subunits, RI and RII, of protein kinase A (PKA). We observed that RI alpha decreased within 24 h of 8-Cl-cAMP treatment, that RII beta increased after as few as 3 h of treatment, and that PKA catalytic activity remained unchanged during 48 h of 8-Cl-cAMP treatment. The results are consistent with the hypothesis that mdr-1 expression is regulated in part by changes in PKA isoenzyme levels. Although 8-Cl-cAMP has been used to differentiate cells in other model systems, the only differentiating effect that could be detected after 8-Cl-cAMP treatment in the MCF-7TH cells was an increase in cytokeratin expression. Evidence that the reduction of mdr-1 mRNA occurred at the level of gene transcription was obtained by measuring chloramphenicol acetyltransferase (CAT) mRNA in MCF-7TH cells transfected with an mdr-1 promoter-CAT construct prior to 8-Cl-cAMP treatment. Thus, 8-Cl-cAMP is able to downregulate mdr-1 expression and suggests a new approach to reversal of drug resistance in human breast cancer.
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PMID:Downregulation of mdr-1 expression by 8-Cl-cAMP in multidrug resistant MCF-7 human breast cancer cells. 754 90